全文获取类型
收费全文 | 655篇 |
免费 | 63篇 |
国内免费 | 123篇 |
专业分类
安全科学 | 89篇 |
废物处理 | 25篇 |
环保管理 | 144篇 |
综合类 | 317篇 |
基础理论 | 89篇 |
污染及防治 | 51篇 |
评价与监测 | 25篇 |
社会与环境 | 81篇 |
灾害及防治 | 20篇 |
出版年
2024年 | 5篇 |
2023年 | 8篇 |
2022年 | 31篇 |
2021年 | 28篇 |
2020年 | 31篇 |
2019年 | 31篇 |
2018年 | 28篇 |
2017年 | 39篇 |
2016年 | 36篇 |
2015年 | 32篇 |
2014年 | 26篇 |
2013年 | 45篇 |
2012年 | 45篇 |
2011年 | 64篇 |
2010年 | 33篇 |
2009年 | 40篇 |
2008年 | 29篇 |
2007年 | 52篇 |
2006年 | 44篇 |
2005年 | 30篇 |
2004年 | 21篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有841条查询结果,搜索用时 203 毫秒
441.
Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or
diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion
constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and
air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated
with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion
and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge
concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well
as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic
jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes.
Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented.
New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence
level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses
show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble
chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements
showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as
well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary
conditions on the turbulence structure. 相似文献
442.
Meiring Wendy Sampson Paul D. Guttorp Peter 《Environmental and Ecological Statistics》1998,5(3):197-222
We present an approach to estimate hourly grid-cell surface ozone concentrations based on observations from point monitoring sites in space, for comparison with grid-based results from the SARMAP photochemical air-quality model for a region of northern California. Statistical estimation is carried out on a transformed (square root) scale, followed by back-transforming to the original scale of ozone in parts per billion, adjusting for bias and variance. We estimate a spatially-varying diurnal mean structure and a non-separable space-time correlation structure on the transformed scale. Temporal pre-whitening is followed by modelling of a spatially non-stationary, diurnally-varying spatial correlation structure using a spatial deformation approach. Comparisons of SARMAP model results with the estimated grid-cell ozone levels are presented. 相似文献
443.
基于污染控制的畜禽养殖场适度规模的理论分析 总被引:1,自引:0,他引:1
当前,规模化逐渐成为我国畜禽养殖业发展的主要思路,而现实中大规模养殖在带来经济效益的同时也带来了严重的环境污染。从污染控制的角度看是否存在最优养殖规模成为一个需要研究的问题。基于耕地对氮磷的承载能力、运输成本、排污费等变量构建了数理模型,探讨追求利润最大化的畜禽养殖场的最优规模问题。结果表明:在养殖场自由选择养殖规模时,出售一个养殖单位获得的经济收益越高、耕地对处理剩余物的承载能力越大,则最优养殖规模越大;而一个养殖单位的直接生产成本和粪便处理成本越高、畜禽粪便经处理后的剩余物越多、运输成本越高、排污费越高,则最优规模越小。在养殖规模既定的情况下,提高排污收费时畜禽养殖场将提高其处理剩余物的还田处置比例。最后,指出在畜禽粪便处理技术难以有效去除氮磷、对养殖场是否合理处置最终剩余物难以监管的条件下,对养殖场进行规模控制将是畜禽养殖污染控制的一个政策方向 相似文献
444.
中国跨界水污染冲突环境政策分析 总被引:1,自引:0,他引:1
跨界水污染纠纷已经严重影响到区域间环境和社会稳定.在我国传统条块结合的环境管理体制下,由跨界水污染引发的利益冲突和纠纷持续不断.尽管我国跨区域水污染纠纷协调机制尚未建立,但在许多地区已经进行了有益的探索和实践,发现了一些不足之处.应用多准则决策分析法可以评估和比较跨界水环境管理条约,识别最可取的条约,同时可以对现有的条约提供进一步完善的建议.本文应用多准则决策分析之一的消元法,通过三个主要指标共11条标准,对我国跨国界、省界、市界和跨流域4个不同层次的单边和多边跨界环境管理条约进行评估和比较.结果显示,我国跨界水环境条约存在的问题主要有:我国各层级跨界水环境管理政策在法律上缺乏有效的程序性立法;执行上缺乏相应的法律保障和配套机制,执行不力;争端解决机制缺乏有效的管理机构、依法处理程序和磋商解决机制.通过对现存条约的分析比较和提供建议,为构建我国跨区域水污染纠纷协调机制提供技术和政策支持. 相似文献
445.
