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赵黎明 《湖南农业大学学报(自然科学版)》2011,(2):90-94
传统的经典理论分析了政府供给公共产品和消费者无差别消费时的经济问题。然而在市场经济中消费者的类型是不相同的,对公共产品的消费需求也各不相同。对此,需要研究不同消费需求、不同供给模式下具有“消费信号”的公共产品自愿供给问题。研究发现,提高公共产品消费的信号性,优化公共产品的供给模式对于公共产品的自愿供给非常重要。同时,识别出“信号消费”下的异质消费者,并使公共产品具有私人产品的消费特征时,公共产品自愿供给的意愿将会增加。 相似文献
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Flow alteration and thermal pollution depress modelled growth rates of an iconic riverine fish,the Murray cod Maccullochella peelii
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Nick S. Whiterod Shaun N. Meredith Paul Humphries Bradford S. Sherman John D. Koehn Robyn J. Watts Brett A. Ingram Tom Ryan 《Ecology of Freshwater Fish》2018,27(3):686-698
The serial discontinuity concept (SDC) proposes that hypolimnetic‐releasing impoundments cause major disruptions to the naturally occurring physical, chemical and biological gradients of rivers but that this impact diminishes with distance downstream. Such a gradient in discharge, flow velocity and temperature regime occurs below a large hypolimnetic‐releasing impoundment, the Hume Dam, on the River Murray in south‐eastern Australia. To examine the effects of this disturbance gradient on a warm‐water large‐bodied freshwater fish, the Murray cod (Maccullochella peelii), a bioenergetics model was developed and calibrated to explore energy expended under differing water velocities and temperature regimes. Model simulations predicted negative growth of juveniles directly downstream of the impoundment, due largely to the energetic costs associated with active and, to a lesser extent, standard metabolism outweighing the achievable energetic gains through food consumption. As flow velocity and temperature regimes became more favourable downstream, so did the simulated growth of the species. It was not until +239 km downstream of the impoundment that the model predicted that flow velocity and temperature regimes were suitable for greater weight gains. The modelled growth responses of juvenile Murray cod are consistent with the predictions of the SDC, emphasising that changes in the bioenergetics of individuals are likely to be reflected in reduced growth rates under the changed flow velocity and temperature regimes imposed by disturbance gradients. This research represents a valuable step in the biological understanding of Murray cod within variable riverine environments and emphasises the urgency required to mitigate impacts associated with hypolimnetic impoundments. 相似文献
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王磊 《信阳农业高等专科学校学报》2013,(3):32-34,40
以透析中西方隐私权观念差异为视角,分析中西方文化差异,并探究缩小中西交流中的文化差异的有效途径。 相似文献
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A developing method is given which based on object-oriented modeling techniques for management information systems.The modeling techniques,especially,from CDM to PDM conversion,make it possible that the method can be used for developing such management information systems which based on relational database.The result shows that it can raise the efficency of the system developing,improve the system tability,enhance the system maintenability. 相似文献
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