全文获取类型
收费全文 | 199篇 |
免费 | 10篇 |
专业分类
化学 | 146篇 |
数学 | 49篇 |
物理学 | 14篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 22篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 1篇 |
排序方式: 共有209条查询结果,搜索用时 0 毫秒
71.
Xin Wang Guokai Liu Xiu‐Hua Xu Naoyuki Shibata Etsuko Tokunaga Norio Shibata 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(7):1858-1862
S‐((Phenylsulfonyl)difluoromethyl)thiophenium salts were designed and prepared by a triflic acid catalyzed intramolecular cyclization of ortho‐ethynyl aryldifluoromethyl sulfanes. The thiophenium salts were found to be efficient as electrophilic difluoromehtylating reagents for introduction of a CF2H group to sp3‐hybridized carbon nucleophiles such as of β‐ketoesters and dicyanoalkylidenes. The (phenylsulfonyl)difluoromethyl group can be readily transformed into CF2H under mild reaction conditions. Enantioselective electrophilic difluoromethylation was also achieved in the presence of bis(cinchona) alkaloids. 相似文献
72.
Hiroto Uno Nagender Punna Etsuko Tokunaga Motoo Shiro Norio Shibata 《Angewandte Chemie (International ed. in English)》2020,59(21):8187-8194
The two enantiomers of trifluoromethyl‐benzo[c][1,5]oxazonines, (R)‐ 4 and (S)‐ 4 , can be selectively accessed with high enantiopurity by the Pd‐catalyzed ring‐expansion reaction of trifluoromethyl‐benzo[d][1,3]oxazinones ( 1 ) with vinyl ethylene carbonates ( 3 ) using one antipode of a chiral ligand. Initially, the reaction proceeds by a double decarboxylative ring‐expansion with kinetic resolution of 1 in the presence of a Pd‐catalyst/chiral ligand to provide (R)‐ 4 with high enantiopurity. At the same time, the nonreactive antipode of 1 , (S)‐ 1 , which was recovered with an impeccable s factor of up to 713 and an ideal chemical yield, was transferred into the antipode of the products, (S)‐ 4 , with high enantiopurity by a second run of the Pd‐catalyzed double decarboxylation reaction, but this time without any chiral auxiliary. Thus, both antipodes of the chiral trifluoromethyl heterocycles 4 can be obtained in excellent enantiopurity using only a single antipode of the chiral catalyst. 相似文献
73.
74.
E Bannai A Blokhuis J.J Seidel Ph Delsarte 《Journal of Combinatorial Theory, Series A》1984,36(3):332-341
The addition formula for Gegenbauer polynomials on the Euclidean sphere is generalized to the unit hyperboloid. Applications are given in terms of new bounds on the cardinality of few-distance sets in Lobatchevski space. 相似文献
75.
A primitive symmetric association scheme of class 2 is naturally embedded as a two-distance set in the unit sphere of Euclidean space, with respect to the primitive idempotent E1 of the Bose–Mesner algebra of the association scheme. Then it is shown that the ratio of the two distances of the two-distance set is instantly read from the character table (i.e., the first eigen matrix P) of the association scheme. 相似文献
76.
Eiichi Bannai 《Journal of Combinatorial Theory, Series A》1979,26(2):157-161
Let G be a finite subgroup of the orthogonal group O(d). It is shown that many spherical t-designs are constructed from G, if some particular irreducible representations of O(d) remain irreducible when restricted to G. 相似文献
77.
78.
79.
We prove the uniqueness of the two association schemes which appear in recent work of Henry Cohn and others in connection with their study of universally optimal spherical codes in Euclidean spaces: one is the class 4 association scheme with 40 vertices in and the other one is the class 3 association scheme with 64 vertices in . We prove the uniqueness mainly by geometric considerations with some computational help. 相似文献
80.
Agarwal J Sanders BC Fujita E Schaefer HF Harrop TC Muckerman JT 《Chemical communications (Cambridge, England)》2012,48(54):6797-6799
We have investigated the reaction of Re(dmb)(CO)(3)COOH with CO(2) using density functional theory, and propose a mechanism for the production of CO. This mechanism supports the role of Re(dmb)(CO)(3)COOH as a key intermediate in the formation of CO. Our new experimental work supports the proposed scheme. 相似文献