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21.
Baojing Gu Ying Ge Scott X. Chang Weidong Luo Jie Chang 《Global Environmental Change》2013,23(5):1112-1121
Identifying the sources of reactive nitrogen (N) and quantifying their contributions to groundwater nitrate concentrations are critical to understanding the dynamics of groundwater nitrate contamination. Here we assessed groundwater nitrate contamination in China using literature analysis and N balance calculation in coupled human and natural systems. The source appointment via N balance was well validated by field data via literature analysis. Nitrate was detected in 96% of groundwater samples based on a common detection threshold of 0.2 mg N L?1, and 28% of groundwater samples exceeded WHO's maximum contaminant level (10 mg N L?1). Groundwater nitrate concentrations were the highest beneath industrial land (median: 34.6 mg N L?1), followed by urban land (10.2 mg N L?1), cropland (4.8 mg N L?1), and rural human settlement (4.0 mg N L?1), with the lowest found beneath natural land (0.8 mg N L?1). During the period 1980–2008, total reactive N leakage to groundwater increased about 1.5 times, from 2.0 to 5.0 Tg N year?1, in China. Despite that the contribution of cropland to the total amount of reactive N leakage to groundwater was reduced from 50 to 40% during the past three decades, cropland still was the single largest source, while the contribution from landfill rapidly increased from 10 to 34%. High reactive N leakage mainly occurred in relatively developed agricultural or urbanized regions with a large population. The amount of reactive N leakage to groundwater was mainly driven by anthropogenic factors (population, gross domestic product, urbanization rate and land use type). We constructed a high resolution map of reactive N source appointment and this could be the basis for future modeling of groundwater nitrate dynamics and for policy development on mitigation of groundwater contamination. 相似文献
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Carbon,nitrogen and phosphorus coupling relationships and their influencing factors in the critical zone of Dongting Lake wetlands,China
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Wetland is a transition zone between terrestrial and aquatic ecosystems, and is the source and sink of various biogenic elements in the earth’s epipelagic zone. In order to investigate the driving force and coupling mechanism of carbon (C), nitrogen (N) and phosphorus (P) migration in the critical zone of lake wetland, this paper studies the natural wetland of Dongting Lake area, through measuring and analysing the C, N and P contents in the wetland soil and groundwater. Methods of Pearson correlation, non-linear regression and machine learning were employed to analyse the influencing factors, and to explore the coupling patterns of the C, N and P in both soils and groundwater, with data derived from soil and water samples collected from the wetland critical zone. The results show that the mean values of organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in groundwater are 1.59 mg/L, 4.19 mg/L and 0.5 mg/L, respectively, while the mean values of C, N and P in the soils are 18.05 g/kg, 0.86 g/kg and 0.52 g/kg. The results also show that the TOC, TN and TP in the groundwater are driven by a variety of environmental factors. However, the concentrations of C, N and P in the soils are mainly related to vegetation abundance and species which influence each other. In addition, the fitted curves of wetland soil C-N and C-P appear to follow the power function and S-shaped curve, respectively. In order to establish a multivariate regression model, the soil N and P contents were used as the input parameters and the soil C content used as the output one. By comparing the prediction effects of machine learning and nonlinear regression modelling, the results show that coupled relationship equation for the C, N and P contents is highly reliable. Future modelling of the coupled soil and groundwater elemental cycles needs to consider the complexity of hydrogeological conditions and to explore the quantitative relationships among the influencing factors and chemical constituents. 相似文献
