全文获取类型
收费全文 | 142篇 |
免费 | 19篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 14篇 |
地球物理 | 52篇 |
地质学 | 51篇 |
海洋学 | 6篇 |
综合类 | 8篇 |
自然地理 | 24篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有177条查询结果,搜索用时 15 毫秒
101.
济南某地区裂隙岩溶地下水硝酸盐污染现状及溯源浅析 总被引:1,自引:0,他引:1
通过对历史资料的对比,揭示了济南某地裂隙岩溶地下水中硝酸根污染现状,并通过三线图法对硝酸根进行溯源分析,显示研究区地下水硝酸根含量受人类活动影响明显,并有进一步发展的趋势。相关性分析法分析结果显示地下水硝酸根含量与Cl相关,说明其与工业废水联系密切,而土壤剖面中硝酸根含量显示,土壤中硝酸根含量的顺序为:禽畜粪便污染类污水排放污染类垃圾堆放污染类。分析认为,研究区裂隙盐溶承压水硝酸根污染的来源主要为补给区及径流区强烈渗漏携带牲畜粪便及氮肥和农家肥的施用、生活污水、工业废水及浅层水混入。 相似文献
102.
103.
104.
Assessment of detachment and sediment transport capacity of runoff by field experiments on a silt loam soil 总被引:2,自引:0,他引:2
The detachment capacity (Dc) and transport capacity (Tc) of overland flow are important variables in the assessment of soil erosion. They determine respectively the lower and upper limit of sediment transport by runoff and therefore control detachment and deposition pro‐cesses. In this study, the detachment and transport capacity of runoff was investigated by rainfall simulations and overland flow experiments on small field plots. On the bare field plots, it was found that Tc was strongly related to total runoff discharge. This was also observed for the plots covered by maize residues, but Tc was less due to the lower runoff velocity. A simple regression equation was derived to estimate Tc for both bare and covered soil. Comparing our observations with Tc equations mentioned in the literature revealed that Tc equations based on laboratory experiments overestimated, on average, our measurements. Although Tc can be assessed more easily in laboratory experiments, the applicability of the results to field conditions remains questionable. Detachment by runoff was also related to total runoff discharge. The Dc values were, however, 4–50 times smaller than the Tc at corresponding high and low runoff discharge. This indicates that detachment by runoff constitutes only part of the transported sediment. Interrill erosion supplies an important additional amount of sediment. In this study, however, only sealed soils were considered. In the case of freshly tilled, loose soils, the Dc of runoff may be larger, resulting in a larger contribution to the total soil loss. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
105.
极化雷达目标分解方法用于岩性分类 总被引:8,自引:0,他引:8
雷达遥感中地表不同岩石类别的后向散射一般判别不大,因此以散射幅度为主要探测因子常规雷达遥感数据不利于岩性分类。极化雷达以散射矩阵或Stokes短阵的形式,记录了更多的地物回波信息。信息源的增多,有利于提高岩性分类的精度。但是,由于不同极化状态回波信号之间的关性,极化数据不可避免地产生数据冗余,反而增大了岩性分类的误差。 相似文献
106.
Rainfall simulators can be a useful research tool for some purposes but are quite unsuitable for others. They have been useful in soil erosion and infiltration studies for over eight decades, but the possibility of using a rainfall simulator in urban nonpoint source pollution involving urban non-erodible surfaces has not been fully explored. In this review, the versatility of different rainfall simulators of varying sizes, configurations and styles used in the past two decades are appraised for possible adaptation to urban sealed surfaces. Recommended criteria for detailed rainfall simulator reporting are also outlined.
EDITOR M.C. AcremanASSOCIATE EDITOR not assigned 相似文献
107.
