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   402958篇
  免费   5369篇
  国内免费   1350篇
电工技术   7565篇
综合类   314篇
化学工业   59554篇
金属工艺   16433篇
机械仪表   13493篇
建筑科学   8366篇
矿业工程   2155篇
能源动力   11529篇
轻工业   28495篇
水利工程   4262篇
石油天然气   7914篇
武器工业   17篇
无线电   49238篇
一般工业技术   83014篇
冶金工业   75011篇
原子能技术   9182篇
自动化技术   33135篇
  2022年   2304篇
  2021年   3881篇
  2020年   2941篇
  2019年   3810篇
  2018年   6485篇
  2017年   6486篇
  2016年   6924篇
  2015年   4325篇
  2014年   7140篇
  2013年   20037篇
  2012年   11418篇
  2011年   15277篇
  2010年   12160篇
  2009年   13725篇
  2008年   14064篇
  2007年   13827篇
  2006年   12423篇
  2005年   11123篇
  2004年   10511篇
  2003年   10419篇
  2002年   9831篇
  2001年   9734篇
  2000年   9136篇
  1999年   9523篇
  1998年   24340篇
  1997年   16728篇
  1996年   12809篇
  1995年   9524篇
  1994年   8366篇
  1993年   8385篇
  1992年   6055篇
  1991年   5696篇
  1990年   5685篇
  1989年   5317篇
  1988年   5043篇
  1987年   4420篇
  1986年   4300篇
  1985年   4813篇
  1984年   4421篇
  1983年   3996篇
  1982年   3655篇
  1981年   3729篇
  1980年   3428篇
  1979年   3326篇
  1978年   3334篇
  1977年   3752篇
  1976年   4850篇
  1975年   2850篇
  1974年   2663篇
  1973年   2730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