全文获取类型
收费全文 | 397篇 |
免费 | 46篇 |
出版年
2015年 | 7篇 |
2013年 | 8篇 |
2012年 | 4篇 |
2011年 | 4篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2005年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1960年 | 4篇 |
1959年 | 10篇 |
1958年 | 22篇 |
1957年 | 19篇 |
1956年 | 19篇 |
1955年 | 16篇 |
1954年 | 17篇 |
1953年 | 15篇 |
1952年 | 14篇 |
1951年 | 11篇 |
1950年 | 11篇 |
1949年 | 9篇 |
1948年 | 8篇 |
排序方式: 共有443条查询结果,搜索用时 15 毫秒
1.
VEGETATION'S FOURTH DIMENSION 总被引:3,自引:1,他引:2
D. WALKER 《The New phytologist》1982,90(3):419-429
2.
3.
Jeff A Johnson Heather RL Lerner Pamela C Rasmussen David P Mindell 《BMC evolutionary biology》2006,6(1):65-12
Background
Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis. 相似文献4.
5.
6.
7.
8.
Butterfly migration from and to peninsular Florida 总被引:1,自引:0,他引:1
THOMAS J. WALKER 《Ecological Entomology》1991,16(2):241-252
Abstract.
- 1 Migrating butterflies were monitored with traps for 10 years at a site in north peninsular Florida, to determine seasonal and annual variation in numbers and directions of flight.
- 2 In the spring, 81–96% of the principal migrants, Phoebis sennae (L.), Agraulis vanillae (L.), Precis coenia (Hübner) and Urbanus proteits (L.), flew northward; in the autumn, 86–95% flew southward.
- 3 Estimated mean net numbers of these four species flying northward in spring across each ENE-WSW metre were 3, 6, 69 and <1 respectively; numbers flying southward in autumn were 222, 413, 37 and 146.
- 4 During a 5-year period, the ratio of highest to lowest seasonal migration for a species did not exceed 9.3.
- 5 The average median date of spring migration was 27 March for P.sennae, 23 April for P.coenia, and 12 May for A.vanillae. The average median date of autumn migration was 2–5 October except for U.proteus, whose average date was 14 October.
- 6 The autumn migratory period, as measured by the duration of the middle half of migration, was about 2 weeks in P.coenia and about 4 weeks in the other three species.
- 7 Compared to previously reported butterfly migrations, the ones studied here were notably uniform in magnitude and regular in timing.
- 8 These and other data suggest that 4 million or more of these butterflies migrate northward from peninsular Florida almost every spring and that 40 million or more migrate southward to peninsular Florida almost every autumn.
9.
FLANDRIAN ENVIRONMENTAL HISTORY OF THE ISLE OF MULL, SCOTLAND. 总被引:4,自引:4,他引:0
10.
Estimation in change-point hazard rate models 总被引:1,自引:0,他引:1