全文获取类型
收费全文 | 44038篇 |
免费 | 17319篇 |
国内免费 | 7篇 |
专业分类
61364篇 |
出版年
2022年 | 310篇 |
2021年 | 789篇 |
2020年 | 2382篇 |
2019年 | 3954篇 |
2018年 | 4132篇 |
2017年 | 4329篇 |
2016年 | 4541篇 |
2015年 | 4822篇 |
2014年 | 4502篇 |
2013年 | 5057篇 |
2012年 | 3096篇 |
2011年 | 2762篇 |
2010年 | 3782篇 |
2009年 | 2461篇 |
2008年 | 1661篇 |
2007年 | 1237篇 |
2006年 | 1200篇 |
2005年 | 1173篇 |
2004年 | 1102篇 |
2003年 | 1076篇 |
2002年 | 975篇 |
2001年 | 494篇 |
2000年 | 410篇 |
1999年 | 382篇 |
1998年 | 256篇 |
1997年 | 159篇 |
1996年 | 171篇 |
1995年 | 155篇 |
1994年 | 147篇 |
1993年 | 172篇 |
1992年 | 216篇 |
1991年 | 177篇 |
1990年 | 183篇 |
1989年 | 152篇 |
1988年 | 164篇 |
1987年 | 151篇 |
1986年 | 131篇 |
1985年 | 137篇 |
1984年 | 131篇 |
1983年 | 141篇 |
1982年 | 123篇 |
1981年 | 124篇 |
1980年 | 102篇 |
1979年 | 136篇 |
1978年 | 124篇 |
1977年 | 95篇 |
1976年 | 110篇 |
1975年 | 87篇 |
1974年 | 109篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Enhanced fluorescence of the ATP analogue 2',3'-O-(2,4,6-trinitrocyclohexyldienylidine)adenosine 5'-triphosphate (TNP-ATP), bound to the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum, is closely related to phosphoenzyme levels (Bishop, J. E., Johnson, J. D., and Berman, M. C. (1984) J. Biol. Chem. 259, 15163-15171) and has an emission maximum consistent with decreased polarity of the TNP-ATP-binding site. The phosphoenzyme conformation responsible for increased nucleotide-binding site hydrophobicity has been studied by redistribution of phosphoenzyme intermediates following specific thiol group modification. N-Ethylmaleimide, in the presence of 50 microM Ca2+, 1 mM adenyl-5'-yl imidodiphosphate, pH 7.0, at 25 degrees C for 30 min, selectively modified the SH group essential for phosphoenzyme decomposition, which resulted in decreased ATPase activity, Ca2+ uptake, and a decrease in ATP-induced TNP-ATP fluorescence. Phosphorylated (Ca2+, Mg2+)-ATPase levels from [gamma-32P] ATP remained relatively unaffected (3.1 nmol/mg), but the ADP-insensitive fraction decreased from 56 to 15%. Phosphoenzyme levels from 32Pi were also decreased to the same extent as turnover, with equivalent loss of Pi-induced TNP-ATP fluorescence. The E1 to E2 transition, as monitored by the change in intrinsic tryptophan fluorescence, was unaffected. Modification of thiol groups of unknown function did not modify turnover-induced TNP-ATP fluorescence. It is concluded that the ADP-insensitive phosphoenzyme, E2-P, is responsible for enhanced TNP-ATP fluorescence. This suggests that the conformational transition, 2Ca2+outE1 approximately P----2Ca2+inE2-P, is associated with altered properties of the noncatalytic, or regulatory, nucleotide-binding site. 相似文献
22.
23.
P. Cruz C. H. Mejia‐Ruiz R. Perez‐Enriquez A. M. Ibarra 《Molecular ecology resources》2002,2(3):239-241
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies. 相似文献
24.
D G Davidson 《BMJ (Clinical research ed.)》1984,289(6451):1078-1079
25.
26.
Elizabeth M. A. Valleley Christine J. Harrison Yvonne Cook Mark W. J. Ferguson Paul T. Sharpe 《Chromosoma》1994,103(7):502-507
Comparative mapping studies of X-linked genes in mammals have provided insights into the evolution of the X chromosome. Many reptiles including the American alligator, Alligator mississippiensis, do not appear to possess heteromorphic sex chromosomes, and sex is determined by the incubation temperature of the egg during embryonic development. Mapping of homologues of mammalian X-linked genes in reptiles could lead to a greater understanding of the evolution of vertebrate sex chromosomes. One of the genes used in the mammalian mapping studies was ZFX, an X-linked copy of the human ZFY gene which was originally isolated as a candidate for the mammalian testis-determining factor (TDF). ZFX is X-linked in eutherians, but maps to two autosomal locations in marsupials and monotremes, close to other genes associated with the eutherian X. The alligator homologue of the ZFY/ZFX genes, Zfc, has been isolated and described previously. A detailed karyotype of A. mississippiensis is presented, together with chromosomal in situ hybridisation data localising the Zfc gene to chromosome 3. Further chromosomal mapping studies using eutherian X-linked genes may reveal conserved chromosomal regions in the alligator that have become part of the eutherian X chromosome during evolution. 相似文献
27.
G. R. Davidson B. Nurcombe G. E. Kearney K. Davis 《Culture, medicine and psychiatry》1978,2(4):359-372
Critical incidents adapted to presentation in picture form were used to investigate responses of Aboriginal adolescents from Elcho Island mission in the Northern Territory of Australia in conflict situations arising from culture contact. These Aboriginal youths are part of a complex environment where choice behaviour is mediated by specific and broader situational characteristics of the social environment. Results showed a relationship between conflict responses and orientation to traditional values and skills, but no apparent relationship between conflict responses and modern value orientation or psychopathology variables. Adolescents who attended high school in Darwin were seen as more mission and academically oriented than locally educated youth. Contrary to expected patterns, males appeared to be less involved in both mission and traditional activities and more restricted by traditional social expectations than were females. 相似文献
28.
29.
30.