全文获取类型
收费全文 | 916篇 |
免费 | 55篇 |
国内免费 | 233篇 |
专业分类
安全科学 | 72篇 |
废物处理 | 12篇 |
环保管理 | 175篇 |
综合类 | 368篇 |
基础理论 | 328篇 |
环境理论 | 3篇 |
污染及防治 | 90篇 |
评价与监测 | 45篇 |
社会与环境 | 92篇 |
灾害及防治 | 19篇 |
出版年
2024年 | 9篇 |
2023年 | 17篇 |
2022年 | 24篇 |
2021年 | 40篇 |
2020年 | 27篇 |
2019年 | 35篇 |
2018年 | 43篇 |
2017年 | 46篇 |
2016年 | 59篇 |
2015年 | 36篇 |
2014年 | 39篇 |
2013年 | 86篇 |
2012年 | 57篇 |
2011年 | 81篇 |
2010年 | 38篇 |
2009年 | 68篇 |
2008年 | 43篇 |
2007年 | 73篇 |
2006年 | 67篇 |
2005年 | 39篇 |
2004年 | 28篇 |
2003年 | 37篇 |
2002年 | 31篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 2篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1204条查询结果,搜索用时 31 毫秒
771.
772.
Bangladesh suffered the century's worst flood during July-October 1998 and appealed for assistance. To provide information for appropriate interventions to tackle nutritional problems, a rapid assessment survey was conducted to look at the nutritional situation, problems encountered by the community, their coping mechanisms and rehabilitation priorities in six rural areas. The survey was repeated after four months to measure the outcome of activities during the flood and the necessity for future assistance. There were 3,048 children measured in both surveys (1,597 and 1,451). The sample of most interest was a sub-group of 180 children present in two previous independent surveys. The analysis found that while moving from the crisis period to post-flood phase there was evidence of a 'crossover phenomenon' in the recovery pattern of nutritional status. Sixty-eight per cent of the children who were malnourished (WHZ < -2SD) during the crisis period (18 per cent) recovered enough to cross the cut-off point and became normal after four months. Another 8 per cent of children (9 per cent of all normal) who were normal during the crisis period, after four months had deteriorated to be malnourished. Thus, despite there being a shift in the overall distribution of nutritional status, there has been another shift that reduced the net effect. Subsequent episodes of diarrhoea, access to food and loan burden had also influenced the recovery pattern of the children's nutritional status as evident from the statistically significant associations. These findings raise questions about targeting acute malnutrition during emergencies, and using the same criteria during both the crisis and rehabilitation phases. 相似文献
773.
Preston BL 《Environmental management》2002,29(3):311-323
Understanding toxicant effects at higher levels of biological organization continues to be a challenge in ecotoxicology and
ecological risk assessment. This is due in part to a tradition in ecotoxicology of considering the direct effects of toxicants
on a limited number of model test species. However, the indirect effects of toxicity may be a significant factor influencing
the manner in which ecosystem structure and function respond to anthropogenic stressors. Subsequently, failure to incorporate
indirect effects into risk assessment paradigms may be a significant source of uncertainty in risk estimates. The current
paper addresses the importance of indirect effects in an ecotoxicological context. Laboratory, mesocosm, and whole ecosystem
research into indirect effects is reviewed. The implications of indirect effects for ecological risk assessment and potential
areas of profitable future research are also discussed. 相似文献
774.
Mountain biking is an increasingly popular leisure pursuit. Consequences are trail degradation and conflicts with hikers and other users. Resource managers often attempt to resolve these problems by closing trails to mountain biking. In order to estimate the impact of these developments, a model has been devised that predicts the effects of changes in trail characteristics and introduction of access fees, and correlates these with biker preference on trail selection. It estimates each individual's per-ride consumer's surplus associated with implementing different policies. The surplus varies significantly as a function of each individual's gender, budget, and interest in mountain biking. Estimation uses stated preference data, specifically choice experiments. Hypothetical mountain bike trails were created and each surveyed biker was asked to make five pair-wise choices. A benefit-transfer simulation is used to show how the model and parameter estimates can be transferred to estimate the benefits and costs to mountain bikers in a specific area. 相似文献
775.
ABSTRACT: Catch in standard (unshielded) rain gages exposed 3 feet above the land surface was compared with catch in pit (buried) gages exposed 1 inch above the land surface. These tests confirmed that catch in standard gages under estimates point rainfall in forest openings, as well as in conventional weather stations. Pit gages caught significantly (P=0.05) more rain than did standard gages at each of four locations tested. Catch increases ranged from 2.3 to 3.4 percent. 相似文献
776.
