全文获取类型
收费全文 | 538443篇 |
免费 | 5357篇 |
国内免费 | 1949篇 |
专业分类
化学 | 269693篇 |
晶体学 | 7678篇 |
力学 | 26663篇 |
综合类 | 11篇 |
数学 | 84985篇 |
物理学 | 156719篇 |
出版年
2021年 | 3150篇 |
2020年 | 3554篇 |
2019年 | 3750篇 |
2018年 | 14192篇 |
2017年 | 13867篇 |
2016年 | 12748篇 |
2015年 | 5869篇 |
2014年 | 7659篇 |
2013年 | 21312篇 |
2012年 | 19585篇 |
2011年 | 29411篇 |
2010年 | 18071篇 |
2009年 | 18330篇 |
2008年 | 24059篇 |
2007年 | 26348篇 |
2006年 | 17981篇 |
2005年 | 17179篇 |
2004年 | 16037篇 |
2003年 | 14767篇 |
2002年 | 13580篇 |
2001年 | 14522篇 |
2000年 | 11278篇 |
1999年 | 8853篇 |
1998年 | 7175篇 |
1997年 | 7045篇 |
1996年 | 6954篇 |
1995年 | 6324篇 |
1994年 | 5954篇 |
1993年 | 5759篇 |
1992年 | 6402篇 |
1991年 | 6268篇 |
1990年 | 5983篇 |
1989年 | 5667篇 |
1988年 | 5943篇 |
1987年 | 5691篇 |
1986年 | 5382篇 |
1985年 | 7555篇 |
1984年 | 7775篇 |
1983年 | 6329篇 |
1982年 | 6838篇 |
1981年 | 6811篇 |
1980年 | 6509篇 |
1979年 | 6637篇 |
1978年 | 6799篇 |
1977年 | 6776篇 |
1976年 | 6766篇 |
1975年 | 6490篇 |
1974年 | 6358篇 |
1973年 | 6586篇 |
1972年 | 4002篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
J. Matkowski 《Aequationes Mathematicae》2002,64(3):297-303
Summary. Iteration semigroups of weighted quasi-arithmetic mean-type mappings are considered. Existence and uniqueness of a mean which is invariant with respect to a continuous semigroup of mean-type mapping is proved. 相似文献
62.
63.
64.
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
65.
66.
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
67.
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
68.
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
69.
70.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献