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   422篇
  免费   2篇
  2014年   3篇
  2013年   7篇
  2012年   5篇
  2011年   19篇
  2010年   16篇
  2009年   29篇
  2008年   8篇
  2007年   24篇
  2006年   9篇
  2005年   10篇
  2004年   6篇
  2003年   5篇
  1999年   4篇
  1998年   3篇
  1997年   12篇
  1996年   9篇
  1995年   14篇
  1994年   7篇
  1993年   7篇
  1992年   11篇
  1991年   9篇
  1990年   8篇
  1989年   8篇
  1988年   9篇
  1987年   5篇
  1986年   8篇
  1985年   9篇
  1984年   9篇
  1983年   5篇
  1982年   9篇
  1981年   6篇
  1980年   10篇
  1979年   10篇
  1978年   7篇
  1977年   6篇
  1976年   4篇
  1975年   8篇
  1974年   3篇
  1972年   7篇
  1971年   4篇
  1970年   3篇
  1959年   7篇
  1958年   13篇
  1955年   5篇
  1954年   4篇
  1953年   2篇
  1952年   4篇
  1951年   4篇
  1950年   5篇
  1948年   4篇
排序方式: 共有424条查询结果,搜索用时 0 毫秒
421.
ABSTRACT Feral swine (Sus scrofa) impact resources through their destructive feeding behavior, competition with native wildlife, and impacts to domestic animal agriculture. We studied aerial gunning on feral swine to determine if aerial gunning altered home range and core area sizes, distances between home range centroids, and distances moved by surviving individuals. We collected data before, during, and after aerial gunning in southern Texas. Using Global Positioning System collars deployed on 25 adult feral swine at 2 study sites, we found home range and core area sizes did not differ before and after aerial gunning. However, feral swine moved at a greater rate during the aerial gunning phase than during the before and after periods. We concluded that aerial gunning had only minor effects on the behavior of surviving swine and that this removal method should be considered a viable tool in contingency planning for a foreign animal disease outbreak.  相似文献   
422.
423.
Strategies to assess long-term atmosphere-ecosystem exchange of CO2 and H2O must deal not only with time trends but also with spatial variability. Flux towers efficiently measure time trends, but only at discrete sites, always limited in number. Representativeness of these sites and the causes of spatial variation between sites are difficult to investigate from tower data alone. Such issues are better addressed with flux measurements from moving vehicles, particularly aircraft. Recent technological advancements in aircraft and instrumentation now allow mobile flux measurement with enhanced precision, greater ease, and lower cost. Results are presented which illustrate the importance of spatial variability, and some suggestions are given for assessment of flux-tower representativeness. Unfortunately, airborne observations of the kind presented here are practical only during a part of the daylight hours in brief intensive field campaigns. Extrapolation of spatial-structure information derived from these measurements to night-time or to long-term averages thus remains problematic. For the foreseeable future this extrapolation will require models that faithfully simulate both space and time characteristics of H2O and CO2 exchange. The development and validation of such models will be greatly enhanced by the increased availability of measurements from moving vehicles, which record spatial as well as temporal structure.  相似文献   
424.
Pericarp structure and generic affinities in the Anacardiaceae   总被引:1,自引:0,他引:1  
Pericarp structure is surveyed in 29 genera. Homologous regions termed exocarp, mesocarp and endocarp are established. While exocarp and mesocarp structure show some uniformity, there are two very distinct types of endocarp, designated the Anacardium- type and the Spondias- type . The distribution of these indicates that the current division of the family into five tribes is artificial. The occurrence of the Spondias-type in Canarium , a member of the sister group Burseraceae, suggests that this type is plesiomorphic in the Anacardiaceae. In addition, the presence of the Anacardium- type in Blepharocarya (Blepharocaryaceae) and Orthopterygium Qulianiaceae) further supports the inclusion of these taxa in the Anacardiaceae.  相似文献   
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