首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Western Europe, now largely dependent on oil imports, has to prepare for strong competition for oil and energy imports in general before the year 2000. The more unlikely it is for Western Europe to secure from outside rich supplies of coal or uranium at readily acceptable economic and political conditions, the more serious this competition becomes. Even exceptionally low projections of economic growth and optimistic assumptions about energy conservation urgently call for vigorous and simultaneous development of indigenous coal and nuclear sources, including the breeder. Long-term contracts for the possession and deployment of foreign oil, gas, and coal deposits are mandatory and should be negotiated in view of the possible aggravation of north-south confrontation.  相似文献   

2.
Therborn G 《Science (New York, N.Y.)》1987,237(4819):1183-1188
The 1960s meant a historical turn of Western Europe, becoming an immigration area. Net immigration has been concentrated to some of the prosperous Western European countries and has been mainly determined by the demand of their particular national labor regimes. The size of alien employment has been very differently affected by the 1973 crisis, but a multiethnical society will remain a novel feature of most Western European countries. Political abdication from full employment and technological change makes a ghetto of un(der)employment a likely prospect of a large part of the second generation of recent immigrants into Western Europe.  相似文献   

3.
边坡侵蚀的理论分析   总被引:3,自引:0,他引:3  
自然边坡侵蚀在世界各地随处可见 ,然而对自然边坡的侵蚀过程缺乏相关的理论研究 ,包括面蚀、渗透破坏和渠道冲刷。冲刷破坏是由于对土体的切割引起的 ,它与季节性融冻深度密切相关 ,因为融冻状态下 ,土壤的抗剪强度较低 ,水跃发生在渠坡下游 ,土体切割会加速边坡侵蚀进程 ,渗流将引起严重的深层破坏。这些主要受土壤性质和作用在坡面上的附加荷载的影响。最大渗流通常发生在融雪季节 ,研究边坡浸蚀破坏的机理将有助于城市、乡村和保护区的水管理  相似文献   

4.
坡度对伊犁河流域土壤侵蚀的试验分析   总被引:2,自引:0,他引:2  
【目的】通过模拟降雨试验,分析坡度对伊犁河流域土壤侵蚀的影响,从而为该区域水土保持工作提供借鉴.【方法】以伊犁河流域作为研究对象,基于前人研究的临界坡度,利用ArcGIS对该流域的坡度进行分级;同时,通过模拟降雨实验,选定3个不同的坡度为研究基础(5°,10°,15°),从土壤结构出发,对坡度侵蚀进行分析.【结果】伊犁河流域的土壤侵蚀主要集中在该流域坡度为10°~15°的高山区雪线以下至山前洪积平原,坡度由陡变缓的区域,占伊犁河流域面积的11.75%,而该区域受气候等因素的影响,土壤大块、团粒结构容易被破坏,容易发生土壤侵蚀.【结论】在该流域进行水土保持工作时,建议把预防工作重点放在这些容易被侵蚀的区域.  相似文献   

5.
闽南地区地形坡度与土壤侵蚀的关系研究   总被引:7,自引:0,他引:7  
在GIS的支持下,研究了闽南地区地形坡度与土壤侵蚀之间的关系.结果表明,水力侵蚀是闽南地区的主要土壤侵蚀类型,其面积占总侵蚀面积的97.4%;水力侵蚀中有1/3的面积分布在≤5°的坡地上,而且>25°坡地的土壤侵蚀面积最小;大部分的风蚀和工程侵蚀分布在≤5°的坡地上.  相似文献   

6.
7.
8.
闽南坡地果园水土流失现状及生态整治   总被引:2,自引:0,他引:2  
根据生态学的原理和方法,分析闽南坡地果园水土流失的现状和原因,结合闽南农村所处的自然和社会经济条件,提出以生物治理、坡改工程、调控水工程和社会管护工程为主体的综合防治体系,是治理闽南坡地果园水土流失的有效途径。  相似文献   

9.
A detailed high-resolution geophysical study of part of the continental slope along the mid-Atlantic margin of the United States indicates that it is an ancient, relict landscape largely unmodified by modern slope processes. The slope morphology is heavily influenced by bedrock outcrops, including joints and bedding planes, rather than by any single degradational process. A pelagic drape averaging 3 to 5 meters in thickness blankets the slope. Carbon-14 dates from eight drop cores show that the drape was deposited in late Pleistocene and Holocene times. The Holocene part of the drape, comprising the uppermost 1 meter, was deposited at a continuous rate of 10 centimeters per 1000 years. Most features on the slope predate the drape cover.  相似文献   

10.
11.
路基边坡草灌植被消减降雨侵蚀定量分析   总被引:1,自引:0,他引:1  
为了揭示路基边坡草灌植被护坡作用的本质,提高生态防护效益,2005-2008年选择路基边坡不同土壤类型和草灌植被为研究对象,利用野外径流小区法和数据分析,结果表明:1)确定了项目区的侵蚀性降雨指标;2)确定了降雨侵蚀力被草灌植被消减的量化方法,揭示了植被覆盖度在其中所起的决定作用;3)不同土壤类型边坡植被消减降雨侵蚀力效果。砂姜黑土:紫花苜蓿95.8%、高羊茅95.4%、紫穗槐93.2%、狗牙根89.6%、小叶扶芳藤82.3%;黄黏土:紫穗槐93.9%、紫花苜蓿91.4%、高羊茅90.7%、小叶扶芳藤85.8%、狗牙根83.1%;粉砂土:高羊茅96.1%、紫花苜蓿94.7%、狗牙根94.6%、紫穗槐93.8%、小叶扶芳藤83.2%。研究对路基边坡生态防护具有实际指导作用。  相似文献   

