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   664232篇
  免费   9287篇
  国内免费   4066篇
化学   343296篇
晶体学   9438篇
力学   32257篇
综合类   148篇
数学   100543篇
物理学   191903篇
  2021年   5136篇
  2020年   5778篇
  2019年   6230篇
  2018年   17264篇
  2017年   17050篇
  2016年   17124篇
  2015年   8353篇
  2014年   11661篇
  2013年   27328篇
  2012年   24809篇
  2011年   35528篇
  2010年   23452篇
  2009年   23631篇
  2008年   29969篇
  2007年   31655篇
  2006年   22431篇
  2005年   21114篇
  2004年   19625篇
  2003年   17883篇
  2002年   16788篇
  2001年   17925篇
  2000年   13712篇
  1999年   10494篇
  1998年   8860篇
  1997年   8580篇
  1996年   8447篇
  1995年   7479篇
  1994年   7409篇
  1993年   7191篇
  1992年   7871篇
  1991年   7950篇
  1990年   7591篇
  1989年   7361篇
  1988年   7258篇
  1987年   7128篇
  1986年   6840篇
  1985年   8965篇
  1984年   9087篇
  1983年   7377篇
  1982年   7609篇
  1981年   7404篇
  1980年   6856篇
  1979年   7377篇
  1978年   7701篇
  1977年   7613篇
  1976年   7540篇
  1975年   6998篇
  1974年   7075篇
  1973年   7061篇
  1972年   5178篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
6.
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   
7.
8.
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   
9.
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   
10.
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   
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