Application of a sequential regime shift detection method to the Bering Sea ecosystem   总被引：7，自引：0，他引：7  

Rodionov  Sergei; Overland  James E. 《ICES Journal of Marine Science》2005,62(3):328-332

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偏心海链藻形态变异的观察及原因的初步研究   总被引：2，自引：1，他引：2  

曹吉祥  潘震球  卞伯仲  李明仁 《海洋科学》1994,18(5):50-53

观察研究了偏心海链藻壳面形态的变异及变异的原因。结果表明，壳面形态变异是偏心海链藻的典型特征，依变异程度不同可分为４种类型；硅含量对其壳面形态影响显著，但硅质不足是形态变异的唯一原因。  相似文献   

Dietary Shifts in the Queen Triggerfish, Balistes vetula, in the Absence of its Primary Food Item, Diadema antillarum     

Peter N.  Reinthal  Brian  Kensley Sara M.  Lewis 《Marine Ecology》1984,5(2):191-195

Abstract. The long-spined sea urchin Diadema antillarum has been reported to be the major food item of the queen triggerfish, Balistes vetula in the Caribbean. This sea urchin has undergone a massive mortality on reefs throughout the Caribbean during 1983. The dietary habits of twenty-three queen triggerfish from patch reef habitats in Belize were examined. It was found that crabs and chitons now form the major dietary items when D. antillarum is not available. It is suggested that this predator, which was previously specialized on a single food item, is able to shift resource utilization in the absence of its primary food source, and that the queen triggerfish can capture diverse prey from a wide variety of habitats.  相似文献   

转型时期广东二元经济结构演进分析     

李辉  詹伟芳 《云南地理环境研究》2006,18(5):73-78

自1979年以来，中国二元经济结构在改革开放的推动下，出现了双重的二元经济结构格局，在此背景下，为了更好地考察广东经济的发展情况，利用比较劳动生产率、二元对比系数、二元反差指数等指标对转型时期广东双重二元经济结构的演进进行测度．发现广东双重二元经济经济结构的显著性，并且有加剧的趋势．与珠三角相比差距也较为明显。造成这种现象的根源是产值比重和就业比重转换的不同步，最后在对广东二元经济结构演进过程和原因的分析基础上，提出一些建议和意见。  相似文献   

经贸科学理论中心全球地域转移的特征--以国际贸易理论为例     

陈修颖  Fredrik Edin 《世界地理研究》2003,12(2):10-16

经贸科学理论的孕育和形成需要特殊的地理环境——地域温床，随着社会生产力水平在全球不同地域范围内的此消彼长，地域温床不停地发生空间转移，从而导致经贸科学理论中心的全球地域转移。通过研究得出四个结论：①创新环境是决定经贸科学理论形成的地域温床；②经贸科学理论中心存在清晰的自西向东全球空间转移路径；③随着经济全球化和区域经济一体化的不断深入，经贸科学理论的阶级性在削弱、理性在成长；④经贸科学理论中心的地域转移总是发生在社会生产力大变革的转型时期。  相似文献   

阻抗张量分解进行大地电磁静校正的研究   总被引：3，自引：0，他引：3  

高红伟 《地质科技情报》1998,17(1):91-96

地表电性不均匀体对大地电磁测深的静态影响,会使大地电磁测深曲线产生十分严重的畸变,如何进行静校正以获得合理的区域构造响应,引起了国内外大地电磁专家的广泛关注。阻抗张量分解就是近几年发展起来的一种有效的方法。在全面论述阻抗张量分解进行大地电磁静校正原理的基础上,通过模型试算证明了该方法的有效性。  相似文献   

REDESCRIPTION OF A STROMATEOID FISH PAMPUS PUNCTATISSIMUS AND COMPARISON WTTH PAMPUS ARGENTEUS FROM CHINESE COASTAL WATERS     

刘静  李春生 《中国海洋湖沼学报》1998,(2)

MODUcrIONThestromaboidFishesofthefaInilyStrornateidaearewidelydistributedinChinesecoastalwatersandtheIndosoternPadfic.WiththededproduCtionofsomecom~alspedes,suchasyellowcroackerandhairtailfishes,moreandmoreattentionispaidtothesbornateOidfisheSwhoseoutputisabout3OOoo~4Ooo()t/ainChina.PampuspunCtabousboncketSchlegel,l845)andpampusargenteUsffiuphrasen,l788)aretwomportantspedesofthegenusPampus.DuetotheirmerphologicalsedaritAs,PpunctatiwtuswnregardedasasynonyInofPargenteUsbyrnanyworkers…  相似文献   

江西九江地区晚更新世生态变迁的土壤有机质碳同位素证据   总被引：4，自引：1，他引：3  

张平中 《冰川冻土》1998,20(2):150-156

根据我国江西九江地区４个土壤剖面的土壤有机质及其δ１３Ｃ值的分析结果,认为末次冰期旋回内生态转型是由于季风效应和ＣＯ２共同作用的表现;北大西洋末次冰期内的Ｈｅｉｎｒｉｃｈ事件对中国东部的气候也产生剧烈的影响,其分布直接控制着Ｃ３和（或）Ｃ４植物的转型及其沉积物的类型．ＣＯ２及其温室气体可能是Ｈｅｉｎｒｉｃｈ事件的重要驱动因素之一．  相似文献   

广义纵弯褶皱叠加机制、类型及其应用   总被引：1，自引：0，他引：1  

杜思清  魏显贵  刘援朝 《矿物岩石》1998,(Z1)

早期褶皱的迁移机制和迁移型叠加类型的发现扩大了对广义纵弯褶皱叠加机制和类型的认识。广义叠加机制有多种,其中包括迁移和位移,褶皱变缓和展平,岩层变陡和变缓等。广义叠加类型中除基本类型外还有限制型、展平残留型、叠加挠曲、共轴重褶等。本文将用几个地质实例予以说明。此外还将讨论叠加褶皱层应变和小构造的多成因和应用问题,其中包括斜纵弯应变和褶皱变缓展平引起的应变和小构造。  相似文献   

Phase‐shifts in shear stress as an explanation for the maintenance of pool–riffle sequences     

Scott N. Wilkinson  Robert J. Keller  Ian D. Rutherfurd 《地球表面变化过程与地形》2004,29(6):737-753

The stability of the pool–rif?e sequence is one of the most fundamental features of alluvial streams. For several decades, the process of velocity, or shear stress, reversal has been proposed as an explanation for an increase in the amplitude of pool–rif?e sequence bars during high ?ows, offsetting gradual scour of rif?es and deposition in pools during low ?ows. Despite several attempts, reversal has rarely been recorded in ?eld measurements. We propose that, instead of being reversed, maxima and minima in shear stress are phase‐shifted with respect to the pool–rif?e sequence bedform pro?le, so that maximum shear stress occurs upstream of rif?e crests at high ?ow, and downstream at low ?ow. Such phase‐shifts produce gradients of shear stress that explain rif?e deposition, and pool scour, at high ?ow, in accord with sediment continuity. The proposal is supported by results of a one‐dimensional hydraulic model applied to the surveyed bathymetry of a pool–rif?e sequence in a straight reach of a gravel‐bed river. In the sequence studied, the upstream phase‐shift in shear stress at high ?ow was associated with variations in channel width, with width minima occurring upstream of rif?e crests, approximately coincident with shear stress maxima, and width maxima occurring downstream of rif?e crests. Assuming that the width variation is itself the result of ?ow de?ection by rif?e crests at low ?ow, and associated bank‐toe scour downstream, low and high ?ow can be seen to have complementary roles in maintaining alluvial pool–rif?e sequences. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献