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   170篇
  免费   16篇
  国内免费   10篇
安全科学   3篇
环保管理   54篇
综合类   60篇
基础理论   35篇
污染及防治   9篇
评价与监测   10篇
社会与环境   17篇
灾害及防治   8篇
  2023年   1篇
  2022年   3篇
  2021年   10篇
  2020年   4篇
  2019年   5篇
  2018年   7篇
  2017年   13篇
  2016年   10篇
  2015年   8篇
  2014年   7篇
  2013年   19篇
  2012年   5篇
  2011年   14篇
  2010年   1篇
  2009年   9篇
  2008年   4篇
  2007年   10篇
  2006年   14篇
  2005年   6篇
  2004年   8篇
  2003年   5篇
  2002年   4篇
  2001年   3篇
  2000年   4篇
  1999年   1篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   2篇
  1993年   2篇
  1991年   2篇
  1988年   2篇
  1987年   1篇
  1984年   1篇
  1983年   2篇
  1979年   1篇
排序方式: 共有196条查询结果,搜索用时 31 毫秒
51.
The economic inputs and outputs for the Possum Point Biological Station in Belize during 1990–1992 are described to illustrate some aspects of an ecotourism operation. Eight hundred fifty-four people in 59 groups visited Possum Point during the study period to tour rain forests, estuaries, and coral reefs. The economic input to Possum Point from these groups increased from $74,552 in 1990 to $166,268 in 1992. Outputs were for license fees, capital improvements, goods and services, labor, fossil fuels, and development of a historic sugar mill site. An annual donation was also made to a scholarship fund for local Belizean students. The net cash balance of income and outputs changed from negative (−$6678) in 1990 to positive (+$4811) in 1992, suggesting development of the economic operation. Possum Point meets the economic criteria for ecotourism by feeding back some tourist monies for community and environmental support, particularly donations for the sugar mill site and the scholarship fund. Most of the outputs from Possum Point (about 80%) were retained in the local economy through employment and purchases, which have a positive influence on the local community. We conclude that ecotourism operations, such as Possum Point, offer important sustainable development opportunities for Belize.  相似文献   
52.
在对大连市凌水地区实施集中供热前后的环境效益进行定性分析比较的基础上,应用环境经济学的费用效益分析方法,对集中供热的环境效益进行了效益定量化估算,结果表明:实行区域集中供热联片取暖10年后投资费效比为1∶3.3。  相似文献   
53.
Urbanization can exert a profound influence on land covers and landscape characteristics. In this study, we characterize the impact of urbanization on land cover and lacustrine landscape and their consequences in a large urban lake watershed, Donghu Lake watershed (the largest urban lake in China), Central China, by using Landsat TM satellite images of three periods of 1987, 1993 and 1999 and ground-based information. We grouped the land covers into six categories: water body, vegetable land, forested land, shrub-grass land, open area and urban land, and calculated patch-related landscape indices to analyze the effects of urbanization on landscape features. We overlaid the land cover maps of the three periods to track the land cover change processes. The results indicated that urban land continuously expanded from 9.1% of the total watershed area in 1987, to 19.4% in 1993, and to 29.6% in 1999. The vegetable land increased from 7.0% in 1987, 11.9% in 1993, to 13.9% in 1999 to sustain the demands of vegetable for increased urban population. Concurrently, continuous reduction of other land cover types occurred between 1987 and 1999: water body decreased from 30.4% to 23.8%, and forested land from 33.6% to 24.3%. We found that the expansion of urban land has at least in part caused a decrease in relatively wild habitats, such as urban forest and lake water area. These alterations had resulted in significant negative environmental consequences, including decline of lakes, deterioration of water and air quality, and loss of biodiversity.  相似文献   
54.
We assessed relationships between environmental characteristicsand macroinvertebrate assemblages in lotic habitats of California's Central Valley with community metric and multivariate statistical approaches. Using canonical ordinationanalyses, we contrasted results when assemblage structure was assessed with macroinvertebrate metrics, as suggested for use inindices of biotic integrity, or with genera abundances. Our objectives were to identify metrics or taxa diagnostic of loticenvironmental stressors and compare the capacity of theseapproaches to detect stressors in order to suggest how they mightbe used to diagnose stressors. For macroinvertebrate metrics,redundancy analysis (RDA) extracted three axes correlated withchannel morphology and substrates. For genera abundances, canonical correspondence analysis (CCA) extracted two axescorrelated with soluble salts and with channel morphology andsubstrates but did not separate these gradients onto differentaxes. Cluster analyses identified five RDA and five CCA sitegroups, which exhibited differences for environmental variables,metrics, or genera abundances, and agreement between the analysesin partitioning of sites was greater than if sites were partitioned randomly. These approaches differ in their abilityto detect environmental stressors, because they measure differentaspects of assemblages and would be complementary in design ofnew metrics diagnostic of stressors.  相似文献   
55.
The thawing and subsequent decomposition of large stocks of soil organic carbon (SOC) currently stored in the northern circumpolar permafrost region are projected to result in a ‘positive’ feedback on global warming. The magnitude of this feedback can only be assessed with improved knowledge about the total size and geographic distribution of the permafrost SOC pool. This study investigates SOC storage in an under-sampled mountain permafrost area in the Russian High Altai. SOC stocks from 39 soil pits are upscaled using a GIS-based land cover classification. We found that the top 100 cm of soils in Aktru Valley and the adjacent Kuray Basin only holds on average 2.6 ± 0.6 kg C m−2 (95% confidence interval), of which only c. 1% is stored in permafrost. Global warming will result in an upward shift of alpine life zones, with new plant cover and soil development at higher elevations. As a result, this type of mountain permafrost area might act as a net C sink in the future, representing a ‘negative’ feedback on global warming.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01433-6) contains supplementary material, which is available to authorized users.  相似文献   
56.