Drouet JL Capian N Fiorelli JL Blanfort V Capitaine M Duretz S Gabrielle B Martin R Lardy R Cellier P Soussana JF 《Environmental pollution (Barking, Essex : 1987)》2011,159(11):3156-3161
Modelling complex systems such as farms often requires quantification of a large number of input factors. Sensitivity analyses are useful to reduce the number of input factors that are required to be measured or estimated accurately. Three methods of sensitivity analysis (the Morris method, the rank regression and correlation method and the Extended Fourier Amplitude Sensitivity Test method) were compared in the case of the CERES-EGC model applied to crops of a dairy farm. The qualitative Morris method provided a screening of the input factors. The two other quantitative methods were used to investigate more thoroughly the effects of input factors on output variables. Despite differences in terms of concepts and assumptions, the three methods provided similar results. Among the 44 factors under study, N2O emissions were mainly sensitive to the fraction of N2O emitted during denitrification, the maximum rate of nitrification, the soil bulk density and the cropland area. 相似文献
446.
Duretz S Drouet JL Durand P Hutchings NJ Theobald MR Salmon-Monviola J Dragosits U Maury O Sutton MA Cellier P 《Environmental pollution (Barking, Essex : 1987)》2011,159(11):3162-3170
Modelling nitrogen transfer and transformation at the landscape scale is relevant to estimate the mobility of the reactive forms of nitrogen (Nr) and the associated threats to the environment. Here we describe the development of a spatially and temporally explicit model to integrate Nr transfer and transformation at the landscape scale. The model couples four existing models, to simulate atmospheric, farm, agro-ecosystem and hydrological Nr fluxes and transformations within a landscape. Simulations were carried out on a theoretical landscape consisting of pig-crop farms interspersed with unmanaged ecosystems. Simulation results illustrated the effect of spatial interactions between landscape elements on Nr fluxes and losses to the environment. More than 10% of the total N2O emissions were due to indirect emissions. The nitrogen budgets and transformations of the unmanaged ecosystems varied considerably, depending on their location within the landscape. The model represents a new tool for assessing the effect of changes in landscape structure on Nr fluxes. 相似文献
447.
长江三角洲都市连绵区城市体系的分形特征 总被引:4,自引:0,他引:4
分形研究是现代理论地理的重要内容之一,分形维数是刻画城市体系结构的有效参数。为定量分析长江三角洲都市连绵区城市体系的分形特征,通过计算豪斯道夫维数分析了长江三角洲城市体系规模分布的分形特征,通过计算关联维数和集聚维数,从城市要素的空间相关性和城市随机集聚的向心性两方面,分析了长江三角洲都市连绵区城市体系空间结构的分形特征。测算结果表明:(1)城市体系规模结构符合位序 规模分布类型,但首位城市的垄断性还很强,处于由首位型分布向序列型分布转变的过程之中,中间位序的城市数量偏少,城市之间呈竞争发展态势;(2)城市体系空间结构呈现出均匀分布的特征,城市的空间关联性强,空间相互作用强度大。在上述结论的基础上对长江三角洲都市连绵区城市体系的优化发展提出了建议. 相似文献
448.
449.
环己酮生产废水厌氧生物处理实验及中试研究 总被引:1,自引:0,他引:1
采用经絮凝Fe/C微电解pH调节预处理过的某化工厂环己酮生产废水对自制UBF反应器的启动和运行进行了厌氧生物处理研究,该废水主要成分为环己酮、环己醇、环己烷等难降解有机物,COD=10 000~40 000 mg/L,pH=1~4,此外废水中还含有部分有机酸、Na2SO4、油类物质及少量的苯。通过对实验数据的分析得出UBF的最佳运行参数:VLR=2.36~3.26 kg COD/(m3·d)时,COD去除效率为61.74%~65.86%。中试工程依据本研究的实验结果并结合实际情况对废水进行了有效的处理,经6个多月的调试,出水水质符合相关技术标准。 相似文献
450.
Geoffrey R. Squire Cathy Hawes Graham S. Begg Mark W. Young 《Environmental science and pollution research international》2009,16(1):85-94