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   529072篇
  免费   7406篇
  国内免费   1472篇
电工技术   9571篇
综合类   527篇
化学工业   79958篇
金属工艺   19985篇
机械仪表   15271篇
建筑科学   12815篇
矿业工程   2279篇
能源动力   14600篇
轻工业   48266篇
水利工程   5260篇
石油天然气   9360篇
武器工业   37篇
无线电   60051篇
一般工业技术   102188篇
冶金工业   103590篇
原子能技术   10564篇
自动化技术   43628篇
  2022年   3433篇
  2021年   5186篇
  2020年   3626篇
  2019年   4731篇
  2018年   7969篇
  2017年   7767篇
  2016年   8130篇
  2015年   5708篇
  2014年   9434篇
  2013年   24367篇
  2012年   14906篇
  2011年   20424篇
  2010年   16018篇
  2009年   17905篇
  2008年   18267篇
  2007年   17930篇
  2006年   15621篇
  2005年   14303篇
  2004年   13678篇
  2003年   13452篇
  2002年   12685篇
  2001年   12851篇
  2000年   11896篇
  1999年   12627篇
  1998年   32830篇
  1997年   22905篇
  1996年   17459篇
  1995年   13041篇
  1994年   11296篇
  1993年   10979篇
  1992年   7921篇
  1991年   7419篇
  1990年   7263篇
  1989年   7025篇
  1988年   6472篇
  1987年   5772篇
  1986年   5658篇
  1985年   6270篇
  1984年   5903篇
  1983年   5172篇
  1982年   4903篇
  1981年   4967篇
  1980年   4707篇
  1979年   4609篇
  1978年   4411篇
  1977年   5334篇
  1976年   6973篇
  1975年   3796篇
  1974年   3550篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Photonic networks based on the optical path concept and wavelength division multiplexing (WDM) technology require unique operation, administration, and maintenance (OAM) functions. In order to realize the required OAM functions, the optical path network must support an effective management information transfer method. The method that superimposes a pilot tone on the optical signal appears very interesting for optical path overhead transfer. The pilot tone transmission capacity is determined by the carrier to noise ratio which depends on the power spectral density of the optical signal. The pilot tone transmission capacity of an optical path network employing WDM technology is elucidated; 4.5 kb/s transmission can be realized when the pilot tone modulation index is set at 3%  相似文献   
82.
83.
84.
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   
85.
86.
Abstract This article presents a study of a large scale incorporation of one data acquisitionsystem into physics teaching in Israel. By 1994 about 30% of the schools throughout the country used the V-scope, a 3-D multibody motion tracing system, in their lab programme. The views and reactions of post-training teachers, experienced teachers and students on various aspects of using the system are described, analysed and compared.  相似文献   
87.
Gilbenclamide, a widely used potent hypoglycaemic agent was solubllized using β -Cyclodextrin and β -Cyclodextrin derivatives. Complexes were prepared by kneading method in a molar ratio of 1:1 of the drug and the cyclodextrlns respectively. The Glibenclamide β -Cyelocextrin complex was characterized and evaluated by I.R. studies, Differential Scanning Calorimotry 6 X-ray diffractometry. The in-vitro dissolution rates of drug from inclusion complexes of β Cyclodextrins and its derivatives were compared. A significant Improvement In dissolution lor, rates of Gllbenclamide was observed with Inclusion complexes of all the Cyclodextrins. However, the solubilizing effect was more in case of β-Cyclodextrin derivatives.  相似文献   
88.
89.
The paper presents the results of research in the convection drying of unidirectional glass fibre bobbins on the basis of which the relations are suggested required to calculate the process of drying in the design of drying equipment.  相似文献   
90.
Field surveys of a series of conjugated diunsaturated straight-chain primary alcohols, acetates, and aldehydes (dienes), including the 3,5-dode-cadienyl, 8,10-dodecadienyl, 3,5-tetradecadienyl, 8,10-tetradecadienyl, 9,11-tetradecadienyl, and 10,12-tetradecadienyl primary alcohols, acetates, and most aldehydes, and the related monounsaturated straight-chain primary alcohols, acetates, and aldehydes (monoenes), including the 3-dodecadienyl alcohol and acetates, attracted the following species from the title families. Diene attractants have been demonstrated for at least onePhyllonorycter sp.,Chionodes lugubrella (Fabr.),Leptostales ferruminaria (Zell.),Drepana bilineata (Pack.),Pyrausta fodinalis (Led.),Notocelia purpurissatana Heinr.,Phaneta alterana Heinr. Monoene attractants were demonstrated forHedya separatana (Kft.),Cydia fletcherana (Kft.),Barbara mappana Free.,Ancylis burgessiana (Zell.),Ancylis nubeculana Clem.,Evippe prunifoliella Cham.,Phlyctaenia coronata tertialis (Gn.), aChionodes sp., a Gelechiidae sp., and an unidentifiedPhyllonorycter sp. Replicated field experiments showed attraction-inhibition relationships for most species. Electroantennagram data are presented forLeptostales ferruminaria andDrepana bilineata.  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