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41.
Walter G. Whitford Gustavo Martinez-Turanzas Ernesto Martinez-Meza 《Environmental monitoring and assessment》1995,37(1-3):319-332
Studies of rainfall partitioning by shrubs, responses of shrub-dominated ecosystems to herbicide treatment, and experiments using drought and supplemental rainfall were conducted to test the hypothesis that the shrub-dominated ecosystems that have replaced desert grasslands are resistant and resilient to disturbance. Between 16 and 25% of the intercepted rainfall is channelized to deep soil storage by stemflow and root channelization. Stemflow water is nutrient enriched and contributes to the islands of fertility that develop under desert shrubs. Drought and rainfall augmentation experiments during the growing season after 5 consecutive years of summer drought found that (1) growth of creosotebushes, Larrea tridentata, was not significantly affected, (2) perennial grasses and forbs disappeared on droughted plots, (3) nitrogen mineralization increased in the short term, and (4) densities and biomass of spring annual plants increased on the droughted plots. Doubling summer rainfall for 5 consecutive years had less-significant effects. Coppice dunes treated with herbicide in 1979 to kill mesquite (Prosopis glandulosa) had the same frequency of occurrence of the shrub as the untreated dunes when remeasured in 1993. These data indicate that the shrub-dominated ecosystems persist because they are resistant and resilient to climatic and anthropogenic stresses.Notice: The U.S. Environmental Protection Agency (EPA), through its Office of Research and Development (ORD), partially funded and collaborated in the research described herein. This paper has been subjected to EPA's peer review and has been approved as an EPA publication. The U.S. Government has a nonexclusive, royalty-free license in and to any copyright covering this article. 相似文献
42.
Jorge Alberto Achcar Douglas Ernesto Fazioni Sousa Eliane R. Rodrigues Guadalupe Tzintzun 《Environmental Modeling and Assessment》2011,16(3):251-264
Ozone air pollution is a serious problem in several cities of the world. Hence, to analyse the behaviour of this pollutant
is a very important issue. One problem of interest is to study the behaviour of the inter-occurrences times between two ozone
exceedances, i.e. between two days in which the pollutant’s measurement surpasses a given threshold. Another interest resides
in comparing the behaviour of ozone measurements in different seasons of the year. In this paper we use some Poisson models
to analyse this problem. The time interval at which the ozone measurements were taken is split into subintervals corresponding
roughly to the seasons of the year. We consider three parametric forms for the mean of the Poisson model, and consequently
for the mean of the inter-occurrences times. In each model, the parameters describing its mean are estimated using Bayesian
inference via Markov chain Monte Carlo methods. The models are applied to the ozone measurements provided by the Mexico City
monitoring network. Theoretical results suggest that an increase has occurred in the mean inter-exceedances times and this
is corroborated by the observed data. Differences between the behaviour of the pollutant during different seasons of the year
are also detected as well as similarities in the same season in different years. Besides estimating the mean of the Poisson
models, inference for the possible presence and location of change-points indicating change of parameters of the model is
also performed. 相似文献
43.
44.
Alessandro Tugnoli Gabriele Landucci Ernesto Salzano Valerio Cozzani 《Journal of Loss Prevention in the Process Industries》2012,25(5):830-842
Effective support of inherent safety implementation in process design requires a quantitative metric for monitoring and communicating the expected safety performance of alternative design options. The Inherent Safety Key Performance Indicators (IS-KPIs) methodology was developed to provide both a flexible procedure for the identification of the hazards, and a sound consequence-based quantification of the safety performance. The integration of different hazard identification techniques yields the relevant accident scenarios for each unit in the plant. The calculation of credible damage distances by consolidate consequence simulation models provides a sound basis for the definition of the KPIs based on worst case effects. Specific indicators were devoted to hazards from external actions, as natural events and intentional malicious acts. The methodology was demonstrated by the comparison of alternative technological options for LNG regasification. The application evidenced the potential of the IS-KPI method in pinpointing the critical issues related to each alternative configuration. 相似文献
45.
