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   3343篇
  免费   12篇
公路运输   710篇
综合类   716篇
水路运输   1117篇
铁路运输   43篇
综合运输   769篇
  2023年   4篇
  2022年   20篇
  2021年   13篇
  2020年   14篇
  2019年   14篇
  2018年   363篇
  2017年   328篇
  2016年   315篇
  2015年   26篇
  2014年   65篇
  2013年   231篇
  2012年   151篇
  2011年   290篇
  2010年   279篇
  2009年   132篇
  2008年   242篇
  2007年   171篇
  2006年   34篇
  2005年   83篇
  2004年   64篇
  2003年   78篇
  2002年   43篇
  2001年   23篇
  2000年   33篇
  1999年   22篇
  1998年   25篇
  1997年   26篇
  1996年   25篇
  1995年   41篇
  1994年   7篇
  1993年   22篇
  1992年   15篇
  1991年   14篇
  1990年   9篇
  1989年   4篇
  1988年   6篇
  1987年   10篇
  1986年   9篇
  1985年   8篇
  1984年   10篇
  1983年   8篇
  1982年   5篇
  1981年   7篇
  1980年   12篇
  1979年   14篇
  1978年   10篇
  1977年   6篇
  1975年   9篇
  1974年   7篇
  1972年   4篇
排序方式: 共有3355条查询结果,搜索用时 343 毫秒
731.
Equipment has dual nature: physical objects existing in nature, and artificial objects designed by human. The decision on the configuration and structural parameters of equipment is made by engineers based on technical-physical effects which control the behavioral parameters of the equipment. Sensors are mounted on the equipment to monitor the equipment state. Current methods for state monitoring and diagnosis mostly use mathematics and artificial intelligence technology to construct evaluation methods. This paper presents an integrated design and state maintenance method, in which graph and dual graph are used for recording design data and sensor arrangement and for mapping method from signals to substructures and connection pairs. An example of state maintenance of hydro power generating equipment is illustrated.  相似文献   
732.
733.
Transportation - Bikeshare operators routinely explore options to improve ridership and revenue by studying interaction among pricing, service and operations. The objective of this research is to...  相似文献   
734.
Directionality of image plays a very important role in human visual system and it is important prior information of image. In this paper we propose a weighted directional total variation model to reconstruct image from its finite number of noisy compressive samples. A novel self-adaption, texture preservation method is designed to select the weight. Inspired by majorization-minimization scheme, we develop an efficient algorithm to seek the optimal solution of the proposed model by minimizing a sequence of quadratic surrogate penalties. The numerical examples are performed to compare its performance with four state-of-the-art algorithms. Experimental results clearly show that our method has better reconstruction accuracy on texture images than the existing scheme.  相似文献   
735.
A novel high-voltage electrostatics corona ions pre-charger apparatus and methods were invented earlier by Hamade related to treat various types of receptors such as but not limited to electret polymer, air filters, particulates, catalytic converters, bioaerosols, fluids, pollutants, virus, and bacteria. It is shown in this article that his work led to the construction of various prototype chargers, customized differently for each type of a receptor. In particular his recent development of biological matter corona charger (BMCC) prototype related to expose, treat, sanitize, and disinfect bioaerosols, virus, bacteria, and contaminated fluids and blood such as human immunodeficiency virus (HIV) - acquired immune deficiency syndrome (AIDS). It is shown in this paper that each previous investigated research contemplated ionized corona charger attendant to a charging process and the corona, imparts and provides enough treatment charges to receptors including the aforementioned receptors. Researchers often relied on adopting prior corona charger methods that do not necessarily and effectively solve the problems associated with them or utilize them for optimum treatment effect. The inventor exhaustively studied the characteristics of corona discharge, and has found that the greatest difficulty in corona discharge has to do with the maintenance of the corona, particularly when the receptor is being charged. This is due to variations in either the dielectric value between the corona electrode and a grounded base or flaws in the design as the receptor passes there between suppressing or hindering corona and its effectiveness. What is needed in-the-art is an apparatus and method to achieve maximum possible charge on a receptor, a charge order of magnitude greater than that used by other investigators. This often requires customizing each apparatus and method and does not just merely use one type of a charger to satisfy all applications. To satisfy this need, we build a low cost prototype BMCC that generates self-sustaining charge corona, eliminates many previous design flaws such as spark over, and make it ready for testing remotely or with apparatus.  相似文献   
736.
Abstract

Part 1 elicited major research issues and opportunities in the transport sector in the EEC from an examination of a range of planning scenarios. This article relates those issues and opportunities to the needs of the EEC transport sector policy formation and derives a set of research recommendations. The respective roles of the EEC and other institutions in developing and meeting the research needs are then discussed, concluding with some institutional proposals for the strengthening of the organization of the strategic research effort of the EEC in the transport sector.  相似文献   
737.
‘Coastal-zone management is ideally founded on a consideration of the full range of bio-physical and socio-economic elements integrated through problem perception, decision making and remedial strategy planning. Specification of the framework indicates a variety of potential links between the coastal zone and continental shelf development.’  相似文献   
738.

High-speed rail operations have the potential to reduce the long-term decline in rail passenger travel demand for the medium to long distance inter-urban markets. Such decline has been evident through most of the industrialized countries where air and road transport tend to be the dominant modes. In China, the operations of long distance high-speed rail on fully dedicated track is not very easy to implement, due to the high proportion of passengers who travel between high-speed and conventional railways. An alternative approach would be to allow for mixed operations with trains of various speeds on the same track. This article puts forward a simulation model designed to allow an evaluation of the most efficient distance for high-speed rail operations under mixed train speed scenarios. The model takes into account the main operating parameters such as passenger volumes, train speeds, capital and maintenance costs, train operating costs and energy consumption. The distance of high-speed train running on conventional rail that will yield the most economic benefit can be estimated using the model. The article includes the results of using the model for a specific example. It is concluded that large-scale high-speed trains have the potential to be successfully operated on conventional rail networks.  相似文献   
739.
The North American Free Trade Agreement (NAFTA) signed by Canada, the U.S.A. and Mexico and which came into effect on 1 January 1994, is a significant move towards further integration of the North American economies. This paper examines the likely impact of NAFTA on Canadian ports. Three channels of impact are identified. First, there are direct impacts on trade flows between Canada and its North American trading partners. In this regard we find that ports do not typically handle the types of products that are likely to be affected by NAFTA, and so the direct impacts may be minimal. Second, and more significantly, port catchment areas are likely to undergo substantial changes as they respond to a more competitive environment within the free trade area. Third, the transportation sector has itself been included in NAFTA, and Canadian ports will face increased competition from land based transportation modes. We conclude that ports in Canada must learn to work more consciously as agents of regional economic development.  相似文献   
740.
The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In efforts to fulfill this task, concept of the minimum rank perturbation theory has been utilized. The present article introduces a promising methodology to select frequency points effectively. To achieve this goal, modal strain energy ratio of each member was evaluated at different natural frequencies of structure in order to identify the sensitive frequency domain for damage detection. The proposed methodology opens up the possibility of much greater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology.  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