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11.
Most of existing route guidance strategies achieves user optimal equilibrium by comparing travel time. Measuring travel time, however, might be uneasy on an urban road network. To contend with the issue, the paper mainly considers easily obtained inflow and outflow of a link and road capacity as input, and proposes a route guidance strategy for a single destination road network based on the determination of free-flow or congested conditions on alternative routes. An extended strategy for a complex network and a feedback approximation for avoiding forecast are further explored. Weaknesses of the strategy are also explicitly analyzed. To test the strategy, simulation investigations are conducted on two networks with multiple parallel routes. The results indicate that the strategy is able to provide stable splitting rates and to approximate user optimal equilibrium in different conditions, in particular when traffic demand is high. This strategy has potential to be applied in an urban road network due to its simplicity and easily obtained input data. The strategy is also applicable for single destination if some alternatives and similar routes are available. 相似文献
12.
采用Abaqus软件建立多个非线性有限元计算模型,对完整和破损后的船体梁进行非线性有限元计算。通过与Smith方法的结果对比分析,确定船体梁残存强度非线性有限元计算模型和边界条件,并研究破口周围边界对残存强度的影响。 相似文献
13.
Sandy sediments in shallow coastal waters of the Baltic Sea are often characterised by large numbers of biogenic structures which are produced by macrozoobenthos species. A series of experiments was devised to quantify how the interaction of such structures with the near-bed flow regime affects the sediment flux. Most experiments were done with simplified replicates of structures generated by typical species commonly found in the Mecklenburg Bight, starting with solitary structures and regularly-spaced arrays in a range of characteristic population densities, followed by a complex benthic macrofauna community, both artificial and alive. A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a topography scanning laser, was used for high-resolution measurements (2 mm horizontal step size and 0.3 mm vertical resolution) of sand erosion (220 µm median grain size, at 20 cm s− 1) and fine particle deposition (8 µm grain size, at 5 cm s− 1). Sediment transport threshold values were measured for each layout. As a rule-of-thumb, both the erosion fluxes and the deposition of suspended matter increased considerably at low population densities (below 2%, expressed as percent of the sediment surface covered, i.e. roughness density RD). Above densities of 4%, erosion almost stopped inside the test arrays, and deposition remained well below the level of unpopulated areas. An attempt to extrapolate these findings to field conditions (using field current velocity data from 2001) showed that the net flux switched from erosion to deposition for densities above 5%. These parameters can now be integrated into a numerical sediment transport model coupling waves, currents, sediment dynamics and biological processes, which is currently under construction at the Baltic Sea Research Institute (IOW), Rostock, Germany. 相似文献
14.
A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a bottom scanning laser, was used for detailed, non-intrusive flow measurements (at 2 cm s− 1 and 10 cm s− 1) around solitary biogenic structures, combined with high-resolution mapping of the structure shape and position. The structures were replicates of typical macrozoobenthic species commonly found in the Mecklenburg Bight and with a presumed influence on both, the near-bed current regime and sediment transport dynamics: a worm tube, a snail shell, a mussel, a sand mound, a pit, and a cross-stream track furrow. The flow was considerably altered locally by the different protruding structures (worm tube, snail, mussel and mound). They reduced the horizontal approach velocity by 72% to 79% in the wake zone at about 1–2 cm height, and the flow was deflected around the structures with vertical and lateral velocities of up to 10% and 20% of the free-stream velocity respectively in a region adjacent to the structures. The resulting flow separation (at flow Reynolds number of about 4000 and 20,000 respectively) divided an outer deflection region from an inner region with characteristic vortices and the wake region. All protruding structures showed this general pattern, but also produced individual characteristics. Conversely, the depressions (track and pit) only had a weak influence on the local boundary layer flow, combined with a considerable flow reduction within their cavities (between 29% and 53% of the free-stream velocity). A longitudinal vortex formed, below which a stagnant space was found. The average height affected by the structure-related mass flow rate deficit for the two velocities was 1.6 cm and 1.3 cm respectively (80% of height and 64%) for the protruding structures and 0.6 cm and 0.9 cm (90% and 127% of depth) for the depressions. Marine benthic soft-bottom macrozoobenthos species are expected to benefit from the flow modifications they induce, particularly in terms of food particle capture due to altered particle pathways and residence times, but also for the exchange of gases, solutes and spawn. The present results confirm previous studies on flow interaction effects of various biogenic structures, and they add a deeper level of detail for a better understanding of the fine-scale effects. 相似文献
15.
The two-dimensional water entry of a bow-flare ship section with constant roll angle, or heel angle, was studied by using
a boundary element method. The fully nonlinear free surface conditions and exact body boundary conditions were satisfied.
Nonviscous flow separation from the knuckles of the section or from the curved bottom could be simulated. The numerical calculations
were compared with existing experimental results. First, the effects of roll angle were investigated and then the characteristics
associated with large roll angles were examined in particular. The evolution of the free surfaces and the pressure distributions
on the section surface are illustrated and the influence of nonviscous flow separation from the leeward section surface is
discussed. 相似文献
16.
Katharina ParryMartin L. Hazelton 《Transportation Research Part B: Methodological》2012,46(1):175-188
Estimation of origin-destination (OD) matrices from link count data is a challenging problem because of the highly indeterminate relationship between the observations and the latent route flows. Conversely, estimation is straightforward if we observe the path taken by each vehicle. We consider an intermediate problem of increasing practical importance, in which link count data is supplemented by routing information for a fraction of vehicles on the network. We develop a statistical model for these combined data sources and derive some tractable normal approximations thereof. We examine likelihood-based inference for these normal models under the assumption that the probability of vehicle tracking is known. We show that the likelihood theory can be non-standard because of boundary effects, and provide conditions under which such irregular behaviour will be observed in practice. For regular cases we outline connections with existing generalised least squares methods. We then consider estimation of OD matrices under estimated and/or misspecified models for the probability of vehicle tracking. Theoretical developments are complemented by simulation experiments and an illustrative example using a section of road network from the English city of Leicester. 相似文献
17.
Modelling the impact of weather conditions on active transportation travel behaviour 总被引:1,自引:0,他引:1
Sheyda Saneinejad Matthew J. RoordaChristopher Kennedy 《Transportation Research Part D: Transport and Environment》2012,17(2):129-137
Three weather sensitive models are used to explore the relationship between weather and home-based work trips within the City of Toronto, focusing on active modes of transportation. The data are restricted to non-captive commuters who have the option of selecting among five basic modes of auto driver, auto passenger, transit, bike and walk. Daily trip rates in various weather conditions are assessed. Overall, the results confirm that impact of weather on active modes of transportation is significant enough to deserve attention at the research, data collection and planning levels. 相似文献
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