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   1317893篇
  免费   39036篇
  国内免费   15330篇
化学   665713篇
晶体学   20572篇
力学   76260篇
综合类   554篇
数学   242454篇
物理学   366706篇
  2021年   15032篇
  2020年   17999篇
  2019年   19070篇
  2018年   12222篇
  2016年   29598篇
  2015年   23410篇
  2014年   33762篇
  2013年   78531篇
  2012年   38735篇
  2011年   32707篇
  2010年   38411篇
  2009年   41529篇
  2008年   32688篇
  2007年   26490篇
  2006年   34780篇
  2005年   25649篇
  2004年   27688篇
  2003年   26716篇
  2002年   28767篇
  2001年   25856篇
  2000年   23662篇
  1999年   22184篇
  1998年   21095篇
  1997年   21094篇
  1996年   21329篇
  1995年   19397篇
  1994年   18800篇
  1993年   18234篇
  1992年   17677篇
  1991年   17989篇
  1990年   17222篇
  1989年   17259篇
  1988年   16780篇
  1987年   16816篇
  1986年   15677篇
  1985年   22145篇
  1984年   23500篇
  1983年   19769篇
  1982年   21508篇
  1981年   20764篇
  1980年   20086篇
  1979年   20095篇
  1978年   21509篇
  1977年   21058篇
  1976年   20717篇
  1975年   19381篇
  1974年   19011篇
  1973年   19492篇
  1972年   14017篇
  1967年   12270篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Russian Journal of General Chemistry - Hybrid liquid crystal systems with different ratios of the components have been prepared on the basis of 5,5′-di(heptadecyl)-2,2′-bipyridine...  相似文献   
22.
23.
24.
The European Physical Journal Special Topics - The removal of suspended particles from the interior of a thermocapillary liquid bridge via a finite-particle-size effect restricting the particle...  相似文献   
25.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
26.
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   
27.
28.
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   
29.
30.
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   
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