全文获取类型
收费全文 | 3386篇 |
免费 | 251篇 |
出版年
2023年 | 13篇 |
2022年 | 15篇 |
2021年 | 57篇 |
2020年 | 30篇 |
2019年 | 48篇 |
2018年 | 61篇 |
2017年 | 49篇 |
2016年 | 77篇 |
2015年 | 142篇 |
2014年 | 143篇 |
2013年 | 217篇 |
2012年 | 259篇 |
2011年 | 220篇 |
2010年 | 170篇 |
2009年 | 136篇 |
2008年 | 178篇 |
2007年 | 182篇 |
2006年 | 164篇 |
2005年 | 156篇 |
2004年 | 169篇 |
2003年 | 158篇 |
2002年 | 136篇 |
2001年 | 43篇 |
2000年 | 26篇 |
1999年 | 28篇 |
1998年 | 35篇 |
1997年 | 27篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 22篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 28篇 |
1987年 | 32篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1972年 | 10篇 |
1969年 | 11篇 |
1855年 | 13篇 |
排序方式: 共有3637条查询结果,搜索用时 13 毫秒
1.
Major climatic changes in the Pleistocene had significant effects on marine organisms and the environments in which they lived. The presence of divergent patterns of demographic history even among phylogenetically closely-related species sharing climatic changes raises questions as to the respective influence of species-specific traits on population structure. In this work we tested whether the lifestyle of Antarctic notothenioid benthic and pelagic fish species from the Southern Ocean influenced the concerted population response to Pleistocene climatic fluctuations. This was done by a comparative analysis of sequence variation at the cyt b and S7 loci in nine newly sequenced and four re-analysed species. We found that all species underwent more or less intensive changes in population size but we also found consistent differences between demographic histories of pelagic and benthic species. Contemporary pelagic populations are significantly more genetically diverse and bear traces of older demographic expansions than less diverse benthic species that show evidence of more recent population expansions. Our findings suggest that the lifestyles of different species have strong influences on their responses to the same environmental events. Our data, in conjunction with previous studies showing a constant diversification tempo of these species during the Pleistocene, support the hypothesis that Pleistocene glaciations had a smaller effect on pelagic species than on benthic species whose survival may have relied upon ephemeral refugia in shallow shelf waters. These findings suggest that the interaction between lifestyle and environmental changes should be considered in genetic analyses. 相似文献
2.
3.
4.
The reproductive biology of 13 South American taxa of Bothriochloa was studied. All surveyed species reproduce sexually and are self-compatible. Several elements also point to self-pollination as their main breeding system: (i) bud pollination that occurs in most species enhancing cleistogamy, (ii) presence of pits in the glumes that impede the opening of flowers and (iii) reduction in the number of stamens, a trend associated with outbreeding. 相似文献
5.
6.
Anton Val de Lièvre 《Plant Systematics and Evolution》1856,6(24):185-187
Ohne Zusammenfassung 相似文献
7.
Anton Tomaschek 《Plant Systematics and Evolution》1888,38(4):134-136
Ohne Zusammenfassung 相似文献
8.
9.
Anton J. Rozsypal 《Biological cybernetics》1985,52(1):15-22
A model for lateral inhibition is presented in the context of the auditory channel. The mechanical analyzing system of the inner ear cannot alone account for the frequency resolution of hearing. Some additional mechanism, possibly lateral inhibition located in the auditory neural network, is needed to achieve the frequency selectivity observed in electrophysiological and psychoacoustical experiments. In a computer simulation study, the shape of an ideal lateral inhibition function was obtained. Such a function is applicable to all sensory modalities. In hearing, this function permits the sharpest possible frequency resolution as it can completely remove the frequency desharpening effect of the mechanical properties of the basilar membrane. In vision, it can compensate for abberations caused by the imperfections of the optical system of the eye.An expanded version of a paper presented at the XIth Intenational Congress on Acoustics, Paris, 1983 相似文献
10.
Anton Koch 《Zoomorphology》1938,34(4):584-609
Ohne Zusammenfassung 相似文献