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991.
992.
A new pterosaur (Pterosauria) from Middle Jurassic Tiaojishan Formation of western Liaoning,China 总被引:1,自引:0,他引:1
A new pterosaur Archaeoistiodactylus linglongtaensis gen.et sp.nov.is erected based on an incomplete skeleton with a partial skull and lower jaw.The new taxon is characterized by circular tooth sockets of anterior mandibular teeth,the anterior teeth of the upper jaw bearing posteriorly directed crowns,a relatively short metacarpus,and wing phalanges 2 and 3 and the tibia subequal in length.It possesses some plesiomorphic characters such as short metacarpals and circular tooth sockets.The pointed jaw tip present in the new taxon indicates that the expanded jaw tips of later istiodactylids are a derived character state,and the new taxon represents the first istiodactylus-like pterosaur found from the pre-Late Jurassic deposits,which provides a key role in our understanding the origin and evolution of the known istiodactylid pterosaurs.Archaeoistiodactylus is regarded as the ancestor form of the known istiodactylid pterosaur. 相似文献
993.
994.
干旱地区灌丛沙堆研究现状与展望 总被引:12,自引:1,他引:11
从灌丛沙堆的形成演变、形态特征及其空间格局、表面气流特征及其风蚀堆积平衡、表面植被生态生理特性及其对降水和地下水的响应、土壤理化性质和保育措施等几个方面进行综述。认为目前灌丛沙堆研究只是针对某一区域或多个区域的静态研究,对灌丛沙堆演化过程中的形态、气流、土壤以及植被等因素的变化特征及其相互作用研究不足,难以解释灌丛沙堆的演化机制及其影响因素。同时灌丛沙堆研究过于强调其作为土地退化的指示,而忽略了其在退化生态系统中的重要生态功能,不利于干旱和半干旱区的生态环境恢复。今后的研究应该加强对灌丛沙堆演化过程中的土壤、植被、水分的变化特征及其不同影响因素之间相互作用过程的研究,深入探讨灌丛沙堆在干旱半干旱退化生态系统中的积极作用。基于以上基础数据和理论依据,对灌丛沙堆的保育措施进行探索,找出合理的灌丛沙堆保育措施。 相似文献
995.
针对目前大跨穿煤隧道的研究热点,以重庆市绕城高速公路环山坪隧道为研究对象,在界定大跨度隧道及分析其围岩稳定性关键影响因素的基础上,结合现场监测和数值模拟对大跨度穿煤隧道围岩结构稳定性进行了分析。结果表明,大跨度隧道各处等效应力集中对扁平率变化敏感程度不同,拱脚最为敏感,拱顶基本不随扁平率的改变而变化。隧道穿越软弱煤层段时,围岩应力重分布受影响明显,拱顶位移随开挖面不断推进急剧增加,且隧道围岩塑形圈不断向拱顶围岩内部发展。尤其当煤层软弱带与隧道顺层相交时,隧道荷载结构偏压效应凸显,偏压荷载随煤层倾角变陡而增大,易造成支护结构失稳破坏,在设计及施工中应特别加以重视。 相似文献
996.
目前,草地生态系统退化成为全球关注的问题。生态补偿机制(PES)是为了草地生态系统的恢复/保护,采取补贴或支付费用的方式,改变使用者资源利用方式的制度安排。科学、合理的生态补偿制度需要全面地考虑可能出现的风险和挑战:如环境效益的滞后性,不可预见的监督、管理成本和社会经济目标(足额补偿标准、公平)的实现。本文的目标是通过中德两国生态补偿措施的对比(选取中国内蒙古锡林郭勒盟,德国勃兰登堡州为案例区域进行研究),为今后中德两国的生态补偿理论和实践提供依据。研究着重以下四个方面进行分析:中德两国生态补偿的实施框架,目标人群,实施效果评估等。研究结果表明,由于缺乏有效的激励机制,农户作为最基层的执行单位和实施者,其参与的主动性不够,中德两国生态补偿措施实施的成效有待提高。基于研究结果,提出了今后生态补偿项目设计中,中国应侧重于项目实施的监控和管理制度;而德国应在空间目标规划和具体管理措施和方式等方面进行完善。 相似文献
997.
