全文获取类型
收费全文 | 3321篇 |
免费 | 302篇 |
国内免费 | 613篇 |
专业分类
安全科学 | 555篇 |
废物处理 | 67篇 |
环保管理 | 644篇 |
综合类 | 1603篇 |
基础理论 | 415篇 |
污染及防治 | 307篇 |
评价与监测 | 150篇 |
社会与环境 | 219篇 |
灾害及防治 | 276篇 |
出版年
2024年 | 10篇 |
2023年 | 47篇 |
2022年 | 103篇 |
2021年 | 127篇 |
2020年 | 130篇 |
2019年 | 92篇 |
2018年 | 96篇 |
2017年 | 137篇 |
2016年 | 144篇 |
2015年 | 166篇 |
2014年 | 176篇 |
2013年 | 208篇 |
2012年 | 232篇 |
2011年 | 269篇 |
2010年 | 199篇 |
2009年 | 227篇 |
2008年 | 155篇 |
2007年 | 224篇 |
2006年 | 203篇 |
2005年 | 185篇 |
2004年 | 142篇 |
2003年 | 122篇 |
2002年 | 107篇 |
2001年 | 106篇 |
2000年 | 113篇 |
1999年 | 71篇 |
1998年 | 44篇 |
1997年 | 53篇 |
1996年 | 32篇 |
1995年 | 50篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 27篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1976年 | 4篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 3篇 |
排序方式: 共有4236条查询结果,搜索用时 31 毫秒
991.
为了研究植物根系对不同基质结构潜流人工湿地水力特性的影响,根据填料渗透系数,分别设置单层及多层基质结构潜流人工湿地小试实验系统,以美人蕉作为湿地植物,在植物栽种前与成熟后对两系统分别开展示踪试验研究.实验结果表明,美人蕉根系对于单层结构人工湿地水力特性有较明显的改善作用,有效体积从0.49提高到了0.53,短路值由0.60降低到0.41,水力效率提高最大由43%提高到59%.比较而言,植物根系对多层结构湿地有效体积和短路值有轻微负面影响,而对水力效率则有明显的改善作用(由64%提高到83%).此外,植物成熟后,两人工湿地系统中示踪剂回收率均有所下降,其中,单层结构湿地降低较显著,回收率由72%降到62%.可见,植物根系对系统水力特性有较大影响,应在人工湿地设计过程中给予考虑. 相似文献
992.
铅元素人为循环环境释放物形态分析 总被引:4,自引:1,他引:3
环境中铅污染物来自于物质人为循环的环境释放,铅释放物的形态差异意味着其在环境介质中迁移和转化的起始状态不同.确定铅元素人为循环环境释放物的形态,可以为环境风险评估和源头管理提供科学依据.本研究通过追踪铅元素人为循环流动过程,应用物理化学分析方法,辨识生命周期各阶段环境释放物中铅元素的形态,并以2010年为例,定量分析中国铅元素人为循环中环境释放物的形态分布特征.结果表明,2010年中国铅人为循环中环境释放物主要形态表现为PbSO4,约占总量的23.4%;其次是PbO、Pb和PbCO3,共占总释放量的46.2%.国内每消费1 kt精铅,将向环境释放547.9 t的铅,这些环境释放物中73.3%来源于产品使用阶段和废物处置与回收阶段;从形态看,PbSO4占释放物的量为128.2 t,主要来源于生产阶段和废物处置与回收阶段,PbO、Pb和PbCO3则分别主要来源于废物处置与回收、产品使用和生产几个阶段. 相似文献
993.
Despite increasing attention to management of headwater streams as sources of water, sediment, and wood to downstream rivers,
the extent of headwater channels and perennial flow remain poorly known and inaccurately depicted on topographic maps and
in digital hydrographic data. This study reports field mapping of channel head and perennial flow initiation locations in
forested landscapes underlain by sandstone and basalt lithologies in Washington State, USA. Contributing source areas were
delineated for each feature using a digital elevation model (DEM) as well as a Global Positioning System device in the field.
Systematic source area–slope relationships described in other landscapes were not evident for channel heads in either lithology.
In addition, substantial variability in DEM-derived source area sizes relative to field-delineated source areas indicates
that in this area, identification of an area–slope relationship, should one even exist, would be difficult. However, channel
heads and stream heads, here defined as the start of perennial flow, appear to be co-located within both of the lithologies,
which together with lateral expansion and contraction of surface water around channel heads on a seasonal cycle in the basalt
lithology, suggest a controlling influence of bedrock springs for that location. While management strategies for determining
locations of channel heads and perennial flow initiation in comparable areas could assign standard source area sizes based
on limited field data collection within that landscape, field-mapped source areas that support perennial flow are much smaller
than recognized by current Washington State regulations. 相似文献
994.
Zhu N An P Krishnakumar B Zhao L Sun L Mizuochi M Inamori Y 《Journal of environmental management》2007,85(4):936-943
The emission of methane from two constructed wetlands [a free water surface flow system (FWS) and a subsurface flow system (SF)], constructed for the treatment of waste water, was evaluated at different sites inhabited by reeds (Phragmites communis), to test the effects of plant harvest. High methane emission was recorded immediately after harvesting in both wetlands. Several days after harvesting, the emission decreased in the FWS but remained high in the SF. The variation was significantly influenced by temperature, with lower emission and higher dissolved CH(4) in water occurring at lower temperatures. Both the emission and concentration of dissolved CH(4) were also influenced significantly by water quality, wetland design, level of stalk butt left above the water level, etc. The methane flux was explained on the basis of rizhospheric methanogenic and methanotrophic microbial populations. FISH analysis indicated the presence of Type A and Type B methanotrophs in both wetlands, and the methane flux was directly influenced by the quantitative variation in methanogenic and methanotrophic bacteria in both wetlands. 相似文献
995.
