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471.
We present a coupled sea ice–ocean-biological (including ice algae) model in the Arctic Ocean. The 1D model was developed and implemented on the Canadian Beaufort Sea shelf to examine the importance of different physical processes in controlling the timing and magnitude of primary production and biogenic particle export over an annual cycle (1987). Our results show that the snow and sea ice cover melt and/or break-up controls the timing of the phytoplankton bloom but primary producers (ice algae and phytoplankton) on the outer shelf are essentially nutrient limited. The total annual primary production (22.7 to 27.7 g-C m? 2) is thus controlled by nutrient “pre-conditioning” in the previous fall and winter and by the depth of wind mixing that is controlled in part by the supply of fresh water at the end of spring (ice melt or runoff). The spring bloom represents about 40% of the total annual primary production and occurs in a period of the year when sampling is often lacking. Time interpolation of observed values to obtain total annual primary production, as done in many studies, was shown to lead to an underestimation of the actual production. Our simulated ratios of export to primary production vary between 0.42 and 0.44. 相似文献
472.
Environmental improvement and energy issues are increasingly becoming more important as worldwide concerns. Natural gas is
a good alternative fuel that can help to improve these issues because of its large quantity and clean burning characteristics.
This paper provides the experimental performance results of a Bi-Fuel engine that uses Compressed Natural Gas as its Primary
fuel and gasoline as its secondary fuel. This engine is a modification of the basic 1.4-liter gasoline engine. Generally,
on the unmodified base engine, torque and power for CNG fuel are considerably lower than gasoline fuel. In this paper, the
influence of fuels on wall temperature, performance and emissions are investigated. 相似文献
473.
474.
Anders Karlström Joel P. Franklin 《Transportation Research Part A: Policy and Practice》2009,43(3):283-296
This paper assesses the horizontal and vertical equity effects of the Stockholm Trial with Congestion Pricing for morning commuters, in terms of both travel behavioral adjustments and welfare effects, as a result of the toll’s direct effects and the behavioral adjustments. We consider specifically two behavioral adjustments: mode choice and departure time choice. Initial car drivers crossing the toll cordon had a 15 percentage-points higher rate of switching to public transit as compared with those not crossing the cordon. We also find some evidence of peak spreading, in particular toward a later departure time, as a result of the charging scheme, but most people choose a departure time within 15 min both before and during the trial. In the welfare analysis, we found no clear pattern of increasing burden by either increasing income or decreasing income, and the increase in the Gini Coefficient was insignificant. We also found no significant difference in either the mode-switching behavior or the average welfare effect for women versus for men. 相似文献
475.
Safety of hybrid-electric and fuel cell vehicles is a critical aspect of these new technologies, since any accident exposing
occupants of such vehicles to unconventional hazards may result in significant setbacks to successful market penetration.
Fuel cell and hybrid-electric drive systems are complex, and it is essential to perform a thorough analysis to determine critical
failure conditions. There are several safety concerns for routine operation of such systems, particularly for hydrogen-fueled
vehicles. A modified Failure Modes and Effect Analysis (FMEA) has been developed, along with a Criticality Analysis (CrA),
to identify potentially hazardous conditions for crash and non-crash situations. A mathematical model of fuel cell operation
has been developed and used here in conjunction with the FMEA. Component failures during the event modes are simulated using
vehicle models developed with Matlab Simulink tools. Six simulation models were created using the software. In addition, a
preliminary finite element model of a fuel cell vehicle, using a Ford Taurus (91′) model year sedan, has been developed and
implemented. This finite element model is used as a demonstration of the crash simulation of the vehicle. 相似文献
476.
Henry X. Liu Xinkai Wu Wenteng Ma Heng Hu 《Transportation Research Part C: Emerging Technologies》2009,17(4):412-427
How to estimate queue length in real-time at signalized intersection is a long-standing problem. The problem gets even more difficult when signal links are congested. The traditional input–output approach for queue length estimation can only handle queues that are shorter than the distance between vehicle detector and intersection stop line, because cumulative vehicle count for arrival traffic is not available once the detector is occupied by the queue. In this paper, instead of counting arrival traffic flow in the current signal cycle, we solve the problem of measuring intersection queue length by exploiting the queue discharge process in the immediate past cycle. Using high-resolution “event-based” traffic signal data, and applying Lighthill–Whitham–Richards (LWR) shockwave theory, we are able to identify traffic state changes that distinguish queue discharge flow from upstream arrival traffic. Therefore, our approach can estimate time-dependent queue length even when the signal links are congested with long queues. Variations of the queue length estimation model are also presented when “event-based” data is not available. Our models are evaluated by comparing the estimated maximum queue length with the ground truth data observed from the field. Evaluation results demonstrate that the proposed models can estimate long queues with satisfactory accuracy. Limitations of the proposed model are also discussed in the paper. 相似文献
477.
Bernard F. Byrne 《Transportation Research Part B: Methodological》1980,14(3):241-242
The macroscopic traffic flow models developed from the car following models of Gazis et al. (1961) are shown to have a flaw in that they do not meet certain of the boundary conditions that researchers have said that they do. This does not affect many existing models but, nevertheless, should be cleared up. 相似文献
478.
Luis Baeza David J. Thompson Giacomo Squicciarini Francisco D. Denia 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2018,56(11):1734-1746
This work presents a robust methodology for calculating inter-penetration areas between railway wheel and rail surfaces, the profiles of which are defined by a series of points. The method allows general three-dimensional displacements of the wheelset to be considered, and its characteristics make it especially suitable for dynamic simulations where the wheel–rail contact is assumed to be flexible. The technique is based on the discretisation of the geometries of the surfaces in contact, considering the wheel as a set of truncated cones and the rail as points. By means of this approach, it is possible to reduce the problem to the calculation of the intersections between cones and lines, the solution for which has a closed-form expression. The method has been used in conjunction with the CONTACT algorithm in order to solve the static normal contact problem when the lateral displacement of the wheelset, its yaw angle and the vertical force applied in the wheelset centroid are prescribed. The results consist of smooth functions when the dependent coordinates are represented as a function of the independent ones, lacking the jump discontinuities that are present when a rigid contact model is adopted. Example results are shown and assessed for the normal contact problem for different lateral and yaw positions of the wheelset on the track. 相似文献
479.
480.