全文获取类型
收费全文 | 53194篇 |
免费 | 7756篇 |
国内免费 | 10051篇 |
专业分类
测绘学 | 6093篇 |
大气科学 | 8131篇 |
地球物理 | 8544篇 |
地质学 | 24341篇 |
海洋学 | 5061篇 |
天文学 | 3488篇 |
综合类 | 3614篇 |
自然地理 | 11729篇 |
出版年
2024年 | 325篇 |
2023年 | 862篇 |
2022年 | 1814篇 |
2021年 | 2225篇 |
2020年 | 2120篇 |
2019年 | 2478篇 |
2018年 | 1814篇 |
2017年 | 2335篇 |
2016年 | 2348篇 |
2015年 | 2523篇 |
2014年 | 3098篇 |
2013年 | 3543篇 |
2012年 | 3154篇 |
2011年 | 3388篇 |
2010年 | 2872篇 |
2009年 | 3477篇 |
2008年 | 3378篇 |
2007年 | 3439篇 |
2006年 | 3353篇 |
2005年 | 3051篇 |
2004年 | 2632篇 |
2003年 | 2441篇 |
2002年 | 2167篇 |
2001年 | 1885篇 |
2000年 | 1807篇 |
1999年 | 1576篇 |
1998年 | 1401篇 |
1997年 | 1080篇 |
1996年 | 830篇 |
1995年 | 738篇 |
1994年 | 662篇 |
1993年 | 548篇 |
1992年 | 395篇 |
1991年 | 335篇 |
1990年 | 240篇 |
1989年 | 187篇 |
1988年 | 150篇 |
1987年 | 86篇 |
1986年 | 57篇 |
1985年 | 42篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
101.
This paper focuses on a series of quantitative analysis models, such as grey relational analysis model, hierarchical cluster analysis model, principal component analysis model, linear regression model and elastic coefficient model. These models are used to analyze the comprehensive function and effect of driving forces systemically, including analysis on features, analysis for differentiating the primary and the secondary, analysis on comprehensive effects, analysis of elasticity, analysis of prediction. The primary and characteristic factors can be extracted by analysis of features and analysis for differentiating the primary and the secondary. Analysis on prediction and elasticity can predict the area of cultivated land in the future and find out which factors exert great influence on the cultivated land supply. 相似文献
102.
《International Journal of Digital Earth》2013,6(3):258-270
Abstract Land use and land cover change, perhaps the most significant anthropogenic disturbance to the environment, mainly due to rapid urbanization/industrialization and large scale agricultural activities. In this paper, an attempt has been made to appraise land use/land cover changes over a century (1914–2007) in the Neyyar River Basin (L=56 km; Area = 483.4 km2) in southern Kerala – a biodiversity hot spot in Peninsular India. In this study, digital remote sensing data of the Indian Remote Sensing satellite series I-D (LISS III, 2006–2007) on 1:50,000 scale, Survey of India (SOI) toposheet of 1914 (1:63,360) and 1967 (1:50,000) have been utilized to map various land use/land cover changes. Maps of different periods have been registered and resampled to similar geographic coordinates using ERDAS Imagine 9.0. The most notable changes include decreases in areas of paddy cultivation, mixed crops, scrub lands and evergreen forests, and increases in built-up areas, rubber plantations, dense mixed forests, and water bodies. Further, large scale exploitation of flood plain mud and river sand have reached menacing proportions leading to bank caving and cut offs at channel bends. Conservation of land and water resources forms an important aspect of ecosystem management in the basin. 相似文献
103.
A long-term Global LAnd Surface Satellite (GLASS) data-set for environmental studies 总被引:1,自引:0,他引:1
《International Journal of Digital Earth》2013,6(6):5-33
Recently, five Global LAnd Surface Satellite (GLASS) products have been released: leaf area index (LAI), shortwave broadband albedo, longwave broadband emissivity, incident short radiation, and photosynthetically active radiation (PAR). The first three products cover the years 1982–2012 (LAI) and 1981–2010 (albedo and emissivity) at 1–5 km and 8-day resolutions, and the last two radiation products span the period 2008–2010 at 5 km and 3-h resolutions. These products have been evaluated and validated, and the preliminary results indicate that they are of higher quality and accuracy than the existing products. In particular, the first three products have much longer time series, and are therefore highly suitable for various environmental studies. This paper outlines the algorithms, product characteristics, preliminary validation results, potential applications and some examples of initial analysis of these products. 相似文献
104.
