全文获取类型
收费全文 | 1544篇 |
免费 | 131篇 |
国内免费 | 152篇 |
专业分类
化学 | 202篇 |
晶体学 | 1篇 |
力学 | 155篇 |
综合类 | 37篇 |
数学 | 870篇 |
物理学 | 562篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 42篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 40篇 |
2018年 | 38篇 |
2017年 | 26篇 |
2016年 | 39篇 |
2015年 | 36篇 |
2014年 | 47篇 |
2013年 | 107篇 |
2012年 | 51篇 |
2011年 | 59篇 |
2010年 | 62篇 |
2009年 | 79篇 |
2008年 | 111篇 |
2007年 | 97篇 |
2006年 | 69篇 |
2005年 | 96篇 |
2004年 | 64篇 |
2003年 | 85篇 |
2002年 | 74篇 |
2001年 | 58篇 |
2000年 | 88篇 |
1999年 | 64篇 |
1998年 | 48篇 |
1997年 | 49篇 |
1996年 | 43篇 |
1995年 | 18篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有1827条查询结果,搜索用时 31 毫秒
71.
72.
73.
74.
Jorge Almeida 《Transactions of the American Mathematical Society》2002,354(1):387-411
This work gives a new approach to the construction of implicit operations. By considering ``higher-dimensional' spaces of implicit operations and implicit operators between them, the projection of idempotents back to one-dimensional spaces produces implicit operations with interesting properties. Besides providing a wealth of examples of implicit operations which can be obtained by these means, it is shown how they can be used to deduce from results of Ribes and Zalesski, Margolis, Sapir and Weil, and Steinberg that the pseudovariety of -groups is tame. More generally, for a recursively enumerable extension closed pseudovariety of groups , if it can be decided whether a finitely generated subgroup of the free group with the pro- topology is dense, then is tame.
75.
Roman Frič 《Czechoslovak Mathematical Journal》2002,52(4):861-874
We show that each sequentially continuous (with respect to the pointwise convergence) normed measure on a bold algebra of fuzzy sets (Archimedean MV-algebra) can be uniquely extended to a sequentially continuous measure on the generated ukasiewicz tribe and, in a natural way, the extension is maximal. We prove that for normed measures on ukasiewicz tribes monotone (sequential) continuity implies sequential continuity, hence the assumption of sequential continuity is not restrictive. This yields a characterization of the ukasiewicz tribes as bold algebras absolutely sequentially closed with respect to the extension of probabilities. The result generalizes the relationship between fields of sets and the generated -fields discovered by J. Novák. We introduce the category of bold algebras and sequentially continuous homomorphisms and prove that ukasiewicz tribes form an epireflective subcategory. The restriction to fields of sets yields the epireflective subcategory of -fields of sets. 相似文献
76.
Linear partial differential algebraic equations (PDAEs) of the form Au
t(t, x) + Bu
xx(t, x) + Cu(t, x) = f(t, x) are studied where at least one of the matrices A, B R
n×n
is singular. For these systems we introduce a uniform differential time index and a differential space index. We show that in contrast to problems with regular matrices A and B the initial conditions and/or boundary conditions for problems with singular matrices A and B have to fulfill certain consistency conditions. Furthermore, two numerical methods for solving PDAEs are considered. In two theorems it is shown that there is a strong dependence of the order of convergence on these indexes. We present examples for the calculation of the order of convergence and give results of numerical calculations for several aspects encountered in the numerical solution of PDAEs. 相似文献
77.
G.Ya. Korenman 《Hyperfine Interactions》1999,119(1-4):227-233
Effect of medium density on shift and broadening of (
) spectral lines is considered in the framework of binary-collision approximation with an effective (
)–He potential including the long-range attraction and short-range repulsion. Quantum calculations of the scattering phase
shifts at reasonable values of the potential parameters allow to explain the main features of the observed density effect
on the shape of (
) spectral lines in low-temperature helium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
78.
Emilio Musso Lorenzo Nicolodi 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》1999,69(1):123-138
We study surfaces with plane lines of curvature in the framework of Laguerre geometry and provide explicit representation
formulae for these surfaces in terms of a potential function. As an application, we explicitly integrate allL- minimal surfaces with plane curvature lines.
Partially supported by MURST 40. 相似文献
79.
Consider a closed Jackson type network in which each queue has a single exponential server. Assume that N customers are moving among k queues. We establish simple closed form bounds on the network throughput (both lower and upper), which are sharper than those that are currently available. Numerical evaluation indicates that the improvements are significant. 相似文献
80.
Time dependent problems in Partial Differential Equations (PDEs) are often solved by the Method Of Lines (MOL). For linear parabolic PDEs, the exact solution of the resulting system of first order Ordinary Differential Equations (ODEs) satisfies a recurrence relation involving the matrix exponential function. In this paper, we consider the development of a fourth order rational approximant to the matrix exponential function possessing real and distinct poles which, consequently, readily admits a partial fraction expansion, thereby allowing the distribution of the work in solving the corresponding linear algebraic systems in essentially Backward Euler-like solves on concurrent processors. The resulting parallel algorithm possesses appropriate stability properties, and is implemented on various parabolic PDEs from the literature including the forced heat equation and the advection-diffusion equation.Dedicated to Professor J. Crank on the occasion of his 80th birthday 相似文献