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   399437篇
  免费   3956篇
  国内免费   1399篇
电工技术   7154篇
综合类   367篇
化学工业   60345篇
金属工艺   19854篇
机械仪表   12424篇
建筑科学   9019篇
矿业工程   2349篇
能源动力   8668篇
轻工业   31789篇
水利工程   4418篇
石油天然气   9934篇
武器工业   15篇
无线电   43878篇
一般工业技术   80526篇
冶金工业   75097篇
原子能技术   10555篇
自动化技术   28400篇
  2021年   3014篇
  2019年   2906篇
  2018年   5148篇
  2017年   5184篇
  2016年   5655篇
  2015年   3486篇
  2014年   5955篇
  2013年   16637篇
  2012年   9400篇
  2011年   12762篇
  2010年   10376篇
  2009年   11472篇
  2008年   12033篇
  2007年   12049篇
  2006年   10756篇
  2005年   9907篇
  2004年   9520篇
  2003年   9454篇
  2002年   9349篇
  2001年   9495篇
  2000年   8854篇
  1999年   9274篇
  1998年   22461篇
  1997年   15987篇
  1996年   12253篇
  1995年   9220篇
  1994年   8160篇
  1993年   8166篇
  1992年   6151篇
  1991年   6152篇
  1990年   5850篇
  1989年   5685篇
  1988年   5595篇
  1987年   4980篇
  1986年   4963篇
  1985年   5575篇
  1984年   5154篇
  1983年   4772篇
  1982年   4421篇
  1981年   4677篇
  1980年   4402篇
  1979年   4459篇
  1978年   4574篇
  1977年   5155篇
  1976年   7097篇
  1975年   4076篇
  1974年   4040篇
  1973年   4067篇
  1972年   3562篇
  1971年   3189篇
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
81.
82.
In the development of a novel freeze-drying technique in a fluidized bed at atmospheric pressure, a parallel study was undertaken using a conventional vacuum equipment. Two kinetically distinct phases were observed during freeze drying of representative Pood samples:

(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure  相似文献   
83.
Existing duality principles in structural optimisation are briefly reviewed and then they are extended to structures with segment-wise constant cross-sections. All theories are discussed in the particular context of optimal plastic beam design with symmetric convex specific cost functions and are confirmed by independent calculations on illustrative examples. It is shown that the optimal solution is always associated with a displacement field in which the mean absolute curvature value for each segment equals the subgradient of the specific cost function, with respect to the maximum absolute moment value for that segment. Moreover, the dual problem consists of the maximisation of the difference of two terms: the first one is the integral of the product of load and deflection (external work), and the second is the sum of products of segment lengths and the mean complementary cost values (taken with respect to the mean absolute curvature for that segment). Finally, some tentative proposals for a class of non-convex optimisation problems are presented. For special cases, the proposed general statements reduce to theorems by Heyman, Foulkes and Hemp.  相似文献   
84.
Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 111–113, August, 1989.  相似文献   
85.
86.
87.
88.
We have designed, developed, and tested a very promising thermal image analysis method for polygraph testing. The method achieved a correct classification rate of CCR= 84% on the test population to our avail. This method, once refined, can serve as an additional channel for increasing the reliability and accuracy of traditional polygraph examination. We extract subtle facial temperature fluctuation patterns through nonlinear heat transfer modeling. The modeling transforms raw thermal data to blood flow rate information. Then, we use the slope of the average periorbital blood flow rate as the feature of a binary classification scheme. The results come to support our previous laboratory findings about the importance of periorbital blood flow in anxious states.  相似文献   
89.
90.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present.  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