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基于RS、GIS的松嫩沙地土地利用变化研究——以吉林省前郭县为例 总被引:8,自引:0,他引:8
土地利用变化是自然与人文因素综合作用的结果。在较短时间尺度上,社会经济因素是土地利用变化的主要驱动力。本文以吉林省前郭尔罗斯县为例,运用1987年和1996年TM影像及相关统计数据,采用空间分析、统计分析和遥感信息与空间化非遥感信息集成等方法,研究了10a来该县土地利用变化过程及其社会经济驱动机制。结果表明,近10a来,耕地面积明显增加,林地、牧草地面积减少,其它土地利用类型面积变化不大,农业产值、牧业产值、农业人口数和粮食产量是该县土地利用变化的主要社会经济驱动力. 相似文献
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基于多时相Landsat数据的城市扩张及其驱动力分析 总被引:10,自引:0,他引:10
以长沙市为例,在多时相Landsat遥感数据支持下,采用监督分类、非监督分类和归一化裸露指数(NDBI)等方法提取城市用地信息。通过对比多期城市用地的熵值变化,定量分析城市扩张的时空特性; 运用叠加、缓冲区分析等方法,分析城市扩张和中心城区的关系,绘制城市扩张速度玫瑰图。研究结果表明,长沙市建成区总面积不断扩展,其中,1973~1986年扩张主要表现在东南方向,1987~1993年为西部方向,1994~2001年南和东南方向成为快速扩张方向; 对长沙城市扩张驱动力进行分析,认为人口迅速增加是城市扩张的最主要驱动力。 相似文献
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Seasonal variability of the Antarctic Coastal Current and its driving mechanisms in the Weddell Sea 总被引:2,自引:0,他引:2
Ismael Núez-Riboni Eberhard Fahrbach 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):1927-1941
Insight into the dynamics of the Antarctic Coastal Current (ACoC) is achieved by quantifying the contributions of its driving mechanisms to the seasonal variability of its barotropic and baroclinic components. These mechanisms are sought out in the local wind, the sea-ice concentration, wind curl of the Weddell Gyre (Sverdrup transport) and the thermohaline forcing related to warming/cooling and ice melting and freezing. These driving mechanisms induce most of the seasonal variability of both the barotropic and baroclinic components of the ACoC by deepening the pycnocline towards the coast and sharpening the baroclinic profile following thermal wind balance. The resulting coastal current has mainly a barotropic transport (82%) and a major annual cycle, which explains 37% of this component's variability (tides and other high-frequency events generate 40%). The wind contributes with 58% of the seasonal variability of the barotropic component and 23% of the baroclinic; the sea-ice concentration contributes with 8% and 18%, respectively; Sverdrup transport with 4% and 30% and the thermohaline forcing with 30% and 29%. The results of this study are obtained with analysis of fifteen CTD sections (potential density and geostrophic velocities) of RV-Polarstern obtained between 1992 and 2005, as well as composite, spectral and harmonic analyses of 9 years of time series from moored instruments (current speed and temperature), wind speed, atmospheric pressure and sea-ice concentration of satellite imagery. 相似文献
29.
Spatial differentiation of tourism impact based on the perception of residents in mountainous valley resorts 总被引:1,自引:1,他引:0
Valley economy is a type of economy that comprehensively utilizes the natural economic and social resources of the region based on environmental protection. This economy utilizes the basic role of the market in disposing resources and achieving regional development and social progress. In this paper we studied the town of Yanqi, a valley resort that has developed tourism-based valley economy for several years in the mountainous area of Beijing. This research identifies the spatial differentiation of tourism-related economic, socio-cultural, and environmental impact and level of support for tourism according to the perception and attitude of residents of Yanqi. The research area was divided into three zones (i.e., core, transition, and peripheral) according to the standard proposed by Jaakson. The residents in all three zones showed a positive attitude toward the tourism industry, and the residents in the core zone had a stronger perception toward the impact of tourism. However, several items indicated the converse. Correlation analysis and analysis of variance were used to explore the correlative factors associated with the attitudes of residents toward the tourism industry. Results indicated major differences among the three zones. Multiple factors, including natural conditions, policies, scenic spots, dependence on the tourism industry, and external investment in the three zones resulted in the spatial differentiationof the perception and attitude of residents toward the impact of tourism. 相似文献
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