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   524980篇
  免费   8074篇
  国内免费   1455篇
电工技术   9583篇
综合类   525篇
化学工业   78496篇
金属工艺   19993篇
机械仪表   15207篇
建筑科学   12689篇
矿业工程   2271篇
能源动力   14613篇
轻工业   47093篇
水利工程   5213篇
石油天然气   9336篇
武器工业   37篇
无线电   59997篇
一般工业技术   101976篇
冶金工业   103628篇
原子能技术   10569篇
自动化技术   43283篇
  2021年   4903篇
  2020年   3488篇
  2019年   4571篇
  2018年   7831篇
  2017年   7643篇
  2016年   7966篇
  2015年   5580篇
  2014年   9272篇
  2013年   24144篇
  2012年   14677篇
  2011年   20205篇
  2010年   15854篇
  2009年   17757篇
  2008年   18136篇
  2007年   17823篇
  2006年   15530篇
  2005年   14234篇
  2004年   13631篇
  2003年   13417篇
  2002年   12662篇
  2001年   12853篇
  2000年   11886篇
  1999年   12604篇
  1998年   32850篇
  1997年   22916篇
  1996年   17475篇
  1995年   13054篇
  1994年   11296篇
  1993年   10983篇
  1992年   7925篇
  1991年   7433篇
  1990年   7274篇
  1989年   7021篇
  1988年   6481篇
  1987年   5776篇
  1986年   5664篇
  1985年   6276篇
  1984年   5911篇
  1983年   5179篇
  1982年   4908篇
  1981年   4969篇
  1980年   4711篇
  1979年   4622篇
  1978年   4418篇
  1977年   5343篇
  1976年   6978篇
  1975年   3802篇
  1974年   3552篇
  1973年   3667篇
  1972年   2979篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
992.
993.
994.
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   
995.
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   
996.
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   
997.
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   
998.
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   
999.
A one-dimensional mesoscopic ring with one input and two output leads acts as a spintronic beam splitter. The spatial degree of freedom, i.e., the presence of two different possible output channels, gets intertwined with the spin direction as a consequence of quantum interference and spin-orbit interaction. We investigate this kind of spatial-spin correlation, and show that the output density operator contains no quantum entanglement in the important special case when the device polarizes a perfectly random input spin state. However, the correlations are in general not purely classical, we also present specific input states with maximal spatial-spin entanglement after the ring.  相似文献   
1000.
Comparison measurements on reference standards are reported in which 13 partners with different instruments took part. A set of prototype standards which had been produced and calibrated within a European project were used for the measurements. Here, results of measurements on a 240 nm step height standard and a two-dimensional lateral standard with a nominal pitch of 1 μm are reported.  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