全文获取类型
收费全文 | 2446篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 1673篇 |
晶体学 | 11篇 |
力学 | 31篇 |
数学 | 393篇 |
物理学 | 392篇 |
出版年
2020年 | 21篇 |
2019年 | 27篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 40篇 |
2015年 | 50篇 |
2014年 | 43篇 |
2013年 | 108篇 |
2012年 | 92篇 |
2011年 | 95篇 |
2010年 | 70篇 |
2009年 | 86篇 |
2008年 | 94篇 |
2007年 | 107篇 |
2006年 | 77篇 |
2005年 | 97篇 |
2004年 | 88篇 |
2003年 | 59篇 |
2002年 | 64篇 |
2001年 | 32篇 |
2000年 | 54篇 |
1999年 | 62篇 |
1998年 | 55篇 |
1997年 | 53篇 |
1996年 | 43篇 |
1995年 | 28篇 |
1994年 | 47篇 |
1993年 | 54篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 29篇 |
1987年 | 41篇 |
1986年 | 45篇 |
1985年 | 45篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 52篇 |
1981年 | 33篇 |
1980年 | 53篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 24篇 |
1976年 | 34篇 |
1975年 | 28篇 |
1974年 | 19篇 |
1973年 | 14篇 |
1972年 | 18篇 |
1971年 | 14篇 |
排序方式: 共有2500条查询结果,搜索用时 31 毫秒
51.
52.
Diestel Reinhard; Shelah Saharon; Steprans Juris 《Journal London Mathematical Society》1994,49(1):16-24
A graph is called dominating if its vertices can be labelledwith integers in such a way that for every function : thegraph contains a ray whose sequence of labels eventually exceeds. We obtain a characterization of these graphs by producinga small family of dominating graphs with the property that everydominating graph must contain some member of the family. 相似文献
53.
54.
Reinhard Honegger 《Letters in Mathematical Physics》1993,27(3):191-203
By means of cocycle techniques in a recent paper, the global dynamics of mean field-boson couplings has been studied. Here, by restricting to the bosonic system the infinite time limit (t ) for very general initial states, one obtains time-asymptotic states on the bosonicC
*-Weyl algebra, in which one partially rediscovers the collective ordering of the infinite mean field lattice. 相似文献
55.
Motivated by the concept of maximum entropy methods in signal and image processing, we introduce and discuss a class of ‘directed diffusion equations’ with suitable boundary conditions. The paradigmatic ‘directed diffusion equation’ is The relative entropy $ Sb[f](t): = - \int_\Omega {f(t,x)} \;\ln \;(f(t,x)/b(x))dx $ is rapidly increasing along solution trajectories of (i). This suggests that solving (i) will yield efficient procedures for entropy maximization. We also discuss the asymptotic behavior of solutions of (i)—this is readily done because (i) has a large family of Ljapunov functionals. 相似文献
56.
Walter Fischer Cyril A. Grob Reinhard Hanreich Georg von Sprecher Adrian Waldner 《Helvetica chimica acta》1981,64(7):2298-2311
The solvolysis rates and products of the 6-exo-substituted 2-exo- 1a - 1u , and 2-endo-norbornyl p-toluenesulfonates 2a - 2u , have been determined. In general, the rate constants for 1 and 2 (log k) correlate well with the inductive constants σ of the substitutents at C(6); however, their sensitivity to σ is much larger in the 2-exo-series 1 than in the 2-endo-series 2 . This differential transmission of polar effects is the cause of decreasing 2-exo/2-endo rate ratios from 2388 for R = t-C4H9 to 0.37 for R = Br, i. e. with increasing electron attraction by the substituent. The high sensitivity of the rate constants for the 2-exo-p-toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)-atom, i. e. to 1,3-bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3-bridging, lead to faster reactions and to the formation of 2-exo substitution products. Conversely, acceptor substituents reduce 1,3-bridging, decrease rates and facilitate the formation of 2-endo substitution products. Graded 1,3-bridging is discussed in the light of Winstein's nonclassical ion concept. 相似文献
57.
58.
59.
60.