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   326903篇
  免费   3643篇
  国内免费   835篇
电工技术   5087篇
综合类   2573篇
化学工业   50819篇
金属工艺   14048篇
机械仪表   10417篇
建筑科学   7739篇
矿业工程   1960篇
能源动力   6338篇
轻工业   28591篇
水利工程   3767篇
石油天然气   5433篇
武器工业   32篇
无线电   34512篇
一般工业技术   61054篇
冶金工业   49308篇
原子能技术   6245篇
自动化技术   43458篇
  2021年   2139篇
  2019年   2048篇
  2018年   17708篇
  2017年   16582篇
  2016年   13505篇
  2015年   2866篇
  2014年   4173篇
  2013年   10506篇
  2012年   9285篇
  2011年   17621篇
  2010年   14711篇
  2009年   12728篇
  2008年   14286篇
  2007年   15369篇
  2006年   7116篇
  2005年   7306篇
  2004年   6994篇
  2003年   6816篇
  2002年   6261篇
  2001年   5725篇
  2000年   5622篇
  1999年   5441篇
  1998年   12970篇
  1997年   9155篇
  1996年   7059篇
  1995年   5456篇
  1994年   4852篇
  1993年   4744篇
  1992年   3730篇
  1991年   3459篇
  1990年   3656篇
  1989年   3538篇
  1988年   3366篇
  1987年   2940篇
  1986年   2985篇
  1985年   3442篇
  1984年   3280篇
  1983年   2952篇
  1982年   2780篇
  1981年   2866篇
  1980年   2773篇
  1979年   2666篇
  1978年   2729篇
  1977年   3010篇
  1976年   3892篇
  1975年   2399篇
  1974年   2283篇
  1973年   2404篇
  1972年   1993篇
  1971年   1881篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Suppose that an equilibrium is asymptotically stable when external inputs vanish. Then, every bounded trajectory which corresponds to a control which approaches zero and which lies in the domain of attraction of the unforced system, must also converge to the equilibrium. This "well-known" but hard-to-cite fact is proved and slightly generalized here.  相似文献   
102.
Ozone measurement based on the optical absorption of visible light at 603 nm using polymer optical fibres is investigated and tested. Comparisons with a commercial UV based sensor demonstrate the ability of the visible based sensor to measure high concentrations over a range 27-127 mg/litre. A resolution of 5 mg/litre is also demonstrated for this sensor.  相似文献   
103.
104.
This paper discusses another generalization of the direct Routh table truncation method for interval systems. It is shown that the existing generalization of the direct Routh table truncation fails to produce a stable system, in contradiction to the equivalent result for fixed-coefficients systems. The present method guarantees a stable reduced order model for interval systems as well.  相似文献   
105.
106.
Experimental Study of Ice Jam Thickening under Dynamic Flow Conditions   总被引:1,自引:0,他引:1  
River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory.  相似文献   
107.
A construction of a globally asymptotically stable time-invariant system which can be destabilized by some integrable perturbation is given. Besides its intrinsic interest, this serves to provide counterexamples to an open question regarding Lyapunov functions.  相似文献   
108.
Abstract The purpose of this exploratory study was to investigate the influence of two individual characteristics (Web experience and academic focus) of adolescents on the Web perception, using off-line questionnaires (a Lickert response scale) constituted on the basis of a series of interviews. Questions concerned: perceptions about the nature of information found in the Web; 'strategies' of access to the interesting Internet sites and the reliability of different information resources (libraries, television, Web, etc.). Results lead to the assumption that adolescents with high Web experience became more critical, less confident and less enthusiastic than adolescents with low Web experience and that, in some dimensions, perceptions of literature students are different to those of science students. Even if some interesting results were obtained, further research is needed to explore users' perceptions related to individuals' characteristics and to determine the generalisability of the influences identified in this exploratory study.  相似文献   
109.
110.
An investigation of the effect of reaction conditions on product distribution in the skeletal isomerisation reaction of linear butenes has been carried out. The main reaction routes over ferrierite have been identified. Beside the main product isobutene, major by-product formation occurs. The unwanted reactions include dimerisation of butene to form octenes, hydrogen transfer yielding small amounts of saturated C3 and C4 hydrocarbons and disproportionation producing propene and pentenes. The most abundant by-products were pentene and propene, though these were not formed in equimolar amounts as could be expected. Oligomerisation experiments of propene over ferrierite produced large amounts of butene and pentene, revealing the presence of adsorbed nonene. The cracking of this surface species to hexene and propene is the most likely reaction route for the excess propene formation. This additional path to propene formation operates mainly at temperatures above 623 K.  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