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141.
This article attempts to study both returns to scale and optimal size of production. Specifically, the authors estimate a ray-homothetic production function which allows the returns to scale to vary with ouput size and input mix. The production model is estimated using data from the Welsh coal industry for the period 1961–1976. Findings showed that, first, the Welsh coal industry suffers from a level of production which is either too small or below its optimal level and, second, this discrepancy between actual and optimal production worsened over the period considered. 相似文献
142.
Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/DFs), including 2378-substituted isomers were present in samples of shellfish and fish, and ambient air collected from Masan Bay, and Masan City, South Korea. Total concentrations of PCDDs/DFs in mussel and clam were 750 pg g(-1), lipid weight (lw), and 3418 pg g(-1), lw, respectively. Total concentrations of PCDDs/DFs in mullet, gizzard and flounder were 52, 82, and 122 pg g(-1), lw, respectively. Shellfish tissues contained a greater number of PCDD/DF isomers, contributing greater total concentrations of PCDDs/DFs compared to fish collected from the same locations. The predominance of 2378-substituted PCDDs/DFs in fish is represented in greater total concentrations of 2378-TeCDD equivalents (TEQs), whereas there was very limited occurrence of 2378-substituted isomers in shellfish. TEQ concentrations in samples of mussel and clam were 0.97 and 12 pg g(-1), lw, respectively. Total TEQs in mullet, gizzard and flounder were 12, 22 and 18 pg g(-1), lw, respectively. In fish 2378-substituted PCDDs accounted for 100% of the total concentrations of PCDDs, and 2378-substituted PCDFs accounted from 59% to 73% of the total PCDFs. The 2378-substituted isomers accounted for only 3% of the total PCDDs/DFs in shellfish. Ambient air collected from two sites contained a wide range of isomers of tetra- through heptachlorinated PCDDs/DFs. Even though the total concentration of PCDDs/DFs in ambient air (12.8 pgm(-3)) collected from an industrial area was 2-fold greater than that in air samples (6.3 pgm(-3)) collected from an urban/rural area, total TEQs (0.07 and 0.08 pgm(-3)) there was no statistical difference between the two samples. 相似文献
143.
The determination of quantum yields for the photolysis of Fe(III)-hydroxo complexes is important for the quantitative investigation of hydroxyl radical (*OH) production, not only in a natural water body, but also in the photo-Fenton process. A novel kinetic method, using a *OH probe compound, was established for the determination of the quantum yields in this study. The method was based on measuring the pseudo-first-order rate constant of the photodecomposition of dimethylsulfoxide (DMSO) in which DMSO and its primary products scavenged the *OH at an identical rate. The preliminary experiments for the photodecomposition kinetics supported the suitability of DMSOs as a probe compound for determining quantum yields. The individual quantum yields for the photolysis of the monomeric Fe(III) complexes, in the wavelength range 240-380 nm, were determined by the photodecomposition kinetics of the hydroxyl radical (*OH) probe compound (DMSO). The determined values of the individual quantum yields were 0.046+/-0.00052 for Fe3+ (H2O)6 (hexaaquo ion) and 0.69+/-0.025 for Fe(OH)2+ (H2O)5 (hydroxypentaaquo ion) at 254 nm, and showed decreasing values with increasing wavelength, in the ranges of 240-380 nm. The quantum yields between 240 and 280 nm were newly reported in this study, and the values obtained between 280 and 380 nm were in good agreement with the literature values. 相似文献
144.
Chemical-mechanical characteristics of crushed oyster-shell 总被引:2,自引:0,他引:2
Enormous amount of oyster-shell waste has been illegally disposed at oyster farm sites along the southern coast of Korea. To seek for a possibility to recycle the waste as construction materials, chemical and mechanical characteristics of crushed oyster-shell were investigated. Chemical and microstructure analyses showed that oyster-shells are predominantly composed of calcium carbonate with rare impurities. Compressive strength tests for soil mortar specimens with varying blending ratio of cement, water, sand, and oyster-shell were compared with normal cement mortar. There was no significant reduction in the compressive strength up to 40% of dosages of oyster-shell instead of sand. The experimental results demonstrate that oyster-shells can be resources of pure calcareous materials and effective in replacement of sand, indicating promising reusable construction materials. 相似文献
145.
