全文获取类型
收费全文 | 54124篇 |
免费 | 8832篇 |
国内免费 | 4134篇 |
专业分类
化学 | 11011篇 |
晶体学 | 382篇 |
力学 | 11550篇 |
综合类 | 745篇 |
数学 | 15867篇 |
物理学 | 27535篇 |
出版年
2024年 | 96篇 |
2023年 | 569篇 |
2022年 | 1056篇 |
2021年 | 1385篇 |
2020年 | 1632篇 |
2019年 | 1424篇 |
2018年 | 1358篇 |
2017年 | 1867篇 |
2016年 | 2183篇 |
2015年 | 1741篇 |
2014年 | 2973篇 |
2013年 | 4250篇 |
2012年 | 3207篇 |
2011年 | 3859篇 |
2010年 | 3169篇 |
2009年 | 3671篇 |
2008年 | 3632篇 |
2007年 | 3630篇 |
2006年 | 3100篇 |
2005年 | 2846篇 |
2004年 | 2519篇 |
2003年 | 2235篇 |
2002年 | 2007篇 |
2001年 | 1703篇 |
2000年 | 1568篇 |
1999年 | 1322篇 |
1998年 | 1249篇 |
1997年 | 926篇 |
1996年 | 773篇 |
1995年 | 715篇 |
1994年 | 636篇 |
1993年 | 583篇 |
1992年 | 466篇 |
1991年 | 407篇 |
1990年 | 327篇 |
1989年 | 265篇 |
1988年 | 266篇 |
1987年 | 227篇 |
1986年 | 188篇 |
1985年 | 210篇 |
1984年 | 191篇 |
1983年 | 99篇 |
1982年 | 156篇 |
1981年 | 91篇 |
1980年 | 49篇 |
1979年 | 59篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 24篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this paper, we consider a viscoelastic wave equation of variable coefficients in the presence of past history with nonlinear damping and delay in the internal feedback and dynamic boundary conditions. Under suitable assumptions, we establish an explicit and general decay rate result without imposing restrictive assumption on the behavior of the relaxation function at infinity by Riemannian geometry method and Lyapunov functional method. 相似文献
32.
《中国物理 B》2021,30(5):56201-056201
A new three-dimensional(3 D) cellular model based on hinging open-cell Kelvin structure is proposed for its negative compressibility property. It is shown that this model has adjustable compressibility and does exhibit negative compressibility for some certain conformations. And further study shows that the images of compressibility are symmetrical about the certain lines, which indicates that the mechanical properties of the model in the three axial directions are interchangeable and the model itself has a certain geometric symmetry. A comparison of the Kelvin model with its anisotropic form with the dodecahedron model shows that the Kelvin model has stronger negative compressibility property in all three directions.Therefore, a new and potential method to improve negative compressibility property can be derived by selecting the system type with lower symmetry and increasing the number of geometric parameters. 相似文献
33.
34.
35.
An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
36.
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
37.
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
38.
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
39.
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
40.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献