The effect of scattering in surface wave tomography   总被引：6，自引：1，他引：6  

Jesper Spetzler  Jeannot Trampert  Roel Snieder 《Geophysical Journal International》2002,149(3):755-767

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Tiller recruitment and mortality in the dryland bunchgrass Eragrostis curvula as affected by defoliation intensity     

Changgui Wan  Ronald E. Sosebee 《Journal of Arid Environments》2002,51(4):577

A greenhouse experiment was conducted to investigate the effects of moderate (14 cm) vs. severe (7 cm) defoliation on tiller recruitment and mortality within the interior and on the perimeter of weeping lovegrass (Eragrostis curvula) tussocks. Tiller number per marked shoot within the interior was significantly greater in plants defoliated at 14-cm stubble height than at 7-cm stubble height (2·37 vs. 0·43, p<0·05) 28 weeks after defoliation; likewise, tiller number per marked shoot was also greater on the perimeter of tussocks in the higher stubble than the lower stubble defoliation treatment (5·10 vs. 2·03, p<0·05). Tiller natality increased significantly 4 weeks after defoliation except for tillers cut to 7-cm stubble height within the interior of tussocks where tiller natality reached a peak at 4·5 weeks after defoliation. During the later stages of canopy development, tiller numbers per marked shoot gradually declined as tiller mortality increased. Tillers began senescing 13 weeks after defoliation, and the senescence rate was 52% greater in the 7-cm stubble height treatment than in the 14-cm stubble height treatment (2·33 vs. 1·53, p<0·0001). Within the interior of tussocks, number of the marked tillers more than doubled under the 14-cm stubble height treatment, whereas the plants lost 57% of the monitored tillers under the 7-cm stubble height treatment. We concluded that the central dieback process in weeping lovegrass is accelerated by severe defoliation.  相似文献   

京、津、冀区域群发性强沙尘暴分析   总被引：1，自引：2，他引：1  

刘学锋  安月改  田国强 《地理与地理信息科学》2003,19(6):74-76

利用1954—2002年82个站的气象观测资料，探讨京、津、冀区域群发性强沙尘暴的认定标准，构建较完整的群发性强沙尘暴序列，并分析该地区群发性强沙尘暴的时空分布特征和气候变化趋势。近50a京、津、冀区域共出现了39例群发性强沙尘暴，河北省的冀西北高原区和石家庄、保定、衡水、沧州四市交接处饶阳一带是京、津、冀区域强沙尘暴天气的多发区。多发季节为3—5月，占全年总数的76．9％，其中4月份最多，占全年总数的51．3％。群发性强沙尘暴年代际变化呈现总体减少趋势，其发生次数、覆盖面积均是以20世纪90年代为最低值．  相似文献   

山东省省际边界地区发展研究   总被引：17，自引：0，他引：17  

贾若祥  侯晓丽 《地域研究与开发》2003,22(2):30-34

省际边界地区有其自身的发展特点，对于区域的发展起着特殊的作用。文章分析了山东省省际边界地区的特点，并根据康维斯（P.D.Converse)断裂点理论，对山东省及周边中心城市的引力范围进行了计算，比较分析了目前山东省省界城市和省内城市吸引范围及竞争力差异，提出了山东省发展省际边界地区的相应对策。  相似文献   

滇西北亚高山针叶林、硬叶栎类林的树种多样性   总被引：2，自引：0，他引：2  

于洋  曹敏  刘文胜 《山地学报》2003,21(5):568-575

在滇西北香格里拉地区,以长苞冷杉(Abiesgeorgei)林、丽江云杉(Picealikiangensis)林作为亚高山针叶林的代表,以川滇高山栎(Quercusaquifolioides)林作为硬叶栎类林的代表,分别选择了6块样地,采用Shannon-Wiener多样性指数(H)、Simpson多样性指数的倒数(D')、Pielou均匀度指数(JH、JD)分别测定其树种多样性,并进行了比较研究。结果表明,三个森林类型的Shannon Wiener指数、Simpson指数的倒数、物种丰富度的顺序均为:长苞冷杉林>川滇高山栎林>丽江云杉林;而前两类森林的Pielou均匀度指数差异不大,但都高于丽江云杉林的均匀度指数值。滇西北的川滇高山栎具有很强的萌生能力。人工种植的亚高山针叶林的树种多样性较原始林低,需要较长时间的恢复过程。亚高山针叶林的存在极大地丰富了云南省的树种多样性,使云南植被的垂直地带性得到了充分体现。  相似文献   