Confronting limitations: new solutions required for urban water management in Kunming City 总被引:1,自引:0,他引:1
Huang DB Bader HP Scheidegger R Schertenleib R Gujer W 《Journal of environmental management》2007,84(1):49-61
Despite continuous investment and various efforts to control pollution, urban water environments are worsening in large parts of the developing world. In order to reveal potential constraints and limitations of current practices of urban water management and to stimulate proactive intervention, we conducted a material flow analysis of the urban water system in Kunming City. The results demonstrate that the current efficiency of wastewater treatment is only around 25% and the emission of total phosphorous from the city into its receiving water, Dianchi Lake, is more than 25 times higher than its estimated tolerance. With regard to the crisis of water quantity and quality, the goal of a sustainable urban water environment cannot be attained with the current problem-solving approach in the region due to the technical limitations of the conventional urban drainage and treatment systems. A set of strategies is therefore proposed. The urban drainage system in Zurich is used as a reference for a potential best-available technology for conventional urban water management (BAT) scenario in terms of its low combined frequency of sewer overflow. 相似文献
996.
Greater emphasis is being placed on indicators of agri-environmental efficiency of organic production systems. Linking environmental measures with profitability measures based on net income is the only way to develop such indicators. A stochastic production frontier model that explicitly incorporates farm decisions about acquiring and managing organic soil-improving inputs is used to measure efficiency. The results confirm that on-farm self-sufficiency in soil-improving inputs is positively related to farm-level efficiency. 相似文献
997.
998.
MATTHEW A. BOWKER MARK E. MILLER JAYNE BELNAP THOMAS D. SISK NANCY C. JOHNSON 《Conservation biology》2008,22(6):1533-1543
Abstract: Conservation prioritization usually focuses on conservation of rare species or biodiversity, rather than ecological processes. This is partially due to a lack of informative indicators of ecosystem function. Biological soil crusts (BSCs) trap and retain soil and water resources in arid ecosystems and function as major carbon and nitrogen fixers; thus, they may be informative indicators of ecosystem function. We created spatial models of multiple indicators of the diversity and function of BSCs (species richness, evenness, functional diversity, functional redundancy, number of rare species, number of habitat specialists, nitrogen and carbon fixation indices, soil stabilization, and surface roughening) for the 800,000‐ha Grand Staircase‐Escalante National Monument (Utah, U.S.A.). We then combined the indicators into a single BSC function map and a single BSC biodiversity map (2 alternative types of conservation value) with an unweighted averaging procedure and a weighted procedure derived from validations performance. We also modeled potential degradation with data from a rangeland assessment survey. To determine which areas on the landscape were the highest conservation priorities, we overlaid the function‐ and diversity‐based conservation‐value layers on the potential degradation layer. Different methods for ascribing conservation‐value and conservation‐priority layers all yielded strikingly similar results (r= 0.89–0.99), which suggests that in this case biodiversity and function can be conserved simultaneously. We believe BSCs can be used as indicators of ecosystem function in concert with other indicators (such as plant‐community properties) and that such information can be used to prioritize conservation effort in drylands. 相似文献
999.
复合垂直流人工湿地氧化还原特征及不同功能区净化作用研究 总被引:1,自引:0,他引:1
研究了复合垂直流人工湿地系统氧化还原电位(Eh)的时空变化规律及不同功能区中污染物的净化效果。结果表明:湿地系统下行流池表层、两池底层、上行流池表层Eh的变化范围分别为402~585、-87~-130、308~432 mV,沿水流方向依次形成了好氧A区/缺氧、厌氧区/好氧B区3个功能区。好氧A区是污染物去除的主要区域,BOD5、CODCr、NH+4- N的去除率分别为430%、484%、541%,特别是NH+4 N去除率占总去除率的79%;缺氧、厌氧区主要是进行反硝化反应和有机物的厌氧分解;好氧B区则主要是去除厌氧分解后的有机物以及进一步脱氮。另外,NH+4 N的去除率与系统各功能区Eh呈显著相关关系(〖WTBX〗p〖WTBZ〗<001),而BOD5、CODCr、NO-3-N的去除率与系统各功能区Eh相关性不显著。 相似文献
1000.
郑太福 《中国环境管理干部学院学报》2010,20(3):33-35,43
雨水收集设施等水工程日益得到应用,需要解决雨水收集设施等水工程设施收集的水资源的所有权。因大气降水是一种自由资源,不属于《宪法》中的"水流"或《水法》中的"水资源"的范畴,雨水收集设施等水工程设施收集的水资源所有权不能适用《宪法》、《水法》的规定,而是取决于雨水收集设施等水工程设施的所有权。雨水收集设施等水工程设施不是土地的组成部分,所有权包括国家所有、集体所有、其他组织和个人所有等形式,因此,雨水收集设施等水工程设施收集的水资源所有权自然包括国家所有、集体所有、其他组织和个人所有。但水工程设施不是公益性、大中型的水利设施,允许其他投资主体投资,其所有权应以集体、个人所有为主要形式 相似文献