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   1640篇
  免费   41篇
  国内免费   10篇
安全科学   64篇
废物处理   67篇
环保管理   437篇
综合类   162篇
基础理论   477篇
污染及防治   274篇
评价与监测   132篇
社会与环境   55篇
灾害及防治   23篇
  2023年   11篇
  2022年   10篇
  2021年   24篇
  2020年   16篇
  2019年   18篇
  2018年   32篇
  2017年   34篇
  2016年   51篇
  2015年   39篇
  2014年   38篇
  2013年   105篇
  2012年   82篇
  2011年   91篇
  2010年   67篇
  2009年   60篇
  2008年   83篇
  2007年   94篇
  2006年   96篇
  2005年   67篇
  2004年   62篇
  2003年   74篇
  2002年   54篇
  2001年   36篇
  2000年   39篇
  1999年   27篇
  1998年   29篇
  1997年   31篇
  1996年   28篇
  1995年   27篇
  1994年   18篇
  1993年   16篇
  1992年   22篇
  1991年   11篇
  1990年   14篇
  1989年   13篇
  1988年   13篇
  1987年   10篇
  1986年   12篇
  1985年   10篇
  1984年   14篇
  1983年   14篇
  1982年   12篇
  1981年   22篇
  1980年   10篇
  1979年   15篇
  1978年   8篇
  1977年   7篇
  1976年   8篇
  1975年   3篇
  1974年   3篇
排序方式: 共有1691条查询结果,搜索用时 93 毫秒
1.
Fifty percent of the dry zone areas in Sri Lanka have fluoride levels above 1 ppm. This paper discusses the ground conditions and recommends an appropriate range of fluoride in drinking water which can support preventive practices for improving the oral health of children 8-years old and younger. In efforts to address the Chronic Kidney Disease of Unknown etiology (CKDU), water treatment to reduce contaminant level in potable water has been implemented. Such treatment would also remove fluoride and has resulted in potable water with various fluoride levels, depending on concentrations in the raw water. While it is important to reduce fluoride levels, it is important to have appropriate residual levels for prevention of dental caries. It needs, however, to be noted fluoride in excess can cause dental fluorosis. In Sri Lanka's dry zone areas increasing prevalence of dental fluorosis with decreasing prevalence of dental caries has been noted. Consumption of tea and powdered milk could increase total intake of fluoride. Fluoridated toothpaste, when used properly, may, however, result in negligible intake of fluoride. Sri Lanka's hot tropical climate which results in substantial intake of fluids reinforces the need to consider reduction in water fluoride. Consideration of local studies and international standards indicate fluoride levels should be in the range of 0.225–0.500 ppm. In the range of 0.225–0.500 ppm, the prevalence of dental fluorosis and caries was only 14% and 8%, respectively, in an endemic district. When fluoride levels are above 0.500 ppm, the issue of dental fluorosis shall need to be addressed. When levels are below 0.225 ppm, oral health care services shall need to be directed at preventing dental caries.  相似文献   
2.
Objective: Currently only 5 out of the 50 states in the United States have laws restricting the age of passengers permitted to ride on a motorcycle. This study sought to characterize the visits by patients under the age of 16 to U.S. emergency departments (EDs) for injuries sustained as a passenger on a motorcycle.

Methods: In this retrospective cohort study, data were obtained from the Nationwide Emergency Department Sample (NEDS) for the years 2006 to 2011. Pediatric patients who were passengers on a motorcycle that was involved in a crash were identified using International Classification of Diseases, Ninth Revision (ICD-9) External Cause of Injury codes. We also examined gender, age, disposition, regional differences, common injuries, and charges.

Results: Between 2006 and 2011 there were an estimated 9,689 visits to U.S. EDs by patients under the age of 16 who were passengers on a motorcycle involved in a crash. The overall average patient age was 9.4 years, and they were predominately male (54.5%). The majority (85%) of these patients were treated and released. The average charges for discharged patients were $2,116.50 and amounted to roughly $17,500,000 during the 6 years. The average cost for admission was $51,446 per patient and totaled over $54 million. The most common primary injuries included superficial contusions; sprains and strains; upper limb fractures; open wounds of head, neck, and trunk; and intracranial injuries.

