收费全文 | 12574篇 |
免费 | 124篇 |
国内免费 | 95篇 |
安全科学 | 362篇 |
废物处理 | 471篇 |
环保管理 | 1801篇 |
综合类 | 2195篇 |
基础理论 | 3280篇 |
环境理论 | 7篇 |
污染及防治 | 3122篇 |
评价与监测 | 785篇 |
社会与环境 | 679篇 |
灾害及防治 | 91篇 |
2022年 | 106篇 |
2021年 | 111篇 |
2020年 | 90篇 |
2019年 | 104篇 |
2018年 | 181篇 |
2017年 | 162篇 |
2016年 | 239篇 |
2015年 | 212篇 |
2014年 | 280篇 |
2013年 | 956篇 |
2012年 | 382篇 |
2011年 | 537篇 |
2010年 | 429篇 |
2009年 | 502篇 |
2008年 | 563篇 |
2007年 | 564篇 |
2006年 | 489篇 |
2005年 | 437篇 |
2004年 | 371篇 |
2003年 | 400篇 |
2002年 | 373篇 |
2001年 | 482篇 |
2000年 | 359篇 |
1999年 | 213篇 |
1998年 | 138篇 |
1997年 | 166篇 |
1996年 | 171篇 |
1995年 | 198篇 |
1994年 | 210篇 |
1993年 | 170篇 |
1992年 | 136篇 |
1991年 | 175篇 |
1990年 | 171篇 |
1989年 | 161篇 |
1988年 | 119篇 |
1987年 | 114篇 |
1986年 | 124篇 |
1985年 | 99篇 |
1984年 | 114篇 |
1983年 | 122篇 |
1982年 | 128篇 |
1981年 | 115篇 |
1980年 | 103篇 |
1979年 | 118篇 |
1978年 | 78篇 |
1977年 | 80篇 |
1975年 | 76篇 |
1973年 | 73篇 |
1972年 | 66篇 |
1967年 | 66篇 |
The first sections outline some of the problems facing host governments and communities in Africa and discuss the changing rhetoric between the first and second International Conferences for Assistance to Refugees in Africa. A number of possible ways in which refugees could affect the individual, agent and environmental causes of disease are considered, as are the characteristics of the refugees, the host communities and the response which may all modify this impact.
Policy implications of the impact of the refugees, both negative and positive, are discussed, and detailed consideration is given to the pros and cons of integrated and parallel approaches to health care provision. The need to monitor carefully the health status and services of host communities is emphasized and recommendations are made for this and other essential developments relating to training and research. 相似文献
The review highlights the need to reallocate resources away from high visibility emergency aid to development activities, such as training, that will create an infrastructure for primary health care and promote self-reliance. 相似文献
Both China’s national subsidy policies for plug-in electric vehicles (PEVs) purchasers and passenger cars corporate average fuel consumption and new vehicle credit regulation (dual-credit policy) favor long-range 300+ km battery electric vehicles (BEVs) and 80+ km plug-in hybrid electric vehicles (PHEVs). However, these electric vehicles tend to have lower energy efficiency and higher purchase and operation costs. Vehicle with larger batteries can also be less equitable because the subsidies are often provided to more expensive vehicles and wealthier owners. This study takes advantage of a novel dataset of daily driving data from 39,854 conventional gasoline vehicles in Beijing and 4999 PHEVs in Shanghai to determine the optimal range of BEVs and PHEVs within their respective cities. We simulate a model to explore ranges with which PEVs emit less GHGs than that of a baseline hybrid and conventional gasoline vehicle while ensuring that all daily travel demands are met. Our findings indicate that in both cities, the optimal ranges to balance cost and travel demand for BEVs are 350 km or less and for PHEVs are 60 km or less in Beijing and 80 km or less in Shanghai. We also find that to minimize carbon dioxide (CO2) emissions, the ranges are even lower 10 km in Beijing and 30 km in Shanghai. Our study suggests that instead of encouraging long-range PEVs, governments should subsidize PEV models with shorter ranges. Parallel efforts should also be made to both increase renewable energy over fossil fuels and expand charging facilities. Although individual mobility demand varies, the government could reduce occasional long-distance driving by subsidizing alternative transportation choices. Providing week-long driving trials to consumers before their purchases may help decrease the demand of very long range PEVs by alleviating the range anxiety through a learning process.
相似文献