全文获取类型
收费全文 | 17798篇 |
免费 | 3457篇 |
国内免费 | 4552篇 |
专业分类
测绘学 | 1435篇 |
大气科学 | 3347篇 |
地球物理 | 4481篇 |
地质学 | 9367篇 |
海洋学 | 2399篇 |
天文学 | 680篇 |
综合类 | 1859篇 |
自然地理 | 2239篇 |
出版年
2024年 | 107篇 |
2023年 | 347篇 |
2022年 | 1027篇 |
2021年 | 1180篇 |
2020年 | 969篇 |
2019年 | 1113篇 |
2018年 | 1215篇 |
2017年 | 1041篇 |
2016年 | 1135篇 |
2015年 | 1003篇 |
2014年 | 1162篇 |
2013年 | 1149篇 |
2012年 | 1149篇 |
2011年 | 1136篇 |
2010年 | 1115篇 |
2009年 | 1000篇 |
2008年 | 926篇 |
2007年 | 814篇 |
2006年 | 670篇 |
2005年 | 629篇 |
2004年 | 479篇 |
2003年 | 448篇 |
2002年 | 430篇 |
2001年 | 455篇 |
2000年 | 478篇 |
1999年 | 671篇 |
1998年 | 571篇 |
1997年 | 518篇 |
1996年 | 508篇 |
1995年 | 394篇 |
1994年 | 377篇 |
1993年 | 334篇 |
1992年 | 292篇 |
1991年 | 192篇 |
1990年 | 157篇 |
1989年 | 135篇 |
1988年 | 104篇 |
1987年 | 79篇 |
1986年 | 60篇 |
1985年 | 49篇 |
1984年 | 39篇 |
1983年 | 32篇 |
1982年 | 29篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1975年 | 5篇 |
1958年 | 11篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Many regions around the world require improved gravimetric data bases to support very accurate geoid modeling for the modernization
of height systems using GPS. We present a simple yet effective method to assess gravity data requirements, particularly the
necessary resolution, for a desired precision in geoid computation. The approach is based on simulating high-resolution gravimetry
using a topography-correlated model that is adjusted to be consistent with an existing network of gravity data. Analysis of
these adjusted, simulated data through Stokes’s integral indicates where existing gravity data must be supplemented by new
surveys in order to achieve an acceptable level of omission error in the geoid undulation. The simulated model can equally
be used to analyze commission error, as well as model error and data inconsistencies to a limited extent. The proposed method
is applied to South Korea and shows clearly where existing gravity data are too scarce for precise geoid computation. 相似文献
993.
月面形貌的3维可视化算法 总被引:1,自引:0,他引:1
基于大范围地形可视化算法研究的基础上,对平面geometry clipmaps算法进行改进,利用GPU的顶点着色器实现平面地形向球面地形的投影变换,并综合利用球面视域裁剪、球面视点控制等技术,使geometry clipmaps算法适用于球面海量地形数据的3维可视化;收集处理月球全球影像和形貌高程数据,对算法进行验证,实现月球表面形貌的实时动态3维可视化.试验表明:绘制算法可不受数据量大小的限制、绘制效率高、效果逼真,但存在两极变形较大的缺点.Abstract: Based on the study of visualization arithmetic of large area terrain, plane geometry clipmaps algorithm is improved. Projection transformation from plane landform to sphere landform was realized by using GPU vertex shader. In that improved algorithm, methods such as sphere vision field culling and sphere viewpoint control are used.That makes geometry clipmops algorithm more effective in 3D visualization of massive sphere terrain data. The whole moon image and DEM data are collected and disposed, which are used to verify the capability of that algorithm, realizing dynamic and real time 3D visualization of moon surface. The experiments show that the graphic algorithm isn't limited by data quantity, which is of high efficiency and reality simulation, but the two-pole distortion is serious. 相似文献
994.
995.
996.
997.
Qingmin Meng Chris Cieszewski Marguerite Madden 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):27-36
Large area forest inventory is important for understanding and managing forest resources and ecosystems. Remote sensing, the Global Positioning System (GPS), and geographic information systems (GIS) provide new opportunities for forest inventory. This paper develops a new systematic geostatistical approach for predicting forest parameters, using integrated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images, GPS, and GIS. Forest parameters, such as basal area, height, health conditions, biomass, or carbon, can be incorporated as a response variable, and the geostatistical approach can be used to predict parameter values for uninventoried points. Using basal area as the response and Landsat ETM+ images of pine stands in Georgia as auxiliary data, this approach includes univariate kriging (ordinary kriging and universal kriging) and multivariable kriging (co-kriging and regression kriging). The combination of bands 4, 3, and 2, as well as the combination of bands 5, 4, and 3, normalized difference vegetation index (NDVI), and principal components (PCs) were used in this study with co-kriging and regression kriging. Validation based on 200 randomly sampling points withheld field inventory was computed to evaluate the kriging performance and demonstrated that band combination 543 performed better than band combination 432, NDVI, and PCs. Regression kriging resulted in the smallest errors and the highest R-squared indicating the best geostatistical method for spatial predictions of pine basal area. 相似文献
998.
公交车搭乘是武汉市市民日常出行的主要手段之一。合理的公交搭乘方案能够减少市民出行在时间和精力方面的损耗,本文以武汉市道路网为基础,阐述了通过ArcGIS进行公交网络数据模型构建的过程,并利用VisualC++和Map Objects实现了公交简易查询系统的开发。 相似文献
999.
格网DEM地形模拟的形态保真度研究 总被引:3,自引:0,他引:3
分析了现有格网DEM地形模拟的失真现象,研究DEM地形模拟失真的根源.提出了DEM地形形态保真度的概念,探讨了建设高保真DEM必须解决的问题. 相似文献
1000.