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   357839篇
  免费   3827篇
  国内免费   864篇
电工技术   6531篇
综合类   242篇
化学工业   54427篇
金属工艺   18007篇
机械仪表   13564篇
建筑科学   8271篇
矿业工程   2509篇
能源动力   7439篇
轻工业   27380篇
水利工程   4179篇
石油天然气   8210篇
武器工业   17篇
无线电   38074篇
一般工业技术   75060篇
冶金工业   57401篇
原子能技术   8454篇
自动化技术   32765篇
  2021年   2156篇
  2018年   11431篇
  2017年   11933篇
  2016年   8319篇
  2015年   3023篇
  2014年   4411篇
  2013年   12206篇
  2012年   9337篇
  2011年   16925篇
  2010年   14939篇
  2009年   14852篇
  2008年   15003篇
  2007年   16726篇
  2006年   8011篇
  2005年   10600篇
  2004年   8737篇
  2003年   8193篇
  2002年   7325篇
  2001年   6648篇
  2000年   6395篇
  1999年   6347篇
  1998年   15071篇
  1997年   11241篇
  1996年   8719篇
  1995年   6613篇
  1994年   6020篇
  1993年   5900篇
  1992年   4549篇
  1991年   4498篇
  1990年   4342篇
  1989年   4345篇
  1988年   4294篇
  1987年   3630篇
  1986年   3638篇
  1985年   4188篇
  1984年   3995篇
  1983年   3654篇
  1982年   3459篇
  1981年   3587篇
  1980年   3453篇
  1979年   3399篇
  1978年   3476篇
  1977年   3984篇
  1976年   5117篇
  1975年   3186篇
  1974年   3026篇
  1973年   3042篇
  1972年   2668篇
  1971年   2488篇
  1970年   2124篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The behavior of a superelastic Cu?14.2% Al?4%Ni single crystal in the case of high reversible strains under a longitudinal bending force was investigated. The effect of strain confinement along the crystal length was revealed and studied. The highest reversible strains (up to 10%) were shown to be confined within the central part of the bent crystal.  相似文献   
132.
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   
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