全文获取类型
收费全文 | 4347篇 |
免费 | 111篇 |
国内免费 | 20篇 |
专业分类
化学 | 2423篇 |
晶体学 | 37篇 |
力学 | 104篇 |
数学 | 777篇 |
物理学 | 1137篇 |
出版年
2021年 | 25篇 |
2020年 | 36篇 |
2019年 | 41篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 64篇 |
2015年 | 77篇 |
2014年 | 73篇 |
2013年 | 192篇 |
2012年 | 162篇 |
2011年 | 190篇 |
2010年 | 115篇 |
2009年 | 122篇 |
2008年 | 182篇 |
2007年 | 168篇 |
2006年 | 177篇 |
2005年 | 197篇 |
2004年 | 134篇 |
2003年 | 138篇 |
2002年 | 154篇 |
2001年 | 76篇 |
2000年 | 82篇 |
1999年 | 63篇 |
1998年 | 51篇 |
1997年 | 63篇 |
1996年 | 69篇 |
1995年 | 62篇 |
1994年 | 84篇 |
1993年 | 92篇 |
1992年 | 80篇 |
1991年 | 61篇 |
1990年 | 56篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 56篇 |
1986年 | 54篇 |
1985年 | 54篇 |
1984年 | 69篇 |
1983年 | 51篇 |
1982年 | 62篇 |
1981年 | 72篇 |
1980年 | 65篇 |
1979年 | 56篇 |
1978年 | 62篇 |
1977年 | 59篇 |
1976年 | 57篇 |
1975年 | 35篇 |
1974年 | 44篇 |
1973年 | 53篇 |
1970年 | 31篇 |
排序方式: 共有4478条查询结果,搜索用时 0 毫秒
1.
2.
High-temperature series expansions of the susceptibility and second moment to 15th order are calculated for zero external field on the linear chain (LC), plane square (PSQ), simple cubic (SC), and body-centered cubic (BCC) lattices. Checks for specific models against pertinent work in the literature are detailed. 相似文献
3.
Felix Klein 《Mathematische Annalen》1870,2(2):198-226
Ohne Zusammenfassung 相似文献
4.
F. Klein 《Mathematische Annalen》1883,22(2):246-248
Ohne ZusammenfassungAus den Sitzungsberichten der physikalisch-medicinischen Societät zu Erlangen vom 10. November 1873Es ist dies diejenige Arbeit, auf welche Hr. Wedekind bei seiner Definition des complexen Doppelverhältnisses von vier Punkten der Kugel Bezug nimmt, Bd. 9 dieser Annalen, pag. 209 ff. [Febr. 1883]. 相似文献
5.
F. Klein 《Fresenius' Journal of Analytical Chemistry》1885,24(1):379-388
Ohne ZusammenfassungNieder-Ingelheim, 3. Mai 1885. 相似文献
6.
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
7.
Many biological and medical studies have as a response of interest the time to occurrence of some event, such as the occurrence of a particular symptom or disease, remission, relapse, death due to some specific disease, or simply death. In this paper we study the problem of assessing the effect of potential risk factors on the outcome event of interest through a parametric or semi-parametric frailty model where the lifetimes have a reason to be considered dependent. This dependence may arise because of multiple endpoints within the same individual or because, when studying a single endpoint, there are natural groupings between study subjects. The objective of this paper is to extend both parametric and semi-parametric approaches to regression analysis in which the lifetimes of individuals in a group are effected by the same random frailty which follows a positive stable distribution. Some comparisons of the properties of this frailty distribution with other frailty distributions are made and an example which assesses the effect of a treatment in a litter-matched tumorigenesis study is presented. 相似文献
8.
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
9.
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
10.
Bart M. J. M. Suijkerbuijk Duncan M. Tooke Anthony L. Spek Gerard van Koten Robertus J. M. Klein Gebbink Prof. Dr. 《无机化学与普通化学杂志》2007,633(15):2649-2653
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures. 相似文献