全文获取类型
收费全文 | 15912篇 |
免费 | 1322篇 |
国内免费 | 1655篇 |
专业分类
测绘学 | 7014篇 |
大气科学 | 941篇 |
地球物理 | 1767篇 |
地质学 | 3985篇 |
海洋学 | 1327篇 |
天文学 | 62篇 |
综合类 | 1709篇 |
自然地理 | 2084篇 |
出版年
2024年 | 53篇 |
2023年 | 154篇 |
2022年 | 535篇 |
2021年 | 664篇 |
2020年 | 651篇 |
2019年 | 666篇 |
2018年 | 451篇 |
2017年 | 791篇 |
2016年 | 742篇 |
2015年 | 797篇 |
2014年 | 847篇 |
2013年 | 1138篇 |
2012年 | 947篇 |
2011年 | 982篇 |
2010年 | 777篇 |
2009年 | 823篇 |
2008年 | 874篇 |
2007年 | 950篇 |
2006年 | 872篇 |
2005年 | 775篇 |
2004年 | 757篇 |
2003年 | 634篇 |
2002年 | 533篇 |
2001年 | 461篇 |
2000年 | 357篇 |
1999年 | 275篇 |
1998年 | 313篇 |
1997年 | 251篇 |
1996年 | 186篇 |
1995年 | 110篇 |
1994年 | 109篇 |
1993年 | 100篇 |
1992年 | 89篇 |
1991年 | 52篇 |
1990年 | 53篇 |
1989年 | 32篇 |
1988年 | 27篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Determination of subcatchment and watershed boundaries in a complex and highly urbanized landscape
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Urban development significantly alters the landscape by introducing widespread impervious surfaces, which quickly convey surface run‐off to streams via stormwater sewer networks, resulting in “flashy” hydrological responses. Here, we present the inadequacies of using raster‐based digital elevation models and flow‐direction algorithms to delineate large and highly urbanized watersheds and propose an alternative approach that accounts for the influence of anthropogenically modified land cover. We use a semi‐automated approach that incorporates conventional drainage networks into overland flow paths and define the maximal run‐off contributing area. In this approach, stormwater pipes are clustered according to their slope attributes, which define flow direction. Land areas drained by each cluster and contributing (or exporting) flow to a topographically delineated catchment were determined. These land masses were subsequently added or removed from the catchment, modifying both the shape and the size. Our results in a highly urbanized Toronto, Canada, area watershed indicate a moderate net increase in the directly connected watershed area by 3% relative to a topographically forced method; however, differences across three smaller scale subcatchments are greater. Compared to topographic delineation, the directly connected watershed areas of both the upper and middle subcatchments decrease by 5% and 8%, respectively, whereas the lower subcatchment area increases by 15%. This is directly related to subsurface storm sewer pipes that cross topographic boundaries. When directly connected subcatchment area is plotted against total streamflow and flashiness indices using this method, the coefficients of variation are greater (0.93 to 0.97) compared to the use of digital elevation model‐derived subcatchment areas (0.78 to 0.85). The accurate identification of watershed and subcatchment boundaries should incorporate ancillary data such as stormwater sewer networks and retention basin drainage areas to reduce water budget errors in urban systems. 相似文献
2.
景观生态分类与制图浅议 总被引:12,自引:0,他引:12
程维明 《地球信息科学学报》2002,4(2):61-65
本文在查阅分析大量文献和前人研究的基础上 ,对目前景观生态分类和景观制图作了详细的对比分析 ,认为景观分类需要结合实际区域现状 ,采用逐级分类的方法 ;同时利用 ETM遥感影像为数据源 ,以天山北麓为示范区.研制其土地利用土地覆盖变化的景观类型图。 相似文献
3.
试论新世纪地理信息科学的发展 总被引:1,自引:0,他引:1
本文重点分析了当前国内外地理信息科学的形成与发展趋势和地理信息科学不断发展的历程 ,提出近期发展的前沿 ,以及当前地理信息产业化面临的一些重要问题。最后提出对地理信息科学发展的意见。 相似文献
4.
利用“地震预报计算机专家系统”的思想对大同 -阳高 Ms6 .1地震前每一前兆异常事件进行综合评估 ,以每一异常的最可能发震时间来计算发震概率 ,利用地震前兆综合加权信息熵研究了系统熵值与地震的关系。对华北地区的地震前兆综合加权信息熵研究表明 ,在大同 -阳高 Ms6 .1地震前 ,信息熵出现了明显的减熵有序变化 相似文献
5.
中国1∶100万景观生态制图设计 总被引:5,自引:0,他引:5
中国1∶100万景观生态图系借鉴国内外传统景观制图方法和制图规范,在遥感、地理信息系统先进技术的支持下,设计研制其制图方法、制图内容、样图和技术流程,同时提出初步的景观分类系统,为今后编制中国1∶100万景观生态图奠定基础。 相似文献
6.
7.
Richard J. Pike 《The Professional geographer》1987,39(2):131-145
Extraterrestrial geography has become a reality, as we move from Earth's moon to the planets. A broad-scale regional physiography is being established on twenty planets and satellites through remote sensing techniques. Spacecraft images yield most of the information on Solar System landscapes. Topographic measurements are extracted by monoscopic image-processing, stereophotogrammetry, and radar analysis. Invisible parts of the spectrum furnish non-topographic data. 相似文献
8.
罗卫敏 《成都信息工程学院学报》2004,19(2):209-213
针对信息系统安全的考虑,介绍在PowerBuilder环境中对用户权限的具体控制. 相似文献
9.
Qian Huaisui 《中国地理科学(英文版)》1997,8(3):204-211
The crop estimates by remote sensing, developing quickly in recent decades, is a up-to-date technique. Regionalization for
large area crop estimates by remote sensing, a special applied regionalization, is the foundation of crop estimates in a large
area by remote sensing. According to the actual demands of wheat yield estimation by remote sensing and wheat agroclimatic
demarcation of China, this paper first puts forward some principles upheld in this regionalization and analyses its main bases.
Secondly, it works out the classificatory schemes about the optimum temporal for estimating wheat yield by remote sensing,
information sources of space remote sensing and landuse structure in China. Finally, According to the regionalization indices,
this study divides the wheat plantable region of China into 14 regions of crop yield estimates and 31 subregions of crop yield
estimates. 相似文献
10.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献