全文获取类型
收费全文 | 17317篇 |
免费 | 1947篇 |
国内免费 | 3774篇 |
专业分类
测绘学 | 2010篇 |
大气科学 | 2946篇 |
地球物理 | 1782篇 |
地质学 | 6428篇 |
海洋学 | 1793篇 |
天文学 | 5625篇 |
综合类 | 936篇 |
自然地理 | 1518篇 |
出版年
2024年 | 69篇 |
2023年 | 205篇 |
2022年 | 495篇 |
2021年 | 580篇 |
2020年 | 620篇 |
2019年 | 758篇 |
2018年 | 509篇 |
2017年 | 597篇 |
2016年 | 615篇 |
2015年 | 679篇 |
2014年 | 986篇 |
2013年 | 1053篇 |
2012年 | 1070篇 |
2011年 | 1152篇 |
2010年 | 1126篇 |
2009年 | 1515篇 |
2008年 | 1424篇 |
2007年 | 1398篇 |
2006年 | 1273篇 |
2005年 | 1063篇 |
2004年 | 967篇 |
2003年 | 789篇 |
2002年 | 641篇 |
2001年 | 591篇 |
2000年 | 535篇 |
1999年 | 499篇 |
1998年 | 372篇 |
1997年 | 228篇 |
1996年 | 189篇 |
1995年 | 158篇 |
1994年 | 146篇 |
1993年 | 161篇 |
1992年 | 84篇 |
1991年 | 72篇 |
1990年 | 69篇 |
1989年 | 65篇 |
1988年 | 48篇 |
1987年 | 23篇 |
1986年 | 36篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 18篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 17篇 |
1976年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
Yifei Sun 《Journal of Geographical Systems》2002,4(4):359-370
Based on a four-point evaluation system consisting of accuracy, consistency, power, and chance to commit type I errors, this study compares Tango's minimum p (MinP) and Stone's maximum relative risk (MaxRR) methods for detecting focused cluster size through simulations in GIS. It
reveals that the MinP method is more effective than the MaxRR method. The MinP method exhibits higher levels of accuracy and
consistency; and its power and chance to commit type I errors are similar to the MinP method. The MaxRR method has a tendency
to underestimate the cluster size, while the MinP method tends to overestimate the cluster size, particularly when the clusters
are relatively big and have high relative risk levels. In addition, the MinP method seems to be most effective in revealing
the size of clusters when clusters are neither too strong nor too weak. The lowest detection rates for clustering occur when
the clustering signal is relatively weak, which is easily understandable. In practice, it might be useful to use both the
methods to estimate a range of possible cluster sizes, where the MaxRR method indicates the lower estimate, while the MinP
method gives the higher estimate of the cluster size.
Received: 24 August 2002 / Accepted: 20 December 2002 相似文献
912.
Eric J.E. Molin Harmen Oppewal Harry J.P. Timmermans 《Journal of Geographical Systems》2002,4(4):343-358
In this paper, two approaches for measuring residential group preferences, based on the method of Hierarchical Information
Integration (HII), are compared. In particular, the hypothesis that group-based preference models estimated from integrated
HII experiments better predict group preferences than part individual-based group models estimated from classical HII experiments
is tested. To that effect, the models' ability to predict group preferences for new residential alternatives is compared in
a study of residential preferences of co-ops. Results indicate that integrated HII group experiments indeed result in better
predictions of residential preferences. 相似文献
913.
Geostatistical incorporation of spatial coordinates into supervised classification of hyperspectral data 总被引:1,自引:0,他引:1
P. Goovaerts 《Journal of Geographical Systems》2002,4(1):99-111
This paper presents a methodology to incorporate both hyperspectral properties and spatial coordinates of pixels in maximum
likelihood classification. Indicator kriging of ground data is used to estimate, for each pixel, the prior probabilities of
occurrence of classes which are then combined with spectral-based probabilities within a Bayesian framework. In the case study
(mapping of in-stream habitats), accounting for spatial coordinates increases the overall producer's accuracy from 85.8% to
93.8%, while the Kappa statistic rises from 0.74 to 0.88. Best results are obtained using only indicator kriging-based probabilities,
with a stunning overall accuracy of 97.2%. Significant improvements are observed for environmentally important units, such
as pools (Kappa: 0.17 to 0.74) and eddy drop zones (Kappa: 0.65 to 0.87). The lack of benefit of using hyperspectral information
in the present study can be explained by the dense network of ground observations and the high spatial continuity of field
classification which might be spurious.
Received: 12 April 2001 / Accepted: 7 September 2001 相似文献
914.
915.
Toward micro-scale spatial modeling of gentrification 总被引:1,自引:0,他引:1
David O'Sullivan 《Journal of Geographical Systems》2002,4(3):251-274
A simple preliminary model of gentrification is presented. The model is based on an irregular cellular automaton architecture
drawing on the concept of proximal space, which is well suited to the spatial externalities present in housing markets at
the local scale. The rent gap hypothesis on which the model's cell transition rules are based is discussed. The model's transition
rules are described in detail. Practical difficulties in configuring and initializing the model are described and its typical
behavior reported. Prospects for further development of the model are discussed. The current model structure, while inadequate,
is well suited to further elaboration and the incorporation of other interesting and relevant effects.
Received: 1 November 2001 / Accepted: 12 April 2002
Town centres data were made available by kind permission of the UK Department of the Environment, Transport and the Regions. 相似文献
916.
多部多普勒雷达同步探测三维风场反演系统 总被引:18,自引:5,他引:18
“我国重大气候和天气灾害的形成机理与预测理论研究”项目首次启用双多普勒雷达组网同步观测,如何从同步观测的暴雨资料中反演三维场,具有重要的理论和现实意义,根据项目需要,建立了国内首套多部多普勒天气雷达同步探测三维风场反演软件系统,并反演出2001年7月13日由双多普勒雷达同步观测到的一个中β尺度暴雨系统的三维风场,结果显示,该三维风场结构合理,系统能满足外场试验的要求。 相似文献
917.
918.
919.
地形引起的雷达辐射畸变及其校正 总被引:3,自引:3,他引:3
合成孔径雷达影像由于其侧视特点 ,存在着严重的地形引起的几何畸变及辐射畸变。辐射畸变不仅对 SAR辐射标定造成困难 ,而且严重影响了影像分类、土壤湿度信息提取、森林蓄积量信息提取等应用。本文将辐射畸变归结为面积效应和局部入射角效应 ,推导了散射面积归一化因子 ,以消除辐射畸变的面积效应。提出了一种以局部入射角的线性函数表达的后向散射模型 ,在此基础上 ,给出了消除局部入射角效应的校正函数。最后 ,以RADARSAT SAR影像进行地形辐射畸变校正的试验与分析 相似文献
920.