首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
  示例: 沙坡头地区,人工植被区,变化  检索词用空格隔开表示必须包含全部检索词,用“,”隔开表示只需满足任一检索词即可!
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9790篇
  免费   46篇
  国内免费   2篇
安全科学   8篇
废物处理   772篇
环保管理   1219篇
综合类   1014篇
基础理论   3137篇
污染及防治   1762篇
评价与监测   1019篇
社会与环境   907篇
  2024年   1篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   8篇
  2019年   3篇
  2018年   1481篇
  2017年   1377篇
  2016年   1200篇
  2015年   133篇
  2014年   25篇
  2013年   22篇
  2012年   475篇
  2011年   1348篇
  2010年   697篇
  2009年   606篇
  2008年   882篇
  2007年   1231篇
  2006年   12篇
  2005年   29篇
  2004年   47篇
  2003年   69篇
  2002年   98篇
  2001年   19篇
  2000年   11篇
  1999年   4篇
  1998年   10篇
  1997年   1篇
  1996年   4篇
  1995年   1篇
  1994年   3篇
  1992年   2篇
  1990年   2篇
  1988年   1篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   11篇
  1983年   8篇
  1982年   1篇
  1969年   1篇
  1961年   1篇
  1935年   2篇
排序方式: 共有9838条查询结果,搜索用时 23 毫秒
901.
902.
This paper examines predictors of vegetative cover on private lands in Baltimore, Maryland. Using high-resolution spatial data, we generated two measures: “possible stewardship,” which is the proportion of private land that does not have built structures on it and hence has the possibility of supporting vegetation, and “realized stewardship,” which is the proportion of possible stewardship land upon which vegetation is growing. These measures were calculated at the parcel level and averaged by US Census block group. Realized stewardship was further defined by proportion of tree canopy and grass. Expenditures on yard supplies and services, available by block group, were used to help understand where vegetation condition appears to be the result of current activity, past legacies, or abandonment. PRIZM™ market segmentation data were tested as categorical predictors of possible and realized stewardship and yard expenditures. PRIZM™ segmentations are hierarchically clustered into 5, 15, and 62 categories, which correspond to population density, social stratification (income and education), and lifestyle clusters, respectively. We found that PRIZM 15 best predicted variation in possible stewardship and PRIZM 62 best predicted variation in realized stewardship. These results were further analyzed by regressing each dependent variable against a set of continuous variables reflective of each of the three PRIZM groupings. Housing age, vacancy, and population density were found to be critical determinants of both stewardship metrics. A number of lifestyle factors, such as average family size, marriage rates, and percentage of single-family detached homes, were strongly related to realized stewardship. The percentage of African Americans by block group was positively related to realized stewardship but negatively related to yard expenditures.  相似文献   
903.
Agri-environment programs aim to secure environmental and social stewardship services through payments to farmers. A critical component of many agri-environment programs is an agri-environment index (AEI) used to quantify benefits and target investments. An AEI will typically comprise multiple indicators, which are weighted and combined using a utility function, to measure the benefit of investment options (e.g., projects, farms, regions). This article presents a review of AEIs with 11 case studies from agri-environment programs in the United States, Australia, and the United Kingdom. We identify a generic procedure used to define AEIs and explore the implications of alternative methodological approaches. We conclude that AEIs have become an extremely important policy instrument and make suggestions for their improvement.  相似文献   
904.
The microbiological and physico-chemical characteristics of the drinking water supplied by the Central Borehole at the University of Benin, Ugbowo Campus were investigated. The investigation entailed assessment of the pH, turbidity, total suspended solids, total dissolved solids, dissolved oxygen, temperature, salinity, conductivity, nitrate, nitrite, phosphate, sulphate, chloride, N-nitroso compounds, cadmium, chromium, nickel, lead, zinc, manganese, iron, coliform count, BOD5 and COD of the water at the Central Borehole and at ten residential quarters. The assessment indicated that the water was fit for drinking and other domestic applications. Results were also compared with WHO, EU and Nigeria FEPA standards. The results showed that the pH values of the water (5.01–5.86) and total coliform count (1–2/100 ml) expressed as MPN were outside the limits set by the WHO, EU and FEPA. The data also showed that the other water quality parameters assessed were within WHO, EU and FEPA permissible limits. The results of ANOVA showed that significant changes occurred during distribution.  相似文献   
905.
