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   102185篇
  免费   4267篇
  国内免费   2755篇
化学   41231篇
晶体学   1073篇
力学   8129篇
综合类   109篇
数学   34557篇
物理学   24108篇
  2024年   71篇
  2023年   523篇
  2022年   947篇
  2021年   962篇
  2020年   1007篇
  2019年   992篇
  2018年   11031篇
  2017年   10808篇
  2016年   7134篇
  2015年   1970篇
  2014年   1620篇
  2013年   2081篇
  2012年   6084篇
  2011年   12705篇
  2010年   7110篇
  2009年   7419篇
  2008年   8117篇
  2007年   10126篇
  2006年   1554篇
  2005年   2419篇
  2004年   2333篇
  2003年   2583篇
  2002年   1601篇
  2001年   682篇
  2000年   720篇
  1999年   662篇
  1998年   613篇
  1997年   578篇
  1996年   645篇
  1995年   472篇
  1994年   380篇
  1993年   326篇
  1992年   286篇
  1991年   259篇
  1990年   218篇
  1989年   201篇
  1988年   155篇
  1987年   166篇
  1986年   144篇
  1985年   128篇
  1984年   89篇
  1983年   79篇
  1982年   76篇
  1981年   56篇
  1980年   57篇
  1979年   54篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
It is shown that time-dependent temperatures in a transient, conductive system can be approximately modeled by a fractional-order differential equation, the order of which depends on the Biot number. This approximation is particularly suitable for complex shapes for which a first-principles approach is too difficult or computationally time-consuming. Analytical solutions of these equations can be written in terms of the Mittag-Leffler function. The approximation is especially useful if a suitable fractional-order controller is to be designed for the system.  相似文献   
22.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite. The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials. The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang  相似文献   
23.
The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
24.
A method was proposed for the simultaneous determination of trace cadmium and mercury by vapor generation non-dispersive atomic fluorescence spectrometry using an intermittent flow system. The effects of the parameters on the performance were studied systematically. The parameters such as acid concentration of the reaction medium, flow rate of the carrier gas and shield gas, the observation height and the atomizer temperature, etc. which affected the sensitivity, were optimized. Ascorbic acid, cobalt ion and thiourea were used as enhancement reagents or masking agents to enhance the generation efficiency of the volatile species of Cd and Hg. The mechanisms of their effects on vapor generation were investigated. In the presence of thiourea and ascorbic acid, the influences of some coexisting elements on the determination of cadmium and mercury were investigated. The detection limits (3sigma) were 0.010 microg l(-1) for Cd and 0.019 microg l(-1) for Hg, respectively. The relative standard deviations for Cd and Hg at 1.00 microg l(-1) were 2.6% and 0.97% (n = 11), respectively. The proposed method has been satisfactorily applied to the determination of trace cadmium and mercury in Chinese herbal medicine.  相似文献   
25.
26.
Calendar     
  相似文献   
27.
28.
29.
30.
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