全文获取类型
收费全文 | 11841篇 |
免费 | 935篇 |
国内免费 | 2篇 |
出版年
2023年 | 82篇 |
2022年 | 173篇 |
2021年 | 368篇 |
2020年 | 206篇 |
2019年 | 267篇 |
2018年 | 346篇 |
2017年 | 350篇 |
2016年 | 420篇 |
2015年 | 680篇 |
2014年 | 707篇 |
2013年 | 894篇 |
2012年 | 1081篇 |
2011年 | 999篇 |
2010年 | 605篇 |
2009年 | 504篇 |
2008年 | 676篇 |
2007年 | 684篇 |
2006年 | 581篇 |
2005年 | 534篇 |
2004年 | 510篇 |
2003年 | 455篇 |
2002年 | 423篇 |
2001年 | 117篇 |
2000年 | 115篇 |
1999年 | 110篇 |
1998年 | 98篇 |
1997年 | 75篇 |
1996年 | 67篇 |
1995年 | 53篇 |
1994年 | 40篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 61篇 |
1989年 | 26篇 |
1988年 | 20篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1976年 | 9篇 |
1974年 | 15篇 |
1973年 | 18篇 |
1968年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
Gabriel S. Lopes Camila Righetto Cassano Laila Santim Mureb Flavia Regina Miranda Ariovaldo P. Cruz-Neto Gastón Andrés Fernandez Giné 《Austral ecology》2023,48(7):1344-1360
Changes in ambient temperature and solar radiation may affect sloths' metabolic rate and body temperature, with consequent changes in activities, postures and microhabitat selection. Although the separate effect of temperature and solar radiation on sloth's behaviour have been previously studied, the combined effect of these climatic factors on behavioural aspects of sloths has never been systematically evaluated in field conditions. Here we evaluated the influence of hourly ambient temperature variation on maned sloth (Bradypus torquatus) activities, postures and tree crown positions, under sunny and cloudy conditions; and tested if any of the animal posture and position increase their exposure to human detection. We performed 350 h of visual observation on eight maned sloths, equipped with radio-backpacks, in northern Bahia, Brazil, recording their activities, and their resting postures and positions on tree crowns. We also recorded the time taken to visualize the sloths on 58 days to analyse if sloths' detection is affected by posture and position. Higher ambient temperature, within a range of 21–33°C, increased the sloths' activity levels in cloudy conditions but reduced their activity in sunny conditions. Increasing ambient temperature also reduced the frequency of huddled posture and increased the frequency of extended posture and permanence in the inner tree crown. Lastly, the postures and positions did not influence sloths' detectability. Thus, the direction of the temperature–activity relationship depends on climatic conditions (sunny/cloudy), and individuals rely on resting postures and positions to thermoregulate. The warmer and drier future climate, expected to occur in the northern Atlantic Forest, may impose change in the diurnal activity levels and postural pattern for this threatened species, leading maned sloths to reduce its activity on sunny and warmer days and adopting an extended posture. 相似文献
74.
Martine de Boer Maaike te Lintel Hekkert Jiang Chang Bibi S. van Thiel Leonie Martens Maxime M. Bos Marion G. J. de Kleijnen Yanto Ridwan Yanti Octavia Elza D. van Deel Lau A. Blonden Renata M. C. Brandt Sander Barnhoorn Paula K. Bautista-Niño Ilona Krabbendam-Peters Rianne Wolswinkel Banafsheh Arshi Mohsen Ghanbari Christian Kupatt Leon J. de Windt A. H. Jan Danser Ingrid van der Pluijm Carol Ann Remme Monika Stoll Joris Pothof Anton J. M. Roks Maryam Kavousi Jeroen Essers Jolanda van der Velden Jan H. J. Hoeijmakers Dirk J. Duncker 《Aging cell》2023,22(3):e13768
75.
76.
