中国农村剩余劳动力转移的趋向和措施     

范宇  姚士谋  Kam Wing Chan 《热带地理》2002,22(1):3-8

在对中国农村剩余劳动力现状描述的基础上 ,对剩余劳动力形成的原因进行了分析与阐述 ;结合目前形势 ,指出未来农村剩余劳动力的转移前景不容乐观 ;并在此基础上阐述了中国剩余劳动力转移途径和主要措施  相似文献   

云南省金沙江流域土壤流失方程研究   总被引：17，自引：2，他引：17  

杨子生 《山地学报》2002,(Z1)

云南金沙江流域是长江中上游水土流失最严重的区域。本项研究以“通用土壤流失方程”(USLE)为蓝本,运用小区实验等手段,综合分析了各个侵蚀因子,建立了云南金沙江流域土壤流失方程A=R·K·LS·c·P,并确定了方程中诸因子的求算方法和数值,以及该流域土壤允许流失量,为方程的应用提供了基本的技术数据。同时,还进行了方程的检验,方程计算值与小区实测值的相对误差在6.3％以下,表明该方程在实际应用中是可靠的。该方程的建立,可为云南金沙江流域预测预报土壤侵蚀,制定土地合理利用规划方案、水土保持措施和土地生态安全格局提供了一套可靠的科学方法和依据。  相似文献   

Palaeolimnology of Lake Piene-Kuuppalanlampi (Kurkijoki, Karelian Republic, Russia): isolation history, lake ecosystem development and long-term agricultural impact     

Juha Miettinen  Elisabeth Grönlund  Heikki Simola  Pertti Huttunen 《Journal of Paleolimnology》2002,27(1):29-44

The post-glacial history of Lake Pieni-Kuuppalanlampi, western Lake Ladoga region, was studied by means of stratigraphic pollen and diatom analyses. Diatoms were analysed to track the isolation history of the basin and the limnological effects of the early land-use phases indicated by pollen analysis. Chrysophycean stomatocysts and Isoëtes spores were also employed in the limnological reconstructions. Sediment dating was provided by six conventional radiocarbon dates.The lower part of the 370-cm long sediment sequence represents early Holocene, large lake conditions: the (freshwater) Yoldia and Ancylus stages of the Baltic basin, with a short-term lagoonal or isolation phase at the end of Yoldia. The basin was isolated due to Ancylus lake regression at 9785 cal B.P. For the small-lake sequence (0–250 cm) we used diatom inferences (WA-method) for hindcasting water chemistry. The post-isolation limnology of Pieni-Kuuppalanlampi reflects the development of vegetation on its small hill-top catchment. In its early development, the lake was mesotrophic, but became more acidic (pH about 6) and oligotrophic after the decline of temperate hardwood trees and the spread of spruce to the area after around 5000 B.P. The lake ecosystem appears to have reacted sensitively to agricultural land-use in the catchment from AD 400–800 onwards: inferred total phosphorus levels and pH both rise during these periods.  相似文献   

Modeling the relationship of land use change and some geophysical indicators for the interlock area of farming and pasturing in China     

DENG Xiangzheng  LIU Jiyuan  ZHUANG Dafang  ZHAN Jinyan  ZHAO Tao 《地理学报》2002,12(4):397-404

This paper discusses land-use changes in the interlock area of farming and pasturing (IAFP)in northern China. It presents detailed analyses of land-use features in the IAFP, which are controlled by the macro geomorphic units and geophysical conditions-constraints or advantages. Additionally, it selects some indicators, according to the availability in acquiring and processing their quantitative data, to analyze the canonical correlations between the typical conversion of grassland and geophysical conditions. The preliminary study indicates that the physical conditions are of great advantages to the development of grassland. There exists significant correlation between land use change and some geophysical conditions.  相似文献   

Natural environmental changes and human impact reflected in sediments of a high alpine lake in Switzerland   总被引：1，自引：0，他引：1  

C. Ohlendorf  M. Sturm  S. Hausmann 《Journal of Paleolimnology》2003,30(3):297-306

From the high alpine Sägistalsee (1935 m a.s.l.), 13.50 m of continuously laminated sediments comprising the last 9050 years, were analyzed. Even though Sägistalsee is a high elevation site, human-induced environmental changes start as early as 4300 cal. BP and leave a clearly detectable signal in the mineralogy of the sediments, which is much stronger than the signal from natural environmental changes that occurred before this time. Variations in the physical and mineralogical sediment properties of this clastic sequence reflect erosional changes in the catchment, where almost pure limestone contrasts with carbonaceous, quartz-bearing marl, and shist. The calcite/quartz (Cc/Qz) ratio was found to be most indicative of these changes, which occurred around AD 1850 and at 650, 2000, 3700, and 6400 cal. BP. The first four are interpreted as erosion events, which are related to human-induced changes in the vegetation cover and land use. We associate them to the recent development of tourism and grazing, the medieval intensification of pasturing, Roman forest clearance, and Bronze Age forest clearance, respectively. The Cc/Qz-ratio increases significantly within less than 100 years during these events, reflecting the erosion of unweathered or poorly weathered soils. The time intervals in between are characterized by a gradually decreasing Cc/Qz-ratio and reflect the stabilization or formation of new soils. Only the change at 6400 cal. BP, which represents the initial gradual stabilization of the catchment, is related to the immigration of Picea abies.  相似文献   

