全文获取类型
收费全文 | 14614篇 |
免费 | 1077篇 |
国内免费 | 1120篇 |
专业分类
化学 | 1105篇 |
晶体学 | 9篇 |
力学 | 718篇 |
综合类 | 148篇 |
数学 | 3723篇 |
物理学 | 3234篇 |
综合类 | 7874篇 |
出版年
2024年 | 31篇 |
2023年 | 73篇 |
2022年 | 194篇 |
2021年 | 170篇 |
2020年 | 251篇 |
2019年 | 271篇 |
2018年 | 260篇 |
2017年 | 396篇 |
2016年 | 394篇 |
2015年 | 396篇 |
2014年 | 747篇 |
2013年 | 750篇 |
2012年 | 791篇 |
2011年 | 867篇 |
2010年 | 716篇 |
2009年 | 946篇 |
2008年 | 1055篇 |
2007年 | 1250篇 |
2006年 | 1103篇 |
2005年 | 957篇 |
2004年 | 845篇 |
2003年 | 712篇 |
2002年 | 613篇 |
2001年 | 511篇 |
2000年 | 452篇 |
1999年 | 393篇 |
1998年 | 331篇 |
1997年 | 288篇 |
1996年 | 191篇 |
1995年 | 150篇 |
1994年 | 139篇 |
1993年 | 90篇 |
1992年 | 73篇 |
1991年 | 67篇 |
1990年 | 53篇 |
1989年 | 50篇 |
1988年 | 67篇 |
1987年 | 38篇 |
1986年 | 21篇 |
1985年 | 42篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1957年 | 3篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Frictionless indentation responses of transversely isotropic piezoelectric film/rigid substrate systems under circular cylindrical indenter (i.e., punch), conical indenter (i.e., cone), and spherical indenter (i.e., sphere) are investigated. Both insulating and conducting indenters are considered. The technique of Hankel transformation is employed to derive the corresponding dual integral equations for the mixed boundary value indentation problems. For the two limiting cases of infinitely thick and infinitely thin piezoelectric films, closed-form solutions are obtained. For piezoelectric films of finite thickness, a numerical method is constructed to solve the dual integral equations and semi-empirical models having only two unknown parameters are proposed for the responses of indentation force, electric charge and electric potential, and contact radius. With the two parameters inferred from the numerical results, the semi-empirical formulae are found to provide good estimates of the indentation responses for the two limiting cases of infinitely thick and thin piezoelectric films, as well as those in between. The inferred parameters in the proposed semi-empirical formulae for normalized indentation force and electric charge are checked against four different piezoelectric materials and are found to be insensitive to the selection of piezoelectric materials. It is believed that the proposed semi-empirical indentation formulae are useful in developing experimental indentation techniques to extract the material properties of piezoelectric films. 相似文献
122.
A hybrid technique using constraint programming and linear programming is applied to the problem of scheduling with earliness and tardiness costs. The linear model maintains a set of relaxed optimal start times which are used to guide the constraint programming search heuristic. In addition, the constraint programming problem model employs the strong constraint propagation techniques responsible for many of the advances in constraint programming for scheduling in the past few years. Empirical results validate our approach and show, in particular, that creating and solving a subproblem containing only the activities with direct impact on the cost function and then using this solution in the main search, significantly increases the number of problems that can be solved to optimality while significantly decreasing the search time. 相似文献
123.
设n为正整数,f(n)是可以用1以及任意多个 号和×号(以及括号)来表示n时所用1的最少的个数.本文确定了n在若干情形时f(n)的值,改进了参考文献的部分结果,并提出了若干新的猜想. 相似文献
124.
Michaël Lejeune Andrea Valsesia Martin Kormunda Pascal Colpo François Rossi 《Surface science》2005,583(1):L142
In this work, chemically and topographically nanopatterned surfaces were produced by a top-down processing approach for biosensing devices. The nanopatterning was the result of the combination of plasma polymerisation (pp) of biofunctional materials and colloidal lithography techniques. The morphological and chemical properties induced by the plasma deposition-etching treatment were characterised by optical method combining ellipsometry and Fourier Transform Infrared spectroscopy studies. This method supported by atomic force microscopy measurements, allowed the full optical characterization of each step of the top-down process. The optical characterization of the end-up nanopatterned samples demonstrated that the chosen process is able to produce well-defined nanostructured surfaces with controlled chemical and morphological properties. 相似文献
125.
In this paper, the authors obtain sharp upper and lower hounds for the heat kernel associated with Jacobi transform, and get some analogues of Hardy‘s Theorem for Jacobi transform by using the sharp estimate of the heat kernel. 相似文献
126.
127.
128.
Radon变换和衰减Radon变换的分析研究 总被引:1,自引:0,他引:1
衰减Radon变换出现在单光子放射型计算机层析成像中。本文首先回顾和研究了Radon变换和衰减Radon变换及其反演的有关结论,进而提出了Tretiak-Metz结果的一种新证明方法,对于一般对象,本文用变换方法非滤子背投影法导出了衰减Radon变换的反演公式。 相似文献
129.
130.
This article concerns the existence of global smooth solution for scalar conservation laws with degenerate viscosity in 2-dimensional space. The analysis is based on successive approximation and maximum principle. 相似文献