Jorma K. Miettenen 《Environmental management》1988,12(1):1-3
Summary The risks of radioactivity are a really complicated matter, yet they are much better known than are the risks relating to thousands of chemical poisons that occur in our environment. The greatest mistakes are probably made in the definition of safety margins. Except for the bombs dropped in Japan and one other case in the Marshall Islands, there has always—luckily—been a wide safety margin between fallout radiation and doses dangerous to health; the margin has actually been about 1000-fold. The Chernobyl dose of 0.5 mGy/year that we received is only 1/1000 of the acute dose of 0.5 Gy which would cause a slight and nonpermanent change in the blood picture.There is no such safety margin with respect to many air pollutants. The safety standards for sulfuric or nitric oxides, ozone and so on, have been set only just below the level that already causes a health hazard, and these standards are exceeded once in a while. Otherwise, traffic would have to be forbidden and many industrial plants, especially power stations using coal, would have to stop working whenever a low-temperature inversion occurred. Environmental radioactivity does not represent a likely health risk in Finland unless a nuclear war breaks out. Air pollutants, on the contrary, are a real and almost daily health risk that should be carefully considered when decisions about our energy production are being made.In spite of what happened at Chernobyl, global consumption of nuclear power will double by the year 2000, since there are about 140 nuclear power plants presently under construction. It is not likely that another catastrophe like Chernobyl will happen, yet nuclear plant accidents are of course possible, even if their likelihood is diminished by improving reactor safety and even if any eventual damage could be expected to be smaller. If a reactor is hooded by a containment structure, no significant release of radioactive materials should be possible even in case of an accident. However, we must be prepared to protect the population with carefully planned civil defense and radiation protection measures.I would like to sum up all of this as follows: The risks of radiation are a fact, but the fear they arouse is often disproportionate. There are risks related to all other methods of energy production as well; nuclear power is no exception in that respect. It is good that we aim at greater safety, but I hope that false presumptions will not lead us to mistaking a less safe alternative for a safer one. 相似文献
777.
Natural factors and human modifications contribute to the estimated annual loss of 10,200 ha of coastal land in the Mississippi River Deltaic Plain Region of south Louisiana. This paper combines information on regional geology and human-induced habitat alterations to evaluate the relative importance of human and natural factors to marsh loss. Data on marsh area and habitat type for 139 7.5-min quadrangles were calculated from maps based on aerial photographs from 1955/56 and 1978, and data on regional geology obtained from published maps were used to construct multivariate model relating initial marsh area, change in urban and agricultural area, change in canal and spoil area, canal area in 1978, depth of sediment overlying the Prairie terrace, and subdelta age to marsh loss. The model indicated that between 25.0% and 39.0% of the marsh loss that occurred during the 23-year period was related to canal and spoil construction, and between 9.5% and 12.7% was related to urban and agricultural development. These are minimal estimates of loss because they do not include many secondary effects (for example, canal orientation, saltwater intrusion, and eutrophication) that can also result in indirect loss. Depth of sediment, initial marsh area, delta lobe age by 1978 canal and spoil area interaction, and indirect effects not included in the model accounted for remaining marsh loss. 相似文献
778.
周宏春 《中国人口.资源与环境》1993,3(4):31-35
水资源危机在我国已显端倪。本文主要讨论水资源分布特征,随着人口急增以及水资源超采不合理使用,已产生了一系列的环境地质问题,如地下水位持续下降、地面沉降、海水入侵、地面塌陷和地裂缝、水质恶化等。为此,提出了地下水资源开发利用的建议。 相似文献
779.
Philip Irvin 《Journal of the American Water Resources Association》1986,22(4):597-599
ABSTRACT: The annual distribution of flow in a drainage basin within a given region is a function of many factors. These may include annual distribution of rainfall, basin orientation, ground cover, or presence of glaciers. Since the North Cascades region of northern Washington State has little variation in precipitation distribution by month, and the region has significant snowpack, one would predict that in an unregulated basin, basin elevation would be one of the most important factors impacting an annual hydrograph distribution. Such a prediction can be made since the higher a drainage basin is, the larger the portion of runoff that would occur as late spring snowmelt. Given that there is a relationship between elevation distribution and annual hydrograph, the problem becomes one of how to use this relationship to model an ungaged basin's hydrograph. This study concludes that, within the North Cascades region and perhaps within other regions, an effective method of determining annual flow distribution is to model ungaged flows in the same manner as flows from a gaged basin with an elevation distribution similar to that of the subject basin. 相似文献
780.
Patrick Squires 《Journal of the American Water Resources Association》1971,7(5):951-955
ABSTRACT. A review of the development of weather modification to augment precipitation including the cloud-physical foundation is presented. Recent work has tended to re-emphasize the importance of physical understanding of storm systems and of the effects of cloud seeding. The Pyramid Lake Seeding Project is discussed. 相似文献