1961-2005年水利水保措施对潮河流域年径流量的影响(英文) 总被引:1,自引:0,他引:1
Taking the Chaohe River Basin above the Miyun Reservoir in North China as a study area,the characteristics and variation trends of annual runoff and annual precipitation during 1961-2005 were analyzed applying Mann-Kendall test method on the basis of the hydrologic data of the major hydrological station(Xiahui Station) located at the outlet of the drainage basin and the meteorological data of 17 rainfall stations.Human activities including water conservancy projects construction and water diversion as well as implementation of soil and water conservation from 1961 to 2005 were carefully studied using time series contrasting method.The referenced period(1961-1980) that influenced slightly by human activities and the compared period(1981-2005) that influenced significantly by water conservancy and soil conservation measures were identified according to the runoff variation process analysis and abrupt change points detection during 1961-2005 applying double accumulative curve method,mean shift t-test method and Mann-Kendall mutation test technique.Based on the establishment of a rainfall-runoff empirical statistical model,impacts and the runoff-reducing effects of water conservancy and soil conservation measures on runoff reduction were evaluated quantitatively.The major results could be summarized as follows:(1) The annual precipitation in the drainage basin tends to decrease while the runoff has declined markedly since the 1960s,the average annual runoff from 1991 to 2000 was only 90.9% in proportion to that from 1961 to 1970.(2) The annual runoff variations in the drainage basin are significantly related to human activities.(3) During 1981-1990,1991-2000,2001-2005 and 1981-2005,the average annual runoff reduction amounts were 1.15×108,0.28×108,1.10×108 and 0.79×108 m3 respectively and the average annual runoff-reducing effects were 31.99%,7.13%,40.71% and 23.79% accordingly.Runoff-reducing effects by water conservancy and soil conservation measures are more prominent in the low water period. 相似文献
998.
Taking the Chaohe River Basin above the Miyun Reservoir in North China as a study area, the characteristics and variation
trends of annual runoff and annual precipitation during 1961–2005 were analyzed applying Mann-Kendall test method on the basis
of the hydrologic data of the major hydrological station (Xiahui Station) located at the outlet of the drainage basin and
the meteorological data of 17 rainfall stations. Human activities including water conservancy projects construction and water
diversion as well as implementation of soil and water conservation from 1961 to 2005 were carefully studied using time series
contrasting method. The referenced period (1961–1980) that influenced slightly by human activities and the compared period
(1981–2005) that influenced significantly by water conservancy and soil conservation measures were identified according to
the runoff variation process analysis and abrupt change points detection during 1961–2005 applying double accumulative curve
method, mean shift t-test method and Mann-Kendall mutation test technique. Based on the establishment of a rainfall-runoff
empirical statistical model, impacts and the runoff-reducing effects of water conservancy and soil conservation measures on
runoff reduction were evaluated quantitatively. The major results could be summarized as follows: (1) The annual precipitation
in the drainage basin tends to decrease while the runoff has declined markedly since the 1960s, the average annual runoff
from 1991 to 2000 was only 90.9% in proportion to that from 1961 to 1970. (2) The annual runoff variations in the drainage
basin are significantly related to human activities. (3) During 1981–1990, 1991–2000, 2001–2005 and 1981–2005, the average
annual runoff reduction amounts were 1.15×108, 0.28×108, 1.10×108 and 0.79×108 m3 respectively and the average annual runoff-reducing effects were 31.99%, 7.13%, 40.71% and 23.79% accordingly. Runoff-reducing
effects by water conservancy and soil conservation measures are more prominent in the low water period. 相似文献
999.
1000.
混合气体驱替煤层气技术的可行性研究 总被引:1,自引:0,他引:1
气体驱替煤层气技术是近年来发展起来的具有温室气体减排和提高煤层气采收率双赢效果的新兴技术,相关研究受到世界主要发达国家的广泛重视。对于温室气体减排的压力,发达国家的研究主要着眼于该技术在高渗透、不可采煤层中的应用,注入气体主要为CO2,目的是尽可能多地封存CO2,同时提高煤层气采收率。目前,国内在这方面的研究刚刚起步。国内煤层具有渗透率普遍较低、不开采煤层与要开采煤层难以界定的特点,注CO2气体驱替煤层气在这种煤层中的可行性值得商榷。针对国内煤层特点和煤矿瓦斯抽采率低的现状,建议采用富N2混合气体驱替煤层气技术,以提高煤层气产采收率。通过理论分析、数值模拟和现场试验研究分析了实施混合气体驱替煤层气技术的可行性。研究结果表明,混合气体驱替煤层气技术适用于国内低渗透、可开采煤层,可以提高煤层气采收率和单产量。 相似文献