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   292篇
  免费   9篇
  2012年   6篇
  2010年   8篇
  2009年   6篇
  2008年   6篇
  2007年   7篇
  2006年   6篇
  2005年   7篇
  2004年   6篇
  2001年   7篇
  2000年   6篇
  1999年   3篇
  1998年   8篇
  1997年   7篇
  1996年   11篇
  1995年   6篇
  1994年   5篇
  1993年   4篇
  1992年   5篇
  1991年   6篇
  1990年   7篇
  1989年   7篇
  1988年   5篇
  1987年   3篇
  1986年   9篇
  1985年   6篇
  1984年   4篇
  1983年   4篇
  1982年   4篇
  1981年   5篇
  1980年   4篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1975年   3篇
  1974年   5篇
  1972年   5篇
  1971年   5篇
  1970年   3篇
  1959年   6篇
  1958年   6篇
  1957年   6篇
  1956年   6篇
  1955年   3篇
  1954年   9篇
  1953年   14篇
  1952年   3篇
  1951年   5篇
  1950年   4篇
  1949年   4篇
  1948年   4篇
排序方式: 共有301条查询结果,搜索用时 15 毫秒
121.
A linguistico-semantic pattern associated with the designation of foods in English can be used in convenient classroom demonstrations of the concept of a cultural code and its importance.  相似文献   
122.
123.
124.
Abstract Birds have been widely regarded as a key element in monitoring biodiversity both in Australia and elsewhere. We believe that, although birds are unlikely to be an umbrella or indicator taxon for other biota (other vertebrates, invertebrates, plants, microorganisms), they do represent a taxon that can be monitored more easily and with less effort per datum than other biotic components. It has been shown by the great participation rate of lay observers (whom we call monitors) in several schemes (notably the Birds Australia Atlas programs) that there is a capacity to mobilize the public to undertake bird surveying. Although there are many limitations to acquiring high‐quality information (scale, dynamism, mobility, irruptiveness, paucity of monitors over much of the rangelands), we think that these can be dealt with to allow the use of birds as a key component of biodiversity monitoring. We outline some of the possible options for statistically characterizing monitoring data for rangeland birds.  相似文献   
125.
Abstract Ecologists have long sought to understand why some species are rare and others common. For the most part, inconsistent relationships between local rarity and underlying mechanisms have emerged. One possibility for this inconsistency is that locally rare species may not always be rare. However, it is largely unknown whether most locally rare species in a community possess the capacity to become abundant elsewhere in their geographical range. Here, we identified 57 locally rare plant species of open forest in south‐eastern Australia. We found that most of these species (91%) occurred in higher abundance at other sites within their geographical range (somewhere‐abundant species), while the remaining small percentage of locally rare species were consistently rare (everywhere‐sparse species). Somewhere‐abundant species had significantly smaller seeds on average than everywhere‐sparse species in cross‐species regression analysis. This pattern was not maintained when the influence of other life‐history attributes was controlled for, or when phylogenetic relatedness among species was considered explicitly in phylogenetic regression analysis. In both cross‐species and phylogenetic regressions, somewhere‐abundant and everywhere‐sparse species did not differ significantly with respect to growth form, height, regeneration‐after‐fire strategy, or dispersal. Our findings provide further evidence for the notion that theories to account for local rarity which are couched in terms of within‐community interactions alone are incomplete for the majority of species, because they need to account for different outcomes in different places.  相似文献   
126.
A nutrient, slant-board technique was developed in order to estimate the losses to roots of white clover (Trifolium repens L.), caused by the feeding of the larvae of Sitona weevils. In this preliminary experiment losses of up to 50% of root length were found. This simple technique was straightforward to use and has the potential for applications in a large range of root-pest/feeding studies.  相似文献   
127.
128.
129.
130.
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