全文获取类型
收费全文 | 451篇 |
免费 | 6篇 |
专业分类
化学 | 309篇 |
力学 | 7篇 |
数学 | 29篇 |
物理学 | 112篇 |
出版年
2020年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 23篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 23篇 |
2007年 | 29篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 20篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1966年 | 2篇 |
1943年 | 2篇 |
1907年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 890 毫秒
11.
Ronald G. Sutherland Adam Pirko Udai S. Gill Choi Chuck Lee 《Journal of heterocyclic chemistry》1982,19(4):801-803
A method for the synthesis of heterocylic systems related to 9,10-dihydroanthracene with two hetero-atoms at the 9,10-positions is described. It involves the nucleophilic substitution reaction of η6-o-dichlorobenzene-η5-cyclopentadienyliron hexafluorophosphate with two nucleophilic groups (OH, SH and/or NH2) located in the 1,2-positions of a benzene ring to give a cyclopentadienyliron complexed heterocycle. Upon pyrolytic sublimation of the complex, the free heterocyclic compound is then obtained. 相似文献
12.
DNA photoreactivating enzyme from human tissues 总被引:4,自引:0,他引:4
S E Ogut S M D'Ambrosio M Samuel B M Sutherland 《Journal of photochemistry and photobiology. B, Biology》1989,4(1):47-56
Photoreactivating enzyme activity has been quantitated in human fetal skin, kidney, lung, liver, brain and intestine, and in neonatal human foreskin. In all the tissues examined there were at least two activities: one nominally greater than 10,000 Da, and one nominally less than 10,000 Da. Both can photolyze pyrimidine dimers in DNA using only light of wavelengths greater than 320 nm, thus excluding tryptophan-mediated dimer splitting as an important mechanism for these activities. The activities are inactivated by digestion with trypsin or pronase, and decreased partially or totally by heating to 65 degrees C. The activities from all six tissues, as well as that from neonatal foreskin, act catalytically in dimer photolysis. The properties of macromolecular size, heat lability, protease sensitivity and catalytic pyrimidine dimer photolysis by a non-tryptophan-mediated mechanism correspond to those of a true photoreactivating enzyme. 相似文献
13.
14.
15.
16.
17.
7,9-Bisdeoxycarminomycinone has been synthesised from 5-hydroxyquinizarin by two annelation routes involving nitronate addition to C-2 and aldol condensation at C-3. 4-Demethoxy-7,9-bisdeoxydaunomycinone has been synthesised efficiently by similar methods. 相似文献
18.
19.
p-AMINOBENZOIC ACID-SUNLAMP SENSITIZATION OF PYRIMIDINE DIMER FORMATION AND TRANSFORMATION IN HUMAN CELLS 总被引:1,自引:0,他引:1
Abstract In the presence of sunlamp radiation, p -aminobenzoic acid sensitizes pyrimidine dimer formation in the DNA of human skin fibroblasts. It also sensitizes the sunlamp-induced transformation of such cells to anchorage-independent growth. 相似文献
20.
Ronald G. Sutherland Adam Pirko Choi Chuck Lee Stanley H. Simonsen Vincent M. Lynch 《Journal of heterocyclic chemistry》1988,25(6):1911-1916
Synthesis of the heterocyclic skeletons of some biologically active compounds from (η6-o-dichlorobenzene)(η5-cyclopentadienyrl)iron hexafluorophosphate in a two step procedure is described. Cyclopentadienyliron hexafluorophosphate complexes of 1,4-benzodioxino[2,3-b]pyridine, 1,4-benzoxathiino[3,2-b]pyridine, 10H-pyrido[3,2-b]benzoxazine, benzo[b]naphtho[2,3-e][1,4]dioxin, 4-methylbenzo[b]benzopyran-2-one[7,6-e][1,4]dioxin and benzo[b]anthracen-9,10-diono[1,2-e][1,4]dioxin were isolated and characterized. Upon pyrolytic sublimation of these complexes the free heterocycles were obtained and characterized. (η6-1,4-Benzoxathiino[3,2-b]pyridine)(η5-cyclopentadienyl)iron hexafluorophosphate crystalizes in the orthothombic system, space group Pbca; the dihedral angle between the planes of outer rings was found to be 176.8 (1). 相似文献