全文获取类型
收费全文 | 826篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
化学 | 711篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 67篇 |
物理学 | 82篇 |
出版年
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 22篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 51篇 |
2010年 | 24篇 |
2009年 | 28篇 |
2008年 | 48篇 |
2007年 | 40篇 |
2006年 | 41篇 |
2005年 | 39篇 |
2004年 | 24篇 |
2003年 | 28篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 3篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 18篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1978年 | 12篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有862条查询结果,搜索用时 15 毫秒
1.
Let R be a discrete nonsingular equivalence relation on a standard probability space , and let V be an ergodic strongly asymptotically central automorphism of R. We prove that every V-invariant cocycle with values in a Polish group G takes values in an abelian subgroup of G.
The hypotheses of this result are satisfied, for example, if A is a finite set, a closed, shift-invariant subset, V is the shift, μ a shift-invariant and ergodic probability measure on X, the two-sided tail-equivalence relation on X, a shift-invariant subrelation which is μ-nonsingular, and a shift-invariant cocycle. 相似文献
2.
3.
4.
R. P. Wallner 《General Relativity and Gravitation》1991,23(6):623-639
We investigate the energy-momentum and spin field equations of gravity theory on a Riemann-Cartan space-time (including metric and torsion,U
4-manifold). The structure of the rather complicated nonlinear differential equations of second order is made considerably easier to survey by decomposing curvature into its self and anti-self double dual parts. This leads to an obvious ansatz for the self double dual curvature, whereby the field equations are reduced to Einstein's equations with cosmological term. To solve the double dual ansatz, we choose proper variables adopted to its double duality, and perform a (3+1)-decomposition of exterior calculus. We examine these equations further on a Kerr background with cosmological constant for the Riemannian geometry. 相似文献
5.
6.
The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH2O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH2O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k1a = 5.0 × 1015 exp(‐308 kJ mol?1/RT) cm3 mol?1 s?1. The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M → H2 + CO + M, and the branching fraction β = k1a/(kA1a + k1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH2O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH2O molecules. At high initial CH2O mole fractions the reverse of reaction (6), CH2OH + HCO ? CH2O + CH2O becomes noticeable. The rate of the forward reaction was roughly measured to be k6 = 1.5 × 1013 cm3 mol?1 s?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004 相似文献
7.
8.
Andreas Wallner Margit Hölbling Judith Baumgartner Christoph Marschner 《Silicon Chemistry》2007,3(3-4):175-185
A number of cyclo-and bicyclosilanes have been prepared and structurally characterized by X-ray crystallography and Raman
spectroscopy. 1,1,4,4- and 1,1,3,3-tetrakis(trimethylsilyl)octamethylcyclohexasilanes were found to exhibit unusual twist- and twisted boat-conformations. The UV absorption properties of all compounds were studied and found to show absorption maxima red shifted
compared to the parent compound dodecamethylcyclohexasilane.
Dedicated to Prof. Mitsuo Kira on the occasion of his reception of the Wacker Silicon Award 2005 and in recongnition of his
numerous outstanding achievements in organosilicon chemistry. 相似文献
9.
10.