全文获取类型
收费全文 | 1915篇 |
免费 | 108篇 |
国内免费 | 115篇 |
专业分类
化学 | 202篇 |
力学 | 217篇 |
综合类 | 11篇 |
数学 | 1222篇 |
物理学 | 486篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 35篇 |
2020年 | 54篇 |
2019年 | 45篇 |
2018年 | 36篇 |
2017年 | 46篇 |
2016年 | 43篇 |
2015年 | 52篇 |
2014年 | 89篇 |
2013年 | 171篇 |
2012年 | 77篇 |
2011年 | 108篇 |
2010年 | 87篇 |
2009年 | 148篇 |
2008年 | 148篇 |
2007年 | 151篇 |
2006年 | 105篇 |
2005年 | 71篇 |
2004年 | 81篇 |
2003年 | 78篇 |
2002年 | 53篇 |
2001年 | 53篇 |
2000年 | 42篇 |
1999年 | 52篇 |
1998年 | 49篇 |
1997年 | 33篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 27篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有2138条查询结果,搜索用时 15 毫秒
931.
We carry out an extensive investigation of conservation laws and potential symmetries for the class of linear (1+1)-dimensional
second-order parabolic equations. The group classification of this class is revised by employing admissible transformations,
the notion of normalized classes of differential equations and the adjoint variational principle. All possible potential conservation
laws are described completely. They are in fact exhausted by local conservation laws. For any equation from the above class
the characteristic space of local conservation laws is isomorphic to the solution set of the adjoint equation. Effective criteria
for the existence of potential symmetries are proposed. Their proofs involve a rather intricate interplay between different
representations of potential systems, the notion of a potential equation associated with a tuple of characteristics, prolongation
of the equivalence group to the whole potential frame and application of multiple dual Darboux transformations. Based on the
tools developed, a preliminary analysis of generalized potential symmetries is carried out and then applied to substantiate
our construction of potential systems. The simplest potential symmetries of the linear heat equation, which are associated
with single conservation laws, are classified with respect to its point symmetry group. Equations possessing infinite series
of potential symmetry algebras are studied in detail. 相似文献
932.
Tobias Lamm 《偏微分方程通讯》2013,38(2):245-262
In this paper a one-dimensional Keller–Segel model with a logarithmic chemotactic-sensitivity and a non-diffusing chemical is classified with respect to its long time behavior. The strength of production of the non-diffusive chemical has a strong influence on the qualitative behavior of the system concerning existence of global solutions or Dirac-mass formation. Further, the initial data play a crucial role. 相似文献
933.
《Physics and Chemistry of Liquids》2012,50(2):91-113
Abstract When molecules of chemical compounds are represented by graphs, thermodynamic properties may be connected with numbers of certain classes of walks on graphs. The basic proposition of summing up contributions resulting from interactions of walks is related to fluid distribution functions. The principle of corresponding volumes and structural schemes are discussed. Exemplary calculations for normal alkanes and their binary mixtures give in many cases values within limits of the experimental accuracy 相似文献
934.
This work investigates the effects of the excluded volume and especially those of the chain stiffness on the structural and dynamical properties of a model polymer chain.The theoretical framework is the same as in the recent works by Steinhauser et al.,where a Rouse approach is adopted.Our model differs in that our chains have a finite average bending angle.As in the works by Steinhauser et al.,Langevin dynamic simulations were performed without hydrodynamic interactions.Whereas this doesn’t impact the static properties we obtain,it also allows us to compare our results on dynamic properties to those predicted by Rouse theory,where hydrodynamic interactions are also neglected.Our results show that the structural properties are very sensitive to the chain stiffness,whereas the dynamic scaling laws remain the same as those by Rouse theory,with the prefactor depending on the persistence length. 相似文献
935.
A novel hierarchy of differential integral equations and their generalized bi-Hamiltonian structures
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
With the aid of the zero-curvature equation, a novel integrable hierarchy of nonlinear evolution equations associated with a 3 x 3 matrix spectral problem is proposed. By using the trace identity, the bi-Hamiltonian structures of the hierarchy are established with two skew-symmetric operators. Based on two linear spectral problems, we obtain the infinite many conservation laws of the first member in the hierarchy. 相似文献
936.
937.
Małgorzata Peszyńska 《Numerical Methods for Partial Differential Equations》2014,30(1):239-264
We consider approximation of solutions to conservation laws with memory represented by a Volterra term with a smooth decreasing but possibly unbounded kernel. The numerical scheme combines Godunov method with a treatment of the integral term following from product integration rules. We prove stability for both linear and nonlinear flux functions and demonstrate the expected order of convergence using numerical experiments. The problem is motivated by modeling advective transport in heterogeneous media with subscale diffusion.Copyright © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 239–264, 2014 相似文献
938.
We introduce a class of isotropic time dependent random fields on the non-homogeneous sphere which is represented by a time-changed spherical Brownian motion of order ν∈(0,1]. We can capture some anisotropies in Cosmology with this model. This process is a time-changed rotational diffusion (TRD) or the stochastic solution to the equation involving the spherical Laplace operator and a time-fractional derivative of order ν. TRD is a diffusion on the non-homogeneous sphere and therefore, the spherical coordinates given by TRD represent the coordinates of a non-homogeneous sphere by means of which an isotropic random field is indexed. The time dependent random fields we present in this work are therefore realized through composition and can be viewed as isotropic random field on randomly varying sphere. 相似文献
939.
函数单向S粗集对偶(dual offunction one direction singular rough sets)是函数S粗集的基本形式之一,函数单向S-粗集对偶具有动态特性与规律(函数)特性.函数S粗集(function singular rough sets)是把函数概念引入到S粗集内(singular rough sets)改进S粗集得到的把导数概念与函数单向S粗集对偶交叉、渗透给出粗边际规律F-粗边际规律概念;给出粗边际规律F-粗边际规律特征;给出F-粗边际规律与粗边际规律的关系;给出F-粗边际规律在经济信息系统中的应用 相似文献
940.
利用Adams谱序列与May谱序列, 发掘了球面稳定同伦群中一族$\xi_n$的相关元素.
这里$\xi_n\in\pi_* M$在Adams 谱序列中由$h_0h_n\in \ext_A^{2,p^n q+q}(H^* M,\zz_p)$所表示, 其中$p\geqslant 7,\ n>3,\ q=2(p-1).$ 相似文献