全文获取类型
收费全文 | 21675篇 |
免费 | 2201篇 |
国内免费 | 2622篇 |
专业分类
测绘学 | 8497篇 |
大气科学 | 2557篇 |
地球物理 | 2972篇 |
地质学 | 4645篇 |
海洋学 | 2040篇 |
天文学 | 1267篇 |
综合类 | 2036篇 |
自然地理 | 2484篇 |
出版年
2024年 | 116篇 |
2023年 | 276篇 |
2022年 | 767篇 |
2021年 | 971篇 |
2020年 | 979篇 |
2019年 | 1027篇 |
2018年 | 740篇 |
2017年 | 1140篇 |
2016年 | 1047篇 |
2015年 | 1111篇 |
2014年 | 1201篇 |
2013年 | 1525篇 |
2012年 | 1294篇 |
2011年 | 1227篇 |
2010年 | 995篇 |
2009年 | 1246篇 |
2008年 | 1270篇 |
2007年 | 1415篇 |
2006年 | 1260篇 |
2005年 | 1079篇 |
2004年 | 1019篇 |
2003年 | 795篇 |
2002年 | 677篇 |
2001年 | 575篇 |
2000年 | 454篇 |
1999年 | 386篇 |
1998年 | 366篇 |
1997年 | 288篇 |
1996年 | 229篇 |
1995年 | 197篇 |
1994年 | 169篇 |
1993年 | 142篇 |
1992年 | 116篇 |
1991年 | 91篇 |
1990年 | 60篇 |
1989年 | 53篇 |
1988年 | 38篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 11篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Annett Bartsch Martin Gude Christer Jonasson & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):171-178
Sediment transport processes in the Kärkevagge are investigated concerning their spatial and temporal characteristics due to long–term monitoring. Within this study remote sensing techniques and GIS modelling in connection with geomorphic mapping are applied for identification and characterization of geomorphic process units. Relationships between geomorphometric parameters and slope processes like solifluction, talus creep and rockfall have been analysed. Multitemporal Landsat–TM5 scenes are used as source for landcover characteristics (Normalized Difference Vegetation Index) after preprocessing involving orthorectification and topographic normalization in order to remove possible terrain–induced effects. Additionally, a digital elevation model with a resolution of 20 m for the Kärkevagge catchment is developed and parameters like slope gradient, slope aspect and profile curvature are extracted as input for the analysis of the sediment transport system. The combination of landcover information, geomorphometrical and topological features allows the definition of areas for single process activities. They show specific sediment displacement characteristics depending on material conditions, topological and geometrical features. Geomorphic process units, which show a homogenous composition, are extracted from these available layers. 相似文献
152.
The Global Rainforest Mapping (GRFM) project was initiated in 1995 and, through a dedicated data acquisition policy by the National Space Development Agency of Japan (NASDA), data acquisitions could be completed within a 1.5-year period, resulting in a spatially and temporally homogeneous coverage to contain the entire Amazon Basin from the Atlantic to the Pacific; Central America up to the Yucatan Peninsular in Mexico; equatorial Africa from Madagascar and Kenya in the east to Sierra Leone in the west; and Southeast Asia, including Papua New Guinea. To some extent, GRFM project is an international endeavor led by NASDA, with the goal of producing spatially and temporally contiguous Synthetic Aperture Radar (SAR) data sets over the tropical belt on the Earth by use of the JERS-1 L-band SAR, through the generation of semi-continental, 100m resolution, image mosaics. The GRFM project relies on extensive collaboration with the National Aeronautics and Space Administration (NASA), the Joint Research Center of the European Commission (JRC) and the Japanese Ministry of International Trade and Industry (MITI) for data acquisition, processing, validation and product generation. A science program is underway in parallel with product generation. This involves the agencies mentioned above, as well as a large number of international organizations, universities and individuals to perform field activities and data analysis at different levels. 相似文献
153.
Poyang Lake is the largest freshwater lake in China. This paper conducted a digital and rapid investigation of the lake’s wetland vegetation biomass using Landsat ETM data acquired on April 16, 2000. First, utilizing the false color composite derived from the ETM data as one of the main references, the authors designed a reasonable sampling route for field measurement of the biomass, and carried it out on April 18-28, 2000. Then after both the sampling data and the ETM data were geometrically corrected to an equal-area projection of Albers, linear relationships among the sampling data and some transformed data derived from the ETM data and the ETM 4 were calculated. The results show that the sampling data is best relative to the band 4 data with a high correlation coefficient of 0.86, followed by the DVI and NDVI data with 0.83 and 0.80 respectively. Therefore, a linear regression model, which was based on the field data and band 4 data, was used to estimate the total biomass of entire Poyang Lake, and then the map of the biomass distribution was compiled. 相似文献
154.
GIS专题数据综合的研究 总被引:7,自引:0,他引:7
随着GIS技术在各种应用领域的推广使用,各领域的专业数据与G1S的空间数据相结合,形成描述特定地理现象的各种专题数据。与GIS空间数据一样,专题数据的应用也由微观的、较为详细地描述小区域地理现象特征,转向宏观的、较为概略地描述较大范围地理现象特征,这是专题数据综合的主要任务。该文在讨论GIS专题数据类型及特征的基础上,着重分析了专题数据综合的基本类型,并提出了专题数据综合的概念模型,为GIS专题数据自动综合的实施提供理论依据和实施方案。 相似文献
155.
156.
157.
Chih Hoong Sin 《Area》2003,35(3):305-312
The intersubjective dialogic exercise through which identities and knowledge are constructed exists in a dialectic relation with the 'place' of the interview. The in situ nature of interviewing should not be overlooked. Two case studies of interviews conducted with older people in Britain about their social network and support are used to illuminate two aspects of the socio-spatial construction of interview data. First, interview sites can yield important information about the way participants construct their individual and social identities. Second, such identities can influence interviewer–interviewee dynamics. 相似文献
158.
介绍了面向对象数据模型的基本概念,重点讨论了面向对象数据模型在地理信息系统中的应用及具体实现途径。 相似文献
159.
介绍了两台计算机之间通过电话线和Modem互联通讯的原理及应用,详细论述了在这种组网方式下如何通过SLIP协议(或PPP协议)实现SCO UNIX主机和Windows主机、SCO UNIX主机相连来实现文件的远程传输,并提出解决方案,给出实例。 相似文献
160.