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   464940篇
  免费   6299篇
  国内免费   1560篇
电工技术   8702篇
综合类   356篇
化学工业   68399篇
金属工艺   20449篇
机械仪表   16953篇
建筑科学   11605篇
矿业工程   2092篇
能源动力   11652篇
轻工业   42085篇
水利工程   4619篇
石油天然气   6235篇
武器工业   6篇
无线电   55473篇
一般工业技术   91254篇
冶金工业   79455篇
原子能技术   8012篇
自动化技术   45452篇
  2021年   2843篇
  2019年   2666篇
  2018年   12297篇
  2017年   12929篇
  2016年   9036篇
  2015年   3944篇
  2014年   5896篇
  2013年   18396篇
  2012年   12755篇
  2011年   22473篇
  2010年   18937篇
  2009年   19460篇
  2008年   19633篇
  2007年   21431篇
  2006年   12256篇
  2005年   14593篇
  2004年   12540篇
  2003年   11843篇
  2002年   10430篇
  2001年   10317篇
  2000年   9565篇
  1999年   10055篇
  1998年   24475篇
  1997年   17251篇
  1996年   13118篇
  1995年   10052篇
  1994年   8633篇
  1993年   8497篇
  1992年   6186篇
  1991年   5920篇
  1990年   5608篇
  1989年   5440篇
  1988年   5316篇
  1987年   4472篇
  1986年   4307篇
  1985年   5189篇
  1984年   4702篇
  1983年   4345篇
  1982年   3990篇
  1981年   4104篇
  1980年   3786篇
  1979年   3644篇
  1978年   3445篇
  1977年   4036篇
  1976年   5138篇
  1975年   2976篇
  1974年   2907篇
  1973年   2989篇
  1972年   2380篇
  1971年   2192篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
The authors have determined the causes of drop in performance of induced block caving using fans of blastholes 105 mm in diameter and single blastholes 250 mm in diameter, as well as the sources of increased drilling cost and expansion of start-up time of production blocks in Abakan underground mine. Alternatives of improvement in drilling efficiency under current conditions are discussed.  相似文献   
92.
93.
94.
Manente  F.  Pietrobon  L.  Ronchin  L.  Vavasori  A. 《Catalysis Letters》2021,151(12):3543-3549
Catalysis Letters - In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid...  相似文献   
95.
96.
97.
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes.  相似文献   
98.
One-third of all proteins are estimated to require metals for structural stability and/or catalytic activity. Desthiobiotin probes containing metal binding groups can be used to capture metalloproteins with exposed active-site metals under mild conditions so as to prevent changes in metallation state. The proof-of-concept was demonstrated with carbonic anhydrase (CA), an open active site, Zn2+-containing protein. CA was targeted by using sulfonamide derivatives. Linkers of various lengths and structures were screened to determine the optimal structure for capture of the native protein. The optimized probes could selectively pull down CA from red blood cell lysate and other protein mixtures. Pull-down of differently metallated CAs was also investigated.  相似文献   
99.
International Journal of Computer Vision - Anticipating future situations from streaming sensor data is a key perception challenge for mobile robotics and automated vehicles. We address the problem...  相似文献   
100.
Application of brown titanium dioxide (TiO2-x) and its modified composite forms in the photocatalytic decomposition of organic pollutants in the environment is a promising way to provide solutions for environmental redemption. Herein, we report the synthesis of effective and stable TiO2-x nanoparticles with g-C3N4, RGO, and multiwalled carbon nanotubes (CNTs) using a simple hydrothermal method. Among all the as-synthesized samples, excellent photocatalytic degradation activity was observed for RGO-TiO2-x nanocomposite with high rate constants of 0.075 min?1, 0.083 min?1 and 0.093 min?1 for methylene blue, rhodamine-B, and rosebengal dyes under UV–Visible light irradiation, respectively. The altered bandgap (1.8 eV) and the large surface area of RGO-TiO2-x nanocomposite impacts on both absorption of visible light and efficiency of photogenerated charge electron (e?)/hole (h+) pair separation. This resulted in enhanced photocatalytic property of carbon-based TiO2-x nanocomposites. A systematic study on the influence of different carbon nanostructures on the photocatalytic activity of brown TiO2-x is carried out.  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