首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   936篇
  免费   81篇
  2023年   18篇
  2022年   23篇
  2021年   51篇
  2020年   22篇
  2019年   36篇
  2018年   34篇
  2017年   34篇
  2016年   40篇
  2015年   87篇
  2014年   82篇
  2013年   104篇
  2012年   95篇
  2011年   73篇
  2010年   45篇
  2009年   41篇
  2008年   44篇
  2007年   24篇
  2006年   19篇
  2005年   23篇
  2004年   13篇
  2003年   10篇
  2002年   7篇
  2001年   5篇
  1997年   2篇
  1996年   2篇
  1993年   2篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1986年   4篇
  1985年   4篇
  1984年   2篇
  1983年   3篇
  1982年   3篇
  1981年   5篇
  1980年   5篇
  1979年   2篇
  1978年   2篇
  1974年   4篇
  1973年   2篇
  1972年   2篇
  1971年   2篇
  1938年   3篇
  1934年   2篇
  1928年   2篇
  1921年   2篇
  1919年   2篇
  1918年   2篇
  1916年   4篇
排序方式: 共有1017条查询结果,搜索用时 31 毫秒
11.
A new support system has been developed which provides long-term maintenance of non-dividing adult rat liver parenchymal cells in monolayer cultures. The hepatocytes, attached to Millipore (MP) filters, are maintained as free-floating cultures which express differentiated liver cell functions for up to 13 days. After 8 days of culture on MP filters, the hepatocytes are still capable of inducing tyrosine aminotransferase 3- to 4-fold and phosphoenolpyruvate carboxykinase 10-to 15-fold. The advantage of using floating MP filters to support the hepatocytes over the more conventional culture supports such as glass or plastic dishes are: (1) the functional lifespan of cultured hepatocytes is doubled, permitting experiments requiring 4–8 days to complete; (2) it permits rapid and easy transfer of cells from one set of culture conditions to another; (3) sections can be cut from one filter permitting multiple samples from a single culture; (4) the filters containing the cells can be processed without losing the orientation of cell surfaces, an important consideration when employing techniques such as autoradiography and/or electron microscopy; and (5) this culture technique can readily be adapted for co-cultivation experiments in order to directly examine biological and biochemical effects of secreted products of one cell type on another.  相似文献   
12.
13.
Biomechanics and Modeling in Mechanobiology - It is well known that residual deformations/stresses alter the mechanical behavior of arteries, e.g., the pressure–diameter curves. In an effort...  相似文献   
14.
The primate adolescent period is characterized by a series of changes in physiology, behavior, and social relationships. Orangutans have the slowest life history and the longest period of dependency of all primates. As members of a semisolitary species with high levels of sexual coercion, adolescent female orangutans face a unique combination of challenges when achieving independence from their mother. This study examined the mating behavior of adolescent female orangutans and compared it with that of adult females to assess whether mating behavior reflects distinct strategies at these different points in the life cycle. Data were collected in Gunung Palung National Park on the island of Borneo over 20 years. Mating events from adolescent (n = 19) and adult females (n = 26) were scored and compared. Adolescent female mating events had significantly higher mating scores (indicating more proceptivity) than those of adult females (β = 1.948, p = .001). Adolescent females also engaged in elaborate sociosexual interactions with different flanged males, behaviors that were never observed during mating events of adult females. These interactions involved characteristic behavior on the part of both the adolescent females and the flanged males. Given these findings and the documentation of similar accounts of adolescent female–flanged male mating from the island of Sumatra, we propose that adolescent female orangutans display distinctive behavioral repertoires throughout the genus Pongo which serves to overcome male ambivalence toward nulliparous females, establish familiarity, and evaluate coercive tendencies in flanged males. We suggest that these behavioral patterns are an integral part of female social development in a female philopatric, but highly dispersed species where consistent social support is absent after ranging independence is achieved.  相似文献   
15.
16.
17.
18.
19.
Facilitating coexistence between people and wildlife is a major conservation challenge in East Africa. Some conservation models aim to balance the needs of people and wildlife, but the effectiveness of these models is rarely assessed. Using a case‐study approach, we assessed the ecological performance of a pastoral area in northern Tanzania (Manyara Ranch) and established a long‐term wildlife population monitoring program (carried out intermittently from 2003 to 2008 and regularly from 2011 to 2019) embedded in a distance sampling framework. By comparing density estimates of the road transect‐based long‐term monitoring to estimates derived from systematically distributed transects, we found that the bias associated with nonrandom placement of transects was nonsignificant. Overall, cattle and sheep and goat reached the greatest densities and several wildlife species occurred at densities similar (zebra, wildebeest, waterbuck, Kirk's dik‐dik) or possibly even greater (giraffe, eland, lesser kudu, Grant's gazelle, Thomson's gazelle) than in adjacent national parks in the same ecosystem. Generalized linear mixed models suggested that most wildlife species (8 out of 14) reached greatest densities during the dry season, that wildlife population densities either remained constant or increased over the 17‐year period, and that herbivorous livestock species remained constant, while domestic dog population decreased over time. Cross‐species correlations did not provide evidence for interference competition between grazing or mixed livestock species and wildlife species but indicate possible negative relationships between domestic dog and warthog populations. Overall, wildlife and livestock populations in Manyara Ranch appear to coexist over the 17‐year span. Most likely, this is facilitated by existing connectivity to adjacent protected areas, effective anti‐poaching efforts, spatio‐temporal grazing restrictions, favorable environmental conditions of the ranch, and spatial heterogeneity of surface water and habitats. This long‐term case study illustrates the potential of rangelands to simultaneously support wildlife conservation and human livelihood goals if livestock grazing is restricted in space, time, and numbers.  相似文献   
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号