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51.
Caching or storing surplus prey may reduce the risk of starvation during periods of food deprivation. While this behaviour occurs in a variety of birds and mammals, it is infrequent among invertebrates. However, golden orb-web spiders, Nephila edulis, incorporate a prey cache in their relatively permanent web, which they feed on during periods of food shortage. Heavier spiders significantly reduced weight loss if they were able to access a cache, but lost weight if the cache was removed. The presence or absence of stored prey had no effect on the weight loss of lighter spiders. Furthermore, N. edulis always attacked new prey, irrespective of the number of unprocessed prey in the web. In contrast, females of Argiope keyserlingi, who build a new web every day and do not cache prey, attacked fewer new prey items if some had already been caught. Thus, a necessary preadaptation to the evolution of prey caching in orb-web spiders may be a durable or permanent web, such as that constructed by Nephila.  相似文献   
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Trisomy 12 mosaicism diagnosed at 16 weeks' amniocentesis in a 42-year-old woman was not confirmed at 18 weeks' gestational age in amniotic fluid or fetal blood. Fetal skin biopsy performed at the same time did, however, allow the detection of trisomy 12 in 1 of 14 fibroblasts analysed. Fetal skin biopsy can be included within the diagnostic procedures to be performed when a level III mosaicism is found in the amniotic fluid.  相似文献   
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化学混凝-SBR法处理肉禽屠宰废水的研究   总被引:7,自引:0,他引:7  
针对肉禽屠宰废水的特点,采取了先混凝后生化的处理方法。在实验中确定了最佳混凝剂和最佳工艺条件。实验结果表明,采取此方法处理肉禽屠宰废水,其各项指标可达国家规定的排放标准。  相似文献   
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ABSTRACT: The objective of this article is to open a dialogue on integrating service‐learning into community based watershed management programs and to discuss opportunities and challenges that a service‐learning program presents to universities and communities. The article presents the concept and definition of service‐learning, and arguments concerning why institutions of higher education and university faculty and students should be involved with community based watershed management programs. The article describes a case study for developing a service‐learning program for watershed management at Virginia Tech and discusses lessons learned from the case study. The paper concluded that to make a service‐learning program sustainable, there should be a long term plan, regular and effective communication with the stakeholders, and some incentives for faculty and students for long term commitment to the community based watershed management programs.  相似文献   
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The article focuses on fossil energy resources in the Andean Group and Mexico, and argues for a dynamic approach to calculating reserves to production ratios. Individual countries are surveyed in terms of estimated reserves of fossil energy resources, current production rates and future prospects; energy policy options for individual countries are analysed. As a primary objective of energy policy is to ensure security of supply, it is important that calculations of reserves to production ratios accurately estimate the desired level of investment in exploration. The calculations need to take into account a variety of parameters, including different energy sources, availability and risk; geographic considerations including proximity, transport, storage capacity and commercial aspects; the competitive and environmental implications of developing indigenous resources; and the use of instruments to establish contingency plans for emergencies.
The opinions expressed in this article are those of the authors, and do not necessarily reflect the views of OLADE, ECLAC or GTZ. The authors apologize for any inaccuracies or omissions in the article.  相似文献   
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Synthesis of poly(hydroxyalkanoate) from hydrolyzed linseed oil   总被引:3,自引:0,他引:3  
Pseudomonas putida was grown on a mixture of long-chain fatty acids obtained by hydrolysis of linseed oil. A poly(3-hydroxyalkanoate) containing 51.2% of unsaturated monomers was obtained. A considerable percentage (13.6%) was constituted by C14 and C16 monomers containing three double-bonds in the side chains. The polymer showed a high tendency to crosslink when it was kept in presence of air. In the crosslinked polymer no polyunsaturated monomers could be detected.  相似文献   
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