全文获取类型
收费全文 | 2331篇 |
免费 | 99篇 |
国内免费 | 30篇 |
专业分类
化学 | 1397篇 |
晶体学 | 12篇 |
力学 | 64篇 |
数学 | 554篇 |
物理学 | 433篇 |
出版年
2023年 | 27篇 |
2022年 | 37篇 |
2021年 | 64篇 |
2020年 | 55篇 |
2019年 | 42篇 |
2018年 | 51篇 |
2017年 | 39篇 |
2016年 | 80篇 |
2015年 | 94篇 |
2014年 | 98篇 |
2013年 | 155篇 |
2012年 | 165篇 |
2011年 | 160篇 |
2010年 | 112篇 |
2009年 | 105篇 |
2008年 | 145篇 |
2007年 | 133篇 |
2006年 | 129篇 |
2005年 | 113篇 |
2004年 | 91篇 |
2003年 | 50篇 |
2002年 | 72篇 |
2001年 | 24篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 22篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1956年 | 6篇 |
排序方式: 共有2460条查询结果,搜索用时 132 毫秒
991.
Ernst Lücker Horst K?nig Wolfgang Gabriel Anton Rosopulo 《Fresenius' Journal of Analytical Chemistry》1992,342(12):941-949
Summary The function of solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) in the laboratory-internal preparation, production and standardization of several animal tissue reference materials is described. SS-GFAAS is successfully applied in the production of a bovine liver reference material with a low content of Pb and Cd. The lab-internal production of 5 bovine teeth and 2 bovine bone reference materials illustrates some of the basic problems entailed in the analysis of Pb in osseus matrices and in the production of the reference material itself. In the production of muscle tissue reference material focal or generalized calcification is a serious source of endogenous Pb contamination. This is shown, by way of example, in the calcification of the larval states of Taenia saginata (Cysticercus bovis) in the bovine muscle. Finally, as further examples of the application of SS-GFAAS, the lab-internal production of reference material from bovine blood and equine renal cortex is described. 相似文献
992.
The hyperfine interaction between quarks suggested in chromodynamics can, without free parameters, explain the size and pattern of the splittings and the mixing angles observed experimentally in nonstrange, negative parity baryons. 相似文献
993.
From a theoretical analysis we predict large fractions of circular polarization of light emitted by ions scattered from surfaces of ferromagnetic single crystals. Maximum enhancement of circular polarization as compared to surface ion scattering from non-magnetic materials is again expected at grazing incidence. A circular polarization of 89% was estimated for the case of Ar+ ions scattered from the (110) plane of a Ni single crystal. 相似文献
994.
995.
The paper is concerned with a problem in the theory of congruence function fields which is analogous to a conjecture of Gross in Iwasawa Theory. Zp-extensions K∞/K0 of congruence function fields K0 of characteristic p≠2 involving no new constants are considered such that the set S of ramified primes is finite and these primes are fully ramified. Is the set of S-classes invariant under Gal(K∞/K0) finite ? Gross' conjecture asserts that a similar question has an affirmative answer for the class of cyclotomic Zp- extensions of CM-type if S is the set of p-primes and the classes considered are minus S-classes. Using a formula of Witt for the norm residue symbol in cyclic p-extensions of local fields of characteristic p, a necessary and sufficient condition for the validity of the analogue of Gross' conjecture is given for a class of extensions K∞/K0. It is shown by examples that the analogue of Gross' conjecture is not always true. 相似文献
996.
997.
Summary. This paper presents an a posteriori error analysis of the discretization methods used in computational quantum chemistry on the Hartree-Fock equations. Upper and lower bounds for the energy are obtained from any discrete approximation strategy of the solution and the estimator proposed is shown to possess further approximation virtues. 相似文献
998.
The pyrolysis of methyl 4-bromocrotonate in the temperature range 300–340°C and pressure range 74–170 torr has been shown to be homogeneous, unimolecular, and to follow a first-order rate law. The reaction was carried out in a static system, seasoned with allyl bromide, and in the presence of the radical chain exhibitor toluene. The rate coefficients are represented by the Arrhenius expression: log k1(s?1) = (13.30 ± 0.66) ? (185.2 ± 7.5) kJ mol?1 (2.303RT)?1. The carbomethoxy group appears to provide anchimeric assistance in the process of dehydrobromination and lactone products formation. The partial rates for the parallel reaction have been estimated, reported, and discussed. The pyrolysis elimination is explained in terms of an intimate ion pair-type of mechanism. 相似文献
999.
We introduce the notion of distinguished tree relation and give applications. We prove in ZFC an old conjecture of A.V. Ostrovsky about the image of a Borel space under a compact covering mapping. We also prove that if is countable then any compact covering mapping from a Δ11 space onto a Σ01+ξ+2 or Π01+ξ+2 space is inductively perfect. The converse of last statement is shown. To cite this article: G. Debs, J. Saint Raymond, C. R. Acad. Sci. Paris, Ser. I 336 (2003). 相似文献
1000.
Summary In this paper we apply the coupling of boundary integral and finite element methods to solve a nonlinear exterior Dirichlet problem in the plane. Specifically, the boundary value problem consists of a nonlinear second order elliptic equation in divergence form in a bounded inner region, and the Laplace equation in the corresponding unbounded exterior region, in addition to appropriate boundary and transmission conditions. The main feature of the coupling method utilized here consists in the reduction of the nonlinear exterior boundary value problem to an equivalent monotone operator equation. We provide sufficient conditions for the coefficients of the nonlinear elliptic equation from which existence, uniqueness and approximation results are established. Then, we consider the case where the corresponding operator is strongly monotone and Lipschitz-continuous, and derive asymptotic error estimates for a boundary-finite element solution. We prove the unique solvability of the discrete operator equations, and based on a Strang type abstract error estimate, we show the strong convergence of the approximated solutions. Moreover, under additional regularity assumptions on the solution of the continous operator equation, the asymptotic rate of convergenceO (h) is obtained.The first author's research was partly supported by the U.S. Army Research Office through the Mathematical Science Institute of Cornell University, by the Universidad de Concepción through the Facultad de Ciencias, Dirección de Investigación and Vicerretoria, and by FONDECYT-Chile through Project 91-386. 相似文献