全文获取类型
收费全文 | 6932篇 |
免费 | 248篇 |
国内免费 | 45篇 |
专业分类
化学 | 4504篇 |
晶体学 | 46篇 |
力学 | 212篇 |
数学 | 1284篇 |
物理学 | 1179篇 |
出版年
2023年 | 34篇 |
2022年 | 82篇 |
2021年 | 120篇 |
2020年 | 123篇 |
2019年 | 137篇 |
2018年 | 134篇 |
2017年 | 136篇 |
2016年 | 210篇 |
2015年 | 217篇 |
2014年 | 213篇 |
2013年 | 422篇 |
2012年 | 490篇 |
2011年 | 502篇 |
2010年 | 318篇 |
2009年 | 284篇 |
2008年 | 381篇 |
2007年 | 381篇 |
2006年 | 374篇 |
2005年 | 340篇 |
2004年 | 279篇 |
2003年 | 248篇 |
2002年 | 197篇 |
2001年 | 115篇 |
2000年 | 96篇 |
1999年 | 75篇 |
1998年 | 60篇 |
1997年 | 54篇 |
1996年 | 59篇 |
1995年 | 41篇 |
1994年 | 53篇 |
1993年 | 31篇 |
1992年 | 41篇 |
1991年 | 55篇 |
1990年 | 52篇 |
1989年 | 50篇 |
1988年 | 45篇 |
1987年 | 38篇 |
1985年 | 45篇 |
1984年 | 67篇 |
1983年 | 33篇 |
1982年 | 43篇 |
1981年 | 36篇 |
1980年 | 40篇 |
1979年 | 31篇 |
1978年 | 33篇 |
1977年 | 44篇 |
1976年 | 31篇 |
1975年 | 30篇 |
1974年 | 31篇 |
1973年 | 28篇 |
排序方式: 共有7225条查询结果,搜索用时 31 毫秒
961.
We prove that each n-vertex plane graph with girth g≥4 admits a vertex coloring with at least ⌈n/2⌉+1 colors with no rainbow face, i.e., a face in which all vertices receive distinct colors. This proves a conjecture of
Ramamurthi and West. Moreover, we prove for plane graph with girth g≥5 that there is a vertex coloring with at least
if g is odd and
if g is even. The bounds are tight for all pairs of n and g with g≥4 and n≥5g/2−3.
* Supported in part by the Ministry of Science and Technology of Slovenia, Research Project Z1-3129 and by a postdoctoral
fellowship of PIMS.
** Institute for Theoretical Computer Science is supported by Ministry of Education of CzechR epublic as project LN00A056. 相似文献
962.
963.
We have found photoinduced second harmonic generation at wavelength 1064 nm during bicolor Nd:YAG laser coherent treatment of TeO2-ZnO and GeO2-PbO amorphous films. The maximally achieved second order susceptibility was equal to about 1.02 pm/V. Correlation of the induced second order susceptibility with local sample heating and induced birefringence may indicate an occurrence of local phase transitions from amorphous glass-like phase to non-centrosymmetry metastable phases. 相似文献
964.
Extensive measurements of macroscopic stress in a 2D Lennard-Jones glass, over a broad range of temperatures (T) and strain rates (γ), demonstrate a very significant decrease of the flowing stress with T, even much below the glass transition. A detailed analysis of the interplay between loading, thermal activation, and mechanical noise leads us to propose that over a broad (γ, T) region, the effect of temperature amounts to a mere lowering of the strains at which plastic events occur, while the athermal avalanche dynamics remains essentially unperturbed. Up to the vicinity of the glass transition, temperature is then shown to correct the athermal stress by a (negative) additive contribution which presents a universal form, thus bringing support to and extending an expression proposed by Johnson and Samwer [Phys. Rev. Lett. 95, 195501 (2005)]. 相似文献
965.
Kai Zhou Mustafa R. Kılınç Xi Chen Nikolaos V. Sahinidis 《Journal of Global Optimization》2018,70(3):497-516
Solving mixed-integer nonlinear programming (MINLP) problems to optimality is a NP-hard problem, for which many deterministic global optimization algorithms and solvers have been recently developed. MINLPs can be relaxed in various ways, including via mixed-integer linear programming (MIP), nonlinear programming, and linear programming. There is a tradeoff between the quality of the bounds and CPU time requirements of these relaxations. Unfortunately, these tradeoffs are problem-dependent and cannot be predicted beforehand. This paper proposes a new dynamic strategy for activating and deactivating MIP relaxations in various stages of a branch-and-bound algorithm. The primary contribution of the proposed strategy is that it does not use meta-parameters, thus avoiding parameter tuning. Additionally, this paper proposes a strategy that capitalizes on the availability of parallel MIP solver technology to exploit multicore computing hardware while solving MINLPs. Computational tests for various benchmark libraries reveal that our MIP activation strategy works efficiently in single-core and multicore environments. 相似文献
966.
In this paper we give irrationality results for numbers of the form where the numbers an behave like a geometric progression for a while. The method is elementary, not using differentiation or integration. In particular, we derive elementary proofs of the irrationality of π and em for Gaussian integers m≠0. 相似文献
967.
Effective algebraic degeneracy 总被引:1,自引:0,他引:1
We show that for every smooth projective hypersurface X⊂ℙ
n+1 of degree d and of arbitrary dimension n
≥2, if X is generic, then there exists a proper algebraic subvariety Y
⊊
X such that every nonconstant entire holomorphic curve f
:ℂ→X has image f(ℂ) which lies in Y, as soon as its degree satisfies the effective lower bound
d\geqslant 2n5d\geqslant 2^{n^{5}}
. 相似文献
968.
For k, d?2, a Bethe tree is a rooted tree with k levels which the root vertex has degree d, the vertices from level 2 to k-1 have degree d+1 and the vertices at the level k are pendent vertices. So et al, using a theorem by Ky Fan have obtained both upper and lower bounds for the Laplacian energy of bipartite graphs. We shall employ the above mentioned theorem to obtain new and improved bounds for the Laplacian energy in the case of Bethe trees. 相似文献
969.
Mohamed Saleh Rogelio Oliva Christian Erik Kampmann Pål I. Davidsen 《European Journal of Operational Research》2010
Formal tools to link system dynamics model’s structure to the system modes of behavior have recently become available. In this paper, we aim to expand the use of these tools to perform the model’s policy analysis in a more structured and formal way than the exhaustive exploratory approaches used to date. We consider how a policy intervention (a parameter change) affects a particular behavior mode by affecting the gains of particular feedback loops as well as how it affects the presence of that mode in the variable of interest. The paper demonstrates the utility of considering both of these aspects since the analysis provides an assessment of the overall impact of a policy on a variable and explains why the impact occurs in terms of structural changes in the model. Particularly in the context of larger models, this method enables a much more efficient search for leverage policies, by ranking the influence of each model parameter without the need for multiple simulation experiments. 相似文献
970.
Berna Bülbül Mustafa Gülsu Mehmet Sezer 《Numerical Methods for Partial Differential Equations》2010,26(5):1006-1020
The aim of this article is to present an efficient numerical procedure for solving nonlinear integro‐differential equations. Our method depends mainly on a Taylor expansion approach. This method transforms the integro‐differential equation and the given conditions into the matrix equation which corresponds to a system of nonlinear algebraic equations with unkown Taylor coefficients. The reliability and efficiency of the proposed scheme are demonstrated by some numerical experiments and performed on the computer program written in Maple10. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010 相似文献