首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   54篇
  免费   2篇
测绘学   1篇
大气科学   2篇
地球物理   7篇
地质学   3篇
海洋学   3篇
综合类   1篇
自然地理   39篇
  2023年   2篇
  2022年   2篇
  2021年   6篇
  2019年   5篇
  2018年   3篇
  2017年   3篇
  2016年   5篇
  2015年   4篇
  2014年   3篇
  2013年   5篇
  2011年   1篇
  2009年   2篇
  2008年   2篇
  2006年   7篇
  2005年   1篇
  2004年   1篇
  2003年   1篇
  1999年   2篇
  1997年   1篇
排序方式: 共有56条查询结果,搜索用时 28 毫秒
41.
There is a strong connection between cultural and biological diversity at a global scale, especially in the linguistic domain, but less is known at regional scales. Indicators of such reciprocity are found in the linguistic expression of natural elements, and their representation in the landscape through toponymy. Here we evaluate the geographic distribution of phyto-toponyms, places named after a native local flora, in Galicia, NW Spain. We created the concept of toponymic species (topo-species) for groups of places named after a plant taxon. By using different regression models assuming global effects of the variables (Ordinary Least Squares, OLS) or non-stationarity (Geographically Weighted Regression, GWR), we explored the connection of topo-species richness and diversity with environmental (river density, altitude and natural habitats density) and social (total density of toponyms, population density) factors.Topo-species richness and diversity were significantly correlated with the studied factors. Total density of toponyms, river density, altitude and natural habitats density showed significant positive values in the models, while population density had little or no effects. GWR performed better for all variables, especially for Shannon diversity index. We conclude that place names of natural elements depict human’s interaction with the environment. They are stable, spatially-explicit elements that may be used as indicators of bio-cultural diversity. In addition, they represent an intangible cultural heritage that should also be preserved.  相似文献   
42.
Armed conflicts are globally widespread and can strongly influence societies and the environment. However, where and how armed conflicts affect agricultural land-use is not well-understood. The Caucasus is a multi-ethnic region that experienced several conflicts shortly after the collapse of the Soviet Union, most notably the two Chechen Wars, raising the question how agricultural lands were changed. Here, we investigated how the distance to conflicts and conflict intensity, measured as the number of conflicts and the number of casualties, affected agricultural land abandonment and subsequent re-cultivation, by combining social, environmental and economic variables with remotely-sensed maps of agricultural change. We applied logistic and panel regression analyses for both the First Chechen War (1994–1996) and the Second Chechen War (1999–2009) and interacted conflict distance with conflict intensity measures. We found that agricultural lands closer to conflicts were more likely to be abandoned and less likely to be re-cultivated, with stronger effects for the First Chechen War. Conflict intensity was positively correlated with agricultural land abandonment, but the effects differed based on distance to conflicts and the intensity measure. We found little re-cultivation after the wars, despite abundant subsidies, indicating the potentially long-lasting effects of armed conflicts on land-use. Overall, we found a clear relationship between the Chechen Wars and agricultural land abandonment and re-cultivation, illustrating the strong effects of armed conflicts on agriculture.  相似文献   
43.
In Nepal, changing demographic patterns are leading to changes in land use. The high level of outmigration of men in the hills of Kaski District, Western Development Region of Nepal, is affecting the household structure but also land management. Land is often abandoned, as the burden on those left behind is too high. How do these developments affect the state of the land in terms of land degradation? To find out, we studied land degradation, land abandonment caused by outmigration, and existing sustainable land management practices in a subwatershed in Kaski District. Mapping was done using the methodology of the World Overview of Conservation Approaches and Technologies (WOCAT). While previous studies expected land abandonment to exacerbate slope erosion, we demonstrate in this paper that it is in fact leading to an increase in vegetation cover due to favourable conditions for ecosystem recovery. However, negative impacts are several, including the increase of invasive species harmful to livestock and a decline in soil fertility. Traditional land management practices such as terraces and forest management exist. To date, however, these measures fail to take account of the changing population dynamics in the region, making the question of how migration and land degradation are linked worth revisiting.  相似文献   
44.
45.
中国山区耕地利用边际化表现及其机理   总被引:15,自引:4,他引:15  
李升发  李秀彬 《地理学报》2018,73(5):803-817
耕地利用边际化是当前中国山区土地利用主要变化趋势。利用《全国农产品成本收益资料汇编》资料,本文首先分析2003年以来农业劳动力价格快速上涨的背景下,中国农业生产成本的结构变化以及农户的响应,并对比平原和山区农户对劳动力成本上升的响应方式及程度的差异,发现平原地区能够通过大规模的农业机械替代减少劳动投入,进而有效减少劳动力价格上升所带来的影响,而山区因地形条件限制,劳动生产率提升相对缓慢,并与平原地区的差距不断扩大,导致农业劳动力成本占比不断上涨。随着劳动力成本的快速上涨,中国山区耕地边际化特征明显,以玉米为代表的种植业净利润在2013年普遍降至零以下。2000年以来,中国山区土地利用和植被变化表现为耕地面积减少、森林面积增加、NDVI指数增强,而且在省级层次上,山区县范围NDVI变化率与耕地和森林面积变化率分别具有很强的负相关(r = -0.70)和正相关(r = 0.91),证实了中国山区耕地当前边际化的发展态势。基于以上分析,本文最后对务农机会成本上升、农业劳动力快速析出背景下的山区耕地利用边际化机理进行了总结。这一研究有助于深入认识山区耕地撂荒和森林转型的发展过程。  相似文献   
46.
