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   473080篇
  免费   4762篇
  国内免费   1448篇
电工技术   9499篇
综合类   375篇
化学工业   66488篇
金属工艺   21260篇
机械仪表   17042篇
建筑科学   10596篇
矿业工程   2197篇
能源动力   11482篇
轻工业   33658篇
水利工程   4595篇
石油天然气   6915篇
武器工业   22篇
无线电   60439篇
一般工业技术   96294篇
冶金工业   86680篇
原子能技术   8747篇
自动化技术   43001篇
  2021年   3193篇
  2020年   2383篇
  2019年   2986篇
  2018年   12419篇
  2017年   12889篇
  2016年   9398篇
  2015年   3977篇
  2014年   6206篇
  2013年   18158篇
  2012年   12104篇
  2011年   20883篇
  2010年   17918篇
  2009年   18548篇
  2008年   19061篇
  2007年   20778篇
  2006年   11807篇
  2005年   13887篇
  2004年   12128篇
  2003年   11927篇
  2002年   10439篇
  2001年   10584篇
  2000年   9880篇
  1999年   10460篇
  1998年   27286篇
  1997年   18828篇
  1996年   14646篇
  1995年   10950篇
  1994年   9673篇
  1993年   9593篇
  1992年   6784篇
  1991年   6600篇
  1990年   6436篇
  1989年   6086篇
  1988年   5848篇
  1987年   4835篇
  1986年   4810篇
  1985年   5359篇
  1984年   4895篇
  1983年   4590篇
  1982年   4226篇
  1981年   4257篇
  1980年   3971篇
  1979年   3707篇
  1978年   3501篇
  1977年   4272篇
  1976年   5795篇
  1975年   2981篇
  1974年   2908篇
  1973年   2830篇
  1972年   2444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.
 A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation. The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest. Sponsored by The Research Council of Norway, project number 125676/410 Dedicated to the memory of Prof. Mike Crisfield, a respected colleague  相似文献   
46.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture.  相似文献   
47.
48.
For pt.I see ibid., p.42-55 (2003). The development of a comprehensive decision support system, GMCR II, for the systematic study of real-world interactive decision problems is presented. The companion paper (Part I), discusses how GMCR II elicits, stores, and manages conflict models; here (Part II), the focus is on GMCR IIs analysis and output interpretation subsystems. Specifically, this paper describes the powerful and efficient analysis engine contained in GMCR II, its informative output presentation and interpretation facilities, and a number of follow-up analyses. Furthermore, an illustrative case study is used to demonstrate how GMCR II can be conveniently applied in practice.  相似文献   
49.
The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment.  相似文献   
50.
Open Shortest Path First (OSPF) traffic engineering (TE) is intended to bring long-awaited traffic management capabilities into IP networks, which still rely on today's prevailing routing protocols: OSPF or IS-IS. In OSPF, traffic is forwarded along, and split equally between, equal cost shortest paths. In this letter, we formulate the basic requirements placed on a practical TE architecture built on top of OSPF and present a theoretical framework meeting these requirements of practicality. The main contribution of our work comes from the recognition that coupled with an instance of the maximum throughput problem there exists a related inverse shortest-path problem yielding optimal OSPF link weights.  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