全文获取类型
收费全文 | 299369篇 |
免费 | 3390篇 |
国内免费 | 1688篇 |
专业分类
化学 | 147741篇 |
晶体学 | 3564篇 |
力学 | 15529篇 |
综合类 | 61篇 |
数学 | 56509篇 |
物理学 | 81043篇 |
出版年
2020年 | 1792篇 |
2019年 | 1936篇 |
2018年 | 12690篇 |
2017年 | 12586篇 |
2016年 | 9690篇 |
2015年 | 3355篇 |
2014年 | 3991篇 |
2013年 | 9592篇 |
2012年 | 11511篇 |
2011年 | 19785篇 |
2010年 | 12197篇 |
2009年 | 12402篇 |
2008年 | 15360篇 |
2007年 | 17535篇 |
2006年 | 8828篇 |
2005年 | 9119篇 |
2004年 | 8493篇 |
2003年 | 8067篇 |
2002年 | 7059篇 |
2001年 | 7002篇 |
2000年 | 5398篇 |
1999年 | 3852篇 |
1998年 | 3256篇 |
1997年 | 3178篇 |
1996年 | 3246篇 |
1995年 | 2775篇 |
1994年 | 2816篇 |
1993年 | 2711篇 |
1992年 | 2930篇 |
1991年 | 2938篇 |
1990年 | 2728篇 |
1989年 | 2649篇 |
1988年 | 2618篇 |
1987年 | 2551篇 |
1986年 | 2558篇 |
1985年 | 3358篇 |
1984年 | 3411篇 |
1983年 | 2859篇 |
1982年 | 3101篇 |
1981年 | 2838篇 |
1980年 | 2667篇 |
1979年 | 2840篇 |
1978年 | 3070篇 |
1977年 | 3064篇 |
1976年 | 3094篇 |
1975年 | 2830篇 |
1974年 | 2945篇 |
1973年 | 3000篇 |
1972年 | 2350篇 |
1971年 | 1853篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
932.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
933.
Starting with a partition of a rectangular box into subboxes, it is shown how to construct a natural tetrahedral (type-4) partition and associated trivariate C 1 quintic polynomial spline spaces with a variety of useful properties, including stable local bases and full approximation power. It is also shown how the spaces can be used to solve certain Hermite and Lagrange interpolation problems. 相似文献
934.
Lá szló L. Stachó Borut Zalar 《Proceedings of the American Mathematical Society》2004,132(10):3019-3025
We prove that every JB* triple with rank one bicircular projection is a direct sum of two ideals, one of which is isometrically isomorphic to a Hilbert space.
935.
In this paper a predictive control strategy is applied to a periodic-review dynamic inventory system with deteriorating items.
Given the current inventory level, we determine the optimal production rates to be implemented at the beginning of each of
the following periods over the control horizon. The effectiveness of this approach is the use of future information of the
inventory target level and the desired production rate, which are available, along the fixed horizon. The deterioration coefficient
may be known or unknown and both cases are considered. In the case where it is unknown, the self-tuning predictive control
is applied. The proposed control algorithms are illustrated by simulations. 相似文献
936.
L-Curve and Curvature Bounds for Tikhonov Regularization 总被引:1,自引:0,他引:1
The L-curve is a popular aid for determining a suitable value of the regularization parameter when solving linear discrete ill-posed problems by Tikhonov regularization. However, the computational effort required to determine the L-curve and its curvature can be prohibitive for large-scale problems. Recently, inexpensively computable approximations of the L-curve and its curvature, referred to as the L-ribbon and the curvature-ribbon, respectively, were proposed for the case when the regularization operator is the identity matrix. This note discusses the computation and performance of the L- and curvature-ribbons when the regularization operator is an invertible matrix. 相似文献
937.
Using a high resolution Raman spectrometer, we have measured Ar-broadening coefficients in the ν2Q branch of C2H2 for 22 lines at 295 K, 20 lines at 174 K, and 16 lines at 134 K. These lines with J values ranging from 1 to 23 are located in the spectral range 1970.9-1974.3 cm−1. The collisional widths are obtained by fitting each spectral line with a Rautian profile. The resulting broadening coefficients are compared with theoretical values arising from close coupling and coupled states calculations. A satisfactory agreement is obtained at room as well as at low temperatures, especially for odd J lines. By comparing broadening coefficients at 295, 174, and 134 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally, and theoretically. 相似文献
938.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
939.
We study quantum antiferromagnetism on the highly frustrated planar pyrochlore lattice, also known as the square lattice with crossings. The quantum Heisenberg antiferromagnet on this lattice is of interest as a two-dimensional analogue of the pyrochlore lattice magnet. By combining several approaches we conclude that this system is most likely ordered for all values of spin, S, with a two-fold degenerate valence-bond solid being the ground state for small S. We show next that the Ising antiferromagnet with a weak four-spin exchange, equivalent to square ice with the leading quantum dynamics, exhibits analogous plaquette order. As a byproduct of this analysis we obtain, in the system of weakly coupled ice planes, a sliding phase with XY symmetry; at intermediate couplings, long range “anti-ferroelectric” order is stabilized. 相似文献
940.
Journal of Statistical Physics - 相似文献