全文获取类型
收费全文 | 5738篇 |
免费 | 907篇 |
国内免费 | 786篇 |
专业分类
测绘学 | 1767篇 |
大气科学 | 794篇 |
地球物理 | 1115篇 |
地质学 | 1268篇 |
海洋学 | 742篇 |
天文学 | 307篇 |
综合类 | 854篇 |
自然地理 | 584篇 |
出版年
2024年 | 21篇 |
2023年 | 63篇 |
2022年 | 167篇 |
2021年 | 224篇 |
2020年 | 241篇 |
2019年 | 283篇 |
2018年 | 180篇 |
2017年 | 308篇 |
2016年 | 291篇 |
2015年 | 337篇 |
2014年 | 296篇 |
2013年 | 417篇 |
2012年 | 388篇 |
2011年 | 326篇 |
2010年 | 224篇 |
2009年 | 300篇 |
2008年 | 348篇 |
2007年 | 385篇 |
2006年 | 329篇 |
2005年 | 293篇 |
2004年 | 281篇 |
2003年 | 252篇 |
2002年 | 158篇 |
2001年 | 185篇 |
2000年 | 149篇 |
1999年 | 115篇 |
1998年 | 134篇 |
1997年 | 119篇 |
1996年 | 105篇 |
1995年 | 87篇 |
1994年 | 102篇 |
1993年 | 73篇 |
1992年 | 53篇 |
1991年 | 38篇 |
1990年 | 34篇 |
1989年 | 42篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1954年 | 6篇 |
排序方式: 共有7431条查询结果,搜索用时 15 毫秒
101.
102.
Comparison of methods to model the gravitational gradients from topographic data bases 总被引:7,自引:0,他引:7
A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1" elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical–vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods. 相似文献
103.
Spherical Slepian functions and the polar gap in geodesy 总被引:4,自引:0,他引:4
The estimation of potential fields such as the gravitational or magnetic potential at the surface of a spherical planet from noisy observations taken at an altitude over an incomplete portion of the globe is a classic example of an ill-posed inverse problem. We show that this potential-field estimation problem has deep-seated connections to Slepian's spatiospectral localization problem which seeks bandlimited spherical functions whose energy is optimally concentrated in some closed portion of the unit sphere. This allows us to formulate an alternative solution to the traditional damped least-squares spherical harmonic approach in geodesy, whereby the source field is now expanded in a truncated Slepian function basis set. We discuss the relative performance of both methods with regard to standard statistical measures such as bias, variance and mean squared error, and pay special attention to the algorithmic efficiency of computing the Slepian functions on the region complementary to the axisymmetric polar gap characteristic of satellite surveys. The ease, speed, and accuracy of our method make the use of spherical Slepian functions in earth and planetary geodesy practical. 相似文献
104.
Brian Emmerson James Jackson Dan McKenzie Keith Priestley 《Geophysical Journal International》2006,167(3):1233-1272
105.
106.
107.
概述了深空测控网的基本技术要求,总结了我国卫星测控网和国内现有射电观测设施的技术、组成和分布,分析和论述了将我国现有的测控设施建设成深空测控网的具体方案。 相似文献
108.
CHENChujiang LIDeren ZHUQing 《地球空间信息科学学报》2005,8(1):33-38
This paper presents the studies of the refining of IKONOS-2 RPC, the transform of the datum, the mode of the control point distribution and the method of IKONOS stereo triangulation, so that IKONOS imagery can be used to collect the precise geospatial data and produce the large scale map. The transform between the IKONOS-2 image space and the national coordinate system based on the RPC have been developed, and the results of block adjustment with various control schemes in a practical project near Himalayas have been examined and analysed. The encouraging results of high positioning accuracy have been obtained. 相似文献
109.
内蒙古中部重、磁场特征与地壳密度结构 总被引:2,自引:2,他引:2
中亚造山带中的古生代——中生代花岗岩普遍具有正εNd值,在世界上是十分独特的。美国西部加利福尼亚中生代-新生代花岗岩同样具有正εNd值,并且其地壳的速度分布特征与内蒙古中部十分相似。本文通过与美国加利福尼亚的地球物理研究成果进行对比,来研究内蒙古中部的地壳密度结构,特别是下地壳的组成,试图探讨产生正£。值花岗岩的深部地质原因。研究结果表明,在大兴安岭-内蒙古造山带下地壳中可能存在与美国加里福尼亚类似的洋壳物质。此外,还对重、磁异常进行了处理,以确定蛇绿岩带的延展情况。由于在西拉木伦河附近存在切割至莫霍面的深断裂,结合地表出现的蛇绿岩带,故提出温都尔庙-西拉木伦河一线可能是内蒙古中部最重要的地质构造界线。 相似文献
110.
刘基余 《武汉大学学报(信息科学版)》2005,30(10):870-872,880
依据地月激光测距的成功实践和对卫星激光定轨的基础研究,提出了用地面对嫦娥卫星作激光测距的方法,高精度地测定嫦娥卫星绕月飞行时的实时在轨位置,论述了多站激光定轨和单站激光定轨的解算数模。 相似文献