全文获取类型
收费全文 | 258篇 |
免费 | 8篇 |
国内免费 | 29篇 |
专业分类
安全科学 | 2篇 |
环保管理 | 90篇 |
综合类 | 136篇 |
基础理论 | 32篇 |
污染及防治 | 18篇 |
评价与监测 | 9篇 |
社会与环境 | 8篇 |
出版年
2023年 | 3篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 11篇 |
2012年 | 22篇 |
2011年 | 26篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 14篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有295条查询结果,搜索用时 15 毫秒
61.
洪泽湖湿地资源保护与可持续利用研究 总被引:20,自引:0,他引:20
洪泽湖湿地生物多样性比较丰富,湿地植被群丛多样,重点保护鸟类种类众多,种群数量大。调查结果显示:洪泽湖湿地共鉴定出浮游植物165种、水生高等植物81种、浮游动物91种、底栖动物69种、鱼类102种、鸟类194种。我们研究了洪泽湖湿地的大气、河流、湖泊环境质量,在分析洪泽湖湿地的破坏程度和原因后,提出了洪泽湖湿地保护对策和可持续利用途径。 相似文献
62.
洞庭湖区湿地生物多样性保护及其可持续利用 总被引:9,自引:0,他引:9
洞庭湖区是我国最大的淡水湖泊湿地之一,复杂多样的湿地类型和生态环境蕴含了丰富的生物资源,但长期以来由于人类不合理的开放利用,导致了洞庭湖区湿地面积和景观结构发生了很大变化,湿地生态功能也遭到严重破坏,生物多样性不断减少,本文分析了洞庭湖区湿地生物多样性现状及保护的意义,湿地生物多样性面临的威胁,并提出了洞庭湖区湿地生物多样性保护及其可持续利用的主要对策。 相似文献
63.
64.
65.
研究构建了2组表流人工湿地模拟系统和3组潜流人工湿地模拟系统,种植菖蒲、芦苇,在平均进水COD、TN、NH_4~+-N、NO_3~--N、NO_2~--N浓度分别为110、21、6、9以及6 mg/L,进水流速为42 m L/min,水力停留时间为6 h的条件下,研究典型内分泌物双酚A(BPA)和2,4-二氯苯酚在浓度为2 mg/L时对人工湿地的运行效果影响。结果表明,两种内分泌干扰物对人工湿地的污染物去除均有抑制作用。在COD去除上,两种内分泌干扰物对表流人工湿地的负面影响要高于潜流人工湿地。在各类N元素的去除上,在潜流人工湿地中,添加BPA的负面影响要高于添加2,4-二氯苯酚。 相似文献
66.
湿地土壤有机碳及其活性组分分布特征影响因素研究 总被引:1,自引:0,他引:1
红碱淖湖泊湿地是西北半干旱荒漠区重要的生态屏障,随着湖泊面积的减少以及土壤退化程度的加剧,逐渐形成5种典型的景观类型(盐碱沼泽、沼泽化草甸、草地、草原化沙地、沙地)。基于野外实地调查,选取红碱淖湖泊湿地流域蟒盖兔和尔林兔2个典型子流域,研究湖泊退化后不同景观类型土壤有机碳及其活性组分的分布特征及其影响因素。结果表明,5种景观类型土壤有机碳(SOC)、土壤可溶性有机碳(DOC)、土壤易氧化态有机碳(EOC)含量均较低。土壤SOC和EOC在垂直剖面上分布特征一致,土壤EOC与土壤有机质动态变化密切相关,土壤砂砾含量高是研究区土壤有机碳含量较低的主要原因。 相似文献
67.
