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   1333篇
  免费   16篇
公路运输   572篇
综合类   46篇
水路运输   350篇
铁路运输   28篇
综合运输   353篇
  2023年   9篇
  2022年   21篇
  2021年   10篇
  2019年   12篇
  2018年   32篇
  2017年   41篇
  2016年   80篇
  2015年   19篇
  2014年   67篇
  2013年   211篇
  2012年   73篇
  2011年   82篇
  2010年   78篇
  2009年   59篇
  2008年   81篇
  2007年   35篇
  2006年   29篇
  2005年   25篇
  2004年   24篇
  2003年   10篇
  2002年   13篇
  2001年   19篇
  2000年   31篇
  1999年   16篇
  1998年   15篇
  1997年   18篇
  1996年   23篇
  1995年   27篇
  1994年   10篇
  1993年   18篇
  1992年   13篇
  1991年   13篇
  1990年   6篇
  1989年   4篇
  1988年   12篇
  1987年   5篇
  1986年   10篇
  1985年   10篇
  1984年   8篇
  1983年   5篇
  1982年   8篇
  1981年   7篇
  1980年   8篇
  1979年   13篇
  1978年   5篇
  1977年   6篇
  1976年   5篇
  1975年   7篇
  1974年   6篇
  1973年   5篇
排序方式: 共有1349条查询结果,搜索用时 15 毫秒
281.
The national-flag fleets of most of the traditional martitime nations have, in virtually every case, been in decline in the 1980s and 1990s, despite the continued growth of ocean shipping. They have declined in terms of numbers of vessels and numbers of sea-going jobs, although not necessarily in terms of cargo carried. However, a number of those nations have responded to the changed technological and competitive conditions with some success by attempting to adjust crewing and work practices on vessels at sea. Neither the USA nor Australia has been in the forefront of such change. However, considerably more progress has been made in modernizing crewing practices and work rules in the Australian-flag fleet than in the US-flag fleet. There are a variety of reasons for this, inluding government policy. However, it is our argument that one of the principal reasons the US fleet lags behind the Australian fleet in the adoption of modern crewing practices and work rules is the much greater degree of union rivalry in the US shipping industry. In fact, while the degree of fragmentation and rivalry among unions in the Australian flag fleet has declined dramatically since 1980, their US cousins have continued, and in some ways expanded, their pattern of fratricidal behavior. First we shall discuss some of the technological and competitive imperatives that are driving human resource management practices in shipping and the crewing and industrial relations adjustments that are being made around the world to adjust to them. Then we shall indicate how the Australian and US fleets have responded to these challenges. This will be followed by a discussion of unionism in the Australian and US maritime industrics as it has devloped in the last two decades of the twentieth century. Finally, we shall draw conclusions about the impact of different patterns of unionization.  相似文献   
282.
The object of my book British Shipping and World Competitionwas to answer the question: 'Why has the tonnage of ships registered in the United Kingdom declined from over 45% of the world total in 1900 to about 16% of that total in 1960?'. There was never any normative element to this question, a point which has been much misunderstood. In answering the question, two different methodologies were used. Chapters II through VIII are industrial economic history, whereas Chapters IX through XIV are applied economics. When the two groups are thought of as siblings, not as Siamese twins, it can be seen that the first group has worn rather well, but that the applied economics chapters have a distinctly dated air. Most of this article is concerned with the applied economics chapters, where I try to examine what is said in the book in the light of my subsequent experience and thinking. There is one absolutely gross error in the material. Unfortunately, this is implicitly reflected in the Code of Conduct and in the EC Maritime Regulations. The original answer to the question has been rephrased in the article; I hope this will put to rest the idea that the question was normative in intent. The rephrasing does not alter the answer: the decline which needed to be accounted for can be explained solely in terms of internal constraints. The remainder was a 'natural' result of changing international patterns in resource allocation.  相似文献   
283.
In the long debate about the UNCTAD Code, many opinions have been put forward about the consequences of cargo reservation. Some have been based on theory, whilist others have transposed behaviour patterns from other industries or other periods of time. Several countries, however, have been operating cargo reservation laws for sufficiently long to enable some initial observations to be made. This article outlines recent experience in Brazil.  相似文献   
284.
285.
