全文获取类型
收费全文 | 508篇 |
免费 | 39篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 6篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 21篇 |
2014年 | 18篇 |
2013年 | 39篇 |
2012年 | 46篇 |
2011年 | 34篇 |
2010年 | 27篇 |
2009年 | 16篇 |
2008年 | 33篇 |
2007年 | 38篇 |
2006年 | 30篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1965年 | 3篇 |
排序方式: 共有547条查询结果,搜索用时 31 毫秒
541.
542.
543.
544.
Human tracks discovered in 1874 at a site named El Cauce or Acahualinca near the shores of Lake Managua, Nicaragua, are the most famous and abundant human tracks in the Americas. They represent a landmark ichnological discovery during the late 19th century that generated much debate regarding their age and origins. Reported dates for the tracks range from 2,120 to 6,500 B.P. The site, which is now situated within the limits of Nicaragua's capital city of Managua, forms the basis of the Acahualinca Tracks Museum (Huellas de Acahualinca) and has been in place since 1953. However, it is still little known and has not been systematically studied, despite being an important window into Meso-American prehistory. Two exposures of a surface of volcanic ash reveal hundreds of human tracks comprising a minimum of 12 clearly defined trackways, and a trampled zone or path representing at least three more individuals, all heading in the same northwesterly direction. Tracks of deer, opossum and at least one bird are also present. Bison tracks collected from another nearby site (El Recreo) that is no longer accessible are on display at the museum. The Acahualinca tracks are noteworthy for the exceptional quality of preservation. We herein present the first maps of the two exposures, which combine to tell a story of human and animal activity along the shores of ancient Lake Managua several thousand years ago. 相似文献
545.
Synaptic activity‐induced glycolysis facilitates membrane lipid provision and neurite outgrowth
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
546.
547.
Paulo Emilio Llambías María Milagros Jefferies Daniel Pascual Cáceres Apaza Paula Sabrina Garrido Agustín Zarco Ramiro Santiago Arrieta José Benjamin Bender 《Ibis》2020,162(1):75-89
Grass Wrens Cistothorus platensis build two types of non-breeding nest structures: platforms and dummy nests. Platforms are rudimentary accumulations of grasses concealed between vegetation. Dummy and breeding nests are dome-shaped with a similar structural layer. We used a nest-removal experiment and observational data to evaluate several hypotheses regarding the adaptive significance of building multiple nests in a south temperate population of Grass Wrens. Building non-breeding nests was not a strategy of males to attract additional females, as most of these nests were built after pair formation and both sexes collaborated during building. Building non-breeding nests was not a post-pairing display as the presence of multiple nests did not increase female investment in the breeding attempt: clutch size and female provisioning to nestlings did not differ between experimental and control territories where no non-breeding nests were removed. Similarly, in non-manipulated territories, clutch size and female provisioning were not correlated with the number of non-breeding nests or with males’ nest-building effort. Contrary to this hypothesis, the number of non-breeding nests was associated with delayed clutch initiation and reduced hatching success. The presence of non-breeding nests did not reduce nest predation and brood parasitism, which did not differ between experimental and control territories. We did not detect differences in concealment between non-breeding and breeding nests, suggesting that non-breeding nests were not the result of abandonment before egg-laying to reduce subsequent nest predation. Dummy nests did not provide shelter; they were not used frequently for roosting over the breeding season and were not maintained during the non-breeding season. We suggest that building non-breeding nests may be an attempt by males to manipulate the decision of females to breed with a mate they might otherwise reject or to start reproduction earlier than optimal for the females. 相似文献