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   242770篇
  免费   2684篇
  国内免费   431篇
电工技术   4300篇
综合类   258篇
化学工业   39667篇
金属工艺   9388篇
机械仪表   7404篇
建筑科学   5526篇
矿业工程   1392篇
能源动力   5175篇
轻工业   25079篇
水利工程   2492篇
石油天然气   5096篇
武器工业   32篇
无线电   25109篇
一般工业技术   45030篇
冶金工业   45723篇
原子能技术   5951篇
自动化技术   18263篇
  2021年   2168篇
  2019年   2062篇
  2018年   3525篇
  2017年   3459篇
  2016年   3719篇
  2015年   2277篇
  2014年   3956篇
  2013年   10250篇
  2012年   6214篇
  2011年   8408篇
  2010年   6626篇
  2009年   7309篇
  2008年   7683篇
  2007年   7812篇
  2006年   6975篇
  2005年   6120篇
  2004年   5888篇
  2003年   5650篇
  2002年   5712篇
  2001年   5576篇
  2000年   5404篇
  1999年   5322篇
  1998年   12591篇
  1997年   8911篇
  1996年   6889篇
  1995年   5344篇
  1994年   4750篇
  1993年   4639篇
  1992年   3675篇
  1991年   3392篇
  1990年   3599篇
  1989年   3476篇
  1988年   3306篇
  1987年   2902篇
  1986年   2938篇
  1985年   3380篇
  1984年   3223篇
  1983年   2898篇
  1982年   2744篇
  1981年   2825篇
  1980年   2723篇
  1979年   2625篇
  1978年   2687篇
  1977年   2950篇
  1976年   3808篇
  1975年   2369篇
  1974年   2243篇
  1973年   2376篇
  1972年   1970篇
  1971年   1858篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
42.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
43.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included  相似文献   
44.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  相似文献   
45.
46.
47.
Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.  相似文献   
48.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
49.
The criterion for crack growth instability in an elastic-softening material that is subjected to displacement control loading conditions is examined. A theoretical analysis of the model of a solid containing two symmetrically situated deep cracks and with tensile loading of the remaining ligament, defines the criterion for crack growth instability. The criterion is expressed in terms of the material's softening characteristics and the solid's geometrical parameters. The analysis covers the complete spectrum of material behaviour from the case where the softening zone is very small to the case where instability does not occur until the softening zone traverses the ligament between the crack tips.  相似文献   
50.
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