首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   304篇
  免费   0篇
公路运输   63篇
综合类   4篇
水路运输   110篇
铁路运输   6篇
综合运输   121篇
  2022年   1篇
  2019年   5篇
  2018年   3篇
  2017年   12篇
  2016年   7篇
  2015年   6篇
  2014年   3篇
  2013年   58篇
  2012年   4篇
  2011年   6篇
  2010年   19篇
  2009年   21篇
  2008年   22篇
  2007年   23篇
  2006年   12篇
  2005年   6篇
  2004年   6篇
  2003年   4篇
  2002年   5篇
  2001年   2篇
  2000年   4篇
  1999年   3篇
  1998年   3篇
  1997年   3篇
  1996年   7篇
  1995年   6篇
  1994年   1篇
  1993年   6篇
  1992年   4篇
  1991年   4篇
  1990年   2篇
  1988年   2篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1983年   1篇
  1982年   2篇
  1981年   4篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1976年   7篇
  1975年   4篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有304条查询结果,搜索用时 31 毫秒
31.
关于铁路隧道内安全的新UIC规程适用于新建和既有隧道。该规程制定了可靠的基础设施、车辆和运输调度措施来提高隧道内的安全性,尤其注意了隧道内的防火问题。  相似文献   
32.
33.
黄炜炳 《汽车杂志》2010,(1):270-270
前段时间和国内几家权威IT媒体主编交流,他们无一例外地抱怨现在导航厂商都不投放广告,令网站的内容更新与生存倍感压力。  相似文献   
34.
Oscillating point absorber buoys may rise out of the water and be subjected to bottom slamming upon re-entering the water. Numerical simulations are performed to estimate the power absorption, the impact velocities and the corresponding slamming forces for various slamming constraints. Three buoy shapes are considered: a hemisphere and two conical shapes with deadrise angles of 30° and 45°, with a waterline diameter of 5 m. The simulations indicate that the risk of rising out of the water is largely dependent on the buoy draft and sea state. Although associated with power losses, emergence occurrence probabilities can be significantly reduced by adapting the control parameters. The magnitude of the slamming load is severely influenced by the buoy shape. The ratio between the peak impact load on the hemisphere and that on the 45° cone is approximately 2, whereas the power absorption is only 4–8% higher for the 45° cone. This work illustrates the need to include slamming considerations aside from power absorption criteria in the buoy shape design process and the control strategy.  相似文献   
35.
This paper offers an overview of the currently available Ballast Water Treatment systems, their efficacy in reducing the number of organisms in relation with the IMO and other, future standards, and explores potentially new and promising technologies and current gaps.  相似文献   
36.
A flow-dependent critical-point method for investigating topographically controlled flow in natural channels is applied to the bottom current through the Irbe Strait connecting the Baltic proper and the Gulf of Riga. This approach is based on the functional formalism due to Gill [Gill, A.E., 1977. The hydraulics of rotating-channel flow. J. Fluid Mech., 80, 641–671.], and here is used for the stratified flow structure observed during the IRBEX-95 field campaign. A critical section of the realizable flow regime was found to be located slightly downstream of the most pronounced horizontal constriction of the channel. The predicted baroclinic volume flux 7200 m3 s−1 overestimates the observed mean bottom-water transport by around 30%, a discrepancy which most likely can be explained by the lack of sea level conditions and friction in the model.  相似文献   
37.
严峻问题     
今年关于太平洋航线有两个不确定因素,即美国进口量增长将会大大放缓,同时美国出口量会继续增加.因此,几乎所有其他的问题都是不确定的:进口量是否会增长还是会减少?  相似文献   
38.
今年关于太平洋航线有两个不确定因素,即美国进口量增长将会大大放缓,同时美国出口量会继续增加。因此,几乎所有其他的问题都是不确定的:进口量是否会增长还是会减少?航运公司是否会随着船只规模的增加,而为贸易业务分配更多运力,或者仅仅保持现有运力?他们是否能够成功增加运费以弥补成本的增长?发货人是否同意支付完全不固定的船舶燃油附加费?  相似文献   
39.
The efficient integration of logistics modes is critical for international cargo shipping. The local transportation connecting to the export port then plays a vital role in such integration. This paper investigates the problems of carrier selection in the China Pearl River delta area, with respect to international shipping. The analytical hierarchy process (AHP) model is constructed based on a comprehensive industrial interviews and statistical analysis. Rather than simply ranking the given alternatives, we use AHP is used to analyse the weakness and strength of impacting factors in carrier selection. The model is implemented under different types of shipper. Seven criteria are statistically summarized from the questionnaire for evaluating eight different modes. The results are useful to those liner companies serving the PRD region in relationship to port selection and fleet deployment.  相似文献   
40.
The physical–biological linkages controlling the dispersal of spores produced by macroalgae that reside in kelp forests are complicated and laced with feedbacks. Here we discuss the fundamental elements of these interactions. Biological considerations include spore swimming and sinking speeds, their periods of viability in the plankton, and the height of spore release above the seafloor, which together determine the durations over which spores can be swept by horizontal currents before they contact the seafloor. Morphologies and material properties of canopy forming kelps may also influence the drag exerted on passing waters by the kelps, the plants' ability to persist in the face of rapid flows, and thereby the degree to which impinging currents are redirected around, or slowed within, kelp forests. Macroalgal life histories, and the size of spore sources as controlled by the dimensions of kelp forests and the density and fecundity of individuals within them, influence effective dispersal distances as well. Physical considerations encompass the mean speed, direction, and timescales of variability of currents relative to spore suspension times, the interaction of surface gravity waves with currents in producing turbulence in the benthic boundary layer, wind-driven surface mixing, water stratification, and shoreline bathymetry and substratum roughness, all of which can affect the interplay of vertical and horizontal transport of macroalgal spores. Intricate within-forest processes may induce attenuation of current speeds and consequent reductions in seabed shear, along with simultaneous production of small-scale turbulence in kelp wakes. Slower mean currents and smaller eddy scales in turn may attenuate vertical mixing within forests, thus extending spore suspension times. Further complexities likely arise due to changes in the relative rates of horizontal and vertical dispersion, modifications to the overall profiles of vertical mixing, and the creation of fine-scale secondary flows around kelp individuals and substratum features. Under conditions of more rapid currents, submergence of the surface canopy and the establishment of skimming flows at the canopy–fluid interface may introduce additional coherent flow structures that alter rates of fluid exchange to and from the forest. Many of these coupled physical–biological processes are just beginning to be examined in a rigorous fashion in kelp forests, but their potential importance is clear.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号