全文获取类型
收费全文 | 8376篇 |
免费 | 108篇 |
专业分类
公路运输 | 1987篇 |
综合类 | 604篇 |
水路运输 | 2587篇 |
铁路运输 | 781篇 |
综合运输 | 2525篇 |
出版年
2022年 | 117篇 |
2021年 | 67篇 |
2020年 | 55篇 |
2019年 | 88篇 |
2018年 | 211篇 |
2017年 | 136篇 |
2016年 | 202篇 |
2015年 | 93篇 |
2014年 | 251篇 |
2013年 | 1247篇 |
2012年 | 363篇 |
2011年 | 457篇 |
2010年 | 322篇 |
2009年 | 380篇 |
2008年 | 353篇 |
2007年 | 280篇 |
2006年 | 234篇 |
2005年 | 273篇 |
2004年 | 297篇 |
2003年 | 191篇 |
2002年 | 155篇 |
2001年 | 134篇 |
2000年 | 139篇 |
1999年 | 103篇 |
1998年 | 129篇 |
1997年 | 113篇 |
1996年 | 139篇 |
1995年 | 149篇 |
1994年 | 84篇 |
1993年 | 189篇 |
1992年 | 160篇 |
1991年 | 77篇 |
1990年 | 84篇 |
1989年 | 58篇 |
1988年 | 74篇 |
1987年 | 65篇 |
1986年 | 59篇 |
1985年 | 77篇 |
1984年 | 73篇 |
1983年 | 73篇 |
1982年 | 73篇 |
1981年 | 95篇 |
1980年 | 68篇 |
1979年 | 91篇 |
1978年 | 56篇 |
1977年 | 69篇 |
1976年 | 53篇 |
1975年 | 65篇 |
1974年 | 51篇 |
1973年 | 45篇 |
排序方式: 共有8484条查询结果,搜索用时 15 毫秒
941.
The background and the literature in liner fleet scheduling is reviewed and the objectives and assumptions of our approach are explained. We develop a detailed and realistic model for the estimation of the operating costs of liner ships on various routes, and present a linear programming formulation for the liner fleet deployment problem. Independent approaches for fixing both the service frequencies in the different routes and the speeds of the ships, are presented. 相似文献
942.
Rao V. Dukkipati Renguang Dong 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1999,31(2):95-111
Available experimental data of the dynamic force at a rail joint are used to validate the Discrete Support (DS) model of vehicle-track system. The validated DS model is employed to investigate the characteristics of dynamic forces due to a dipped rail joint. The results show that increasing axle load and rail equivalent mass significantly increases the first peak load. The wheel (unsprung) mass, stiffness of bearing rubber pad, and ballast stiffness mainly affect the second peak load. Properly designing a profile near the rail joint may reduce the dynamic load at the joint. The results obtained also indicate that the dynamic load generated at one wheel partially transmits to a neighboring wheel. 相似文献
943.
В.В.НОВИКОВ 《国外铁道车辆》2002,39(3):37-38
针对运用中因轨距减小而导致轮缘磨加剧的问题,设计并试验了统一型减薄轮缘厚度的修理用车轮踏面外形,试验表明,对减少轮缘磨耗,延长车轮使用寿命均有明显效果。 相似文献
944.
The first part of this paper presented the required statistics and stochastic models for reliability analysis of the fatigue fracture of welded plate joints. This present Part 2 suggests a probabilistic damage tolerance supplement to the design S–N curves for welded joints. The goal is to provide the practising engineer with simple tools that predict the reliability against fatigue fracture during service life. The impact of the chosen fatigue design factors (FDF) and the uncertainty in the applied stresses is revealed. The effect of an in-service inspection programme is also predicted. The results are presented as dimensionless matrices and suggested for use in support of decision-making at the design stage, without any advanced fracture mechanics modelling and stochastic simulation. One important advantage of this format is that the probability levels are presented regardless of actual weld class and target service life (TSL). This is obtained by introducing the FDF as a key parameter to the results. This parameter is defined as the ratio of predicted fatigue life over TSL. FDF is always calculated in the S–N approach which is mandatory in fatigue life prediction. Various welded details (classes) will have the same reliability level for the same FDF. This is true at the end of TSL and at earlier stages, i.e. fractions of TSL. The absolute value of TSL is immaterial for a given FDF. In the case of in-service inspection, the inspection interval is also given without dimensions as a fraction of TSL.
Only the influence of future scheduled inspections is treated. Updating based on actual inspection results is not included as the scope of work is inspection planning at the design stage. Results for some frequent cases occurring in practice are readily derived and presented. 相似文献
945.
New Large Aircraft (NLA) are new aircraft developments larger than any existing aircraft. The NLA's higher seat capacity will significantly impact passenger terminal design and operations. This paper focuses on the issues regarding the departure lounge. Deterministic queuing theory is used to determine the size and seating configuration of the lounge, as well as to decide whether a second level should be built to accommodate the increase in the number of passengers. The paper also discusses the use of the satellite section of a pier‐satellite terminal as a single lounge for the NLA. Spreadsheets are used to implement the analyses. 相似文献
946.
