全文获取类型
收费全文 | 25615篇 |
免费 | 2745篇 |
国内免费 | 3058篇 |
出版年
2024年 | 71篇 |
2023年 | 345篇 |
2022年 | 876篇 |
2021年 | 1344篇 |
2020年 | 1047篇 |
2019年 | 1252篇 |
2018年 | 1141篇 |
2017年 | 896篇 |
2016年 | 1167篇 |
2015年 | 1664篇 |
2014年 | 1950篇 |
2013年 | 1987篇 |
2012年 | 2346篇 |
2011年 | 2132篇 |
2010年 | 1403篇 |
2009年 | 1233篇 |
2008年 | 1440篇 |
2007年 | 1265篇 |
2006年 | 1168篇 |
2005年 | 979篇 |
2004年 | 932篇 |
2003年 | 947篇 |
2002年 | 850篇 |
2001年 | 533篇 |
2000年 | 399篇 |
1999年 | 365篇 |
1998年 | 226篇 |
1997年 | 198篇 |
1996年 | 182篇 |
1995年 | 154篇 |
1994年 | 164篇 |
1993年 | 107篇 |
1992年 | 103篇 |
1991年 | 85篇 |
1990年 | 79篇 |
1989年 | 74篇 |
1988年 | 56篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 40篇 |
1984年 | 25篇 |
1983年 | 29篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
We released seeds of two sympatric tree species, Corylus mandshurica (seed with thinner seed hull, higher nutrition) and C. heterophylla (seeds with thicker seed hull, lower nutrition) in the masting year of C. mandshurica in 2008, and C. heterophylla in 2009, respectively, to investigate how seed masting of the two sympatric Corylus species affects seed removal and dispersal fitness of the two species differently at both intra- and inter-specific levels.
At intra-specific level, the authors found mast seeding of both C. mandshurica and C. heterophylla significantly reduced seed removal, seed consumption, but increased seed dispersal distance and seed dispersal fitness of
the released seeds. Mast seeding of C. mandshurica increased seed caching of C. mandshurica. At inter-specific level, the authors found mast seeding of C. mandshurica reduced seed removal of C. heterophylla, but mast seeding of C. heterophylla did not significantly reduce seed removal of C. mandshurica. Mast seeding of C. mandshurica reduced seed consumption of C. heterophylla, while mast seeding of C. heterophylla reduced seed consumption of C. mandshurica. We found mast seeding of C. mandshurica significantly reduced seed dispersal distance of C. heterophylla, while mast seeding of C. heterophylla significantly increased seed dispersal distance of C. mandshurica. We found that mast seeding of C. mandshurica significantly increased seed dispersal fitness of C. heterophylla, while mast seeding of C. heterophylla did not significantly increase seed dispersal fitness of C. mandshurica. More studies are needed to reveal the ecological consequences of mast seeding at inter-specific or community-level. Seed
traits may attribute the differences of mast seeding at inter-specific level. Because seeds with thinner seed hull and higher
nutrition were more harvested and eaten by rodents, mast seeding of C. mandshurica might have reduced seed removal and seed consumption, but increased dispersal fitness of C. heterophylla (seeds with thicker seed hull, lower nutrition). Therefore, synchrony among species is, or is not, selectively beneficial
to the focus species depends on seed traits which determine gains from mast seeding at inter-specific level. 相似文献
3.
4.
5.
6.
7.
8.
Zhaohua Zhang LiLi Ge Shanshan Zhang Jue Wang Wen Jiang Qian Xin Yun Luan 《Journal of cellular and molecular medicine》2020,24(23):13938
The aim of the study was to explore the mechanism of mesenchymal stem cell‐derived exosomes (MSC‐EXO) to protect against experimentally induced pulmonary hypertension (PH). Monocrotaline (MCT)‐induced rat model of PH was successfully established by a single intraperitoneal injection of 50 mg/kg MCT, 3 weeks later the animals were treated with MSC‐EXO via tail vein injection. Post‐operation, our results showed that MSC‐EXO could significantly reduce right ventricular systolic pressure (RVSP) and the right ventricular hypertrophy index, attenuate pulmonary vascular remodelling and lung fibrosis in vivo. In vitro experiment, the hypoxia models of pulmonary artery endothelial cell (PAEC) and pulmonary vascular smooth muscle cell (PASMC) were used. We found that the expression levels of Wnt5a, Wnt11, BMPR2, BMP4 and BMP9 were increased, but β‐catenin, cyclin D1 and TGF‐β1 were decreased in MSC‐EXO group as compared with MCT or hypoxia group in vivo or vitro. However, these increased could be blocked when cells were transfected with Wnt5a siRNA in vitro. Taken together, these results suggested that the mechanism of MSC‐EXO to prevent PH vascular remodelling may be via regulation of Wnt5a/BMP signalling pathway. 相似文献
9.
10.