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61.
Doñana National Park is an area of approximately 500 km2 located on the SW coast of Spain that shows one of the greatest geoid gradients on the entire Iberian Peninsula, due to its peculiar tectonic characteristics. So, it is necessary to elaborate an accurate geoid model that can be used with GPS for precise surveying, since the existing ones are insufficient, due to their poor resolution and their limited adaptation to a small area with such a strong gradient. The least squares prediction method was tested in order to obtain the undulation from GPS/orthometric points. The results obtained were unsatisfactory because of the strong geoid gradient. In order to improve accuracy the remove-restore technique was used. Global geopotential model EIGEN-CG01C and a Digital Elevation Model (DEM) with a 25 × 25 m resolution and an accuracy better than 3 m were used. Thus, the final geometrical geoid obtained reaches the precision required by other disciplines (3 cm in any point within the Park). Particularly, the geoid model has allowed for the acquisition of a precision DEM that is essential to formulate a hydrodynamic model for the Doñana marsh functions. 相似文献
62.
Contributions of terrestrial and GRACE data to the study of the secular geoid changes in North America 总被引:1,自引:0,他引:1
This paper tests and discusses different statistical methods for modelling secular rates of change of the geoid in North America. In particular, we use the method of principal component/empirical orthogonal functions (PC/EOF) analysis to model the geoid rates from Gravity Recovery and Climate Experiment (GRACE) satellite data. As demonstrated, the PC/EOF analysis is useful for studying the contributions from different signals (mainly residual hydrology signals and leakage effects) to the GRACE-derived geoid rates. The PC/EOF analysis leads to smaller geoid rates compared to the conventional least-squares fitting of a trend and annual and semi-annual cycles to the time series of the spherical harmonic coefficients. This is because we filter out particular spatiotemporal modes of the regional geoid changes.We apply the method of least-squares collocation with parameters to combine terrestrial data (GPS vertical velocities from the Canadian Base Network and terrestrial gravity rates from the Canadian Gravity Standardization Net) with the GRACE-derived vertical motion to obtain again the geoid rates. The combined model has a peak geoid rate of 1.4 mm/year in the southeastern area of Hudson Bay contrary to the GRACE-derived geoid rates that show a large peak of 1.6–1.7 mm/year west of Hudson Bay. We demonstrate that the terrestrial data, which have a longer time span than the GRACE data, are important for constraining the GRACE-derived secular signal in the areas that are well sampled by the data. 相似文献
63.
64.
利用FFT技术计算大地水准面高若干问题研究 总被引:5,自引:1,他引:4
本文首先从普通二维 FFT算法的基本定义和要求出发 ,深入分析和比较了大地水准面二维平面和二维球面 FFT算法的特点和差异 ,找出了影响二维球面 FFT计算精度的主要误差源 ,并给出了二维球面 FFT计算公式的改进形式。在此基础上 ,本文详细分析讨论了参考场选取、积分球冠半径确定以及核函数改化对大地水准面计算结果的作用和影响。最后 ,本文利用全国 5′× 5′实测重力异常对我国海陆大地水准面进行了试算 ,并将计算结果分别同陆上GPS水准和海上卫星测高观测值作了比较。 相似文献
65.
The atmospheric geoid effects in Stokes' formula 总被引:2,自引:0,他引:2
66.
The reduction of aliasing in gravity anomalies and geoid heights using digital terrain data 总被引:8,自引:0,他引:8
Observations of gravity can be aliased by virtue of the logistics involved in collecting these data in the field. For instance, gravity measurements are often made in more accessible lowland areas where there are roads and tracks, thus omitting areas of higher relief in between. The gravimetric determination of the geoid requires mean terrain-corrected free-air anomalies; however, anomalies based only on the observations in lowland regions are not necessarily representative of the true mean value over the topography. A five-stage approach is taken that uses a digital elevation model, which provides a more accurate representation of the topography than the gravity observation elevations, to reduce the unrepresentative sampling in the gravity observations. When using this approach with the Australian digital elevation model, the terrain-corrected free-air anomalies generated from the Australian gravity data base change by between 77.075 and −84.335 mgal (−0.193 mgal mean and 2.687 mgal standard deviation). Subsequent gravimetric geoid computations are used to illustrate the effect of aliasing in the Australian gravity data upon the geoid. The difference between 'aliased' and 'non-aliased' gravimetric geoid solutions varies by between 0.732 and −1.816 m (−0.058 m mean and 0.122 m standard deviation). Based on these conceptual arguments and numerical results, it is recommended that supplementary digital elevation information be included during the estimation of mean gravity anomalies prior to the computation of a gravimetric geoid model. 相似文献
67.
用神经网络方法确定测区似大地水准面 总被引:3,自引:0,他引:3
本文提出一种用神经网络确定测区似大地水准面的方法,并给出了相应的神经网络结构和算法。研究了一个测区中用该方法确定的似大地水准面的精度,结果表明用该方法确定的似大地水准面的精度为厘米级,并与二次多项式曲面拟合似大地水准面的方法作了比较,神经网络方法的精度较优。 相似文献
68.
有限元法逼近局域大地水准面的数学模型 总被引:2,自引:0,他引:2
顾及到大地水准面的物理特性,依据其在局部所应满足的数学物理方程,讨论了有限元法逼近局域大地水准面的数学思想,给出了相应的数学模型. 相似文献
69.
70.
A. B. Watts D. P. McKenzie B. E. Parsons M. Roufosse 《Geophysical Journal International》1985,83(1):263-298
Summary. Surface-ship and satellite derived data have been compiled in new free-air gravity anomaly, bathymetry and geoid anomaly maps of the Pacific Ocean basin and its margin. The maps are based on smoothed values of the gravity anomaly, bathymetry and geoid interpolated on to a 90 × 90 km grid. Each smoothed value was obtained by Gaussian filtering measurements along individual ship and subsatellite tracks. The resulting maps resolve features in the gravity, bathymetry and geoid with wavelengths that range from a few hundred to a few thousand kilometres. The smoothed values of bathymetry and geoid anomaly have been corrected for age. The resulting maps show the Pacific ocean basin is associated with a number of ENE–WSW-trending geoid anomaly highs with amplitudes of about ± 5 m and wavelengths of about 3000 km. The most prominent of these highs correlate with the Magellan seamounts–Marshall Gilbert Islands–Magellan rise and the Hess rise–Hawaiian ridge regions. The correlation between geoid anomaly and bathymetry cannot be explained by models of static compensation, but is consistent with a model in which the geoid anomaly and bathymetry are supported by some form of dynamic compensation. We suggest that the dynamic compensation, which characterizes oceanic lithosphere older than 80 Myr, is the result of mantle convection on scales that are smaller than the lithospheric plates themselves. 相似文献