Statistic forecast of typhoons going over the Chinese coasts     

FENG Lihua  WU Zhanghua 《地理学报》2003,13(3):305-308

According to the measured data of typhoons going over the Chinese coasts in 1949-2002, a statistic relative equation showing the relation between the central atmospheric pressure of typhoons in a certain region at a certain period of time and their accumulation of frequency is established, and the concept of recurrence interval of typhoons is put forward, which is of actual significance for typhoon disaster reduction along the coastal area.  相似文献   

斑岩铜矿中铂族元素的研究现状及展望   总被引：4，自引：0，他引：4  

李晓峰  毛景文  张作衡 《矿床地质》2003,22(1):95-98

文章对当前国内外斑岩铜矿中铂族元素的研究现状进行了较为详细的阐述，指出研究与铂族元素矿化有关的斑岩铜矿的流体包裹体及其富集成矿过程，以及铂族元素对斑岩铜矿成矿环境，成岩岩浆的起源和成矿物质来源示踪是该领域的发展方向和前沿。  相似文献   

峨眉山玄武岩分布区内铂族元素异常分析及其找矿远景预测   总被引：2，自引：1，他引：2  

李晓敏  郝立波  甘树才  来雅文 《矿物岩石》2003,23(3):21-25

区域地球化学填图成果表明，在中国西南川-滇-黔交界地区存在一个与产出规模巨大的峨眉山玄武岩分布范围相吻合的Pt，Pd地球化学巨省。作为地幔热柱成因的峨眉山玄武岩的铂族元素丰度虽略有偏高，但玄武岩中铂族元素很难形成可以利用的铂族矿物，故该异常是“非找矿异常”。在该区内寻找铂族元素矿床应在基性岩-超基性岩体出露较多的中岩区南段，注意沿循已知的矿床、矿化或较小型基性岩侵入体，将矿区(或岩体)的整体地质特征、地球化学特征等与典型的岩浆型铂族元素矿床相比较，进而研究、预测本矿区或本岩体的铂族元素成矿的可能性及远景规模等，寻找岩浆型铂族元素矿床，而在岩浆型矿床的周边地质体内注意寻找热液型铂族元素矿床。  相似文献   

城步-桃江断裂在涟源盆地的基本特征     

朱景文  戴长华 《华南地质与矿产》2003,(2):41-45

通过对涟源盆地区域地球物理、地质和矿产资料的综合研究，系统地总结了湘中地区重要的区域性基底断裂——城步—桃江断裂两侧深部地球物理特征的差异及其对涟源盆地沉积作用、盖层形变、岩浆活动和成矿作用的控制特征，探讨了锡矿山F75断层的属性，在此基础上，重新厘定了该断裂在涟源盆地的位置，认为F75断层属盖层断层。  相似文献   

Isotopic Ages of the Carbonatitic Volcanic Rocks in the Kunyang Rift Zone in Central Yunnan, China     

ZHANGYongbei WANGGuilan NIEJianfeng ZHAOChongshun XUChengyan QIUJiaxiang WangHao 《《地质学报》英文版》2003,77(2):204-211

The Mesoproterozoic Kunyang rift, which is located on the western margin of the Yangtze platform and the southern section of the Kangdian axis, is a rare massive Precambrian iron-copper polymetallic mineralization zone in China. The Mesoproterozoic Wulu (Wuding-Lufeng) basin in the middle of the rift is an elliptic basin controlled by a ring fracture system. Moreover, volcanic activities in the basin display zonation of an outer ring, a middle ring and an inner ring with carbonatitic volcanic rocks and sub-volcanic dykes discovered in the outer and middle rings. The Sm-Nd isochron ages have been determined for the outer-ring carbonatitic lavas (1685 Ma) and basaltic porphyrite of the radiating dyke swarm (1645 Ma) and the Rb-Sr isochron ages for the out-ring carbonatitic lavas (893 Ma) and the middle-ring dykes (1048 Ma). In combination of the U-Pb concordant ages of zircon (1743 Ma) in trachy-andesite of the corresponding period and stratum (1569 Ma) of the Etouchang Formation, as well as the Rb-Sr iso  相似文献