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481.
Sheng-Wei Wang Mohammed A. Majeed Pei-Ling Chu Hui-Chih Lin 《Atmospheric environment (Oxford, England : 1994)》2009,43(14):2296-2302
Socioeconomic and demographic factors have been found to significantly affect time-activity patterns in population cohorts that can subsequently influence personal exposures to air pollutants. This study investigates relationships between personal exposures to eight VOCs (benzene, toluene, ethylbenzene, o-xylene, m-,p-xylene, chloroform, 1,4-dichlorobenzene, and tetrachloroethene) and socioeconomic, demographic, time-activity pattern factors using data collected from the 1999–2000 National Health and Nutrition Examination Survey (NHANES) VOC study. Socio-demographic factors (such as race/ethnicity and family income) were generally found to significantly influence personal exposures to the three chlorinated compounds. This was mainly due to the associations paired by race/ethnicity and urban residence, race/ethnicity and use of air freshener in car, family income and use of dry-cleaner, which can in turn affect exposures to chloroform, 1,4-dichlorobenzene, and tetrachloroethene, respectively. For BTEX, the traffic-related compounds, housing characteristics (leaving home windows open and having an attached garage) and personal activities related to the uses of fuels or solvent-related products played more significant roles in influencing exposures. Significant differences in BTEX exposures were also commonly found in relation to gender, due to associated significant differences in time spent at work/school and outdoors. The coupling of Classification and Regression Tree (CART) and Bootstrap Aggregating (Bagging) techniques were used as effective tools for characterizing robust sets of significant VOC exposure factors presented above, which conventional statistical approaches could not accomplish. Identification of these significant VOC exposure factors can be used to generate hypotheses for future investigations about possible significant VOC exposure sources and pathways in the general U.S. population. 相似文献
482.
Paul Chu Gary T. Rochelle 《Journal of the Air & Waste Management Association (1995)》2013,63(2):175-179
Previous workers have shown that simultaneous SO2/NOX removal can be obtained in a dry scrubbing system with Ca(OH)2 promoted by an additive such as NaOH, and that fly ash and product recycle improve the reactivity of the solids toward SO2. To test SO2/NOX removal with fly ash and product recycle, bench-scale experiments with a packed bed reactor were performed at bag filter conditions. The most reactive solid for NOX removal was prepared by slurrying Ca(OH)2 with fly ash, CaSO3, and NaOH. The best conditions for NOX removal were the greatest temperature (125°C) and greatest concentrations of SO2 (1500 ppm) and O2 (20 percent). At the best conditions, NOX removed in 1 hour was 3-4 moles per 100 moles Ca(OH)2, compared to 5-10 moles SO2 removed per 100 moles Ca(OH)2. The best SO2 removal was obtained at the highest relative humidities/lowest temperatures (55% RH/ 65°C) with solids prepared by slurrying Ca(OH)2 with fly ash and NaOH. At these conditions, SO2 removed In 1 hour was 60-80 moles per 100 moles Ca(OH)2, compared to 0.5 to 1 moles NOX removed per 100 moles Ca(OH)2. 相似文献
483.
484.
The kinetics of catalytic incineration of dimethyl sulfide and dimethyl disulfide over an MnO/Fe2O3 catalyst 总被引:1,自引:0,他引:1
The catalytic incineration of dimethyl sulfide and dimethyl disulfide [(CH3)2S and (CH3)2S2] over an MnO/Fe2O3 catalyst was carried out in a bench-scale catalytic incinerator. Three kinetic models (i.e., the power-rate law, the Mars and Van Krevelen model, and the Langmuir-Hinshelwood model) were used to analyze the results. A differential reactor design was used for best fit of kinetic models in this study. The results show that the Langmuir-Hinshelwood model may be feasible to describe the catalytic incineration of (CH3)2S and (CH3)2S2. This suggests that the chemical adsorption of O2 molecules is important in this incineration. 相似文献
485.
Paul Chiou Wei Tang Che-Jen Lin Hsing-Wei Chu T. C. Ho 《Environmental Modeling and Assessment》2009,14(3):333-350
Speciated samples of PM2.5 were collected at a site in Jefferson County, Texas by US EPA (Environmental Protection Agency) from July of 2003 to August
of 2005. A total of 269 samples with 52 species were measured; however, 22 species were excluded in this study because of
too many below-detection-limit data. The data set was analyzed by positive matrix factorization (PMF) to infer the sources
of PM observed at the site. The analysis identified ten sources: sulfate-rich secondary aerosol I (35.9%), sulfate-rich secondary
aerosol II (21.0%), cement/carbon-rich (11.7%), wood smoke (8.8%), metal processing (6.3%), motor vehicle/road dust (5.7%),
nitrate-rich secondary aerosol (3.3%), soil (3.2%), sea salt (2.6%), and chloride depleted marine aerosol (1.6%). Sulfate
and nitrate mainly exist as salts. The two sulfate-rich secondary aerosols account for almost 57% of the PM2.5 mass concentration. The factor containing highest concentrations of Cl and Na was attributed to sea salt due to the proximity
of the monitoring site to the Gulf of Mexico. The chloride depleted marine aerosol was related to the sea salt aerosol. Cement/carbon-rich,
wood smoke, metal processing, and motor vehicle/road dust factor were likely to be the local sources. 相似文献
486.
In this study, we report the effects of pH and divalent cations on the adsorption of arsenate (As(V)) by titanium dioxide
(TiO2) nanoparticles. The extent of As(V) adsorption on TiO2 decreased with increasing pH due to the decrease of positively charged binding sites on the TiO2 surface. The Langmuir maximum uptake capacity at pH 4 is about three times higher than that at pH 7. Here we show that the
relatively low As(V) uptake at circumneutral pH could be substantially enhanced by the addition of common divalent cations
such as magnesium and calcium. At a concentration of approximately 7 mM, magnesium and calcium increased the extent of As(V)
adsorption from 2.1 to 6.5 and 7.7 mg As(V)/g TiO2, respectively. 相似文献
487.
Thuoc Van Chu Jean-Pascal Torréton Xavier Mari Huyen Minh Thi Nguyen Kha Thi Pham Thu The Pham Thierry Bouvier Yvan Bettarel Olivier Pringault Corinne Bouvier Emma Rochelle-Newall 《Environmental monitoring and assessment》2014,186(12):8555-8572
Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system. 相似文献
488.
为探究青春期的PFOS暴露对成年后的SD大鼠的生殖毒性,对出生后第21天(PND21)的SD大鼠经口灌胃不同剂量的PFOS(5、10和20mg·kg~(-1)),连续染毒7d,在出生后第56天(PND56)时,对各染毒组SD大鼠的体质量、精子数量、血清中的睾酮浓度,以及睾丸间质细胞睾酮合成的相关基因mRNA水平进行了检测。结果显示,10mg·kg~(-1)剂量组大鼠体质量较对照组明显下降(P<0.01);精子数量在10mg·kg~(-1)和20mg·kg~(-1)剂量组明显降低(P<0.05);血清中睾酮浓度随着PFOS剂量的加大有明显下降的趋势,20mg·kg~(-1)剂量组显著低于对照组(P<0.05);类/胆固醇相关基因star和cyp11α1的mRNA表达水平明显下调。研究表明,青春期的PFOS暴露会导致睾酮合成途径中相关因子的功能缺失,破坏成熟睾丸间质细胞的功能,致使睾酮水平降低,并抑制精子生成,从而破坏生殖系统的功能。 相似文献
489.
490.
The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary. The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas. Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments. 相似文献