全文获取类型
收费全文 | 1404篇 |
免费 | 18篇 |
专业分类
公路运输 | 526篇 |
综合类 | 48篇 |
水路运输 | 420篇 |
铁路运输 | 48篇 |
综合运输 | 380篇 |
出版年
2022年 | 23篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 39篇 |
2017年 | 33篇 |
2016年 | 61篇 |
2015年 | 21篇 |
2014年 | 67篇 |
2013年 | 209篇 |
2012年 | 74篇 |
2011年 | 79篇 |
2010年 | 76篇 |
2009年 | 69篇 |
2008年 | 75篇 |
2007年 | 34篇 |
2006年 | 31篇 |
2005年 | 38篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 26篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 12篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1979年 | 22篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有1422条查询结果,搜索用时 46 毫秒
181.
B. R. Dansie 《Transportation Research Part B: Methodological》1985,19(6):526-528
A particular parameter estimability problem in the multinomial probit model is considered. Making use of a model discussed in the literature, some problems with the usual method of specification are discussed. Some general comments are made on the problem of selecting a normalisation when using the multinomial probit model. 相似文献
182.
183.
184.
185.
186.
S. Motoyama Engineer H. Uki Engineer K. ISODA Manager H. YUASA Manager 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1993,22(5):455-464
The purpose of this study is to clarify vehicle dynamics effected by traction force distribution, not only between the front and rear wheels but also between the left and right wheels. Contribution of traction force distribution to vehicle turning performance was investigated using a mathematical simulation and an experimental vehicle. The results indicates that the control of traction control distribution between the left and right wheels greatly influences vehicle turning characteristics and improve the performance even in a marginal turning condition. 相似文献
187.
G. S. Jung Y. H. Sung B. C. Choi C. W. Lee M. T. Lim 《International Journal of Automotive Technology》2012,13(3):347-353
Although premixed charge compression ignition (PCCI) combustion engines are praised for potentially high efficiency and clean
exhaust, experimental engines built to date emit more hydrocarbons (HCs) and carbon monoxide (CO) than the conventional machines.
These compounds are not only strictly controlled components of the exhaust gas of road vehicles but are also an energy loss
indicator. The prime objective of this study was to investigate the major sources of the HCs formed in the combustion chamber
of an experimental PCCI engine in order to suggest some effective technologies for HC reduction. In this study, to explore
the dominant sources of HC emissions in both operation modes, a single cylinder engine was prepared such that it could operate
using either conventional diesel combustion or PCCI combustion. Specifically, the contributions of the top-ring crevice volume
in the combustion chamber and the bulk quenching of the lean mixture were investigated. To understand the influence of the
shape and magnitude of the crevice on HC emissions, the engine was operated with 12 specially prepared pistons with different
top-ring crevices installed one after another. The engine emitted proportionally more HCs as the depth of the crevice increased
as long as the width remained narrower than the prevailing quench distance. The top-ring-crevice-originated exhaust HCs comprised
approximately 31% of the total HC emissions in the baseline condition. In a series of tests to estimate the effects of bulk
quench on exhaust HC emissions, intake air was heated from 300K to 400K in steps of 25K. With the intake air heated, HC and
CO emissions decreased with a gradually diminishing rate to zero at 375K. In conclusion, the most dominant sources of HC emissions
in PCCI engines were the crevice volumes in the combustion chamber and the bulk quenching of the lean mixtures. The key methods
for reducing HC emissions in PCCI engines are minimizing crevice volume in the combustion chamber and maximizing intake air
temperature allowed based on the permissible NOx level. 相似文献
188.
Improving pedestrian safety at intersections remains a critical issue. Although several types of safety countermeasures, such as reforming intersection layouts, have been implemented, methods have not yet been established to quantitatively evaluate the effects of these countermeasures before installation. One of the main issues in pedestrian safety is conflicts with turning vehicles. This study aims to develop an integrated model to represent the variations in the maneuvers of left-turners (left-hand traffic) at signalized intersections that dynamically considers the vehicle reaction to intersection geometry and crossing pedestrians. The proposed method consists of four empirically developed stochastic sub-models, including a path model, free-flow speed profile model, lag/gap acceptance model, and stopping/clearing speed profile model. Since safety assessment is the main objective driving the development of the proposed model, this study uses post-encroachment time (PET) and vehicle speed at the crosswalk as validation parameters. Preliminary validation results obtained by Monte Carlo simulation show that the proposed integrated model can realistically represent the variations in vehicle maneuvers as well as the distribution of PET and vehicle speeds at the crosswalk. 相似文献
189.
K. S. Song S. O. Kang S. O. Jun H. I. Park J. D. Kee K. H. Kim D. H. Lee 《International Journal of Automotive Technology》2012,13(6):905-914
This study proposes an aerodynamically optimized outer shape of a sedan by using an Artificial Neural Network (ANN), which focused on modifying the rear body shapes of the sedan. To determine the optimization variables, the unsteady flow field around the sedan driving at very fast speeds was analyzed by CFD simulation, and fluctuations of the drag coefficient (C D ) and pressure around the car were calculated. After consideration of the baseline result of CFD, 6 local parts from the end of the sedan were chosen as the design variables for optimization. Moreover, an ANN approximation model was established with 64 experimental points generated by the D-optimal methodology. As a result, an aerodynamically optimized shape for the rear end of the sedan in which the aerodynamic performance is improved by about 5.64% when compared to the baseline vehicle is proposed. Finally, it is expected that within the accepted range of shape modifications for a rear body, the aerodynamic performance of a sedan can be enhanced so that the fuel efficiency of the sedan can be improved. The YF SONATA, a sedan manufactured by Hyundai Motors Corporate, played a major role in this research as the baseline vehicle. 相似文献
190.
Tire intelligence is vital in the improvement of the safety of vehicles because the tire supports the car body and is the contact point between the vehicle and the road. To create an intelligent tire, sensors must be installed to measure the behavior of the tire. However, it is difficult to apply a wired sensor system on the wheel of the tire. Hence, it is necessary to implement a self-powering, wireless system (a type of energy harvesting system) that can be mounted inside the tire. The purpose of this study is to convert the strain energy caused by deformation of the tire while driving into useful electrical energy to supply the sensor system. A flexible piezofiber is utilized for the energy conversion. The variation in strain, due to changes in speed, load, and the internal pressure of the tire, was measured along two axial directions to evaluate the amount of available strain energy. The amount of strain changed from 0.15% to 0.8%. To predict the amount of available energy from a tire, we perform an analysis of the relationship between the strain and the voltage. In addition, experiments for impedance matching between piezofiber and related circuits were conducted to optimize the external loads for transferring energy efficiently. Based on the procedure mentioned above, at least 0.58 mJ of electrical energy can be generated by using the laterally oriented strain (1500 to 2500 micro strain). The result of this study is expected to enhance the potential realization of self-generating wireless sensor systems for so-called ??intelligent?? tires. 相似文献