全文获取类型
收费全文 | 138680篇 |
免费 | 9684篇 |
国内免费 | 244篇 |
专业分类
148608篇 |
出版年
2023年 | 722篇 |
2022年 | 712篇 |
2021年 | 1544篇 |
2020年 | 1334篇 |
2019年 | 1440篇 |
2018年 | 3148篇 |
2017年 | 2831篇 |
2016年 | 4051篇 |
2015年 | 6023篇 |
2014年 | 6113篇 |
2013年 | 8231篇 |
2012年 | 9874篇 |
2011年 | 9354篇 |
2010年 | 5994篇 |
2009年 | 4586篇 |
2008年 | 7697篇 |
2007年 | 7503篇 |
2006年 | 6902篇 |
2005年 | 6671篇 |
2004年 | 6292篇 |
2003年 | 5784篇 |
2002年 | 5228篇 |
2001年 | 3004篇 |
2000年 | 2859篇 |
1999年 | 2536篇 |
1998年 | 1113篇 |
1997年 | 870篇 |
1996年 | 801篇 |
1995年 | 852篇 |
1994年 | 804篇 |
1993年 | 658篇 |
1992年 | 1689篇 |
1991年 | 1589篇 |
1990年 | 1408篇 |
1989年 | 1347篇 |
1988年 | 1246篇 |
1987年 | 1087篇 |
1986年 | 1022篇 |
1985年 | 1092篇 |
1984年 | 934篇 |
1983年 | 778篇 |
1982年 | 649篇 |
1981年 | 646篇 |
1979年 | 831篇 |
1978年 | 665篇 |
1977年 | 602篇 |
1976年 | 552篇 |
1975年 | 624篇 |
1974年 | 648篇 |
1973年 | 641篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Gaelle Jan Violaine Delorme Nehm Saksouk Marie Abrivard Virginie Gonzalez Xavier Cayla Mohamed-Ali Hakimi Isabelle Tardieux 《Microbes and infection / Institut Pasteur》2009,11(12):935-945
Toxoplasma gondii is a human protozoan parasite that belongs to the phylum of Apicomplexa and causes toxoplasmosis. As the other members of this phylum, T. gondii obligatory multiplies within a host cell by a peculiar type of mitosis that leads to daughter cell assembly within a mother cell. Although parasite growth and virulence have been linked for years, few molecules controlling mitosis have been yet identified and they include a couple of kinases but not the counteracting phosphatases. Here, we report that in contrast to other animal cells, type 2C is by far the major type of serine threonine phosphatase activity both in extracellular and in intracellular dividing parasites. Using wild type and transgenic parasites, we characterized the 37 kDa TgPP2C molecule as an abundant cytoplasmic and nuclear enzyme with activity being under tight regulation. In addition, we showed that the increase in TgPP2C activity significantly affected parasite growth by impairing cytokinesis while nuclear division still occurred. This study supports for the first time that type 2C protein phosphatase is an important regulator of cell growth in T. gondii. 相似文献
44.
Mélody Porlier Marc Bélisle Dany Garant 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1523):1543-1554
Improving our knowledge of the links between ecology and evolution is especially critical in the actual context of global rapid environmental changes. A critical step in that direction is to quantify how variation in ecological factors linked to habitat modifications might shape observed levels of genetic variability in wild populations. Still, little is known on the factors affecting levels and distribution of genetic diversity at the individual level, despite its vital underlying role in evolutionary processes. In this study, we assessed the effects of habitat quality on population structure and individual genetic diversity of tree swallows (Tachycineta bicolor) breeding along a gradient of agricultural intensification in southern Québec, Canada. Using a landscape genetics approach, we found that individual genetic diversity was greater in poorer quality habitats. This counter-intuitive result was partly explained by the settlement patterns of tree swallows across the landscape. Individuals of higher genetic diversity arrived earlier on their breeding grounds and settled in the first available habitats, which correspond to intensive cultures. Our results highlight the importance of investigating the effects of environmental variability on individual genetic diversity, and of integrating information on landscape structure when conducting such studies. 相似文献
45.
46.
47.
48.
49.
D J Méwissen J H Rust J Rust 《Comptes rendus des séances de la Société de biologie et de ses filiales》1987,181(4):439-444
A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types. 相似文献
50.