《International Journal of Digital Earth》2013,6(4):334-344
This paper presents a supervised polarimetric synthetic aperture radar (PolSAR) change detection method applied to specific land cover types. For each pixel of a PolSAR image, its target scattering vector can be modeled as having a complex multivariate normal distribution. Based on this assumption, the joint distribution of two corresponding vectors in a pair of PolSAR images is derived. Then, a generalized likelihood ratio test statistic for the equality of two likelihood functions of such joint distribution is considered and a maximum likelihood distance measure for specific land cover types is presented. Subsequently, the Kittler and Illingworth minimum error threshold segmentation method is applied to extract the specific changed areas. Experiments on two repeat-pass Radarsat-2 fully polarimetric images of Suzhou, China, demonstrate that the proposed change detection method gives a good performance in determining the specific changed areas in PolSAR images, especially the areas that have changed to water. 相似文献
105.
《International Journal of Digital Earth》2013,6(6):639-655
ABSTRACTImage fusion techniques that blend multi-sensor characteristics to generate synthetic data with fine resolutions have generated great interest within the remote sensing community. Over the past decade, although many advances have been made in the spatiotemporal fusion models, there still remain several shortcomings in existing methods. In this article, a hierarchical spatiotemporal adaptive fusion model (HSTAFM) is proposed for producing daily synthetic fine-resolution fusions. The suggested model uses only one prior or posterior image pair, especially with the aim being to predict arbitrary temporal changes. The proposed model is implemented in two stages. First, the coarse-resolution image is enhanced through super-resolution based on sparse representation; second, a pre-selection of temporal change is performed. It then adopts a two-level strategy to select similar pixels, and blends multi-sensor features adaptively to generate the final synthetic data. The results of tests using both simulated and actual observed data show that the model can accurately capture both seasonal phenology change and land-cover-type change. Comparisons between HSTAFM and other developed models also demonstrate our proposed model produces consistently lower biases. 相似文献
106.
三维数字城市在道路规划设计中的应用研究 总被引:2,自引:0,他引:2
"数字城市"建设成果在国民经济建设中逐渐得到广泛应用,以直观、可视化、信息更加丰富为显著特点的"三维数字城市"建设成果,成为应用创新的助推剂,而当前,传统的依靠计算机辅助设计软件开展道路设计规划成为一种需要突破的变革趋势,选择基于三维数字城市建设成果开展道路规划设计,以其显著的优势成为道路设计规划变革的新途径。 相似文献
107.
王家耀 《测绘科学技术学报》2017,34(2)
军事测绘学和军事地理学的演进与发展,都有近两千多年的历史,如今都已进入信息时代,成为分属工科和理科的两门独立的学科。本文论述了军事测绘学和军事地理学的研究对象、内容、范围和方法;分析了军事测绘学和军事地理学各自的发展过程,描述了各自的演进轨迹,特别是分析了信息时代的军事测绘学和军事地理学的发展趋势和各自特点;就军事测绘学和军事地理学在战场地理环境信息保障中的作用,分别从战场地理环境信息保障的两种思维、发展过程、发展特点和发展趋势等几个方面,分析了军事测绘学和军事地理学的"分异"与"聚焦";最后,从哲学的高度论述了"空间与时间一起构成运动着的物质存在的两种基本形式"和"空间参照与时间参照是自然与社会现象的两个基本参照系统"的观点,认为军事测绘学和军事地理学都是研究存在于空间和时间之中且运动着的物质,但研究的具体对象、内容、范围和方法有很大区别,必将在无限和有限统一的空间和时间中深化各自的研究内容、开拓各自的研究范围,创新各自的研究方法,同时又更加紧密地聚焦于战场地理环境信息保障。 相似文献
108.
国土移动地图系统以数字城市地理空间框架为依托,基于数字城市地理信息公共平台发布的数据服务进行开发,供国土系统各单位使用,可以更为有效地利用数字城市的建设成果,大力促进国土部门的信息化建设水平。本文旨在探讨实现该系统过程中遇到的具体问题及解决方法。 相似文献
109.
宋亚男 《测绘与空间地理信息》2017,(4)
大气中日益上升的温室气体浓度,已导致温室效应日益增强,从而引发一系列不利的环境与生态后果,并会对世界粮食生产、水资源利用等关系人类生存发展的方面产生重要影响。1994~2014年是平顶山城市化进程不断加快和经济社会高速发展的时期,土地利用、人口、能源消耗和城市植被等影响碳源、碳汇的主要方面也都发生了重大的变化。将1994~2014年河南省平顶山市城区的碳平衡变化情况作为研究对象,计算出碳平衡主要影响因素各自的变化情况并加以分析,得出有关平顶山城区碳环境演变的结论。最后,为促进平顶山城区的碳源碳汇平衡,提出实现城市快速发展过程中低碳效应策略。 相似文献
110.