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   275191篇
  免费   7109篇
  国内免费   3678篇
化学   134128篇
晶体学   4141篇
力学   14737篇
综合类   139篇
数学   40925篇
物理学   91908篇
  2022年   1957篇
  2021年   2346篇
  2020年   2566篇
  2019年   2616篇
  2018年   11593篇
  2017年   12343篇
  2016年   8156篇
  2015年   3919篇
  2014年   4410篇
  2013年   8531篇
  2012年   11936篇
  2011年   21237篇
  2010年   13156篇
  2009年   13144篇
  2008年   18158篇
  2007年   21345篇
  2006年   7158篇
  2005年   12979篇
  2004年   8878篇
  2003年   8287篇
  2002年   6180篇
  2001年   6271篇
  2000年   4744篇
  1999年   3696篇
  1998年   2663篇
  1997年   2714篇
  1996年   2733篇
  1995年   2446篇
  1994年   2340篇
  1993年   2083篇
  1992年   2555篇
  1991年   2591篇
  1990年   2408篇
  1989年   2327篇
  1988年   2259篇
  1987年   2251篇
  1986年   2093篇
  1985年   2537篇
  1984年   2530篇
  1983年   2041篇
  1982年   2029篇
  1981年   1866篇
  1980年   1837篇
  1979年   2140篇
  1978年   2221篇
  1977年   2080篇
  1976年   2042篇
  1975年   1913篇
  1974年   1895篇
  1973年   1969篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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   
2.
3.
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   
4.
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   
5.
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   
6.
7.
8.
9.
10.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  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