Y. H. Rim J. H. Moon G. Y. Kim S. D. Noh 《International Journal of Automotive Technology》2008,9(6):719-728
Automotive general assembly requires many manual assembly operations to be carried out by human workers. Ergonomic analysis
is an important part of the design and evaluation of products, jobs, tools, machines and environments for safe, comfortable
and effective human functioning. Most recent researches have involved the evaluation of working conditions to prevent work-related
musculoskeletal disorders. The majority of previous research on automotive companies has mainly considered the results of
ergonomic analyses such as RULA (Rapid Upper Limb Assessment), REBA (Rapid Entire Body Assessment) and OWAS (Ovako Working
Posture Analysis System). Analysis of static posture including reachability, clearances for arm, hand and tool has also been
used to evaluate working conditions. However, in addition to static posture analysis, a biomechanical analysis in dynamic
conditions should also be conducted. There are no integrated frameworks or standard schema for ergonomic analysis using digital
human models in digital environments. The purpose of this paper is to propose a new framework for the evaluation of working
conditions by ergonomic and biomechanical analysis using digital models based on XML standard schema, including: products,
processes, manufacturing resources and human workers. This paper presents the analysis results using the proposed framework
for automotive general assembly operations. We propose a new framework for the evaluation of the assembly operations and their
environments. Then we apply a digital human model to the dynamic simulation of general automotive assembly operations based
on standard schemas in XML and PPRH (Product, Process, Resource and Human). Using PPRH information based on a standard XML
schema to analyze the ergonomic and biomechanical results, the engineer can visualize, analyze and improve assembly operations
and working environments in automotive general assembly shops using digital models. 相似文献
947.
Prediction of fatigue life and estimation of its reliability on the parts of an air suspension system 总被引:1,自引:0,他引:1
K. J. Jun T. W. Park S. H. Lee S. P. Jung J. W. Yoon 《International Journal of Automotive Technology》2008,9(6):741-747
Air suspension systems have been implemented in various commercial vehicles, such as buses and special purpose trucks, because
of the comfortable ride and easy height control. An evaluation of the durability of vehicle parts has been required for service
life and safety starting in the early stages of design. The cyclic load applied to the vehicle can cause fatigue failure of
parts, such as the suspension frame. This paper presents a method to predict the fatigue life of the suspension frame at the
design stage of the air suspension system used in a heavy-duty vehicle. To estimate the fatigue life using the SN method,
the Dynamic Stress Time History (DSTH) is necessary for the part of interest. DSTH can be obtained from the results of the
flexible body dynamic analysis using the Belgian road simulation and the Modal Stress Recovery (MSR) method. Furthermore,
the reliability of the predicted fatigue life can be evaluated by considering the variations in material properties. The probability
and distribution of the expected life cycle can be obtained using experimental design with a minimum number of simulations.
The advantage of using statistical methods to evaluate the life cycle is the ability to predict replacement time and the probability
of failure of mass-produced parts. This paper proposes a rapid and simple method that can be effectively applied to the design
of vehicle parts. 相似文献
948.
The characteristics of auto-ignition and micro-explosion behaviors of one-dimensional arrays of fuel droplets suspended in
a chamber with high surrounding temperature were investigated experimentally with various droplet spacings, numbers of droplet
and surrounding temperatures. The fuels used were pure n-decane and emulsified n-decane with varied water contents ranging
from 10 to 30%. All experiments were performed under atmospheric conditions with high surrounding temperatures. An imaging
technique using a high-speed camera was adopted to measure ignition delay, flame lifetime, and flame spread speed. The camera
was also used to observe micro-explosion behaviors. As the droplet array spacing increased, the ignition delay also increased,
regardless of water content. However, the lifetime of the droplet array decreased as the droplet spacing increased. The micro-explosion
starting time remained unchanged regardless of the number of the droplets or the droplet spacing; however, it tended to be
delayed slightly as the water percentage and droplet spacing increased. 相似文献
949.
Depth of field effects in laser sheet imaging were considered for droplet sizing of a pre-swirl spray. A pre-swirl spray is
formed before the hollow-cone type main-swirl spray from a D.I. gasoline injector, and shows transient characteristics with
high axial velocity. A microscopic imaging technique was applied to obtain high spatial resolution LIF tomograms of the pre-swirl
spray. A 1 mm thick Nd:YAG laser sheet was used as a light source to make the LIF tomograms that were imaged using a high-resolution
CCD camera. The droplet sizing of the pre-swirl spray was carried out using an image processing technique. In the image processing
procedure, the laser sheet-straddling large-sized droplets were carefully taken into account to remove the errors caused by
the depth of field effects from the limited thickness and the energy distribution of the laser sheet. The mean intensity of
the individual droplets and the line profile of the LIF signal around the droplet edge were inspected to screen the laser
sheet-straddling large-sized droplets. In order to consider the effects of the size-dependent LIF signal intensity, the size-classified
or ensemble-averaged mean intensity of the individual droplets was introduced. The mean droplet sizes such as AMD and SMD
were calculated using only screened droplets, and they slightly increase before considering the depth of field effects. 相似文献
950.
C. -H. Chien J. -Y. Jang Y. -H. Chen S. -C. Wu 《International Journal of Automotive Technology》2008,9(4):437-445
People use cars so frequently that they always consider the air-conditioning, and thermal comfort of the driver and passenger
when buying a new car. Therefore accurate simulation of the thermal performance of automobile air conditioners to improve
human comfort has become increasingly important. In order to improve the thermal comfort of passengers, 3-D flow motion and
thermal behavior within vehicles must be analyzed. In this paper, a numerical simulation was used to investigate thermal behavior
in a vehicle. Because air temperature at an air vent is related to the cooling capacity of the air conditioner, the cooling
capacity was calculated using ɛ-NTU (effective number of transfer unit) theoretical equations. Using the air temperature relationship between inlet and outlet
vents as boundary conditions, a 3-D unsteady κ-ɛ turbulent model was used to give a transient analysis simulation of the temperature field and flow conditions in a vehicle’s
passenger cabin. Cooling cycle analysis and conjugate heat transfer analysis at the inside surface of the cabin’s ceiling,
floor and sides were also considered. The predicted temperature distributions in the vehicles passenger cabin were in good
agreement with those obtained experimentally. 相似文献