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   33352篇
  免费   995篇
  国内免费   66篇
电工技术   370篇
综合类   35篇
化学工业   6797篇
金属工艺   864篇
机械仪表   624篇
建筑科学   1847篇
矿业工程   247篇
能源动力   1025篇
轻工业   2780篇
水利工程   335篇
石油天然气   207篇
武器工业   2篇
无线电   2221篇
一般工业技术   5249篇
冶金工业   6813篇
原子能技术   324篇
自动化技术   4673篇
  2022年   171篇
  2021年   388篇
  2020年   334篇
  2019年   400篇
  2018年   489篇
  2017年   507篇
  2016年   523篇
  2015年   466篇
  2014年   742篇
  2013年   2151篇
  2012年   1252篇
  2011年   1605篇
  2010年   1175篇
  2009年   1266篇
  2008年   1440篇
  2007年   1481篇
  2006年   1266篇
  2005年   1195篇
  2004年   1062篇
  2003年   1032篇
  2002年   1041篇
  2001年   646篇
  2000年   621篇
  1999年   586篇
  1998年   649篇
  1997年   523篇
  1996年   619篇
  1995年   559篇
  1994年   545篇
  1993年   548篇
  1992年   500篇
  1991年   324篇
  1990年   449篇
  1989年   426篇
  1988年   388篇
  1987年   433篇
  1986年   386篇
  1985年   523篇
  1984年   495篇
  1983年   448篇
  1982年   466篇
  1981年   451篇
  1980年   356篇
  1979年   368篇
  1978年   333篇
  1977年   311篇
  1976年   284篇
  1975年   323篇
  1974年   249篇
  1973年   282篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
41.
For users of an executive information system (EIS), the EIS interface is the system and is crucial to the EIS's success. These guidelines for designing EIS interfaces are based on studies of actual EIS interfaces that meet the unique information needs of executives.  相似文献   
42.
43.
44.
Among the photocathodes used for particle identification based on the Cherenkov Ring Imaging technique, the TMAE molecule is still the best in terms of quantum efficiency. Despite the fact that TMAE gaseous photocathodes have already been used in a number of large experiments, one still seeks answers to many detailed questions. We present a systematic study of gaseous photocathodes based on TMAE mixed with helium, hydrocarbon and CF4-based gases at normal pressure. The study includes a measurement of the electron drift velocity, gas quenching properties, single electron pulse height spectra and anode wire aging. The paper makes recommendations for carrier gas mixtures to obtain the best quenching, and suggests how to manage TMAE wire aging. This study was motivated by a specific particle identification detector proposal, the Fast Drift CRID proposed for the B-factory at SLAC.  相似文献   
45.
Characterisation of raw materials for Portland cement manufacture by use of the methylene blue adsorption method is discussed. The method is shown to be a simple, convenient ‘rule of thumb’ procedure. It provides a guide to the quantity and type of argillaceous minerals present in a given raw material sample.  相似文献   
46.
Experiments showing the frequency and amplitude of the flow induced motion of the gate for a 2- and a 4-in. swing check valve have been performed. The gate motion is due to turbulence in approach flow. We have found the dominant turbulent frequency of the approach flow is about half the natural frequency of the valves. The valves appear to be almost critically damped. Because of this, the valves respond almost as they would to a static force of the magnitude characteristic of the turbulent fluctuation in the flow. Both the dimensionless exciting force and the damping ratio have been found to be independent of valve size so the above statements are true for larger valves also. The recommended valve oscillation amplitudes and frequencies are used to calculate the wear at the shaft and at the stop. For an unpegged check valve, such as one of the 10-in. valves which was used at the San Onofre Nuclear Generation Station, it was found that shaft bearing wear would amount to 0.27 in.3/year and stop wear to 0.03 in.3/year.  相似文献   
47.
Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments—on/off, left/right, and above/below—faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance—in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)—faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
49.
50.
The major results reported by R. A. Carlson et al (see record 1989-24864-001) confirm predictions of J. R. Anderson's (1983) ACT* theory. In particular, ACT* predicts the detrimental effects of the transition to randomized practice because of the need to learn new productions, the complexity effect of gate and judgment type because of more complex production conditions, the effects of practice and its interaction with complexity because of the strengthening mechanisms, and the effects of memory load because of the need to hold information active in working memory so that it can be matched by production conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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