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   1982篇
  免费   145篇
  国内免费   127篇
测绘学   217篇
大气科学   22篇
地球物理   248篇
地质学   396篇
海洋学   134篇
天文学   2篇
综合类   170篇
自然地理   1065篇
  2024年   11篇
  2023年   19篇
  2022年   52篇
  2021年   96篇
  2020年   79篇
  2019年   75篇
  2018年   64篇
  2017年   98篇
  2016年   78篇
  2015年   76篇
  2014年   95篇
  2013年   144篇
  2012年   125篇
  2011年   125篇
  2010年   69篇
  2009年   115篇
  2008年   109篇
  2007年   112篇
  2006年   112篇
  2005年   113篇
  2004年   72篇
  2003年   87篇
  2002年   71篇
  2001年   54篇
  2000年   40篇
  1999年   40篇
  1998年   25篇
  1997年   22篇
  1996年   11篇
  1995年   15篇
  1994年   7篇
  1993年   9篇
  1992年   5篇
  1991年   3篇
  1990年   3篇
  1989年   1篇
  1988年   4篇
  1987年   4篇
  1986年   4篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1976年   1篇
排序方式: 共有2254条查询结果,搜索用时 328 毫秒
941.
龙虎山世界地质公园丹霞地貌成景系统特征及其演化   总被引:1,自引:0,他引:1  
龙虎山世界地质公园内分布着大量以石寨、石墙、巷谷、峰林、石峰、石柱、石崖、巷谷、一线天、造型石等景观类型,它们形成于晚白垩系龟峰群,是我国典型的丹霞地貌分布区之一.其形成不仅与红层、构造及流水等外营力等构成了丹霞地貌的成景系统因素有关,而且也与它们在信江盆地内的空间位置相关,共同制约着不同位置上丹霞地貌的演化进程及其景观总体特征.  相似文献   
942.
湿地生态景观构建以水生态环境为基础,它具有原生态环境、动感生态场景、人文生态内蕴等审美特征。湿地旅游的开发建设要特别强调科学,注重生态与文化的保护,产品要主打生态品牌,营销要突出绿色主题,运行要倡导低碳环保,走绿色低碳发展之路。  相似文献   
943.
The geomantic idea of chosan pibo is a particular way of remedying the inadequacies of a geomantic landscape by building small mounds of earth or stones and has been a significant motivation for modifying the environment in Korea. This idea is a part of ancient Chinese geomancy, or feng shui, for determining auspicious sites. Historically, three principal geomantic means have been used to compensate for shortcomings at an auspicious site: building religious structures, such as temples; creating hills, planting trees, or changing directions of watercourses; or making other symbolic gestures, such as naming objects and places. In this article I concentrate on the second, modifying landforms to compensate for the geomantic shortcomings of a place. The quasi‐religious zeal shown by feng shui practitioners in Korea to improve the local geomantic landscape is worthy of comparing and contrasting with the European Christian idea, held by medieval monastic monks, that humanity is a partner of God in improving the environment.  相似文献   
944.
Geographers have a long tradition of using photographs to investigate landscape meaning. I conducted photo‐elicitation research with community members residing in and around one of the National Park Service (nps ) “partnership parks” in order to obtain their conceptions of the park. The nps partners with myriad groups in order to manage the park, resulting in mostly privatized amenities at Michigan's Keweenaw National Historical Park. Participants in my study took photographs of landscapes and used them to discuss their conceptions of the park. Building upon recent scholarship on the perceptions of parks and place attachment in parks, the photo‐elicitation revealed a strikingly complex array of understandings. Social class, not whether one lived within or outside the park's boundaries, was the most important variable in categorizing perceptions of the park. These data help us understand how community members conceive of partnership parks and thus may help inform nps decision making.  相似文献   
945.
Community-based natural resource management in northeast India has a long history. Indigenous knowledge and adaptation are the collective information, with improvement from generation to generation. The expectation is that under community control, local expertise on biodiversity will play a significant role in natural resource management through traditional practices. This paper discusses the characteristics and application of the traditional ecological knowledge of aboriginal peoples in northeast India and its role in natural resource management. Examples are provided in two different eco-cultural landscapes, i.e., Demazong (the Buddhist eco-cultural landscape in Sikkim Himalaya) and the Apatani eco-cultural landscape in Arunachal Pradesh, which illustrate the utility value of traditional ecological knowledge in sustainable natural resource management. Both eco-cultural landscapes are indeed very complex and highly evolved systems with high levels of economic and ecological efficiencies. The paper concludes that traditional ecological knowledge systems and institutions could serve as entry points into the sustainable utilization and management of natural resources. This could be achieved through the exploration of the cultural practices of the local people and integrating useful aspects into the modern natural resource management expertise. With rapidly depleting biodiversity in the developing tropic regions, there is a greater utilization today than ever before of the value of respecting the "Sacred" as a tool towards better conservation of natural resources.  相似文献   
946.
