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   416218篇
  免费   4128篇
  国内免费   1482篇
电工技术   6944篇
综合类   624篇
化学工业   62008篇
金属工艺   18781篇
机械仪表   13143篇
建筑科学   9013篇
矿业工程   3124篇
能源动力   9322篇
轻工业   29891篇
水利工程   5327篇
石油天然气   12802篇
武器工业   54篇
无线电   45040篇
一般工业技术   87588篇
冶金工业   73786篇
原子能技术   12551篇
自动化技术   31830篇
  2021年   3457篇
  2019年   3336篇
  2018年   6022篇
  2017年   6205篇
  2016年   6598篇
  2015年   3901篇
  2014年   6718篇
  2013年   17245篇
  2012年   10596篇
  2011年   14172篇
  2010年   11160篇
  2009年   12808篇
  2008年   13135篇
  2007年   13139篇
  2006年   11223篇
  2005年   10396篇
  2004年   10169篇
  2003年   9857篇
  2002年   9560篇
  2001年   9659篇
  2000年   9193篇
  1999年   9397篇
  1998年   22146篇
  1997年   15843篇
  1996年   12124篇
  1995年   9322篇
  1994年   8182篇
  1993年   8336篇
  1992年   6253篇
  1991年   6094篇
  1990年   6026篇
  1989年   5912篇
  1988年   5647篇
  1987年   5194篇
  1986年   5213篇
  1985年   5604篇
  1984年   5226篇
  1983年   4964篇
  1982年   4584篇
  1981年   4793篇
  1980年   4696篇
  1979年   4607篇
  1978年   4804篇
  1977年   5098篇
  1976年   6636篇
  1975年   4200篇
  1974年   4214篇
  1973年   4271篇
  1972年   3720篇
  1971年   3293篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Ipratropium bromide is a synthetic derivative of atropine with little absorption when used in inhalation, and therefore little secondary effects. The authors review its pharmacological properties and therapeutic efficacy in the treatment of asthma in children. Combined nebulized inhalation of ipratropium bromide and beta 2 sympathomimetic results in a more efficient and more sustained bronchodilatation than beta 2 sympathicomimetic alone in the treatment of acute asthma in children. Ipratropium bromide should be usefully introduced in the therapeutic scheme of acute asthma in children. Further studies will be necessary in order to determine its efficacy and tolerance in infants.  相似文献   
112.
The Inc A/C plasmids, like Inc P and Inc Q plasmids, have a broad host range. However, their maintenance functions remain to be studied. An autoreplicative region of 2.79 kb named RepA/C, able to replicate both in the family Enterobacteriaceae and in Pseudomonas spp., was isolated and sequenced. The stability, copy number, and incompatibility expression of this replicon were determined. RepA/C and a nonautoreplicative fragment of 16 kb of this replicon were used as probes and showed specific hybridizations with the Inc P3-A/C plasmids from Pseudomonas spp. and members of the Enterobacteriaceae. These probes could be used as tools for identification of the plasmids of this epidemiologically important Inc group.  相似文献   
113.
Given the enormous size of the genome and that there are potentially many other types of measurements we need to do to understand it, it has become necessary to pick and choose one's targets to measure because it is still impossible to evaluate the entire genome all at once. What has emerged is a need to have rapidly customizable microarrays. There are two dominant methods to accomplish custom microarray synthesis, Affymetrix-like microarrays manufactured using light projection rather than semiconductor-like masks used by Affymetrix to mass manufacture their GeneChip/sup TM/ arrays now, or the ink-jet printing method employed by Agilent. The manufacture of these custom Affymetrix-like microarrays can now be done on a digital optical chemistry (DOC) machine developed at the University of Texas Southwestern Medical Center, and this method offers much higher feature numbers and feature density than is possible with ink-jet printed arrays. On a microarray, each feature contains a single genetic measurement. The initial DOC prototype has been described in several publications, but that has now led to a second-generation machine. This machine reliably produces a number of arrays daily, has been deployed against a number of biomedical questions, is being used in new ways and has also led to a number of spin-off technologies.  相似文献   
114.
A new system based on the harnessing of solar and wind power is presented for heat dissipation in air conditioning facilities. The innovation offered by the new system is the integration of two well-known subsystems: a cooling tower and a solar chimney which increases the air flow without the use of electric power. The system is described and presented together with a model for its study. The field data acquired from the prototype built in southern Spain establishes the actual potential of the system, which provides a new approach to a sustainable technological development.  相似文献   
115.
116.
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow.  相似文献   
117.
118.
119.
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   
120.
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   
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