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   170507篇
  免费   32149篇
  国内免费   17568篇
化学   130540篇
晶体学   2030篇
力学   9915篇
综合类   1063篇
数学   18508篇
物理学   58168篇
  2024年   456篇
  2023年   2726篇
  2022年   4864篇
  2021年   5268篇
  2020年   6446篇
  2019年   7445篇
  2018年   5540篇
  2017年   5181篇
  2016年   9560篇
  2015年   9643篇
  2014年   11075篇
  2013年   13942篇
  2012年   15185篇
  2011年   14806篇
  2010年   11371篇
  2009年   11152篇
  2008年   11240篇
  2007年   9810篇
  2006年   8919篇
  2005年   7841篇
  2004年   6124篇
  2003年   5109篇
  2002年   5704篇
  2001年   4456篇
  2000年   3856篇
  1999年   3184篇
  1998年   2391篇
  1997年   2197篇
  1996年   2282篇
  1995年   1851篇
  1994年   1774篇
  1993年   1428篇
  1992年   1304篇
  1991年   1170篇
  1990年   974篇
  1989年   673篇
  1988年   571篇
  1987年   456篇
  1986年   459篇
  1985年   376篇
  1984年   276篇
  1983年   188篇
  1982年   155篇
  1981年   120篇
  1980年   85篇
  1979年   64篇
  1978年   40篇
  1976年   41篇
  1975年   39篇
  1974年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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   
44.
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   
45.
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   
46.
47.
汪已琳  任哲  赵志然  张威 《人工晶体学报》2018,47(12):2659-2662
本文对减压扩散机理及高阻密栅技术作了详细的分析,并就设备及工艺方面的关键技术进行了阐述,最后对减压扩散高方阻工艺及密栅匹配技术电池效率进行了对比分析,有以下结论:(1)减压扩散在工艺优化后,方阻均匀性得到大幅改善,达到3;以内.(2)减压扩散电池效率完全可达到常规产线的水平,且在高阻密栅方面更有优势,可有效提升太阳电池效率.  相似文献   
48.
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   
49.
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   
50.
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