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   1592篇
  免费   57篇
  国内免费   10篇
化学   1286篇
晶体学   21篇
力学   21篇
数学   83篇
物理学   248篇
  2021年   12篇
  2020年   18篇
  2019年   17篇
  2018年   12篇
  2017年   20篇
  2016年   39篇
  2015年   27篇
  2014年   42篇
  2013年   68篇
  2012年   77篇
  2011年   86篇
  2010年   44篇
  2009年   62篇
  2008年   88篇
  2007年   81篇
  2006年   93篇
  2005年   89篇
  2004年   90篇
  2003年   78篇
  2002年   66篇
  2001年   31篇
  2000年   31篇
  1999年   32篇
  1998年   16篇
  1997年   30篇
  1996年   14篇
  1995年   8篇
  1994年   16篇
  1993年   11篇
  1992年   17篇
  1991年   16篇
  1990年   15篇
  1989年   15篇
  1988年   23篇
  1987年   9篇
  1986年   8篇
  1985年   20篇
  1984年   27篇
  1983年   10篇
  1982年   18篇
  1981年   19篇
  1980年   7篇
  1979年   29篇
  1978年   19篇
  1977年   23篇
  1976年   21篇
  1975年   12篇
  1974年   10篇
  1973年   6篇
  1971年   8篇
排序方式: 共有1659条查询结果,搜索用时 15 毫秒
1.
A new matrix is proposed here which is based on rigid elements. The efficiency and usefulness of this method has been demonstrated for plane problems. The purpose of this paper is to formulate the method and to indicate its validity.  相似文献   
2.
19F NMR techniques were employed to characterize the binding property of the widely used general anesthetic halothane with human serum albumin (HSA). It was found that 19F(1H) NOE and 2D 1H-19F HOESY experiments detected intermolecular NOEs between halothane 19F and HSA protons. Measurements of the diffusion coefficients for halothane were also carried out by 1H and 19F NMR, indicating the interaction of halothane with HSA. The present results indicate that these techniques are very suitable to identify a fluorine-containing ligand binding with a protein receptor in the drug-discovery process.  相似文献   
3.
In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution.  相似文献   
4.
5.
A high-speed and economical optical local access network system is proposed where bi-directional polarization multiplexing is applied to a bi-directional transmission. Experimental results using a prototype system confirmlow optical loss and environmental stabilities.  相似文献   
6.
7.
The photochemical deprotection of alkyl 2,4-dinitrobenzenesulfenate or alkyl 2-nitrobenzenesulfenate was successfully achieved by addition of triethylamine, while it was unsuccessful without triethylamine. The sulfur-oxygen bond cleavage is thought to occur heterolytically in the sulfenate anion radical produced by photoinduced electron transfer with triethylamine.  相似文献   
8.
The first successful example of the formation of polycarbonate from 1-atm carbon dioxide and epoxide was demonstrated by the alternating copolymerization of carbon dioxide and epoxide with manganese porphyrin as a catalyst. The copolymerization of carbon dioxide and cyclohexene oxide with (porphinato)manganese acetate proceeded under the 1-atm pressure of carbon dioxide to give a copolymer with an alternating sequence. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3549–3555, 2003  相似文献   
9.
We discuss the problem of boundedness fromLp(Rn) toLp(Rn) (1/p+1/p′=1, 1?p?2) of operators of the typeM=F−1ei?(ξ)a(ξ) F, which is related to the study of hyperbolic equations with constant coefficients. The boundedness is dependent on a geometrical property ofΣ=?−1(1), and its dependence has been exactly determined in the casesn=2, 1?p?2 andn?3,p=1, 2 (M. Sugimoto,Math. Z.215(1994), 519–531;222(1996), 521–531). This paper is devoted to the unsolved case 1<p<2, and a strange phenomenon is exhibited in the simplest casen=3.  相似文献   
10.
A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities, thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed good agreements with classical antenna theory.  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