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   524145篇
  免费   8037篇
  国内免费   1452篇
电工技术   9558篇
综合类   525篇
化学工业   78261篇
金属工艺   19961篇
机械仪表   15191篇
建筑科学   12668篇
矿业工程   2269篇
能源动力   14525篇
轻工业   47069篇
水利工程   5213篇
石油天然气   9334篇
武器工业   37篇
无线电   59896篇
一般工业技术   101773篇
冶金工业   103606篇
原子能技术   10560篇
自动化技术   43188篇
  2021年   4876篇
  2020年   3475篇
  2019年   4551篇
  2018年   7808篇
  2017年   7610篇
  2016年   7934篇
  2015年   5562篇
  2014年   9245篇
  2013年   24081篇
  2012年   14627篇
  2011年   20150篇
  2010年   15803篇
  2009年   17700篇
  2008年   18100篇
  2007年   17778篇
  2006年   15516篇
  2005年   14215篇
  2004年   13609篇
  2003年   13402篇
  2002年   12635篇
  2001年   12834篇
  2000年   11869篇
  1999年   12599篇
  1998年   32827篇
  1997年   22908篇
  1996年   17453篇
  1995年   13041篇
  1994年   11290篇
  1993年   10981篇
  1992年   7920篇
  1991年   7420篇
  1990年   7265篇
  1989年   7015篇
  1988年   6474篇
  1987年   5770篇
  1986年   5658篇
  1985年   6272篇
  1984年   5906篇
  1983年   5174篇
  1982年   4905篇
  1981年   4973篇
  1980年   4709篇
  1979年   4611篇
  1978年   4413篇
  1977年   5338篇
  1976年   6975篇
  1975年   3801篇
  1974年   3553篇
  1973年   3665篇
  1972年   2980篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
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   
994.
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   
995.
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   
996.
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   
997.
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   
998.
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   
999.
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   
1000.
The aim of this paper is the comparison of the axial flux (AF) structures versus the conventional radial flux (RF) structures for permanent-magnet synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, the AF motors can be an attractive alternative to the conventional RF solutions.  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