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   1602448篇
  免费   24813篇
  国内免费   7214篇
电工技术   35449篇
综合类   6613篇
化学工业   277424篇
金属工艺   66752篇
机械仪表   47269篇
建筑科学   48234篇
矿业工程   11963篇
能源动力   50527篇
轻工业   124656篇
水利工程   16310篇
石油天然气   38513篇
武器工业   170篇
无线电   200463篇
一般工业技术   301280篇
冶金工业   199594篇
原子能技术   34758篇
自动化技术   174500篇
  2021年   15656篇
  2020年   11962篇
  2019年   14758篇
  2018年   19145篇
  2017年   18991篇
  2016年   23027篇
  2015年   17645篇
  2014年   28782篇
  2013年   88139篇
  2012年   38384篇
  2011年   53796篇
  2010年   46290篇
  2009年   54070篇
  2008年   49376篇
  2007年   47489篇
  2006年   46949篇
  2005年   42939篇
  2004年   44054篇
  2003年   43610篇
  2002年   42340篇
  2001年   38973篇
  2000年   37207篇
  1999年   36627篇
  1998年   55778篇
  1997年   45817篇
  1996年   39566篇
  1995年   33307篇
  1994年   30788篇
  1993年   30590篇
  1992年   26872篇
  1991年   24074篇
  1990年   24404篇
  1989年   23494篇
  1988年   21993篇
  1987年   20212篇
  1986年   19607篇
  1985年   22949篇
  1984年   22740篇
  1983年   20757篇
  1982年   19584篇
  1981年   19676篇
  1980年   18375篇
  1979年   18817篇
  1978年   18016篇
  1977年   18454篇
  1976年   20309篇
  1975年   16267篇
  1974年   15724篇
  1973年   15854篇
  1972年   13306篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today.  相似文献   
952.
For the past three decades, IS managers have been faced with the tasks of honing their craft, improving productivity, and serving as the keepers of information technology for the corporation. For the most part, they have done a commendable job. However, the rules of the game are changing. Old solutions are no longer extensible to current problems, and today's problems are unlike any faced in the past. This article takes a fresh look at what the top priorities for IS managers should be in the coming years.  相似文献   
953.
The survey focuses on algebraic-grammatical models of parallel processes, representation of knowledge about classes of algorithms in terms of a variety of production systems (structured design grammars), and program generation tools.Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 5–13, September–October, 1991.  相似文献   
954.
An efficient algorithm to remove redundant dependences in simple loops with constant dependences is presented. Dependences constrain the parallel execution of programs and are typically enforced by synchronization instructions. The synchronization instructions represent a significant part of the overhead in the parallel execution of a program. Some program dependences are redundant because they are covered by other dependences. It is shown that unlike with single loops, in the case of nested loops, a particular dependence may be redundant at some iterations but not redundant at others, so that the redundancy of a dependence may not be uniform over the entire iteration space. A sufficient condition for the uniformity of redundancy in a doubly nested loop is developed  相似文献   
955.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 423–424, June, 1989.  相似文献   
956.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
957.
958.
Geomechanical aspects of the storage of radioactive waste in salt formations have been studied extensively using finite element methods over the last 20 years. In consequence a range of computer programs and associated modelling techniques have been assembled. The paper is based on a benchmark exercise to compare the predictive abilities of a number of these programs and highlights the difficulties of making reliable a-priori estimates of long term behaviour.  相似文献   
959.
960.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained.  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