全文获取类型
收费全文 | 241篇 |
免费 | 2篇 |
专业分类
化学 | 193篇 |
晶体学 | 1篇 |
数学 | 10篇 |
物理学 | 39篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 8篇 |
2013年 | 28篇 |
2012年 | 15篇 |
2011年 | 7篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 3篇 |
1998年 | 3篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 46 毫秒
111.
112.
Linear polyamides having viscosities in the range of 0.12–0.41 dl/g have been prepared from bisbenzoyl propionic acids and aromatic diamines by low temperature solution polycondensation in 80–85% yield. Their solubility characteristics were studied in various solvents e.g. DMF, DMAC, HMPT, H2SO4. These polyamides are amorphous in nature; their densities range from 1.2 to 1.8 g/cm3. Their thermal properties were examined by TGA and DTA. The two stage decomposition phenomenon observed in TGA is in agreement with the DTA results. The integral procedural decomposition temperatures were calculated and found to exceed 250 in almost all cases. 相似文献
113.
Precise densities for sodium of chloride, bromide and iodide and potassium iodide in ethanolamine and water+ethanolamine mixtures
(15, 30, 50, 60, 70, 80 and 90 mass% ethanolamine) up to a maximum salt molality of 0.15 mol-kg−1 are reported from measurements at 25°C using a vibrating tube densimeter. The electrolyte apparent molar volumes were calculated
and extrapolated to infinite dilution using the Masson equation to yield the limiting electrolyte partial molar volumes. The
limiting ionic partial molar volumes V
ion
o
were estimated using Mukerjee's method. A correspondence principle proposed earlier for predicting ionic entropies could
be used for the estimation of V
ion
o
for rubidium and cesium salts. The estimates of the contributions from geometric and the electrostrictive effects to V
ion
o
are also reported. The variations in these contributions with the change in solvent composition are discussed in terms of
the changes in the solvent structure. 相似文献
114.
Subasini Lenka Padma L. Nayak Sanjay K. Nayak 《Journal of polymer science. Part A, Polymer chemistry》1987,25(2):703-709
Aqueous polymerization of methyl methacrylate in visible light was studied using isoquinoline–sulphur dioxide (IQ–SO2) charge–transfer complex as the photoinitiator. Analysis of kinetic and other data indicate that the polymerization proceed via a radical mechanism and the termination is dependent on the initiator concentration. Chain–termination via degradative chain (initiator) transfer appears to be predominant here. 相似文献
115.
Silicon tetrafluoride undergoes halogen exchange reactions with both phosphorus trichloride and phosphoryl chloride at temperatures of 500–600°C yielding mixed chlorofluorides of silicon and phosphorus. It is interesting to note that, at these high temperatures, PCl3 undergoes complete exchange to form PF3 while POCl3 reacts only with partial substitution, the major products being phosphorus chloride difluoride and silicon trichloride fluoride. 相似文献
116.
D.K. Padma V. Subrahmanya Bhat A.R. Vasudevamurthy 《Journal of fluorine chemistry》1978,11(2):187-190
It has been observed that a suspension of sodium fluoride in boiling acetonitrile could be used for the preparation of fluorine compounds such as silicon tetrafluoride [1], thiophosphoryl fluoride [2], sulphur tetrafluoride [3,4], and fluorocyclophosphazenes [5]. This method, when adopted for the fluorination of sulphuryl chloride [6], it is observed that a mixture of sulphuryl fluoride and sulphuryl chloro fluoride is obtained. On the other hand, when lead fluoride is substituted for sodium fluoride, pure sulphuryl chloro fluoride is evolved. Based on this observation, a new method has been standardised for the preparation of a pure sample of sulphuryl chlorofluoride by fluorinating sulphuryl chloride by lead fluoride in acetonitrile medium. 相似文献
117.
The reduction of a number of 4-piperidones by different methods afforded epimeric pairs of 4-piperidinols. Methods of formation, isomerization studies and the degree of adsorption on alumina indicate their conformation. The stereochemical course of the reductions is discussed. 相似文献
118.
Thiophosphoryl fluoride and phosphoryl fluoride have been found to initiate the polymerisation of tetrahydrofuran. The living polymer formed has a high molecular weight of the order of a million and the density is found to be between 0.98 - 1.02 g/cc. A cationic mechanism for the polymerisation has been proposed. 相似文献
119.
The kinetics of polymerization of acrylonitrile initiated by V5+-thiourea or V5+-ethylene thiourea have been studied at 30, 35 and 40°C in nitrogen. The rates of polymerization and V5+ disappearance, and the chain lengths of polymers were measured. The kinetics are consistent with the formation of an intermediate complex between the thiol form of thiourea or ethylene thiourea and the oxidant decomposition of which leads to the initiating radical. The effects of certain organic solvents (water miscible) and salts on the rate of polymerization have been studied. A kinetic scheme has been proposed and the various rate and energy parameters evaluated. 相似文献
120.
The Preparation of Sulphur Tetrafluoride from the Elements at low Temperature in an Inert Solvent Pure sulphurtetrafluoride cna be prepared by the fluorination of elemental sulphur in CCl3F at ?78°C in high yields. 相似文献