全文获取类型
收费全文 | 12047篇 |
免费 | 874篇 |
国内免费 | 906篇 |
专业分类
化学 | 838篇 |
晶体学 | 48篇 |
力学 | 2113篇 |
综合类 | 104篇 |
数学 | 2671篇 |
物理学 | 1645篇 |
综合类 | 6408篇 |
出版年
2024年 | 44篇 |
2023年 | 117篇 |
2022年 | 186篇 |
2021年 | 244篇 |
2020年 | 289篇 |
2019年 | 233篇 |
2018年 | 218篇 |
2017年 | 338篇 |
2016年 | 364篇 |
2015年 | 342篇 |
2014年 | 554篇 |
2013年 | 675篇 |
2012年 | 570篇 |
2011年 | 634篇 |
2010年 | 541篇 |
2009年 | 567篇 |
2008年 | 662篇 |
2007年 | 719篇 |
2006年 | 658篇 |
2005年 | 664篇 |
2004年 | 538篇 |
2003年 | 544篇 |
2002年 | 510篇 |
2001年 | 455篇 |
2000年 | 384篇 |
1999年 | 388篇 |
1998年 | 346篇 |
1997年 | 308篇 |
1996年 | 267篇 |
1995年 | 206篇 |
1994年 | 210篇 |
1993年 | 159篇 |
1992年 | 149篇 |
1991年 | 139篇 |
1990年 | 147篇 |
1989年 | 116篇 |
1988年 | 106篇 |
1987年 | 72篇 |
1986年 | 60篇 |
1985年 | 30篇 |
1984年 | 14篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
对T型管节点的疲劳试验进行分析,研究疲劳裂纹的扩展规律,用“柔度法”计算应力强度因子范围ΔK,确定材料常数c,m,提出并运用“直线-曲线模式法”估算管节点疲劳寿命,结果与试验吻合,具有一定的实用参考价值。 相似文献
22.
Neutral Community Theory: How Stochasticity and Dispersal-Limitation Can Explain Species Coexistence
Neutral community theory explains biodiversity, i.e. the coexistence of several species, as the result of a stochastic balance
between immigration and extinction on a local level, and between speciation and extinction on a regional level. The most popular
model, presented by Hubbell in 2001, has seen many analytical developments in recent years, which can be used in model analysis,
model testing and model comparison. We review these developments here, and present alternative derivations and shine previously
unnoticed lights on them. 相似文献
23.
In this paper we describe the design and manufacture of an axial-torsion test specimen, and provide relationships needed when
conducting stress-strain characterization experiments with the specimen. The specimen is a short hollow cylinder of rubber
bonded between two steel mounting rings, in which simultaneous axial and shear strains are produced via independently controlled
axial and twist displacements. We present calculations for the strain-displacement and stress-load relationships, and strain
energy density. These relationships have been established and validated via a combination of analytical and experimental techniques,
and finite element analysis. We have investigated the extent and effects of strain and stress field non-uniformity in the
test specimen. The specimen design is sufficiently simple that a closed-form expression for the strain-displacement relationship
has been successfully developed. 相似文献
24.
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
25.
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
26.
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
27.
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
28.
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
29.
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
30.
Summary Our purpose is to extend results due to P. Chandra and L. Leindler concerning the order of approximation by means of Fourier series for functions belonging to generalized Lipschitz-classes. 相似文献