全文获取类型
收费全文 | 381篇 |
免费 | 5篇 |
专业分类
化学 | 240篇 |
晶体学 | 2篇 |
力学 | 18篇 |
数学 | 23篇 |
物理学 | 103篇 |
出版年
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 6篇 |
2013年 | 24篇 |
2012年 | 18篇 |
2011年 | 6篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 7篇 |
1970年 | 10篇 |
1969年 | 4篇 |
1968年 | 10篇 |
1967年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有386条查询结果,搜索用时 15 毫秒
91.
92.
We construct the supersymmetric σ-model, in six dimensions, for an arbitrary hyper-Kähler manifold, and its minimal coupling to super-Yang-Mills theory. Non-trivial reduction to five or four dimensions yields the corresponding five- or four-dimensional N = 2 supersymmetric model with general scalar potential. We discuss briefly the coupling to supergravity in six dimensions and we give the on-shell supergravity torsion constraints. 相似文献
93.
1-Methylisoguanosine was synthesized by a one-pot reaction involving a condensation of 5-amino-1-(β--ribofuranosyl)imidazole-4-carboxamide (1) with methyl isothiocyanate, treatment of the resulting thiourea derivative with DCC furnished 5-(3-methyl-1-ureido)-1-(β--ribofuranosyl)imidazole-4-carbonitrile (4) which was then annulated with ethanolic ammonia to furnish doridosine in a 68% yield from 1. 相似文献
94.
Calculations of the longitudinal and transverse momentum distributions for 3H production at large momentum in alpha-12C collisions near 2 A GeV are compared to experiment. Triton exchange and final-state interactions are shown to represent large corrections to the impulse approximation for proton knockout. A method for calculating interference effects for inelastic fragmentation is discussed. Good agreement with experiment is found using a phenomenological overlap function for 3H-p successful in describing 3H production in pion-induced reactions. Comparisons to momentum distributions obtained through (p, 2p) and (e, ep) reactions on 4He are made. 相似文献
95.
The nocardicins are members of a class of monocyclic beta-lactam antibiotics produced by the actinomycete Nocardia uniformis subsp. tsuyamanesis (ATCC 21806). The oxime moiety in nocardicin A is required for full biological activity and is rare among natural products. A putative gene cluster encoding the enzymes of the nocardicin biosynthetic pathway has been identified. Among these, NocL shows similarity to cytochromes P450. We describe its heterologous expression and demonstrate its role in the formation of this unusual structural feature in nocardicin A. This is the first gene from this pathway to be expressed and its function established, and it is the first example of oxime formation from a primary amine in bacteria unambiguously linked to a cytochrome P450. 相似文献
96.
Richard L. Tolman Roland K. Robins Leroy B. Townsend 《Journal of heterocyclic chemistry》1967,4(2):230-238
The first synthesis of a 7-β-D-ribofuranosylpyrrolo[2,3-d]pyrimidine by direct ribosidation of a preformed pyrrolo[2,3-d]pyrimidine has now been accomplished via the fusion procedure. Subsequent functional group transformations furnished the 6-methyl-thio derivative of the nucleoside antibiotic toyocamycin. Preparation of the 1-, 3- and 7-methyl isomers of 4-amino-5-cyano-6-methylthiopyrrolo[2,3-d]pyrimidine was accomplished and has provided an unequivocal assignment for the actual site of ribosidation by a comparison of ultraviolet absorption spectra. Factors utilized for the assignment of anomeric configuration are discussed. 相似文献
97.
98.
99.
Synthesis of imidazo[1,2-b]pyridazines: Fenbendazole,oxifenbendazole analogs and related derivatives
Alaa E. Mourad Dean S. Wise Leroy B. Townsend 《Journal of heterocyclic chemistry》1993,30(5):1365-1372
A series of imidazo[1,2-b]pyridazines has been prepared and evaluated for macrofilaricidal activity against Brugia pahangi or Acanthocheilonema viteae infections in jirds. The imidazo[1,2-b]pyridazine analogs of fen-bendazole and oxifenbendazole are reported. In addition, several 6-aminoimidazo[1,2-b]pyridazine derivatives have been prepared. None of these compounds possessed significant activity against human cytomega-lovirus (HCMV) or filarial infections. 相似文献
100.
The disappearance of collective flow effects in heavy ion collisions is investigated using a microscopic optical model formalism for estimating collision momentum transfers. Phenomenological expressions for the balance energy are obtained which agree very well with measurements for various experimental collision pairs and with results obtained from Boltzmann-Uehling-Uhlenbeck simulations. 相似文献