全文获取类型
收费全文 | 72786篇 |
免费 | 8201篇 |
国内免费 | 8358篇 |
专业分类
化学 | 36532篇 |
晶体学 | 1506篇 |
力学 | 5961篇 |
综合类 | 764篇 |
数学 | 19229篇 |
物理学 | 25353篇 |
出版年
2024年 | 148篇 |
2023年 | 764篇 |
2022年 | 1884篇 |
2021年 | 1820篇 |
2020年 | 2269篇 |
2019年 | 2200篇 |
2018年 | 1936篇 |
2017年 | 2462篇 |
2016年 | 2689篇 |
2015年 | 2290篇 |
2014年 | 3533篇 |
2013年 | 5579篇 |
2012年 | 3812篇 |
2011年 | 5310篇 |
2010年 | 4300篇 |
2009年 | 4988篇 |
2008年 | 5006篇 |
2007年 | 4859篇 |
2006年 | 4258篇 |
2005年 | 3906篇 |
2004年 | 3441篇 |
2003年 | 2863篇 |
2002年 | 2644篇 |
2001年 | 2026篇 |
2000年 | 1951篇 |
1999年 | 1677篇 |
1998年 | 1429篇 |
1997年 | 1202篇 |
1996年 | 1055篇 |
1995年 | 1035篇 |
1994年 | 956篇 |
1993年 | 817篇 |
1992年 | 690篇 |
1991年 | 507篇 |
1990年 | 388篇 |
1989年 | 340篇 |
1988年 | 292篇 |
1987年 | 258篇 |
1986年 | 232篇 |
1985年 | 261篇 |
1984年 | 239篇 |
1983年 | 143篇 |
1982年 | 191篇 |
1981年 | 144篇 |
1980年 | 118篇 |
1979年 | 100篇 |
1978年 | 91篇 |
1977年 | 71篇 |
1976年 | 45篇 |
1973年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A. Foussats C. Repetto O. P. Zandron O. S. Zandron 《International Journal of Theoretical Physics》2002,41(6):1053-1082
In order to describe the dynamics of the t–J model, two different families of first-order Lagrangians in terms of the generators of the Hubbard algebra are found. Such families correspond to different dynamical second-class constrained systems. The quantization is carried out by using the path-integral formalism. In this context the introduction of proper ghost fields is needed to render the model renormalizable. In each case the standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. In the first case a nonperturbative large-N expansion is considered with the purpose of studying the generalized Hubbard model describing N-fold-degenerate correlated bands. In this case the 1/N correction to the renormalized boson propagator is computed. In the second case the perturbative Lagrangian formalism is developed and it is shown how propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our formalism is studied in details. As an example the thermal softening of the magnon frequency is computed. The antiferromagnetic case is also analyzed, and the results are confronted with previous one obtained by means of the spin-polaron theories. 相似文献
42.
Masaaki Sugihara 《Numerische Mathematik》1997,75(3):379-395
Summary. In the light of the functional analysis theory we establish the optimality of the double exponential formula. The argument
consists of the following three ingredients: (1) introduction of a number of spaces of functions analytic in a strip region
about the real axis, each space being characterized by the decay rate of their elements (functions) in the neighborhood of
the infinity; (2) proof of the (near-) optimality of the trapezoidal formula in each space introduced in (1) by showing the
(near-) equality between an upper estimate for the error norm of the trapezoidal formula and a lower estimate for the minimum
error norm of quadratures; (3) nonexistence theorem for the spaces, the characterizing decay rate of which is more rapid than
the double exponential.
Received September 15, 1995 / Accepted December 14, 1995 相似文献
43.
44.
Addition of functionalized zinc-copper reagents to the title complexes proceeds in a highly diastereoselective fashion to afford dienol complexes. The relative configurations of adducts 3d were determined by single X-ray diffraction analysis. 相似文献
45.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
46.
V. Dzhunushaliev 《Foundations of Physics》2002,32(7):1069-1090
An approximate model of a spacetime foam is presented. It is supposed that in the spacetime foam each quantum handle is like to an electric dipole and therefore the spacetime foam is similar to a dielectric. If we neglect of linear sizes of the quantum handle then it can be described with an operator containing a Grassman number and either a scalar or a spinor field. For both fields the Lagrangian is presented. For the scalar field it is the dilaton gravity + electrodynamics and the dilaton field is a dielectric permeability. The spherically symmetric solution in this case give us the screening of a bare electric charge surrounded by a polarized spacetime foam and the energy of the electric field becomes finite one. In the case of the spinor field the spherically symmetric solution give us a ball of the polarized spacetime foam filled with the confined electric field. It is shown that the full energy of the electric field in the ball can be very big. 相似文献
47.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
48.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
49.
50.