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   3918篇
  免费   14篇
公路运输   953篇
综合类   716篇
水路运输   1280篇
铁路运输   54篇
综合运输   929篇
  2023年   11篇
  2022年   37篇
  2021年   17篇
  2020年   17篇
  2019年   18篇
  2018年   398篇
  2017年   337篇
  2016年   331篇
  2015年   27篇
  2014年   90篇
  2013年   324篇
  2012年   170篇
  2011年   313篇
  2010年   321篇
  2009年   161篇
  2008年   283篇
  2007年   169篇
  2006年   41篇
  2005年   90篇
  2004年   71篇
  2003年   87篇
  2002年   40篇
  2001年   25篇
  2000年   39篇
  1999年   21篇
  1998年   30篇
  1997年   36篇
  1996年   31篇
  1995年   46篇
  1994年   21篇
  1993年   20篇
  1992年   15篇
  1991年   11篇
  1990年   14篇
  1989年   12篇
  1988年   15篇
  1987年   15篇
  1986年   11篇
  1985年   19篇
  1984年   17篇
  1983年   15篇
  1982年   22篇
  1981年   27篇
  1980年   18篇
  1979年   33篇
  1978年   12篇
  1977年   18篇
  1976年   8篇
  1975年   10篇
  1974年   8篇
排序方式: 共有3932条查询结果,搜索用时 218 毫秒
711.
712.
713.
714.
In this paper, an improved clamping force estimator is proposed for Electro-Mechanical Brake (EMB) systems by using the motor rotor position information and the hysteresis characteristics of mechanical parts in the EMB. A cascaded type of a force/position control system with a force sensor or an estimator was designed and implemented to control the clamping force and to keep the clearance gap in EMB systems. The EMB Hardware-In-the-Loop-Simulation (HILS) results show that the proposed force estimator yields better estimation performance than the existing estimator and that the clamping force control system based on the estimator can be also used for the fault tolerant control of the system.  相似文献   
715.
级配曲线是由富勒模型中最大粒径和形状系数两个参数来确定的,富勒模型能够很好地拟合使用性能良好的级配.级配曲线图是由形状系数和最大粒径组成的直角坐标系,它可以表示出级配范围、砂石比和相关的性能参数.该文分析了Superpave沥青混合料力学和水稳性能的试验结果,提出了根据级配曲线推荐的集料设计出满足路面各项性能的自由设计理念.  相似文献   
716.
该文进行了一个三维有限元参数量化的粘弹性路面响应研究,由于不同的轮胎配置:双轮和宽基轮胎在3种温度(5、25和40℃)和两种速度(8、72 km/h);还有影响路面响应的3种因素:移动车轮荷载幅值(连续,梯形),层间界面条件(简单的摩擦和粘弹性模型)和横向力共同对路面响应的影响进行了研究.研究发现连续加载幅值,不但可以模拟路面对运动轮荷载的响应,并且是一种比目前使用的梯形荷载幅值更准确的研究模型.粘弹性模型极大地提高了双轮胎对预测路面的响应,而简单的摩擦模型更接近宽基轮胎的实地测量.侧向剪力是积极改善预测轮底的表面磨损和底部热拌沥青(沥青)基层的较小程度上的应变.研究表明:使用连续加载幅值和非均匀压力分布模拟移动轮,侧向剪切力和适当的界面摩擦可显著改善有限元模型对车辆加载路面响应的预测能力.  相似文献   
717.
The shipping industry operates in a regulatory framework, where the International Maritime Organization (IMO) is the leading regulatory body. The role of the IMO is to propose maritime regulations to its member states. The successful worldwide implementation of a maritime regulation depends on how many member states adopt it. However, many maritime regulations are not adequately implemented worldwide. As a result, ship operators have found themselves in an uncomfortable position in developing their business in an unstable regulatory regime. This paper proposes an extendable and applicable methodology involving a System of Hierarchical Scorecards (SHS) to measure the implementation costs and benefits of a newly introduced or existing maritime regulation by ship operators. The regulators may use the results in evaluating newly introduced and/or existing regulations through taking into account the economic burden that will be generated to ship operators. In this paper, SHS is extended to demonstrate its applicability on evaluating a ship operator’s organization with regard to his regulatory implementation performance by the means of a case study.  相似文献   
718.
This research study attempts to conceptualize models based on the relationship between characterization factors and port performance. By selecting a universe of the 230 largest European ports in terms of cargo throughput, 43 valid answers were obtained. Factor analysis and K–W (Kruskal–Wallis) tests were carried out taking as a reference the port performance theory. Findings reveal the existence of a relationship between port performance and its characterization factors, delving into the development of conceptualized models that contribute to deepen the knowledge of port competition structure and dynamics within Europe.  相似文献   
719.
This article presents the results of a three-year effort at applying information technology to the problem of collaborative natural resource management in San Diego Bay. As such, it represents an approach to integrated coastal zone management (ICZM). This effort resulted from a collaboration between the San Diego Supercomputer Center at the University of California, San Diego and the San Diego Bay Interagency Water Quality Panel for the purpose of (1) developing an environmental data repository to facilitate the acquisition and sharing of data and (2) the development of a visual model of the bay in support of the development of a comprehensive, coordinated management plan for San Diego Bay. It was determined from this study that information technology is an important and key component to ICZM but that sociopolitical factors may override the benefits of decision-support systems and should be considered at the outset of any project of this kind.  相似文献   
720.
Findings are reported of the VALCOAST project that had as one of its research objectives to ascertain: (a) stakeholder willingness to participate and cooperate in coastal management (CM), given local and national CM practices; and (b) stakeholder assessment of the "accessibility" and "friendliness" of current CM processes. The project involved case studies and stakeholder interviews in Belgium, Greece, Spain, and the UK. Major findings include: (1) most stakeholders are willing to cooperate in three out of the four case areas, but not to the same extent; (2) the participating "officials" in the case studies are expecting the stakeholders to be less willing to cooperate than the latter indicate; (3) stakeholders in all case studies do not expect to be heard by those responsible for CM, find it difficult to learn about the relevant institutional arrangements, and consider the communication of the objectives and anticipated impacts of CM policies to be inadequate. It is concluded that the strong evidence of stakeholders' potential willingness to cooperate in local initiatives is very encouraging for a devolved, regional approach to European Union coastal management policies, provided that this potential is capitalized upon in such policy processes.  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