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:      
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   125篇
  免费   2篇
  国内免费   2篇
安全科学   4篇
废物处理   3篇
环保管理   12篇
综合类   31篇
基础理论   46篇
环境理论   1篇
污染及防治   19篇
评价与监测   4篇
社会与环境   8篇
灾害及防治   1篇
  2023年   2篇
  2022年   2篇
  2021年   5篇
  2020年   7篇
  2019年   2篇
  2018年   8篇
  2017年   9篇
  2016年   9篇
  2015年   6篇
  2014年   5篇
  2013年   8篇
  2012年   8篇
  2011年   13篇
  2010年   8篇
  2009年   11篇
  2008年   4篇
  2007年   3篇
  2006年   9篇
  2005年   1篇
  2004年   2篇
  2003年   2篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1987年   1篇
  1984年   1篇
排序方式: 共有129条查询结果,搜索用时 31 毫秒
81.
The concept of environmental innovation strategies (EIS) is introduced and discussed. The notion refers to the conduct by which non-governmental organisations (NGOs) act as policy entrepreneurs seeking to address environmental issues by going beyond the provisions of public regulations. Environmental innovation is understood as the product of a process of social interactions between heterogeneous types of actors, including NGOs. Three social mechanisms are introduced in order to capture the conditions enabling and motivating NGOs to pursue EIS, as well as the politics through which EIS are produced. These mechanisms are then discussed in the light of two in-depth case studies in Indonesia and Switzerland. The findings highlight the institutional frustration and mix of concerns that push NGOs to engage in EIS, as well as the non-spontaneous nature of environmental innovations. Innovation represents, in the end, a game of power that should be analysed as such.  相似文献   
82.
Forest reference levels (FRLs) provide a benchmark for assessing reduced emissions from deforestation and forest degradation (REDD+), and they are central to demonstrate additionality of REDD+. Attaining realistic FRLs, however, is challenging, especially in complex mosaic landscapes. We established FRLs in northern Laos for different reference periods and tested them against actual carbon stock changes. Annual time series of Landsat satellite images were used to capture the subtle changes in carbon stocks in complex landscapes characterized by shifting cultivation. We found that FRLs differ considerably depending on the reference period chosen. Abrupt land-use changes occurred when hybrid maize replaced traditional shifting cultivation and forests, and this invalidated carbon stock trends that would have been predicted had the FRL been projected into the future. We conclude that demonstrating additionality of REDD+ in fast developing areas is difficult and that payment systems rewarding potential emission reductions against hypothetical extrapolation of FRLs are unlikely to be a cost-effective strategy.  相似文献   
83.
The official environmental discourse in Laos describes a “chain of degradation” stretching from upland shifting cultivation, increased runoff and soil erosion to the siltation of wetlands and reservoirs. This perspective has had wide‐ranging impacts on rural development policy which, in the uplands, has long favoured forest conservation over agriculture. Integrating soil erosion and water sediment data with local perceptions of land degradation in an upland village of northern Laos, this study tests the validity of the official environmental discourse. Biophysical measurements made in a small agricultural catchment indicate a significant correlation between the spatial extent of cultivation and soil erosion rates. However, sediment yields recorded at the outlet of the catchment highlight relatively low levels of off‐site sediment exportation. Furthermore, farmers' perceptions suggest that local land degradation issues and crop yield declines could be less related to soil erosion than to agricultural land shortage, increased weed competition, and fertility losses resulting from the intensification of shifting cultivation. The study concludes that a better understanding and management of land degradation issues can be achieved by developing more inclusive and scientifically‐informed approaches to environmental perceptions and narratives.  相似文献   
84.
Activity sensors are increasingly being used to monitor animal activity but current methods, used to validate the relationship between the motion sensor information and the actual behavior of animals, have weaknesses. This study aims to improve the methods used to estimate activity level from dual axis activity sensors and to validate the Tellus activity sensor for reindeer (Rangifer tarandus). We developed a new approach, the recursive model (a recursive application of a logistic regression), to predict continuous values of activity without biased estimations or previous modifications of the dataset. We compared this new recursive model approach with two traditional approaches: the tree classification method and the standard model (based on simple logistic regression). Estimations from the tree classification and the standard model were dependent on the dataset used for validation, whereas the recursive model gave unbiased estimations. Estimations from standard and recursive models were also more accurate (lower average absolute errors) than those from the tree classification method and they had a slightly better discriminatory power (higher percentage of good classification). We successfully applied the recursive model for the first time and validated the Tellus activity sensor for reindeer. Any user can apply our methodology to obtain their own equations of the relationship between activity sensor values and the level of activity of the individual, and users monitoring reindeer activity with Tellus activity sensor can directly apply the provided equations under appropriate conditions.  相似文献   
85.
