全文获取类型
收费全文 | 840篇 |
免费 | 4篇 |
专业分类
公路运输 | 237篇 |
综合类 | 20篇 |
水路运输 | 275篇 |
铁路运输 | 23篇 |
综合运输 | 289篇 |
出版年
2022年 | 16篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 12篇 |
2014年 | 30篇 |
2013年 | 116篇 |
2012年 | 31篇 |
2011年 | 35篇 |
2010年 | 41篇 |
2009年 | 34篇 |
2008年 | 40篇 |
2007年 | 15篇 |
2006年 | 21篇 |
2005年 | 22篇 |
2004年 | 12篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1972年 | 5篇 |
排序方式: 共有844条查询结果,搜索用时 15 毫秒
601.
John R. MacKay Malcolm J. Smith Fred van Keulen Theo N. Bosman Neil G. Pegg 《Marine Structures》2010,23(3):339-359
A submarine may have to operate for a period of time with local corrosion damage in the pressure hull if a suitable repair method is unavailable or too expensive for implementation. This paper describes collapse tests on twenty ring-stiffened aluminium cylinders, which were conducted to study the effect of corrosion damage on hull strength and stability. Artificial hull thinning was found to reduce the collapse strength of experimental models through high local stresses in the corroded region, leading to early onset of yielding and inelastic buckling. Bending associated with the eccentricity due to one-sided thinning was found to further increase the local stresses in the hull. Overall collapse pressures were more severely affected by corrosion damage than interframe collapse pressures. The percentage reduction in overall collapse pressure, compared with intact experimental models, was found to be closely related to the percentage depth of thinning. The accuracy of conventional collapse pressure predictions for the experimental models was significantly better for intact than for corroded cylinders. 相似文献
602.
H. T. Sun J. Wang G. Z. Shen P. Hu 《International Journal of Automotive Technology》2013,14(4):605-610
Aluminum alloys are important technological materials for the application on lightweight design and development of vehicle body. The research works for characterizing warm forming behavior of aluminum alloys have generally reported. However, there were few researches focused on the flow behavior of warm forming aluminum alloy parts for the energy absorbing performance during crash. The tensile stress-strain response for warm forming AA5182 specimens tested under the strain rates of 0.0015 s?1, 0.015 s?1, 0.15 s?1 and 1.5 s?1 are presented in this paper. The data were fit to the Johnson-Cook constitutive model for the simulation of frontal impact. The energy absorbing performance of warm forming AA5182 parts were analyzed. The results show the higher flow stresses and lower fractured strain of warm forming aluminum alloy parts with the strain rate increasing. The flow stresses of warm forming aluminum alloy parts are insensitive to strain rate, while the fractured strain and elongation are sensitive to strain rate. The intrusion displacement of the warm forming aluminum alloy parts is appropriate for the satisfaction of vehicle body design avoiding the excessive deformation for the injury of passenger or the failure of frontal door opening. The feasibility of warm forming aluminum alloy parts is verified with the analysis of energy absorbing performance, stiffness and modal of vehicle body. 相似文献
603.
This paper investigates the impact of a variety of travel information types on the quality of travel choices. Choice quality
is measured by comparing observed choices made under conditions of incomplete knowledge with predicted choice probabilities
under complete knowledge. Furthermore, the potential impact of travel information is considered along multiple attribute-dimensions
of alternatives, rather than in terms of travel time reductions only. Data is obtained from a choice experiment in a multimodal
travel simulator in combination with a web-based mode-choice experiment. A Structural Equation Model is estimated to test
a series of hypothesized direct and indirect relations between a traveler’s knowledge levels, information acquisition behavior
and the resulting travel-choice quality. The estimation results support the hypothesized relations, which provides evidence
of validity and applicability of the developed measure of travel-choice quality. Furthermore, found relations in general provide
some careful support for the often expected impact of information on the quality of travel choices. The effects are largest
for information services that generate previously unknown alternatives, and lowest for services that provide warnings in case
of high travel times only.
