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   2148篇
  免费   11篇
公路运输   723篇
综合类   60篇
水路运输   676篇
铁路运输   57篇
综合运输   643篇
  2023年   11篇
  2022年   37篇
  2021年   15篇
  2020年   11篇
  2019年   21篇
  2018年   63篇
  2017年   54篇
  2016年   79篇
  2015年   21篇
  2014年   78篇
  2013年   348篇
  2012年   100篇
  2011年   103篇
  2010年   108篇
  2009年   110篇
  2008年   117篇
  2007年   69篇
  2006年   48篇
  2005年   42篇
  2004年   33篇
  2003年   32篇
  2002年   28篇
  2001年   25篇
  2000年   38篇
  1999年   23篇
  1998年   32篇
  1997年   38篇
  1996年   36篇
  1995年   50篇
  1994年   21篇
  1993年   26篇
  1992年   18篇
  1991年   14篇
  1990年   15篇
  1989年   12篇
  1988年   17篇
  1987年   15篇
  1986年   14篇
  1985年   20篇
  1984年   17篇
  1983年   14篇
  1982年   23篇
  1981年   29篇
  1980年   18篇
  1979年   35篇
  1978年   14篇
  1977年   20篇
  1976年   14篇
  1975年   14篇
  1974年   9篇
排序方式: 共有2159条查询结果,搜索用时 31 毫秒
991.
MULTI-AGENT BASED DISTRIBUTED PROCESS PLANNING MANAGEMENT   总被引:1,自引:0,他引:1  
IntroductionProcessplanningdealswiththeselectingofthemanufacturingprocessandparameterstobeusedtoconvertapartfromrawmaterialtoagivenshape.Itsroleshouldnotbeonlyseenastoprovideunambiguousinstructions,butalsotoseekout,developandaidintheimplementationoft…  相似文献   
992.
在列车基础制动产品中,包括盘形制动单元和踏面制动单元在内,都广泛使用了牙式离合器结构。现以城轨踏面制动单元中的典型零件吊耳为例进行工艺分析,制定加工方案、进行工装和专用刀具设计,确保加工精度、提高加工效率。  相似文献   
993.
A key question is whether the very successful, largely short-haul LCC business model can work over long-haul sectors? This paper compares the cost and other advantages of LCCs and evaluates how far they might be applied to long-haul sectors. It is estimated that cost advantages might be much lower than the 50-60% on short-hauls. Other factors such as the adoption by network airlines of some LCC features and their likely competitive response, the limited potential for market stimulation, the need for dense markets and feed traffic all combine to cast doubt on the widespread establishment of the business model for long-haul flights.  相似文献   
994.
A first order mass balance of six different trace metals (Mn, Fe, Pb, Zn, Cu, Ni) was presented for a 1-year period for the different compartments of the Adriatic Sea: compartment 1 (northern Adriatic Sea), compartment 2 (central Adriatic Sea and surface layer of the southern Adriatic Sea) and compartment 3 (deep water of the southern Adriatic Sea). The Adriatic Sea appeared to be a source of dissolved Cu, Mn and Fe for the Mediterranean Sea through the Strait of Otranto whereas for dissolved Zn and Pb the Adriatic Sea appeared to be a net sink. For dissolved Ni, inputs and outputs through the Strait of Otranto balanced each other. The residence times of all metals in compartment 1 were significantly shorter than that of water indicating significant removal. In compartments 2 and 3, residence times of Mn and Fe were relatively short suggesting removal from the water column whereas for the other metals their residence times were similar to that of water. Calculations of turnover times of metals with respect to different processes showed that in compartments 1 and 2, sedimentation was the main process that affected the content of the reservoirs whereas in compartment 3, the water flux exchanges played an important role for Zn, Cu and Ni.Most of the metals clearly undergo a very dynamic cycle of sedimentation/remobilization particularly in the Northern Adriatic Sea. In the northern Adriatic Sea, most of the Mn and Fe in deposited sediment were remobilized. This was related to diagenetic processes involving the utilisation and solubilisation of Mn and Fe oxides, which occur in the surface of the sediment in the northern Adriatic Sea. In the central Adriatic Sea, remobilization of Mn and Fe was less than in the northern Adriatic Sea, suggesting that diagenesis processes appear deeper in the sediment. Advective transport of sediment was a major source of metals for the deep basin. As much as 80% of the sediments in the South Adriatic Pit might be advected from the shelf. Remobilization fluxes in the South Adriatic Pit were significantly less than in the Northern and Central Adriatic Sea reflecting hemi-pelagic sediments.  相似文献   
995.
