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921.
Oxford Street in London, is the capital's principal shopping street and famous throughout the Western World; it is also the most obvious route from the city of London to the West, the Midlands and the North of England.The conflict between its twin roles of shopping centre and major traffic route was demonstrated in its accident record which put Oxford Street top of the list of accident blackspots in London, whilst its location in the most fashionable area of London make the costs of new road construction prohibitive.A comprehensive accident analysis defined the pedestrian/vehicle conflict by time and place and facilitated the detail design of a limited traffic ban with associated rerouting.Considerable uncertainties in prediction of the resulting traffic conditions, in the absence of data on demand elasticity, dominated the design of the experiment and led to the inclusion of an avert chaos policy. Traffic predictions which included details of the probable manner in which congestion would spread were assisted by a new network simulation model developed by one of the authors and described here.The report outlines the history of the experiment from conception to implementation (in record time) and reports some early and generally encouraging results. On the strength of which the Greater London Council has confirmed the scheme (August 1973) and has announced plans for its extension to the remaining half of Oxford Street — from Oxford Circus to St. Giles' Circus — which still carries the full weight of traffic.Previously undertaking doctoral research at Imperial College, London. 相似文献
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Zulema D. Garraffo Arthur J. Mariano Annalisa Griffa Carmela Veneziani Eric P. Chassignet 《Journal of Marine Systems》2001,29(1-4)
A model/data comparison was performed between simulated drifters from a high-resolution numerical simulation of the North Atlantic and a data set from in situ surface drifters. The comparison makes use of pseudo-Eulerian statistics such as mean velocity and eddy kinetic energy, and Lagrangian statistics such as integral time scales. The space and time distribution of the two data sets differ in the sense that the in situ drifters were released inhomogeneously in space and time while the simulated drifters were homogeneously seeded at the same time over a regular 1° grid. Despite this difference, the total data distributions computed over the complete data sets show some similarities that are mostly related to the large-scale pattern of Ekman divergence/convergence.Comparisons of eddy kinetic energy and root mean square velocity indicate that the numerical model underestimates the eddy kinetic energy in the Gulf Stream extension and in the ocean interior. In addition, the model Lagrangian time scales are longer in the interior than the in situ time scales by approximately a factor of 2. It is suggested that this is primarily due to the lack of high-frequency winds in the model forcing, which causes an underestimation of the directly forced eddy variability. Regarding the mean flow, the comparison has been performed both qualitatively and quantitatively using James' statistical test. The results indicate that over most of the domain, the differences between model and in situ estimates are not significant. However, some areas of significant differences exist, close to high-energy regions, notably around the Gulf Stream path, which in the model lies slightly north of the observed path, although its strength and structure are well represented overall. Mean currents close to the buffer zones, primarily the Azores Current, also exhibit significant differences between model results and in situ estimates. Possibilities for model improvement are discussed in terms of forcings, buffer zone implementations, turbulence and mixed layer parameterizations, in light of our model/data comparison. 相似文献
926.
Seung-Bok Choi Hwan-Soo Lee Young-Pil Park 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2002,38(5):341-360
Summary This paper presents an investigation of the feedback control performance of a full-vehicle suspension system featuring magnetorheological (MR) dampers. A cylindrical MR damper is designed and manufactured by incorporating a Bingham model of aMR fluid which is commercially available. After evaluating the field-dependent damping characteristics of the MR damper, a full-vehicle suspension system installed with 4 independent MR dampers is constructed and its governing equations of motion which include vertical, pitch and roll motions are derived. A H 8 controller which has inherent robustness against system uncertainties is formulated by treating the sprung mass of the vehicle as uncertain parameter. This is accomplished by adopting the loop shaping design procedure. For the demonstration of a practical feasibility, control performance characteristics for vibration suppression of the proposed MR suspension system are evaluated under various road conditions through the hardware-in-the-loop simulation (HILS) methodology. 相似文献
927.
T. X. Wu D. J. Thompson 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2004,41(1):27-49
Summary A theoretical model is developed to explore the high frequency wheel/rail interaction with coupling between the vertical and lateral directions. This coupling is introduced through the track dynamics due to the offset of the wheel/rail contact point from the rail centre line. Equivalent models of the railway track in the time domain are developed according to the rail vibration receptances in the frequency domain. The wheel is represented by a mass in each direction with no vertical-lateral coupling. The vertical wheel/rail interaction is generated through a non-linear Hertzian contact stiffness, allowing for the possibility of loss of contact between the wheel and rail. The lateral interaction is represented by a contact spring and a creep force damper in series and their values depend on the vertical contact force. The vibration source is the roughness on the wheel and rail contact surfaces which forms a relative displacement excitation in the vertical direction. Using the combined interaction model with this relative displacement excitation, the wheel/rail interactions with coupling between the vertical and lateral vibrations are simulated. It is found that the lateral interaction force caused by the offset is usually less than thirty percent of the vertical dynamic force. The lateral vibration of the rail is significantly reduced due to the presence of the lateral coupling, whereas the vertical interaction is almost unaffected by the lateral force. 相似文献
928.
始于上世纪70年代初的交流电传动技术已经从晶闸管技术发展到GTO技术.交流电传动技术的不断成熟,使其真正成为所有新机车动车的标准.在最近几年中实现了IGBT取代GTO晶闸管的重要技术转型.作为最新进步,该技术转型现在还涵盖了大功率应用范围.德国铁路公司新型的BR189四电流制电力机车最早将该项革新技术应用于极限功率范围.新的交流传动调节方法SITRAC融合动力学、耐用性和具有自调节的最佳调制为一体,其运行可不用速度传感器.展望未来以及铁路工业试验室不断加强对超导变压器、静态能量储存、无传动齿轮箱的直接传动和燃料电池的前景的关注,这里不仅是考虑能源价格的日益增涨.预计在2010年前一些革新技术将用于铁路中. 相似文献
929.
D. J. Ashley 《Transportation》1987,14(2):147-157
The differing demand forecasting approaches adopted on a variety of European international travel studies are described in this paper. These include four models used on the studies of the Paris-Brussels-Cologne/Amsterdam high speed rail line, the model used in appraising the proposed Channel Tunnel rail services and the EC TASC model system. Contrasting features of these forecasting procedures are highlighted. 相似文献
930.
This paper describes a set of specialized spreadsheets that model the cost and performance of transit system options including light rail transit, guideway bus, express bus, and ride sharing. These spreadsheets are demonstrated by comparing a guideway bus (GWB) transit system and a light rail transit (LRT) system proposed for construction in an active rail corridor. The comparisons for assumed levels of transit ridership include guideway geometry, travel time, headways, vehicle requirements, grade crossing protection, and capital and operating costs. The planned GWB system runs on an exclusive dual guideway in the rail right-of-way, and the alternative LRT system operates on the existing rails with new bridges and track as needed for a dual guideway system. The analysis compares the two options for mode splits between 0.5% and 50%. Results show that while both options have approximately the same travel time, the GWB system costs approximately 30% less than the LRT system. The cost difference results primarily from lower GWB vehicle purchase and operating costs. The spreadsheets are available through the McTrans Center at the University of Florida, Gainesville, Florida. 相似文献