全文获取类型
收费全文 | 719篇 |
免费 | 71篇 |
国内免费 | 113篇 |
出版年
2024年 | 6篇 |
2023年 | 12篇 |
2022年 | 26篇 |
2021年 | 51篇 |
2020年 | 35篇 |
2019年 | 33篇 |
2018年 | 46篇 |
2017年 | 28篇 |
2016年 | 40篇 |
2015年 | 40篇 |
2014年 | 45篇 |
2013年 | 50篇 |
2012年 | 58篇 |
2011年 | 57篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 30篇 |
2007年 | 32篇 |
2006年 | 38篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 36篇 |
2002年 | 26篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1982年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有903条查询结果,搜索用时 31 毫秒
1.
2.
Cerebral glucose metabolism is a reliable index of neural activity and may provide evidence for brain function in healthy adults. We studied the correlation between cerebral glucose metabolism and age under the resting-state in both sexes with position emission tomography. Statistical test of age effect on cerebral glucose metabolism was performed using the statistical parametric mapping software with a voxel-by-voxel approach ( family wise error corrected, -voxel threshold). The subjects consisted of 108 females (mean S.D. = 4510 years) and 126 males (mean S.D. = 4911 years). We showed here that brain activity in the frontal and temporal lobes in both sexes decreased significantly with normal aging. The glucose metabolism in the caudate bilaterally showed a negative correlation with age in males, but not in females. Few regions in males were shown with an increased glucose metabolism with age. Although the mechanisms of brain aging are still unknown, a map of brain areas susceptible to age was described in this report. 相似文献
3.
4.
5.
6.
7.
8.
9.
Pengcheng Wang John T Burley Yang Liu Jiang Chang De Chen Qi Lu Shou-Hsien Li Xuming Zhou Scott Edwards Zhengwang Zhang 《Molecular biology and evolution》2021,38(1):263
Population genetic theory and empirical evidence indicate that deleterious alleles can be purged in small populations. However, this viewpoint remains controversial. It is unclear whether natural selection is powerful enough to purge deleterious mutations when wild populations continue to decline. Pheasants are terrestrial birds facing a long-term risk of extinction as a result of anthropogenic perturbations and exploitation. Nevertheless, there are scant genomics resources available for conservation management and planning. Here, we analyzed comparative population genomic data for the three extant isolated populations of Brown eared pheasant (Crossoptilon mantchuricum) in China. We showed that C. mantchuricum has low genome-wide diversity and a contracting effective population size because of persistent declines over the past 100,000 years. We compared genome-wide variation in C. mantchuricum with that of its closely related sister species, the Blue eared pheasant (C. auritum) for which the conservation concern is low. There were detrimental genetic consequences across all C. mantchuricum genomes including extended runs of homozygous sequences, slow rates of linkage disequilibrium decay, excessive loss-of-function mutations, and loss of adaptive genetic diversity at the major histocompatibility complex region. To the best of our knowledge, this study is the first to perform a comprehensive conservation genomic analysis on this threatened pheasant species. Moreover, we demonstrated that natural selection may not suffice to purge deleterious mutations in wild populations undergoing long-term decline. The findings of this study could facilitate conservation planning for threatened species and help recover their population size. 相似文献
10.