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   32945篇
  免费   991篇
  国内免费   66篇
电工技术   368篇
综合类   35篇
化学工业   6788篇
金属工艺   858篇
机械仪表   621篇
建筑科学   1839篇
矿业工程   247篇
能源动力   1016篇
轻工业   2762篇
水利工程   335篇
石油天然气   207篇
武器工业   2篇
无线电   2149篇
一般工业技术   5194篇
冶金工业   6641篇
原子能技术   322篇
自动化技术   4618篇
  2022年   196篇
  2021年   386篇
  2020年   332篇
  2019年   399篇
  2018年   488篇
  2017年   506篇
  2016年   520篇
  2015年   463篇
  2014年   736篇
  2013年   2132篇
  2012年   1240篇
  2011年   1590篇
  2010年   1169篇
  2009年   1258篇
  2008年   1436篇
  2007年   1467篇
  2006年   1256篇
  2005年   1172篇
  2004年   1052篇
  2003年   1023篇
  2002年   1031篇
  2001年   634篇
  2000年   615篇
  1999年   575篇
  1998年   599篇
  1997年   499篇
  1996年   605篇
  1995年   547篇
  1994年   532篇
  1993年   534篇
  1992年   486篇
  1991年   321篇
  1990年   438篇
  1989年   424篇
  1988年   379篇
  1987年   425篇
  1986年   382篇
  1985年   515篇
  1984年   491篇
  1983年   443篇
  1982年   464篇
  1981年   445篇
  1980年   353篇
  1979年   365篇
  1978年   329篇
  1977年   307篇
  1976年   268篇
  1975年   318篇
  1974年   243篇
  1973年   279篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Springs have long been recognized as being significant places in the landscape, and there is ample evidence of later-prehistoric and Roman activity at spring sites. The Christian appropriation of springs as 'places', either indirectly by assigning their origin to saints, or directly by building chapels and churches on spring-head sites, is also well evidenced. The possibility that the material of petrifying springs - tufa - was both transplanted and appropriated, and that the symbolic properties of the material may go back well into British prehistory, is explored.  相似文献   
232.
Although the association between marital conflict and child adjustment problems has been well documented, there is no empirical evidence that conflict actually causes maladjustment. The investigation of causation requires theoretically and empirically informed longitudinal research. Two topics are addressed to facilitate such research. First, how marital conflict may lead to adjustment problems is outlined, with a focus on constructs that are likely to be critical to any theory on this topic. Second, several issues are identified that need to be addressed in longitudinal research on the mechanisms underlying the link between marital and child problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
233.
234.
Morphological study of conducting polymer thin films obtained by spin coating is reported. Poly(o-methoxyaniline) films were deposited onto glass substrates and analyzed by profilometry and atomic force microscopy (AFM). It is shown that final thickness is correlated by a power law with spin speed with a solution concentration varying coefficient and that surface roughness decreases with increasing spin speed.  相似文献   
235.
236.
237.
Computer based discrete event simulation (DES) is one of the most commonly used aids for the design of automotive manufacturing systems. However, DES tools represent machines in extensive detail, while only representing workers as simple resources. This presents a problem when modelling systems with a highly manual work content, such as an assembly line. This paper describes research at Cranfield University, in collaboration with the Ford Motor Company, founded on the assumption that human variation is the cause of a large percentage of the disparity between simulation predictions and real world performance. The research aims to improve the accuracy and reliability of simulation prediction by including models of human factors.  相似文献   
238.
Mastication of gutta percha (trans-polyisoprene) resulted in the selective scission of molecules, producing a narrower distribution of lower molecular weights. The mechanical properties of the samples also underwent a significant change due to mastication. The greater the content of incompatible substances (salts and oxides) in commercial gutta percha. the more substantial were these effects. The atmosphere (air, N2, O2) in which the experiments were conducted yielded significantly different results. The decrease in molecular weight was far greater in an O2 atmosphere than under a current of nitrogen or air, owing to the combination of double bonds with O2.  相似文献   
239.
A variety of materials have been toughened via the addition of a ductile phase. Brittle silicide intermetallics such as Nb5Si3 have been significantly toughened by niobium particles incorporated during in-situ processing techniques. In the work described here, toughness tests conducted on Nb5Si3 were monitored in a scanning electron microscope to view the process of toughening provided by the niobium particles. In particular, the behavior of the ductile phase was monitored and related to the toughness obtained. In an attempt to vary the behavior of the ductile phase, the composite materials were exposed to a variety of gaseous environments and subsequently tested in air. The resulting toughness, resistance-curve behavior, and in-situ results highlight the importance of the behavior of the ductile phase on subsequent properties.  相似文献   
240.
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