全文获取类型
收费全文 | 5597篇 |
免费 | 438篇 |
国内免费 | 653篇 |
专业分类
化学 | 983篇 |
晶体学 | 24篇 |
力学 | 460篇 |
综合类 | 97篇 |
数学 | 3762篇 |
物理学 | 1362篇 |
出版年
2024年 | 4篇 |
2023年 | 60篇 |
2022年 | 80篇 |
2021年 | 123篇 |
2020年 | 139篇 |
2019年 | 141篇 |
2018年 | 140篇 |
2017年 | 142篇 |
2016年 | 196篇 |
2015年 | 117篇 |
2014年 | 254篇 |
2013年 | 362篇 |
2012年 | 235篇 |
2011年 | 293篇 |
2010年 | 262篇 |
2009年 | 301篇 |
2008年 | 381篇 |
2007年 | 320篇 |
2006年 | 347篇 |
2005年 | 292篇 |
2004年 | 272篇 |
2003年 | 290篇 |
2002年 | 381篇 |
2001年 | 204篇 |
2000年 | 212篇 |
1999年 | 174篇 |
1998年 | 195篇 |
1997年 | 129篇 |
1996年 | 106篇 |
1995年 | 74篇 |
1994年 | 62篇 |
1993年 | 51篇 |
1992年 | 53篇 |
1991年 | 51篇 |
1990年 | 44篇 |
1989年 | 33篇 |
1988年 | 20篇 |
1987年 | 11篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有6688条查询结果,搜索用时 42 毫秒
41.
关于局部对称空间中2-调和子流形 总被引:6,自引:0,他引:6
本文研究局部对称完备黎曼流形中的紧致2-调和子流形,得到了这类流形第二基本模式长平方的Pinching定理及推广的J.Simons型积分不等式。 相似文献
42.
In this paper we discuss thermodynamics parameters of black hole horizon and cosmological horizon in general high-dimensional space-time. We obtain that the entropy of a cosmological horizon can be described by the Cardy-Verlinde formula. However, the entropy of black hole horizon will be expressed in a form of the Cardy-Verlinde formula, if one adopts the methods given by Abbott and Deser to compute the mass of a black hole in general high-dimensional space-time. Through discussion, relation among various thermodynamics parameters of the black hole in general high-dimensional space-time is given. That is, differential formula of the first law of thermodynamics is obtained. Because we discuss the general high-dimensional space-time, our result has universality.
PACS: 04.20.Dw, 97.60.Lf 相似文献
43.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献
44.
A planar map is a 2-cell embedding of a connected planar graph, loops and parallel edges allowed, on the sphere. A plane map is a planar map with a distinguished outside (“infinite”) face. An unrooted map is an equivalence class of maps under orientation-preserving homeomorphism, and a rooted map is a map with a distinguished oriented edge. Previously we obtained formulae for the number of unrooted planar n-edge maps of various classes, including all maps, non-separable maps, eulerian maps and loopless maps. In this article, using the same technique we obtain closed formulae for counting unrooted plane maps of all these classes and their duals. The corresponding formulae for rooted maps are known to be all sum-free; the formulae that we obtain for unrooted maps contain only a sum over the divisors of n. We count also unrooted two-vertex plane maps. 相似文献
45.
用三个关系式与Mathematica软件求第二类自然数幂和公式 总被引:1,自引:1,他引:0
首先介绍三个第二类自然数幂和关系式并对其中的两式给出证明,接着利用这些关系式与数学软件M athem atica4.0,给出求解第二类自然数幂和公式的若干机械计算方法. 相似文献
46.
The classical Hardy theorem asserts that ■ and its Fourier transform ■ can not both be very rapidly decreasing.This theorem was generalized on Lie groups and also for the Fourier-Jacobi transform.However,on SU(1,1)there are infinitely many"good"functions in the sense that ■ and its spherical Fourier transform ■ both have good decay. In this paper,we shall characterize such functions on SU(1,1). 相似文献
47.
Masamichi Takase 《Topology》2004,43(6):1425-1447
Haefliger has shown that a smooth embedding of the (4k−1)-sphere in the 6k-sphere can be knotted in the smooth sense. In this paper, we give a formula with which we can detect the isotopy class of such a Haefliger knot. The formula is expressed in terms of the geometric characteristics of an extension, analogous to a Seifert surface, of the given embedding. In particular, the Hopf invariant associated to the extension plays a crucial role. This leads us to a new characterisation of Haefliger knots. 相似文献
48.
We show that there is a threshold in energy for the onset of chaos in cosmology for the Universe described as a dynamical system derived from the Einstein equations of General Relativity (GR). In the case of the mixmaster model (homogeneous and anisotropic cosmology with a Bianchi IX metric), the chaos occurs precisely at the prescribed necessary value H
vac=0 of the GR for the energy of the Universe while the system is found to be regular for H<0 and chaotic for H>0 with respect to its pure vacuum part. In the case of generalized scalar tensor theories within the Bianchi IX model, we show using the ADM formalism and a conformal transformation that the energy of the dynamical system as compared to vacuum lies below the zero energy threshold. The system is thus not exhibiting chaos and the conclusion still holds in the presence of ordinary matter as well. The suppression of chaos occurs in a similar way for stiff matter alone. 相似文献
49.
50.
We extend the previously found accelerated Kerr-Schild metrics for Einstein-Maxwell-null dust and Einstein-Born-Infeld-null dust equations to the cases including the cosmological constant. This way we obtain the generalization of the charged de Sitter metrics in static space-times. We also give a generalization of the zero acceleration limit of our previous Einstein-Maxwell and Einstein-Born-Infeld solutions. 相似文献