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   563233篇
  免费   7212篇
  国内免费   986篇
电工技术   10445篇
综合类   461篇
化学工业   87849篇
金属工艺   23337篇
机械仪表   18433篇
建筑科学   12503篇
矿业工程   4307篇
能源动力   14445篇
轻工业   45408篇
水利工程   6940篇
石油天然气   14904篇
武器工业   39篇
无线电   60258篇
一般工业技术   116264篇
冶金工业   95661篇
原子能技术   14687篇
自动化技术   45490篇
  2021年   5516篇
  2020年   4071篇
  2019年   5323篇
  2018年   9278篇
  2017年   9486篇
  2016年   9905篇
  2015年   6093篇
  2014年   10304篇
  2013年   26201篇
  2012年   15848篇
  2011年   21169篇
  2010年   17025篇
  2009年   18873篇
  2008年   19108篇
  2007年   18800篇
  2006年   16312篇
  2005年   14768篇
  2004年   14024篇
  2003年   13700篇
  2002年   13255篇
  2001年   12866篇
  2000年   12335篇
  1999年   12023篇
  1998年   27687篇
  1997年   20003篇
  1996年   14994篇
  1995年   11927篇
  1994年   10756篇
  1993年   10515篇
  1992年   8238篇
  1991年   8023篇
  1990年   7943篇
  1989年   7673篇
  1988年   7387篇
  1987年   6661篇
  1986年   6464篇
  1985年   7333篇
  1984年   6641篇
  1983年   6359篇
  1982年   5717篇
  1981年   5850篇
  1980年   5587篇
  1979年   5689篇
  1978年   5634篇
  1977年   6152篇
  1976年   7660篇
  1975年   5070篇
  1974年   4868篇
  1973年   4943篇
  1972年   4256篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Journal of Communications Technology and Electronics - Abstract—The article considers the two-dimensional diffraction problem of a TM-type plane electromagnetic wave on a cylindrical silver...  相似文献   
102.
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   
103.
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   
104.
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   
105.
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   
106.
107.
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   
108.
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   
109.
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   
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