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271.
Prenatal diagnosis of cystic hygromata by means of ultrasound examination is possible and highly accurate. Although this is usually associated with Turner's syndrome especially if there is co-existent hydrops fetalis we report three cases in which cystic hygromata were associated with trisomies; two cases of trisomy 21 and one of trisomy 18. 相似文献
272.
273.
Bruce C. Forbes Nancy Fresco Anatoly Shvidenko Kjell Danell F. Stuart Chapin III 《Ambio-人类环境杂志》2004,33(6):355-360
横跨北极的地区,可更新资源和不可更新资源、人口密度、资产投资、住宅与交通基础设施的分布存在着很大差异,这些差异被公认为是研究当前和未来社会-生态系统变化的热点.由于当前政治和经济的稳定,芬诺斯堪的亚地区北部社会-生态系统呈现出相对良好的形势,而俄罗斯北部从苏联解体开始便一直经历着急速且消极的变化,这些变化反映了俄罗斯普遍存在的危机状态.北美洲虽然处在一个相对稳定有序的制度下,采取了一些措施用于防止和减轻与工业有关的环境退化,但大多即将出台的新发展计划仍将会显著扩大社会-生态系统受到潜在影响的空间范围.制度或管理条款与生态系统服务功能对环境变化的缓冲能力紧密相关.无论气候是否变暖,某些地理区域对外来破坏作用表现得特别脆弱,这有可能威胁到这些区域在将来提供产品和服务的能力.尽管某些地区的气候变化有可能会使这种形势恶化,但从长远来看,气候变化也有可能会使其恢复力得到加强. 相似文献
274.
Ultrasound scanning during the second trimester of pregnancy revealed cysts of the choroid plexus in the posterior horn of the lateral ventricle in five cases. All disappeared spontaneously between 20 and 23 weeks and normal infants were subsequently delivered. 相似文献
275.
Stuart A. Manktelow MSc MIM CEng John G. Paterson MSc PhD PEng John A. Meech MSc PhD PEng 《Environmental geochemistry and health》1984,6(1):5-9
The removal of copper and cyanide from aqueous solution by activated carbon has been investigated. Using a coal-based activated carbon, initial concentrations of 244 to 2441 mg/litre total cyanide combined with 61 to 610 mg/litre copper were reduced to a minimum of 3.6 mg/litre total cyanide and 0.6 mg/litre copper in the presence of a fixed initial quantity of air.Cyanide removal was, found to be augmented by the presence of copper in solution, and by the supply of additional air.It is suggested that cyanide removal is accomplished by catalytic oxidation on the carbon surfaces, and that additional cyanide is removed in the presence of copper by adsorption of cyano-cuprate complexes onto the activated carbon. 相似文献
276.
Stuart Mestelman 《Journal of Environmental Economics and Management》1982,9(2):186-193
Several recent attempts have been made to demonstrate that corrective subsidies and taxes do not have symmetric allocation effects. These demonstrations have utilized graphical partial equilibrium analysis. In this paper a general equilibrium model is introduced to show that a standard partial equilibrium result may be incorrect and that subsidies may lead to equilibrium states which are socially preferred to the status quo position. 相似文献
277.
278.
Stuart Oliver 《Environmental management》1993,17(4):433-444
The geology, relief, neotectonics, climate, and vegetation of Basilicata make the region vulnerable to landslides, but the
number of reported landslides in the region has increased over recent centuries, and this has been interpreted as a result
of changes in land use. This interpretation is confirmed by documentary evidence presented in this article (concentrating
on the example of the town of Grassano, where urban landslides are an almost exclusively 20th-century phenomenon), which shows
the increase in landslides to have been real, rapid, and caused by humankind. 相似文献
279.
Michael Martin Linda Cox Stuart Nakamoto John Halloran 《Journal of the American Water Resources Association》1990,26(1):35-39
ABSTRACT: Accurately estimating the price elasticity of demand for irrigation electricity is important to major electricity suppliers such as the Bonneville Power Administration (BPA) of the Pacific Northwest. The BPA has a revenue maximization objective, and the elasticity of demand is central to its rate setting process. Several studies have attempted to estimate demand for irrigation electricity, but none has explicitly included federal agricultural policy and program variables. Tins paper discusses how agricultural programs may influence farmers irrigation decisions and thus their demand for irrigation electricity. It suggests that existing programs serve to make farmers more responsive to electricity rate increases than would otherwise be the case. Thus, studies that fail to include them may underestimate the responsiveness of farmers to electricity rate increases. 相似文献
280.
Stuart G. Fisher 《Environmental management》1990,14(5):725-736
The concept of succession has a distinguished history in general ecology and has been applied to stream ecosystems with some
success. Succession in streams is largely secondary, follows initial floristics models, and occurs through a variety of mechanisms.
The process is moderately predictable but is highly influenced by “climatic” factors, particularly nutrient chemistry. In
desert streams, succession does not result in a climax state. While evidence is slim, succession may not be a significant
process in streams of certain types or in certain regions.
Successional theory is difficult to apply in spatially heterogeneous, hierarchically organized ecosystems. It also suffers
in being only one component of a better integrated concept, that of ecosystem stability, which deals more directly with disturbance
and ecosystem resistance in addition to resilience (which encompasses succession). Succession has so suffered from a half
century of confusion that a strong case can be made for abandoning the term, at least as it applies in streams, in favor of
the broader view provided by stability theory. 相似文献