Li Li Mark A. Nearing Mary H. Nichols Viktor O. Polyakov Michelle L. Cavanaugh 《地球表面变化过程与地形》2020,45(2):484-495
Terrestrial LiDAR scanning (TLS) technology is widely used to detect terrain elevation changes. This study examines the potential use of terrestrial LiDAR to measure erosion on small experimental plots at high resolution. Multitemporal TLS scans were conducted at six positions around plots (12 m2) with three slope treatments through 11 simulated rainfall applications. Surface elevation changes were quantified by comparing scans between rainfall simulations, and elevation changes greater than the level of detection were used to obtain volumetric change estimations. Erosion mass was estimated both by using soil bulk density and the density of sediment collected in runoff, and then compared to the erosion estimated from the runoff samples. Results showed: (1) with the aid of fixed reference controls in the form of concrete target surfaces of varying roughness, registration accuracy was better than 1 mm and mean level of change detection was less than 2.2 mm; (2) the average absolute relative errors of TLS-estimated eroded mass ranged from 6.8% to 31.8%, with greater values on 5% slope; (3) the TLS-estimated erosion accuracy was affected by erosion magnitude, the utilized material density and number of scan positions, and a grid size of 10 mm was found to be appropriate for this scale to estimate the volumetric changes; (4) the number of scan positions could be reduced to three while not significantly impacting volumetric change estimations; and (5) elevating the scanner resulted in much better accuracy for eroded mass estimations. This study suggests that using LiDAR to monitor soil erosion at the plot scale is feasible, and provides guidance about the level of accuracy one might expect in doing so. © 2019 John Wiley & Sons, Ltd. 相似文献
108.
城市居住小区环境归属感评价——以大连市为例 总被引:12,自引:3,他引:9
研究居民对居住小区环境归属感,进行定量评价并揭示其规律,可为指导城市小区规划设计提供依据。本文以调查问卷的形式,对大连市的居住小区进行调查,充分考虑评价因子的代表性和多层次性的特点,选取5项一级指标和25个单项指标建立评价指标体系;采用层次分析法与地理信息系统软件Surfer 8.0相结合的方法,对大连市居住小区归属感进行初步评价。研究结果表明:影响居住小区归属感的主要因子有舒适感、识别感、安全感、交流感、成就感;大连市居住小区归属感的整体评价较好,市内四区存在差异;归属感的高值区域分布在生态环境风景区、商务活动中心、靠近海岸线的地方及交通便利的地方。 相似文献
109.
In this paper, a recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, is tested experimentally on plots of varying slopes in which mobile bed rills are incised. Initially, measurements of flow velocity, water depth, cross‐sectional area, wetted perimeter and bed slope conducted in 106 reaches of rills incised on an experimental plot having a slope of 14% were used to calibrate the flow resistance equation. Then, the relationship between the velocity profile parameter Γ, the channel slope, and the flow Froude number, which was calibrated using the 106 rill reach data, was tested using measurements carried out in plots having slopes of 22% and 9%. The measurements carried out in the latter slope conditions confirmed that (a) the Darcy–Weisbach friction factor can be accurately estimated using the proposed theoretical approach, and (b) the data were supportive of the slope independence hypothesis of rill velocity stated by Govers. 相似文献
110.
基于中国Argo实时资料中心发布的2004年1月至2017年12月Argo全球温盐资料,运用直线定位法和隶属关系,对吕宋岛以东海域(120°~140°E,10°~30°N)水团进行分析,划分出北太平洋次表层水团(NPSSW)和北太平洋中层水团(NPIW)的分布范围。次表层水团位于50~220 m深度,分布在10°~28°N范围内,温度16.61~27.60℃,盐度34.68~35.14,核心范围春夏季较大,秋冬季较小。中层水团位于280~900 m深度,分布在10~30°N范围内,温度3.67~16.55℃,盐度34.11~34.67,核心范围季节变化较弱,整体位于18°N以北。次表层与中层水团核心温盐具有一定的年际变化特征,次表层水团与气候变化相关性较好,核心温度和盐度均存在4 a的变化周期;而中层水团与气候变化相关性较差,核心温度和盐度则分别具有3.5 a和3 a的变化周期。 相似文献