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991.
对苏皖下扬子区上白垩统浦口组(K2P)的三个砂岩样品进行了磷灰石裂变径迹(AFT)研究。结果显示:2个样品的AFT合并年龄为(88.8±4.4)Ma(径迹长度为(12.0±0.3)μm)和(82.1±6.8)Ma(径迹长度为(14.4±0.3)μm)与浦口组沉积年龄相近,说明它们沉降的幅度达到但没有超过AFT部分退火区间,1个样品的AFT合并年龄(117.3±5.9)Ma(径迹长度为(13.3±0.3)μm)大于浦口组沉积年龄,代表物源区抬升、剥露的冷却年龄。根据热历史模拟结果,识别出黄桥事件(110~90Ma)、仪征事件(70~60Ma)和三垛事件(35~22Ma)三期重要的构造事件,并将下扬子区晚白垩世以来的盆地演化划分为四个阶段:110~70Ma断坳复合型伸展盆地、70~35Ma拉张断陷盆地、35~22Ma挤压抬升阶段和22Ma至今坳陷盆地。 相似文献
992.
993.
人工藻礁是进行藻场建设的重要手段,但由于海胆等食藻类生物的摄食,将会影响藻类的生长,从而影响人工藻场的建设效果.为解决人工藻场建设中海胆的食害问题,从礁体自身设计出发,实验设计了8种不同形状的藻礁,选用光棘球海胆和中间球海胆为实验对象,观察比较了不同形状藻礁对海胆攀爬的阻碍效果,实验发现:侧周面为锯齿形或侧周面缠挂多孔柔性材料的礁型可有效阻止海胆攀爬,起到防止海胆摄食礁顶藻类的目的.研究结果为人工藻礁的设计提供了参考依据. 相似文献
994.
With rapid urbanization process, the pace of urban sprawl has been quickened and most metropolises have experienced expansions in leaps and bounds in suburbanization, which has greatly changed the urban and rural spatial structure of the metropolis fringe area. In this paper, Shuangliu County is taken as a case, since it is a typical fringe area of Chengdu Metropolis. Based on Landsat TM images of Chengdu City and Shuangliu County obtained in 1985, 2000 and 2004, characteristics of urban and rural spatial structure in Shuangliu County were analyzed, such as core-periphery spatial structure and some obvious integration trends. Then the influencing factors for the formation of urban and rural spatial structure were identified, including some natural, social, economic and political factors. According to the discussion of this paper, Shuangliu County is undergoing a key transition and reform period. Its formation of urban and rural spatial structure was affected not only by such common factors as the location, natural background, industrial transition, migration, etc., but also by some unique factors such as city planning and policy guidance, which played an important role in accelerating its uneven spatial structure. The understanding of the role of the influencing factors would be useful for carrying out spatial management and development planning of metropolis fringe area. 相似文献
995.
TANG Zhi-li 《极地研究(英文版)》2008,19(2):149-158
An overview of the seasonal variation of sea-ice cover in Baffin Bay and the Labrador Sea is given. A coupled ice-ocean model, CECOM, has been developed to study the seasonal variation and associated ice-ocean processes. The sea-ice component of the model is a multi-category ice model in which mean concentration and thickness are expressed in terms of a thickness distribution function. Ten categories of ice thickness are specified in the model. Sea ice is coupled dynamically and thermodynamically to the Princeton Ocean Model. Selected results from the model including the seasonal variation of sea ice in Baffin Bay, the North Water polynya and ice growth and melt over the Labrador Shelf are presented. 相似文献
996.
Clara Deal 《极地研究(英文版)》2008,19(2):218-229
Primary production in the Bering and Chukchi Seas is strongly influenced by the annual cycle of sea ice. Here pelagic and sea ice algal ecosystems coexist and interact with each other. Ecosystem modeling of sea ice associated phytoplankton blooms has been understudied compared to open water ecosystem model applications. This study introduces a general coupled ice-ocean ecosystem model with equations and parameters for 1-D and 3-D applications that is based on 1-D coupled ice-ocean ecosystem model development in the landfast ice in the Chukchi Sea and marginal ice zone of Bering Sea. The biological model includes both pelagic and sea ice algal habitats with 10 compartments: three phytoplankton (pelagic diatom, flagellates and ice algae: D, F, and Ai) , three zooplankton (copepods, large zooplankton, and microzooplankton : ZS, ZL, ZP) , three nutrients ( nitrate + nitrite, ammonium, silicon : NO3 , NH4, Si) and detritus (Det). The coupling of the biological models with physical ocean models is straightforward with just the addition of the advection and diffusion terms to the ecosystem model. The coupling with a multi-category sea ice model requires the same calculation of the sea ice ecosystem model in each ice thickness category and the redistribution between categories caused by both dynamic and thermodynamic forcing as in the physical model. Phytoplankton and ice algal self-shading effect is the sole feedback from the ecosystem model to the physical model. 相似文献
997.
蒋海良 《地球信息科学学报》2008,10(3):357-362
第二次全国农业普查户表、村表与农业用地表的耕地面积差异,主要是由设计普查指标、普查时点、统计口径、登录技术等因素所致。另外,村与村之间界线不清,普查员对三权(所有权、使用权、承包经营权)理解模糊,对农户承包口粮田、种粮大户、户之间土地流转等混淆,以及土地全部征收、土地部分征收、土地未征收、"预征土地"等导致耕地面积的差异。由于城市不断向四周拓展,占用了大量的耕地,土地整理、易地待保、占补平衡进入实质性操作,人们的生存环境受到影响,对耕地面积的差异评估,产生诸多值得深思的问题。 相似文献
998.
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999.
1000.