Analysis tools that combine large spatial and temporal scales are necessary for efficient management of wildlife species, such as the burrowing owl (Athene cunicularia). We assessed the ability of Ripley’s K-function analysis integrated into a geographic information system (GIS) to determine changes in burrowing owl nest clustering over two years at NASA Ames Research Center. Specifically, we used these tools to detect changes in spatial and temporal nest clustering before, during, and after conducting management by mowing to maintain low vegetation height at nest burrows. We found that the scale and timing of owl nest clustering matched the scale and timing of our conservation management actions over a short time frame. While this study could not determine a causal link between mowing and nest clustering, we did find that Ripley’s K and GIS were effective in detecting owl nest clustering and show promise for future conservation uses.  相似文献   
906.
It has traditionally been argued that recycling municipal solid waste (MSW) is usually not economically viable and that only when externalities, long-term dynamic considerations, and/or the entire product life cycle are taken into account, recycling becomes worthwhile from a social point of view. This article explores the results of a wide study conducted in Israel in the years 2000–2004. Our results reveal that recycling is optimal more often than usually claimed, even when externality considerations are ignored. The study is unique in the tools it uses to explore the efficiency of recycling: a computer-based simulation applied to an extensive database. We developed a simulation for assessing the costs of handling and treating MSW under different waste-management systems and used this simulation to explore possible cost reductions obtained by designating some of the waste (otherwise sent to landfill) to recycling. We ran the simulation on data from 79 municipalities in Israel that produce over 60% of MSW in Israel. For each municipality, we were able to arrive at an optimal method of waste management and compare the costs associated with 100% landfilling to the costs born by the municipality when some of the waste is recycled. Our results indicate that for 51% of the municipalities, it would be efficient to adopt recycling, even without accounting for externality costs. We found that by adopting recycling, municipalities would be able to reduce direct costs by an average of 11%. Through interviews conducted with representatives of municipalities, we were also able to identify obstacles to the utilization of recycling, answering in part the question of why actual recycling levels in Israel are lower than our model predicts they should be.  相似文献   
907.
A historical perspective on MPA identification and governance in South Africa reflects the continued influence of a top-down and natural science-based paradigm, that has hardly changed over the past half century, despite the wealth of literature, and a growing consensus, that advocates the need to adopt a more integrated and human-centered approach. Based on extensive research in two coastal fishing communities, the paper highlights impacts and conflicts arising from this conventional approach to MPA identification, planning and management. It argues that failure to understand the particular fishery system in all its complexity, in particular the human dimensions, and involve resource users in planning and decision-making processes, undermines efforts to achieve conservation and fisheries management objectives. The customary rights of local resource users, and their food and livelihood needs in relation to marine resources, need to be acknowledged, prioritized and integrated into planning and decision-making processes. Convincing ecologists, fisheries scientists and managers, that MPA success depends on addressing the root causes of resource decline and incorporating social factors into MPA identification, planning and management, remains a huge challenge in South Africa.  相似文献   
908.
Adaptations in infrastructure may be necessitated by changes in temperature and precipitation patterns to avoid losses and maintain expected levels of service. A roster of adaptation strategies has emerged in the climate change literature, especially with regard to timing: anticipatory, concurrent, or reactive. Significant progress has been made in studying climate change adaptation decision making that incorporates uncertainty, but less work has examined how strategies interact with existing infrastructure characteristics to influence adaptability. We use a virtual testbed of highway drainage crossings configured with a selection of actual culvert emplacements in Colorado, USA, to examine the effect of adaptation strategy and culvert characteristics on cost efficiency and service level under varying rates of climate change. A meta-model approach with multinomial regression is used to compare the value of better climate change predictions with better knowledge of existing crossing characteristics. We find that, for a distributed system of infrastructural units like culverts, knowing more about existing characteristics can improve the efficacy of adaptation strategies more than better projections of climate change. Transportation departments choosing climate adaptation strategies often lack detailed data on culverts, and gathering that data could improve the efficiency of adaptation despite climate uncertainty.  相似文献   
909.
910.
Fish production and marketing are as old as the rural communities involved in the lucrative occupation in Badagry area of Lagos State, Nigeria. A random sampling of 200 fishermen using Participatory Rural Appraisal techniques (PRA) in five Badagry villages was used to explore coastal fishing and socio-economic development in the study area with a view to enhancing local productivity and sustainability. The findings show that an average fisherman in Badagry is aware of the resources available in his environment, and can affect productivity levels positively if given adequate incentives. There are two lessons from this study; one has to do with what PRA tells us about the fishing community, the other is the importance of facilitators that have, amongst other things, good listening skills. The experience also revealed that field workers’ ability to listen and learn from local fishermen was a critical factor in collecting in-depth information that could be used for rural community planning.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号