全文获取类型
收费全文 | 2734篇 |
免费 | 386篇 |
国内免费 | 1篇 |
专业分类
3121篇 |
出版年
2022年 | 28篇 |
2021年 | 47篇 |
2020年 | 32篇 |
2018年 | 40篇 |
2017年 | 29篇 |
2016年 | 73篇 |
2015年 | 86篇 |
2014年 | 101篇 |
2013年 | 113篇 |
2012年 | 157篇 |
2011年 | 141篇 |
2010年 | 76篇 |
2009年 | 63篇 |
2008年 | 105篇 |
2007年 | 107篇 |
2006年 | 90篇 |
2005年 | 86篇 |
2004年 | 82篇 |
2003年 | 80篇 |
2002年 | 67篇 |
2001年 | 69篇 |
2000年 | 68篇 |
1999年 | 64篇 |
1998年 | 26篇 |
1997年 | 36篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 49篇 |
1991年 | 50篇 |
1990年 | 45篇 |
1989年 | 51篇 |
1988年 | 62篇 |
1987年 | 44篇 |
1986年 | 54篇 |
1985年 | 51篇 |
1984年 | 40篇 |
1983年 | 42篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 45篇 |
1978年 | 28篇 |
1977年 | 34篇 |
1973年 | 37篇 |
1972年 | 28篇 |
1971年 | 33篇 |
1970年 | 27篇 |
1968年 | 26篇 |
排序方式: 共有3121条查询结果,搜索用时 0 毫秒
991.
Proto WR Castanys-Munoz E Black A Tetley L Moss CX Juliano L Coombs GH Mottram JC 《The Journal of biological chemistry》2011,286(46):39914-39925
Metacaspases are caspase family cysteine peptidases found in plants, fungi, and protozoa but not mammals. Trypanosoma brucei is unusual in having five metacaspases (MCA1-MCA5), of which MCA1 and MCA4 have active site substitutions, making them possible non-enzymatic homologues. Here we demonstrate that recombinant MCA4 lacks detectable peptidase activity despite maintaining a functional peptidase structure. MCA4 is expressed primarily in the bloodstream form of the parasite and associates with the flagellar membrane via dual myristoylation/palmitoylation. Loss of function phenotyping revealed critical roles for MCA4; rapid depletion by RNAi caused lethal disruption to the parasite's cell cycle, yet the generation of MCA4 null mutant parasites (Δmca4) was possible. Δmca4 had normal growth in axenic culture but markedly reduced virulence in mice. Further analysis revealed that MCA4 is released from the parasite and is specifically processed by MCA3, the only metacaspase that is both palmitoylated and enzymatically active. Accordingly, we have identified that the multiple metacaspases in T. brucei form a membrane-associated proteolytic cascade to generate a pseudopeptidase virulence factor. 相似文献
992.
Henry LK Iwamoto H Field JR Kaufmann K Dawson ES Jacobs MT Adams C Felts B Zdravkovic I Armstrong V Combs S Solis E Rudnick G Noskov SY DeFelice LJ Meiler J Blakely RD 《The Journal of biological chemistry》2011,286(35):30823-30836
Na(+)- and Cl(-)-dependent uptake of neurotransmitters via transporters of the SLC6 family, including the human serotonin transporter (SLC6A4), is critical for efficient synaptic transmission. Although residues in the human serotonin transporter involved in direct Cl(-) coordination of human serotonin transport have been identified, the role of Cl(-) in the transport mechanism remains unclear. Through a combination of mutagenesis, chemical modification, substrate and charge flux measurements, and molecular modeling studies, we reveal an unexpected role for the highly conserved transmembrane segment 1 residue Asn-101 in coupling Cl(-) binding to concentrative neurotransmitter uptake. 相似文献
993.
994.
Socioecological models suggest competition for food, foraging efficiency, predation, infanticide risk, and the costs of dispersal
regulate primate social structure and organization. Wild populations of squirrel monkeys (Saimiri spp.) appear to conform to the predictions of the predation/competition socioecological model (Sterck et al. in Behav Ecol
Sociobiol 41:291–309, 1997) and the dispersal/foraging efficiency model (Isbell in Kinship and behavior in primates. Oxford University, New York, pp
71–108, 2004). However, squirrel monkeys in captivity are reported to maintain patterns of social behavior observed in their wild conspecifics
despite different food distribution, predation risk, and dispersal options. This behavioral similarity suggests squirrel monkeys’
social behavior has limited flexibility to respond to environmental changes. In this study, we experimentally evaluated the
flexibility of social behavior within a captive group of S. sciureus. First, we determined whether dominance and affiliative relationships observed under normal laboratory conditions (with abundant,
widely distributed, food; no dispersal option; and no predators) better matched published reports of relationships among wild
conspecifics or the predictions of the predation/competition model. Second, we made preferred food items defensible to determine
whether dominance interactions would become more frequent and linear, as predicted by the model. The model correctly predicted
rates of dominance behavior in both conditions and a linear hierarchy in the defensible food condition but did not predict
the consistent affiliative relationships and linear dominance hierarchy observed in normal lab conditions. Although hierarchies
were linear and male dominant, manipulating food distribution changed the dominant individual within each sex. Our findings
suggest interaction rates adapt more rapidly than social structure to environmental changes in Saimiri and recommend caution in interpreting tests of socioecological models. 相似文献
995.
Archer M Beck R Gott M Hand S Godthelp H Black K 《Proceedings. Biological sciences / The Royal Society》2011,278(1711):1498-1506
Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely 'transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these-the dental morphology known as zalambdodonty-was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages-marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene. 相似文献
996.
Devakaram R Black DS Andrews KT Fisher GM Davis RA Kumar N 《Bioorganic & medicinal chemistry》2011,19(17):5199-5206
7-Methoxyflavenes and 5,7,8-trimethoxyflavenes were found to undergo stereoselective acid-catalyzed rearrangement to generate the benzopyrano[4,3-b]benzopyran ring system present in the natural product, dependensin. Dependensin and its analogs were subjected to antimalarial growth inhibition assays against Plasmodium falciparum and found to have IC(50) values ranging between 1.9 and 3.9 μM. 相似文献
997.
998.
999.
1000.
Harold Black 《BMJ (Clinical research ed.)》1913,1(2729):852-853