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   766822篇
  免费   9747篇
  国内免费   2487篇
电工技术   14468篇
综合类   666篇
化学工业   114326篇
金属工艺   31916篇
机械仪表   24176篇
建筑科学   16875篇
矿业工程   4831篇
能源动力   19752篇
轻工业   58823篇
水利工程   8503篇
石油天然气   16667篇
武器工业   60篇
无线电   88977篇
一般工业技术   155681篇
冶金工业   143838篇
原子能技术   17461篇
自动化技术   62036篇
  2021年   6708篇
  2020年   4999篇
  2019年   6487篇
  2018年   11154篇
  2017年   11309篇
  2016年   11895篇
  2015年   7621篇
  2014年   12868篇
  2013年   34840篇
  2012年   20135篇
  2011年   27600篇
  2010年   22217篇
  2009年   25195篇
  2008年   25725篇
  2007年   25619篇
  2006年   22468篇
  2005年   20438篇
  2004年   19649篇
  2003年   19125篇
  2002年   18398篇
  2001年   18307篇
  2000年   17409篇
  1999年   17783篇
  1998年   44199篇
  1997年   31113篇
  1996年   24226篇
  1995年   18145篇
  1994年   16221篇
  1993年   15904篇
  1992年   11671篇
  1991年   11392篇
  1990年   11166篇
  1989年   10744篇
  1988年   10135篇
  1987年   8861篇
  1986年   8774篇
  1985年   9880篇
  1984年   8865篇
  1983年   8339篇
  1982年   7598篇
  1981年   7806篇
  1980年   7263篇
  1979年   7227篇
  1978年   7067篇
  1977年   8013篇
  1976年   10362篇
  1975年   6256篇
  1974年   6030篇
  1973年   6022篇
  1972年   5181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