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   743789篇
  免费   8847篇
  国内免费   1562篇
电工技术   14046篇
综合类   618篇
化学工业   111895篇
金属工艺   32304篇
机械仪表   24501篇
建筑科学   16284篇
矿业工程   5028篇
能源动力   18149篇
轻工业   56009篇
水利工程   8614篇
石油天然气   16579篇
武器工业   45篇
无线电   83279篇
一般工业技术   152125篇
冶金工业   133307篇
原子能技术   17058篇
自动化技术   64357篇
  2021年   6244篇
  2019年   6028篇
  2018年   14706篇
  2017年   14926篇
  2016年   13708篇
  2015年   7218篇
  2014年   11948篇
  2013年   31772篇
  2012年   19843篇
  2011年   29374篇
  2010年   24336篇
  2009年   26131篇
  2008年   26868篇
  2007年   27731篇
  2006年   20163篇
  2005年   20156篇
  2004年   18793篇
  2003年   18271篇
  2002年   17148篇
  2001年   16619篇
  2000年   15858篇
  1999年   16026篇
  1998年   39583篇
  1997年   27952篇
  1996年   21580篇
  1995年   16399篇
  1994年   14645篇
  1993年   14425篇
  1992年   10730篇
  1991年   10446篇
  1990年   10251篇
  1989年   9953篇
  1988年   9427篇
  1987年   8331篇
  1986年   8216篇
  1985年   9315篇
  1984年   8365篇
  1983年   7888篇
  1982年   7148篇
  1981年   7386篇
  1980年   6917篇
  1979年   6921篇
  1978年   6816篇
  1977年   7673篇
  1976年   9770篇
  1975年   6080篇
  1974年   5853篇
  1973年   5865篇
  1972年   5069篇
  1971年   4663篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Grachev  A. I. 《Semiconductors》2022,56(2):67-70
Semiconductors - In this work, we discuss for the first time the principle of rotation in the constant electric field of a conducting particle with participation of the Lorentz force, which ensures...  相似文献   
4.
Koroteev  A. S. 《Atomic Energy》2021,130(4):202-208
Atomic Energy - The history and direction of further development of space nuclear energetics are examined. The functional diagram and principle of operation of a promising, powerful,...  相似文献   
5.
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.  相似文献   
6.
Journal of Computer and Systems Sciences International - It is shown that the Lyapunov theorem on the distribution properties of the sum of random variables with different distribution densities...  相似文献   
7.
Refractories and Industrial Ceramics - The paper introduces a promising technology for utilizing a traditional scheme for implementing a flow-through micro-arc oxidation method to restore localized...  相似文献   
8.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  相似文献   
9.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
10.
Multimedia Tools and Applications - The three-dimensional models of brain tumors serve as diagnostic assistance for physicians, surgeons, and radiologists. The proposed system establishes an...  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