全文获取类型
收费全文 | 3715篇 |
免费 | 357篇 |
出版年
2024年 | 10篇 |
2023年 | 40篇 |
2022年 | 91篇 |
2021年 | 172篇 |
2020年 | 65篇 |
2019年 | 109篇 |
2018年 | 118篇 |
2017年 | 96篇 |
2016年 | 189篇 |
2015年 | 250篇 |
2014年 | 244篇 |
2013年 | 263篇 |
2012年 | 371篇 |
2011年 | 308篇 |
2010年 | 181篇 |
2009年 | 160篇 |
2008年 | 215篇 |
2007年 | 209篇 |
2006年 | 177篇 |
2005年 | 162篇 |
2004年 | 173篇 |
2003年 | 118篇 |
2002年 | 135篇 |
2001年 | 14篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 28篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1974年 | 5篇 |
1970年 | 3篇 |
1967年 | 2篇 |
1900年 | 2篇 |
1899年 | 1篇 |
排序方式: 共有4072条查询结果,搜索用时 15 毫秒
861.
Phenological shifts and associated changes in the temporal match between trophic levels have been a major focus of the study of ecological consequences of climate change. Previously, the food peak has been thought to respond as an entity to warming temperatures. However, food peak architecture, that is, timings and abundances of prey species and the level of synchrony between them, determines the timing and shape of the food peak. We demonstrate this with a case example of three passerine prey species and their predator. We explored temporal trends in the timing, height, width, and peakedness of prey availabilities and explained their variation with food peak architecture and ambient temperatures of prebreeding and breeding seasons. We found a temporal match between the predator's breeding schedule and food availability. Temporal trends in the timing of the food peak or in the synchrony between the prey species were not found. However, the food peak has become wider and more peaked over time. With more peaked food availabilities, predator's breeding success will depend more on the temporal match between its breeding schedule and the food peak, ultimately affecting the timing of breeding in the predator population. The height and width of the food peak depended on the abundances and breeding season lengths of individual prey species and their reciprocal synchronies. Peakednesses of separate prey species' availability distributions alone explained the peakedness of the food peak. Timing and quantity of food production were associated with temperatures of various time periods with variable relevance in different prey species. Alternating abundances of early and late breeding prey species caused high annual fluctuation in the timing of the food peak. Interestingly, the food peak may become later even when prey species' schedules are advanced. Climate warming can thus produce unexpected changes in the food availabilities, intervening in trophic interactions. 相似文献
862.
Emma J. Dunston Jackie Abell Rebecca E. Doyle Megan Evershed Rafael Freire 《Journal of Ethology》2016,34(3):277-290
Increasing our understanding of personality, at an individual and group level, is crucial to the pre-release assessment of social species within ex situ reintroduction programs. We conducted the first exploration into the personality of a captive-origin pride of African lions (Panthera leo), assessing behavioural variations and consistencies in daily activity, social and hunting behaviour, and boldness. Data were collected via direct observations, while a species-specific protocol for testing boldness, using playbacks, was developed. Differences in sex, age and session time for the activity budget were evaluated using Pearson correlations and repeated-measures ANOVA, while social interactions were analysed using social network analysis. Spearman’s correlations were conducted to assess for associations between boldness scores, activity and sociality. The two boldness tests provided a range of scores per lion, indicating that the test was effective. Correlations and variations in individual behaviour indicated that adults and sub-adults have specific roles within pride behaviour. Correlations between boldness and activity and social behaviours provided information on the role of individuals, allowing investigation into the behaviour of a dominant and a social keystone. Our study indicates that evaluating various aspects of behaviour in conjunction with boldness has the potential to assist the pre-release assessment of a pride within an ex situ reintroduction program. 相似文献
863.
Emma?G?theEmail author Allan?Timmermann Kathrin?Januschke Annette?Baattrup-Pedersen 《Hydrobiologia》2016,783(1):79-91
Most river restoration projects have applied relatively small-scale measures focused on improving specific instream conditions, with only limited outcomes for biodiversity in rivers and their adjacent riparian habitats. Here, we investigate the effects of both small- and large-scale restoration projects on floodplain vegetation across 20 European catchments. We focused on the roles of different restoration parameters (i.e., the number, spatial extent and type of restoration measure applied and restoration age) and specific environmental characteristics in regulating changes in plant diversity and trait composition following restoration. Among restoration characteristics, restoration type was the only significant determinant of plant community responses, with stream channel widening having the strongest effects, particularly on the diversity and composition of species traits favoured by increases in physical disturbance (e.g. flooding) and open habitat patch availability (e.g. plant growth form, life strategy and life span). Of the environmental variables, altitude and discharge were positively and most strongly related to responses of both species and trait diversity. Our results emphasise the value of (i) choosing relevant restoration measures that affect environmental conditions of importance for the target organism group and (ii) conducting restoration projects in environmental settings where the likelihood of restoration “success” is maximised. 相似文献
864.
865.
866.
867.
868.
The early colonial atlantic world: New insights on the African Diaspora from isotopic and ancient DNA analyses of a multiethnic 15th–17th century burial population from the Canary Islands,Spain
下载免费PDF全文
![点击此处可从《American journal of physical anthropology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
869.
870.
Emma Ojala Ville Uusitalo Terhi Virkki-Hatakka Antti Niskanen Risto Soukka 《The International Journal of Life Cycle Assessment》2016,21(8):1092-1105