全文获取类型
收费全文 | 20838篇 |
免费 | 1647篇 |
国内免费 | 1156篇 |
专业分类
化学 | 2417篇 |
晶体学 | 59篇 |
力学 | 2030篇 |
综合类 | 200篇 |
数学 | 15435篇 |
物理学 | 3500篇 |
出版年
2024年 | 41篇 |
2023年 | 208篇 |
2022年 | 313篇 |
2021年 | 348篇 |
2020年 | 512篇 |
2019年 | 519篇 |
2018年 | 533篇 |
2017年 | 560篇 |
2016年 | 575篇 |
2015年 | 447篇 |
2014年 | 858篇 |
2013年 | 1782篇 |
2012年 | 921篇 |
2011年 | 1083篇 |
2010年 | 932篇 |
2009年 | 1264篇 |
2008年 | 1332篇 |
2007年 | 1406篇 |
2006年 | 1223篇 |
2005年 | 998篇 |
2004年 | 918篇 |
2003年 | 945篇 |
2002年 | 795篇 |
2001年 | 655篇 |
2000年 | 651篇 |
1999年 | 574篇 |
1998年 | 508篇 |
1997年 | 480篇 |
1996年 | 343篇 |
1995年 | 301篇 |
1994年 | 230篇 |
1993年 | 189篇 |
1992年 | 181篇 |
1991年 | 170篇 |
1990年 | 112篇 |
1989年 | 60篇 |
1988年 | 69篇 |
1987年 | 70篇 |
1986年 | 69篇 |
1985年 | 91篇 |
1984年 | 79篇 |
1983年 | 47篇 |
1982年 | 52篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 33篇 |
1978年 | 21篇 |
1977年 | 25篇 |
1976年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
The satisfiability (SAT) problem is a core problem in computer science. Existing studies have shown that most industrial SAT instances can be effectively solved by modern SAT solvers while random SAT instances cannot. It is believed that the structural characteristics of different SAT formula classes are the reasons behind this difference. In this paper, we study the structural properties of propositional formulas in conjunctive normal form (CNF) by the principle of structural entropy of formulas. First, we used structural entropy to measure the complex structure of a formula and found that the difficulty solving the formula is related to the structural entropy of the formula. The smaller the compressing information of a formula, the more difficult it is to solve the formula. Secondly, we proposed a -approximation strategy to approximate the structural entropy of large formulas. The experimental results showed that the proposed strategy can effectively approximate the structural entropy of the original formula and that the approximation ratio is more than 92%. Finally, we analyzed the structural properties of a formula in the solution process and found that a local search solver tends to select variables in different communities to perform the next round of searches during a search and that the structural entropy of a variable affects the probability of the variable being flipped. By using these conclusions, we also proposed an initial candidate solution generation strategy for a local search for SAT, and the experimental results showed that this strategy effectively improves the performance of the solvers CCAsat and Sparrow2011 when incorporated into these two solvers. 相似文献
12.
13.
14.
文[1]提出了两个DEA的逆问题,并用搜索法来解.而本文根据所证的定理,对每个问题一般只要解二、三个线性规划问题就能得到答案. 相似文献
15.
It is proved that for any integerk≥ 54 000, there isN
k
>0 depending onk only such that every even integer ≥N
k
is a sum of two odd prime numbers andk powers of 2.
Project partially supported by RGC Research Grant (No.HKU 7122/97P) and Post-Doctoral Fellowship of the University of Hong
Kong. 相似文献
16.
Ji-Ming Peng 《Mathematical Programming》1997,78(3):347-355
In this paper we propose a class of merit functions for variational inequality problems (VI). Through these merit functions,
the variational inequality problem is cast as unconstrained minimization problem. We estimate the growth rate of these merit
functions and give conditions under which the stationary points of these functions are the solutions of VI.
This work was supported by the state key project “Scientific and Engineering Computing”. 相似文献
17.
本文给出了混合型多项式Hammerstein积分方程正解的迭代求法,并将所得结果应用到二阶非线性常微分方程的边值问题 相似文献
18.
J.V.P. de OliveiraA.V. Cardona M.T. VilhenaR.C. Barros 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,73(1):55-62
We describe a semi-analytical numerical method for coherent isotropic scattering time-dependent radiative transfer problems in slab geometry. This numerical method is based on a combination of two classes of numerical methods: the spectral methods and the Laplace transform (LTSN) methods applied to the radiative transfer equation in the discrete ordinates (SN) formulation. The basic idea is to use the essence of the spectral methods and expand the intensity of radiation in a truncated series of Laguerre polynomials in the time variable and then solve recursively the resulting set of “time-independent” SN problems by using the LTSN method. We show some numerical experiments for a typical model problem. 相似文献
19.
Lin Surong 《Annals of Differential Equations》2006,22(4):517-523
The singularly perturbed boundary value problem for nonlinear higher order ordinary differential equation involving two small parameters has been considered. Under appropriate assumptions, for the three cases:ε/μ2→0(μ→0),μ2/ε→0 (ε→0) andε=μ2, the uniformly valid asymptotic solution is obtained by using the expansion method of two small parameters and the theory of differential inequality. 相似文献
20.