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   554495篇
  免费   8392篇
  国内免费   2223篇
电工技术   10596篇
综合类   578篇
化学工业   82796篇
金属工艺   20588篇
机械仪表   16041篇
建筑科学   15138篇
矿业工程   1262篇
能源动力   15017篇
轻工业   58469篇
水利工程   4242篇
石油天然气   3497篇
武器工业   11篇
无线电   70771篇
一般工业技术   100461篇
冶金工业   108851篇
原子能技术   7876篇
自动化技术   48916篇
  2021年   3598篇
  2019年   3441篇
  2018年   5180篇
  2017年   5142篇
  2016年   5738篇
  2015年   4406篇
  2014年   7363篇
  2013年   25510篇
  2012年   12978篇
  2011年   18658篇
  2010年   14691篇
  2009年   16602篇
  2008年   17800篇
  2007年   17917篇
  2006年   16508篇
  2005年   15167篇
  2004年   14647篇
  2003年   14572篇
  2002年   14084篇
  2001年   14553篇
  2000年   13273篇
  1999年   14470篇
  1998年   35157篇
  1997年   24867篇
  1996年   19261篇
  1995年   14648篇
  1994年   13009篇
  1993年   12672篇
  1992年   9305篇
  1991年   8939篇
  1990年   8344篇
  1989年   8134篇
  1988年   7873篇
  1987年   6612篇
  1986年   6472篇
  1985年   7923篇
  1984年   7084篇
  1983年   6527篇
  1982年   6105篇
  1981年   6064篇
  1980年   5664篇
  1979年   5349篇
  1978年   5073篇
  1977年   6174篇
  1976年   8395篇
  1975年   4388篇
  1974年   4091篇
  1973年   4103篇
  1972年   3283篇
  1971年   2965篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019  相似文献   
46.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  相似文献   
47.
48.
The Journal of Supercomputing - Infrastructure-as-a-service container-based virtualization is gaining interest as a platform for running distributed applications. With increasing scale of cloud...  相似文献   
49.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015  相似文献   
50.
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