Decomposition of root litter and related microbial population dynamics of a Negev Desert shrub, Zygophyllum dumosum     

Y. Steinberger  R. Degani  G. Barness 《Journal of Arid Environments》1995,31(4)

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星载合成孔径雷达成像处理     

陈艳玲   《中国科学院上海天文台年刊》2005,(1):22-30

合成孔经雷达(Synthetic Aperture Radar,SAR)是当今微波遥感领域的研究热点,其全天候、全天时、高分辨率以及穿透地表等特点使其具备其他传感器不可比拟的优势,因此得到了极其广泛的应用。成像处理是SAR技术的核心部分。分析了星载SAR点目标回波信号模型和几种常用的星载SAR数字成像处理算法。以距离-多普勒算法为例,阐述了距离压缩和方位压缩的实质,详细讨论了多普勒参数估计、距离徙动校正和斑点噪声的去除等几个关键的问题。采用ERS-1卫星数据做了成像实验,并对SAR成像技术加以总结。  相似文献   

镉在包气带中的迁移与积累特征     

张光辉 《地球科学与环境学报》1995,(2)

本文论述了镉在包气带中迁移积累问题，提出了镉在包气带中的迁移和积累模式并用实验结果与之加以验证，指出了镉在各类土壤中的存在形式及在不同地球化学环境镉的危害性是有所不同的。  相似文献   

On the theory of Chebyshev polynomials in wave-equation migration     

Panos G. Kelamis 《Geophysical Journal International》1988,94(3):421-426

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Aspects of larval,post-larval and juvenile ecology of Macrobrachium petersi (Hilgendorf) in the Keiskamma estuary,South Africa     

G.H.L. Read 《Estuarine, Coastal and Shelf Science》1985,21(4):501-510

Although Macrobrachium petersi has nine larval stages, only stage I and a minimal number of stage II M. petersi larvae were caught in the Keiskamma estuary. Stage I larvae undergo a vertical migration at night which is markedly influenced by salinity, especially under stratified conditions. Larvae remain in the water column on the ebb tide, a behavioural pattern which effectively carried them to favourable salinities for growth and development. Stage I larvae show an association with salt front regions. The sudden decline in larval abundance from stage I to stage II downstream from the front suggests a change from a pelagic to an epibenthic existence. Later larval stages failed to appear in the plankton. However, post-larvae were caught in the estuary and a juvenile migration from the estuary to freshwater was monitored.  相似文献   

湘东某铁帽型金银矿床特征与成因探讨     

陆玉梅  沈瑞锦 《湖南地质》1993,(4)

湘东某铁帽型金银矿床,位于某多金属矿床中部,受一压扭性走向断裂及潜水面控制.主矿体赋存在印支期花岗班岩与下石炭统大塘阶页岩或砾岩的接触面上。矿区处于亚热带潮湿气候的低山丘陵区,氧化带比较发育,矿区中部氧化带深度较大。含金银的硫化矿体经风化剥蚀裸露地表,一些元素淋漓、迁移、流失,另一些元素残余富集,金、银极其稳定,附着在铁矿物的裂隙、空洞、晶隙中,或被吸附在粘土矿物表面,形成金银矿体。  相似文献   

THE SOURCES OF REGIONAL ELDERLY POPULATION GROWTH: MIGRATION AND AGING-IN-PLACE *     

Andrei Rogers  Jennifer Woodward 《The Professional geographer》1988,40(4):450-459

A region's elderly population has two sources of growth: net migration and the net aging-in-place of its resident population. This paper outlines a method for identifying the projected relative contribution of these two sources of elderly population growth over time, and illustrates it with data for the states of Arizona, California, Florida, Illinois, and New York. The sources of elderly population growth differ between regions and over time.  相似文献   

COUNTER-URBANIZATION IN SOCIETAL CONTEXT: LONG-DISTANCE MIGRATION TO THE HIGHLANDS AND ISLANDS OF SCOTLAND*     

Huw Jones  Nicholas Ford  James Caird  William Berry 《The Professional geographer》1984,36(4):437-444

Recent growth in long-distance migration by non-Scots to remote parts of the Scottish Highlands is evaluated in relation to key explanatory themes in counter-urbanization literature: rural-urban convergence, expansion of the affluent middle class, and changing residential preferences. A survey of in-migrants' motivations and livelihood adjustments reveals the primacy of quality of life considerations and a ‘satisficing’ approach to work, lifestyle and residential location. It is concluded that peripheral area counter-urbanization could be maintained without the context of societal affluence that spawned the movement in the 1960s.  相似文献   

广东省人口局部收缩特征及其影响因素 ——以东莞莞城为例     

符家铭  刘毅华 《热带地理》2018,38(4):525-535

21世纪以来,广东省在经济和城镇化高速发展的同时也面临着人口的局部收缩,使经济发展的时空格局复杂化。通过实地调研、数理统计、GIS空间分析等定性与定量相结合的方法,分析了广东省人口收缩特征、类型及影响因素,并对东莞莞城进行典例个案分析。结果表明：2000―2010年广东省存在人口局部收缩现象,但总体程度较为轻微且在空间和类型上存在分异;区域发展不平衡、产业结构转型升级、郊区化和行政区划调整等因素导致了广东省人口收缩;莞城的收缩特征主要表现为外来人口持续减少、经济增速持续放缓和城镇功能地位转变3个方面;在主观和客观的推拉力因素作用下,外来人口未来预期发展下降及莞城自身劳动力需求减少共同导致了莞城的人口收缩。  相似文献   

人口老龄化对乡村发展影响研究进展与展望   总被引：3，自引：1，他引：2  

廖柳文  高晓路 《地理科学进展》2018,37(5):617-626

人口老龄化是人类发展进程中一个重要的人口现象,研究人口老龄化对乡村发展的影响并探讨相应对策具有重要意义。本文首先分析了乡村人口老龄化特征及原因,随后从生产、生活、生态三个视角梳理了人口老龄化对乡村生产要素投入、农业生产、社会保障、乡村治理、消费结构、土地利用变化和生态空间等方面影响的研究进展。在此基础上提出今后应结合产业兴旺、生态宜居、乡风文明、治理有效、生活富裕的乡村振兴战略总体要求,从生态环境—经济发展—社会发展三个维度开展乡村人口老龄化的影响与适应相关研究,重点研究方向有：①基于人口流动视角的乡村人口老龄化对生态系统服务价值的影响;②乡村人口老龄化空间差异及其对农业现代化的影响;③应对人口老龄化的乡村振兴路径。  相似文献