Caspar Chorus holds a PhD in Technical Sciences (cum laude) from Delft University of Technology, and is currently an Assistant Professor at Eindhoven University of Technology’s Urban Planning Group. His general interests include traveler behavior research / decision making under knowledge limitations / discrete choice analysis. Theo Arentze received a Ph.D. in Decision Support Systems for urban planning from the Eindhoven University of Technology. He is now an Associate Professor at the Urban Planning Group at the same university. His main fields of expertise and current research interests are decision support systems, activity-based modeling, discrete choice modeling, knowledge discovery and learning-based systems with applications in urban and transport planning. Harry Timmermans received a Ph.D. in Spatial Sciences from the University of Nijmegen. He is Chair of the Urban Planning Group and Director of the European Institute of Retailing and Consumer Services. His main fields of expertise concern behavioral modeling, consumer studies and computer systems in a variety of application contexts including transportation. 相似文献
Caspar G. ChorusEmail: |
Caspar Chorus holds a PhD in Technical Sciences (cum laude) from Delft University of Technology, and is currently an Assistant Professor at Eindhoven University of Technology’s Urban Planning Group. His general interests include traveler behavior research / decision making under knowledge limitations / discrete choice analysis. Theo Arentze received a Ph.D. in Decision Support Systems for urban planning from the Eindhoven University of Technology. He is now an Associate Professor at the Urban Planning Group at the same university. His main fields of expertise and current research interests are decision support systems, activity-based modeling, discrete choice modeling, knowledge discovery and learning-based systems with applications in urban and transport planning. Harry Timmermans received a Ph.D. in Spatial Sciences from the University of Nijmegen. He is Chair of the Urban Planning Group and Director of the European Institute of Retailing and Consumer Services. His main fields of expertise concern behavioral modeling, consumer studies and computer systems in a variety of application contexts including transportation. 相似文献
604.
This paper focuses on the mechanisms of combustion noise during the accelerating operation of multi-cylinder diesel engines
using testing technology for the transient conditions of IC engines. Based on impact factors, such as the gas dynamic load
and cylinder pressure oscillations, tests and analysis of the combustion noise during transient and steady-state conditions
for different loads are made on four-cylinder naturally aspirated engines, turbocharged engines, EGR-introduced engines, and
high pressure common rail engines. The laws of combustion noise difference for the same engine speed and load are researched
during transient and steady-state conditions. It is found that during transient conditions, the maximum pressure rise rate
and the high frequency oscillation amplitude of the cylinder pressure are all higher than those observed during steadystate
conditions for the same engine speed and load. With their joint action, the combustion noise during transient conditions is
greater than that during steady-state conditions. Turbocharging is useful in reducing the combustion noise during transient
conditions. Turbocharging has a better effect on the control over the combustion noise during transient conditions with a
constant engine speed and an increasing torque than in conditions with a constant torque and an increasing engine speed. One
of the main reasons for different control effects on the combustion noise is that turbocharging causes different wall temperatures
inside combustion chambers. The introduction of the appropriate EGR is helpful in the reduction of the combustion noise during
transient conditions. The key to the control of combustion noise with EGR during transient conditions is whether a real-time
adjustment to the EGR rate can be made to achieve the optimization of the EGR rates for different transient conditions. By
means of analyzing the differences in the combustion noise between the transient and steady-state conditions for different
pilot injection controls, we obtain a strategy for controlling the combustion noise during transient conditions with a pilot
injection. Compared with the steady-state conditions, a larger pilot injection quantity and a longer interval between the
main injection and pilot injection should be selected for transient conditions, and this is verified through tests. 相似文献
605.
This paper introduces an adaptive scheme for robustly detecting multiple preceding vehicles in crowded traffic conditions. The scheme focuses on issues frequently observed in the interpretation of traffic scenes recorded by cameras installed in vehicles: stable extraction of features and accurate classification in spite of the vehicle??s constant vibrations and dynamic changes in the distance between vehicles. To address these issues, we introduce the concept of integral features and a method of utilizing the scene geometry information. Each of the simple attributes, such as edges, shadows, and symmetry, is compiled in the window confined by the scene geometry to improve the expressiveness and robustness of the extracted features. The scene geometry information that is then estimated from the perspective view is extensively utilized in constituent system components, including not only feature extraction/integration but also neural network-based classification and distance-adaptive clustering. In addition, employing the Kalman filter along with a confidence measure makes the detection and tracking of potential vehicles robust. Experimental results prove that the system employing the proposed scheme detects and tracks multiple vehicles more effectively, even in crowded traffic conditions, with a lower rate of false positives. 相似文献
606.
Smooth motion control of the adaptive cruise control system by a virtual lead vehicle 总被引:1,自引:0,他引:1
The adaptive cruise control system maintains the appropriate distance to the lead vehicle when the lead vehicle exists and
maintains the desired speed when no lead vehicle is detected. A virtual lead vehicle scheme is introduced to make the switching
between the speed control algorithm and the distance control algorithm unnecessary and simplify the structure of the control
system. The speed and the position of the virtual vehicle can be decided by the control system according to the current situation.
Smoother responses are achieved by the virtual lead vehicle scheme compared to the conventional mode switching scheme. This
method is also shown to provide a good reaction for when a lead vehicle cuts in or out. A linear quadratic controller with
variable weights is suggested to control the virtual lead vehicle. This scheme shows improved performance in terms of passenger
comfort and fuel efficiency of the host vehicle. 相似文献
607.
