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   582620篇
  免费   7822篇
  国内免费   1949篇
电工技术   11046篇
综合类   441篇
化学工业   84653篇
金属工艺   23086篇
机械仪表   18525篇
建筑科学   13081篇
矿业工程   2803篇
能源动力   16624篇
轻工业   43558篇
水利工程   5859篇
石油天然气   10096篇
武器工业   29篇
无线电   73261篇
一般工业技术   117467篇
冶金工业   110752篇
原子能技术   12509篇
自动化技术   48601篇
  2021年   5358篇
  2020年   4111篇
  2019年   5169篇
  2018年   8683篇
  2017年   8745篇
  2016年   9236篇
  2015年   5935篇
  2014年   9878篇
  2013年   28132篇
  2012年   15603篇
  2011年   21206篇
  2010年   16954篇
  2009年   19190篇
  2008年   19865篇
  2007年   19576篇
  2006年   17473篇
  2005年   15624篇
  2004年   14892篇
  2003年   14938篇
  2002年   14017篇
  2001年   14248篇
  2000年   13290篇
  1999年   14017篇
  1998年   35890篇
  1997年   24865篇
  1996年   19199篇
  1995年   14385篇
  1994年   12681篇
  1993年   12606篇
  1992年   9059篇
  1991年   8668篇
  1990年   8546篇
  1989年   7965篇
  1988年   7649篇
  1987年   6610篇
  1986年   6450篇
  1985年   7144篇
  1984年   6541篇
  1983年   6068篇
  1982年   5587篇
  1981年   5584篇
  1980年   5277篇
  1979年   5068篇
  1978年   4909篇
  1977年   5737篇
  1976年   7700篇
  1975年   4220篇
  1974年   4014篇
  1973年   4029篇
  1972年   3409篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
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   
93.
94.
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   
95.
96.

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   
97.
98.
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   
99.
100.
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   
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