全文获取类型
收费全文 | 3339篇 |
免费 | 395篇 |
国内免费 | 292篇 |
专业分类
化学 | 655篇 |
晶体学 | 36篇 |
力学 | 644篇 |
综合类 | 53篇 |
数学 | 1017篇 |
物理学 | 1621篇 |
出版年
2024年 | 5篇 |
2023年 | 55篇 |
2022年 | 46篇 |
2021年 | 83篇 |
2020年 | 52篇 |
2019年 | 58篇 |
2018年 | 76篇 |
2017年 | 85篇 |
2016年 | 101篇 |
2015年 | 101篇 |
2014年 | 122篇 |
2013年 | 359篇 |
2012年 | 174篇 |
2011年 | 217篇 |
2010年 | 162篇 |
2009年 | 241篇 |
2008年 | 240篇 |
2007年 | 243篇 |
2006年 | 202篇 |
2005年 | 166篇 |
2004年 | 144篇 |
2003年 | 141篇 |
2002年 | 117篇 |
2001年 | 107篇 |
2000年 | 92篇 |
1999年 | 87篇 |
1998年 | 85篇 |
1997年 | 60篇 |
1996年 | 46篇 |
1995年 | 48篇 |
1994年 | 56篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有4026条查询结果,搜索用时 775 毫秒
1.
We propose a conjecture on the relative twist formula of l-adic sheaves, which can be viewed as a generalization of Kato—Saito's conjecture. We verify this conjecture under some transversal assumptions. We also define a relative cohomological characteristic class and prove that its formation is compatible with proper push-forward. A conjectural relation is also given between the relative twist formula and the relative cohomological characteristic class. 相似文献
2.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming. 相似文献
3.
左手介质椭圆光波导基模传播特性 总被引:1,自引:0,他引:1
在椭圆柱坐标系中,采用分离变量方法,得出了左手介质椭圆光波导本征方程的近似解,通过数值计算,分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响,并将左介质光波导与右手介质光波导基模特性进行对比,得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论. 相似文献
4.
Masashi Ohkawa Yuki Shirai Takeshi Goto Seishi Sekine Takashi Sato 《Fiber and Integrated Optics》2002,21(2):105-113
In this paper, a silicon-based integrated optic pressure sensor using an intermodal interference between the fundamental TM-like and TE-like modes is described. The sensor consists of a micromachined rectangular diaphragm and a straight polystyrene optical waveguide passing over the diaphragm. Its sensitivity is theoretically known to be strongly dependent on the position of the waveguide over the diaphragm. To experimentally investigate such dependence, we fabricated a sensor with a 1.2 mm ×10 mm ×20 μm diaphragm, over which waveguides were placed at 50 μm intervals. The measured phase sensitivity was 98 mrad/kPa for the waveguide nearest to the diaphragm edge. The measurement was also carried out for the other waveguides. As theoretically expected, the largest sensitivity was obtained for the waveguide nearest to the edge. 相似文献
5.
6.
7.
We introduce the notion of an invariant of characteristics for a system of first-order partial differential equations. We prove that the existence of invariants is connected with passiveness of some systems. We describe a few methods for construction of new invariants from those already known. We give a scheme for application of the invariants to reduction and integration of systems of partial differential equations. As an application we consider the equation of gas dynamics. 相似文献
8.
Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the
directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent
and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite
liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are
presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher
than that of similar structures developed on a “smooth” substrate.
Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 4, pp. 507–512, July–August, 1997. 相似文献
9.
对于那些由代数微分方程描述的具有输入输出关系的非线性控制系统,本文采用两种方法讨论了其最小实现问题:一种方法是直接计算系统的特征列;另一种方法则采用了本原元定理.两种方法给出的最小实现所需的状态变量最小数目是相等的.文中的大量代数与微分运算则可利用数学机械化来完成 相似文献
10.