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   216篇
  免费   1篇
化学   189篇
数学   1篇
物理学   27篇
  2023年   2篇
  2020年   1篇
  2018年   2篇
  2017年   4篇
  2016年   5篇
  2015年   3篇
  2014年   3篇
  2013年   5篇
  2012年   4篇
  2011年   7篇
  2010年   1篇
  2009年   6篇
  2008年   4篇
  2007年   7篇
  2006年   8篇
  2005年   4篇
  2004年   5篇
  2003年   1篇
  2002年   5篇
  2001年   7篇
  2000年   6篇
  1999年   5篇
  1998年   3篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1994年   5篇
  1993年   6篇
  1992年   7篇
  1991年   9篇
  1990年   9篇
  1989年   6篇
  1988年   5篇
  1987年   2篇
  1986年   7篇
  1985年   6篇
  1984年   6篇
  1983年   4篇
  1982年   7篇
  1981年   4篇
  1980年   1篇
  1979年   3篇
  1978年   3篇
  1976年   4篇
  1975年   5篇
  1974年   3篇
  1973年   3篇
  1969年   2篇
  1967年   1篇
  1966年   1篇
排序方式: 共有217条查询结果,搜索用时 15 毫秒
1.
Alkanesulfonic peracids RSO4H effectively oxidize olefins to the corresponding epoxides. The kinetics and mechanism of this reaction are studied. It was shown that both the monomer and dimer form of the peracid act as oxidizing agents. The dependence of the weight constant of the reaction of monomer RSO4H with substituted acyclic olefins on the structure of the latter is described by the Taft equation. A linear correlation is established between log k2 and the inductive constants of the substituents on the oxygen atom in the peracid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 333–337, February, 1991.  相似文献   
2.
The mechanisms of liquid-phase phenol ozonation are revised. A new mechanism in which a significant role is played by free-radical reactions is suggested for this process.  相似文献   
3.
4.
The macrocyclic title compound crystallizes as a dioxane solvate, C30H22Cl2N4O4·C4H8O2, with two independent formula units in the unit cell. The observed syn conformation is controlled by both intramolecular N—H...O hydrogen bonds and intermolecular C—H...π interactions. The relative macrocyclic inner bore is estimated to be 4.19 Å. In the crystal structure, molecules form dimers via intermolecular C—H...π interactions, and these dimers are, in turn, linked to form columns along the a axis by intermolecular C—H...O hydrogen bonds. Both X‐ray diffraction analysis and density functional theory (DFT) calculations reveal that the macrocycle possesses very high flexibility. This property, as well as the presence of six donor atoms accessible for coordination, makes the title macrocycle a very promising ligand for complexation with the majority of transition metals.  相似文献   
5.
Data were obtained on the composition of products and kinetics of the reaction of SO2 with Ph(R)CN2 (R=Ph, Me) in solutions of isooctane, 1,4-di-oxane, and ethanol at 295 K. A mechanism was proposed for the process in accordance with which the sulfene being formed participates in concurrent reactions with the starting reagents. The relative rate constants for the process stages were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2496–2500, November, 1990.  相似文献   
6.
Thermolysis of di-(tert-butyl)-trioxide produces IR and visible chemiluminescence (CL) which may be ascribed to emission by singlet oxygen (IR-CL) and triplet acetone (vis. CL).  相似文献   
7.
By the peptide map method, a phosphorylated peptide has been isolated from a tryptic hydrolysate of phosphorylated yeast inorganic pyrophosphatase (I), and this is a direct proof of the formation of a covalent bond between (I) and phosphate in the course of this reaction. The isolation and analysis of the peptide from the tryptic hydrolysate shows that the phosphate acceptor is probably the aspartic acid residue 240 or 248. Analysis of a tryptic hydrolysate of (I) modified with O-phosphoethanolamine has shown that O-phosphoethanolamine forms an amide bond with the carboxy group of the same aspartic acid residue. In an alkaline medium, the phosphate residue migrates to the imidazole ring of a histidine residue, apparently that present in position 222.  相似文献   
8.
Mannich bases exhibiting photo- and thermochromic properties in solutions were synthesized from 3,5-di-tert-butyl-4-hydroxybenzaldehyde and 2-naphthols. An investigation of an acetyl derivative of methylenequinone, modeling a product of photo- and thermochromic transformations, proved that the color change of solutions of the Mannich bases is due to reversible dissociation into colored methylenequinones and morpholine. On the basis of data of x-ray diffraction analysis of one of the Mannich bases, characteristics of their molecular structure were determined, and reasons were stated for their effect on the dissociation mechanism.  相似文献   
9.
The electronic spectroscopy of UO(2) has been examined using multiphoton ionization with mass-selected detection of the UO(2) (+) ions. Supersonic jet cooling was used to reduce the spectral congestion. Twenty-two vibronic bands of neutral UO(2) were observed in the range from 17,400 to 32,000 cm(-1). These bands originated from the U(5fphi(u)7ssigma(g))O(2) X (3)Phi(2u) and (3)Phi(3u) states. The stronger band systems are attributed to metal-centered 7p<--7s transitions. Threshold ionization measurements were used to determine the ionization potentials of UO and UO(2). These were found to be higher than the values obtained previously from electron impact measurements but in agreement with the results of recent theoretical calculations.  相似文献   
10.
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