全文获取类型
收费全文 | 3891篇 |
免费 | 234篇 |
国内免费 | 2篇 |
出版年
2023年 | 41篇 |
2022年 | 42篇 |
2021年 | 127篇 |
2020年 | 90篇 |
2019年 | 102篇 |
2018年 | 132篇 |
2017年 | 126篇 |
2016年 | 151篇 |
2015年 | 194篇 |
2014年 | 267篇 |
2013年 | 273篇 |
2012年 | 293篇 |
2011年 | 335篇 |
2010年 | 214篇 |
2009年 | 154篇 |
2008年 | 227篇 |
2007年 | 165篇 |
2006年 | 166篇 |
2005年 | 154篇 |
2004年 | 120篇 |
2003年 | 111篇 |
2002年 | 105篇 |
2001年 | 54篇 |
2000年 | 65篇 |
1999年 | 44篇 |
1998年 | 29篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 9篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 34篇 |
1991年 | 25篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1972年 | 6篇 |
1971年 | 9篇 |
1966年 | 5篇 |
排序方式: 共有4127条查询结果,搜索用时 125 毫秒
21.
22.
Solvent effects on the catalytic activity of subtilisin suspended in compressed gases 总被引:1,自引:0,他引:1
We studied a model transesterification reaction catalyzed by subtilisin Carlsberg suspended in carbon dioxide, propane, and mixtures of these solvents under pressure. To account for solvent effects due to differences in water partitioning between the enzyme and the bulk solvents, we measured water sorption isotherms for the enzyme in each solvent. We measured catalytic activity as a function of enzyme hydration and obtained bell-shaped curves with maxima at the same enzyme hydration (12%) in all the solvents. However, the activity maxima were different in all media, being much higher in propane than in either CO(2) or the mixtures with 50 and 10% CO(2). Considerations based on the solvation ability of the solvents did not offer an explanation for the differences in catalytic activity observed. Our results suggest that CO(2) has a direct adverse effect on the catalytic activity of subtilisin. (c) 1996 John Wiley & Sons, Inc. 相似文献
23.
Maria Ieda Siqueira Linhares Yoshito Eizuru Gildete Patriota de Andrade Ivailda Barbosa Fonseca Luiz Bezerra Carvalho Ivanildo Tenorio Moreira Yoichi Minamishima 《Microbiology and immunology》1994,38(6):475-478
The seroprevalence of human T cell leukemia virus type 1 (HTLV-1) infection was investigated in Brazilians (570): native inhabitants (298) and descendants from Japanese (272) living in Recife and its neighborhoods—North-east of Brazil. Furthermore, polytransfused renal transplanted patients (54) were also examined for the serological status to this virus. The seropositivity to HTLV-1, screened by enzyme-linked immunosorbent assay (ELISA), was low: 1.34% for the local population and 0.73% for the descendants from Japanese. However, the seropositivity for the renal transplanted patients was found to be 11.1%. This higher value suggests that this retrovirus infection seems to be of importance in this clinical condition. 相似文献
24.
The ATP-binding-cassette transmembrane transporters (ABC transporters)
known from vertebrates belong to four major subfamilies: (1) the P-
glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance
regulators (CFTR); (3) the Tap proteins encoded with the major
histocompatibility complex of mammals; and (4) the peroxisomal membrane
proteins. Both Pgp and CFTR have a structure suggesting a past internal
gene duplication; a phylogenetic analysis indicated that these duplications
occurred independently, while an independent tandem gene duplication
occurred in the case of the Tap family. Both the Pgp and Tap proteins show
evidence of relationship to bacterial ABC transporters lacking internal
duplication, and both are significantly more closely related to the HlyB
and MsbA families of transporters from purple bacteria than they are to ABC
transporters from nonpurple bacteria. The simplest hypothesis to explain
this observation is that eukaryotic Pgp and Tap genes are descended from a
mitochondrial gene or genes that were subsequently translocated to the
nuclear genome. The Pgp genes of eukaryotes are characterized by a
remarkable degree of convergent evolution between the ATP-binding cassettes
of their N- terminal and C-terminal halves, whereas no such convergence is
seen between the two halves of CFTR genes or between the duplicated Tap
genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain
not found in other ABC transporters apart from CFTR, showed high levels of
both synonymous and nonsynonymous difference in comparisons among different
mammalian species, suggesting that this region is a mutational hot spot.
相似文献
25.
26.
Efficient foraging and a reduction in predation risk have been proposed as reasons for shoal formation. Some behaviours in cyprinid shoals are at first sight altruistic (e.g. predator inspection behaviour, reactions to alarm substance), such that kin selection may have been involved in their evolution. If shoaling behaviour does evolve through kin selection, then genetic differentiation is expected to be greater between shoals than within shoals. Such a hypothesis was tested here by examining shoal integrity and the relatedness of individuals within and between shoals in the European minnow, Phoxinus phoxinus , using nuclear and mitochondrial DNA markers. The breeding structure of 13 minnow shoals collected from Dorset and North Wales, U.K., was examined using allozymes. Genetic affinity within and between shoals was tested using mitochondrial DNA and multi-locus DNA fingerprinting. Shoals consisted of a random assortment of allozyme genotypes, shoal members did not share the same maternal mtDNA lineages and DNA fingerprint profiles were as varied within shoals as between them. The data indicate that it is unlikely that kin selection occurs in P. phoxinus and there is no apparent relationship between shoaling behaviour and genotype distribution in this species. 相似文献
27.
Mayer Alejandro M. S. Paul Valerie J. Fenical William Norris James N. de Carvalho M. S. Jacobs Robert S. 《Hydrobiologia》1993,260(1):521-529
Twelve out of twenty-nine compounds isolated from benthic marine algae from the phyla Chlorophyta, Phaeophyta and Rhodophyta have been found to be potent inhibitors of bee venom derived phospholipase A2 (PLA2) (> 50%) in the M range. The compounds investigated were from: Bryopsis pennata, Rhipocephalus phoenix, Caulerpa prolifera, C. racemosa, C. bikinensis, Cymopolia barbata, Laurencia cf. palisada, Laurencia sp., Ochtodes crockeri, Liagora farinosa, Sphaerococcus coronipifolius, Phacelocarpus labillardieri, Dictyota sp., B furcaria galapagensis, Stypopodium zonale, Dictyopteris undulata, Stoechospermum marginatum, Dictyopteris divaricata, Dilophus fasciola and Dilophus sp. This is the first report of bee venom PLA2 inhibition in vitro by pure compounds isolated from marine algae. 相似文献
28.
29.
30.
Niraj Shrestha Pallavi Chaturvedi Xiaoyun Zhu Michael J. Dee Varghese George Christopher Janney Jack O. Egan Bai Liu Mark Foster Lynne Marsala Pamela Wong Celia C. Cubitt Jennifer A. Foltz Jennifer Tran Timothy Schappe Karin Hsiao Gilles M. Leclerc Lijing You Christian Echeverri Catherine Spanoudis Ana Carvalho Leah Kanakaraj Crystal Gilkes Nicole Encalada Lin Kong Meng Wang Byron Fang Zheng Wang Jin-an Jiao Gabriela J. Muniz Emily K. Jeng Nicole Valdivieso Liying Li Richard Deth Melissa M. Berrien-Elliott Todd A. Fehniger Peter R. Rhode Hing C. Wong 《Aging cell》2023,22(5):e13806