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   478630篇
  免费   4630篇
  国内免费   1347篇
化学   248286篇
晶体学   7838篇
力学   21635篇
综合类   16篇
数学   54607篇
物理学   152225篇
  2021年   4118篇
  2020年   4542篇
  2019年   5103篇
  2018年   6678篇
  2017年   6925篇
  2016年   9798篇
  2015年   5716篇
  2014年   9452篇
  2013年   22461篇
  2012年   17022篇
  2011年   20459篇
  2010年   14915篇
  2009年   14831篇
  2008年   18289篇
  2007年   18132篇
  2006年   16878篇
  2005年   14870篇
  2004年   13784篇
  2003年   12331篇
  2002年   12142篇
  2001年   14436篇
  2000年   10864篇
  1999年   8399篇
  1998年   6948篇
  1997年   6778篇
  1996年   6402篇
  1995年   5722篇
  1994年   5563篇
  1993年   5289篇
  1992年   6194篇
  1991年   6315篇
  1990年   6056篇
  1989年   6045篇
  1988年   5801篇
  1987年   5917篇
  1986年   5570篇
  1985年   7130篇
  1984年   7189篇
  1983年   5855篇
  1982年   6053篇
  1981年   5867篇
  1980年   5579篇
  1979年   6119篇
  1978年   6155篇
  1977年   6247篇
  1976年   6088篇
  1975年   5667篇
  1974年   5539篇
  1973年   5582篇
  1972年   3933篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
123.
The structural change in the depth direction of a polyimide (UPILEX‐S) film treated in alkaline solution, which was a representative surface treatment used to form a seed layer for plating and to improve the adhesive strength, was analyzed by means of micro Fourier transform infrared attenuated total reflection (FTIR‐ATR) line analysis with gradient shaving preparation. The polyimide film was treated with KOH. The imide ring opened through the alkaline treatment, and the amide structure and carboxylic acid salt were formed. The attainment depth of this structural change was almost proportional to the treatment time, and it reached about 8 μm after a 30‐min treatment. The degree of structural change through the alkaline treatment was almost constant after it reached a considerably degraded stage, and the chemically changed region penetrated into the inner part of the film from the surface. An intermediate layer before the final degraded stage appeared in the treated layer, and its thickness increased with the treatment time. The region that was changed chemically by the alkaline treatment progressed to the inner part simultaneously and continuously as the treatment time increased. The combined use of gradient shaving preparation and micro FTIR‐ATR line analysis was found to be extremely effective for the depth profiling of organic materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2071–2078, 2003  相似文献   
124.
An arbitrary operator-valued function from the generalized Shur class is realized as the transfer function of a minimal optimal and minimal *-optimal dissipative scattering system with the Pontryagin state space. These results generalize Arov's results for the case of the Hilbert state space. Bibliography: 11 titles.  相似文献   
125.
126.
127.
The ZnS:Cu,Al,Au (P22G) phosphor powder was bombarded by an electron beam in an O2 ambient, Ar ambient and other mixture of gases. These gases consisted of mixtures of O2 and COx, and O2, COx and Ar gas. Auger electron spectroscopy (AES) was used to monitor changes in the surface composition of the P22G phosphor during electron bombardment. When the P22G phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. The electron beam degradation of the P22G phosphor powder was also performed in a dry O2 ambient and a layer of ZnSO4 was formed on the surface. The ZnSO4 formation decayed exponentially with time and it is postulated that this was due to the diffusion of the charge reactants through the ZnSO4 film to the reaction interfaces. The P22G phosphor exposed to the electron beam in an Ar ambient and to the other gas mixtures degraded at a lower rate than in the case of the O2 ambient. This suggests that Ar and COx may suppress the degradation of the P22G phosphor powder.  相似文献   
128.
Russian Journal of General Chemistry -  相似文献   
129.
The study deals with estimating the reliability of classification algorithms. The present article (the first of three) examines the statistical methods used for point estimation of the reliability of classifiers in the frequency approach. The estimation results are applicable to the small-sample case, which is of considerable importance in practice.  相似文献   
130.
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