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   458934篇
  免费   5486篇
  国内免费   1390篇
电工技术   8857篇
综合类   386篇
化学工业   65899篇
金属工艺   21904篇
机械仪表   17536篇
建筑科学   9473篇
矿业工程   2735篇
能源动力   12022篇
轻工业   29160篇
水利工程   5110篇
石油天然气   8818篇
武器工业   17篇
无线电   54397篇
一般工业技术   97630篇
冶金工业   79111篇
原子能技术   9863篇
自动化技术   42892篇
  2021年   3853篇
  2020年   2938篇
  2019年   3796篇
  2018年   12827篇
  2017年   13228篇
  2016年   10621篇
  2015年   4713篇
  2014年   7205篇
  2013年   20071篇
  2012年   13441篇
  2011年   21739篇
  2010年   18426篇
  2009年   18943篇
  2008年   19282篇
  2007年   20634篇
  2006年   12460篇
  2005年   13887篇
  2004年   12017篇
  2003年   11687篇
  2002年   10362篇
  2001年   9779篇
  2000年   9253篇
  1999年   9533篇
  1998年   24329篇
  1997年   16709篇
  1996年   12810篇
  1995年   9526篇
  1994年   8384篇
  1993年   8398篇
  1992年   6069篇
  1991年   5715篇
  1990年   5679篇
  1989年   5317篇
  1988年   5050篇
  1987年   4419篇
  1986年   4256篇
  1985年   4768篇
  1984年   4377篇
  1983年   3945篇
  1982年   3607篇
  1981年   3678篇
  1980年   3399篇
  1979年   3304篇
  1978年   3302篇
  1977年   3719篇
  1976年   4824篇
  1975年   2836篇
  1974年   2637篇
  1973年   2705篇
  1972年   2266篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Wireless Personal Communications - In the fusion experiment, sensitive radio frequency signal diagnostic instruments need to be protected against high power stray radiation coming from the Electron...  相似文献   
62.
Sustainable and efficient food supply chain has become an essential component of one’s life. The model proposed in this paper is deeply linked to people's quality of life as a result of which there is a large incentive to fulfil customer demands through it. This proposed model can enhance food quality by making the best possible food quality accessible to customers, construct a sustainable logistics system considering its environmental impact and ensure the customer demand to be fulfilled as fast as possible. In this paper, an extended model is examined that builds a unified planning problem for efficient food logistics operations where four important objectives are viewed: minimising the total expense of the system, maximising the average food quality along with the minimisation of the amount of CO2 emissions in transportation along with production and total weighted delivery lead time minimisation. A four objective mixed integer linear programming model for intelligent food logistics system is developed in the paper. The optimisation of the formulated mathematical model is proposed using a modified multi-objective particle swarm optimisation algorithm with multiple social structures: MO-GLNPSO (Multi-Objective Global Local Near-Neighbour Particle Swarm Optimisation). Computational results of a case study on a given dataset as well as on multiple small, medium and large-scale datasets followed by sensitivity analysis show the potency and effectiveness of the introduced method. Lastly, there has been a scope for future study displayed which would lead to the further progress of these types of models.  相似文献   
63.
64.
Puzanov  A. S.  Obolenskiy  S. V.  Kozlov  V. A. 《Semiconductors》2020,54(8):946-950
Semiconductors - On the basis of the Monte Carlo algorithm, a method for calculating the energy spectrum of hot nonequilibrium electrons and holes in the track of a primary recoil atom after being...  相似文献   
65.
66.

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

  相似文献   
67.
68.
69.
70.
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