Abstract This paper reports on research conducted in support of a coastal zone management effort to reduce erosion and sedimentation impacts in a wetland watershed, Elkhorn Slough, Monterey County, California. The research reviews methods of determining soil erosion susceptibility and relating it to land‐use intensity within the watershed, measured by a land disturbance index. Erosion susceptibility is measured in three ways: by a combination of slope and the erosion factor of the Universal Soil Loss Equation; by field measurement of erosion and deposition on selected sites; and by computer‐assisted terrain analysis of data from secondary sources. Land use is shown to be a more important factor than landform in influencing relative erosion susceptibility. 相似文献
608.
We have evaluated the impact of assimilating chlorophyll, nitrate, phosphate, silicate and ammonium into a coupled 1D hydrodynamic ecosystem model (GOTM-ERSEM) in an upwelling influenced estuary. The assimilation method chosen is the Ensemble Kalman Filter (EnKF), which has been demonstrated to improve field estimates of key variables (chlorophyll, nutrients) for bulk algal bloom prediction. The 1D model has been set up for a central station inside the Ría de Vigo (Spain). Data from bi-weekly surveys are used to constrain the model. Temperature and salinity profiles are used to ensure the correct representation of the water structure through a relaxation scheme. Chlorophyll extracts and nutrients at three depths are assimilated sequentially during 1 year simulation (1991). The assimilation period includes episodes of active upwelling and downwelling. All five assimilated variables are successfully constrained and represent a large improvement on the reference simulation (without assimilation). Small divergences can be related to poorly resolved physical processes in the model. The assimilation was further evaluated by comparing observed biomass partitioning with model results. Diatoms accounted for the largest biomass update and the largest improvement in terms of percentage of variance explained (R2). This is particularly significant as they represent the 46% of the yearly integrated observed biomass of the planktonic autotrophs. Nonetheless the R2 value was low for all phytoplankton groups. Bacteria and nanoflagellates showed an improvement with respect to their yearly Root Mean Square (RMS), while the other functional groups worsen or remained unaffected. Chlorophyll assimilation was responsible for most of the impact on the phytoplankton biomass with small contributions from the silicate. It had minor impact on the updates of nutrients which in turn corrected the state variables related to the detrital pool. In this current setting, combined assimilation of chlorophyll and nutrients is not sufficient to produce a skillful simulation of the phytoplankton succession. 相似文献
609.
This special issue provides insight into global conservation science by analyzing a 5-year, $12.5 million global marine conservation science and policy program that included over 50 studies in four priority regions involving over 100 scientists and numerous partners. In doing so, it provides reflections on critical challenges for any conservation science program that is intended to inform policymaking, including how to (1) ensure that science process and products influence conservation actions, (2) build global learning from a network of site-based projects, (3) strengthen in-region capacity, and (4) manage relationships across scales among scientists, conservationists, headquarters, and field-based staff. Information is presented on the development and progress of the program as a whole in addition to specific articles covering each of four focal geographic areas: Belize, Brazil, the Eastern Tropical Pacific Seascape, and Fiji. 相似文献
610.
Dimitrios V. Lyridis Nikolaos P. Ventikos Panayotis G. Zacharioudakis Konstantinos Dilzas Harilaos N. Psaraftis 《WMU Journal of Maritime Affairs》2005,4(1):33-55
This paper proposes a tool to estimate crew composition based on safety/operational and financial requirements. As there is
a tendency of ship owners to implement improved technologies on board their vessels, there is no systematic way to predict
their potential effect on crew size and composition (typically determined by flag state authorities on a case-to-case basis)
nor on the type and complexity of on board duties new technologies might dictate. The main aim of this paper is to develop
a tool to assist in determining crew composition, by taking into account both administration’s and the ship owner’s point
of view. Based on data collected from ship owners, a data mining technique is implemented in order to form a generalized framework
that estimates crew composition as a function of ship type, size, and degree of automation. The agreement of model predictions
with records from specific (vessel) cases is very good in terms of safety (for operations such as watchkeeping, mooring/unmooring,
loading/unloading). The specific intended use of this tool is to help a ship owner decide whether it is cost-beneficial to
retrofit a conventional vessel with advanced technologies that would potentially entail a reduced crew (probably dealing with
different and more complex on board duties). Its main benefits are that it can be used to estimate crew composition before
any vessel construction or upgrade has actually taken place and that it allows crew composition to be easily adapted to the
technological evolution of ship systems even at their current rapid pace. 相似文献