全文获取类型
收费全文 | 9102篇 |
免费 | 821篇 |
国内免费 | 12篇 |
出版年
2023年 | 33篇 |
2022年 | 37篇 |
2021年 | 182篇 |
2020年 | 103篇 |
2019年 | 141篇 |
2018年 | 187篇 |
2017年 | 185篇 |
2016年 | 265篇 |
2015年 | 460篇 |
2014年 | 502篇 |
2013年 | 645篇 |
2012年 | 792篇 |
2011年 | 765篇 |
2010年 | 500篇 |
2009年 | 422篇 |
2008年 | 644篇 |
2007年 | 591篇 |
2006年 | 554篇 |
2005年 | 532篇 |
2004年 | 483篇 |
2003年 | 435篇 |
2002年 | 430篇 |
2001年 | 90篇 |
2000年 | 53篇 |
1999年 | 78篇 |
1998年 | 100篇 |
1997年 | 57篇 |
1996年 | 46篇 |
1995年 | 34篇 |
1994年 | 50篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 31篇 |
1990年 | 36篇 |
1989年 | 25篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 30篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1974年 | 21篇 |
1972年 | 16篇 |
1971年 | 12篇 |
排序方式: 共有9935条查询结果,搜索用时 93 毫秒
1.
Tom P. Moorhouse Cecilia A. L. Dahlsj? Sandra E. Baker Neil C. D'Cruze David W. Macdonald 《PloS one》2015,10(10)
Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20–40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6–6 million tourists per year, and compared our scores to tourists’ feedback on TripAdvisor. Six WTA types (impacting 1,500–13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000–340,000 individuals) had negative conservation impacts and 18 (230,000–550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide. 相似文献
2.
3.
4.
Sandra Bell 《Curtis's Botanical Magazine》1996,13(3):157-163
Summary. The Marianne North Gallery at the Royal Botanic Gardens, Kew includes many orchid paintings. The orchids depicted in the paintings, and Marianne North's travels in search of them, are described. 相似文献
5.
Adriana R. Aguilar-Melo Sophie Calmé Braulio Pinacho-Guendulain Sandra E. Smith-Aguilar Gabriel Ramos-Fernández 《American journal of primatology》2020,82(1):e23077
Some social species exhibit high levels of fission–fusion dynamics (FFD) that improve foraging efficiency. In this study, we shed light on the way that FFD allows animal groups to cope with fluctuations in fruit availability. We explore the relative contribution of fruit availability and social factors like sex in determining association and proximity patterns in spider monkeys. We tested the influence of fruit availability and social factors on the association and proximity patterns using three-year data from a group of spider monkeys in the Yucatan Peninsula of Mexico. We identified subgroup members and estimated their Interindividual distances through instantaneous scan sampling. We evaluated fruit availability by monitoring the phenology of the 10 most important food tree species for spider monkeys in the study site. Social network analyses allowed us to evaluate association and proximity patterns in subgroups. We showed that association patterns vary between seasons, respond to changes in fruit availability, and are influenced by the sex of individuals, likely reflecting biological and behavioral differences between sexes and the interplay between ecological and social factors. In contrast, proximity patterns were minimally affected by changes in fruit availability, suggesting that social factors are more important than food availability in determining cohesion within subgroups. 相似文献
6.
Maxime Lenormand Guillaume Papuga Olivier Argagnon Maxence Soubeyrand Guilhem De Barros Samuel Alleaume Sandra Luque 《Ecology and evolution》2019,9(1):237-250
The delimitation of bioregions helps to understand historical and ecological drivers of species distribution. In this work, we performed a network analysis of the spatial distribution patterns of plants in south of France (Languedoc‐Roussillon and Provence‐Alpes‐Côte d'Azur) to analyze the biogeographical structure of the French Mediterranean flora at different scales. We used a network approach to identify and characterize biogeographical regions, based on a large database containing 2.5 million of geolocalized plant records corresponding to more than 3,500 plant species. This methodology is performed following five steps, from the biogeographical bipartite network construction to the identification of biogeographical regions under the form of spatial network communities, the analysis of their interactions, and the identification of clusters of plant species based on the species contribution to the biogeographical regions. First, we identified two sub‐networks that distinguish Mediterranean and temperate biota. Then, we separated eight statistically significant bioregions that present a complex spatial structure. Some of them are spatially well delimited and match with particular geological entities. On the other hand, fuzzy transitions arise between adjacent bioregions that share a common geological setting, but are spread along a climatic gradient. The proposed network approach illustrates the biogeographical structure of the flora in southern France and provides precise insights into the relationships between bioregions. This approach sheds light on ecological drivers shaping the distribution of Mediterranean biota: The interplay between a climatic gradient and geological substrate shapes biodiversity patterns. Finally, this work exemplifies why fragmented distributions are common in the Mediterranean region, isolating groups of species that share a similar eco‐evolutionary history. 相似文献
7.
8.
9.
An RCAS-TVA-based approach to designer mouse models 总被引:9,自引:0,他引:9
Sandra Orsulic 《Mammalian genome》2002,13(10):543-547
10.