全文获取类型
收费全文 | 4132篇 |
免费 | 567篇 |
国内免费 | 297篇 |
专业分类
化学 | 981篇 |
晶体学 | 40篇 |
力学 | 519篇 |
综合类 | 144篇 |
数学 | 1279篇 |
物理学 | 2033篇 |
出版年
2023年 | 43篇 |
2022年 | 63篇 |
2021年 | 110篇 |
2020年 | 95篇 |
2019年 | 97篇 |
2018年 | 102篇 |
2017年 | 151篇 |
2016年 | 177篇 |
2015年 | 137篇 |
2014年 | 205篇 |
2013年 | 279篇 |
2012年 | 231篇 |
2011年 | 242篇 |
2010年 | 190篇 |
2009年 | 254篇 |
2008年 | 273篇 |
2007年 | 271篇 |
2006年 | 279篇 |
2005年 | 230篇 |
2004年 | 208篇 |
2003年 | 180篇 |
2002年 | 170篇 |
2001年 | 148篇 |
2000年 | 121篇 |
1999年 | 99篇 |
1998年 | 92篇 |
1997年 | 92篇 |
1996年 | 65篇 |
1995年 | 68篇 |
1994年 | 61篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 24篇 |
1988年 | 21篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有4996条查询结果,搜索用时 15 毫秒
991.
联合击中击不中变换相关器 总被引:9,自引:3,他引:6
将联合击中击 中变换相关器用于二值图像的目标识别。与常用的联合变换相关器相比,联合击中击不中变换相关器对联合变换相关器输入图像和参考图像进行互补编码。编码的目的在于通过联合变换相关器来一步实现形态学中的击中击不中变换。 相似文献
992.
993.
R. T. Tagiyeva 《Pramana》2004,63(3):633-641
Localized magnetic polaritons are investigated in the systems consisting of two magnetic superlattices, coupled by a ferromagnetic
contact layer. The general dispersion relation for localized magnetic polaritons are derived in the framework of the electromagnetic
wave theory in the Voigt geometry by the ‘transfer’ matrix method. The numerical calculations were carried out for different
parameters of the superlattices and contact layer and then discussed. 相似文献
994.
Hiroo Kanamori 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(7):297
Earthquakes exhibit diverse characteristics. Most shallow earthquakes are “brittle” in the sense that they excite seismic waves efficiently. However, some earthquakes are slow, as characterized by tsunami earthquakes and even slower events without any obvious seismic radiation. Also, some earthquakes, like the 1994 Bolivian deep earthquake, involved a large amount of fracture and thermal energy and may be more appropriately called a thermal event, rather than an earthquake. Some earthquakes are caused by processes other than faulting, such as landslides. This diversity can be best understood in terms of the difference in the partition of the released potential energy to radiated, fracture, and thermal energies during an earthquake. This approach requires detailed studies on quantification of earthquakes and estimation of various kinds of energies involved in earthquake processes. This paper reviews the progress in this field from historical and personal points of view and discusses its implications for earthquake damage mitigation. 相似文献
995.
N. G. Semaltianos A. De Rossi B. Vinter V. Berger M. Calligaro V. Ortiz 《Optics & Laser Technology》2004,36(8):669-676
AlGaAs-based quantum well laser structures with third-order waveguide mode emission at 775 nm are a promising route toward compact twin-photon sources at 1.55 μm based on the principle of modal phase matching between the pumping frequency and fundamental modes at half frequency in III–V semiconductor waveguides. Following the demonstration and characterization of an optically pumped third-order mode semiconductor laser, in this paper we present data of the corresponding structure under conditions of electrical pumping. By pumping electrically and optically the same sample made for current injection, identical transverse far-field angular laser mode profiles are measured and with very low parasitic losses. Although they do not follow the third-order mode emission pattern as it is expected, however this means that the different way of pumping, that of the electrical one as compared to optical pumping is not responsible for the absence of third-order mode emission. Furthermore, since the undoped optically pumped laser sample correctly emits on the third-order mode, it is concluded that the cladding layers of the structure still need to be optimized in doping and thickness, in order to reduce the internal losses for the third-order mode. 相似文献
996.
Two-dimensional cellular automata 总被引:11,自引:0,他引:11
A largely phenomenological study of two-dimensional cellular automata is reported. Qualitative classes of behavior similar to those in one-dimensional cellular automata are found. Growth from simple seeds in two-dimensiona! cellular automata can produce patterns with complicated boundaries, characterized by a variety of growth dimensions. Evolution from disordered states can give domains with boundaries that execute effectively continuous motions. Some global properties of cellular automata can be described by entropies and Lyapunov exponents. Others are undecidable.This work was supported in part by the U.S. Office of Naval Research under Contract No. N00014-80-C-0657. 相似文献
997.
998.
D. Magos 《Journal of Global Optimization》1996,8(1):35-48
Tabu Search is a very effective method for approximately solving hard combinatorial problems. In the current work we implement Tabu Search for solving the Planar Three-Index Assignment Problem. The problem deals with finding the minimum cost assignment between elements of three distinct sets demanding that every pair of elements, each representing a different set, appears in the same solution exactly once. The solutions of the problems correspond to Latin squares. These structures form the basis of the move generation mechanism employed by the Tabu Search procedures. Standard Tabu Search ideas such as candidate move list, variable tabu list size, and frequency-based memory are tested. Computational results for a range of problems of varying dimensions are presented. 相似文献
999.
1000.
回归系数的Bayes估计与最小二乘估计的相对效率 总被引:3,自引:0,他引:3
考察在错误指定在先验假定下的回归系数的Bayes估计(BE),并将其与最小二乘估计(LSE)进行比较,对BE与LSE的两种新的相对效率导出了它们的上下界。 相似文献