全文获取类型
收费全文 | 15540篇 |
免费 | 1375篇 |
国内免费 | 983篇 |
专业分类
化学 | 6773篇 |
晶体学 | 87篇 |
力学 | 1027篇 |
综合类 | 197篇 |
数学 | 3927篇 |
物理学 | 5887篇 |
出版年
2023年 | 136篇 |
2022年 | 210篇 |
2021年 | 366篇 |
2020年 | 325篇 |
2019年 | 337篇 |
2018年 | 332篇 |
2017年 | 380篇 |
2016年 | 414篇 |
2015年 | 353篇 |
2014年 | 590篇 |
2013年 | 1005篇 |
2012年 | 652篇 |
2011年 | 690篇 |
2010年 | 605篇 |
2009年 | 899篇 |
2008年 | 981篇 |
2007年 | 1009篇 |
2006年 | 889篇 |
2005年 | 657篇 |
2004年 | 623篇 |
2003年 | 596篇 |
2002年 | 614篇 |
2001年 | 529篇 |
2000年 | 489篇 |
1999年 | 414篇 |
1998年 | 421篇 |
1997年 | 276篇 |
1996年 | 222篇 |
1995年 | 205篇 |
1994年 | 171篇 |
1993年 | 185篇 |
1992年 | 261篇 |
1991年 | 149篇 |
1990年 | 111篇 |
1989年 | 94篇 |
1988年 | 100篇 |
1987年 | 100篇 |
1986年 | 81篇 |
1985年 | 77篇 |
1984年 | 84篇 |
1983年 | 48篇 |
1982年 | 101篇 |
1981年 | 174篇 |
1980年 | 185篇 |
1979年 | 181篇 |
1978年 | 166篇 |
1977年 | 103篇 |
1976年 | 108篇 |
1973年 | 76篇 |
1972年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
近年来,决定椭圆型方程系数反问题在地磁、地球物理、冶金和生物等实际问题上有着广泛的应用.本文讨论了二维的决定椭圆型方程系数反问题的数值求解方法.由误差平方和最小原则,这个反问题可化为一个变分问题,并进一步离散化为一个最优化问题,其目标函数依赖于要决定的方程系数.本文着重考察非线性共轭梯度法在此最优化问题数值计算中的表现,并与拟牛顿法作为对比.为了提高算法的效率我们适当选择加快收敛速度的预处理矩阵.同时还考察了线搜索方法的不同对优化算法的影响.数值实验的结果表明,非线性共轭梯度法在这类大规模优化问题中相对于拟牛顿法更有效. 相似文献
52.
Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR. 相似文献
53.
V. S. Gorelik P. P. Sverbil' A. B. Fadyushin V. V. Vasil'ev 《Journal of Russian Laser Research》2004,25(1):54-63
A possibility of application of semiconductor lasers of the visible range as exciting sources for Raman spectroscopy is studied. An experimental set-up for measuring Raman spectra of polycrystalline dielectrics and broad-gap semiconductors excited by a semiconductor laser with a wavelength of 640 nm was created. The conditions under which the spectral width of the lasing line of a semiconductor laser was within 10-3 cm-1 in the continuous mode with a power of 10 mW are realized. The characteristics of various types of exciting sources used in Raman spectroscopy are compared. The results of studies of the characteristic Raman spectra excited with a semiconductor laser in polycrystalline sulfur are presented. 相似文献
54.
55.
56.
M. A. Diniz-Ehrhardt M. A. Gomes-Ruggiero J. M. Martínez S. A. Santos 《Journal of Optimization Theory and Applications》2004,123(3):497-517
The spectral projected gradient method SPG is an algorithm for large-scale bound-constrained optimization introduced recently by Birgin, Martínez, and Raydan. It is based on the Raydan unconstrained generalization of the Barzilai-Borwein method for quadratics. The SPG algorithm turned out to be surprisingly effective for solving many large-scale minimization problems with box constraints. Therefore, it is natural to test its perfomance for solving the sub-problems that appear in nonlinear programming methods based on augmented Lagrangians. In this work, augmented Lagrangian methods which use SPG as the underlying convex-constraint solver are introduced (ALSPG) and the methods are tested in two sets of problems. First, a meaningful subset of large-scale nonlinearly constrained problems of the CUTE collection is solved and compared with the perfomance of LANCELOT. Second, a family of location problems in the minimax formulation is solved against the package FFSQP. 相似文献
57.
Lahcne Mezrag 《Mathematische Nachrichten》2004,266(1):60-67
In [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Ka?in cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
58.
A carousel is a dynamical system that describes the movement of an equilateral linkage in which the midpoint of each rod travels parallel to it. They are closely related to the floating body problem. We prove, using the work of Auerbach, that any figure that floats in equilibrium in every position is drawn by a carousel. Of special interest are such figures with rational perimetral density of the floating chords, which are then drawn by carousels. In particular, we prove that for some perimetral densities the only such figure is the circle, as the problem suggests. 相似文献
59.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
60.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献