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大气中真菌粒子的衰亡和净化,除与真菌自身的因素有关外,与日光辐射也有密切关系。此文现场观测了日光辐射对大气真菌粒子的影响。结果表明,一天内大气真菌粒子浓度与日光辐射强度呈反比:大气真菌粒数直径中值与日光辐射强度呈正比:随着日光辐射强度的增大,<3.0μm的大气真菌粒子,其浓度减小的速度比>3.0μm的快。 相似文献
64.
分析了一种新型直流旋风分离器的分离机理及结构特点 ,推导出了这种旋风分离器内颗粒的运动规律和被分离的临界粒径。 相似文献
65.
Simulation of Ekman Boundary Layers by Large Eddy Model with Dynamic Mixed Subfilter Closure 总被引:2,自引:0,他引:2
I. Esau 《Environmental Fluid Mechanics》2004,4(3):273-303
Theoretical analysis of boundary layer turbulence has suggested a feasibility of sufficiently accurate turbulence resolving
simulations at relatively coarse meshes. However, large eddy simulation (LES) codes, which employ traditional eddy-viscosity
turbulence closures, fail to provide adequate turbulence statistics at coarse meshes especially within a surface layer. Manual
tuning of parameters in these turbulence closures may correct low order turbulence statistics but severely harms spectra of
turbulence kinetic energy (TKE). For more than decade, engineering LES codes successfully employ dynamic turbulence closures.
A dynamic Smagorinsky turbulence closure (DSM) has been already tried in environmental LES. The DSM is able to provide adequate
turbulence statistics at coarse meshes but it is not completely consistent with the LES equations. This paper investigates
applicability of an advanced dynamic mixed turbulence closure (DMM) to simulations of Ekman boundary layers of high Reynolds
number flows. The DMM differs from the DSM by explicit calculation of the Leonard term in the turbulence stress tensor. The
Horizontal Array Turbulence Study (HATS) field program has revealed that the Leonard term is indeed an important component
of the real turbulence stress tensor.
This paper presents validation of a new LES code LESNIC. The study shows that the LES code with the DMM provides rather accurate
low order turbulence statistics and the TKE spectra at very coarse meshes. These coarse LES maintain more energetic small
scale fluctuations of velocity especially within the surface layer. This is critically important for success of simulations.
Accurate representation of higher order turbulence statistics, however, requires essentially better LES resolution. The study
also shows that LES of the Ekman boundary layer cannot be directly compared with conventionally neutral atmospheric boundary
layers. The depth of the boundary layer is an important scaling parameter for turbulence statistics. 相似文献
66.
We review the fundamentals of a new numerical modeling technique called Renormalized Numerical Simulation (RNS). The goal
of RNS is to model the drag force produced by high Reynolds-number turbulent flow over objects that display scale-invariant
properties, objects such as tree-like fractals. The hallmark of RNS in this application is that the drag of the unresolved
tree branches is modeled using drag coefficients measured from the resolved branches and unresolved branches (as modeled in
previous iterations of the procedure). In the present paper, RNS is used to study the effects of branch orientation on the
drag force generated by highly idealized trees in which trunk and branches have square cross-section, and the branches all
lie in a plane perpendicular to the incoming flow. Then, the procedure is generalized to the more general case of non-planar
branch arrangements. Results illustrate that RNS may enable numerical modeling of environmental flow processes associated
with fractal geometries using affordable computational resolution. 相似文献
67.
68.
Small diameter gravity sewers(SDGS) are extensively used to collect rural sewage as they are low in cost and quick to construct.However,the characteristics of biofilms in rural SDGS are still not clear.In this study,biofilms characteristics of aerobic rural SDGS were investigated using simulations in a lab under different flow conditions and slopes.Results indic ated that the average thickness of aerobic rural SDGS biofilms was in the range of 350-650 μm,decreasing at locations with variable flow and high slopes.Protein was the most abundant substance in extracellular polymeric substance of SDGS biofilms.The most abundant bacteria,Proteobacteria,Actinobacteria,and Bacteroidetes,and functional bacteria showed different distributions when analyzed through Illumina HiSeq sequencing of 16 S rRNA.The relative abundances of denitrifying bacteria,nitrite-oxidizing bacteria,and sulfate-reducing bacteria(SRB) were lower during variable flow than during stable flow.High slopes(15‰) decreased SRB presence,which could be used to mitigate H_2 S accumulation in aerobic SDGS.Overall,this study describes the characteristics of aerobic rural SDGS biofilms and provides valuable suggestions for the optimal design of SDGS based on these characteristics. 相似文献
69.
在设有水平机械搅拌、高径比(H/D)为1.2的圆柱形鼓风曝气SBR中,考察了活性污泥的颗粒化情况,对成熟颗粒污泥表面所受水力剪切速率进行了定量研究,分析了水平搅拌在颗粒化过程中的作用.结果表明:有水平搅拌存在下污泥逐渐颗粒化,形成了均值粒径为1.12mm的好氧颗粒污泥,污泥沉降速度为21.41m/h;计算结果表明污泥表面所受的平均剪切速率为27.25s-1,剪切应力为3.38×10-2N/m2;污泥表面所受平均剪切速率与机械搅拌速率和表观气速均呈正相关关系;实验条件下机械搅拌对剪切速率的贡献要远大于表观气速的贡献,前者指数约为后者的37.48倍.研究认为水平搅拌在反应器中形成的具有足够剪切强度的旋涡二次流是促使低高径比反应器好氧污泥颗粒化的关键水力条件. 相似文献
70.
Ziyang Lou Bernd Bilitewski Nanwen Zhu Xiaoli Chai Bing Li Youcai Zhao 《环境科学学报(英文版)》2015,27(4):173-179
Large-scale incinerators are applied widely as a result of the heavy burden of municipal solid waste(MSW) generated, while strong opposition is arising from the public living nearby. A large-scale working incineration plant of 1500 ton/day was chosen for evaluation using life cycle assessment. It was found that the corresponding human toxicity impacts via soil(HTs), human toxicity impacts via water(HTw) and human toxicity impacts via air(HTa)categories are 0.213, 2.171, and 0.012 personal equivalents(PE), and global warming(GW100)and nutrient enrichment(NE) impacts are 0.002 and 0.001 PE per ton of waste burned for this plant. Heavy metals in flue gas, such as Hg and Pb, are the two dominant contributors to the toxicity impact categories, and energy recovery could reduce the GW100 and NE greatly. The corresponding HTs, HTw and HTa decrease to 0.087, 0.911 and 0.008 PE, and GW100 turns into savings of- 0.007 PE due to the increase of the heating value from 3935 to5811 k J/kg, if a trommel screener of 40 mm mesh size is used to pre-separate MSW. MSW sorting and the reduction of water content by physical pressure might be two promising pre-treatment methods to improve the combustion performance, and the application of stricter standards for leachate discharge and the flue gas purification process are two critical factors for improvement of the environmental profile identified in this work. 相似文献