全文获取类型
收费全文 | 521029篇 |
免费 | 6055篇 |
国内免费 | 1687篇 |
专业分类
化学 | 265645篇 |
晶体学 | 7486篇 |
力学 | 24392篇 |
综合类 | 14篇 |
数学 | 72580篇 |
物理学 | 158654篇 |
出版年
2020年 | 2829篇 |
2019年 | 2810篇 |
2018年 | 11501篇 |
2017年 | 12375篇 |
2016年 | 9440篇 |
2015年 | 5546篇 |
2014年 | 6347篇 |
2013年 | 19561篇 |
2012年 | 19060篇 |
2011年 | 30308篇 |
2010年 | 18640篇 |
2009年 | 18603篇 |
2008年 | 27058篇 |
2007年 | 30464篇 |
2006年 | 17073篇 |
2005年 | 22387篇 |
2004年 | 17340篇 |
2003年 | 15333篇 |
2002年 | 13213篇 |
2001年 | 13795篇 |
2000年 | 10778篇 |
1999年 | 8300篇 |
1998年 | 6632篇 |
1997年 | 6449篇 |
1996年 | 6579篇 |
1995年 | 5965篇 |
1994年 | 5590篇 |
1993年 | 5313篇 |
1992年 | 5951篇 |
1991年 | 5814篇 |
1990年 | 5352篇 |
1989年 | 5219篇 |
1988年 | 5516篇 |
1987年 | 5125篇 |
1986年 | 4946篇 |
1985年 | 7202篇 |
1984年 | 7244篇 |
1983年 | 5903篇 |
1982年 | 6357篇 |
1981年 | 6300篇 |
1980年 | 6090篇 |
1979年 | 6176篇 |
1978年 | 6240篇 |
1977年 | 6120篇 |
1976年 | 6049篇 |
1975年 | 5918篇 |
1974年 | 5716篇 |
1973年 | 5973篇 |
1972年 | 3467篇 |
1971年 | 2481篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
We present a new approach to study the convergence of Newton's method in Banach spaces, which relax the conditions appearing in the usual studies. The approach is based on the bound required for the second derivative of the operator involved. An application to a nonlinear integral equation is presented. 相似文献
282.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
283.
A comprehensive study of the excited electronic states of HCl is reported. Using resonance enhanced multiphoton ionization ((2 + 1) REMPI) and time-of-flight mass spectrometry (TOFMS) over 120 band systems are analyzed. Supersonic jet techniques are used to prepare rotationally cold species for laser spectroscopy in the 77 000 to 96 000 cm−1 region. At least 50 new electronic states are characterized as well as several features only tentatively assigned previously. A long vibrational progression consisting of 29 vibrational levels of the deeply bound V1Σ+(0+) valence/ion-pair state is studied. We also extend the identification and analysis to high vibrational levels of low-lying Rydberg states. The assignments of [2Πi] Rydberg state complexes are evaluated in terms of spin-orbit coupling and united-atom calculations. In several band systems, the spectra exhibit anomalous rotational line intensities and broadened linewidths which are consistent with predissociation. Multiphoton ionization with mass spectrometry permits the investigation of isotope effects as well as the appearance of fragment species associated with repulsive potential curves. 相似文献
284.
In the following we find all of the three-dimensional flat spacetimes which are static and rotationally symmetric. 相似文献
285.
V. De Sabbata C. Sivaram H.-H. v. Borzeszkowski H.-J. Treder 《Annalen der Physik》1991,503(7):497-502
It is shown that in gravitational theories with torsion one is led to commutation rules corresponding to Landau-Peierls type uncertainty relations. 相似文献
286.
287.
We study a site analogue of directed percolation. Random trajectories are generated and their critical behavior is studied. The critical behavior corresponds to that of simple percolation in some of the parameter space, but elsewhere the exponents reveal new universality classes. As a byproduct, we use the model to make an improved estimate of the percolation hull exponents and to calculate the site percolation probability for the square lattice. 相似文献
288.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
289.
290.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献