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   353282篇
  免费   3713篇
  国内免费   860篇
电工技术   6485篇
综合类   238篇
化学工业   53048篇
金属工艺   17921篇
机械仪表   13513篇
建筑科学   8071篇
矿业工程   2506篇
能源动力   7361篇
轻工业   26765篇
水利工程   4151篇
石油天然气   8205篇
武器工业   16篇
无线电   37805篇
一般工业技术   74463篇
冶金工业   56466篇
原子能技术   8406篇
自动化技术   32435篇
  2021年   2091篇
  2018年   11384篇
  2017年   11889篇
  2016年   8257篇
  2015年   2956篇
  2014年   4340篇
  2013年   12097篇
  2012年   9235篇
  2011年   16792篇
  2010年   14802篇
  2009年   14755篇
  2008年   14885篇
  2007年   16621篇
  2006年   7901篇
  2005年   10515篇
  2004年   8656篇
  2003年   8112篇
  2002年   7252篇
  2001年   6570篇
  2000年   6312篇
  1999年   6257篇
  1998年   14776篇
  1997年   11045篇
  1996年   8589篇
  1995年   6539篇
  1994年   5944篇
  1993年   5821篇
  1992年   4500篇
  1991年   4467篇
  1990年   4286篇
  1989年   4306篇
  1988年   4266篇
  1987年   3603篇
  1986年   3596篇
  1985年   4166篇
  1984年   3965篇
  1983年   3622篇
  1982年   3423篇
  1981年   3558篇
  1980年   3379篇
  1979年   3308篇
  1978年   3406篇
  1977年   3867篇
  1976年   4995篇
  1975年   3114篇
  1974年   2968篇
  1973年   2988篇
  1972年   2622篇
  1971年   2432篇
  1970年   2053篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
131.
X-ray diffraction analysis has been used to study the structure of the α-Zr matrix phase and the precipitation of β-Nb particles upon the annealing of a Zr–2.5% Nb deformed alloy. It has been found that the process of the precipitation of the strengthening β-Nb particles in the alloy is accompanied by the appearance of fields of elastic interphase deformations in the matrix α phase of the alloy due to the difference in the specific atomic volumes of the crystal structures of the matrix and precipitated phases. It has been shown experimentally that, as a result of the presence of interphase deformations in the alloy, the bcc crystal structure of the precipitating β-Nb particles undergoes monoclinic distortions.  相似文献   
132.
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.  相似文献   
133.
134.
The cracks in the workpiece specimens can reduce the fatigue life of any machine components. Since the residual stress has a considerable amount of influence on determining crack formation over the machined surface, it is very essential to analyze the residual stress developed in any machining process. However, it is a very tedious process to compute the residual stress over the machined surface. In the present study, an endeavor has been made to measure and analyze the residual stress of machined silicon steel as a workpiece using the EDM process with different energy distribution. The nano-indentation method was used to compute the residual stress produced over the machined surface. From the experimental results, it was found that the uniform energy distribution has produced higher compressive residual stress owing to the tiny and uniform spark energy distribution. It has also been observed that the tool electrode has a considerable amount of influence on determining development of residual stress in the EDM process.  相似文献   
135.
136.
137.
138.
Sidorov  G. V.  Myasoedov  N. F. 《Radiochemistry》2020,62(2):260-263
Radiochemistry - Reaction of solid-phase catalytic heterogeneous isotope exchange of 2-deoxy-D-glucose and its derivative, O(6)-(4-bromothiophenyl)guanine-C8-β-D-glucose with tritium has been...  相似文献   
139.
140.
We show that in the presence of magnetic field, two superconducting phases with the center-of-mass momentum of Cooper pair parallel to the magnetic field are induced in Dresselhaus spin–orbit-coupled superconductor. Specifically, at small magnetic field, the center-of-mass momentum is induced due to the energy-spectrum distortion and no unpairing region with vanishing singlet correlation appears. We refer to this superconducting state as the drift-BCS state. By further increasing the magnetic field, the superconducting state falls into the Fulde–Ferrell state with the emergence of the unpairing regions. The observed abrupt enhancement of the center-of-mass momenta and suppression on the order parameters during the transition indicate the occurrence of a first-order phase transition. Enhanced Pauli limit and hence enlarged magnetic-field regime of the Fulde–Ferrell state, due to the spin-flip terms of the spin–orbit coupling, are revealed. We also address the triplet correlations induced by the spin–orbit coupling, and show that the Cooper-pair spin polarizations, generated by the magnetic field and center-of-mass momentum with the triplet correlations exhibit totally different magnetic-field dependences between the drift-BCS and Fulde–Ferrell states.  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