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   514篇
  免费   1篇
  国内免费   2篇
化学   401篇
晶体学   1篇
力学   21篇
数学   40篇
物理学   54篇
  2020年   12篇
  2019年   6篇
  2016年   12篇
  2015年   6篇
  2014年   5篇
  2013年   10篇
  2012年   13篇
  2011年   21篇
  2010年   13篇
  2009年   10篇
  2008年   9篇
  2007年   14篇
  2006年   10篇
  2005年   8篇
  2004年   12篇
  2003年   13篇
  2002年   11篇
  2001年   5篇
  2000年   8篇
  1999年   7篇
  1998年   12篇
  1997年   10篇
  1996年   9篇
  1995年   16篇
  1994年   13篇
  1993年   8篇
  1992年   9篇
  1991年   11篇
  1990年   6篇
  1989年   6篇
  1988年   10篇
  1987年   5篇
  1986年   7篇
  1985年   10篇
  1984年   8篇
  1983年   11篇
  1982年   5篇
  1981年   5篇
  1980年   9篇
  1978年   11篇
  1976年   4篇
  1975年   5篇
  1974年   9篇
  1964年   4篇
  1955年   4篇
  1912年   4篇
  1905年   4篇
  1903年   5篇
  1902年   5篇
  1900年   5篇
排序方式: 共有517条查询结果,搜索用时 0 毫秒
1.
Contributions to the Chemistry of Transition Metal Alkyl Compounds. XIV. Investigations on Benzyl Tungsten Compounds. – On the Formation and Characterization of Tetrabenzyl Tungsten Unstable benzyl tungsten pentachloride is formed from tribenzyl boron and tungsten hexachloride. Other benzylating agents yield only less defined reduction products. – Reacting WCl4 · 2 THF with dibenzyl magnesium W(CH2C6H5)4 can be obtained. The new compound is stable at room temperature and is thoroughly characterized.  相似文献   
2.
Dimethyl zinc reacts with diethyl amine, piperidine and morpholine forming definite 1:2- or 1:1-complexes. The weaker basic secondary amines pyrroline, pyrazolidine and imidazoline cause the evolution of methane and the formation of the corresponding zinc amides. In this way zinc pyrrolide, zinc pyrazolide and zinc imidazolide were obtained in form of pure substances.  相似文献   
3.
On Pentaiodoplatinates(II, IV) M2PtI5 · 2 H2O (M ? K, Rb, NH4). Mixed-valence Compounds with Linear Chain Iodobridged Anions Pentaiodoplatinates M2PtI5 · 2 H2O (M ? K, Rb, NH4) are obtainable by crystallization from aqueous solutions formed by dissolving of tetrachloroplatinates(II) in highly concentrated solutions of alkali iodides MI. The structural parameters were determinated from single crystal data. The compounds are classed with the group of linear chain mixed-valence platinum complexes from Wolffram's Salt type. In the crystal structures PtI4-units are connected by asymnetric I-bridges to [PtI4I2/2] chains. There was no evidence of the existence of crystalline tetraiodoplatinates(II) M2PtI4.  相似文献   
4.
On Potassium Dihalogenomonocyanomercurates(II) KHgX2CN · H2O (X = Cl, Br) Hydrates of the dihalogenomonocyanomercurates KHgX2CN · H2O (X = Cl, Br) are obtained by reactions of equimoleculare amounts of HgX2 and KCN in aqeuous solutions. The crystal structure of the rhombic KHgBr2CN · H2O (a = 454.2 pm; b = 1738.1 pm; c = 465.1 pm; Pmmm; Z = 2) contains linear HgBr2 and Hg(CN)2 groups and isolated Br? and K+ ions. Therefore the compound can be formulated as a double salt Hg(CN)2 · HgBr2 · 2 KBr · 2 H2O. The chloro compound is isotype.  相似文献   
5.
Preparation and Crystal Structure of Bis(heptaquocalcium)-decachlorodithallat(III) [Ca(OH2)7]2Tl2Cl10 Colourless, hygroscopic crystals of the compound CaTlCl5 · 7H2O were obtained by crystallization from aqueous solutions of CaCl2 and TlCl3. The crystal structure consists of [Ca(OH2)7]2+ cations and [Tl2Cl10]4?anions.  相似文献   
6.
 Analysis of high-resolution NMR spectra elucidation has been known for many years. Hard-and software development now permits the implementation of such programs on personal computers. The structural information hidden in complex proton NMR spectra becomes easily accessible by using graphical user interfaces and direct data exchange between programs. A new mode has been implemented in 1D WIN-NMR to support the analysis of multiplet patterns with first order rules. Structure display, direct export mechanisms to the simulation program WIN-DAISY, and an archiving possibility complete the state-of-the-art data analysis. Some practical examples are given. Received: 25 October 1996/Revised: 6 March 1997/Accepted: 10 March 1997  相似文献   
7.
    
Zusammenfassung Phosphatide lassen sich auf Kieselgel G mit Diisobutylketon-Ameisensäure-Wasser (40152) dünnschichtchromatographisch trennen. Auch im mikropräparativen Maßstab gelingt eine solche Trennung, wobei das von der Chromatographieplatte abgekratzte Material mit geeigneten Lösungsmitteln extrahiert wird. Die so getrennten Phosphatide werden alkalisch hydrolysiert. Die aus dem Hydrolysat erhaltenen Fettsäuren können gaschromatographisch, die Amine dünnschichtchromatographisch auf Kieselgel G und die Phosphatester auf Celluloseplatten analysiert werden.
Summary Phosphatides can be separated by thin-layer chromatography using silica gel G as adsorbent and diisobutyl ketone-formic acid-water (40152) as solvent. The separation in a micro preparative scale is carried out in the same way. The material scraped off the thin-layer plate is extracted with a suitable solvent. After alkahne hydrolysis of the pure phosphatides separated in this manner the fatty acids are analyzed by gas chromatography, the amines by thin-layer chromatography on silica gel G plates, and the phosphate esters on cellulose plates.
  相似文献   
8.
Contributions to the Chemistry of Transition Metal Alkyl Compounds. XLIII. Tetrakis(alkoxycarbonylmethyl)titanium Compounds Organotitanium(IV) compounds of the type (ROCOCH2)4Ti (R ? C2H5, i-C3H7, t-C4H9, C6H5, C6H5CH2) were obtained by reactions of ROCOCH2Li derivatives with TiCl4 at low temperature. The compounds which decompose only above 90°C were characterized by the hydrolysis products, anaerobic reactions with iodine, and the i.r. spectra. The bond conditions are discussed.  相似文献   
9.
We construct the exact exchange-correlation potential of time-dependent density-functional theory and the approximation to it that is adiabatic but exact otherwise. For the strong-field double ionization of the Helium atom these two potentials are virtually identical. Thus, memory effects play a negligible role in this paradigm process of nonlinear, nonperturbative electron dynamics. We identify the regime of high-frequency excitations where the adiabatic approximation breaks down and explicitly calculate the nonadiabatic contribution to the exchange-correlation potential.  相似文献   
10.
Colloid and Polymer Science -  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