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   525931篇
  免费   8137篇
  国内免费   1470篇
电工技术   9587篇
综合类   526篇
化学工业   79046篇
金属工艺   19989篇
机械仪表   15223篇
建筑科学   12729篇
矿业工程   2271篇
能源动力   14595篇
轻工业   47212篇
水利工程   5233篇
石油天然气   9336篇
武器工业   37篇
无线电   60050篇
一般工业技术   102058篇
冶金工业   103548篇
原子能技术   10562篇
自动化技术   43536篇
  2022年   3202篇
  2021年   4949篇
  2020年   3505篇
  2019年   4601篇
  2018年   7855篇
  2017年   7666篇
  2016年   7987篇
  2015年   5608篇
  2014年   9323篇
  2013年   24181篇
  2012年   14747篇
  2011年   20270篇
  2010年   15886篇
  2009年   17808篇
  2008年   18205篇
  2007年   17860篇
  2006年   15570篇
  2005年   14249篇
  2004年   13654篇
  2003年   13437篇
  2002年   12673篇
  2001年   12850篇
  2000年   11880篇
  1999年   12613篇
  1998年   32827篇
  1997年   22918篇
  1996年   17459篇
  1995年   13049篇
  1994年   11292篇
  1993年   10979篇
  1992年   7916篇
  1991年   7420篇
  1990年   7266篇
  1989年   7015篇
  1988年   6472篇
  1987年   5768篇
  1986年   5656篇
  1985年   6267篇
  1984年   5902篇
  1983年   5173篇
  1982年   4902篇
  1981年   4966篇
  1980年   4706篇
  1979年   4609篇
  1978年   4408篇
  1977年   5334篇
  1976年   6971篇
  1975年   3796篇
  1974年   3550篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
Conclusions This comparison of two ways of making99Mo shows that there is good scope for making it in any area. If there is a thermal reactor having a high flux, one can make99Mo from98Mo, and in that case, even irradiation in a high flux makes it favorable to use highly enriched98Mo and unblocked targets, which raises the specific activity and thus increases the working life in the99mTc generator.If there is a thermal reactor with low flux or if there is a fast reactor it is best to make99Mo from uranium fission products. The target can be highly enriched235U, which if necessary can be reused, or low-enriched uranium.There are no essential constraints on making99Mo, and the production is mainly based on technological tasks.Translated from Atomnaya Énergiya, Vol. 67, No. 2, pp. 104–108, August, 1989.  相似文献   
992.
993.
994.
995.
996.
Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field  相似文献   
997.
Kumar  A. Sodha  M.S. 《Electronics letters》1987,23(6):275-276
A general formalism for the study of nonlinear pulse propagation in optical fibres is presented. It is then applied to study the time evolution of a Gaussian laser pulse in a fibre with cubic and fifth-order nonlinearity in the index of refraction. The results are presented and discussed.  相似文献   
998.
We report on the Langmuir-Blodgett film deposition and plasma etching of cadmium distearate on n-Gao.47Ino.53As to form a high-barrier-height Schottky barrier. Using this technique to form the gate electrode, we fabricated a 1?m-gate-length inverted InP-GalnAs modulation-doped field-effect transistor (MODFET) with an extrinsic transconductance of 170mS/mm and a cutoff frequencyfT of 19 GHz.  相似文献   
999.
By using integral transform methods, an approach is developed to the solution of a problem on the temprature distribution in multilayer structures heated by cw scanning laser radiation, with phase transitions in the layers taken into account.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 1000–1010, December, 1987.  相似文献   
1000.
A total of 438 manufacturing firms reported their business relocation activity, their overall attitude toward the business climate in Michigan, and their assessment of 34 business climate dimensions. Using a lens model paradigm, we explored reasons for a lack of relation between actual relocation decisions and overall business climate attitudes. Location decisions were most highly correlated with distance and labor considerations, whereas overall business climate was most highly correlated with tax considerations, and secondarily correlated with labor problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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