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   411852篇
  免费   5626篇
  国内免费   1363篇
电工技术   7677篇
综合类   321篇
化学工业   61550篇
金属工艺   16633篇
机械仪表   13656篇
建筑科学   8771篇
矿业工程   2208篇
能源动力   11790篇
轻工业   29065篇
水利工程   4360篇
石油天然气   8017篇
武器工业   17篇
无线电   49805篇
一般工业技术   84521篇
冶金工业   76584篇
原子能技术   9274篇
自动化技术   34592篇
  2022年   2373篇
  2021年   4004篇
  2020年   3046篇
  2019年   3896篇
  2018年   6623篇
  2017年   6613篇
  2016年   7097篇
  2015年   4468篇
  2014年   7363篇
  2013年   20681篇
  2012年   11744篇
  2011年   15694篇
  2010年   12465篇
  2009年   14067篇
  2008年   14457篇
  2007年   14167篇
  2006年   12769篇
  2005年   11407篇
  2004年   10783篇
  2003年   10651篇
  2002年   10060篇
  2001年   9892篇
  2000年   9286篇
  1999年   9673篇
  1998年   24528篇
  1997年   16886篇
  1996年   12956篇
  1995年   9639篇
  1994年   8497篇
  1993年   8502篇
  1992年   6175篇
  1991年   5799篇
  1990年   5778篇
  1989年   5446篇
  1988年   5135篇
  1987年   4518篇
  1986年   4406篇
  1985年   4934篇
  1984年   4559篇
  1983年   4097篇
  1982年   3757篇
  1981年   3814篇
  1980年   3506篇
  1979年   3418篇
  1978年   3410篇
  1977年   3847篇
  1976年   4936篇
  1975年   2928篇
  1974年   2754篇
  1973年   2800篇
排序方式: 共有10000条查询结果,搜索用时 562 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