全文获取类型
收费全文 | 518799篇 |
免费 | 4473篇 |
国内免费 | 1906篇 |
专业分类
化学 | 262043篇 |
晶体学 | 7659篇 |
力学 | 25335篇 |
综合类 | 68篇 |
数学 | 72563篇 |
物理学 | 157510篇 |
出版年
2020年 | 3527篇 |
2019年 | 3804篇 |
2018年 | 12030篇 |
2017年 | 12709篇 |
2016年 | 10647篇 |
2015年 | 5258篇 |
2014年 | 7213篇 |
2013年 | 18082篇 |
2012年 | 17603篇 |
2011年 | 27105篇 |
2010年 | 17933篇 |
2009年 | 17678篇 |
2008年 | 24557篇 |
2007年 | 27499篇 |
2006年 | 15712篇 |
2005年 | 19065篇 |
2004年 | 15438篇 |
2003年 | 14242篇 |
2002年 | 12535篇 |
2001年 | 12641篇 |
2000年 | 9935篇 |
1999年 | 7278篇 |
1998年 | 6287篇 |
1997年 | 6270篇 |
1996年 | 6141篇 |
1995年 | 5517篇 |
1994年 | 5722篇 |
1993年 | 5285篇 |
1992年 | 5947篇 |
1991年 | 5947篇 |
1990年 | 5728篇 |
1989年 | 5593篇 |
1988年 | 5616篇 |
1987年 | 5417篇 |
1986年 | 5272篇 |
1985年 | 6992篇 |
1984年 | 7303篇 |
1983年 | 6137篇 |
1982年 | 6463篇 |
1981年 | 6166篇 |
1980年 | 5990篇 |
1979年 | 6158篇 |
1978年 | 6627篇 |
1977年 | 6486篇 |
1976年 | 6583篇 |
1975年 | 6033篇 |
1974年 | 6230篇 |
1973年 | 6403篇 |
1972年 | 4711篇 |
1971年 | 3866篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
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
82.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
83.
In a twisted nematic liquid crystal cell we report and study the self-transparency effect induced by the creation of an isotropic droplet. A simple theoretical model is presented and good agreement with experimental data is found. In a two beams configuration transistor-like behavior is observed and theoretically discussed. 相似文献
84.
85.
E. V. Zakharov A. G. Davydov Yu. V. Pimenov G. M. Tikhonov 《Computational Mathematics and Modeling》1991,2(1):79-84
Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 119–127. 相似文献
86.
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
87.
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
88.
89.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
90.
The direct regioselective C–H arylation of 3-methoxythiophene and 3,4-ethylenedioxythiophene (EDOT) was performed successfully under ‘Heck-type’ experimental conditions. This novel synthetic methodology has been used to prepare in a more simple way a series of oligothiophenes interesting for the electronic industry to build new synthetic organic materials. 相似文献