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   587029篇
  免费   8565篇
  国内免费   2070篇
电工技术   10602篇
综合类   527篇
化学工业   87644篇
金属工艺   19601篇
机械仪表   16631篇
建筑科学   16320篇
矿业工程   1277篇
能源动力   16272篇
轻工业   62168篇
水利工程   4665篇
石油天然气   3388篇
武器工业   16篇
无线电   76687篇
一般工业技术   106421篇
冶金工业   111665篇
原子能技术   7688篇
自动化技术   56092篇
  2021年   4003篇
  2020年   2877篇
  2019年   3648篇
  2018年   5654篇
  2017年   5731篇
  2016年   6231篇
  2015年   4947篇
  2014年   8281篇
  2013年   27739篇
  2012年   14747篇
  2011年   21294篇
  2010年   16396篇
  2009年   18666篇
  2008年   19865篇
  2007年   20178篇
  2006年   18344篇
  2005年   16889篇
  2004年   16319篇
  2003年   16000篇
  2002年   15270篇
  2001年   15605篇
  2000年   14325篇
  1999年   15335篇
  1998年   36223篇
  1997年   25924篇
  1996年   20038篇
  1995年   15519篇
  1994年   13704篇
  1993年   13320篇
  1992年   9722篇
  1991年   9260篇
  1990年   8749篇
  1989年   8383篇
  1988年   8090篇
  1987年   6710篇
  1986年   6559篇
  1985年   8082篇
  1984年   7474篇
  1983年   6627篇
  1982年   6100篇
  1981年   6165篇
  1980年   5744篇
  1979年   5456篇
  1978年   5063篇
  1977年   6151篇
  1976年   8133篇
  1975年   4267篇
  1974年   4046篇
  1973年   3969篇
  1972年   3122篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The aim of this article is to illustrate a framework for flood risk mapping at pan-European scale produced by the Weather-Driven Natural Hazards (WDNH) action of the EC-JRC-IES. Early results are presented in the form of flood risk index maps. We assess several flood risk factors that contribute to the occurrence of flood disasters. Among the causal factors of a flood disaster one is triggering a natural event in the form of extreme precipitation and consequently extreme river discharge and extreme flood water levels. The threatening natural event represents the hazard component in our assessment. Furthermore exposure and vulnerability are anthropogenic factors that contribute also to flood risk. In the proposed approach, flood risk is considered on the light of exposure, vulnerability and hazard. We use a methodology with a marked territorial approach for the assessment of the flood risk. Hence, based on mathematical calculations, risk is the product of hazard, exposure and vulnerability. Improvements on datasets availability and spatial scale are foreseen in the next phases of this study. This study is also a contribution to the discussion about the need for communication tools between the natural hazard scientific community and the political and decision making players in this field.  相似文献   
992.
A comparison is made between passive ring-resonator and interferometric fiber-optic gyroscope sensitivity to the radiation darkening of optical fibers. The radiation degradation factor for each type of gyroscope is developed, and figures of merit are given for comparing gyroscopes independently of the specific mechanization or modulation scheme used. It is shown that for most practical situations, interferometric gyros offer superior performance in radiation environments  相似文献   
993.
Environmentally enhanced crack growth data for 33% Na2O-67% SiO2 and 33% Li2O-67% SiO2 (mol%) were obtained. Corrosion data for the same glasses as determined by infrared reflection spectroscopy and atomic absorption spectroscopy were also measured. It was determined that, of the tested environments, those and only those environments which caused surface corrosion also enhanced crack growth. Crack growth curves were more complicated for these materials than for fused silica. Water-dominated regions occurred even in environments which are known to enhance crack growth.  相似文献   
994.
We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.  相似文献   
995.
996.
The effects of receiver misplacement and the trough pointing towards the sun on the concentration characteristics of a composite parabolic trough are discussed. Results from some numerical calculations are presented graphically and discussed.  相似文献   
997.
Survey of natural radiation is conducted in France since 1981, with the assessment of the components resulting from external sources (ground and building materials) using thermoluminescent dosemeters. In addition, the internal exposure to Rn-222 and the potential alpha energy due to radon daughters, are estimated by passive track detectors in the first case and active dosemeters in the second one. This paper presents the French program methods and results with an analysis and discussion of the observed levels.  相似文献   
998.
A knowledge of building wake characteristics is useful in a variety of applications including dispersion of pollutants downwind of conventional or nuclear power plants, airport runway interference effect, take-off/landing limitations at heliports, pedestrian wind comfort, and wind loads on structures. Recent investigations have advanced both understanding of physical flow processes occurring in the near and far wake regions and theoretical predictive capability for flow and diffusion in the far wake region. These studies have shown, for example, that separation cavities immediately downwind are not enclosed by free streamlines as in two-dimensional separation/reattachment, that organized vortices can play an important role in wake development, and that theoretical solutions for some wake regions are possible.  相似文献   
999.
Immune defences at mucosal surfaces in ruminants   总被引:5,自引:0,他引:5  
  相似文献   
1000.
The scientific community and general public can best take advantage of the benefits of 3D digital reconstructions if they are stored in a Web-accessible, easy-to-access database. We describe MorphologyNet/sup /spl copy// a Web-based digital library of realistic, 3D interactive and customizable images of anatomy currently in development at the University of Missouri-Rolla.  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