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   524528篇
  免费   8082篇
  国内免费   1454篇
电工技术   9556篇
综合类   527篇
化学工业   78289篇
金属工艺   19969篇
机械仪表   15196篇
建筑科学   12699篇
矿业工程   2272篇
能源动力   14534篇
轻工业   47115篇
水利工程   5213篇
石油天然气   9333篇
武器工业   38篇
无线电   59962篇
一般工业技术   101900篇
冶金工业   103550篇
原子能技术   10565篇
自动化技术   43346篇
  2021年   4895篇
  2020年   3490篇
  2019年   4583篇
  2018年   7835篇
  2017年   7625篇
  2016年   7968篇
  2015年   5585篇
  2014年   9275篇
  2013年   24105篇
  2012年   14665篇
  2011年   20204篇
  2010年   15835篇
  2009年   17733篇
  2008年   18139篇
  2007年   17819篇
  2006年   15539篇
  2005年   14229篇
  2004年   13614篇
  2003年   13410篇
  2002年   12654篇
  2001年   12839篇
  2000年   11875篇
  1999年   12602篇
  1998年   32817篇
  1997年   22899篇
  1996年   17452篇
  1995年   13039篇
  1994年   11284篇
  1993年   10976篇
  1992年   7918篇
  1991年   7420篇
  1990年   7268篇
  1989年   7017篇
  1988年   6468篇
  1987年   5768篇
  1986年   5655篇
  1985年   6273篇
  1984年   5904篇
  1983年   5175篇
  1982年   4904篇
  1981年   4970篇
  1980年   4705篇
  1979年   4610篇
  1978年   4409篇
  1977年   5334篇
  1976年   6972篇
  1975年   3796篇
  1974年   3550篇
  1973年   3665篇
  1972年   2978篇
排序方式: 共有10000条查询结果,搜索用时 15 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