全文获取类型
收费全文 | 1319篇 |
免费 | 15篇 |
专业分类
公路运输 | 250篇 |
综合类 | 300篇 |
水路运输 | 317篇 |
铁路运输 | 147篇 |
综合运输 | 320篇 |
出版年
2023年 | 11篇 |
2022年 | 38篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 16篇 |
2018年 | 41篇 |
2017年 | 25篇 |
2016年 | 42篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 135篇 |
2012年 | 78篇 |
2011年 | 109篇 |
2010年 | 79篇 |
2009年 | 97篇 |
2008年 | 74篇 |
2007年 | 82篇 |
2006年 | 84篇 |
2005年 | 68篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 10篇 |
1998年 | 21篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
排序方式: 共有1334条查询结果,搜索用时 906 毫秒
281.
Roger L. Tobin 《运输规划与技术》2013,36(4):215-223
This paper develops an analytic approach for measuring the effect of vehicle scheduling and of metering methods required to balance entrance rates among stations on lane capacity utilization of automated automobile guideways. The scheduling process at each entrance is represented by a probabilistic model which generates a system of nonlinear equations. The solution of this system yields the maximum steady state input rates at the entrances to the guideway system. The method developed is applicable to network configurations in which a small number of merges must be scheduled for each vehicle before it enters the guideway. It is demonstrated by application to a corridor guideway serving a major activity center during peak inbound demand, and also it is shown how the approach may be extended to more complex networks. 相似文献
282.
For the complex structure and vibration characteristics of the seat and cab system of truck, there is no reliable theoretical model for the suspensions design at present, which seriously restricts the improvement of ride comfort. In this paper, a 4 degree-of-freedom seat-cab coupled system model was presented; using the mechanism modeling method, its vibration equations were built; then, by the tested cab suspensions excitations and seat acceleration response, its parameters identification mathematical model was established. Combining the tested signals and a simulation model with the parameters identification mathematical model, a new method of hybrid modeling of seat-cab coupled system was presented. With a practical example of seat and cab system, the parameters values were identified and validated by simulation and test. The results show that the model and method proposed are correct and reliable, and lay a good foundation for the optimal design of seat suspension and cab suspensions to improve ride comfort. 相似文献
283.
Since the 1990s, transport project assessments take systematically pollutant emission estimations into account. This paper is about the methodological aspects of these calculations. It focuses more specifically on the car fleet hypothesis, which most often lays on national data, without consideration of local specificities. We use the last household travel survey from Lyon, 2006, and the SIMBAD model to compare the results of CO2 and NOx emissions estimated from the French national car fleet, the aggregated Lyon car fleet and the same fleet disaggregated by household location and income. We show that the error level varies, depending on the pollutant and the observation scale. The use of an aggregated local car fleet seems interesting and satisfactory for a global emission assessment. If the results are required at a more detailed spatial level, the use of this local fleet improves sharply the estimations in comparison of a national fleet; the fleet disaggregation refines the results for NOx. 相似文献
284.
工程实际中,汽车动力总成悬置系统不可避免地存在着一定的参数不确定性,且不确定参数间往往同时存在一定的相关性与独立性。本文中引入多维平行六面体模型处理系统参数相关性和独立性并存的情形,结合蒙特卡洛法提出了一种悬置系统固有特性的不确定性分析方法,并给出了方法的分析步骤。对某悬置系统的数值分析结果表明:该方法能有效处理系统不确定参数的相关性和独立性,与未考虑参数相关性的区间方法相比,该方法能获得更为合理的固有频率和解耦率区间范围;对于给定的研究模型,其左右悬置点的刚度相关性对系统固有特性的影响比较明显,在设计和研究过程中应给予重点关注。 相似文献
285.
