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451.
452.
Blood collected from 62 fetuses aged 20–38 weeks of gestation was studied. The values of ten lipid parameters were determined: cholesterol (TC), triglycerides (TGs), apolipoprotein Al (apo A1), apolipoprotein B (apo B), apolipoprotein E (apo E), total apolipoprotein CIII (apo CIII), apolipoprotein CIII present in particles containing apo B (apo CIII LpB) or not (apo CIII Lp non-B), lipoparticles A1 (LpA1), and lipoprotein a (Lp(a)). The results show that, except for apo E, all the studied parameters were present in lower concentrations than in adults and newborns, and that Lp(a) is not detectable at that stage in life. 相似文献
453.
用平衡实验及动力学实验研究了我国南方4种红壤的表面质子化及铝的溶解与质子缓冲之间的关系.结果表明,由于游离氧化铁的含量、活性及对铝溶解反应位的掩盖程度等与质子化密切相关因素的不同影响,4种红壤的总H+消耗量和铝溶解量不同,宁海红壤和嵊县红壤的质子化程度及H+的总消耗量大于永春红壤和屯溪红壤;屯溪红壤铝的溶解量最大,宁海红壤铝的溶解量最小.尽管屯溪红壤铝的溶解量最大,但H+的总消耗量却最小.当红壤中氧化铁含量较高时,铝的溶解在H+消耗中只起次要作用,质子化过程是H+消耗的主要途径. 相似文献
454.
455.
In both predictive theoretical and empirical models for aquatic plant communities in running waters, the development and competition are many times explained in terms of nutrients. Minerals necessary for growth are generally not assumed to be limiting, although they influence the important pH-value. At the same time it is known that factors such as oxygen-concentration, solar energy, salinity, dimension of the system and soil characteristics (including river sediments) influence the development of the community, and should be considered in modelling. Effects of water quantity and water quality on macrophytes are reviewed. These conditions are caused by processes in the landscape, characterised by a set of nested variables which explain the distribution of macrophyte species and communities. Relevant variables are described and grouped on three scales: regional, local and site conditions. Case studies with direct and indirect gradient analysis are presented. Statistical tests (stepwise regression with forward selection) reveal that each species distribution is explained by a characteristic set of relevant variables, ranging from soil type and dimension of the system, to nutrient and salinity concentration. 相似文献
456.
H. Doing 《Journal of Coastal Conservation》1995,1(2):145-172
This paper is a summary and elaboration of an earlier publication in Dutch on the compilation of a landscape-ecological map,
scale 1 : 50 000, of the Dutch coast. It is argued that such an integrated map is the best basis for the conservation and
management of the coastal dunes and salt marshes. It may be combined with local more detailed vegetation maps, some examples
of which are mentioned in the context of management.
The Dutch North Sea coast is a ca. 350 km long chain of sandy beaches and sand dunes, from only 100 m to more than 10 km wide.
On sheltered stretches of dune coasts along estuaries in the Southwest and on the Wadden Sea islands, salt marshes have developed.
The small-scale gradient structure of the beach-dune-salt marsh complex is emphasized. 相似文献
457.
为了从价值观和调节焦点的双重视角给煤矿企业新生代员工的安全管理提供科学依据,在文献研究和问卷调查的基础上,对 244 个有效样本进行分析,揭示煤矿企业新生代员工工作价值观的具体内容,结合动机理论和调节焦点理论,构建煤矿企业新生代员工工作价值观、调节焦点和安全绩效的结构方程模型。研究结果表明:煤矿企业新生代员工的工作价值观包含发展导向、自我导向、关系认同、独立自主、利益导向和创造导向6个因子结构;煤矿企业新生代员工的工作价值观、调节焦点和安全绩效两两之间均显著相关;煤矿企业新生代员工的工作价值观不仅可以直接预测安全绩效,还可以通过调节焦点的中介作用间接影响煤矿员工的安全绩效。 相似文献
458.
200 years of sustainability in forestry: Lessons from history 总被引:4,自引:0,他引:4
K. Freerk Wiersum 《Environmental management》1995,19(3):321-329
Since the end of the 1980s the concept of sustainable development has gained general acceptance, but much uncertainty still
exists on how to operationalize this concept. In forestry the concept of sustainability has been an accepted principle since
the 18th century. The experiences with its application in forestry may contribute towards obtaining a better insight into
the implications and operational significance of the concept of sustainability. This article describes the history of sustainability
in forestry, including the various social values on which its interpretation has been based. The original principle of sustained
yield has gradually been broadened to a more inclusive principle of sustainable forest management. The dynamics in social
valuation of forest resources resulted in various attempts at practical operationalization of the principle. Notwithstanding
200 years of efforts to operationalize the concept of sustainability, its exact application in forestry remains troublesome.
Three lessons are drawn: (1) the need to recognize the different nature of ecological limits and social dynamics, (2) the
role of dynamic social values with respect to forest resources, and (3) the significance of operational experiences in trying
to attain sustainability within a concrete context. 相似文献
459.
A broad and objective perspective of ecological and socioenomic knowledge is required to underlie a scientific approach to
the problems of terrestrial restoration ecology. Uncertainty associated with limited scientific knowledge highlights the crucial
importance of the interaction between science and policy in weighing ecological restoration alternatives in relation to other
management options. In this paper, we provide a pragmatic definition for restoration ecology that is suitable for extensive
terrestrial applications and present a decision framework to help organize and clarify different phases of the decision process
as it is related to ecological restoration. We argue that restoration planning should include a wider spectrum of participants
and decisions than have traditionally been employed. 相似文献
460.
A landscape-level approach was applied to eight rural watersheds to assess the role that wetlands play in reducing phosphorus loading to surface waters in the Lake Champlain Basin. Variables summarizing various characteristics of wetlands within a watershed were calculated using a geographic information system and then compared to measured phosphorus loading through multiple regression analyses. The inclusion of a variable based on the area of riparian wetlands located along low- and medium-order streams in conjunction with the area of agricultural and nonwetland forested lands explained 88% of the variance in phosphorus loading to surface waters. The best fit model coefficients (Pload = 0.86Ag + 0.64For – 30Ripwet + 160) suggest that a hectare of riparian wetland may be many times more important in reducing phosphorus than an agricultural hectare is in producing phosphorus. These results provide additional support for the concept that protection of riparian wetlands is an important management strategy for controlling stream water quality in multiuse landscapes. 相似文献