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   435670篇
  免费   21489篇
  国内免费   11043篇
化学   235997篇
晶体学   6563篇
力学   22759篇
综合类   541篇
数学   50897篇
物理学   151445篇
  2022年   5970篇
  2021年   7023篇
  2020年   7574篇
  2019年   7918篇
  2018年   8776篇
  2017年   8741篇
  2016年   12562篇
  2015年   9078篇
  2014年   13055篇
  2013年   23745篇
  2012年   21797篇
  2011年   24603篇
  2010年   17524篇
  2009年   17132篇
  2008年   19807篇
  2007年   19175篇
  2006年   17651篇
  2005年   15047篇
  2004年   13218篇
  2003年   11374篇
  2002年   11073篇
  2001年   12401篇
  2000年   9489篇
  1999年   8059篇
  1998年   6852篇
  1997年   6539篇
  1996年   6393篇
  1995年   5398篇
  1994年   5317篇
  1993年   4890篇
  1992年   5187篇
  1991年   5311篇
  1990年   4911篇
  1989年   4592篇
  1988年   4262篇
  1987年   4295篇
  1986年   4066篇
  1985年   4960篇
  1984年   4938篇
  1983年   4041篇
  1982年   4121篇
  1981年   3822篇
  1980年   3737篇
  1979年   3969篇
  1978年   3951篇
  1977年   3945篇
  1976年   3919篇
  1975年   3716篇
  1974年   3660篇
  1973年   3681篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.  相似文献   
83.
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   
84.
85.
86.
87.
88.
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   
89.
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   
90.
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   
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