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   426024篇
  免费   5145篇
  国内免费   1326篇
电工技术   7920篇
综合类   467篇
化学工业   61612篇
金属工艺   16831篇
机械仪表   13360篇
建筑科学   10256篇
矿业工程   2257篇
能源动力   10720篇
轻工业   36610篇
水利工程   4501篇
石油天然气   7352篇
武器工业   75篇
无线电   52817篇
一般工业技术   83048篇
冶金工业   78661篇
原子能技术   9389篇
自动化技术   36619篇
  2021年   3368篇
  2019年   3345篇
  2018年   5558篇
  2017年   5710篇
  2016年   5996篇
  2015年   3838篇
  2014年   6559篇
  2013年   18846篇
  2012年   10734篇
  2011年   14694篇
  2010年   11691篇
  2009年   13135篇
  2008年   13905篇
  2007年   13928篇
  2006年   12315篇
  2005年   11387篇
  2004年   10971篇
  2003年   10743篇
  2002年   10081篇
  2001年   10228篇
  2000年   9859篇
  1999年   10097篇
  1998年   23751篇
  1997年   17112篇
  1996年   13472篇
  1995年   10271篇
  1994年   9231篇
  1993年   9005篇
  1992年   7098篇
  1991年   6693篇
  1990年   6385篇
  1989年   6216篇
  1988年   5944篇
  1987年   5207篇
  1986年   5023篇
  1985年   5905篇
  1984年   5488篇
  1983年   5023篇
  1982年   4623篇
  1981年   4829篇
  1980年   4444篇
  1979年   4437篇
  1978年   4260篇
  1977年   4959篇
  1976年   6379篇
  1975年   3863篇
  1974年   3814篇
  1973年   3826篇
  1972年   3056篇
  1971年   2855篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
It is suggested that the chord length distribution method could be useful for predicting double-bit upset rates in certain circumstances. A chord length distribution function for simultaneous path lengths in two parallelepipeds, applicable to a unidirectional flux, is derived. A proof of the system is outlined for the case under consideration  相似文献   
82.
We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.  相似文献   
83.
84.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy.  相似文献   
85.
86.
87.
88.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration.  相似文献   
89.
90.
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