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   608376篇
  免费   7597篇
  国内免费   1644篇
电工技术   11334篇
综合类   500篇
化学工业   95662篇
金属工艺   24970篇
机械仪表   19738篇
建筑科学   13648篇
矿业工程   4549篇
能源动力   15631篇
轻工业   49949篇
水利工程   7413篇
石油天然气   15910篇
武器工业   77篇
无线电   64482篇
一般工业技术   125088篇
冶金工业   103481篇
原子能技术   16068篇
自动化技术   49117篇
  2021年   5875篇
  2019年   5578篇
  2018年   9785篇
  2017年   10032篇
  2016年   10499篇
  2015年   6488篇
  2014年   10961篇
  2013年   28086篇
  2012年   16902篇
  2011年   22551篇
  2010年   18192篇
  2009年   20245篇
  2008年   20458篇
  2007年   20159篇
  2006年   17508篇
  2005年   15797篇
  2004年   15107篇
  2003年   14737篇
  2002年   14286篇
  2001年   13879篇
  2000年   13314篇
  1999年   12999篇
  1998年   30200篇
  1997年   21837篇
  1996年   16946篇
  1995年   13050篇
  1994年   11784篇
  1993年   11529篇
  1992年   8964篇
  1991年   8774篇
  1990年   8660篇
  1989年   8401篇
  1988年   8059篇
  1987年   7307篇
  1986年   7082篇
  1985年   7957篇
  1984年   7194篇
  1983年   6892篇
  1982年   6224篇
  1981年   6322篇
  1980年   6056篇
  1979年   6130篇
  1978年   6028篇
  1977年   6677篇
  1976年   8323篇
  1975年   5471篇
  1974年   5262篇
  1973年   5298篇
  1972年   4588篇
  1971年   4306篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Strength of Materials - The statistical analysis performed on the defectiveness of rails in the Kiev subway railway shows that the main cause of the occurrence of most defects is the contact...  相似文献   
102.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
103.
Measurement Techniques - A method is proposed for transferring the unit of mean power of laser radiation by means of measuring high-intensity power (kilowatts), with the possibility of constant...  相似文献   
104.
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   
105.
106.
Theoretical Foundations of Chemical Engineering - A set of measures to establish the technology for manufacturing highly active sources of γ radiation with an active part from...  相似文献   
107.
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   
108.
Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation.  相似文献   
109.
110.
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