全文获取类型
收费全文 | 7938篇 |
免费 | 105篇 |
专业分类
公路运输 | 1719篇 |
综合类 | 587篇 |
水路运输 | 2545篇 |
铁路运输 | 771篇 |
综合运输 | 2421篇 |
出版年
2023年 | 43篇 |
2022年 | 113篇 |
2021年 | 56篇 |
2019年 | 81篇 |
2018年 | 194篇 |
2017年 | 114篇 |
2016年 | 140篇 |
2015年 | 91篇 |
2014年 | 241篇 |
2013年 | 1230篇 |
2012年 | 323篇 |
2011年 | 392篇 |
2010年 | 236篇 |
2009年 | 372篇 |
2008年 | 302篇 |
2007年 | 271篇 |
2006年 | 236篇 |
2005年 | 271篇 |
2004年 | 293篇 |
2003年 | 183篇 |
2002年 | 148篇 |
2001年 | 132篇 |
2000年 | 140篇 |
1999年 | 99篇 |
1998年 | 130篇 |
1997年 | 112篇 |
1996年 | 141篇 |
1995年 | 150篇 |
1994年 | 85篇 |
1993年 | 189篇 |
1992年 | 161篇 |
1991年 | 77篇 |
1990年 | 83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 | 92篇 |
1978年 | 57篇 |
1977年 | 69篇 |
1976年 | 54篇 |
1975年 | 65篇 |
1974年 | 51篇 |
1973年 | 45篇 |
排序方式: 共有8043条查询结果,搜索用时 15 毫秒
991.
992.
993.
Power Requirements for Vehicle Suspension Systems 总被引:1,自引:0,他引:1
D. Karnopp 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1992,21(1):65-71
This paper attempts to analyze the power requirements of a vehicle due solely to its suspension system, neglecting the important powers associated with air and rolling resistance. Power requirements for active and passive suspensions are compared using the simplest possible mathematical model. A mass in a gravity field moves at constant velocity over a surface and is supported by a point contact on the surface by a massless but otherwise arbitrary suspension system. It is shown that the average propulsive power required is equal to the average power lost in the suspension. In the limit cases of very stiff or very soft suspensions this power vanishes. Passive suspensions require no other power, but active suspensions may require significant extra power from the prime mover to generate the suspension forces. 相似文献
994.
Home-based trip end models — A comparison between category analysis and regression analysis procedures 总被引:1,自引:0,他引:1
A. A. Douglas 《Transportation》1973,2(1):53-70
The trip end models which have been used in past transportation studies are briefly summarised. Problems associated with the use of zone-based models are outlined and reasons are given to support the development of models at the household rather than zonal level.It is suggested that recent developments which have taken place in household-based models have not been entirely logical. In particular, arguments between regression models and category analysis models have been confused with the use of aggregate (zonal) as against disaggregate (household) data — regression models being associated with the use of zonal data and category analysis models with household data. Misunderstood arguments and false notions regarding sample sizes have directed attention from the regression analysis approach.A detailed comparison of the category analysis and regression analysis methods for developing household-based trip end models is given. Both methods have been applied using data from the Monmouthshire Land Use Transportation Study. The regression results reported are from a very preliminary analysis and contain a number of anomalies, although it is thought that sufficient work has been done to provide an objective evaluation of the two methods.It is recommended that the household regression approach should be further investigated since it has advantages as a modelbuilding procedure and makes better use of sample data. A certain amount of categorisation of household types is necessary and the investigations would attempt to determine the best balance between categorisation and regression fitting. Further development will be restricted if the trend towards minimum sample sizes of about 1000 households is continued. Larger samples should be taken in certain circumstances to pursue development work. 相似文献
995.
Thomas B. Deen 《Transportation》1984,12(3):195-209
The highway industry in the United States spends about $35 to $40 billion annually. Management of the industry is almost wholly decentralized. This decentralization plus diminishing fuel tax revenues used to finance road improvements have caused road research efforts to decline to a very low level. Comparisons between funds for highway research and those spent by private firms in similar industries show that private firms spend from 5 to 12 times the rate of highway agencies. The problem of how much to spend on research is difficult both for private-sector and for public-sector enterprises. The level of research spending is shown to correlate well with both profitability and growth in U.S. firms. Four methods used for making research decisions in the private sector are discussed. The goals of the Strategic Transportation Research Study (STRS), which is being conducted by the Transportation Research Board to examine highway and transportation needs, are described. 相似文献
996.
A. H. Wickens 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1982,11(2):89-106
For railway vehicles having coned wheels mounted on solid axles, there is a conflict between the stability of lateral deviations from the motion along the track and the ability to steer round curves. A general theory is developed for the two-axle vehicle in which there is a lack of symmetry, fore-and-aft, both of the interwheelset structure and of the equivalent conicities of the wheelsets. It is shown that whilst parameters can be selected which provide static and dynamic stability and perfect steering for both directions of motion, there is a lightly damped mode of oscillation for any practical configuration and the significance of this is discussed. 相似文献
997.
Bernhard J. Abrahamsson 《Maritime Policy and Management》1982,9(3):219-227
In this paper the author explores the nature and scope of social regulation in shipping comparing its nature with that of economic regulation per se. Whilst economic regulation affects liner shipping only, social regulation—impelled by a specific concern for health and environmental protection, rather than a desire for optimal resource allocation—effects all types of shipping. The legislation emerging from this has had important (and often overlooked)economic impact; focusing on the conditions, under which a carrier discharges his duties, these regulations may determine, to a greater or lesser degree, the levels of cost and service. He concludes that, whilst the concept of social regulation has a valid, humanitarian base, the cost of its implementation should not be underestimated. 相似文献
998.
Anton Th. Van Zanten Allan I. Krauter 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1978,7(4):203-231
This paper is concerned with the braking performance and the handling behavior of the tractor-semitrailer truck under optimal braking. Optimal control theory is used in order to deal with the problem and a combination of the steepest descent method and the Davidon Fletcher Powell method is used to solve it numerically. Results for some chosen braking maneuvers are obtained for a nonlinear truck model which has 14 degrees of freedom. These results show that, for the chosen maneuvers an idealized anti-skid braking is close to being optimal in the sense defined in this paper. Implementation of an idealized anti-skid braking on the tractor-semitrailer truck, however, may be not desirable. 相似文献
999.
1000.
Hossain Poorzahedy Mark A. Turnquist 《Transportation Research Part B: Methodological》1982,16(1):45-55
The discrete network design problem is one of finding a set of feasible actions (projects) from among a collection of possible actions, that when implemented, optimizes some objective function(s). This is a combinatorial optimization problem that is very expensive to solve exactly. This paper proposes two algorithms for obtaining approximate solutions to the discrete network design problem with much less computational effeort. The computational savings are achieved by approximating the original problem with a new formulation which is easier to solve. The first algorithm proposed solves this approximate problem exactly, while the second is even more efficient, but provides only a near-optimal solution to the approximate problem. Experience with test problems indicates that these approximations can reduce the computational effort by a factor of 3–5, with little loss in solution accuracy. 相似文献