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   621篇
  免费   26篇
  国内免费   3篇
化学   439篇
晶体学   14篇
力学   14篇
数学   42篇
物理学   141篇
  2023年   6篇
  2022年   14篇
  2021年   16篇
  2020年   23篇
  2019年   22篇
  2018年   12篇
  2017年   18篇
  2016年   15篇
  2015年   28篇
  2014年   22篇
  2013年   59篇
  2012年   46篇
  2011年   45篇
  2010年   31篇
  2009年   24篇
  2008年   27篇
  2007年   32篇
  2006年   28篇
  2005年   22篇
  2004年   27篇
  2003年   12篇
  2002年   13篇
  2001年   7篇
  2000年   15篇
  1999年   2篇
  1998年   5篇
  1997年   7篇
  1996年   2篇
  1995年   4篇
  1994年   8篇
  1993年   5篇
  1992年   4篇
  1991年   4篇
  1990年   8篇
  1989年   4篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1983年   2篇
  1981年   2篇
  1980年   5篇
  1978年   1篇
  1977年   2篇
  1976年   3篇
  1973年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1959年   1篇
  1954年   1篇
排序方式: 共有650条查询结果,搜索用时 31 毫秒
101.
We examine the possibility to employ neutrinos to communicate within the galaxy. We discuss various issues associated with transmission and reception, and suggest that the resonant neutrino energy near 6.3 PeV may be most appropriate. In one scheme we propose to make ZoZo particles in an overtaking e+−ee+e collider such that the resulting decay neutrinos are near the WW resonance on electrons in the laboratory. Information is encoded via time structure of the beam. In another scheme we propose to use a 30 PeV pion accelerator to create neutrino or anti-neutrino beams. The latter encodes information via the beam CP state as well as timing. Moreover the latter beam requires far less power, and can be accomplished with presently foreseeable technology. Such signals from an advanced civilization, should they exist, will be eminently detectable in existing neutrino detectors.  相似文献   
102.
103.
A highly sensitive, rapid assay method has been developed and validated for the estimation of omeprazole (OPZ) in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The assay procedure involves alkalinization of plasma followed by simple liquid-liquid extraction of OPZ and lansoprazole (internal standard, IS) from human plasma with acetonitrile. Chromatographic separation was achieved with 0.01 M ammonium acetate:acetonitrile (40:60, v/v) at a flow rate of 0.25 mL/min on an Inertsil ODS 3 column with a total run time 2.5 min. The MS/MS ion transitions monitored were 346.1 --> 198.1 for OPZ and 370.1 --> 252.1 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.05 ng/mL and the linearity was observed from 0.05 to 10.0 ng/mL. The intra-day and inter-day precisions were in the ranges 2.09-8.56 and 5.29-8.19%, respectively. This novel method has been applied to a pharmacokinetic study of OPZ in humans.  相似文献   
104.
An unprecedented copper-catalyzed C-H addition of arenes to aryl acetylenes provides a facile route to 1,1-diaryl ethylenes in moderate to excellent yields. Arylboronic acids were likewise used along with aryl acetylenes in generating 1,1-diaryl ethylene.  相似文献   
105.
106.
Biosensing and drug delivery by polypyrrole   总被引:1,自引:0,他引:1  
Conducting polypyrrole is a biological compatible polymer matrix wherein number of drugs and enzymes can be incorporated by way of doping. The polypyrrole, which is obtained as freestanding film by electrochemical polymerization, has gained tremendous recognition as sophisticated electronic measuring device in the field of sensors and drug delivery. In drug delivery the reversing of the potential 100% of the drug can be released and is highly efficient as a biosensor in presence of an enzyme. In this review we discuss the applications of conducting polypyrrole as biosensor for some biomolecules and drug delivery systems.  相似文献   
107.
108.
This paper describes an improved liquid chromatographic (LC) method involving a prechromatographic derivatization step for the estimation of solasodine from berries of various Solanum species, market samples of Solanum xanthocarpum herb, extract, and its market formulations. Solasodine has heterocyclic nitrogen but has no conjugated double bonds in its structure. However, in all reported LC methods, detection was made in the ultraviolet range of 200-213 nm. In the present study, a prechromatographic derivatization of solasodine was done by forming an ion-pair complex of the heterocyclic nitrogen using the acidic dye methyl orange and acetate buffer of pH 4.7. Detection could be made in the visible range at 530 nm in this method. The method was validated and successfully applied to determine solasodine content in various plant samples and polyherbal formulations. The relative standard deviation was found to be 0.025% for system precision, and 0.8% for the linearity of the method, and the correlation coefficient was 0.999. Plant samples and market formulations were analyzed and found to contain solasodine in the range of 0.113-0.227% (w/w) on a fresh weight basis in berries; 0.3-1.278% (w/w) and 0.412% (w/w) on a dry weight basis in S. xanthocarpum herb powder and extract, respectively; and 0.245-0.525% (w/w) on dry weight basis in formulations containing S. xanthocarpum herb powder. No matrix interference was encountered. The method was found to be accurate, with a mean recovery of 100.5 +/- 0.83%. The method has good reproducibility and was found to be suitable for estimation of solasodine.  相似文献   
109.
Electroosmotic flow in a straight micro-channel of rectangular cross-section is computed numerically for several situations where the wall zeta-potential is not constant but has a specified spatial variation. The results of the computation are compared with an earlier published asymptotic theory based on the lubrication approximation: the assumption that any axial variations take place on a long length scale compared to a characteristic channel width. The computational results are found to be in excellent agreement with the theory even when the scale of axial variations is comparable to the channel width. In the opposite limit when the wavelength of fluctuations is much shorter than the channel width, the lubrication theory fails to describe the solution either qualitatively or quantitatively. In this short wave limit the solution is well described by Ajdari's theory for electroosmotic flow between infinite parallel plates (Ajdari, A., Phys. Rev. E 1996, 53, 4996-5005.) The infinitely thin electric double layer limit is assumed in the theory as well as in the simulation.  相似文献   
110.
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