全文获取类型
收费全文 | 255篇 |
免费 | 89篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 101篇 |
大气科学 | 3篇 |
地球物理 | 121篇 |
地质学 | 18篇 |
海洋学 | 11篇 |
天文学 | 4篇 |
综合类 | 82篇 |
自然地理 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 19篇 |
2011年 | 16篇 |
2010年 | 15篇 |
2009年 | 30篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1986年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有356条查询结果,搜索用时 46 毫秒
91.
Alla Skaskevych Jejung Lee Hahn Chul Jung John Bolten John L. David Frederick S. Policelli Ibrahim B. Goni Guillaume Favreau Soma San Charles M. Ichoku 《水文研究》2020,34(4):941-955
The present study is to explore the feasibility of GRACE-based estimation of a groundwater storage change in a data-poor region using a case study of the Ngadda catchment in the Lake Chad Basin. Although the Ngadda catchment has only one set of in situ time series data of groundwater from 2006 to 2009 and a limited number of groundwater measurements in 2005 and 2009, GRACE-based groundwater storage change can be evaluated against the in situ groundwater measurements combined with specific yield data. The cross-correlation analysis in the Ngadda catchment shows that maximum rainfall reached in July and August, whereas both the maximum total water storage anomaly and the maximum groundwater storage anomaly occurred 2months later. Whereas the mean annual amplitude of total water storage anomaly is about 17cm from both the average total water storage anomaly from three mascon products and the one from three spherical harmonic products, the mean annual amplitude of soil moisture storage anomaly is substantially varied from 5.58cm for CLM to about 14cm for NOAH and Mosaic. The goodness-of-fit tests show that CLM soil moisture produces the closest estimation of groundwater storage anomaly to the in situ groundwater measurements. The present study shows that GRACE-based estimation for groundwater storage anomaly can be a cost-effective and alternative tool to observe how groundwater changes in a basin scale under the limitation of modelling and in situ data availability. 相似文献
92.
多通道奇异谱组合滤波反演水储量变化 总被引:1,自引:0,他引:1
针对GRACE时变重力场球谐系数的高阶次项中含有的较高噪声会造成反潢结果产生误差的问题,该文采用多通道奇异谱分析和高斯滤波相结合的方案来滤除GRACE数据中的噪声,并与普遍使用的去相关滤波和高斯滤波相结合的方案进行了对比验证。首先利用这两种方法分别计算了2007年4、10月份的全球水储量变化,结果显示,这两种方法反演的结果基本相同,而多通道奇异谱分析与高斯滤波相组合的方法提高了信噪比,减弱了信号泄露误差,验证了该组合方案的可行性。然后又分别计算了亚马逊流域2004—2010年的水储量时间变化序列,并与GLDAS水文模型进行了对比验证,结果显示,这两种方法得到的水储量时间序列变化趋势基本相同,各自之间具有强相关性,进一步说明了该文方案在GRACE数据滤波中的可行性。 相似文献
93.
利用GRACE反演长江流域水储量变化 总被引:3,自引:0,他引:3
利用GRACE重力卫星2003年1月~2006年9月共计43个月的时变重力场数据,反演了长江流域水储量的变化.结果显示,基于GRACE数据的反演结果和CPC模型符合得相当好;若考虑低阶项的影响,对GRACE的反演结果有很明显的改进. 相似文献
94.
本文在法方程层面融合GOCE卫星的Vxx、Vyy、Vzz和Vxz重力梯度分量观测数据和GRACE卫星观测数据,采用直接法解算了220阶次的重力场模型Tongji-GOGR2019S.首先利用ⅡR带通滤波器在5~41 mHz的重力梯度带宽范围内对约24个月的GOCE重力梯度观测方程进行无相移滤波处理,并组成解算220阶次重力场模型的法方程,各梯度分量根据相对于参考模型统计精度进行定权;然后与13.5 a GRACE数据建立的180阶次Tongji-Grace02s重力场模型的法方程进行叠加,解算了220阶次的无约束纯卫星重力场模型Tongji-GOGR2019S.利用EIGEN-6C4重力场模型、GNSS/水准数据、DTU15重力异常数据以及欧洲区域似大地水准面模型EGG2015等数据对Tongji-GOGR2019S模型精度进行全面的检核评定,结果表明:引入GOCE卫星梯度数据后,高于72阶的位系数精度优于Tongji-Grace02s模型,Tongji-GOGR2019S模型的整体精度接近同阶次的DIR-R6等GOCE卫星第6代模型. 相似文献
95.
