全文获取类型
收费全文 | 1299篇 |
免费 | 12篇 |
专业分类
公路运输 | 532篇 |
综合类 | 48篇 |
水路运输 | 394篇 |
铁路运输 | 35篇 |
综合运输 | 302篇 |
出版年
2023年 | 10篇 |
2022年 | 20篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 62篇 |
2017年 | 47篇 |
2016年 | 51篇 |
2015年 | 13篇 |
2014年 | 61篇 |
2013年 | 178篇 |
2012年 | 64篇 |
2011年 | 82篇 |
2010年 | 64篇 |
2009年 | 90篇 |
2008年 | 80篇 |
2007年 | 25篇 |
2006年 | 19篇 |
2005年 | 24篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 20篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有1311条查询结果,搜索用时 12 毫秒
401.
Many porting systems for internal combustion engines have been tried and tested over the years, however the basic spring actuated poppet valve system has prevailed over the last century. In the goal to lower engine output parasitic losses, a simple rotary valve porting system design is proposed and analyzed. The proposed design concept takes into consideration and combines all the prominent advantages of many ealier mutlitiple design variations over the past century. The inherent primary advantage of such a rotary porting system is the elimination of reciprocating components, thus lowering vibration, and removal of highly stiff springs which contribute to considerable system power loss. Comparable sized 3-D representations of both systems are constructed in CAD (Computer Aided Design) software in order to run mechanical and fluid simulations to validate the efficiency advantage of a rotary valve porting system. Using Pro/Engineer Mechanism Dynamics module, the minimum torque required to actuate both systems at 2000 rpm and 3000 rpm is determined. Fluid simulations are performed using a commercial software CFDesign V10. Volumetric flow rates are compared during the intake stroke as well as turbulence intensity factors which characterizes a systems ability to properly mix the Air/Fuel mixture and the combustion efficiency. Some possible improvement on the rotary geometry is suggested. 相似文献
402.
403.
In this paper, we propose the theory of Rational Beliefs as the model of expectations that extends the theory of rational expectations to the postulated environments. Under the rational beliefs paradigm, drivers do not have structural knowledge of traffic conditions and they choose their routes based only on personal experiences and decision‐making rules. We found that if drivers have different decision‐making rules and experiences, then they form different beliefs of traffic conditions (e.g. average travel time) even though they have the same public information and use the same routes. Under the rational beliefs model, drivers are not motivated to renew their beliefs because the beliefs are compatible with their experiences. Therefore, the heterogeneity of beliefs does not disappear even though they have long‐term learning. In order to investigate how drivers form their beliefs of traffic conditions under bounded information environments, numerical experiment is carried out. 相似文献
404.
Influences on bicycle use 总被引:2,自引:0,他引:2
A stated preference experiment was performed in Edmonton in Canada to both examine the nature of various influences on bicycle
use and obtain ratios among parameter values to be used in the development of a larger simulation of household travel behaviour.
A total of 1128 questionnaires were completed and returned by current cyclists. Each questionnaire presented a pair of possible
bicycle use alternatives and asked which was preferred for travel to a hypothetical all-day meeting or gathering (business
or social). Alternatives were described by specifying the amounts of time spent on three different types of cycling facility
and whether or not showers and/or secure bicycle parking were available at the destination. Indications of socio-economic
character and levels of experience and comfort regarding cycling were also collected. The observations thus obtained were
used to estimate the parameter values for a range of different utility functions in logit models representing this choice
behaviour. The results indicate, among other things, that time spent cycling in mixed traffic is more onerous than time spent
cycling on bike lanes or bike paths; that secure parking is more important than showers at the destination; and that cycling
times on roadways tend to become less onerous as level of experience increases. Some of these results are novel and others
are consistent with findings regarding bicycle use in work done by others, which is seen to add credence to this work. A review
of previous findings concerning influences on cycling behaviour is also included. 相似文献
405.
Yuhwa Lee Mark Hickman Simon Washington 《Transportation Research Part A: Policy and Practice》2007,41(10):1004-1020
In order to examine time allocation patterns within household-level trip-chaining, simultaneous doubly-censored Tobit models are applied to model time-use behavior within the context of household activity participation. Using the entire sample and a sub-sample of worker households from Tucson’s Household Travel Survey, two sets of models are developed to better understand the phenomena of trip-chaining behavior among five types of households: single non-worker households, single worker households, couple non-worker households, couple one-worker households, and couple two-worker households. Durations of out-of-home subsistence, maintenance, and discretionary activities within trip chains are examined. Factors found to be associated with trip-chaining behavior include intra-household interactions with the household types and their structure and household head attributes. 相似文献
406.
407.
D. Swaroop Assistant Professor R. Huandra Graduate Student 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1998,30(5):319-344
This paper investigates the problem of designing Intelligent Cruise Control (ICC) algorithms for partially and fully automated highways. ICC algorithms must guarantee that density disturbances attenuate as they propagate upstream. Such a desirable property of traffic is dependent on the spacing policy employed by automated vehicles and on the availability of information required to synthesize a string stable control law consistent with the employed spacing policy. The first part of the paper is concerned with the design of the spacing policy and the latter part is concerned with synthesizing ICC algorithms. Various other issues relating to the design of ICC are also discussed. 相似文献
408.
409.
A. D. May 《Transportation》1992,19(4):313-333
This paper reviews experience with road pricing in Europe and Asia. It considers the objectives of road pricing, and demonstrates that differences in objectives lead to differences in scheme design and performance. It reviews the criteria for design of road pricing systems, and the development of charging structures and technologies to meet those criteria. In particular it discusses the relative merits of pre-determined and congestion-dependent charging structures, and of off-vehicle and on-vehicle charging systems. It assesses the performance of road pricing systems to date, discusses objections to road pricing and demonstrates that the role of road pricing within a wider transport strategy and the use made of the revenue generated, will be important determinants of public acceptability. Finally it assesses the relative merits of alternative approaches to implementation and argues that these will need to pay as much regard to public acceptability as to technical performance. 相似文献
410.
In this note, a simple network equilibrium based approach for estimating a trip matrix using link traffic count data is proposed. In essence a combined distribution and assignment model is formulated in which the link flow data serve to furnish an estimate for the sum of the integrals of the link cost functions. A comparison of this model with others proposed previously is made. 相似文献