全文获取类型
收费全文 | 40163篇 |
免费 | 7751篇 |
国内免费 | 8504篇 |
专业分类
测绘学 | 4509篇 |
大气科学 | 5017篇 |
地球物理 | 6870篇 |
地质学 | 22756篇 |
海洋学 | 5372篇 |
天文学 | 3442篇 |
综合类 | 2786篇 |
自然地理 | 5666篇 |
出版年
2024年 | 103篇 |
2023年 | 523篇 |
2022年 | 1455篇 |
2021年 | 1657篇 |
2020年 | 1596篇 |
2019年 | 1754篇 |
2018年 | 1373篇 |
2017年 | 1658篇 |
2016年 | 1637篇 |
2015年 | 1817篇 |
2014年 | 2390篇 |
2013年 | 2446篇 |
2012年 | 2513篇 |
2011年 | 2631篇 |
2010年 | 2206篇 |
2009年 | 2807篇 |
2008年 | 2785篇 |
2007年 | 2859篇 |
2006年 | 2781篇 |
2005年 | 2625篇 |
2004年 | 2286篇 |
2003年 | 2170篇 |
2002年 | 1809篇 |
2001年 | 1625篇 |
2000年 | 1595篇 |
1999年 | 1389篇 |
1998年 | 1200篇 |
1997年 | 881篇 |
1996年 | 700篇 |
1995年 | 608篇 |
1994年 | 592篇 |
1993年 | 486篇 |
1992年 | 344篇 |
1991年 | 307篇 |
1990年 | 198篇 |
1989年 | 159篇 |
1988年 | 142篇 |
1987年 | 81篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 18篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 589 毫秒
991.
Liming He Jing M. Chen Shaoliang Zhang Gustavo Gomez Yude Pan Kevin McCullough Richard Birdsey Jeffrey G. Masek 《International Journal of Applied Earth Observation and Geoinformation》2011
Forest disturbances such as harvesting, wildfire and insect infestation are critical ecosystem processes affecting the carbon cycle. Because carbon dynamics are related to time since disturbance, forest stand age that can be used as a surrogate for major clear-cut/fire disturbance information has recently been recognized as an important input to forest carbon cycle models for improving prediction accuracy. In this study, forest disturbances in the USA for the period of ∼1990–2000 were mapped using 400+ pairs of re-sampled Landsat TM/ETM scenes in 500m resolution, which were provided by the Landsat Ecosystem Disturbance Adaptive Processing System project. The detected disturbances were then separated into two five-year age groups, facilitated by Forest Inventory and Analysis (FIA) data, which was used to calculate the area of forest regeneration for each county in the USA. 相似文献
992.
Hani Abdallah Jean-Stéphane Bailly Nicolas Baghdadi Nicolas Lemarquand 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):833-844
Given that water resources are scarce and are strained by competing demands, it has become crucial to develop and improve techniques to observe the temporal and spatial variations in the inland water volume. Due to the lack of data and the heterogeneity of water level stations, remote sensing, and especially altimetry from space, appear as complementary techniques for water level monitoring. In addition to spatial resolution and sampling rates in space or time, one of the most relevant criteria for satellite altimetry on inland water is the accuracy of the elevation data. Here, the accuracy of ICESat LIDAR altimetry product is assessed over the Great Lakes in North America. The accuracy assessment method used in this paper emphasizes on autocorrelation in high temporal frequency ICESat measurements. It also considers uncertainties resulting from both in situ lake level reference data. A probabilistic upscaling process was developed. This process is based on several successive ICESat shots averaged in a spatial transect accounting for autocorrelation between successive shots. The method also applies pre-processing of the ICESat data with saturation correction of ICESat waveforms, spatial filtering to avoid measurement disturbance from the land–water transition effects on waveform saturation and data selection to avoid trends in water elevations across space. Initially this paper analyzes 237 collected ICESat transects, consistent with the available hydrometric ground stations for four of the Great Lakes. By adapting a geostatistical framework, a high frequency autocorrelation between successive shot elevation values was observed and then modeled for 45% of the 237 transects. The modeled autocorrelation was therefore used to estimate water elevations at the transect scale and the resulting uncertainty for the 117 transects without trend. This uncertainty was 8 times greater than the usual computed uncertainty, when no temporal correlation is taken into account. This temporal correlation, corresponding to approximately 11 consecutive ICESat shots, could be linked to low transmitted ICESat GLAS energy and to poor weather conditions. Assuming Gaussian uncertainties for both reference data and ICESat data upscaled at the transect scale, we derived GLAS deviations statistics by averaging the results at station and lake scales. An overall bias of −4.6 cm (underestimation) and an overall standard deviation of 11.6 cm were computed for all lakes. Results demonstrated the relevance of taking autocorrelation into account in satellite data uncertainty assesment. 相似文献
993.
994.
995.
996.
997.
测绘是卫星遥感应用的重要领域,纵观国内外测绘卫星事业,我国还与国际先进水平存在一定差距,整个卫星测绘产业体系有待发展和提高。资源三号卫星作为我国首颗民用立体测绘卫星对我国卫星测绘事业发展具有重大意义,国家测绘局编制的《测绘部门十二五航天规划(草案)》,详细论述了我国民用测绘卫星的发展规划。我国正处于测绘卫星及其应用发展的黄金机遇期,国家测绘局经多年研究开发,正在积极推动我国测绘卫星遥感事业的飞速发展,努力探索适合我国国情的自主研发道路,推动卫星测绘事业不断前进,为国民经济发展提供精确、及时、可靠的地理信息和测绘高新技术服务。 相似文献
998.
999.
1000.
本文在分析大地水准面精化的目的意义及其发展现状的前提下,阐述了确定(似)大地水准面的原理,并针对贵州山区重力资料缺乏的现实情况,探讨了确定和精化山区局部区域大地水准面的方法;尤其对在贵州山区局部区域范围运用CPS水准资料结合地球重力场模型EGM96,拟合区域大地水准面的方法进行了详细的分析和讨论.通过运用原理和方法对实... 相似文献