Xiao  Guofeng  Zhu  Xiufang  Hou  Chenyao  Xia  Xingsheng 《地理学报(英文版)》2019,29(4):581-597
Journal of Geographical Sciences - Rapid urbanization and continuous loss of rural labor force has resulted in abandonment of large areas of farmland in some regions of China. Remote sensing...  相似文献   
47.
钟巍  熊黑钢 《中国沙漠》1999,19(4):343-347
策勒绿洲沉积地层及地球化学元素的研究表明,虽然近4 ka B.P.来本地区气候环境的干旱状况持续未变,但期间仍有若干次相对湿润与干旱化加剧时期的波动。结合年代学的研究,以约2 000 aB.P.为界,其以前气候以相对湿润为主,而此以后,则以持续干旱为主要特征,且揭示出4 次具有突变性质的气候转干时期,即自约1 500a B.P.开始,类似本地区现今气候环境特征已经出现,自约1 200 a B.P.至1 000 a B.P.、1 000 a B.P.至630 aB.P.期间和200 a B.P.以后,策勒地区沙漠化进程急剧加强。本研究揭示了4 ka B.P.来本地区持续干旱化的特征,并有后期加剧的趋势,而上述气候的转干事件与塔里木盆地古城废弃事件之间具有良好的吻合关系,表明气候环境的自然演化是影响人地关系的重要因素之一。  相似文献   
48.
The sediment budget of the small research catchment of Cal Parisa (Vallcebre, Eastern Pyrenees) was studied by hydrological monitoring and assessment of the erosion rates in the major sediment sources. This area is characterized by clayey mudrock prone to landsliding and badland erosion, but the catchment was selected in an area free of major badland features, as a representative of middle mountain regions where a system of terraces and drainage ditches had been built for agricultural use but is now abandoned. Streamwater chemistry is dominated by Ca2+ and HCO3 at concentrations close to calcite saturation. Total dissolved solids show dilution during runoff peaks and positive hysteresis loops that support a slow contribution of subsurface water. Relative dissolved ion concentrations are different for each event analysed. Particulate sediment yield is very low and represents only about 1 per cent of gross erosion in the catchment. Mineralogical analysis of suspended sediments shows an enrichment in calcite because of precipitation. Chemical analysis of suspended sediments, using common one-litre water samples, shows higher contents of Ca, P and Mn in transported sediment than in sediment source areas, attributed to the precipitation of calcite, and enrichment in organic particulate matter during events respectively for the two first elements, whereas enrichment in Mn remains uncertain. Solid matter yield is therefore clearly dominated by dissolved transport as a result of both high calcium bicarbonate concentrations in runoff waters and strong suspended sediment conveyance discontinuities. Land conservation structures are very effective because they are in good condition whereas the soil is covered by dense permanent vegetation. Nevertheless, this state is unstable because the network of drainage ditches needs maintenance; its spontaneous breakdown after abandonment may result in the rearrangement of the elementary stream network and gullying of old fields in hollows. © 1997 John Wiley & Sons, Ltd.  相似文献   
49.
Land abandonment is an acute problem for shrinking cities throughout the world. The prevailing legal paradigm in the United States relies on market logics to address abandonment—specifically by auctioning abandoned parcels to the highest bidder. This emphasis is reinforced by a variety of structural forces at multiple scales, despite its highly questionable efficacy as a way to return land to “productive use.” In this article, we explore the case of Toledo, Ohio, to illustrate the limitations of market logics in addressing market collapse inherent in land abandonment. We find that the market emphasis is effective neither for city building nor tax generation goals, but is deeply rooted and reinforced by layers of state law, structural forces, and pro-market institutions.  相似文献   
50.
The Atlantic Forest biome has only 13 percent of its pristine vegetation cover left. This article analyzes the consequences of land changes on forest cover in the Paraíba Valley, São Paulo state, Brazil, from 1985 to 2011. Multitemporal satellite image classifications were carried out to map eight land use and land cover classes. The forest cover increased from 2,696 km2 in 1985 to 4,704 km2 in 2011, mostly over areas of degraded pastures. The highest rates of afforestation were observed within protected areas around eucalyptus plantations. On the other hand, deforestation processes were concentrated on areas covered by secondary forests. Socioeconomic changes taking place in particular Brazilian settings, such as industrialization and agricultural modernization, allied to the Paraíba Valley's natural biophysical constraints for agricultural production, have led the region to experience a remarkable case of forest transition.  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