全文获取类型
收费全文 | 1434篇 |
免费 | 44篇 |
国内免费 | 71篇 |
专业分类
安全科学 | 118篇 |
废物处理 | 5篇 |
环保管理 | 305篇 |
综合类 | 479篇 |
基础理论 | 136篇 |
环境理论 | 1篇 |
污染及防治 | 39篇 |
评价与监测 | 134篇 |
社会与环境 | 132篇 |
灾害及防治 | 200篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 34篇 |
2016年 | 36篇 |
2015年 | 34篇 |
2014年 | 34篇 |
2013年 | 66篇 |
2012年 | 63篇 |
2011年 | 102篇 |
2010年 | 93篇 |
2009年 | 112篇 |
2008年 | 90篇 |
2007年 | 136篇 |
2006年 | 108篇 |
2005年 | 111篇 |
2004年 | 84篇 |
2003年 | 87篇 |
2002年 | 68篇 |
2001年 | 48篇 |
2000年 | 47篇 |
1999年 | 36篇 |
1998年 | 33篇 |
1997年 | 25篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 1篇 |
排序方式: 共有1549条查询结果,搜索用时 745 毫秒
991.
ABSTRACT: This study focused on the Sandusky Watershed (SW) in Ohio, located within the Great Lakes Basin, with emphasis on two of its subwatersheds, namely Honey Creek (HC) and Rock Creek (RC). The goal was to assess the capabilities of the Soil and Water Assessment Tool (SWAT) to simulate suspended sediment (SS), phosphorus (P) and nitrogen (N) yield in the SW that contribute major sediment and nutrient loads into Lake Erie. The model was calibrated using water flow and water quality parameters for water years 1998 to 1999 and validated model simulations covering the period of water years 2000 to 2001 for monthly conditions. The validation of SS showed correlation coefficients of 0.29 (SW), 0.75 (HC) and 0.69 (RC). Correlation coefficients for P were 0.68 (SW), 0.78 (HC) and 0.37 (RC); for N02‐N 0.84 (HC) and 0.38 (RC); for N03‐N 0.27 (HC) and 0.76 (RC); for NH3‐N 0.57 (SW), 0.49 (HC), and 0.13 (RC). In addition, mean errors, root mean square errors, Nash‐Sutcliffe coefficients, and graphs were used to compare simulated to measured data. Simulation success was variable with poor and good simulations, but in most cases, simulated water quality values followed the trend of measured data except for extreme (or intense) rainfall/runoff events. Reviews of 17 applications indicated that the SWAT is suitable for long term continuous simulations but not for storm events. A spatially distributed modeling approach generated maps showing the spatial distribution of SS, P, and N for each simulation element across the Sandusky Watershed. 相似文献
992.
Eric W. Larsen Alexander K. Fremier Evan H. Girvetz 《Journal of the American Water Resources Association》2006,42(4):1063-1075
ABSTRACT: Flow regulation impacts the ecology of major rivers in various ways, including altering river channel migration patterns. Many current meander migration models employ a constant annual flow or dominant discharge value. To assess how flow regulation alters river function, variable annual flows ‐ based on an empirical relationship between bank erosion rates and cumulative effective stream power ‐ were added into an existing migration model. This enhanced model was used to evaluate the potential geomorphic and ecological consequences of four regulated flow scenarios (i.e., different hydrographs) currently being proposed on the Sacramento River in California. The observed rate of land reworked correlated significantly with observed cumulative effective stream power during seven time increments from 1956 to 1975 (r2= 0.74, p = 0.02). The river was observed to rework 3.0 ha/yr of land (a mean channel migration rate of 7.7 m/yr) with rates ranging from 0.8 ha/yr to 5.1 ha/yr (2.0 to 13.3 m/yr), during the analyzed time periods. Modeled rates of land reworked correlated significantly with observed rates of land reworked for the variable flow model (r2= 0.78, p = 0.009). The meander migration scenario modeling predicted a difference of 1 to 8 percent between the four flow management scenarios and the base scenario. 相似文献
993.
基于GIS的灾害疏散模拟及救援调度 总被引:11,自引:0,他引:11
台风是我国东南沿海各省夏秋季中经常遭遇的自然灾害。在台风登陆之前,根据气象部门对台风发生过程及发展趋势的分析,预测防御范围,进行必要的应急疏散与救援调度,可以有效地减少人员伤亡和财产损失。研究了城市在风灾情况下进行疏散的模拟方法。将微观离散模型和宏观交通流模型相结合,采用元胞自动机原理和LW宏观交通流理论,建立了城市区域不同类型的疏散模型和应急服务规划模型,进行了人员和车辆的疏散模拟与分析,并在此基础上研制了基于GIS的灾害疏散模拟及救援调度系统,该系统可对城市防灾减灾规划和灾时应急预案的制定提供决策支持。 相似文献
994.
