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   405091篇
  免费   5472篇
  国内免费   1364篇
电工技术   7582篇
综合类   318篇
化学工业   60276篇
金属工艺   16451篇
机械仪表   13525篇
建筑科学   8542篇
矿业工程   2155篇
能源动力   11596篇
轻工业   28893篇
水利工程   4282篇
石油天然气   7917篇
武器工业   17篇
无线电   49323篇
一般工业技术   83367篇
冶金工业   75028篇
原子能技术   9190篇
自动化技术   33465篇
  2022年   2565篇
  2021年   3913篇
  2020年   2974篇
  2019年   3842篇
  2018年   6568篇
  2017年   6535篇
  2016年   6994篇
  2015年   4391篇
  2014年   7202篇
  2013年   20163篇
  2012年   11504篇
  2011年   15409篇
  2010年   12245篇
  2009年   13793篇
  2008年   14157篇
  2007年   13929篇
  2006年   12538篇
  2005年   11189篇
  2004年   10565篇
  2003年   10483篇
  2002年   9890篇
  2001年   9783篇
  2000年   9173篇
  1999年   9562篇
  1998年   24360篇
  1997年   16736篇
  1996年   12822篇
  1995年   9538篇
  1994年   8389篇
  1993年   8397篇
  1992年   6066篇
  1991年   5705篇
  1990年   5689篇
  1989年   5324篇
  1988年   5046篇
  1987年   4424篇
  1986年   4307篇
  1985年   4828篇
  1984年   4444篇
  1983年   4009篇
  1982年   3665篇
  1981年   3742篇
  1980年   3442篇
  1979年   3337篇
  1978年   3338篇
  1977年   3759篇
  1976年   4855篇
  1975年   2858篇
  1974年   2668篇
  1973年   2741篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
63.
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   
64.
65.

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   
66.
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