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   254166篇
  免费   3331篇
  国内免费   857篇
电工技术   4814篇
综合类   193篇
化学工业   36856篇
金属工艺   9555篇
机械仪表   7564篇
建筑科学   6120篇
矿业工程   884篇
能源动力   7268篇
轻工业   21468篇
水利工程   2203篇
石油天然气   3233篇
武器工业   15篇
无线电   34285篇
一般工业技术   50160篇
冶金工业   48828篇
原子能技术   5082篇
自动化技术   19826篇
  2021年   2452篇
  2020年   1643篇
  2019年   1991篇
  2018年   3353篇
  2017年   3405篇
  2016年   3501篇
  2015年   2289篇
  2014年   4037篇
  2013年   11579篇
  2012年   6317篇
  2011年   8646篇
  2010年   6954篇
  2009年   7937篇
  2008年   8450篇
  2007年   8340篇
  2006年   7386篇
  2005年   6525篇
  2004年   6299篇
  2003年   6568篇
  2002年   6048篇
  2001年   6522篇
  2000年   5991篇
  1999年   6400篇
  1998年   16540篇
  1997年   11462篇
  1996年   8833篇
  1995年   6627篇
  1994年   5913篇
  1993年   5869篇
  1992年   4137篇
  1991年   4026篇
  1990年   3864篇
  1989年   3658篇
  1988年   3565篇
  1987年   3022篇
  1986年   2948篇
  1985年   3212篇
  1984年   2932篇
  1983年   2831篇
  1982年   2644篇
  1981年   2554篇
  1980年   2475篇
  1979年   2313篇
  1978年   2111篇
  1977年   2630篇
  1976年   3616篇
  1975年   1766篇
  1974年   1730篇
  1973年   1667篇
  1972年   1468篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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   
42.
Diffusional limitations (the gel, glass, and cage effects) are manifested in several bulk free radical homopolymerizations as well as in random copolymerizations. These are associated with decreases of several orders of magnitude of the rate constants of termination, propagation, and initiation (the initiator efficiency), respectively. These phenomena have been modeled earlier using the free volume theory for the diffusivities of primary radicals, macro‐radicals, and monomer molecules, and have been applied to homopolymerizations. In this study, a similar model is developed for random bulk copolymerizations. The parameters of the model are fitted using isothermal data on styrene acrylonitrile random copolymerization carried out in small ampoules. Thereafter, best‐fit global correlations have been developed for this system. This enables the model to be used for studying non‐isothermal copolymerizations, as well as for carrying out optimization of industrial reactors, where non‐isothermal conditions are a norm. POLYM. ENG. SCI., 55:2098–2110, 2015. © 2014 Society of Plastics Engineers  相似文献   
43.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
44.
45.
46.
47.
48.
This work investigates the performance of the inverted-T (IT) junctionless (JL) FinFET with selective buried oxide (SELBOX) topology. The electrical charac  相似文献   
49.
50.
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