全文获取类型
收费全文 | 2317篇 |
免费 | 91篇 |
国内免费 | 5篇 |
专业分类
化学 | 1910篇 |
晶体学 | 16篇 |
力学 | 29篇 |
数学 | 178篇 |
物理学 | 280篇 |
出版年
2021年 | 23篇 |
2020年 | 42篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2016年 | 38篇 |
2015年 | 42篇 |
2014年 | 59篇 |
2013年 | 84篇 |
2012年 | 84篇 |
2011年 | 90篇 |
2010年 | 55篇 |
2009年 | 44篇 |
2008年 | 105篇 |
2007年 | 80篇 |
2006年 | 78篇 |
2005年 | 75篇 |
2004年 | 55篇 |
2003年 | 43篇 |
2002年 | 29篇 |
2001年 | 29篇 |
2000年 | 22篇 |
1997年 | 18篇 |
1996年 | 29篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 27篇 |
1992年 | 18篇 |
1991年 | 19篇 |
1989年 | 23篇 |
1987年 | 15篇 |
1985年 | 15篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1968年 | 32篇 |
1967年 | 60篇 |
1966年 | 73篇 |
1965年 | 64篇 |
1964年 | 57篇 |
1963年 | 35篇 |
1962年 | 49篇 |
1960年 | 27篇 |
1959年 | 27篇 |
1958年 | 17篇 |
1957年 | 20篇 |
1956年 | 69篇 |
1955年 | 135篇 |
1954年 | 81篇 |
排序方式: 共有2413条查询结果,搜索用时 265 毫秒
1.
2.
Duolite GT-73 resin was used for the preconcentration of Hg(II) from hydrochloric acid media as well as separation of the analyte from diversity of the co-existing metal ions (Al, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn) in off-line column operation. Due to the high affinity of the resin to the transition metals, Hg was adsorbed alongside with the foreign metals investigated. A complete release of the concomitant metals from the resin without the desorption of Hg was carried out using solutions of HCl and HNO3. A quantitative recovery of Hg was obtained by digestion of the resin using a H2SO4 and H2O2 mixture in an open-vessel system. An enrichment factor of 40 was achieved. The devised procedure was applied for the determination of Hg(II) in tap-water samples. 相似文献
3.
Several Pd-catalyzed reactions were explored to further functionalize the bromo-substituted 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one scaffold (Aba). We report in this paper suitable reaction conditions for Suzuki, Buchwald-Hartwig, and Heck reactions. The substitution pattern of the starting aminobenzazepinone turned out to be crucial for the success of these transition metal-catalyzed reactions, which often required modifications of standard literature procedures. The Pd-catalyzed methods provide access to novel substitution patterns of the Aba scaffold. 相似文献
4.
Maria Chudnovsky Jim Geelen Bert Gerards Luis Goddyn Michael Lohman Paul Seymour 《Combinatorica》2006,26(5):521-532
Let G=(V,E) be an oriented graph whose edges are labelled by the elements of a group Γ and let A⊂V. An A-path is a path whose ends are both in A. The weight of a path P in G is the sum of the group values on forward oriented arcs minus the sum of the backward oriented arcs in P. (If Γ is not abelian, we sum the labels in their order along the path.) We are interested in the maximum number of vertex-disjoint
A-paths each of non-zero weight. When A = V this problem is equivalent to the maximum matching problem. The general case also includes Mader's S-paths problem. We prove that for any positive integer k, either there are k vertex-disjoint A-paths each of non-zero weight, or there is a set of at most 2k −2 vertices that meets each of the non-zero A-paths. This result is obtained as a consequence of an exact min-max theorem.
These results were obtained at a workshop on Structural Graph Theory at the PIMS Institute in Vancouver, Canada. This research
was partially conducted during the period the first author served as a Clay Mathematics Institute Long-Term Prize Fellow. 相似文献
5.
6.
7.
8.
9.
Least-Squares Fitting of Algebraic Spline Surfaces 总被引:11,自引:0,他引:11
We present an algorithm for fitting implicitly defined algebraic spline surfaces to given scattered data. By simultaneously approximating points and associated normal vectors, we obtain a method which is computationally simple, as the result is obtained by solving a system of linear equations. In addition, the result is geometrically invariant, as no artificial normalization is introduced. The potential applications of the algorithm include the reconstruction of free-form surfaces in reverse engineering. The paper also addresses the generation of exact error bounds, directly from the coefficients of the implicit representation. 相似文献