杭州华门清水湾别墅区滑坡研究     

陈启国谷英奎  齐跃明吴燕玲 《中国煤田地质》2003,15(4):31-33

通过杭州清水湾别墅区滑坡结构、变形特征及主要控制因素的分析,认为滑坡主要是由于人工不适当开挖边坡造成斜坡地质体临空、雨水渗透诱发土体失稳下滑而形成的,通过计算稳定系数和剩余下滑力,对斜坡稳定性作出评价并提供防治方案。  相似文献   

黄土湿陷性的微结构不平衡吸力成因论   总被引：16，自引：0，他引：16  

汤连生 《工程地质学报》2003,11(1):30-35

分析了黄土粒间吸力的基本特性及其湿陷的微观过程,探讨了黄土在应力状态作用下由于浸水增湿而产生的微结构单元体滑移动力和阻力随饱和度、上覆土压力的变化规律,提出了微结构与广义吸力综合效应的湿陷性控制机理---微结构不平衡吸力成因论及其定量模型,从理论上分析了湿陷性与增湿水量、压力及深度的关系,揭示了土湿陷效应的内在规律。文中认为,湿陷过程就是水的楔入导致小孔隙广义吸力的逐渐丧失和大孔隙湿吸力的逐渐增大引起的微结构重建动力与重建阻力间的动态对抗过程。最后,讨论了湿陷的基本条件及影响因素。  相似文献   

地质基础理念之我见     

丁乾俊 《新疆地质》2003,21(4):463-467

任-侵位的岩浆体，在结晶分异、固化成岩过程中，一般都可分为：已结晶的固相岩体、正(半)结晶的可塑相岩体及未结晶的熔融相岩浆3部分．此时，若发生了地壳运动，地壳运动的构造作用力。使正(半)结晶的可塑相岩体发生可塑相变形，形成片麻化岩体；地壳运动(包括地震)时的构造作用力为脉动性质的挤压作用力；岩体发生片麻化的地壳运动，又使已结晶的固相岩体和围岩发生断裂活动，形成了断裂带控矿、容矿构造；未结晶的熔融相岩浆再度上升侵位，便形成了小侵入岩体控矿构造．残浆的形成与排出，控矿构造的发生、发展与控矿过程，都是在这次地壳运动过程中完成的．因此，对这次地壳运动可称成矿作用．  相似文献   

斜坡地下水渗透力计算与稳定性分析   总被引：21，自引：2，他引：21  

王旭升  常宏  谭建民 《水文地质工程地质》2003,30(2):41-45

分析了基岩山区斜坡区域地下水的渗流模式,指出斜坡堆积体中地下水的一般特征,根据这个特征建立了条分法中斜坡渗透力的简易计算方法,用于改进传统的剩余推力法和Sarma法。该方法不需要额外补充参数,易于工程勘察人员掌握。提出通过极限状态考察斜坡安全储备的思路,对三峡库区某滑坡在水库蓄水前后的稳定性和安全储备进行了评价,结果表明传统方法计算的稳定性系数过高,当库水位快速下降时滑坡稳定性减弱,地下水渗透力是其中不可忽视的影响因素。  相似文献   

全球气候变化及其影响   总被引：20，自引：2，他引：20       下载免费PDF全文

雷·Wen  查尔斯·A·Lin 《水科学进展》2003,14(5):667-674

全球气候变化及其对社会与自然系统产生的影响已日益受到全世界各国政府与广大民众的关注。与天气和气候有关的灾害给人类生命财产造成的损失日益增大,社会与生态系统似乎变得日趋脆弱。人们关心刚刚过去的20世纪的天气与气候发生了什么变化,更希望了解未来的21世纪,人类居住的地球会出现什么样的气候情景。根据一些国家和地区的观测记录、研究成果以及科学家们对气候变化的评估与预测展望,对全球气候变化问题进行概括。首先阐明20世纪地区性气候变化的事实;并根据政府间气候变化委员会(IPCC)科学技术报告中关于20世纪全球气候变化进行的总结性评估以及对21世纪全球气候变化的预测,作为阐述过去与未来全球气候变化的主要依据。同时,还介绍了一些科学家对IPCC关于全球气候变化的结论所持的不同观点或质疑。还就气候变化对社会与自然系统可能产生的影响略作论述。  相似文献