全文获取类型
收费全文 | 3586篇 |
免费 | 10篇 |
专业分类
公路运输 | 945篇 |
综合类 | 716篇 |
水路运输 | 1111篇 |
铁路运输 | 42篇 |
综合运输 | 782篇 |
出版年
2023年 | 4篇 |
2022年 | 21篇 |
2021年 | 17篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 364篇 |
2017年 | 346篇 |
2016年 | 379篇 |
2015年 | 26篇 |
2014年 | 54篇 |
2013年 | 216篇 |
2012年 | 166篇 |
2011年 | 356篇 |
2010年 | 355篇 |
2009年 | 121篇 |
2008年 | 285篇 |
2007年 | 172篇 |
2006年 | 34篇 |
2005年 | 82篇 |
2004年 | 62篇 |
2003年 | 77篇 |
2002年 | 41篇 |
2001年 | 22篇 |
2000年 | 30篇 |
1999年 | 20篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 25篇 |
1995年 | 41篇 |
1994年 | 7篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1972年 | 4篇 |
排序方式: 共有3596条查询结果,搜索用时 62 毫秒
401.
许俊峰 《变流技术与电力牵引》2006,(3):24-32
针对内置式永磁同步电动机传动提出了一种新的无速度传感器控制和转子初始位置估计方法.在内置式永磁同步电动机旋转过程中,采用扩展卡尔曼滤波方法,仅需测量电机定子的电压和电流,便可得到转速和转子位置的估计值.对内置式永磁同步电动机,采用扩展卡尔曼滤波方法的主要困难在于在静止坐标系中其动态模型的复杂性.由于磁路的不对称性,在静止坐标系中建内置式永磁同步电动机的模型比建表面式永磁同步电动机模型更复杂.在无传感器的传动系统中,电机的起动过程是一个问题,因为在起动之前没有任何信息可以获得.转子初始位置估计是在电机静止时,在瞬间对定子绕组施加合适的电压脉冲序列,通过测量峰值电流获得转子位置信息.利用磁饱和效应对凸极性的影响来区分南北磁极.给出基于浮点数字信号处理器TMS320C31平台得到的内置式永磁同步电动机实验结果. 相似文献
402.
M. G. Graham 《Maritime Policy and Management》1998,25(2):129-147
This article considers the perennial topic of how to acheive an equilibrium balance between stability and competition in intermodal shipping. It argues that competition is becoming destructive, but that the imbalance is difficult to correct in a climate where competitive pressures are strog everywhere and restraints on competiiton are unfashionable. In this context, pricing of intermodal services, the emergence of multi-trade alliances, the revelance of contestable market theory and developments in regulatory policies are all examimned. Some points towards restoring an equilibrium balance are offered. 相似文献
403.
This study introduces the concept of loss aversion to consumer behavioral intention at the personal psychological level to
develop an integrative structural equation model for analyzing traveler psychological decision making. In this model, the
relationship between behavioral intention and service quality is a non-smooth function based on the theory of loss aversion.
The expectation service quality in the SERVQUAL model proposed by Parasuraman, Zeithaml, and Berry (PZB) serves as a reference
point. This model can be applied to analyze the effect of non-smooth response of behavioral intention to service quality in
a traveler psychological decision-making process model. Intercity travel among cities in Taiwan is used as an empirical example.
Data were gathered in cities in Taiwan via a questionnaire survey, and the model was tested using path analysis performed
by LISREL. The empirical result shows that all causal relationships are statistically significant. Service quality loss influences
repurchase intention more than does Service quality gain. Finally, this study concludes by discussing managerial implications
and suggesting directions for future research.
相似文献
Jiun-Hung LinEmail: |
404.
