全文获取类型
收费全文 | 82454篇 |
免费 | 18927篇 |
国内免费 | 4901篇 |
专业分类
106282篇 |
出版年
2024年 | 159篇 |
2023年 | 735篇 |
2022年 | 1817篇 |
2021年 | 3136篇 |
2020年 | 3855篇 |
2019年 | 5860篇 |
2018年 | 5977篇 |
2017年 | 5821篇 |
2016年 | 6430篇 |
2015年 | 6848篇 |
2014年 | 7394篇 |
2013年 | 8159篇 |
2012年 | 6644篇 |
2011年 | 5934篇 |
2010年 | 6018篇 |
2009年 | 4453篇 |
2008年 | 3828篇 |
2007年 | 3160篇 |
2006年 | 2773篇 |
2005年 | 2398篇 |
2004年 | 2245篇 |
2003年 | 2162篇 |
2002年 | 1774篇 |
2001年 | 1494篇 |
2000年 | 1196篇 |
1999年 | 899篇 |
1998年 | 525篇 |
1997年 | 407篇 |
1996年 | 392篇 |
1995年 | 381篇 |
1994年 | 348篇 |
1993年 | 271篇 |
1992年 | 344篇 |
1991年 | 301篇 |
1990年 | 247篇 |
1989年 | 227篇 |
1988年 | 146篇 |
1987年 | 195篇 |
1986年 | 154篇 |
1985年 | 133篇 |
1984年 | 111篇 |
1983年 | 102篇 |
1982年 | 89篇 |
1981年 | 84篇 |
1980年 | 54篇 |
1979年 | 64篇 |
1978年 | 67篇 |
1976年 | 53篇 |
1973年 | 65篇 |
1972年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
J. Paupério J. S. Herman J. Melo‐Ferreira M. Jaarola P. C. Alves J.B. Searle 《Molecular ecology》2012,21(24):6015-6032
Species are generally described from morphological features, but there is growing recognition of sister forms that show substantial genetic differentiation without obvious morphological variation and may therefore be considered ‘cryptic species’. Here, we investigate the field vole (Microtus agrestis), a Eurasian mammal with little apparent morphological differentiation but which, on the basis of previous sex‐linked nuclear and mitochondrial DNA (mtDNA) analyses, is subdivided into a Northern and a Southern lineage, sufficiently divergent that they may represent two cryptic species. These earlier studies also provided limited evidence for two major mtDNA lineages within Iberia. In our present study, we extend these findings through a multilocus approach. We sampled 163 individuals from 46 localities, mainly in Iberia, and sequenced seven loci, maternally, paternally and biparentally inherited. Our results show that the mtDNA lineage identified in Portugal is indeed a distinct third lineage on the basis of other markers as well. In fact, multilocus coalescent‐based methods clearly support three separate evolutionary units that may represent cryptic species: Northern, Southern and Portuguese. Divergence among these units was inferred to have occurred during the last glacial period; the Portuguese lineage split occurred first (estimated at c. 70 000 bp ), and the Northern and Southern lineages separated at around the last glacial maximum (estimated at c. 18 500 bp ). Such recent formation of evolutionary units that might be considered species has repercussions in terms of understanding evolutionary processes and the diversity of small mammals in a European context. 相似文献
63.
64.
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
65.
66.
Yu. N. Litvinov N. T. Erzhanov N. V. Lopatina T. Zh. Abylkhasanov 《Contemporary Problems of Ecology》2010,3(5):593-596
Small mammals were studied in the Kazakh Uplands in the spring and fall of 2008. The trapping studies revealed 10 species.
Abundances of the animals were low in the four main distinct characteristic biotopes of Bayanaul National Park, but those
of biotope dominants were high. In the Kazakh Uplands, rodents and insectivores are clearly restricted to certain biotopes.
Biodiversity indices for small mammal communities are low, indicating that the community structure is disturbed. 相似文献
67.
A number of motile strains of Azospirillum brasilense, A. lipoferum, and A. irakense, were found to possess tyrosinase activity both on the surface of and inside the cells. A. brasilense Sp245, Sp7, and A. irakense KBC-1 each possessed two forms of tyrosinase of different molecular masses; A. lipoferum 43, A. lipoferum 59b, and A. irakense KA-3 each had a single tyrosinase form of approximately the same molecular mass; and A. brasilense Sp107 possessed a single form of tyrosinase different from all the other forms. 相似文献
68.
69.
70.
Calorimetric properties of mixtures of ganglioside GM1 and dipalmitoylphosphatidylcholine 总被引:2,自引:0,他引:2
L O Sillerud D E Schafer R K Yu W H Konigsberg 《The Journal of biological chemistry》1979,254(21):10876-10880