全文获取类型
收费全文 | 649745篇 |
免费 | 80613篇 |
国内免费 | 362篇 |
专业分类
730720篇 |
出版年
2016年 | 6938篇 |
2015年 | 10020篇 |
2014年 | 11688篇 |
2013年 | 16758篇 |
2012年 | 18691篇 |
2011年 | 19001篇 |
2010年 | 12917篇 |
2009年 | 12042篇 |
2008年 | 16961篇 |
2007年 | 17498篇 |
2006年 | 16369篇 |
2005年 | 15927篇 |
2004年 | 15444篇 |
2003年 | 15588篇 |
2002年 | 14897篇 |
2001年 | 27617篇 |
2000年 | 27833篇 |
1999年 | 22437篇 |
1998年 | 8268篇 |
1997年 | 8878篇 |
1996年 | 8536篇 |
1995年 | 8024篇 |
1994年 | 7931篇 |
1993年 | 8066篇 |
1992年 | 19425篇 |
1991年 | 19059篇 |
1990年 | 18331篇 |
1989年 | 18109篇 |
1988年 | 16646篇 |
1987年 | 16353篇 |
1986年 | 15229篇 |
1985年 | 15350篇 |
1984年 | 12888篇 |
1983年 | 11303篇 |
1982年 | 8898篇 |
1981年 | 8220篇 |
1980年 | 7701篇 |
1979年 | 12634篇 |
1978年 | 10065篇 |
1977年 | 9347篇 |
1976年 | 8876篇 |
1975年 | 9718篇 |
1974年 | 10269篇 |
1973年 | 10126篇 |
1972年 | 9323篇 |
1971年 | 8461篇 |
1970年 | 7262篇 |
1969年 | 7163篇 |
1968年 | 6385篇 |
1967年 | 5594篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
111.
Genes for the biosynthesis of spinosyns: applications for yield improvement in Saccharopolyspora spinosa 总被引:2,自引:0,他引:2
K Madduri C Waldron P Matsushima M C Broughton K Crawford D J Merlo R H Baltz 《Journal of industrial microbiology & biotechnology》2001,27(6):399-402
Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that
spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type
I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging
of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located
outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the
final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes
involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402.
Received 31 May 2001/ Accepted in revised form 09 July 2001 相似文献
112.
113.
114.
Orotate prevents galactosamine hepatitis 总被引:1,自引:0,他引:1
115.
116.
Synaptonemal complexes and meiosis in myxomycetes 总被引:4,自引:0,他引:4
Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis. 相似文献
117.
118.
119.
As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined. 相似文献
120.