全文获取类型
收费全文 | 2684篇 |
免费 | 77篇 |
国内免费 | 15篇 |
专业分类
化学 | 1930篇 |
晶体学 | 10篇 |
力学 | 47篇 |
数学 | 380篇 |
物理学 | 409篇 |
出版年
2021年 | 15篇 |
2020年 | 25篇 |
2019年 | 29篇 |
2016年 | 52篇 |
2015年 | 50篇 |
2014年 | 46篇 |
2013年 | 100篇 |
2012年 | 131篇 |
2011年 | 158篇 |
2010年 | 80篇 |
2009年 | 74篇 |
2008年 | 159篇 |
2007年 | 120篇 |
2006年 | 126篇 |
2005年 | 113篇 |
2004年 | 92篇 |
2003年 | 85篇 |
2002年 | 95篇 |
2001年 | 43篇 |
2000年 | 40篇 |
1999年 | 51篇 |
1998年 | 35篇 |
1997年 | 41篇 |
1996年 | 40篇 |
1995年 | 34篇 |
1994年 | 33篇 |
1993年 | 38篇 |
1992年 | 32篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 41篇 |
1984年 | 50篇 |
1983年 | 28篇 |
1982年 | 40篇 |
1981年 | 35篇 |
1980年 | 58篇 |
1979年 | 41篇 |
1978年 | 46篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 33篇 |
1974年 | 19篇 |
1973年 | 28篇 |
1971年 | 20篇 |
1966年 | 18篇 |
1959年 | 15篇 |
排序方式: 共有2776条查询结果,搜索用时 15 毫秒
961.
962.
J. D. Petke Gerald M. Maggiora Lester L. Shipman† Ralph E. Christoffersen 《Photochemistry and photobiology》1980,32(5):661-667
Ab initio configuration interaction wavefunctions and energies are reported for 16 doublet states of the anion radical of ethyl bacteriopheophorbide a (Et-BPheo a-˙), and are employed in an analysis of the electronic absorption spectrum. The lowest excited doublet state D1 is predicted to lie 8601 cm-1 above the ground state D0; the D1← D0 transition is nearly forbidden, with a computed oscillator strength f= 0.002. The visible absorption spectrum is shown to consist of transitions to three 2(π, π*) states, D2, D3, and D4. The D4← D0 transition (y-polarized, f= 0.91) appears to account for observed intense absorption at 15 800 cm-1. The Soret band of Et-BPheo a-˙ is shown to consist of transitions to several 2(π,π*) states, D7-D15. Transitions of particularly high intensity include D7← D0 (y-polarized, f= 0.72), D10← D0 (y-polarized, f= 1.1), D12← D0 (xy-polarized, f= 0.86) and D15← D0 (y-polarized, f= 0.83). Spin density data and plots are used to describe and compare the general features of the unpaired spin distributions in D0 and D1, which are in reasonable agreement with other reported calculated values and available experimental data for D0. 相似文献
963.
A London approximation utilizing atomic valence state ionization potentials and static polarizabilities yields C6 results in good agreement with accurate values for a number of systems. Generally there is considerable improvement over the results obtained using the London approximation in conjunction with molecular parameters and reasons for this are discussed. 相似文献
964.
965.
966.
Gerald M. Lerner 《Nuclear Physics A》1973,205(2):385-397
An analysis of 65 MeV elastic proton scattering by 16,17,18O has been made in terms of a reformulated optical model. Matter distributions for 17O and 18O have been obtained relative to 16O. The results for the rms matter radii are R17?R16 = 0.04±0.03 fm and R18?R16 = 0.35± 0.07 fm. 相似文献
967.
968.
Linear response theory is developed for systems whose time dependence is described by a master equation. The fluctuation dissipation theorem expressing the linear response of the system in terms of fluctuation properties of the system in equilibrium is derived. The time-dependent Ising spin system in interaction with a heat bath, the Glauber model, is discussed as a particular case of the formalism.The work of one of the authors (D.B.) was supported in part by the National Science Foundation under Contract GP 10536.On leave of absence from the Institute of Physics, Belgrade, Yugoslavia. 相似文献
969.
Gerald Wilemski 《Journal of statistical physics》1976,14(2):153-169
Differential equations governing the time evolution of distribution functions for Brownian motion in the full phase space were first derived independently by Klein and Kramers. From these so-called Fokker-Planck equations one may derive the reduced differential equations in coordinate space known as Smoluchowski equations. Many such derivations have previously been reported, but these either involved unnecessary assumptions or approximations, or were performed incompletely. We employ an iterative reduction scheme, free of assumptions, and calculate formally exact corrections to the Smoluchowski equations for many-particle systems with and without hydrodynamic interaction, and for a single particle in an external field. In the absence of hydrodynamic interaction, the lowest order corrections have been expressed explicitly in terms of the coordinate space distribution function. An additional application of the method is made to the reduction of the stress tensor used in evaluating the intrinsic viscosity of particles in solution. Most of the present work is based on classical Brownian motion theory, but brief consideration is given in an appendix to some recent developments regarding non-Markovian equations for Brownian motion.Supported by the National Science Foundation. 相似文献
970.
Theoretical calculations of the phonon infrared and Raman response in simple superionic conductors such as AgI, CuI, and CaF2 types are based on two fundamental assumptions. First, most of the response can be understood in terms of a breakdown of the selection rules due to disorder (lack of translational symmetry) and second, harmonic lattice dynamics can be used with a good degree of accuracy. This is tested here experimentally in the superionic conductor K1?xBi1+xF4+2x which has the CaF2 structure (x=0.0 is analogous to 2CaF2). By varying x we increase the disorder (via F-ion interstitials and vacancies) and measure broad temperature independent reduced Raman and infrared responses. The broad response is dependent on x in a manner consistent with the first assumption and the lack of temperature dependence is consistent with the second assumption. In order to understand the transverse optic vibrational frequencies (ωTO) we have found that plots of ωTO2vs. μ-1 (reduced mass) are very helpful. The linearity of such plots, for example, for tetrahedrally bonded AgI, CuI, CuBr, CuCl (formal charge Z=1) and the difference of such results for similar materials but with formal charges of 2, 3, and 4 is surprising and not as yet understood. Other conclusions are discussed at the end of the paper. 相似文献