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排序方式: 共有153条查询结果,搜索用时 15 毫秒
51.
变量查询代数及最短路径分析 总被引:4,自引:1,他引:3
本文简单分析了满足GIS空间查询代数的一般要求,然后形式化地定义了一种适合于GIS究竟查询的变量查询代数。在此代数中,将谓词划分为3类:原子谓词、特征谓高速和空间谓词,以适应目标的空间运算描述;为此代数定义了七类形式的运算,其中的投影运算π、聚集选择σ^Σ、极限选择σ^m和分裂选择σ^s拓广了一般查询代数的查询空间,此查询代数的独特之处在于能完成的网络分析功能;最后给出最短路径查询的实验。 相似文献
52.
城市的空间格局与社会生活各个方面息息相关,若利用GIS卓越的技术能力,探索城市空间格局的结构性特征、要素关联,挖掘其中的空间关系或其他有意义的结构模式,将为城市经济发展、资源分配、交通规划等社会问题提供知识支撑。此外若将城市空间格局与GIS空间分析相融合,将有助于架起图形与文本之间的桥梁与纽带,提升GIS空间数据挖掘水平。本文总结了城市空间格局的要素体系,并利用RCC8模型和区间代数使之与GIS中的空间关系建立对应关联,实现了由城市规划文本生成城市空间格局意向图。丰富了城市空间格局的规律性、本质性知识,弥补了多种空间关系集成研究的不足,为图形和文本的关联性知识挖掘奠定了基础。 相似文献
53.
54.
刘云平 《南京气象学院学报》2011,(3):255-258
针对大规模多体系统动力学建模过程复杂及计算效率、精度不高的难题,在空间算子代数理论的基础上,通过旋量表达的有关力学量和运动量,将包含机构拓扑关系及运动、力递推关系的移位算子直接与Newton-Euler递推动力学计算相结合,实现了广义速度、广义加速度、广义力和广义质量沿着链正向或反向递推,避免了交叉运算和不必要的积分运算,得到了高效率、高精度的动力学建模方法.该方法形式简洁、物理意义明确,适于计算机编程和运算,具有重要的科学意义和工程应用价值,并通过算例验证了结果的正确性和有效性. 相似文献
55.
Liam M. Healy 《Celestial Mechanics and Dynamical Astronomy》2003,85(2):175-207
The Lie transfer map method may be applied to orbit propagation problems in celestial mechanics. This method, described in another paper, is a perturbation method applicable to Hamiltonian systems. In this paper, it is used to calculate orbits for zonal perturbations to the Kepler (two-body) problem, in both expansion in the eccentricity and closed form. In contrast with a normal form method like that of Deprit, the Lie transformations here are used to effect a propagation of phase space in time, and not to transform one Hamiltonian into another. 相似文献
56.
在油田开发方案设计阶段,基础地质资料尤其是钻井资料相对较少,因此对储层分布的认识具有较大的不确定性。沉积相建模为储层分布不确定性的定量表征提供了技术手段,但每种沉积相建模方法具有各自的适应性。以渤海P油田为例,分别应用布尔模拟和示性点过程模拟方法,以河道带和河道内砂体为描述对象建立了2种沉积相模型,定量表征2种储层分布模式,分析2种模拟结果的储层分布规律,指出以河道内砂体为描述对象的建模方法提供了该油田储层分布的最可能模式,而以河道带为描述对象的建模方法提供了储层分布的另一种可能模式,为油藏数值模拟方案设计和敏感性分析提供了地质依据。 相似文献
57.
Spatiotemporal data represent the real-world objects that move in geographic space over time. The enormous numbers of mobile sensors and location tracking devices continuously produce massive amounts of such data. This leads to the need for scalable spatiotemporal data management systems. Such systems shall be capable of representing spatiotemporal data in persistent storage and in memory. They shall also provide a range of query processing operators that may scale out in a cloud setting. Currently, very few researches have been conducted to meet this requirement. This paper proposes a Hadoop extension with a spatiotemporal algebra. The algebra consists of moving object types added as Hadoop native types, and operators on top of them. The Hadoop file system has been extended to support parameter passing for files that contain spatiotemporal data, and for operators that can be unary or binary. Both the types and operators are accessible for the MapReduce jobs. Such an extension allows users to write Hadoop programs that can perform spatiotemporal analysis. Certain queries may call more than one operator for different jobs and keep these operators running in parallel. This paper describes the design and implementation of this algebra, and evaluates it using a benchmark that is specific to moving object databases. 相似文献
58.
R. G. HEALEY 《International journal of geographical information science》2013,27(1):141-142
Cartographic modelling operations provide powerful tools for analysing and manipulating geographic data in the raster data model. This research extends these operations to the vector data model. It first discusses how the spatial scopes of analysis can be defined for point, line, and polygon features analogous to the raster cell. Then it introduces the local, focal, and zonal operations available for vector features, followed by providing a prototype syntax that might guide the implementation of these operations. Through example applications, this research also demonstrates the usefulness of these operations by comparing them with traditional vector spatial analysis. 相似文献
59.
60.
Two-point boundary value problems appear frequently in space trajectory design. A remarkable example is represented by the
Lambert’s problem, where the conic arc linking two fixed positions in space in a given time is to be characterized in the
frame of the two-body problem. Classical methods to numerically solve these problems rely on iterative procedures, which turn
out to be computationally intensive in case of lack of good first guesses for the solution. An algorithm to obtain the high
order expansion of the solution of a two-point boundary value problem is presented in this paper. The classical iterative
procedures are applied to identify a reference solution. Then, differential algebra is used to expand the solution of the
problem around the achieved one. Consequently, the computation of new solutions in a relatively large neighborhood of the
reference one is reduced to the simple evaluation of polynomials. The performances of the method are assessed by addressing
typical applications in the field of spacecraft dynamics, such as the identification of halo orbits and the design of aerocapture
maneuvers. 相似文献