96.
Precise GRACE baseline determination using GPS 总被引:13,自引:1,他引:13
Precision relative navigation is an essential aspect of spacecraft formation flying missions, both from an operational and a scientific point of view. When using GPS as a relative distance sensor, dual-frequency receivers are required for high accuracy at large inter-satellite separations. This allows for a correction of the relative ionospheric path delay and enables double difference integer ambiguity resolution. Although kinematic relative positioning techniques demonstrate promising results for hardware-in-the-loop simulations, they were found to lack an adequate robustness in real-world applications. To overcome this limitation, an extended Kalman Filter modeling the relative spacecraft dynamics has been developed. The filter processes single difference GPS pseudorange and carrier phase observations to estimate the relative position and velocity along with empirical accelerations and carrier phase ambiguities. In parallel, double difference carrier phase ambiguities are resolved on both frequencies using the least square ambiguity decorrelation adjustment (LAMBDA) method in order to fully exploit the inherent measurement accuracy. The combination of reduced dynamic filtering with the LAMBDA method results in smooth relative position estimates as well as fast and reliable ambiguity resolution. The proposed method has been validated with data from the gravity recovery and climate experiment (GRACE) mission. For an 11-day data arc, the resulting solution matches the GRACE K-Band Ranging System measurements with an accuracy of 1 mm, whereby 83% of the double difference ambiguities are resolved. 相似文献
97.
98.
A technique for the analysis of low–low intersatellite range-rate data in a gravity mapping mission is explored. The technique
is based on standard tracking data analysis for orbit determination but uses a spherical coordinate representation of the
12 epoch state parameters describing the baseline between the two satellites. This representation of the state parameters
is exploited to allow the intersatellite range-rate analysis to benefit from information provided by other tracking data types
without large simultaneous multiple-data-type solutions. The technique appears especially valuable for estimating gravity
from short arcs (e.g. less than 15 minutes) of data. Gravity recovery simulations which use short arcs are compared with those
using arcs a day in length. For a high-inclination orbit, the short-arc analysis recovers low-order gravity coefficients remarkably
well, although higher-order terms, especially sectorial terms, are less accurate. Simulations suggest that either long or
short arcs of the Gravity Recovery and Climate Experiment (GRACE) data are likely to improve parts of the geopotential spectrum
by orders of magnitude.
Received: 26 June 2001 / Accepted: 21 January 2002 相似文献
99.
�й���½������GRACE���������仯�о� 总被引:3,自引:2,他引:1
??????????GRACE????????????仯??????????? ??GRACE??????λ??????????????????????????????????????????????????й?????????????????仯???????????800 km??????????ó????????????仯????? 相似文献
100.
利用22个月的GRACE时变重力场,反演了三峡水库补给水系的水储量变化,并按月给出了数值结果.与水文学同化模型(CPC)的两组比较说明基于GRACE重力的反演结果是合理的.当高斯平均半径为1000 km时,该区总水储量变化的峰谷差为14 cm,其年变化振幅为58 cm,相位为-408天,与CPC模型合成重力数据的反演结果进行比较,其总水储量变化均方差为13 cm,年变化振幅相差01 cm,相位相差10天.为进一步检验GRACE能否监测该区真实水储量变化,还将其反演结果与CPC模型的真实平均结果进行比较,结果发现总体均方差为21 cm,年变化振幅相差17 cm,相位相差93天.因此,第一种比较过高地估计了GRACE监测该区水储量变化的能力,第二种比较则较真实地反映了实际情况,尽管反演结果与水文学的结果差别较大,但仍然显示GRACE能监测该区每月的水储量变化. 相似文献