Yann Ourmières Pierre Brasseur Marina Lévy Jean-Michel Brankart Jacques Verron 《Journal of Marine Systems》2009,75(1-2):100-115
A sequential assimilative system has been implemented into a coupled physical–biogeochemical model (CPBM) of the North Atlantic basin at eddy-permitting resolution (1/4°), with the long-term goal of estimating the basin scale patterns of the oceanic primary production and their seasonal variability. The assimilation system, which is based on the SEEK filter [Brasseur, P., Verron, J., 2006. The SEEK filter method for data assimilation in oceanography: a synthesis. Ocean Dynamics. doi: 10.1007/s10236-006-0080-3], has been adapted to this CPBM in order to control the physical and biogeochemical components of the coupled model separately or in combination. The assimilated data are the satellite Topex/Poseidon and ERS altimetric data, the AVHRR Sea Surface Temperature observations, and the Levitus climatology for salinity, temperature and nitrate.In the present study, different assimilation experiments are conducted to assess the relative usefulness of the assimilated data to improve the representation of the primary production by the CPBM. Consistently with the results obtained by Berline et al. [Berline, L., Brankart, J-M., Brasseur, P., Ourmières, Y., Verron, J., 2007. Improving the physics of a coupled physical–biogeochemical model of the North Atlantic through data assimilation: impact on the ecosystem. J. Mar. Syst. 64 (1–4), 153–172] with a comparable assimilative model, it is shown that the assimilation of physical data alone can improve the representation of the mixed layer depth, but the impact on the ecosystem is rather weak. In some situations, the physical data assimilation can even worsen the ecosystem response for areas where the prior nutrient distribution is significantly incorrect. However, these experiments also show that the combined assimilation of physical and nutrient data has a positive impact on the phytoplankton patterns by comparison with SeaWiFS ocean colour data, demonstrating the good complementarity between SST, altimetry and in situ nutrient data. These results suggest that more intensive in situ measurements of biogeochemical nutrients are urgently needed at basin scale to initiate a permanent monitoring of oceanic ecosystems. 相似文献
286.
While authorities consider transit as one of the solutions to enhance sustainable mobility, they do not provide a steady funding for its operation and growth. This inconsistency between political discourse and real intervention has motivated nine transit operators from six metropolitan areas of Quebec to conduct a study on the contribution of transit to sustainability. This article first presents the process of selecting indicators. For some of the indicators developed, the estimation method is detailed, which comprises of the following factors: resources, emission prevention, contribution to daily physical activity, accessibility to public transit and to activity locations, daily savings of using transit in comparison with car use, and the relative safety of transit use. Finally, the article explains the conceptual, methodological, and informational challenges that influenced the selection of indicators and their estimation methodologies. 相似文献
287.
William L. Garrison 《先进运输杂志》2000,34(1):31-63
I critique the innovation processes that yield transportation's technologies, and to aid my analysis I look back to take advantage of the accumulation of experiences and insights marked by the millennium. I identify supply, transport, and user systems. Transport systems move things; supply systems provide fuel, pavements, and other inputs to transport activities; and user systems combine transport with other activities for socially useful purposes. The discussion then shifts from structure to behavior, and a short review of the emergence of today's systems reminds us that technological advances may improve the provision of old services, offer new ways of doing old things, or induce qualitative changes that enable doing new things. With these structural and behavioral matters in mind, I challenge the reader to judge the present situation and the future. 相似文献
288.
杨进峰 《变流技术与电力牵引》2006,(5):26-30,39
论述了IGBT门极驱动器设计新方案,它具有先进的保护功能,如元件采用双电平开通以减小峰值电流,采用双电平关断以限制过电压,以及防止出现桥臂贯通的有源密勒箝位.此外还介绍一种包括双电平关断驱动器和有源密勒箝位功能的新电路,并对所述功能的试验及结果进行阐述,重点介绍双电平关断驱动器的中间电平对IGBT过电压的影响. 相似文献
289.
The key features of the western Galician shelf hydrography and dynamics are analyzed on a solid statistical and experimental basis. The results allowed us to gather together information dispersed in previous oceanographic works of the region. Empirical orthogonal functions analysis and a canonical correlation analysis were applied to a high-resolution dataset collected from 47 surveys done on a weekly frequency from May 2001 to May 2002. The main results of these analyses are summarized bellow. Salinity, temperature and the meridional component of the residual current are correlated with the relevant local forcings (the meridional coastal wind component and the continental run-off) and with a remote forcing (the meridional temperature gradient at latitude 37°N). About 80% of the salinity and temperature total variability over the shelf, and 37% of the residual meridional current total variability are explained by two EOFs for each variable. Up to 22% of the temperature total variability and 14% of the residual meridional current total variability is devoted to the set up of cross-shore gradients of the thermohaline properties caused by the wind-induced Ekman transport. Up to 11% and 10%, respectively, is related to the variability of the meridional temperature gradient at the Western Iberian Winter Front. About 30% of the temperature total variability can be explained by the development and erosion of the seasonal thermocline and by the seasonal variability of the thermohaline properties of the central waters. This thermocline presented unexpected low salinity values due to the trapping during spring and summer of the high continental inputs from the River Miño recorded in 2001. The low salinity plumes can be traced on the Galician shelf during almost all the annual cycle; they tend to be extended throughout the entire water column under downwelling conditions and concentrate in the surface layer when upwelling favourable winds blow. Our evidences point to the meridional temperature gradient acting as an important controlling factor of the central waters thermohaline properties and in the development and decay of the Iberian Poleward Current. 相似文献
290.