建设秦岭国家中央公园的探究   总被引:1,自引:0,他引:1  
杨亭  丁艳平 《资源开发与保护》2012,(5):475-478,F0003
通过对秦岭的综合分析,借鉴国外"国家公园"的建设经验,从秦岭目前开发现状存在的问题及其原因进行分析研究,提出应成立国家秦岭管理局,科学开发保护秦岭,分不同区域建设秦岭国家中央公园;在发展生态旅游的同时,积极整合资源,争取加入世界人与生物圈,联合申遗,推动秦岭走向世界,从而实现秦岭地区人与自然的可持续发展。  相似文献   
57.
In order to evaluate the influence of faulting on the variability of geogenic radon at detailed scale (1:2000), data on gamma ray fluxes, U and Th concentrations in rocks, radon in soil-gas and radon in groundwater were collected in three target areas on the Oliveira do Hospital region (Central Portugal). This region stands on the Iberian Uranium Province, and is dominantly composed of Hercynian granites and metasedimentary rocks of pre-Ordovician age, crosscut by faults with dominant strike N35°E, N55°E and N75°E. Radiometric anomalies are frequent, associated with faults of the referred systems and metasedimentary enclaves; the analytical data confirms that these anomalies are produced by local high uranium contents in rocks and fault-filling materials (n = 34, range 13-724 ppm), while other radiogenic elements are relatively constant (e.g. Th 4-30 ppm). Radon concentration in soil can be extremely high, up to 12,850 kBq m−3 (n = 215), with a large proportion of results above 100 kBq m−3. Unsurprisingly, groundwater also shows high radon concentrations, with observed values in the range 150-4850 Bq.L−1 (n = 17). From the results it is concluded that metasedimentary enclaves, as well as faults, can accumulate uranium from circulating fluids, and as a consequence, strongly locally enhance geogenic radon potential. Due to this fact, for the purpose of land use planning in such uranium-enriched regions, very detailed geological mapping is needed to precisely recognize radon high risk areas. A correlation between radon concentration in soil or in groundwater and gamma ray fluxes was established pointing to the possible use of these fluxes as a first step in assessing geogenic radon potential, at least to geological setting similar to the study area.  相似文献   
58.
Water Resources of Central Asia and Adaptation Measures for Climate Change   总被引:1,自引:0,他引:1  
A large part of the Central Asian region is located within the inner flow of the Aral Sea basin. The water resources are formed from renewed superficial and underground waters of natural origin, and also with returnable waters. The intensive increase of water intake, that took place in the second half of the twentieth century caused practically complete assimilation of the river inflow. That was the main reason for the Aral Sea crisis. On the basis of the analysis of long periodical rows of observation by meterological and hydrological stations, the estimation of regional water resources and calculations of changes of some components of the hydrological cycle due to the expected climate changes are presented. Measures for adaptation in the southern part of the Aral Sea region are considered.  相似文献   
59.
Caballero, Luis A., Alon Rimmer, Zachary M. Easton, and Tammo S. Steenhuis, 2012. Rainfall Runoff Relationships for a Cloud Forest Watershed in Central America: Implications for Water Resource Engineering. Journal of the American Water Resources Association (JAWRA) 48(5): 1022‐1031. DOI: 10.1111/j.1752‐1688.2012.00668.x Abstract: Understanding the basic relationships between rainfall and runoff is vital for effective management and utilization of scarce water resources. Especially, this is important in Central America with widespread potable water shortage during the dry months of the monsoon. Potential good water sources are cloud forests, but little information concerning its potential is available to water supply engineers. Our objective is to define rainfall‐runoff‐base flow relationships for a cloud forest catchment. Flumes were installed for measuring river flow in four subwatersheds in La Tigra National Park, Honduras. One of the four watersheds was a 636‐ha subwatershed (WS1) with 60% cloud forest coverage. Precipitation averaged 1,130 mm/yr over the entire basin. About half of the total rainfall became runoff for the cloud forest watershed whereas, for the adjacent undisturbed forested watershed, the total discharge was <20% of the amount of precipitation. Infiltration rates were generally greater than rainfall rates. Therefore, most rainfall infiltrated into the soil, especially in the upper, steep, and well‐drained portions of the watershed. Direct runoff was generated from saturated areas near the river and exposed bedrock. This research provides compelling evidence that base flow is the primary contributor to streamflow during both wet and dry seasons in cloud forest catchments. Protecting these flow processes over time is critical for the sustained provision of potable water.  相似文献   
60.
本文介绍了碳金融的定义以及中国构建完善碳金融体系的背景,指出我国的CDM市场虽然是全球最大的CDM市场,但碳金融还处于起步阶段,缺乏国际CERs定价权,CDM项目存在巨大的风险,这些问题亟需解决。中国的银行业作为中国金融机构的主要组成部分,在构建完善的碳金融市场上起到了十分关键的作用。分析了目前中国银行业参与碳金融的现状及存在的问题,提出了中央银行和中国商业银行介入碳金融的方法。中央银行应与商业银行相互配合使中国的碳金融市场尽快发展和完善。  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