全文获取类型
收费全文 | 8403篇 |
免费 | 411篇 |
国内免费 | 693篇 |
专业分类
化学 | 965篇 |
晶体学 | 9篇 |
力学 | 395篇 |
综合类 | 58篇 |
数学 | 6843篇 |
物理学 | 1237篇 |
出版年
2023年 | 86篇 |
2022年 | 82篇 |
2021年 | 100篇 |
2020年 | 164篇 |
2019年 | 176篇 |
2018年 | 203篇 |
2017年 | 204篇 |
2016年 | 237篇 |
2015年 | 159篇 |
2014年 | 327篇 |
2013年 | 574篇 |
2012年 | 342篇 |
2011年 | 366篇 |
2010年 | 348篇 |
2009年 | 527篇 |
2008年 | 598篇 |
2007年 | 547篇 |
2006年 | 504篇 |
2005年 | 452篇 |
2004年 | 326篇 |
2003年 | 389篇 |
2002年 | 350篇 |
2001年 | 252篇 |
2000年 | 265篇 |
1999年 | 267篇 |
1998年 | 214篇 |
1997年 | 233篇 |
1996年 | 128篇 |
1995年 | 119篇 |
1994年 | 101篇 |
1993年 | 72篇 |
1992年 | 61篇 |
1991年 | 60篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 54篇 |
1987年 | 39篇 |
1986年 | 40篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 20篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 30篇 |
1977年 | 38篇 |
1976年 | 26篇 |
1974年 | 16篇 |
1973年 | 16篇 |
排序方式: 共有9507条查询结果,搜索用时 15 毫秒
101.
Wei-Shih Yang 《Journal of statistical physics》1987,49(1-2):1-32
The grand canonical ensemble of a two-dimensional Coulomb system with±1 charges is proved to have screening phenomena in its high-temperature region. The Coulomb potential in a finite region is assumed to be (–)–1, where
is the Laplacian with zero boundary conditions on. The hard-core condition is not assumed. The model is set up by separating (–)–1 into a shortrange part and a long-range part depending on a parameter. The self-energies are subtracted only for the short-range part and therefore a choice of is a choice of subtraction of self-energies. The method of proof is in general the same as that of Brydges-Federbush Debye screening, except that here a modification for the short-range part of the potentials is needed. 相似文献
102.
R. Der 《Journal of statistical physics》1987,46(1-2):349-389
The various approaches to nonequilibrium statistical mechanics may be subdivided into convolution and convolutionless (time-local) ones. While the former, put forward by Zwanzig, Mori, and others, are used most commonly, the latter are less well developed, but have proven very useful in recent applications. The aim of the present series of papers is to develop the time-local picture (TLP) of nonequilibrium statistical mechanics on a new footing and to consider its physical implications for topics such as the formulation of irreversible thermodynamics. The most natural approach to TLP is seen to derive from the Fourier-Laplace transform
) of pertinent time correlation functions, which on the physical sheet typically displays an essential singularity at z= and a number of macroscopic and microscopic poles in the lower half-plane corresponding to long- and short-lived modes, respectively, the former giving rise to the autonomous macrodynamics, whereas the latter are interpreted as doorway modes mediating the transfer of information from relevant to irrelevant channels. Possible implications of this doorway mode concept for socalled extended irreversible thermodynamics are briefly discussed. The pole structure is used for deriving new kinds of generalized Green-Kubo relations expressing macroscopic quantities, transport coefficients, e.g., by contour integrals over current-current correlation functions obeying Hamiltonian dynamics, the contour integration replacing projection. The conventional Green-Kubo relations valid for conserved quantities only are rederived for illustration. Moreover,
may be expressed by a Laurent series expansion in positive and negative powers ofz, from which a rigorous, general, and straightforward method is developed for extracting all macroscopic quantities from so-called secularly divergent expansions of
as obtained from the application of conventional many-body techniques to the calculation of
. The expressions are formulated as time scale expansions, which should rapidly converge if macroscopic and microscopic time scales are sufficiently well separated, i.e., if lifetime (memory) effects are not too large. 相似文献
103.
The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained. 相似文献
104.
105.
N-Acyl-β-hydroxy-4-phenyl-oxazolidinethiones could be rapidly converted into their ethyl thiol esters in high yields by treatment with EtSH at 0 ℃ in CH3CN or 9 : 1 (V : V) THF-H2O in the presence of a catalytic amount of K2CO3. 相似文献
106.
Andrea Basso 《Tetrahedron letters》2004,45(3):587-590
Intramolecular Ugi reactions with bicyclic β-amino acids have been performed and the effects of the configuration and N-alkylation have been studied. We have proven that preferential ring contraction or nucleophilic attack by the solvent depend not only on the presence of N-alkylation but also on the relative disposition of the carboxyl group and the amine. Excellent results in terms of stereoselectivity have been obtained in the case of N-alkyl-3-exo-amino-7-oxabicyclo[2.2.1]-2-endo-carboxylic acids. 相似文献
107.
S type Gaussian bond functions are optimized for HF, H2O, NH3, and CH4. The optimization is carried out with respect to the exponent and position in the H-X bond. The position is found to correlate
well with the electronegativity of Pauling and Allred-Rochow. 相似文献
108.
Peter LeemingColin A Ray Stephen J SimpsonTimothy W Wallace Richard A Ward 《Tetrahedron》2003,59(3):341-352
Heterodiene [4π+2π] cycloadditions of (S,S)-4,5-diaryl-2-methylene-1,3-dioxolanes 1 to a series of β-amido-α,β-unsaturated carbonyl compounds are diastereoselective (d.r.≥4:1). The products can be purified by trituration or crystallisation and hydrolysed with acid to generate the corresponding β-amido carbonyl compounds, the overall sequence effecting an auxiliary-based enantioselective conjugate addition of an acetate enolate, leading to β-aminoacid derivatives. 相似文献
109.
J. Hyslop 《Theoretical chemistry accounts》1973,31(3):189-194
An account is given of the use of Gaussian quadrature product formulae in the evaluation of certain six-dimensional, two-centre integrals involving one-electron Green's functions. These integrals occur in a new molecular variational principle recently proposed by Hall, Hyslop and Rees [1] from which an approximate energy may be derived which can be shown to be at least as good as that obtained from the Rayleigh-Ritz principle. Reductions in computing time are realized by removing certain singularities using a subtraction technique and also by using an empirically determined Richardson-type extrapolation formula.This paper was presented during the session on numerical integration methods for molecules of the 1970 Quantum Theory Conference in Nottingham. It has been revised in the light of the interesting discussion which followed. 相似文献
110.
《Thermochimica Acta》2003,401(2):169-173
The heat capacity and the heat content of gallium nitride were measured by calvet calorimetry (320-570 K) and by drop calorimetry (670-1270 K), respectively. The temperature dependence of the heat capacity in the form Cpm=49.552+5.440×10−3T−2.190×106T−2+2.460×108T−3 was derived by the least squares method. Furthermore, thermodynamic functions calculated on the basis of our experimental results and literature data on the molar entropy and the heat of formation of GaN are given. 相似文献