全文获取类型
收费全文 | 485461篇 |
免费 | 59073篇 |
国内免费 | 310篇 |
出版年
2018年 | 4358篇 |
2017年 | 3978篇 |
2016年 | 6324篇 |
2015年 | 9591篇 |
2014年 | 10709篇 |
2013年 | 14922篇 |
2012年 | 17293篇 |
2011年 | 17454篇 |
2010年 | 11511篇 |
2009年 | 10530篇 |
2008年 | 15169篇 |
2007年 | 15638篇 |
2006年 | 14178篇 |
2005年 | 14025篇 |
2004年 | 13774篇 |
2003年 | 13143篇 |
2002年 | 12570篇 |
2001年 | 22048篇 |
2000年 | 22103篇 |
1999年 | 17817篇 |
1998年 | 6730篇 |
1997年 | 6864篇 |
1996年 | 6649篇 |
1995年 | 6033篇 |
1994年 | 6063篇 |
1993年 | 5874篇 |
1992年 | 13976篇 |
1991年 | 13247篇 |
1990年 | 12886篇 |
1989年 | 12731篇 |
1988年 | 11398篇 |
1987年 | 10999篇 |
1986年 | 10079篇 |
1985年 | 9925篇 |
1984年 | 8475篇 |
1983年 | 7297篇 |
1982年 | 5835篇 |
1981年 | 5245篇 |
1980年 | 4880篇 |
1979年 | 7851篇 |
1978年 | 6110篇 |
1977年 | 5614篇 |
1976年 | 5229篇 |
1975年 | 5506篇 |
1974年 | 5976篇 |
1973年 | 5826篇 |
1972年 | 5212篇 |
1971年 | 4814篇 |
1970年 | 4013篇 |
1969年 | 3932篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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
72.
The heart rate and respiratory patterns in hypoxia are not well documented in unanaesthetized intact newborn animals. We studied heart rate and respiratory patterns during quiet sleep in 17% inspired O2 in 31 unanaesthetized newborns of five species: lamb, piglet, puppy, kitten, and rabbit. There was no significant change in mean heart rate and respiratory rate with hypoxia for any species. Brief apneas greater than 5 s were frequent (5-8/h), both in 21 and 17% O2 only in lambs and puppies. No sustained periodic breathing was induced by hypoxia. Thus, mild hypoxia has little steady-state effect on heart rate and respiratory rate and pattern in these unanaesthetized newborns. These findings are compatible with depressed chemoreceptor threshold, but indicate a remarkably mature respiratory pattern in full-term newborns of these species. 相似文献
73.
74.
75.
76.
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
77.
78.
The cell surface of the parasitic protozoan Leishmania mexicana is coated by glycosylphosphatidylinositol (GPI)-anchored glycoproteins, a GPI-anchored lipophosphoglycan and a class of free GPI glycolipids. To investigate whether the anchor or free GPIs are required for parasite growth we cloned the L.mexicana gene for dolichol-phosphate-mannose synthase (DPMS) and attempted to create DPMS knockout mutants by targeted gene deletion. DPMS catalyzes the formation of dolichol-phosphate mannose, the sugar donor for all mannose additions in the biosynthesis of both the anchor and free GPIs, except for a alpha1-3-linked mannose residue that is added exclusively to the free GPIs and lipophosphoglycan anchor precursors. The requirement for dolichol-phosphate-mannose in other glycosylation pathways in L.mexicana is minimal. Deletion of both alleles of the DPMS gene (lmdpms) consistently resulted in amplification of the lmdpms chromosomal locus unless the promastigotes were first transfected with an episomal copy of lmdpms, indicating that lmdpms, and possibly GPI biosynthesis, is essential for parasite growth. As evidence presented in this and previous studies indicates that neither GPI-anchored glycoproteins nor lipophosphoglycan are required for growth of cultured parasites, it is possible that the abundant and functionally uncharacterized free GPIs are essential membrane components. 相似文献
79.
80.