Lawrence Frank Mark Bradley Sarah Kavage James Chapman T. Keith Lawton 《Transportation》2008,35(1):37-54
The primary purpose of this study was to investigate how relative associations between travel time, costs, and land use patterns
where people live and work impact modal choice and trip chaining patterns in the Central Puget Sound (Seattle) region. By
using a tour-based modeling framework and highly detailed land use and travel data, this study attempts to add detail on the
specific land use changes necessary to address different types of travel, and to develop a comparative framework by which
the relative impact of travel time and urban form changes can be assessed. A discrete choice modeling framework adjusted for
demographic factors and assessed the relative effect of travel time, costs, and urban form on mode choice and trip chaining
characteristics for the three tour types. The tour based modeling approach increased the ability to understand the relative
contribution of urban form, time, and costs in explaining mode choice and tour complexity for home and work related travel.
Urban form at residential and employment locations, and travel time and cost were significant predictors of travel choice.
Travel time was the strongest predictor of mode choice while urban form the strongest predictor of the number of stops within
a tour. Results show that reductions in highway travel time are associated with less transit use and walking. Land use patterns
where respondents work predicted mode choice for mid day and journey to work travel.
Lawrence Frank is an Associate Professor and Bombardier Chair in Sustainable Transportation at the University of British Columbia and a Senior Non-Resident Fellow of the Brookings Institution and Principal of Lawrence Frank and Company. He has a PhD in Urban Design and Planning from the University of Washington. Mark Bradley is Principal, Mark Bradley Research & Consulting, Santa Barbara California. He has a Master of Science in Systems Simulation and Policy Design from the Dartmouth School of Engineering and designs forecasting and simulation models for assessment of market-based policies and strategies. Sarah Kavage is a Senior Transportation Planner and Special Projects Manager at Lawrence Frank and Company. She has a Masters in Urban Design and Planning from the University of Washington and is a writer and an artist based in Seattle. James Chapman is a Principal Transportation Planner and Analyst at Lawrence Frank and Company in Atlanta Georgia. He has a Masters in Engineering from the Georgia Institute of Technology. T. Keith Lawton transport modeling consultant and past Director of Technical services, Metro Planning Department, Portland, OR, has been active in model development for over 40 years. He has a BSc. in Civil Engineering from the University of Natal (South Africa), and an M.S. in Civil and Environmental Engineering from Duke University. He is a member and past Chair of the TRB Committee on Passenger Travel Demand Forecasting. 相似文献
T. Keith LawtonEmail: |
Lawrence Frank is an Associate Professor and Bombardier Chair in Sustainable Transportation at the University of British Columbia and a Senior Non-Resident Fellow of the Brookings Institution and Principal of Lawrence Frank and Company. He has a PhD in Urban Design and Planning from the University of Washington. Mark Bradley is Principal, Mark Bradley Research & Consulting, Santa Barbara California. He has a Master of Science in Systems Simulation and Policy Design from the Dartmouth School of Engineering and designs forecasting and simulation models for assessment of market-based policies and strategies. Sarah Kavage is a Senior Transportation Planner and Special Projects Manager at Lawrence Frank and Company. She has a Masters in Urban Design and Planning from the University of Washington and is a writer and an artist based in Seattle. James Chapman is a Principal Transportation Planner and Analyst at Lawrence Frank and Company in Atlanta Georgia. He has a Masters in Engineering from the Georgia Institute of Technology. T. Keith Lawton transport modeling consultant and past Director of Technical services, Metro Planning Department, Portland, OR, has been active in model development for over 40 years. He has a BSc. in Civil Engineering from the University of Natal (South Africa), and an M.S. in Civil and Environmental Engineering from Duke University. He is a member and past Chair of the TRB Committee on Passenger Travel Demand Forecasting. 相似文献
405.
This paper presents a fatigue design method for plug and ring type gas welded joints, which incorporates welding residual
stress effects. A non-linear finite element analysis (FEA) was first performed to simulate the gas welding process. The numerically
predicted residual stresses of the gas welds were then compared to experimental results measured using a hole drilling method.