This study aimed at relating the variability of Ni biogeochemistry along the ultramafic toposequence to pedogenesis and soil mineralogy. Hypereutric Cambisols dominate upslope; Cambic Vertisols and Fluvic Cambisols occur downslope. The soil mineralogy showed abundance of primary serpentine all over the sequence. It is predominant upslope but secondary smectites dominate in the Vertisols. Free Fe-oxides are abundant in all soils but slightly more abundant in the upslope soils. Whereas serpentines hold Ni in a similar and restricted range in every soil (approx. 0.3 %), Ni contents in smectites may vary a lot and Mg-rich and Al-poor smectites in the Vertisol could hold up to 4.9 % Ni. Ni was probably adsorbed onto amorphous Fe-oxides and was also exchangeable in secondary smectites. High availability of Ni in soils was confirmed by DTPA extractions. However, it varied significantly along the toposequence, being higher in upslope soils, where Ni-bearing amorphous Fe-oxides were abundant and total organic carbon higher and sensibly lower downslope on the Vertisols: NiDTPA varied from 285 mg kg?1 in the surface of soil I (upslope) to 95.9 mg kg?1 in the surface of Fluvic Cambisols. Concentration of Ni in Alyssum murale shoots varied from 0.7 % (Hypereutric Cambisols) to 1.4 % (Hypereutric Vertisol). Amazingly, Ni uptake by A. murale was not correlated to NiDTPA, suggesting the existence of specific edaphic conditions that affect the ecophysiology of A. murale upslope.  相似文献   
86.
River systems are increasingly under stress and pressure from agriculture and urbanization in riparian zones, resulting in frequent engineering interventions such as bank stabilization or flood protection. This study provides guidelines for a more sustainable approach to river management based on hydrogeomorphology concepts applied to three contrasted rivers in Quebec (Canada). Mobility and flooding spaces are determined for the three rivers, and three levels of “freedom space” are subsequently defined based on the combination of the two spaces. The first level of freedom space includes very frequently flooded and highly mobile zones over the next 50 years, as well as riparian wetlands. It provides the minimum space for both fluvial and ecological functionality of the river system. On average for the three studied sites, this minimum space was approximately 1.7 times the channel width, but this minimum space corresponds to a highly variable width which must be determined from a thorough hydrogeomorphic assessment and cannot be predicted using a representative average. The second level includes space for floods of larger magnitude and provides for meanders to migrate freely over a longer time period. The last level of freedom space represents exceptional flood zones. We propose the freedom space concept to be implemented in current river management legislation because it promotes a sustainable way to manage river systems, and it increases their resilience to climate and land use changes in comparison with traditional river management approaches which are based on frequent and spatially restricted interventions.  相似文献   
87.
88.
The removal of corn stover or production of herbaceous crops such as switchgrass (Panicum virgatum) or big bluestem (Andropogon gerardii) as feedstocks for bioenergy purposes has been shown to have significant benefits from an energy and climate change perspective. There is potential, however, to adversely impact water and soil quality, especially in the United States Corn Belt where stover removal predominantly occurs and possibly in other areas with herbaceous energy crops depending upon a number of geo-climatic and economic factors. The overall goal of this research was to provide a thorough and mechanistic understanding of the relationship between stover and herbaceous crop production management practices and resulting range of impacts on soil and water quality, with a focus on eastern Iowa, USA. Comparisons of the production of herbaceous bioenergy crops to continuous corn (Zea mays L.) and corn-soybean (Glycine max L.) rotations on five different soils representative of the region were performed. Indices for total nutrient (nitrogen and phosphorus) loss to surface water and groundwater, total soil loss due to water and wind erosion, and cumulative soil carbon loss were derived to assess long-term sustainability. The Agricultural Policy/Environmental eXtender (APEX) agroecosystem model was used to quantify the sustainability indices and to generate sufficient data to provide a greater understanding of variables that affect water and soil quality than previously possible. The results clearly show the superiority of herbaceous crop production from a soil and water quality perspective. They also show, however, that compared to traditional cropping systems (e.g., corn-soybean rotations with conventional tillage), soil and water quality degradation can be reduced under certain conditions at the same time stover is removed.  相似文献   
89.
In this paper, a review of work performed in the area of force modelling in metal cutting processes is presented. Past and present trends are described and criticised to compare their relevance with current requirements. Several approaches are reviewed, such as empirical, mechanistic and analytical models. The models’ ability to predict forces, from rough machining to finish machining, is analysed.  相似文献   
90.
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