Road transportation is a strongly growing source of CO2, and use of biofuels represents one option to reduce end-of-pipe emissions of the existing car fleet. In this contribution, the implementation of the EU Biofuels Directive (2003/30/EC) and related voluntary measures at the local level are examined in Germany, UK, Italy and Finland and the cities of Berlin, London, Milan and Helsinki. Even though they are not directly involved in the implementation of the biofuel directive, all four cities studied have played an important role in emissions reduction by voluntarily participating in research and demonstration projects and by using biofuels in their own fleet. An analysis of the numerous causes and driving forces leading to different local level measures is provided. The environmental sensitivity, usually examined at national level, and the national level implementation of the EU Biofuels Directive (2003/30/EC) were not directly correlated with the city-level activities Instead, support from local businesses and acquisition of EU funds were considered to be valid explanatory factors for the city-level activities. In addition, through horizontal networking cities are starting to exchange know-how gained in their projects, contributing in this way to the accumulation of experience for future policies and technologies.  相似文献   
996.
Strategic re-thinking in shipping companies   总被引:3,自引:0,他引:3  
This article proposes a framework for how successful shipping companies can develop strategies for growth and take advantage of business opportunities. It is essential to strengthen strategy implementation to trigger faster, internallygenerated and profitable business growth. Formal planning and control systems, as they traditionally exist in shipping companies, need to be modified to allow for such growth. The forward-thinkers, the truly dynamic companies, will be able to perceive business opportunities before anyone else, mobilize their people, and implement the necessary strategies. In doing so, a balance must be struck between the everyday and visionary focus, between the top-down and bottom-up focus, between the business and corporate portfolio focus. Shipping companies can learn from the example of the progressive business leaders in other fields, capitalizing on their way to succeed and grow, by developing a dual capability to 'see' new opportunities and to 'mobilize' the relevant organizational resources to implement these. Examples from successful shipping companies are provided.  相似文献   
997.
A data and dynamics driven approach to estimate, decompose, organize and analyze the evolving three-dimensional variability of ocean fields is outlined. Variability refers here to the statistics of the differences between ocean states and a reference state. In general, these statistics evolve in time and space. For a first endeavor, the variability subspace defined by the dominant eigendecomposition of a normalized form of the variability covariance is evolved. A multiscale methodology for its initialization and forecast is outlined. It combines data and primitive equation dynamics within a Monte-Carlo approach.The methodology is applied to part of a multidisciplinary experiment that occurred in Massachusetts Bay in late summer and early fall of 1998. For a 4-day time period, the three-dimensional and multivariate properties of the variability standard deviations and dominant eigenvectors are studied. Two variability patterns are discussed in detail. One relates to a displacement of the Gulf of Maine coastal current offshore from Cape Ann, with the creation of adjacent mesoscale recirculation cells. The other relates to a Bay-wide coastal upwelling mode from Barnstable Harbor to Gloucester in response to strong southerly winds. Snapshots and tendencies of physical fields and trajectories of simulated Lagrangian drifters are employed to diagnose and illustrate the use of the dominant variability covariance. The variability subspace is shown to guide the dynamical analysis of the physical fields. For the stratified conditions, it is found that strong wind events can alter the structures of the buoyancy flow and that circulation features are more variable than previously described, on multiple scales. In several locations, the factors estimated to be important include some or all of the atmospheric and surface pressure forcings, and associated Ekman transports and downwelling/upwelling processes, the Coriolis force, the pressure force, inertia and mixing.  相似文献   
998.
Warmer than average sea surface temperatures were observed by the Tropical Rainfall Mission Microwave Imager in the Angola Benguela Current system in late austral summer 2001 and persisted for about three months. These coastal anomalies extended offshore by 1 to 4° longitude and were not due to local ocean atmosphere interaction or relaxation of the upwelling favorable southerly winds. Instead, they were remotely forced by ocean atmosphere interaction in the Tropical Atlantic. Satellite remote sensing and a linear ocean model suggest that relaxation of trade winds along the equator triggered Kelvin waves that crossed the basin within a month in early 2001. Westerly wind anomalies were also observed in December 2000 and January 2001 over most of the Tropical Atlantic contributing to a warm preconditioning due to an enhancement of the oceanic annual cycle. This led to abnormal sea level heights near equatorial Africa that propagated southwards along the coast towards the Angola Benguela Frontal zone. This process increased the seasonal penetration of warm and salty water of tropical origin into the Angola Benguela upwelling system.  相似文献   
999.
介绍了西门子公司开发的铁路货车在线监测系统.  相似文献   
1000.
The susceptibilities of surface ships and submarines to electromagnetic influence mines and detection systems are generally determined with the aid of mathematical and physical scale models of the vessel's underwater field signatures. In addition, they are the primary tools used in the design of signature reduction systems. However, limitations of model accuracy need to be recognized and identified through verification and validation, and they should not be used blindly as a substitute for critical engineering analysis. The proper use of underwater electromagnetic field models of naval vessels in designing signature reduction systems will be presented.  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