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   1076篇
  免费   31篇
  国内免费   2篇
化学   613篇
晶体学   8篇
力学   39篇
数学   122篇
物理学   327篇
  2022年   13篇
  2021年   19篇
  2020年   21篇
  2019年   21篇
  2018年   19篇
  2017年   23篇
  2016年   25篇
  2015年   31篇
  2014年   39篇
  2013年   115篇
  2012年   46篇
  2011年   55篇
  2010年   43篇
  2009年   41篇
  2008年   41篇
  2007年   43篇
  2006年   25篇
  2005年   30篇
  2004年   32篇
  2003年   24篇
  2002年   21篇
  2001年   15篇
  2000年   14篇
  1999年   15篇
  1998年   12篇
  1997年   6篇
  1996年   11篇
  1995年   10篇
  1994年   9篇
  1993年   9篇
  1992年   16篇
  1991年   6篇
  1990年   9篇
  1989年   7篇
  1988年   9篇
  1987年   13篇
  1986年   12篇
  1985年   17篇
  1984年   21篇
  1983年   13篇
  1982年   11篇
  1981年   16篇
  1980年   26篇
  1979年   13篇
  1978年   19篇
  1977年   17篇
  1976年   6篇
  1975年   6篇
  1973年   7篇
  1972年   7篇
排序方式: 共有1109条查询结果,搜索用时 500 毫秒
91.
The synthesis of a unique tetrasaccharide linked to the serine 61 of human clotting factor IX through an α-l-fucose residue has been achieved for the first time in excellent yield. All glycosylation and protecting group manipulation steps are high yielding and reproducible for a scale-up preparation. A sequential glycosylation strategy has been used to assemble suitably protected monosaccharide synthons for the preparation of the target tetrasaccharide.  相似文献   
92.
93.
The higher order contributions to Jacobian in Fujikawa’s path integral framework is considered and the form of anomaly equation in higher orders is established. An argument for the Adler-Bardeen theorem in this formulation is given.  相似文献   
94.
95.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most frequently prescribed drugs and have multiple therapeutic uses. These drugs are predominantly used for the treatment of musculoskeletal diseases because of their analgesic, antipyretic, and antiplatelet activities. Oxicams constitute an interesting class of organic compounds and have been investigated in the search for new analgesic and anti-inflammatory drugs. In the present work, a theoretical investigation of the molecular structure and spectroscopic properties of a series of five oxicams in different solvents was performed using density functional theory (DFT) methods. The geometric optimizations of the oxicams were carried out using the M06 density functional and the CBSB7 basis set. The infrared data were all obtained at the same theoretical level. The UV-Vis absorption and NMR data of some oxicams were calculated using the DFT and CBSB3 basis sets. The analysis of structural parameters, particularly the bond length and spectroscopic data, indicated that interactions occurred between the hydrogen bond types for 4-meloxicam, isoxicam, and normeloxicam. Stereoelectronic interactions caused by the substitution of alkyl groups caused the bond lengths to elongate. Similarly, the substitution of heteroatoms, such as nitrogen, sulfur, or oxygen, increased the bond lengths and angular stresses.  相似文献   
96.
Metal complexes of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) are being used as a chiral catalysts in many organic reactions. This review highlights recent developments on synthesis of metal BINAPs and its application in various organic synthesis. The studies done on the application of metal BINAPs show a unique reactivity, which enables its use in entirely different sets of chemical transformation.  相似文献   
97.
Temperature dependent molar conductances and fluidities of bisulfate and ethyl sulfate anion-based ionic liquids were measured. The extent of dissociation of the ionic liquids was estimated from the Walden plot in term of ionicity. The ionicity mainly depends on the magnitude of Coulombic forces, altered by the anion’s Lewis basicity. Aqueous solutions of aprotic ionic liquids, in general, possesses ionicity in the range of ≈70–99%. This article reveals that the substitution of the anion by bisulfate and ethylsulfate reduces the ionicity of aqueous solution of these ionic liquids to the range of 10–37%. This is very close to that exhibited by some of the protic ionic liquids and phosphonium based ionic liquids with sweetner anions. The concentration dependent molar conductance of these ionic liquids has been fitted to Mahiuddin and Ismail’s equation. To our surprise, the molar conductances of bisulfate-based aprotic ionic liquids are remarkably high, even though these ionic liquids possess lower ionicity.  相似文献   
98.
The present paper describes a new analytical method developed for direct determination of boron in steels using radio frequency glow discharge optical emission spectrometer. “Single parameter alternative method” technique has been used to optimize the various experimental conditions of glow discharge plasma such as forward power, gas pressure inside plasma chamber, pre-integration time, and integration time. Different emission lines for boron were studied and inter element interference effect is also discussed in the paper. A complete statistical analysis has been done to validate the developed method. A RSD of less than ±5% is achieved for boron in the range of 0.0010–0.020% in Steels using this method.  相似文献   
99.
A series of tungsten-tellurite glasses activated with different concentrations (0–1.5 mol %) of Er3+ has been synthesized. The structural properties of the best luminescent sample and the optical properties of its Er3+ ions, are studied both immediate after its preparation as well as after its ageing. On ageing the glass suffers structural reorganization and generates Er2WO6—nanocrystals in the matrix, which greatly enhances the normal and upconversion green luminescence efficiency of Er3+. The nanocrystal aided enhancement of normal and upconversion luminescence of Er3+ of the glass has been attributed to the crystal field effects of the new environment of Er3+ in the nanocrystals. A phenomenon of preferential enhancement of red upconversion luminescence at the cost of green upconversion luminescence of Er3+ at its higher concentrations in the glass has been observed and the related photo-physics is proposed. The material shows the prospect of being used as NIR solar concentrator.  相似文献   
100.
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