Paula Tatiana Lopes Seixas Antonio Jacinto Demuner Luiz Claudio Almeida Barbosa Cristiane Isaac Cerceau Daiane Einhardt Blank Marcelo Henrique Dos Santos Elizeu de Sá Farias Marcelo Coutinho Picanço 《Journal of Applied Entomology》2023,147(2):116-125
Aedes aegypti L. (Diptera: Culicidae) is a vector for serious diseases in tropical regions. This pest is mainly controlled by commercial larvicides but the application of such products has led to environmental problems. Essential oils (EO) have been consistently reported as molecules with insecticidal activity and can be used to produce more environmentally friendly larvicides in the control of A. aegypti. In this study, the larvicidal effect of essential oils (EO) from the leaves of three Artemisia species was evaluated against A. aegypti. The oils were obtained from steam distillation and their chemical composition was determined by gas chromatography–mass spectrometry. The EO of Artemisia camphorata was the most active in the screening bioassay and presented LC50 and LC95 of 64.95 and 74.18 μg ml−1, respectively. In addition, we found that germacrene D-4-ol was the constituent responsible for the toxicity of this EO. Artemisia camphorata EO and its major constituent, germacrene D-4-ol, are promising for the development of natural larvicides against A. aegypti. 相似文献
77.
Joana Pais De Faria Vitor H. Paiva Sara N. Veríssimo Catarina S. Lopes Rita Soares João Oliveira Ivo dos Santos Ana C. Norte Jaime A. Ramos 《Ibis》2023,165(1):312-321
Gulls, as largely flexible opportunistic individuals, have been increasingly breeding in many cities around the world, but it is still unclear whether urban habitats are of equal or higher quality than traditional natural habitats or represent an ecological trap with immediate reproductive benefits but longer-term detrimental consequences to health. Here we present a study of breeding parameters (nest density, egg dimensions, clutch size, hatching success and adult body condition) and physiological parameters (erythrocyte sedimentation rate, heterophil/lymphocyte ratio, haemoglobin concentration and measurements of oxidative stress) as indicators of the general health condition of Yellow-legged Gull Larus michahellis adults and chicks from natural and urban colonies. Yellow-legged Gulls in the largest urban area (Porto) laid smaller eggs and clutches, showed a significantly lower occurrence of inflammatory processes in chicks, and showed a slower early chick growth than in the natural colony of Deserta. This suggests that urban gulls might be facing important trade-offs between the advantages of breeding in lower density urban colonies, with fewer intraspecific interactions and a lower disease transmission probability, and the disadvantages of having an anthropogenic diet usually lower in nutritional value. 相似文献
78.
79.
Andrea Evangelina Arcángel Emiliano Alexis Rodríguez Juan Francisco Saad Paula de la Barra Maite Andrea Narvarte Lorena Pía Storero Patricio Javier Pereyra 《Journal of phycology》2023,59(6):1310-1322
Population dynamics can be influenced by physical and biological factors, particularly in stressful environments. Introduced species usually have great physiological plasticity, resulting in populations with different traits. Undaria pinnatifida, a macroalga originally described from northeast Asia, was introduced in Northern Patagonia, Argentina (San Matías Gulf) around 2010. To describe the spatio-temporal variability in population structure and morphometry of U. pinnatifida, we conducted monthly field samplings for 2 years at the intertidal area of two contrasting sites in the San Matías Gulf. Individuals of U. pinnatifida were classified by developmental stage, and their morpho-gravimetric variables were measured. In both intertidal sites juveniles were found in higher proportion during austral autumn and grew and matured during the autumn-winter months (from May onwards), and individuals senesced during early austral summer (December and January). Conversely, density and biomass were largely different between sites, and individuals showed slight morphological variability between sites. Environmental (e.g., nutrient concentration, available substrate) and biological factors (e.g., facilitation, competition) may explain the observed differences. Since there is not a macroalga with U. pinnatifida morphometrical characteristics in the intertidal environments of San Matías Gulf, studying this recent introduction gives us a better understanding of its potential ecological effects. 相似文献
80.
Molecular cloning of a gene involved in glucose sensing in the yeast Saccharomyces cerevisiae 总被引:6,自引:1,他引:5
Linda Van Aelst Stefan Hohmann Botchaka Bulaya Wim de Koning Laurens Sierkstra Maria José Neves Kattie Luyten Rafael Alijo José Ramos Paola Coccetti Enzo Martegani Neuza Maria de Magalhães-Rocha Rogelio Lopes Brandão Patrick Van Dijck Mieke Vanhalewyn Peter Durnez Arnold W. H. Jans Johan M. Thevelein 《Molecular microbiology》1993,8(5):927-943