全文获取类型
收费全文 | 57191篇 |
免费 | 7700篇 |
国内免费 | 11066篇 |
专业分类
测绘学 | 10872篇 |
大气科学 | 8846篇 |
地球物理 | 11599篇 |
地质学 | 19187篇 |
海洋学 | 7390篇 |
天文学 | 2755篇 |
综合类 | 4696篇 |
自然地理 | 10612篇 |
出版年
2024年 | 221篇 |
2023年 | 621篇 |
2022年 | 1880篇 |
2021年 | 2234篇 |
2020年 | 2552篇 |
2019年 | 3055篇 |
2018年 | 2152篇 |
2017年 | 2903篇 |
2016年 | 2801篇 |
2015年 | 3046篇 |
2014年 | 3409篇 |
2013年 | 4188篇 |
2012年 | 3686篇 |
2011年 | 3694篇 |
2010年 | 2894篇 |
2009年 | 3450篇 |
2008年 | 3552篇 |
2007年 | 3966篇 |
2006年 | 3815篇 |
2005年 | 3135篇 |
2004年 | 2816篇 |
2003年 | 2316篇 |
2002年 | 1944篇 |
2001年 | 1565篇 |
2000年 | 1553篇 |
1999年 | 1440篇 |
1998年 | 1250篇 |
1997年 | 1007篇 |
1996年 | 844篇 |
1995年 | 724篇 |
1994年 | 628篇 |
1993年 | 581篇 |
1992年 | 440篇 |
1991年 | 309篇 |
1990年 | 226篇 |
1989年 | 243篇 |
1988年 | 169篇 |
1987年 | 107篇 |
1986年 | 103篇 |
1985年 | 92篇 |
1984年 | 56篇 |
1983年 | 23篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1973年 | 21篇 |
1971年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 812 毫秒
631.
632.
SPOT-5影像的高分辨率和高信息量的性质,使其得到了广泛的应用,特别是在全国第二次土地利用调查中得到了更加深入的应用。而数字正射影像的制作是SPOT-5遥感影像应用的关键所在。本文在介绍DOM制作的基础上,依据当前获取GCP主要的三种途径采用ERDAS遥感图像处理软件进行了实验,并对最终的结果精度进行分析,总结了DOM制作过程的相关问题。 相似文献
633.
框架预应力锚杆边坡支护结构的稳定性分析方法及其 应用 总被引:4,自引:0,他引:4
以边坡极限平衡理论及框架预应力锚杆边坡支护结构的圆弧滑动破坏模式为基础,在考虑框架、锚杆对土体边坡稳定性影响的情况下,基于圆弧滑动条分法的思想利用积分法建立了内部稳定性安全系数计算模型和最危险滑移面搜索模型。确定滑移面圆心坐标为几何控制参数,推导了安全系数计算模型中各变量与滑移面圆心坐标之间的函数关系式,从而获得了滑移面几何控制参数与内部稳定性安全系数之间的函数关系。利用网格法对框架预应力锚杆支护结构最危险滑移面的圆心坐标进行动态搜索和求解。最后采用Matlab语言编制了框架预应力锚杆边坡支护结构的稳定性分析程序,并结合工程实例进行了验算,讨论了此种方法的适用条件,结果表明该方法简明适用,较传统的经验分析方法更加合理。 相似文献
634.
When spatial datasets are overlaid, corresponding features do not always coincide. This may be a result of the datasets having differing quality characteristics, being captured at different scales or perhaps being in different projections or datums. Data integration methods have been developed to bring such datasets into alignment. Although these methods attempt to maintain topological relationships within each dataset, spatial relationships between features in different datasets are generally not considered. The preservation of inter‐dataset topology is a research area of considerable current interest. This research addresses the preservation of topology within a data integration process. It describes the functional models established to represent a number of spatial relationships as observation equations. These are used to provide additional information concerning the relative positions of features. Since many topological relationships are best modelled as inequalities, an algorithm is developed to accommodate such relationships. The method, based on least squares with inequalities (LSI), is tested on simulated and real datasets. Results are presented to illustrate the optimal positioning solutions determined using all of the available information. In addition, updated quality parameters are provided at the level of the individual coordinate, enabling communication of local variation in the resultant quality of the integrated datasets. 相似文献
635.
Modelling Positional Uncertainty of Line Features by Accounting for Stochastic Deviations from Straight Line Segments 总被引:1,自引:0,他引:1
Sytze de Bruin 《Transactions in GIS》2008,12(2):165-177
The assessment of positional uncertainty in line and area features is often based on uncertainty in the coordinates of their elementary vertices which are assumed to be connected by straight lines. Such an approach disregards uncertainty caused by sampling and approximation of a curvilinear feature by a sequence of straight line segments. In this article, a method is proposed that also allows for the latter type of uncertainty by modelling random rectangular deviations from the conventional straight line segments. Using the model on a dense network of sub‐vertices, the contribution of uncertainty due to approximation is emphasised; the sampling effect can be assessed by applying it on a small set of randomly inserted sub‐vertices. A case study demonstrates a feasible way of parameterisation based on assumptions of joint normal distributions for positional errors of the vertices and the rectangular deviations and a uniform distribution of missed sub‐vertices along line segments. Depending on the magnitudes of the different sources of uncertainty, not accounting for potential deviations from straight line segments may drastically underestimate the positional uncertainty of line features. 相似文献
636.
637.
638.
639.
Cluster correspondence analysis examines the spatial autocorrelation of multi-location events at the local scale. This paper
argues that patterns of cluster correspondence are highly sensitive to the definition of operational neighborhoods that form
the spatial units of analysis. A subset of multi-location events is examined for cluster correspondence if they are associated
with the same operational neighborhood. This paper discusses the construction of operational neighborhoods for cluster correspondence
analysis based on the spatial properties of the underlying zoning system and the scales at which the zones are aggregated
into neighborhoods. Impacts of this construction on the degree of cluster correspondence are also analyzed. Empirical analyses
of cluster correspondence between paired vehicle theft and recovery locations are conducted on different zoning methods and
across a series of geographic scales and the dynamics of cluster correspondence patterns are discussed.
相似文献
640.
Open source, spatial analysis, and activity-travel behaviour research: capabilities of the aspace package 总被引:2,自引:0,他引:2
This paper reports on recent experience with the development of aspace, an Open Source (OS) library for the geographic visualization and analysis of activity-travel behaviour. The paper begins
with an overview of recent progress with respect to the convergence of Open Source technology, spatial analysis, and travel
behaviour research. The remainder of the paper focuses on aspace; a collection of functions that, when combined with data describing the geographical location of daily activities, can be
used to visualize and describe spatial properties of individual and household activity spaces. These properties include: size,
orientation, shape, and the geographical dispersion of activity locations contained within the activity space. Several planar
geometries are used to transform measurable spatial properties into intuitive objects for visualizing spatial patterns of
activity participation. Experiments are conducted, using data from the first wave of the 2003 Toronto Travel Activity Panel
Survey, to demonstrate the potential application of aspace for basic and applied policy-based research into activity-travel behaviour. The toolkit is distributed as a downloadable
‘package’ from the Open Source R Project for Statistical Computing.
相似文献