12.
Kidd CV 《Science (New York, N.Y.)》1981,212(4492):293-298
During the 1960's, Canada, France, Germany, the United Kingdom, and the United States all experienced periods of rapid growth of research expenditures and of university enrollments followed by declines in growth rates. This sequence has generated the current severe shortages of new academic positions, with a resulting long-range threat to the vitality of academic science. Declines in the 18-year-old cohort in the United States, and especially in Canada, aggravate the problem. The United States is the only one of these countries that has not adopted a modest program to deal with the problems by creating fellowships or new positions.  相似文献   

13.
百色坡地果园水土流失的生物覆盖治理研究   总被引:1,自引:0,他引:1  
为研究生物覆盖治理对坡地果园水土流失的影响,在坡地芒果园边坡种植生物栅篱、在梯面种植绿肥和覆盖秸杆,试验结果表明:生物覆盖综合治理区与对照区相比,平均减少水流失389.85m3/hm2,减少63.72%;土壤侵蚀量年平均减少4.66t/hm2,减少83.65%,土壤含水量平均提高4个百分点,且耕层土壤水分波动较小。  相似文献   

14.
15.
In conclusion, I feel that the energy challenge, tough as it is, does not pose unsurmountable technological problems, even in Europe. At least in principle, the necessary technology is already there. This article is meant to make that statement plausible. It is not the intention to insist on certain ideas. It is important, however, to have a consistent approach, and this means to obey the timing of the problem. Therefore the most important aspect during the transition phase probably is the buildup of a modern secondary energy system. In the long run it will ibe energy embedding and not the production of energy which will be the principal driving force for the development, because in principle at least there is more than one option to provide almost unlimited amounts of energy. In order to meet the demand for an appropriate embedding of energy, the concept of primary energy parks in the open sea seems to be most promising.  相似文献   

16.
黄土残塬沟壑区坡度和坡长对土壤侵蚀的影响分析   总被引:15,自引:5,他引:15  
该研究以黄土区坡地的坡长与坡度对于土壤侵蚀的影响为研究内容 ,旨在为因害设防 ,更好的治理水土流失 ,对黄土高原坡地综合治理提出理论依据和切实可行的实践指导 .根据在山西省吉县黄土残塬沟壑区长期定位水土流失观测与调查资料 ,并结合以往关于黄土区的研究成果分析了坡长和坡度与侵蚀的关系 ,研究表明 :随坡长和坡度的增大 ,径流增大 ,侵蚀量越大 ,侵蚀模数增大 ;年侵蚀模数与坡长呈正相关关系 ;随着坡长增大 ,细沟侵蚀和浅沟侵蚀明显增强 ;坡耕地坡长最好小于 15m .  相似文献   

17.
黄土残塬沟壑区坡度和坡长对土壤侵蚀的影响分析   总被引:10,自引:1,他引:10  
该研究以黄土区坡地的坡长与坡度对于土壤侵蚀的影响为研究内容,旨在为因害设防,更好的治理水土流失,对黄土高原坡地综合治理提出理论依据和切实可行的实践指导. 根据在山西省吉县黄土残塬沟壑区长期定位水土流失观测与调查资料,并结合以往关于黄土区的研究成果分析了坡长和坡度与侵蚀的关系,研究表明:随坡长和坡度的增大,径流增大,侵蚀量越大,侵蚀模数增大;年侵蚀模数与坡长呈正相关关系;随着坡长增大,细沟侵蚀和浅沟侵蚀明显增强;坡耕地坡长最好小于15 m.  相似文献   

18.
19.
通过对天山北麓中段土地类型、河流径流和植被覆盖等土壤侵蚀影响因素的空间分布特征分析认为 :1天山北麓中段主要侵蚀类型为风蚀、水蚀、冻融侵蚀及人为加速侵蚀 ;2侵蚀产沙类型以及产沙强度在空间上具有明显的垂直变化规律 :沙漠以风力侵蚀、高山和亚高山以冻融侵蚀为强烈侵蚀类型 ,普遍存在微度水力侵蚀 ,局部表现为中度甚至强度 ;3水蚀类型有冰川融雪径流侵蚀和降雨径流侵蚀两种方式。天山北麓中段河流产沙时间上主要在每年的 5月初至 8月末 ,且冰川雪水径流产沙要比雨水径流产沙量大 ,空间上则主要位于海拔 80 0~ 1 50 0 m的由第三纪、第四纪地层和黄土堆积所组成的中、低山丘陵地  相似文献   

20.
为识别植被恢复流域侵蚀变化过程,本研究构建了包含RUSLE(Revised Universal Soil Loss Equation)、IC(Index of Connectivity)和基于SWAT(Soil and Water Assessment Tool)的径流侵蚀功率方程所构成的侵蚀过程识别模型方法框架,以探究延河流域侵蚀过程的变化及对植被恢复的响应特征。结果表明:延河流域侵蚀情况总体持续向好,1985—2000年间多个年份的流域平均侵蚀模数超过80 t·hm-2·a-1,而在2015年左右下降至10~30 t·hm-2·a-1,植被恢复造成了流域侵蚀的动态变化,两者呈负相关的年际变化趋势,表明植被增加在较大程度上抑制了土壤侵蚀。径流侵蚀功率时空变异性较大,最大值从1985年的13.28×10-4m4·s-1·km-2下降至2020年的4.40×10-4m4·...  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号