High temperature dependence of 2,4-dichlorophenoxyacetic acid degradation by Fe3+/H(2)O(2) system 总被引:2,自引:0,他引:2
This study demonstrates the importance of reaction temperature on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). In addition, we provide a mechanistic explanation for the temperature dependence of 2,4-D degradation. Thermal enhancement of 2,4-D degradation and H(2)O(2) decomposition was measured in the absence and in the presence of the z.rad;OH scavenger (t-butanol). The half-life for 2,4-D degradation was reduced by more than 70-fold in the absence of t-butanol, and by more than 700-fold, in the presence of t-butanol, when the reaction temperature was increased from 10 to 50 degrees C. In addition, similar temperature relationships were found for H(2)O(2) decomposition. The major reason for the high temperature dependence of the Fe(3+)/H(2)O(2) system in the case of 2,4-D degradation is due to the dependence of the initiation reaction of the Fe(3+)/H(2)O(2) system (i.e., Fe(3+)+H(2)O(2)-->Fe(2+)+HO(2)(z.rad;)+H(+) upon temperature), which is entirely consistent with the kinetics of the activation energy. In the presence of a z.rad;OH scavenger, the initiation reaction of the Fe(3+)/H(2)O(2) system became a determining factor of this temperature dependence, whereas in the absence of z.rad;OH scavenger, several other radical reactions played a role and this result in an apparent decrease in the activation energy for 2,4-D degradation. Moreover, the enhanced 2,4-D removal at higher temperatures did not alter H(2)O(2) utilization. The practical implications of the thermal enhancement of the Fe(3+)/H(2)O(2) system are discussed. 相似文献
146.
The aim of this study was to determine the unit load of NPS (non-point source) pollutants including organic variables such as BOD (biochemical oxygen demand),COD (chemical oxygen demand) and DOC (dissolved organic carbon),nitrogen and phosphorus constituents,and suspended solids (SS) and their event mean concentration (EMC) of runoff flows from a water-shed of mixed forest land use by intensive field experiments.Field monitoring for continuous measurements of rainfall,flow,and water quality was conducted over 12 storm events during 2008–2009 using automated and manual sampling methods.The EMCs of individual runoff event were estimated for each water quality constituent based on the flow rate and concentration data of runoff discharge.The average EMCs of BOD,COD,DOC,SS,TN (total nitrogen),NH 4+ -N,NO 3- -N,TP (total phosphorus),PO 43- -P from the mixed forest land were 1.794,3.498,1.462,10.269,0.862,0.044,0.634,0.034,and 0.005 mg/L,respectively.The annual unit loads of BOD,COD,DOC,SS,TN,NH 4+ -N,NO 3- -N,TP and PO 43--P were estimated as 66.9,133.2,55.5,429.8,36.5,1.6,26.9,1.3 and 0.1 kg/(ha·yr),respectively.In addition,affecting parameters on the EMCs were investigated by statistic analysis of the field data.As a result,significant correlations with precipitation,rainfall intensity,and total runoff flows were found in most constituents. 相似文献
147.
Misun Park Hyeon Yoon Cheolho Yoon Jae-Young Yu 《Environmental geochemistry and health》2011,33(1):49-53
Although numerous hypotheses have been proposed to explain geophagy, the primary driver of this behaviour remains elusive.
Supplementation of scarce nutrients is one commonly cited explanation. We examined the element concentration of three licks
relative to adjacent topsoils to infer the possible reasons for geophagy at Loskop Dam Nature Reserve. Lick samples had greater
concentrations of B, Co, Zn, Se, Mo and Mn (Loskop Main Lick); Cu (Klopperskloof Lick); and Na (Klopperskloof Lick and Rhenosterhoek
Lick) than those of adjacent topsoil. We suggest that supplementation with all or some of these nutrients is a likely driver
of geophagy in this fenced reserve, with different licks providing herbivores with different suites of nutrients. 相似文献
148.
Employees' self‐efficacy and perception of individual learning in teams: The cross‐level moderating role of team‐learning behavior 下载免费PDF全文
Despite the importance of employee learning for organizational effectiveness, scholars have yet to identify the factors that influence employees' perception of individual learning. This paper identified employees' self‐efficacy as a potential antecedent to their perception of individual learning in the context of teamwork. We also hypothesized that team‐learning behavior had a moderating effect on the relationship between employees' self‐efficacy and their perception of individual learning. We conducted a study of 236 teams working in a retail firm, comprising 236 team supervisors and 1397 employees, and analyzed the data using hierarchical linear modeling. This study revealed that employees' individual‐level self‐efficacy was positively associated with their perception of individual learning in teams. Additionally, team‐learning behaviors moderated the positive relationship between employees' self‐efficacy and the perception of individual learning. This study has theoretical and practical implications for a more nuanced understanding of the perception of individual learning in the context of teamwork. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
149.
Yoon Hyun-Sub Yang Keun-Hyeok Kwon Seung-Jun 《Journal of Material Cycles and Waste Management》2022,24(2):582-594
Journal of Material Cycles and Waste Management - In this study, a bacteria coating resistant to sulfate attack using materials with bacteria immobilization has been developed. For core coating... 相似文献
150.
Yoon Sanghyuck Choi Wonyoung Jeon Chansoo 《Journal of Material Cycles and Waste Management》2022,24(5):1878-1892
Journal of Material Cycles and Waste Management - The hydration characteristics of mixed cement containing fine powder of blast-furnace slag and expandable material were examined by X-ray... 相似文献