995.
Land Resource Sustainability for Urban Development: Spatial Decision Support System Prototype 总被引:1,自引:0,他引:1
Banai R 《Environmental management》2005,36(2):282-296
Land resource sustainability for urban development characterizes the problem of decision-making with multiplicity and uncertainty. A decision support system prototype aids in the assessment of incremental land development plan proposals put forth within the long-term community priority of a sustainable growth. Facilitating this assessment is the analytic hierarchy process (AHP), a multicriteria evaluation and decision support system. The decision support system incorporates multiple sustainability criteria, weighted strategically responsive to local public policy priorities and community–specific situations and values, while gauging and directing desirable future courses of development. Furthermore, the decision support system uses a GIS, which facilitates an assessment of urban form with multiple indicators of sustainability as spatial criteria thematically. The resultant land-use sustainability scores indicate, on the ratio-scale of AHP, whether or not a desirable urban form is likely in the long run, and if so, to what degree. The two alternative modes of synthesis in AHP—ideal and distributive—provide assessments of a land development plan incrementally (short-term) and city-wide pattern comprehensively (long-term), respectively. Thus, the spatial decision support system facilitates proactive and collective public policy determination of land resource for future sustainable urban development. 相似文献
996.
Land-Use and Land-Cover Change in Montane Mainland Southeast Asia 总被引:12,自引:1,他引:12
This paper summarizes land-cover and land-use change at eight sites in Thailand, Yunnan (China), Vietnam, Cambodia, and Laos
over the last 50 years. Project methodology included incorporating information collected from a combination of semiformal,
key informant, and formal household interviews with the development of spatial databases based on aerial photographs, satellite
images, topographic maps, and GPS data. Results suggest that land use (e.g. swidden cultivation) and land cover (e.g. secondary
vegetation) have remained stable and the minor amount of land-use change that has occurred has been a change from swidden
to monocultural cash crops. Results suggest that two forces will increasingly determine land-use systems in this region. First,
national land tenure policies—the nationalization of forest lands and efforts to increase control over upland resources by
central governments—will provide a push factor making it increasingly difficult for farmers to maintain their traditional
swidden land-use practices. Second, market pressures—the commercialization of subsistence resources and the substitution of
commercial crops for subsistence crops—will provide a pull factor encouraging farmers to engage in new and different forms
of commercial agriculture. These results appear to be robust as they come from eight studies conducted over the last decade.
But important questions remain in terms of what research protocols are needed, if any, when linking social science data with
remotely sensed data for understanding human-environment interactions. 相似文献
997.
基于GIS的南通市自然灾害风险区划 总被引:2,自引:1,他引:2
本文从自然致灾因子危险性和承灾体易损性2个方面选取评价指标,在南通市基础图件的基础上,通过GIS软件分析分别得到南通市自然致灾因子危险性分区图和社会经济易损性分区图.两图叠加后,生成南通市自然灾害风险区划基本单元,采用自下而上的定量区划方法,合并得到自然灾害风险区划图,最后分别论述了每个风险区的自然灾害和社会经济的特征.通过对风险区划指标和区域划分的探讨,以期为南通市防灾减灾工作提供科学依据. 相似文献
998.
999.
泥石流防治工程信息系统初探 总被引:3,自引:0,他引:3
结合泥石流防治工程的特点与地理信息系统的特征,探讨构建了泥石流防治工程信息系统的框架,定义了信息系统基本数据库的属性及其特征,实现了部分模块.构建泥石流防治工程信息系统主要是要使泥石流防治设计做到科学、高效、可行、可靠,且经济节约.同时西部大开发过程中面临大量的泥石流防治设计任务,目前专业设计人员缺乏,工作量大,该系统可为设计人员提供参考评价的工作平台,促进泥石流防治工作的高效运行. 相似文献
1000.
Soil erosion is a severe problem for many developing regions that lack adequate infrastructure to combat the problem. The
authors established a first-order method for prioritizing areas to be examined and remediated using preexisting data and expert
knowledge where data are lacking. The Universal Soil Loss Equation was applied to the Rio Lempa Basin in Central America using
geographic information systems and remote sensing technologies, and the estimated erosion rates were compared with sediment
delivery ratios. Spatial analysis indicates that agriculture on very steep slopes contributes only a small fraction to the
total estimated soil erosion, whereas agriculture on gentle and moderately steep slopes contributes a large fraction of the
erosion. Although much of the basin is in El Salvador, the greatest estimated amount of erosion is from Honduras. Data quality
and availability were impaired by a lack of coordination among agencies and across countries. Several avenues for improving
the authors’ methods are described. 相似文献