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   71篇
  免费   1篇
  国内免费   1篇
  73篇
  2017年   2篇
  2012年   3篇
  2011年   3篇
  2010年   6篇
  2009年   6篇
  2008年   6篇
  2007年   2篇
  2006年   2篇
  2005年   3篇
  2003年   1篇
  2002年   1篇
  2000年   1篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1987年   3篇
  1985年   3篇
  1984年   3篇
  1983年   1篇
  1981年   1篇
  1979年   2篇
  1978年   2篇
  1976年   1篇
  1975年   4篇
  1973年   3篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1955年   1篇
  1953年   1篇
排序方式: 共有73条查询结果,搜索用时 0 毫秒
1.
The venom glands of four specimens of Elaps lacteus were examined and found to be structurally similar to the glands of other Elapidae and consequently different from the variable glands of the colubrid Aparallactinae, Lycophidinae and Dispholidinae. The recently proposed removal of Elaps from the Elapidae and its inclusion in the Aparallactinae (McDowell, 1968) is discussed, and the conclusion is reached that Elaps should remain within the Elapidae.  相似文献   
2.
    
Extant felids are morphologically homogeneous, probably as a result of recent radiation and constraints from their predatory specializations. The Neotropical assemblage comprises 12 of the 41 extant felid species, which occupy all habitats available, with many species coexisting locally. We studied this assemblage on the basis of 31 craniodental variables reflecting morphofunctional variation, measured from 229 specimens representing all 12 species. Multivariate patterns were summarized allowing for phylogenetic covariation. Additional factors (geographical distribution, use of habitat and stratum, and activity pattern) were coded for each species. As expected, body size accounted for most variation, covarying with membership to three deep clades and, to a lesser extent, with large‐scale geographic variation. The species tend to segregate in morphospace plus one or more factors (e.g. habits) that make interspecific overlap in niche space minimal. Using dated phylogenies, biogeographic history, and the fossil record, we reconstructed the historical assembly of the Neotropical felid guild. We found a pattern of successive invasions and speciation in which new lineages occupied previously vacant areas of morphospace, or new species occupied overlapping areas but with contrasting habits. This may be general among antagonistic species of historically structured guilds, and we predict similar patterns in other continents. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 711–724.  相似文献   
3.
4.
5.
Culture on Tour: Ethnographies of Travel . Edward M. Bruner. Chicago: University of Chicago Press, 2005. 308 pp.  相似文献   
6.
THE STRUCTURE OF FISH GILLS IN RELATION TO THEIR RESPIRATORY FUNCTION   总被引:3,自引:0,他引:3  
1. The general structure of the gills of different fishes is compared and it is concluded that, though essentially the same, there are certain differences by which they can be recognized. Possible ways in which they may have evolved from one another are considered. 2. A detailed account is given of the structure of the secondary lamellae, where gaseous exchange takes place, and it is shown that two epithelial sheets are separated by a vascular axis mainly composed of pillar cells overlain by a basement membrane on each side. Blood pathways through the gills are discussed in relation to their respiratory function. 3. The embryonic development of gills is described and evidence regarding homo-logies of different structures, particularly the pillar cells, is reviewed. 4. The gills of fish having different modes of life show variations in (a) the number of arches, (b) the number and length of the gill filaments, and (c) the size and frequency of the secondary lamellae. Ways in which measurements of gill area may be carried out and some of the complications involved are reviewed and a summary given of measurements made for a wide variety of species. Measurements of the thickness of the water-blood barrier are also discussed; the more active fish generally have thinner water-blood barriers and larger gill areas. 5. The different mechanisms of gill ventilation are summarized and characteristics of gill resistance in elasmobranchs and teleosts are compared. Gas exchange is discussed in relation to available techniques and the current terminology and symbols, and to indicate the value of analogies between gill exchangers and systems studied by engineers. 6. It is outlined how studies of the functioning of gills during coughing, parasitic infection, and in polluted waters add to knowledge of their role in respiration.  相似文献   
7.
8.
An account is given of differences in development at emergence in two strains of Nosopsyllus fasciatus, and of consequent differences in mating behaviour.  相似文献   
9.
2-Methoxy-3-alkylpyrazines have been identified as odour components in Danaus plexippus, Zygaena lonicerae and an Australian Amata species, by means of coupled gas chromatography/mass spectrometry, with selected ion monitoring. Wide variability in pyrazine content was observed with D. plexippus and this was correlated with similar variability in the larval food-plants, Asclepias spp., which are presumed to be the odour sources for this butterfly. The importance of pyrazines in the biology of aposematic insects and their role as ingredients of a generalized warning system are discussed.  相似文献   
10.
To improve our mechanistic understanding and predictive capacities with respect to climate change effects on the spring phytoplankton bloom in temperate marine systems, we used a process‐driven dynamical model to disentangle the impact of potentially relevant factors which are often correlated in the field. The model was based on comprehensive indoor mesocosm experiments run at four temperature and three light regimes. It was driven by time‐series of water temperature and irradiance, considered edible and less edible phytoplankton separately, and accounted for density‐dependent grazing losses. It successfully reproduced the observed dynamics of well edible phytoplankton in the different temperature and light treatments. Four major factors influenced spring phytoplankton dynamics: temperature, light (cloudiness), grazing, and the success of overwintering phyto‐ and zooplankton providing the starting biomasses for spring growth. Our study predicts that increasing cloudiness as anticipated for warmer winters for the Baltic Sea region will retard phytoplankton net growth and reduce peak heights. Light had a strong direct effect in contrast to temperature. However, edible phytoplankton was indirectly strongly temperature‐sensitive via grazing which was already important in early spring at moderately high algal biomasses and counter‐intuitively provoked lower and later algal peaks at higher temperatures. Initial phyto‐ and zooplankton composition and biomass also had a strong effect on spring algal dynamics indicating a memory effect via the broadly under‐sampled overwintering plankton community. Unexpectedly, increased initial phytoplankton biomass did not necessarily lead to earlier or higher spring blooms since the effect was counteracted by subsequently enhanced grazing. Increasing temperature will likely exhibit complex indirect effects via changes in overwintering phytoplankton and grazer biomasses and current grazing pressure. Additionally, effects on the phytoplankton composition due to the species‐specific susceptibility to grazing are expected. Hence, we need to consider not only direct but also indirect effects, e.g. biotic interactions, when addressing climate change impacts.  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