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991.
S. Abdullah W. H. Kurniawan M. Khamas Y. Ali 《International Journal of Automotive Technology》2011,12(1):29-38
In an era in which environmental pollution and depletion of world oil reserves are of major concern, emissions produced by
automotive vehicles need to be controlled and reduced. An ideal solution is to switch to a cleaner fuel such as natural gas,
which generates cleaner emissions. In addition, control over the in-cylinder air-fuel mixture can be best achieved through
a direct-injection mechanism, which can further improve combustion efficiency. This need for cleaner automobiles provides
the motivation for this paper’s examination of the use of computational fluid dynamic (CFD) simulations to analyze the concentrations
of the exhaust gases produced by a compressed natural gas engine with a direct-fuel-injection system. In this work, a compressed
natural gas direct-injection engine has been designed and developed through a numerical simulation using computational fluid
dynamics (CFD) to provide an insight into complex in-cylinder behavior. The emissions analyzed in this study were carbon monoxide
(CO), nitric oxide (NO) and carbon dioxide (CO2), i.e. the main pollutants produced by natural gas combustion. Based on a stoichiometric mixture, the concentrations of CO
and NO were computed using the dissociation of carbon dioxide and the extended Zeldovich mechanism. CO2 was calculated using a mass balance of the species involved in the combustion process. The simulation results were then compared
with the experimental data generated by a single-cylinder research engine test rig. A good agreement was obtained with the
experimental data for the engine speeds considered for all emissions concentrations. 相似文献
992.
Road haulage is nowadays the main transport mode in France, demonstrating its ability to fulfil shippers’ demands. Among other success factors, the possibility for large companies to subcontract to very small ones, with very low fixed costs and greater flexibility, is often quoted as a major advantage. The ECHO survey, conducted in France in 2004, gives information about 10000 shipments made by 3000 shippers. This survey allows the analysis of subcontracting, by following at every stage how each shipment is given to another carrier by contract. The analysis shows that some subcontracts are mainly cost driven, but others aim at using the specialised skills of a particular haulier. For every transport segment (single parcel delivery service, parcel delivery service, less than truck load, full truck load), subcontracting is described in terms of sizes of the companies involved, services provided and the reasons for subcontracting. These results describe the main features of several different types of subcontracts. 相似文献
993.
Evaluation of natural and tracer fluorescent emission methods for droplet size measurements in a diesel spray 总被引:2,自引:0,他引:2
J. V. Pastor R. Payri J. M. Salavert J. Manin 《International Journal of Automotive Technology》2012,13(5):713-724
Spray sizing that records fluorescent emission and scattered light has been widely applied to spray diagnostics over the last two decades. Different experimental strategies have been developed, but comparing the different solutions offered has remained of interest to experimentalists. In this work, a comparison of two fluorescence strategies for measuring droplet size in the liquid phase of a last-generation DI diesel spray is conducted. The natural fluorescent emission of a commercial diesel fuel and the fluorescence emitted by a tracer (Rhodamine B) are compared using theoretical and experimental approaches. The LIF/Mie ratio commonly called Planar Droplet Sizing (PDS) technique is applied in two different ways to elucidate the possible advantages of using a fluorescent dopant. The sprays were injected under non-evaporative conditions into a constant pressure vessel that simulates densities present at the moment of injection in currently used passenger car diesel engines. Characterization of the signal properties was performed by measuring the absorption coefficient, fluorescence emission spectrum, quantum yield and lifetime of both configurations. The scattered light and fluorescence intensities were calculated to verify the dependencies of the droplet surface and volume. When applying the two techniques to quantify droplet size in dense diesel sprays, the results show that signal weakness and lack of control over the properties of natural fluorescence produce distortion in the shape of the spray and cause measurements to be unreliable. 相似文献
994.
In recent years, railway tunnels in karst areas have frequently suffered flooding after high-intensity rainfall, which seriously affects the safety of tunnel operation and the order of transportation, and even interrupts the traffic. Based on the water hazard case in the Yuanbaoshan Tunnel on the Zhijin-Bijie Railway Line, this paper explores the causes of lining damage in terms of geology, rainfall, and the design and construction of water hazard sections, and puts forward the treatment technology for tunnel water hazards with the core concept of "making full use of existing structures and employing open drainage methods in key sections". Besides, this paper simulates and analyzes the formation of hazards and the treatment effect through numerical simulation. The results show that the subjective causes for the damage in tunnel linings include an insufficient understanding of the water-bearing formations at the geological investigation stage, the underestimation of water hazard risks posed by high-intensity rainfall during construction, and the unimproved waterproof and drainage system in the design alteration, while the objective reasons include the development of karst near the tunnel section that passes through the stratum, the strong connectivity of water conduits, and the high-intensity rainfall in a certain period of time on the tunnel site. As for the simulation results, they show that the increase of external water pressure caused by the sudden rise in groundwater level after rainstorm significantly increases the internal force of linings, and eventually leads to a much lower safety factor of sidewall linings and large scale damage, which is in consistency with the characteristics of the actual on-site damage. After on-site emergency treatment, the tunnel structure has become stable and even encountering unprecedentedly heavy rainfall twice, the tunnel has still remained in a good condition. Since then, no water hazards and other disasters have occurred, which proves that the treatment plan is valid. © 2022, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献
995.
