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   241241篇
  免费   2627篇
  国内免费   427篇
电工技术   4292篇
综合类   257篇
化学工业   39369篇
金属工艺   9379篇
机械仪表   7394篇
建筑科学   5446篇
矿业工程   1391篇
能源动力   5152篇
轻工业   24808篇
水利工程   2476篇
石油天然气   5092篇
武器工业   32篇
无线电   25044篇
一般工业技术   44771篇
冶金工业   45343篇
原子能技术   5950篇
自动化技术   18099篇
  2021年   2107篇
  2019年   2017篇
  2018年   3488篇
  2017年   3424篇
  2016年   3687篇
  2015年   2235篇
  2014年   3898篇
  2013年   10184篇
  2012年   6146篇
  2011年   8297篇
  2010年   6546篇
  2009年   7232篇
  2008年   7583篇
  2007年   7712篇
  2006年   6887篇
  2005年   6046篇
  2004年   5815篇
  2003年   5598篇
  2002年   5673篇
  2001年   5560篇
  2000年   5383篇
  1999年   5302篇
  1998年   12570篇
  1997年   8895篇
  1996年   6856篇
  1995年   5329篇
  1994年   4735篇
  1993年   4624篇
  1992年   3667篇
  1991年   3387篇
  1990年   3593篇
  1989年   3472篇
  1988年   3303篇
  1987年   2895篇
  1986年   2932篇
  1985年   3373篇
  1984年   3219篇
  1983年   2892篇
  1982年   2738篇
  1981年   2821篇
  1980年   2719篇
  1979年   2624篇
  1978年   2684篇
  1977年   2948篇
  1976年   3805篇
  1975年   2368篇
  1974年   2242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