In order to evaluate the fatigue strength of the plug and ring type gas welded joints, a stress amplitude (σ
a
)
R
taling the welding residual stress of the gas weld into account was introduced and is based on a modified Goodman equation
incorporating the effect of the residual stress. Using the stress amplitude (σ
a
)
R
, the ΔP-N
f
relations obtained from fatigue tests for plug and ring type gas welded joints having various dimensions and shapes were
systematically rearranged into (σ
a
)
R
-N
f
relations. It was found that the proposed stress amplitude (σ
a
)
R
could provide a systematic and reasonable fatigue design criterion for the plug and ring type gas welded joints. 相似文献
406.
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
407.
E. Zervas 《International Journal of Automotive Technology》2008,9(6):641-647
This work studies the impact of five parameters: CO and HC engine-out emissions, space velocity, average value and profile
of exhaust temperature, on Diesel CO and HC tail-pipe emissions. The first part of this work is conducted on a reactor and
shows that both HC and CO light-off temperature increases with CO and HC input concentration. CO and HC initial concentration
influence the adsorption/desorption capacities of HC only at high temperatures. Space velocity also influences CO and HC conversion
efficiency. The second part of this work studies the impact of different combinations of HC and CO engine-out emissions on
CO and HC conversion and tail-pipe emissions in the case of New European Driving Cycle. This part proposes that a Diesel oxidation
catalyst must be mainly studied at the Urban Part of NEDC, as the CO and HC conversions are very high at the extra-urban part
of NEDC. CO and HC conversion efficiencies are also dependent on exhaust temperature and catalytic volume. In the case of
two different profiles of exhaust temperature with the same average temperature, CO and HC conversion efficiency is lower
in the case of the smoother profile. 相似文献
408.
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
409.
This study summarizes engine speed and load effects on HC species emissions from premixed charge compression ignition (PCI)
and conventional diesel combustion, and it evaluates diesel oxidation catalyst (DOC) formulations on a gas flow reactor for
the purpose of diesel particulate filter regeneration or lean NOx trap desulfation. HC emissions are sampled simultaneously by a Tedlar bag for light HC species and by a Tenax TA™ adsorption
trap for semi-volatile HC species, and they are analyzed by gas chromatography with a flame ionization detector. The bulk
temperature and residence time during combustion are key parameters that are important for understanding the effects of speed
and load on engine-out HC emissions. The degree of post-flame oxidation is higher in PCI than in conventional combustion,
and it is increased for PCI with a higher speed and load, as indicated by a lower fuel alkanes/THC ratio, a higher alkenes/fuel
alkanes ratio, and a higher methane/THC ratio. Ethene and n-undecane are two representative HC species, and they are used
as a surrogate mixture in the gas flow reactor to simulate PCI and conventional combustion with in-cylinder post fuel injection.
Among the three DOC formulations tested, the catalyst with constituent precious metals of platinum and palladium (PtPd) showed
the best light-off performance, followed by PtPd with an addition of cerium dioxide (PtPd+CeO2), and platinum (Pt), regardless of exhaust compositions. Conventional combustion exhaust composition shows a lower light-off
temperature than that of PCI, regardless of catalyst formulation. 相似文献
410.
This work presents an experiment on the relationships between subjective and objective evaluations of vehicle handling. Ten
cars were examined objectively in several open-loop driving dynamics manoeuvres and subjectively by test persons in typical
traffic situations. Results are extracted from a stationary test (the Slowly Increasing Steer Test), and a dynamical test
(the Frequency Response Test). The subjective measurements are obtained from drivers on a rural road course via a questionnaire,
which was developed to separately investigate the quantity level perception, the so-called “Niveau”, and the more qualitative
“Liking”. These subjective “measurements” are embedded into a two-channel definition of “Steering Comfort” as a genus for
“Steering Discomfort” and “Character”. The article concentrates on developing a statistical method for the consideration of
correlations amongst the subjective/objective data. In doing so, the variance in example subjective Niveau ratings can be
significantly explained by several objective quantities. Indicators for co-domains of validated discomfort characteristics
and hints for endeavouring character Liking ranges are detected. 相似文献