Emergy evaluation and economic analysis of three wetland fish farming systems in Nansi Lake area,China 总被引:2,自引:0,他引:2
Emergy and economic methods were used to evaluate and compare three fish production models, i.e., cage fish farming system, pond intensive fish rearing system and semi-natural extensive pond fish rearing system, in Nansi Lake area in China in the year 2007. The goal of this study was to understand the benefits and driving forces of selected fish production models from ecological and economic points of view. The study considered input structure, production efficiency, environmental impacts, economic viability and sustainability. Results show that the main difference among the three production systems was the emergy cost for fish feed associated with their feeding system, i.e., feeding on natural biomass such as plankton and grass or on commercial feedstock. As indicated by EYR, ELR and ESI, it can be clearly shown that the intensive production model with commercial feed is not a sustainable pattern. However, the point is that more environmentally sound patterns do not seem able to provide a competitive net profit in the short run. The intensive pond fish farming system had a net profit of 2.57E+03 $/ha, much higher than 1.27E+03 $/ha for cage fish farming system and slightly higher than 2.37E+03 $/ha for semi-natural fish farming system. With regard to the drivers of local farmer’s decisions, the accessibility of land for the required use and investment ability determine the farmer’s choice of the production model and the scale of operation, while other factors seem to have little effect. Theoretically, the development of environmentally sustainable production patterns, namely water and land conservation measures, greener feed as well as low waste systems is urgently needed, to keep production activities within the carrying capacity of ecosystems. Coupled emergy and economic analyses can provide better insight into the environmental and economic benefits of fish production systems and help solve the problems encountered during policy making. 相似文献
68.
Fertility status and management implications of wetland soils for sustainable crop production in Akwa Ibom State, Nigeria 总被引:1,自引:0,他引:1
Fertility status of soils of three wetland types in Akwa Ibom State, Nigeria, was investigated. The wetland types are Inland
Valley (IV), Flood Plain (FP) and Mangrove (MG). The soils have silt-clay ratios above 0.15 and 0.25 indicating that they
are of young parent materials with low degree of weathering and possible weatherable minerals for plant nutrition. The pH
of the soils was near neutral (>6.4) when wet but extremely acid (>3.5) when dried indicating that the soils are potential
acid sulphate soils. Organic matter content was high with mean values of 12.59, 6.03 and 3.20% for IV, FP and MG soils, respectively.
Total N (nitrogen) was low except in IV soils where the value was above the 0.30% critical level. The C:N ratios were narrow
with mean of 20.90, 12.17 and 12.12 for IV, FP and MG soils, respectively. The contents of basic cations [Calcium (Ca), Magnesium
(Mg), Potasium (K) and Sodium (Na)] were low while acidic cations [Aluminium (Al) and Hydrogen (H)] were high. The Ca:Mg ratios
were below the optimum range of 3:1 to 4:1 required for most crops. The Mg:K ratios were above 1.2, below which yields of
crops like corn and soybean may be reduced. Effective cation exchange capacity (ECEC) was below the 20 cmol/kg. Percent base
saturation was low (<38) indicating that the soils are potentially less fertile. Exchangeable Al and percent Al saturation
were high, above 60% in IV and FP soils. Electrical conductivity was above the critical value of 2 dsm−1 while exchangeable sodium percentage was less than 15. Available Phosphorus (P) and low, <10 ppm and free Fe2O3/clay ratios were <0.15. Positive correlation existed between silt and ECEC, implying that silt contributed to nutrient status
of the soils. Generally, fertility status of the soil is low and would require maintenance of adequate organic matter, application
of lime and organic and inorganic fertilizers, drainage and irrigation if the land is to be used for intensive/sustainable
crop production.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
69.
为了研究湿地不同退水时间条件下土壤种质资源与地表植被关系的特征,在三个不同的水位条件下,通过幼苗萌发法对野鸭湖湿地近十年来退水湿地面积中土壤种子资源的分布格局进行了研究,同时,对该区域的地表植被在不同退水时间条件下进行了春、夏、秋三次统计。结果表明,土壤中的种子与地表植被在不同的退水时间条件下,差异显著。文章同时还分析了在不同退水时间条件下,土壤种质资源与地表植被产生差异的原因,为今后利用土壤种子资源在湿地恢复和湿地保护过程中的应用提供理论参考。 相似文献
70.