256 resultados para 187-1164


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森林认证是缓解全球森林退化、实现可持续发展战略的重要手段之一。它包括森林经营认证和森林产品认证。森林认证将影响到世界森林资源、各国林业发展以及生态、经济和社会。森林认证是一项复杂的系统工程,涉及国家政策和国民经济的方方面面。只有利用系统理论,才能更好分析论证在中国特定条件下的森林认证系统;在系统思想指导下,找出我国森林认证的关键要素、主要子系统和最优结构,才能发挥森林认证体系的最佳功能。

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该文报道了云南西北部分布的蝠蛾属二新种: 白纹蝠蛾 Hepialus albipictus sp. nov., 金沙蝠蛾 Hepialus jinshaensis sp. nov., 两新种采自雪山高寒草甸之中, 是冬虫夏草真菌的寄主昆虫。

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白眉长臂猿和白颊长臂猿的染色体C带核型中除多数染色体有着丝点C带外,一些染色体上还出现插入C带和着丝点C带弱化或减少现象;白眉长臂猿有全异染色质臂;白颊长臂猿有较多的端位C带。白眉长臂猿有两个Ag-NORs,而白颊长臂猿的Ag-NORs雌体有4个,雄体有5个,Y染色体上有NOR。

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The effects of aniracetam on extracellular amino acid levels in the hippocampus of conscious gerbils, with or without transient cerebral ischemia/reperfusion, were measured by microdialysis and reverse phase-high performance liquid chromatography. Increased extracellular levels of aspartate and glutamate that were observed in the hippocampus of conscious gerbils during transient global forebrain ischemia were reversed by aniracetam. In contrast, the level of extracellular gamma-aminobutyric acid was increased, while taurine was maintained at a higher level than other amino acids by administration of aniracetam (100 mg/kg, p.o.) 60 min before ischemia. Further, in contrast to ischemic animals, administration of aniracetam (100 mg/kg, p.o.) enhanced the release of glutamate and aspartate in the normal gerbil hippocampus. The results suggest that these effects might be due to a partial calcium agonist activity of aniracetam, and that the effects of aniracetam on amino acid levels might be a mechanism of protection against delayed neuronal death in the ischemic hippocampus, thereby improving memory dysfunction induced by ischemia/reperfusion. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.

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阐述了人工湿地生态系统服务的定义、分类、项目及其评价方法。介绍了生态系统服务价值评价在国内外的研究现状,指出了当前研究工作的局限性,对将来的发展方向作出了研究展望。论述了人工湿地所具有的服务功能,结合前人的研究初步提出对其进行价值评价的方法及计算公式。

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对5种不同程度富营养化水体中的菖蒲(Acorus calamusL.)在静态培养过程中的叶片长度变化、叶片数目变化进行了观测,比较了培养后各水体中菖蒲根长、根数、鲜重、根活力、叶绿素含量、叶片可溶性总糖含量、鲜重增量和根系活力的差异。研究发现,菖蒲在5种不同程度富营养化水体中均能正常生长。在非极度富营养化的水体组中,水体富营养化程度越高,菖蒲生长越好。但在极度富营养水体中,菖蒲根系生长受到抑制,其根短且须根多,且叶片生长对此水体有一段适应期,试验前8 d,其中菖蒲叶片长度增长明显小于重度富营养,8 d后,

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底质适宜是富营养湖泊恢复沉水植物(水草)的重要前提。大型底栖动物可综合指示底质的污染程度,于2002~2003年在武汉月湖开展了底栖动物水平分布对水草可恢复区指示作用的研究。首先通过月湖底栖动物与环境的相关分析,选择颤蚓科寡毛类作为底质营养状况的指示类群,然后利用同类湖泊群颤蚓与水草数据分析阈值,初步确定颤蚓密度≤100 ind/m2的底质适合水草生长,最后绘制月湖颤蚓分布的水平等值线,显示水草恢复的合适区域。在此基础上构建了应用底栖动物空间格局指示水草恢复区的技术原理框架。