全文获取类型
收费全文 | 53110篇 |
免费 | 3782篇 |
国内免费 | 3862篇 |
专业分类
化学 | 30842篇 |
晶体学 | 683篇 |
力学 | 2194篇 |
综合类 | 246篇 |
数学 | 12537篇 |
物理学 | 14252篇 |
出版年
2023年 | 476篇 |
2022年 | 1115篇 |
2021年 | 972篇 |
2020年 | 1179篇 |
2019年 | 1450篇 |
2018年 | 1153篇 |
2017年 | 1358篇 |
2016年 | 1355篇 |
2015年 | 1271篇 |
2014年 | 1636篇 |
2013年 | 3151篇 |
2012年 | 2167篇 |
2011年 | 2803篇 |
2010年 | 2018篇 |
2009年 | 2695篇 |
2008年 | 2648篇 |
2007年 | 2705篇 |
2006年 | 2443篇 |
2005年 | 2063篇 |
2004年 | 2525篇 |
2003年 | 2295篇 |
2002年 | 3214篇 |
2001年 | 2635篇 |
2000年 | 2315篇 |
1999年 | 2348篇 |
1998年 | 2028篇 |
1997年 | 1366篇 |
1996年 | 946篇 |
1995年 | 703篇 |
1994年 | 644篇 |
1993年 | 392篇 |
1992年 | 400篇 |
1991年 | 262篇 |
1990年 | 308篇 |
1989年 | 293篇 |
1988年 | 254篇 |
1987年 | 203篇 |
1986年 | 225篇 |
1985年 | 276篇 |
1984年 | 256篇 |
1983年 | 104篇 |
1982年 | 215篇 |
1981年 | 337篇 |
1980年 | 341篇 |
1979年 | 220篇 |
1978年 | 259篇 |
1977年 | 173篇 |
1976年 | 133篇 |
1975年 | 99篇 |
1974年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
261.
262.
Multiderivations of Coxeter arrangements 总被引:3,自引:0,他引:3
Hiroaki Terao 《Inventiones Mathematicae》2002,148(3):659-674
Let V be an ℓ-dimensional Euclidean space. Let G⊂O(V) be a finite irreducible orthogonal reflection group. Let ? be the corresponding Coxeter arrangement. Let S be the algebra of polynomial functions on V. For H∈? choose α
H
∈V
* such that H=ker(α
H
). For each nonnegative integer m, define the derivation module D
(m)
(?)={θ∈Der
S
|θ(α
H
)∈Sα
m
H
}. The module is known to be a free S-module of rank ℓ by K. Saito (1975) for m=1 and L. Solomon-H. Terao (1998) for m=2. The main result of this paper is that this is the case for all m. Moreover we explicitly construct a basis for D
(m)
(?). Their degrees are all equal to mh/2 (when m is even) or are equal to ((m−1)h/2)+m
i
(1≤i≤ℓ) (when m is odd). Here m
1≤···≤m
ℓ are the exponents of G and h=m
ℓ+1 is the Coxeter number. The construction heavily uses the primitive derivation D which plays a central role in the theory of flat generators by K. Saito (or equivalently the Frobenius manifold structure
for the orbit space of G). Some new results concerning the primitive derivation D are obtained in the course of proof of the main result.
Oblatum 27-XI-2001 & 4-XII-2001?Published online: 18 February 2002 相似文献
263.
L. Pillier C. Moreau X. Mercier J.F. Pauwels P. Desgroux 《Applied physics. B, Lasers and optics》2002,74(4-5):427-434
Cavity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed
flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding
the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and
spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed
in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the
selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest
influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A–X (0–1) band of
NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of ±13%. NO absorption
in the flame was completely masked using the A–X (0–0) band. Finally, the prompt-NO mole fraction formed in a methane/air
flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques.
Received: 12 October / Revised version: 1 February 2002 / Published online: 14 March 2002 相似文献
264.
J. Limpert T. Gabler A. Liem H. Zellmer A. Tünnermann 《Applied physics. B, Lasers and optics》2002,74(2):191-195
In a fiber amplifier, spectral compression due to self-phase modulation is demonstrated for ultrashort pulses. We report the
generation of near-transform-limited picosecond pulses with peak powers of several kW at a repetition rate of 74 MHz and diffraction-limited
beam quality in a Yb-doped fiber amplifier when seeding with a negative chirped pulse.
Received: 17 September 2001 / Revised version: 22 November 2001 / Published online: 17 January 2002 相似文献
265.
The derivative expansion of the effective action is a perturbative development in derivatives of the fields. The expansion breaks down when some of the derivatives are too large. We show how to sum exactly the first and second derivatives and treat perturbatively derivatives higher than second. 相似文献
266.
Claire Cates Haulk John Drew Charles R. Johnson J. Hunter Tart 《Linear and Multilinear Algebra》1997,43(1):35-51
For a given n-by-n matrix A, we consider the set of matrices which commute with A and all of whose principal submatrices commute with the corresponding principal submatrices of A. The properties of this set are examined, with particular attention to its dimension. 相似文献
267.
相型同步启动时间的M/M/c排队系统 总被引:4,自引:0,他引:4
本文研究带有同步启动时间的M/M/c系统,其中启动时间是相型变量,给出了稳态和等待时间分布等结果。 相似文献
268.
Shu-Cheng Chang 《Mathematische Annalen》2002,324(3):465-490
In this paper, we consider the 2-dimensional local Calabi flow on a complete noncompact surface . Then, based on the Harnack-type estimate, we show the long-time existence and asymptotic convergence of a subsequence of
solutions of such a flow on with and bounded from above by a negative constant on a ball. For its applications, this will lead to the existence of extremal metrics
on a complete noncompact surface of finite topological type. In particular, there exists an extremal metric of nonconstant
Gaussian curvature on or
Received: 21 June 2001 / 18 January 2002 / Published online: 27 June 2002
Research supported in part by NSC and NCTS. 相似文献
269.
Summary. In this paper we are interested in two phase flow problems in porous media. We use a Dual Mesh Method to discretize this
problem with finite volume schemes. In a simplified case (elliptic - hyperbolic system) we prove the convergence of approximate
solutions to the exact solutions. We use the Dual Mesh Method in physically complex problems (heterogeneous cases with non
constant total mobility). We validate numerically the Dual Mesh Method on practical examples by computing error estimates
for different test-cases.
Received March 21, 1997 / Revised version received October 13, 1997 相似文献
270.
《Linear and Multilinear Algebra》2007,55(6):521-533
For each k≥ 0, those nonsingular matrices that transform the set of totally nonzero vectors with k sign variations into (respectively, onto) itself are studied. Necessary and sufficient conditions are provided. The cases k=0,1,2,n-3,n-2,n-1 are completely characterized. 相似文献