全文获取类型
收费全文 | 4347篇 |
免费 | 122篇 |
国内免费 | 14篇 |
专业分类
化学 | 2654篇 |
晶体学 | 25篇 |
力学 | 71篇 |
数学 | 614篇 |
物理学 | 1119篇 |
出版年
2022年 | 39篇 |
2021年 | 36篇 |
2020年 | 51篇 |
2019年 | 60篇 |
2018年 | 38篇 |
2017年 | 35篇 |
2016年 | 74篇 |
2015年 | 110篇 |
2014年 | 98篇 |
2013年 | 175篇 |
2012年 | 185篇 |
2011年 | 201篇 |
2010年 | 130篇 |
2009年 | 141篇 |
2008年 | 185篇 |
2007年 | 191篇 |
2006年 | 168篇 |
2005年 | 205篇 |
2004年 | 131篇 |
2003年 | 133篇 |
2002年 | 137篇 |
2001年 | 101篇 |
2000年 | 81篇 |
1999年 | 61篇 |
1998年 | 56篇 |
1997年 | 56篇 |
1996年 | 69篇 |
1995年 | 65篇 |
1994年 | 84篇 |
1993年 | 79篇 |
1992年 | 77篇 |
1991年 | 58篇 |
1990年 | 57篇 |
1989年 | 51篇 |
1988年 | 38篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 49篇 |
1984年 | 54篇 |
1983年 | 39篇 |
1982年 | 54篇 |
1981年 | 57篇 |
1980年 | 53篇 |
1979年 | 45篇 |
1978年 | 36篇 |
1977年 | 43篇 |
1976年 | 42篇 |
1974年 | 27篇 |
1973年 | 40篇 |
1970年 | 28篇 |
排序方式: 共有4483条查询结果,搜索用时 15 毫秒
1.
2.
3.
F. Klein 《Fresenius' Journal of Analytical Chemistry》1885,24(1):379-388
Ohne ZusammenfassungNieder-Ingelheim, 3. Mai 1885. 相似文献
4.
A time discrete scheme is used to approximate the solution toa phase field system of PenroseFife type with a non-conservedorder parameter. An a posteriori error estimate is presentedthat allows the estimation of the difference between continuousand semidiscrete solutions by quantities that can be calculatedfrom the approximation and given data. 相似文献
5.
Extending to r > 1 a formula of the authors, we compute the expected reflection distance of a product of t random reflections in the complex reflection group G(r, 1, n). The result relies on an explicit decomposition of the reflection distance function into irreducible G(r, 1, n)-characters and on the eigenvalues of certain adjacency matrices.Received December 8, 2003 相似文献
6.
This is the second in a two-part series of articles in which we analyze a system similar in structure to the well-known Zakharov equations from weak plasma turbulence theory, but with a nonlinear conservation equation allowing finite time shock formation. In this article we analyze the incompressible limit in which the shock speed is large compared to the underlying group velocity of the dispersive wave (a situation typically encountered in applications). After presenting some exact solutions of the full system, a multiscale perturbation method is used to resolve several basic wave interactions. The analysis breaks down into two categories: the nonlinear limit and the linear limit, corresponding to the form of the equations when the group velocity to shock speed ratio, denoted by ε, is zero. The former case is an integrable limit in which the model reduces to the cubic nonlinear Schrödinger equation governing the dispersive wave envelope. We focus on the interaction of a “fast” shock wave and a single hump soliton. In the latter case, the ε=0 problem reduces to the linear Schrödinger equation, and the focus is on a fast shock interacting with a dispersive wave whose amplitude is cusped and exponentially decaying. To motivate the time scales and structure of the shock-dispersive wave interactions at lowest orders, we first analyze a simpler system of ordinary differential equations structurally similar to the original system. Then we return to the fully coupled partial differential equations and develop a multiscale asymptotic method to derive the effective leading-order shock equations and the leading-order modulation equations governing the phase and amplitude of the dispersive wave envelope. The leading-order interaction equations admit a fairly complete analysis based on characteristic methods. Conditions are derived in which: (a) the shock passes through the soliton, (b) the shock is completely blocked by the soliton, or (c) the shock reverses direction. In the linear limit, a phenomenon is described in which the dispersive wave induces the formation of a second, transient shock front in the rapidly moving hyperbolic wave. In all cases, we can characterize the long-time dynamics of the shock. The influence of the shock on the dispersive wave is manifested, to leading order, in the generalized frequency of the dispersive wave: the fast-time part of the frequency is the shock wave itself. Hence, the frequency undergoes a sudden jump across the shock layer.In the last section, a sequence of numerical experiments depicting some of the interesting interactions predicted by the analysis is performed on the leading-order shock equations. 相似文献
7.
Holger Poths Erik Wischerhoff Rudolf Zentel Axel Sch nfeld Guido Henn Friedrich Kremer 《Liquid crystals》1995,18(5):811-818
Two new ferroelectric oligosiloxanes, a cyclic tetramer and a twin, have been synthesized. By a comparative study with their corresponding monomer and side chain polysiloxanes, the influence of oligo- and polymerization on the liquid crystalline and ferroelectric properties have been investigated. Polymerization leads to a stabilization of LC phases through increase of the clearing temperatures and suppression of crystallization. Oligomerization also leads to mesophase broadening, but, due to the low degree of polymerization, the effect is inferior to the linear polysiloxanes. The low viscosity of the oligosiloxanes ensures response times in the microsecond region, thus being comparable with their monomer and conventional LMWFLCs. It is found that polymerization increases the spontaneous polarization Ps. This is attributed to the density increase after polymerization, enhancing the inter-mesogenic interactions. The collective and local dynamics of the OFLCs are influenced differently with respect to their molecular structures. Each oligomer is already a good model for its corresponding polymer concerning the soft mode dynamics. For the local β-relaxation a similar temperature dependence of the relaxation times τ for the cyclic tetramer and for the side chain polysiloxanes is observed. The long axial rotation of the twin, having a very efficient decoupling, is significantly faster, thus resembling the monomer. 相似文献
8.
In recent years there has been considerable progress in the application of large-eddy simulation (LES) to increasingly complex flow configurations. Nevertheless a lot of fundamental problems still need to be solved in order to apply LES in a reliable way to real engineering problems, where typically finite-volume codes on unstructured meshes are used. A self-adaptive discretisation scheme, in the context of an unstructured finite-volume flow solver, is investigated in the case of isotropic turbulence at infinite Reynolds number. The Smagorinsky and dynamic Smagorinsky sub-grid scale models are considered. A discrete interpolation filter is used for the dynamic model. It is one of the first applications of a filter based on the approach presented by Marsden et al. In this work, an original procedure to impose the filter shape through a specific selection process of the basic filters is also proposed. Satisfactory results are obtained using the self-adaptive scheme for implicit LES. When the scheme is coupled with the sub-grid scale models, the numerical dissipation is shown to be dominant over the sub-grid scale component. Nevertheless the effect of the sub-grid scale models appears to be important and beneficial, improving in particular the energy spectra. A test on fully developed channel flow at Reτ = 395 is also performed, comparing the non-limited scheme with the self-adaptive scheme for implicit LES. Once again the introduction of the limiter proves to be beneficial. 相似文献
9.
We exhibit timelike geodesic paths for a metric, introduced by Bonnor [11] and considered also by Steadman [13], and show that coordinate time runs backward along a portion of these geodesics. 相似文献
10.
Axel Ruhe 《BIT Numerical Mathematics》2007,47(2):239-240