全文获取类型
收费全文 | 6818篇 |
免费 | 1055篇 |
国内免费 | 894篇 |
专业分类
测绘学 | 646篇 |
大气科学 | 880篇 |
地球物理 | 2054篇 |
地质学 | 2630篇 |
海洋学 | 886篇 |
天文学 | 8篇 |
综合类 | 414篇 |
自然地理 | 1249篇 |
出版年
2024年 | 37篇 |
2023年 | 114篇 |
2022年 | 262篇 |
2021年 | 303篇 |
2020年 | 313篇 |
2019年 | 363篇 |
2018年 | 278篇 |
2017年 | 326篇 |
2016年 | 345篇 |
2015年 | 319篇 |
2014年 | 534篇 |
2013年 | 523篇 |
2012年 | 462篇 |
2011年 | 464篇 |
2010年 | 406篇 |
2009年 | 410篇 |
2008年 | 437篇 |
2007年 | 425篇 |
2006年 | 411篇 |
2005年 | 313篇 |
2004年 | 277篇 |
2003年 | 225篇 |
2002年 | 228篇 |
2001年 | 147篇 |
2000年 | 123篇 |
1999年 | 110篇 |
1998年 | 116篇 |
1997年 | 64篇 |
1996年 | 85篇 |
1995年 | 76篇 |
1994年 | 71篇 |
1993年 | 60篇 |
1992年 | 55篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
排序方式: 共有8767条查询结果,搜索用时 15 毫秒
61.
62.
Calculating Pollution Indices by Heavy Metals in Ecological Geochemistry Assessment and a Case Study in Parks of Beijing 总被引:4,自引:0,他引:4
Pollution index is a powerful tool for ecological geochemistry assessment. The commonly used pollution indices by heavy metals in soils and sediments were classified as two types of single index and integrated index in an algorithm point of view. Four single indices of contamination factor (or concentration factor), ecological risk factor, enrichment factor, and index of geo-accumulation were illustrated, and the reference values for calculating single indices were distinguished into background levels and threshold pollution values. Eight integrated indices were divided into two groups. One group is suitable for the normal distribution single indices including the sum, average, weighted average,vector modulus, and Nemerow pollution indices, and the other for log-normal distribution including the product, root of product, and weighted power product pollution indices. Using background levels as reference values, five contamination classes were divided, and the terminologies are suggested for the single and integrated indices to unify the assessment results. Software of EGAPI was developed in a single document interface to calculate the four single and eight integrated indices by heavy metals to assess the quality of soil and sediment ecological geochemistry. Pollution indices by heavy metals of Cu,Pb, and Zn in soils in parks of Beijing were calculated using EGAPI software, and these five contamination classes and terminologies suggested in this study were evaluated and used. Results ofintegrated indices of Cu, Pb, and Zn in soils indicated that the soil qualities are unpolluted as a whole and varied from low polluted to unpolluted status from the center to the outskirts of Beijing City. 相似文献
63.
Accuracy assessment of lidar-derived digital elevation models 总被引:2,自引:0,他引:2
Despite the relatively high cost of airborne lidar-derived digital elevation models (DEMs), such products are usually presented without a satisfactory associated estimate of accuracy. For the most part, DEM accuracy estimates are typically provided by comparing lidar heights against a finite sample of check point coordinates from an independent source of higher accuracy, supposing a normal distribution of the derived height differences or errors. This paper proposes a new methodology to assess the vertical accuracy of lidar DEMs using confidence intervals constructed from a finite sample of errors computed at check points. A non-parametric approach has been tested where no particular error distribution is assumed, making the proposed methodology especially applicable to non-normal error distributions of the type usually found in DEMs derived from lidar. The performance of the proposed model was experimentally validated using Monte Carlo simulation on 18 vertical error data-sets. Fifteen of these data-sets were computed from original lidar data provided by the International Society for Photogrammetry and Remote Sensing Working Group III/3, using their respective filtered reference data as ground truth. The three remaining data-sets were provided by the Natural Environment Research Council's Airborne Research and Survey Facility lidar system, together with check points acquired using high precision kinematic GPS. The results proved promising, the proposed models reproducing the statistical behaviour of vertical errors of lidar using a favourable number of check points, even in the cases of data-sets with non-normally distributed residuals. This research can therefore be considered as a potentially important step towards improving the quality control of lidar-derived DEMs. 相似文献
64.
居住单元是与人们生活密切相关的社区范围,其交通环境的优劣是衡量居住单元环境好坏的重要标准之一。高分辨遥感影像
的高空间分辨率特点为我们提供了研究居住单元交通环境的可能性。本文从区域交通环境、路网可达性出发,对城市居住单元交通
环境质量的遥感评价方法进行了研究,根据高分辨率遥感影像的特点构建了居住单元交通环境的多级指标评价体系,并对厦门市的
50个居住单元进行了评价分析。实验表明,利用高分辨率影像进行城市交通环境质量评价是一种成本较低,简便可行的方法。 相似文献
65.
通过对当前城市的120急救系统进行了调查和分析,设计了一种基于“3G”--GIS/GPS/GSM三种技术相结合的急救系统。并对此系统的主要功能模块和关键技术作了详细的论述,将GIS空间分析、电子地图匹配和GPS导航、GSM传输信息技术与当前的急救系统相结合,可以在很大程度上提高120急救的智能化程度和可靠性。 相似文献
66.
城市公共卫生安全应急管理系统技术集成研究 总被引:2,自引:1,他引:1
从国内城市公共卫生安全应急管理系统的研究和应用现状出发,指出城市公共卫生安全应急管理系统建设的核心要务是集成现有的卫生信息系统、消除卫生信息孤岛、实现数据共享与交换;并提出了城市公共卫生安全应急管理系统数据采集类型和业务支持部门。在此基础上,构建了一个基于数据仓库、以GIS为应急响应支持平台、能统一管理信息、可与其他电子政务系统互连互通的城市公共卫生安全应急管理系统框架结构,并详细阐述了各业务模块的基本功能和系统实现的关键技术方法。 相似文献
67.
68.
卓万生 《地质灾害与环境保护》2008,19(2):52-56
由于地质灾害的突发性和引发因素的复杂性,在及时和有效地掌握潜在隐患部位上还亟待进一步探索与细化,力求防灾抗灾工作有的放矢,以确保人民群众的生命财产损失降到最低限度。本文就基于山区的基本特征和房后边坡潜在地质安全隐患基本信息调查,简要分析房后边坡孕灾致灾环境,并针对它们的影响程度,采取层次分析(AHP)等方法来确定安全评价因子权重和安全系数,对构造安全评价结构作进一步研究。 相似文献
69.
基于可拓工程方法,在物元模型理论的基础上建立了公路泥石流危险性评价的物元模型,并采用层次分析法计算物元模型中各评价指标的权系数。通过实际公路泥石流危险性等级的关联度计算,对四川地区雅泸高速公路的5条泥石流沟进行了评价,得出与实际相符合的结论。并与其他评价方法相比表明:该方法不仅可以应用在泥石流危险性评价上,而且所得的结果会更加合理,具有较好的适用性。 相似文献
70.