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   229421篇
  免费   35914篇
  国内免费   24613篇
化学   152183篇
晶体学   2397篇
力学   15873篇
综合类   1687篇
数学   30654篇
物理学   87154篇
  2024年   450篇
  2023年   3907篇
  2022年   5294篇
  2021年   7007篇
  2020年   8207篇
  2019年   7893篇
  2018年   7118篇
  2017年   6485篇
  2016年   10115篇
  2015年   9719篇
  2014年   11940篇
  2013年   16044篇
  2012年   19395篇
  2011年   21459篇
  2010年   14321篇
  2009年   13970篇
  2008年   14430篇
  2007年   13165篇
  2006年   12394篇
  2005年   10698篇
  2004年   9033篇
  2003年   6943篇
  2002年   6347篇
  2001年   5400篇
  2000年   4677篇
  1999年   5124篇
  1998年   4478篇
  1997年   4117篇
  1996年   4264篇
  1995年   3646篇
  1994年   3418篇
  1993年   3073篇
  1992年   2835篇
  1991年   2397篇
  1990年   1993篇
  1989年   1602篇
  1988年   1145篇
  1987年   948篇
  1986年   898篇
  1985年   800篇
  1984年   540篇
  1983年   420篇
  1982年   359篇
  1981年   268篇
  1980年   187篇
  1979年   99篇
  1978年   90篇
  1975年   92篇
  1974年   92篇
  1973年   90篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
91.
Cinnamaldehyde (CA), an active ingredient isolated from the traditional Chinese medicine Cortex Cinnamomi, has a wide range of bioactivities. To clarify the distribution characteristics of CA, a selective and sensitive method utilizing gas chromatography–mass spetrometry was initially developed for simultaneously determining the concentration of CA and its metabolite cinnamyl alcohol in rat tissues. Selected ion masses of m/z 131, 105 and 92 were chosen, and separation of the analytes was performed on a DB‐5 ms (30 m × 0.25 mm, 0.25 µm, thickness) capillary column by gas chromatography–mass spectrometry. The calibration curves demonstrated good linearity and reproducibility over the range of 20–2000 and 20–4000 ng/mL for various tissue samples. Recoveries ranged from 86.8 to 107.5%, while intra‐ and interday relative standard deviations were all <11.3%. The analysis method was successfully applied in tissue distribution studies for CA and cinnamyl alcohol. As CA and cinnamyl alcohol may inter‐convert to one another, simultaneous determination of both analytes provides a comparative and accurate data for tissue study. The concentrations of CA and cinnamyl alcohol remaining in spleen were the highest among the main organs, including heart, liver, spleen, lung, kidney and brain. In addition, there was no long‐term accumulation of CA in rat tissues. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
92.
Journal of Sol-Gel Science and Technology - A novel gas sensing material, La–Y co-doped TiO2 nanoparticles, was synthesized by sol–gel method and applied to detect organic pollutants...  相似文献   
93.
Redox-based post-translational modification of protein thiols has become an attractive strategy in cellular homeostasis and cell signaling.Due to the reductive end of the redox buffer network,the vicinal dithiol-containing proteins(VDPs)maintains an appropriate oxidation-reduction state of proteins through the reversible transformation from vicinal dithiols to disulfide,which is responsible for a variety of  相似文献   
94.
95.
96.
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation.  相似文献   
97.
98.
Xu  Jiuping  Tang  Weiyao  Zhang  Yi  Wang  Fengjuan 《Nonlinear dynamics》2020,99(2):1269-1293
Nonlinear Dynamics - With an increasing number of people sharing feelings and opinions online, the online platforms have become one of the most important channels for public opinion dissemination....  相似文献   
99.
Novel pyrene‐fused unsymmetrical phthalocyanine derivatives 2,3,9,10,16,17‐hexakis(2,6‐dimethylphenoxy)‐22,25‐diaza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc complex Zn[Pc(Pz‐pyrene)(OC8H9)6] ( 1 ) and 2,3,9,10‐tra(2,6‐dimethylphenoxy)‐15,18,22,25‐traza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc compound Zn[Pc(Pz‐pyrene)2(OC8H9)4] ( 2 ) were isolated for the first time. These unsymmetrical pyrene‐fused phthalocyanine derivatives have been characterized by a wide range of spectroscopic and electrochemical methods. In particular, the pyrene‐fused phthalocyanine structure was unambiguously revealed on the basis of single crystal X‐ray diffraction analysis of 1 , representing the first structurally characterized phthalocyanine derivative fused with an aromatic moiety larger than benzene.  相似文献   
100.
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