996.
M.J. Smith 《Transportation Research Part B: Methodological》1979,13(2):151-154
Consider a radial road network such that a single ring road is the only connection between the radials. This paper shows that there is, for any fixed origin-destination distribution, a location of the ring road which minimises the impact of radial traffic flow, for almost any criterion used to assess that impact. An optimal ring road has as many relevant trip-ends inside as outside. 相似文献
997.
Ekman transport is studied close to the Galician coast by means of wind data provided by the QuikSCAT satellite from November 1999 to October 2005. Three different coastal zones are identified, western coast from Miño River to Cape Finisterre, middle coast from Cape Finisterre to Cape Ortegal and northern coast, from Cape Ortegal to Cape Peñas. In addition to existence of long-term variations, the periodicity of the transport signal is characterized by an annual component (365 days), a seasonal fluctuation (50–80 days) and a time scale related to passing storms (15–20 days). Although the periodicity of the signal is similar at the three zones due to external meteorological forcing, the Ekman transport is modulated by the presence of the coast, in such a way that seasonal patterns vary in intensity and direction along the coast. Thus, the spring–summer pattern is characterized by high transport at the western coast, pointing seaward perpendicular to the shore-line. The same orientation is observed at the middle coast although with a lower magnitude. Finally, Ekman transport at the northern coast points landward and oblique to the shore-line. The different transport orientations are shown to be responsible for the upwelling probability variation along the coast. On the other hand, the autumn–winter pattern does not show a clear trend with important inter-annual differences showing the high variability of Ekman transport for this period. 相似文献
998.
Y. M. Bontekoning 《先进运输杂志》2000,34(3):391-413
Manufacturers have been promoting new terminal concepts for several years. They claim more efficient operations, shorter handling times and lower costs compared to conventional operations. However, so far no new‐generation terminals have been implemented, nor is there any intention yet to implement them. This is regrettable, because if new‐generation terminal concepts can achieve what their designers claim, these terminals could significantly improve the competitiveness of intermodal transport. It is expected that new‐generation terminals will perform particularly well in complex bundling networks such as hub and spoke, collection‐distribution and line networks. A static‐process analysis is used to evaluate the claimed terminal performances. The method incorporates the terminal function and the type of bundling network. Specific network situations have been defined for each type of bundling network. This study shows that the new concepts perform better than the reference terminal and shunting in complex bundling operations. 相似文献
999.
Catherine Lalande S. Bradley Moran Paul Wassmann Jacqueline M. Grebmeier Lee W. Cooper 《Journal of Marine Systems》2008,73(1-2):103-113
Large-volume sampling of 234Th was conducted to estimate particulate organic carbon (POC) export in conjunction with drifting sediment trap deployments in the northern Barents Sea in July 2003 and May 2005. 234Th-derived POC fluxes averaged 42.3 ± 39.7 mmol C m− 2 d− 1 in 2003 and 47.1 ± 30.6 mmol C m− 2 d− 1 in 2005. Sediment trap POC fluxes averaged 13.1 ± 8.2 mmol C m− 2 d− 1 in 2003 and 17.3 ± 11.4 mmol C m− 2 d− 1 in 2005, but better reflected the transient bloom conditions that were observed at each station within a season. Although 234Th fluxes agreed within a factor 2 at most stations and depths sampled, sediment trap POC fluxes were lower than large-volume POC flux estimates at almost every station. This may represent an under-collection of POC by the drifting sediment traps or, conversely, an over-collection of POC by the large-volume sampling of 234Th. It is hypothesized that the offset between the two methods is partly due to the presence of the prymnesiophyte Phaeocystis pouchetii, which potentially causes a large variation in > 53-μm POC/234Th ratios. Due to the large proportion of dissolved carbon or mucilage released by P. pouchetii, and because it is thought that P. pouchetii does not contribute significantly to the vertical export of biogenic matter in the Barents Sea, the application of large-volume sampling of 234Th may yield relatively high, and possibly inaccurate POC/234Th ratios. Hence, POC fluxes derived from 234Th sampling may be inappropriate and drifting sediment traps might be a more reliable method to measure the vertical export of biogenic matter in regions that have recurrent P. pouchetii blooms, such as the Barents Sea. 相似文献
1000.
M. Delaplace 《Recherche - Transports - Sécurité》2012,28(3-4):290-302
A lot of high-speed lines are planned all around the world. Economic and politic stakeholders of the served areas expect a lot of positive effects in terms of local economic development. If it is not always the case, some local economic dynamic indirectly linked to high-speed rail service (HSRS) can exist in some areas and in some conditions. The aim of this paper is to put in evidence the heterogeneity of the wider effects of a HSRS according to places. Using innovation theories, which underline the coproduction of services, we analyze the arrival of a HSRS in an area as a set of innovation services. We put forward that these innovations are different according to the countries and to the local areas. It is a first level of heterogeneity. Furthermore, potential use and appropriation of innovations linked to HSRS by local stakeholders which depend on the characteristics of the area are very different. This is a second level of heterogeneity. Finally, we put forward that the appropriation depends on the kind of strategies of the stakeholders. This is the third level of heterogeneity. Consequently, we underlined the necessity to go beyond the analysis of HSRS effects because the link between HSRS and local economic development is based on a coproduction. 相似文献