The paper describes some of the key issues that need to be addressed in the design and execution of underground structures to ensure their long term suitability as watertight units and outlines through practical examples of structures that have not achieved their design requirements which situations need to be considered. Waterproofing is not an exact science but a combination of theoretical knowledge and practical experience based on the five key factors: Environment, Design, Materials, Application and Use of the Structure.In conclusion the paper outlines the advances in crack control to date that can provide the necessary long term guarantees.The adoption of re - injectable crack inducers permitted the Client to save over 10% on construction costs and reduced the construction time by six months.  相似文献   
286.
Wright  Derek S. 《Transportation》1990,17(3):239-250
The paper reviews the current situation on-board microprocessor applications. It first describes the aspects of vehicle technology and performance that are the focus for on-board computing equipment, from engine management systems through to fully intergrated driver decision support. In the second section a wider perspective is taken by examining the interaction of the vehicle and its environment. The third and final section of the paper considers elements of communication which permit extensive transmission of vehicle and journey data for public and private use. The conclusion identifies factors which will influence the speed with which further applications will be adopted.  相似文献   
287.
所有由接地的电网系统供电并向可变输出系统供电的开关变流器拓扑结构,都会在负载装置上产生共模电压.系统地分析了用在交流传动装置上的各种变流器拓扑结构的共模电压,包括两点式电压源逆变器(VSI)、电流源逆变器(CSI)以及多点式逆变器.还分析了每种拓扑结构中使用的有源前端整流器.分析了共模电压的来源,并比较了由不同变流器拓扑结构产生的共模电压幅值.讨论了共模电压和降低共模电压技术的实际意义,并提供仿真和试验结果加以证明.  相似文献   
288.
The accelerated service life testing of automotive vehicles for durability to road roughness induced dynamic loads is often accomplished in the laboratory using road roughness simulation facilities [1-5]. However, such tests can also be accomplished by a carefully designed field operation on a test course [6], where both the speed of the vehicle and the roughness of die test course become variables that control the degree of the test acceleration. Field tests are generally harder to control than laboratory tests, but offer a greater degree of realism since the vehicle is fully operational during the test exactly as it will be in service. This paper formulates the criteria for accelerated service life tests on a test course, evaluates the assumptions that must be enforced to obtain valid results, and explores the sensitivity of the results to the critical test parameters, namely, the vehicle speed and the road roughness severity of the test course relative to the service environment.  相似文献   
289.
In railway applications wear prediction in the wheel–rail interface is a fundamental matter in order to study problems such as wheel lifespan and the evolution of vehicle dynamic characteristic with time. However, one of the principal drawbacks of the existing methodologies for calculating the wear evolution is the computational cost. This paper proposes a new wear prediction methodology with a reduced computational cost. This methodology is based on two main steps: the first one is the substitution of the calculations over the whole network by the calculation of the contact conditions in certain characteristic point from whose result the wheel wear evolution can be inferred. The second one is the substitution of the dynamic calculation (time integration calculations) by the quasi-static calculation (the solution of the quasi-static situation of a vehicle at a certain point which is the same that neglecting the acceleration terms in the dynamic equations). These simplifications allow a significant reduction of computational cost to be obtained while maintaining an acceptable level of accuracy (error order of 5–10%). Several case studies are analysed along the paper with the objective of assessing the proposed methodology. The results obtained in the case studies allow concluding that the proposed methodology is valid for an arbitrary vehicle running through an arbitrary track layout.  相似文献   
290.
This paper mainly focuses on the accurate estimation of the torque transferred through the engine clutch installed between the engine and the drive motor in parallel-type hybrid electric vehicles. The estimation of the engine clutch torque primarily relies on the forward-direction observer which uses the nominal engine net torque information. To overcome the limitation of using the nominal engine torque information that it may not be accurate during the transient states or due to the influence of external disturbance such as the road condition and wind, the forward-direction observer is supplemented by the use of reverse-direction observer which uses the driveline model and wheel speed measurements. In addition, the drive motor torque information is used to calibrate the nominal engine torque during the idle charging state, so that the driveline characteristic unique to parallel-type hybrid electric vehicle can be utilized to increase the estimation accuracy. Finally, the estimation performance of the designed observer is tested via simulation and experiments based on a real vehicle.  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