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   34384篇
  免费   2673篇
  国内免费   35篇
电工技术   901篇
综合类   685篇
化学工业   12284篇
金属工艺   491篇
机械仪表   519篇
建筑科学   1646篇
矿业工程   134篇
能源动力   647篇
轻工业   2278篇
水利工程   253篇
石油天然气   75篇
武器工业   1篇
无线电   1878篇
一般工业技术   6101篇
冶金工业   4609篇
原子能技术   203篇
自动化技术   4387篇
  2023年   713篇
  2022年   627篇
  2021年   1101篇
  2020年   898篇
  2019年   872篇
  2018年   969篇
  2017年   766篇
  2016年   1086篇
  2015年   1112篇
  2014年   1322篇
  2013年   2169篇
  2012年   1526篇
  2011年   1760篇
  2010年   1645篇
  2009年   1666篇
  2008年   1387篇
  2007年   1288篇
  2006年   1067篇
  2005年   897篇
  2004年   934篇
  2003年   802篇
  2002年   746篇
  2001年   508篇
  2000年   383篇
  1999年   461篇
  1998年   829篇
  1997年   603篇
  1996年   518篇
  1995年   503篇
  1994年   444篇
  1993年   486篇
  1992年   356篇
  1991年   270篇
  1990年   357篇
  1989年   353篇
  1988年   286篇
  1987年   316篇
  1986年   328篇
  1985年   351篇
  1984年   307篇
  1983年   328篇
  1982年   285篇
  1981年   299篇
  1980年   252篇
  1979年   260篇
  1978年   200篇
  1977年   247篇
  1976年   287篇
  1975年   224篇
  1973年   241篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
93.
94.
95.
Causal learning requires integrating constraints provided by domain-specific theories with domain-general statistical learning. In order to investigate the interaction between these factors, the authors presented preschoolers with stories pitting their existing theories against statistical evidence. Each child heard 2 stories in which 2 candidate causes co-occurred with an effect. Evidence was presented in the form: AB→E; CA→E; AD→E; and so forth. In 1 story, all variables came from the same domain; in the other, the recurring candidate cause, A, came from a different domain (A was a psychological cause of a biological effect). After receiving this statistical evidence, children were asked to identify the cause of the effect on a new trial. Consistent with the predictions of a Bayesian model, all children were more likely to identify A as the cause within domains than across domains. Whereas 3.5-year-olds learned only from the within-domain evidence, 4- and 5-year-olds learned from the cross-domain evidence and were able to transfer their new expectations about psychosomatic causality to a novel task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
96.
The thermal stress on building‐integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field‐testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free‐standing module in Espoo was 50–200%. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
97.
This paper highlights the role of the faculty member in recruiting students currently enrolled in B.S. programs in engineering and the sciences into full-time pursuit of a graduate-level engineering degree. The faculty member is demonstrated to be in a unique position to influence such students, providing strong counterforces to a confluence of attitudes and pressures experienced during the B.S. experience which effectively create a barrier to full-time engineering graduate study. We analyze this barrier via the method of force field analysis, and demonstrate that effective recruitment into full-time graduate study must be based on a four-fold strategy of education, expectations, improved B.S. experience and better control of the B.S. environment. Approaches to implement these strategies are discussed.  相似文献   
98.
A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5---TiO2 catalysts with different V/Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V/Ti ratio.

These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V/Ti ratio would have large V2O5 crystals acting as support of a V/TiO2 solid solution. In contrast, those samples with a low V/Ti ratio, would have the solid solution supporting vanadium pentoxide crystals.  相似文献   

99.
100.
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