全文获取类型
收费全文 | 932篇 |
免费 | 21篇 |
国内免费 | 4篇 |
专业分类
化学 | 442篇 |
晶体学 | 3篇 |
力学 | 31篇 |
数学 | 214篇 |
物理学 | 267篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 19篇 |
2013年 | 29篇 |
2012年 | 35篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 42篇 |
2007年 | 49篇 |
2006年 | 39篇 |
2005年 | 41篇 |
2004年 | 43篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 23篇 |
1995年 | 10篇 |
1994年 | 22篇 |
1993年 | 26篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1988年 | 10篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 16篇 |
1973年 | 8篇 |
排序方式: 共有957条查询结果,搜索用时 15 毫秒
31.
Infrared (4000-50 cm?1) and Raman spectra are reported of methylamine, methylamine-d1 and methylamine-d2 trapped in argon and nitrogen matrices at 4–20 K. An anomalous intensity variation was found for the NH2 wagging mode of methylamine isolated in nitrogen matrices, while in argon matrices the NH2 wagging absorption exhibited a complex structure due to matrix site effects. A normal coordinate analysis was carried out using a new assignment of the NHD twisting frequency. Barriers to internal rotation in argon and nitrogen matrices, calculated from the observed torsional frequencies, are compared with the gas phase value. 相似文献
32.
J.C. Hardy G.C. Ball W.G. Davies J.S. Forster H. Schmeing E.T.H. Clifford 《Nuclear Physics A》1981,357(2):356-364
The Q-value for the 129Xe(3He, d)130Cs reaction is measured to be +5 ± 20 keV. By combining this result with the known neutron separation energy of 130Xe, we derive the total decay energy of 130Cs130Xe to beQEC = 2974 ± 20 keV. This value agrees well with two previous positron end-point measurements but disagrees with the corresponding value derived from the 1977 atomic mass evaluation. This has significance in testing the accuracy of the calculated ratio for 130Cs decay. The mass excess of 130Cs is derived to be ?86908 ± 14 keV. An excited state in 130Cs. was also identified at 121 ± 15 keV with J < 3 and positive parity. The Q-value for 136Xe(3He, d)137Cs was measured to be 1918 ± 12 keV. 相似文献
33.
Jonathan B. Ball Margaret G. Wong Benny Capuano Jacqueline M. Gulbis Maureen F. Mackay Paul F. Alewood 《Journal of heterocyclic chemistry》1990,27(2):279-286
The constrained dipeptide mimic 1 was synthesized from 2 in three steps with 65% overall yield. Analyses of the 1H nmr data of a number of 3-amino-2,5-dioxo-2,3,4,5-tetrahydro-1H-1-benzazepine derivatives led to the conclusion that these compounds adopt a similar conformation and that this ring system is rigid. X-ray crystallography was used to define the structure of 3 , and computer-aided energy minimization of 6 gave a preferred conformation similar to that observed in the crystal of 3 . 相似文献
34.
A Monte Carlo study has been made of commensurate-incommensurate behaviour for Lennard-Jones particles on a square commensurate lattice. For a fixed barrier height a pronounced minimum is found in plots of R, the mean distance of the particles from the nearest commensurate site, against ε*, where ε* is the depth of the potential well. The initial fall in R with increase in ε* is shown to be associated with the repulsive part of the inter-particle interaction. 相似文献
35.
36.
37.
Sulbaek Andersen MP Nielsen OJ Hurley MD Ball JC Wallington TJ Ellis DA Martin JW Mabury SA 《The journal of physical chemistry. A》2005,109(9):1849-1856
Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C(4)F(9)CH(2)CH(2)OH, 4:2 FTOH) in the presence of NO(x) in 700 Torr of N(2)/O(2) diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C(4)F(9)CH(2)CH(2)OH to give C(4)F(9)CH(2)C(*)HOH radicals which add O(2) to give chemically activated alpha-hydroxyperoxy radicals, [C(4)F(9)CH(2)C(OO(*))HOH]*. In 700 Torr of N(2)/O(2) at 296 K, approximately 50% of the [C(4)F(9)CH(2)C(OO(*))HOH]* radicals decompose "promptly" to give HO(2) radicals and C(4)F(9)CH(2)CHO, the remaining [C(4)F(9)CH(2)C(OO(*))HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C(4)F(9)CH(2)C(OO(*))HOH. Decomposition to HO(2) and C(4)F(9)CH(2)CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C(4)F(9)CH(2)C(O(*))HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C(4)F(9)CH(2)(*). The primary products of 4:2 FTOH oxidation in the presence of excess NO(x) are C(4)F(9)CH(2)CHO, C(4)F(9)CHO, and HCOOH. Secondary products include C(4)F(9)CH(2)C(O)O(2)NO(2), C(4)F(9)C(O)O(2)NO(2), and COF(2). In contrast to experiments conducted in the absence of NO(x), there was no evidence (<2% yield) for the formation of the perfluorinated acid C(4)F(9)C(O)OH. The results are discussed with regard to the atmospheric chemistry of fluorotelomer alcohols. 相似文献
38.
39.
Polyphosphates are important but neglected polyelectrolytes that play a major role in biology and in surface science for the stabilization of colloids against flocculation and for the preservation of food. They are also known as “Calgon” ® and intensively used as additives in washing powders. This review aims to review recent developments in which linear polyphosphates are used for the design of new functional coatings using sol–gel processes and layer-by-layer deposition methods. All these methods rely on the high charge density of polyphosphates as inorganic polyelectrolytes, therefore the structure and properties of these molecules are also reviewed. New perspectives will also been given for the design of stimuli responsive coatings at the tiny frontier between biology and materials science. 相似文献
40.