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   829篇
  免费   80篇
  国内免费   79篇
化学   831篇
晶体学   7篇
力学   10篇
综合类   11篇
数学   52篇
物理学   77篇
  2024年   1篇
  2023年   8篇
  2022年   17篇
  2021年   28篇
  2020年   30篇
  2019年   28篇
  2018年   18篇
  2017年   22篇
  2016年   40篇
  2015年   29篇
  2014年   42篇
  2013年   94篇
  2012年   66篇
  2011年   43篇
  2010年   42篇
  2009年   33篇
  2008年   50篇
  2007年   38篇
  2006年   43篇
  2005年   34篇
  2004年   34篇
  2003年   27篇
  2002年   41篇
  2001年   25篇
  2000年   17篇
  1999年   24篇
  1998年   17篇
  1997年   17篇
  1996年   15篇
  1995年   11篇
  1994年   8篇
  1993年   12篇
  1992年   9篇
  1991年   5篇
  1990年   1篇
  1989年   6篇
  1988年   2篇
  1987年   3篇
  1986年   1篇
  1984年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1970年   1篇
  1966年   1篇
排序方式: 共有988条查询结果,搜索用时 15 毫秒
161.
162.
The solid‐state properties of some polycation/azo dye complexes according to the dye structure were studied in this work. One polycation contained about 95 mol % N,N‐dimethyl‐2‐hydroxypropyleneammonium chloride units in the backbone (PCA5), and eight azo dyes, different in either the number of sulfonic groups or their distribution, were used as opposite components. The selected azo dyes were as Crystal Scarlet, Congo Red, Crocein Scarlet MOO, Ponceau SS, Amaranth, Ponceau S, Direct Blue 1, and Direct Red 80. Information on the compensation degree of the oppositely charges was obtained by the elemental analysis of the solid‐state polycation/dye complexes (the experimental contents of chlorine, nitrogen, and sulfur were compared with the calculated values). Differential scanning calorimetry was employed to probe the strength of the intermolecular interactions in the PCA5/dye complexes. Wide‐angle X‐ray diffraction was used to assess the supramolecular order of the solid‐state complexes. The physical properties of the PCA5/azo dye complexes (the complex stoichiometry, glass‐transition temperature, decomposition temperature, and degree of supramolecular order) were influenced mainly by the dye structure but also by the polycation concentration and the presence of NaCl. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 264–272, 2003  相似文献   
163.
王勇竞  郭转运 《光学学报》1994,14(9):005-1008
首次报道了掺偶氮染料液晶盘中相位共轭输出的现象.测量了它的响应时间、衍射效率和阈值功率.讨论了该器件的分辨率.实验表明:它具有ms级的响应时间和mW级的阈值功率,是一种有前途的新型相位共轭器件.  相似文献   
164.
Carbohydrate-protein linkage region of proteoglycans is a key oligosaccharide structure because their sulphated and/or phosphorylated analogues control the biosynthesis of glucosaminoglycans or galactosaminoglycans. Therefore, synthesised sulphated and/or phosphorylated analogues were characterised by tandem mass spectrometry in the negative-ion mode. Results demonstrated that the product ion profile was characterised by glycosidic and cross-ring cleavages depending on the position and the type of the charged group (sulphate, phosphate or carboxylate). When the above compounds were sulphated and phosphorylated, the ion found at m/z 79 was the only one that demonstrated a phosphate group on the structure. The data also suggested that when a sodium cation was present in a sulphated and phosphorylated structure, the phosphate group in most cases was neutralised by the sodium cation, and therefore cleaved off the molecule, while the sulphate group was carrying the negative charge.  相似文献   
165.
166.
Sulfonyl chlorination of sulfonate-containing naphthol azo compounds   总被引:1,自引:0,他引:1  
Chlorosulfonyl-containing naphthol azo compounds were prepared by reaction of the corresponding sulfonate-containing naphthol azo dyes with thionyl chloride in the presence of a catalytic quantity of N,N-dimethylformamide and various solvents. The yields and reaction selectivity of chlorosulfonyl-containing naphthol azo compounds were discussed according to the properties of solvents. It was demonstrated that high chemical selectivity and high yield were achieved by using benzene, toluene or thionyl chloride as solvent. Additionally, on account of unstable properties of sulfonyl chloride compounds in MS and 1H-NMR analyses, a new analytical method using stable sulfonamide is put forward to verify the chemical structures of the corresponding sulfonyl chloride compounds indirectly. __________ Translated from Journal of Dalian University of Technology, 2008, 48(1): 26–32  相似文献   
167.
The synthesis, structure, and dynamic behavior of bistable C- and N-bound isomers of transition-metal cyanocarbanions are described. A series of C-bound cyclopentadienyl (Cp) ruthenium phosphane complexes, [Ru{CH(CN)SO2Ph}(Cp)L1L2] (3), and their N-bound isomers, [Ru+(Cp)(NCCH(-)SO2Ph)L1L2] (4), were prepared by treating [RuCl(Cp)(PR3)2] with the sodium salt of phenylsulfonylacetonitrile and performing ligand-exchange reactions with the resulting compounds. Structural characterization by X-ray diffraction indicates that the cyanocarbanion moiety of 3 has an alpha-metalated structure, whereas that of 4 has a zwitterionic, end-on structure. Heating these complexes in aprotic solvents gives rise to irreversible linkage isomerization between C- and N-bound isomers, in which the relative thermal stabilities vary greatly depending on the steric and electronic nature of the ligands. Mechanistic studies of N-to-C isomerization revealed that the reaction proceeds irreversibly in a unimolecular manner without the formation of coordinatively unsaturated species. A metal-sliding process, which occurs over the -C-C triple chemical bond N pi-conjugated surface of the cyanocarbanion moiety, was suggested by results from kinetic studies and density functional theory (DFT) calculations. C-to-N isomerizations proceed by the above-mentioned intramolecular process, with a temperature-dependent contribution from the formation and cleavage of mu2-C,N coordination dimers [{Ru{CH(CN)SO2Ph}(Cp)(PPh3)}2] (15 and 16).  相似文献   
168.
The investigation of the critical synthesis parameters of germanosilicate of UTL topology, possessing 14- and 12-rings, has been carried out in detail. (6R,10S)-6,10-Dimethyl-5-azoniaspiro[4.5]decane hydroxide was used as the structure-directing agent (SDA). The kinetics of the synthesis, the role of the Si/Ge ratio in the synthesis mixture, and the effect of the calcination procedure were investigated in relation to the crystallinity and textural properties of the synthesized material. The optimum synthesis time was found to be six days for Si/Ge and (Si+Ge)/SDA molar ratios of 2 and 1.7, respectively. The UTL zeolite crystallizes as small sheets of 10 mum in size. The micropore volume of the best crystals is 0.22 cm(3) g(-1) with a micropore diameter of 1.05 nm, based on DFT and Saito-Foley analyses of adsorption data.  相似文献   
169.
The paper describes the effect of molecular mass and copolymer composition on thermal behaviour of homopolymers and copolymers of glycidyl methacrylate and methyl methacrylate. The polymerisation was done by using group transfer polymerization (GTP) and free radical techniques. A multistep decomposition was observed in polymers prepared by free radical technique indicating the presence of weak linkages in the backbone. Copolymers prepared by GTP had fewer weak sites and degraded in single step by a random chain scission.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   
170.
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