Conclusion: Although there were only about 9,700 visits to U.S. EDs for motorcycle crashes involving passengers less than 16 years old for 2006 to 2011, the total cost of visits that resulted in either ED discharge or hospital admission amounted to over $71 million.  相似文献   

3.
Regional Environmental Change - The threat of flooding poses a considerable challenge for justice. Not only are more citizens becoming exposed to risk, but they are expected to play increasingly...  相似文献   
4.
5.
ASTM E2137 (Standard Guide for Estimating Monetary Costs and Liability for Environmental Matters, or E2137) is the guidance for developing estimates of future environmental costs. E2137 provides a hierarchy of cost estimation approaches, and expresses an explicit preference for the use of probabilistic cost analysis to develop expected values for environmental costs. Dr. Ram and his colleagues have published an article (Remediation Journal, Autumn 2013) which rejects the use of EV analysis, arguing that while “good in principle” it has little practical value because it is nearly impossible to develop supportable probabilities. The E2137 principles and processes have been used for more than a decade in the context of addressing future environmental costs, yet their view of E2137 renders the standard meaningless. We conclude that the deficiency is not in the ASTM standard, and that when properly constructed, probabilistic analyses can be used to develop expected values with supportable probabilities. ©2015 Wiley Periodicals, Inc.  相似文献   
6.
This paper provides an overview of a collaborative study on visualizing climate change at the local scale. A conceptual framework has been developed, in which local scenarios and visualizations of climate change impacts and response were created to facilitate local dialogue on incorporating climate change into long-term planning and implementation of community development decisions. As part of a larger effort to generate a new integrated participatory visioning process, this paper describes a case study of the District of North Vancouver which created visualizations of changing mountain snow and landscape conditions, and provides new insights on issues and dilemmas in using realistic landscape visualizations to depict scientific modelling projections, local responses to climate change, and uncertainty. Results from this study suggest that the visualizations, and subsequent dialogue sessions, did influence emotional response to climate change as well as self-assessed understanding of adaptation and mitigation response options. However, there is a need to test this visioning process with larger heterogeneous groups of participants in order to better assess its effectiveness in enabling dialogue on local responses to climate change.  相似文献   
7.
Neanderthals disappeared sometime between 30,000 and 24,000?years ago. Until recently, Neanderthals were understood to have been predominantly meat-eaters; however, a growing body of evidence suggests their diet also included plants. We present the results of a study, in which sequential thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) were combined with morphological analysis of plant microfossils, to identify material entrapped in dental calculus from five Neanderthal individuals from the north Spanish site of El Sidrón. Our results provide the first molecular evidence for inhalation of wood-fire smoke and bitumen or oil shale and ingestion of a range of cooked plant foods. We also offer the first evidence for the use of medicinal plants by a Neanderthal individual. The varied use of plants that we have identified suggests that the Neanderthal occupants of El Sidrón had a sophisticated knowledge of their natural surroundings which included the ability to select and use certain plants.  相似文献   
8.
Ecosystem services (ES), such as biological control, pollination, soil formation, nutrient cycling in agriculture are vital for the sustainable supply of food and fibre. The current trends of decline in the ability of agricultural ecosystems to provide ES pose great threat to food security worldwide. This paper discusses the concept of ES and identifies ES associated with agriculture. It discusses the economic and ecological benefits of these ES on farmland in general and its linkages with organic agriculture. The provision of ES on farmland may help to motivate the redesign of small-scale farms using new eco-technologies based on novel and sound ecological knowledge. This has potential to meet the food demand of growing population without damaging human health and the environment.  相似文献   
9.
Organic farming is a whole-farm management approach believed to encourage biodiversity by excluding the input of agrochemicals and introducing specific management regimes for non-crop habitats. We examined the impact of the hedgerow management regime encouraged for organic farms on small mammal populations, since small mammal numbers influence a range of species at higher trophic levels and, in particular, are key to the conservation of a range of mammalian and avian predators. We compared differences in management and structure of non-crop habitats at the farm-scale between organic and conventional farms, and used within-farm variations in hedgerow size to predict the effect of hedgerow size on small mammals on both farm types. There were no significant differences in the proportion of non-crop habitats between organic and conventional farms, although management differences produced larger hedgerows on organic farms and greater diversity of hedgerow growth stages. However, a difference in hedgerow size between the farm types did not have a significant effect on small mammal abundance or diversity. We conclude that increased hedgerow size is not benefiting small mammal populations on organic farms: significant gains in small mammal numbers may be more effectively achieved by increasing the area of non-crop habitats rather than by improving management regimes.  相似文献   
10.
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