全文获取类型
收费全文 | 584篇 |
免费 | 30篇 |
专业分类
614篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 53篇 |
2011年 | 44篇 |
2010年 | 32篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 29篇 |
2006年 | 35篇 |
2005年 | 15篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 17篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有614条查询结果,搜索用时 4 毫秒
611.
612.
Ladislav Mucina 《Plant Ecology》1989,81(1-2):107-115
Ruderal communities dominated by Onopordum acanthium are encountered in those regions of Europe with a dry and continental climate. Variability in the climate and local phytogeography within these regions is reflected in the floristic variability of the communities studied. A floristic cline within the communities was summarised by means of multivariate classification and ordination methods. Two associations distributed in temperate Europe and belonging to the Onopordetalia, the Onopordetum acanthii s.str. and Carduo acanthoidis-Onopordetum acanthii, were distinguished; The Carduo acanthoidis-Onopordetum is varied and occurs in several geographic races and sub-races. The Onopordetum acanthii s.str. is confined to deep inner-montane valleys with a continental climate. The other Onopordum acanthium communities described from Spain belong to the Scolymo hispanici-Onopordetalia nervosi.Abbreviations CA =
correspondence analysis
- CLC =
complete linkage clustering 相似文献
613.
Marco António Teixeira Zullo Ladislav Kohout Mariangela de Burgos Martins de Azevedo 《Plant Growth Regulation》2003,39(1):1-11
In this paper the definitions of brassinolide, brassinolide activity andbrassins are reviewed, and definitions for the terms brassin, naturalbrassinosteroids and brassinosteroid analogues, based on biosynthetic reasoningand structure similarity are proposed. 相似文献
614.
Capsule In pastured old oak woodland, breeding pairs of Eurasian Nuthatch selected territories with significantly higher densities of trees and cavities.Aims To define territorial borders that exist within a nuthatch population and to compare densities of trees and cavities between used and non-used parts of their available habitat in order to determine habitat preferences.Methods The number and location of territories was estimated by mapping the individual positions of colour-ringed birds. We measured habitat characteristics in regular sampling grid (number of trees and number of cavities per 50?×?50?m) during three successive seasons and modelled probability of occurrence of nuthatch territories in the area.Results Breeding pairs were observed to defend territories of median size between 1.46 and 2.93?ha. These sizes correspond well to high-quality habitat territories for this species. We found that pairs tended to occupy territories with higher densities of trees and cavities. Based on generalized linear mixed-effects model estimates, we found that in pastured oak woodland habitat with density of 60 trees per ha, the estimated probability of occurrence (with 95% confidence interval) of a nuthatch territory was about 96% (83?99). For cavity density, the probability of territory occurrence was about 74% (52?89) at the level of 60 cavities per ha.Conclusion We suggest that higher tree and cavity densities reduce territory defence costs in the species because birds may use less energy during foraging, predation avoidance and competition for a nest hole. 相似文献