全文获取类型
收费全文 | 82361篇 |
免费 | 6330篇 |
国内免费 | 7229篇 |
专业分类
化学 | 31473篇 |
晶体学 | 317篇 |
力学 | 7711篇 |
综合类 | 1290篇 |
数学 | 30450篇 |
物理学 | 24679篇 |
出版年
2023年 | 745篇 |
2022年 | 1369篇 |
2021年 | 1572篇 |
2020年 | 1795篇 |
2019年 | 1946篇 |
2018年 | 1598篇 |
2017年 | 1815篇 |
2016年 | 2264篇 |
2015年 | 2089篇 |
2014年 | 2990篇 |
2013年 | 5494篇 |
2012年 | 3381篇 |
2011年 | 3802篇 |
2010年 | 3155篇 |
2009年 | 4513篇 |
2008年 | 4869篇 |
2007年 | 5173篇 |
2006年 | 4795篇 |
2005年 | 4081篇 |
2004年 | 3749篇 |
2003年 | 3774篇 |
2002年 | 3429篇 |
2001年 | 2930篇 |
2000年 | 2837篇 |
1999年 | 2525篇 |
1998年 | 2375篇 |
1997年 | 1943篇 |
1996年 | 1756篇 |
1995年 | 1554篇 |
1994年 | 1404篇 |
1993年 | 1211篇 |
1992年 | 1150篇 |
1991年 | 898篇 |
1990年 | 741篇 |
1989年 | 652篇 |
1988年 | 600篇 |
1987年 | 465篇 |
1986年 | 416篇 |
1985年 | 516篇 |
1984年 | 521篇 |
1983年 | 267篇 |
1982年 | 398篇 |
1981年 | 424篇 |
1980年 | 321篇 |
1979年 | 317篇 |
1978年 | 260篇 |
1977年 | 252篇 |
1976年 | 192篇 |
1975年 | 120篇 |
1974年 | 127篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A model is developed for the flow of a slightly compressible fluid through a saturated inelastic porous medium. The initial‐boundary‐value problem is a system that consists of the diffusion equation for the fluid coupled to the momentum equation for the porous solid together with a constitutive law which includes a possibly hysteretic relation of elasto‐visco‐plastic type. The variational form of this problem in Hilbert space is a non‐linear evolution equation for which the existence and uniqueness of a global strong solution is proved by means of monotonicity methods. Various degenerate situations are permitted, such as incompressible fluid, negligible porosity, or a quasi‐static momentum equation. The essential sufficient conditions for the well‐posedness of the system consist of an ellipticity condition on the term for diffusion of fluid and either a viscous or a hardening assumption in the constitutive relation for the porous solid. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
102.
Constructive Approximation - Let E = [–1, α] \cup [β, 1], –1 &;lt; α &;lt; β &;lt; 1, and let (pn) be orthogonal on E with respect to the weight function... 相似文献
103.
104.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
105.
106.
107.
德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
108.
A triangulation of a connected closed surface is called weakly regular if the action of its automorphism group on its vertices
is transitive. A triangulation of a connected closed surface is called degree-regular if each of its vertices have the same
degree. Clearly, a weakly regular triangulation is degree-regular. In [8], Lutz has classified all the weakly regular triangulations
on at most 15 vertices. In [5], Datta and Nilakantan have classified all the degree-regular triangulations of closed surfaces
on at most 11 vertices.
In this article, we have proved that any degree-regular triangulation of the torus is weakly regular. We have shown that there
exists ann-vertex degree-regular triangulation of the Klein bottle if and only if n is a composite number ≥ 9. We have constructed two
distinctn-vertex weakly regular triangulations of the torus for eachn ≥ 12 and a (4m + 2)-vertex weakly regular triangulation of the Klein bottle for eachm ≥ 2. For 12 ≤n ≤ 15, we have classified all then-vertex degree-regular triangulations of the torus and the Klein bottle. There are exactly 19 such triangulations, 12 of which
are triangulations of the torus and remaining 7 are triangulations of the Klein bottle. Among the last 7, only one is weakly
regular. 相似文献
109.
反对称正交对称矩阵反问题 总被引:6,自引:0,他引:6
本文讨论一类反对称正交对称矩阵反问题及其最佳逼近.研究了这类矩阵的一些性质,利用这些性质给出了反问题解存在的一些条件和解的一般表达式,不仅证明了最佳逼近解的存在唯一性,而且给出了此解的具体表达式. 相似文献
110.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献