The variable source area (VSA) concept provides the underlying paradigm for managing phosphorus losses in runoff in the north‐eastern USA. This study sought to elucidate factors controlling runoff along two hillslopes with contrasting soils, including characterizing runoff generation mechanisms and hydrological connectivity. Runoff monitoring plots (2 m × 1 m) were established in various landscape positions. Footslope positions were characterized by the presence of a fragipan that contributed to seasonally perched water tables. In upslope positions without a fragipan, runoff was generated primarily via the infiltration‐excess (IE) mechanism (96% of events) and was largely disconnected from downslope runoff. Roughly 80% of total runoff originated from the north footslope landscape position via saturation‐excess (SE) (46% of events; 62% of runoff) and IE (54% of events; 38% of runoff) mechanisms. Runoff from the north hillslope was substantially greater than the south hillslope despite their proximity, and apparently was a function of the extent of fragipan representation. Results demonstrate the influence of subsurface soil properties (e.g. fragipan) on surface runoff generation in variable source area hydrology settings, which could be useful for improving the accuracy of existing runoff prediction tools. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   
947.
The mosaic structure of landscape of the central area of Shanghai Metropolis is studied by quantitative methods of landscape ecology based on Remote Sensing (RS) and Geographic Information System (GIS) in this pa-per. Firstly, landscapes are classified into eight categories: residential quarter, industrial quarter, road, other urban landscape, farmland, village and small town, on-building area, river and other water bodies (such as lake, etc.). Sec-ondly, a GIS is designed and set up based on the remote sensing data and field investigation, and a digital map of landscape mosaic is made. Then the indexes of diversity, dominance, fragmentation and isolation, and fractal dimen-sion of each type of landscape in different periods are calculated by using spatial analysis method of GIS. With refer-ence to the calculated results, a series of relative issues are discussed.  相似文献   
948.
Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ~60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ~4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l?1) than in the south basin (seasonal average: 2 µg l?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l?1) than in the south basin (seasonal average: 12 µg l?1). Total inorganic carbon was low (usually <0·8 mg l?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l?1) than in the south basin (average: 0·2 mg l?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
949.
At pressent, China has about 100 million ha of farmland and 1.1 billion inhabitants, of which, about 80% are still engaged in agriculture. In geographical distribution, primitive shifting cultivation was at first mainly scattered in small patches in Eastern Monsoon China, especially concentrated in the middle and lower reaches of the Huanghe (Yellow) River and the Changjiang (Yangtze) River. The ratio of agriculture to industry in production value changed from 7:3 in the early 1950s to 3:7 in the middle 1980s. Agricultural Regionalization is based upon agricultural development as well as physical regionalization in China. Seven first-level agricultural regions might be identified.  相似文献   
950.
Landscapes of the Nansha Islands may be divided into five types: tropical marine organism-breeding landscape of reef knoll like Zengmu Shoal, Wan’an Bank and so on; tropical marine organism-breeding landscape of atoll including all emerged reefs and most submerged reefs; tropical evergreen arbor-bush forest and phosphorous lime soil landscape of limesand Islets like Taiping Islet, Nanwei islet and so on; tropical shallow sea marine organism-breeding landscape of southern continental shelf; tropical oceanic and deep-sea marine organism landscape in middle and north parts of the Nansha Islands area. These five landscape types may be also summed up as two categories, one is tropical sea landscape including those in shallow and deep sea, the other is tropical coral reef landscape including those of reef knoll, atoll and limesand islet. This paper outlines the evolutional model of landscapes of the Nansha Islands. The distribution and evolution of landscape types are related with palaeogeography and modern environmental conditions. The former shallow sea of the Nansha islands was coastal zone in the Late Pleistocene epoch. Deep sea is evolved from shallow sea due to long and slow subsidence of crust. Modern coral reefs develop on old reef top of the Late pleistocene epoch or on baserock of continental shelf in the Holocene due to the rise of sea level in postglacial. Limesand islet is in the peak of developmental stage.  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