全文获取类型
收费全文 | 669篇 |
免费 | 61篇 |
国内免费 | 59篇 |
专业分类
测绘学 | 283篇 |
大气科学 | 66篇 |
地球物理 | 83篇 |
地质学 | 106篇 |
海洋学 | 31篇 |
天文学 | 8篇 |
综合类 | 97篇 |
自然地理 | 115篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 32篇 |
2021年 | 34篇 |
2020年 | 36篇 |
2019年 | 49篇 |
2018年 | 32篇 |
2017年 | 42篇 |
2016年 | 48篇 |
2015年 | 56篇 |
2014年 | 56篇 |
2013年 | 56篇 |
2012年 | 33篇 |
2011年 | 38篇 |
2010年 | 32篇 |
2009年 | 27篇 |
2008年 | 22篇 |
2007年 | 28篇 |
2006年 | 26篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
排序方式: 共有789条查询结果,搜索用时 15 毫秒
1.
2.
Efficient GOCE satellite gravity field recovery based on least-squares using QR decomposition 总被引:3,自引:0,他引:3
We develop and apply an efficient strategy for Earth gravity field recovery from satellite gravity gradiometry data. Our approach
is based upon the Paige-Saunders iterative least-squares method using QR decomposition (LSQR). We modify the original algorithm
for space-geodetic applications: firstly, we investigate how convergence can be accelerated by means of both subspace and
block-diagonal preconditioning. The efficiency of the latter dominates if the design matrix exhibits block-dominant structure.
Secondly, we address Tikhonov-Phillips regularization in general. Thirdly, we demonstrate an effective implementation of the
algorithm in a high-performance computing environment. In this context, an important issue is to avoid the twofold computation
of the design matrix in each iteration. The computational platform is a 64-processor shared-memory supercomputer. The runtime
results prove the successful parallelization of the LSQR solver. The numerical examples are chosen in view of the forthcoming
satellite mission GOCE (Gravity field and steady-state Ocean Circulation Explorer). The closed-loop scenario covers 1 month
of simulated data with 5 s sampling. We focus exclusively on the analysis of radial components of satellite accelerations
and gravity gradients. Our extensions to the basic algorithm enable the method to be competitive with well-established inversion
strategies in satellite geodesy, such as conjugate gradient methods or the brute-force approach. In its current development
stage, the LSQR method appears ready to deal with real-data applications. 相似文献
3.
协同虚拟环境是网络技术与虚拟现实技术相结合的产物,将单用户虚拟环境扩展为多用户的网络化虚拟环境,实现群组协同工作.目前,协同虚拟环境系统已经在科学可视化、协同设计、战争模拟等很多领域得到了广泛应用.在单用户虚拟环境中导航与多用户的协同虚拟环境中导航是完全不同的,文中论述了协同虚拟环境导航的特点以及导航与视点的关系,探讨了常用的协同虚拟环境三种视点视图界面的导航及其效果,并进行了相关实验测试. 相似文献
4.
5.
生态地理建模中的多尺度问题 总被引:29,自引:0,他引:29
本文在分析生态地理建模内涵的基础上,讨论了生态地理建模中的尺度转换问题、跨尺度相互作用问题、空间尺度与时间尺度的关联问题和多尺度数据处理问题.由于生态地理问题的非线性、生态环境的异质性和随机事件,简单的线性尺度转换方法远不能满足生态地理建模的要求.为了从根本上解决生态地理建模中的时空尺度问题,除需要运用微分几何学和等级理论等经典方法外,还需要引入格点生成法和网格计算等现代理论和技术手段. 相似文献
6.
对空间决策支持系统和计算机系统协同工作环境进行系统分析和总结,概括了较为完整的协同空间决策概念,提出了协同空间决策的空间问题协同分析、方案生成与可视化、方案分析、方案表决等基本过程。在此基础上,作者详细分析了协同空间决策的复杂性、交互可视化、多用户参与、方案探索性分析、多层次协同等基本特征。 相似文献
7.
提出了在异构系统实现负载平衡的区域分解算法和实现负载平衡的计算方法,利用它的负反馈性质解决了异构系统处理机计算速度测量误差造成的负载测量不准问题,并对处理机速度变化,速度测量误差、处理机数量、网格点计算量的分布等因素的影响进行了计算,结果表明本方法具有很强的平衡负载能力和较强的适应性;根据计算结果提出了解决模式网格点计算量不易测量问题的解决方案,并用扩散方程和模拟物理过程进行试验,试验表明这种方法是可行的,平衡负载的效果十分显著。 相似文献
8.
9.
Web Use in Geographical and Environmental Education: An International Survey at the Primary and Secondary Level 总被引:2,自引:0,他引:2
This article aims to study Web use and Web-based co-operation and collaboration in geographical and environmental education
at the primary and secondary level around the world. Recent trends and future opportunities and challenges are taken into
account. The theoretical part of the study considers Web use and different forms of Web-based co-operation. Web use and co-operation
in education are classified as co-operative learning, collaborative learning or communal learning. Web use in geographical
and environmental education is noted to be growing in significance. Web-based co-operation at any level of intensity is associated
with many opportunities and challenges. The empirical part of this study involves a survey of geographical and environmental
education researchers in various countries about their views of Web use in education. The results of this survey indicate
that the Web in general finds minimal use in geographical and environmental education. As access to the Web is limited and
only some pupils can use it, co-operation, particularly collaborative learning on the Web, is still rare in geographical and
environmental education. The most often used application is e-mail. Researchers recognise the potential of the Web to enhance
local, national and international co-operation, and to facilitate a better understanding of geographical and environmental
issues at the grass-root level. Web-based learning can also help to increase and deepen the pupils' cultural understanding.
Before that, however, problems in access, costs and teacher training must be solved.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
自适应空间信息移动服务 总被引:4,自引:0,他引:4
空间信息移动服务系统是空间信息系统继由传统PC计算环境向有线Web分布式计算环境扩展后,向移动计算环境的新发展。文中在分析移动计算环境概念和特点的基础上,讨论了空间信息移动服务的若干特点及关键技术,研究了自适应空间信息移动服务方案。 相似文献