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   538918篇
  免费   6842篇
  国内免费   1780篇
电工技术   9519篇
综合类   2653篇
化学工业   78417篇
金属工艺   25406篇
机械仪表   20388篇
建筑科学   11931篇
矿业工程   3280篇
能源动力   13430篇
轻工业   33111篇
水利工程   6155篇
石油天然气   9308篇
武器工业   17篇
无线电   62507篇
一般工业技术   111308篇
冶金工业   84571篇
原子能技术   10172篇
自动化技术   65367篇
  2022年   2674篇
  2021年   4091篇
  2020年   3116篇
  2019年   4040篇
  2018年   24209篇
  2017年   23635篇
  2016年   18624篇
  2015年   5417篇
  2014年   7785篇
  2013年   21351篇
  2012年   16243篇
  2011年   29296篇
  2010年   24881篇
  2009年   23560篇
  2008年   24771篇
  2007年   26676篇
  2006年   13252篇
  2005年   15250篇
  2004年   13235篇
  2003年   12967篇
  2002年   11234篇
  2001年   10172篇
  2000年   9687篇
  1999年   9882篇
  1998年   24751篇
  1997年   17073篇
  1996年   13177篇
  1995年   9862篇
  1994年   8655篇
  1993年   8721篇
  1992年   6348篇
  1991年   5940篇
  1990年   5921篇
  1989年   5566篇
  1988年   5287篇
  1987年   4650篇
  1986年   4556篇
  1985年   5084篇
  1984年   4690篇
  1983年   4256篇
  1982年   3861篇
  1981年   3964篇
  1980年   3661篇
  1979年   3563篇
  1978年   3541篇
  1977年   3965篇
  1976年   5042篇
  1975年   3034篇
  1974年   2826篇
  1973年   2903篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The purpose of this paper is to provide an analysis of the alternative modelling systems for office information systems. More specifically, we are interested in identifying the current research trends of merging office modelling ideas together with concepts that owe their origin to the object-oriented paradigm and to artificial intelligence. In this respect an office model is defined as encompassing three domains: passive office objects; dynamically defined and manipulated office procedures; and goal-directed office tasks. Following this definition we exploit the potential of using the object-oriented and knowledge representation techniques for modelling each of the three domains using evidence from real-world applications.  相似文献   
993.
The ac susceptibility of lanthanum-diluted cerium magnesium nitrate has been compared to the temperature scales as derived from the (P, T) relation determined by Halperin and that was measured recently by Greywall. It is found that the susceptibility does not obey a simple Curie-Weiss law over the temperature range between 1 and 50 mK. The results of these calibrations are also used to determine the temperatures for the second-order phase transitions into the superfluid phases of3He at several pressures. TheseT c(P) values are compared to results of earlier experiments that used thermometry based on the susceptibility of platinum as well as other thermometry techniques.  相似文献   
994.
995.
The microstructure of a single-crystal nickel-base superalloy, PWA 1480, has been varied by heat treatment and hot isostatic pressing in order to study the role of the γ/yγ′ eutectic and porosity on subsequent tensile behavior. The level of porosity was found not to affect any of the tensile properties, while the γ/γ′ eutectic strongly influenced ductility. Eliminating the γ/γ′ eutectic increased ductility which was attributed to the cleavage fracture of this constituent. It is proposed that such cleavage of the γ/γ′ eutectic is initiated by the stress created from impinging slip bands, promoting shear localization, and final fracture along {111} slip planes. The precise nature of this fracture process is discussed with emphasis on the role of the γ/′ micro-structure. The deformation structure of PWA 1480 was also studied, and while different in some respects from many other single-crystal superalloys, its fracture process appears to be similar. Formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University.  相似文献   
996.
997.
Due to their small size, mammalian oocytes and embryos pose unique problems during preparation for transmission electron microscopy. This paper outlines a method which combines protein embedding with centrifugation to locate the specimens on the face of a Beem capsule mould. This method facilitates both the processing of oocytes with minimal loss and rapid location of the specimens within the block for simultaneous sectioning, staining and examination.  相似文献   
998.
The Highway Loss Data Institute (HLDI) compiles injury and collision claim information from major insurance companies. These data have indicated that a disproportionately large number of injury claims are made for small cars. As a result, it might be concluded that small cars increase injury risk to their occupants. Recent advertisements by a major automobile manufacturer suggest a similar conclusion should be drawn from these data. In this paper it is shown that the apparent higher injury risk attributed to small cars can reflect the behavior of persons driving small cars. The number of injury claim accidents per collision claim accident is examined as an alternative measure of injury risk. Possible problems in interpretation are discussed.  相似文献   
999.
1000.
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