全文获取类型
收费全文 | 249950篇 |
免费 | 2804篇 |
国内免费 | 869篇 |
专业分类
化学 | 124807篇 |
晶体学 | 3725篇 |
力学 | 10946篇 |
综合类 | 17篇 |
数学 | 34698篇 |
物理学 | 79430篇 |
出版年
2021年 | 1887篇 |
2020年 | 2125篇 |
2019年 | 2316篇 |
2018年 | 4245篇 |
2017年 | 4358篇 |
2016年 | 5232篇 |
2015年 | 3406篇 |
2014年 | 4677篇 |
2013年 | 11033篇 |
2012年 | 11316篇 |
2011年 | 12105篇 |
2010年 | 8292篇 |
2009年 | 7876篇 |
2008年 | 9534篇 |
2007年 | 9726篇 |
2006年 | 9260篇 |
2005年 | 11997篇 |
2004年 | 10907篇 |
2003年 | 8454篇 |
2002年 | 6499篇 |
2001年 | 7056篇 |
2000年 | 5391篇 |
1999年 | 4205篇 |
1998年 | 3335篇 |
1997年 | 3294篇 |
1996年 | 3099篇 |
1995年 | 2829篇 |
1994年 | 2712篇 |
1993年 | 2528篇 |
1992年 | 3005篇 |
1991年 | 2955篇 |
1990年 | 2864篇 |
1989年 | 2625篇 |
1988年 | 2660篇 |
1987年 | 2622篇 |
1986年 | 2439篇 |
1985年 | 3178篇 |
1984年 | 3417篇 |
1983年 | 2767篇 |
1982年 | 2932篇 |
1981年 | 2913篇 |
1980年 | 2775篇 |
1979年 | 2848篇 |
1978年 | 2934篇 |
1977年 | 2932篇 |
1976年 | 3038篇 |
1975年 | 2792篇 |
1974年 | 2736篇 |
1973年 | 2886篇 |
1972年 | 1832篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
152.
The problem of the stability of a heavy rigid body, bounded by the surface of an ellipsoid and with a cavity in the form of a coaxial ellipsoid, rolling along a straight line on a horizontal rough plane is investigated. It is shown that in the case of a body that is close to being dynamically symmetrical, parametric resonance always occurs leading to instability of the rolling. Each ellipsoid has its own “individual” resonance angular velocity. In the general case, regions in which the necessary stability conditions are satisfied can be distinguished in parameter space. The problem of calculating the resonance coefficient corresponding to instability for parametric resonance in a reversible third-order system is solved. 相似文献
153.
154.
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
155.
Summary Ductile deformation prior to brittle fracture in rocks causes fracture to take place with a time delay after the critical stress for fracture is reached, in the presence of an increasing load stress. We discuss the stability of a stochastic model of interactive earthquake occurrence under the influence of time delays resulting from the ductile process. A threshold for oscillatory behavior is found for large enough coupling and discrete time delays. The system is stable if the time delays are spread over a broad time interval, even for large coupling. 相似文献
156.
D. A. Tikhomirov O. S. Slyadevskaya A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1991,27(9):966-969
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991. 相似文献
157.
158.
I. L. Davies K. E. Markides M. L. Lee M. W. Raynor K. D. Bartle 《Journal of separation science》1989,12(4):193-207
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review. 相似文献
159.
160.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献