Groundwater Vulnerability Assessment for Organic Compounds: Fuzzy Multicriteria Approach for Mexico City 总被引:1,自引:0,他引:1
Mazari-Hiriart M Cruz-Bello G Bojórquez-Tapia LA Juárez-Marusich L Alcantar-López G Marín LE Soto-Galera E 《Environmental management》2006,37(3):410-421
This study was based on a groundwater vulnerability assessment approach implemented for the Mexico City Metropolitan Area
(MCMA). The approach is based on a fuzzy multicriteria procedure integrated in a geographic information system. The approach
combined the potential contaminant sources with the permeability of geological materials. Initially, contaminant sources were
ranked by experts through the Analytic Hierarchy Process. An aggregated contaminant sources map layer was obtained through
the simple additive weighting method, using a scalar multiplication of criteria weights and binary maps showing the location
of each source. A permeability map layer was obtained through the reclassification of a geology map using the respective hydraulic
conductivity values, followed by a linear normalization of these values against a compatible scale. A fuzzy logic procedure
was then applied to transform and combine the two map layers, resulting in a groundwater vulnerability map layer of five classes:
very low, low, moderate, high, and very high. Results provided a more coherent assessment of the policy-making priorities
considered when discussing the vulnerability of groundwater to organic compounds. The very high and high vulnerability areas
covered a relatively small area (71 km2 or 1.5% of the total study area), allowing the identification of the more critical locations. The advantage of a fuzzy logic
procedure is that it enables the best possible use to be made of the information available regarding groundwater vulnerability
in the MCMA. 相似文献
46.
47.
Moreno F Gramsch E Oyola P Rubio MA 《Journal of the Air & Waste Management Association (1995)》2010,60(12):1410-1421
Santiago de Chile is one of the most polluted South American cities, concentrating its pollution episodes during winter. Daily PM2.5 (particulate matter [PM] < or = 2.5 microm in aerodynamic diameter) concentrations over 80 microg/m3 have been reached frequently since 1998. Despite several regulations introduced over the past 20 yr to improve the air quality, PM concentration levels remain high. In this work, sampling in downtown Santiago was conducted from April 1998 to August 2007 for PM2.5 and from October 2003 to March 2006 for PM10-2.5 (PM between 2.5 and 10 microm in aerodynamic diameter) with dichotomous samplers. Elemental analysis was performed on the samples with X-ray fluorescence. The resuming series of 859 samples and 216 elements identified were divided into semiannual periods and analyzed with factor analysis. Five factors are clearly discerned: soil, motor vehicles, residual oil, marine aerosols, and secondary sulfates. The soil factor in the fine fraction shows a clear increase from 2002 to 2006, whereas the coarse fraction of this factor shows a stable trend. The most probable cause for this trend is the growth in the number of vehicles in Santiago (6.5%/yr), which increases the resuspension of particles from the ground. Another cause for the increase is the growth in the construction activity (4.2%/yr). The motor vehicle factor in the fine fraction shows a decrease between 1998 and 2006. The decrease in the apportionment of this factor can be explained by the improvement in the vehicle fleet. In Santiago, the number of noncatalytic vehicles has been reduced from 389,000 in 2001 to 275,000 in 2006. The residual oil factor also shows a decrease between 1998 and 2006. The decrease could be attributed to the adoption of cleaner technologies and norms regarding gasoline and diesels. 相似文献
48.
Gramsch E Ormeño I Palma G Cereceda-Balic F Oyola P 《Journal of the Air & Waste Management Association (1995)》2004,54(7):799-808
The optical absorption coefficient, particulate matter with an aerodynamic diameter <2.5 microm, and elemental carbon (EC) have been measured simultaneously during winter and spring of 2000 in the western part of Santiago, Chile (Pudahuel district). The optical measurements were carried out with a low-cost instrument recently developed at the University of Santiago. From the data, a site-specific mass absorption coefficient of 4.45+/-0.01 m2/g has been found for EC. In addition, a mass absorption coefficient of 1.02+/-0.03 m2/g has been obtained for PM2.5. These coefficients can be used during the colder months (May-August) to obtain EC concentration or PM2.5 from a measurement of the light absorption coefficient (sigmaa). The high correlation that has been found between these variables indicates that sigmaa is a good indicator of the degree of contamination of urbanized areas. The data also show an increase in PM2.5 and EC concentration during winter and an increase in the ratio of EC to PM2.5. When the EC/PM2.5 ratio is calculated during rush hour (7:00 a.m.-11:00 a.m.) and during part of the night (9:00 p.m.-2:00 a.m.), it is found that the increase is caused by higher concentration levels of EC at night. These results suggest that the rise in the EC concentration is caused by emissions from heating and air mass transport of pollution from other parts of the city, while traffic contribution remains approximately constant. 相似文献
49.
The temporal dynamics of the invertebrate immune response often determines an organism’s success in responding to physiological stress, physical damage, and pathogens. To date, most immune challenge studies have been conducted under highly controlled laboratory conditions, with few attempts to study immune function in the wild. In this study, we characterized the temporal dynamics of the Caribbean sea fan, Gorgonia ventalina, cellular immune response [granular amoebocyte aggregation and prophenoloxidase (PPO) activation] to allogenic grafts in the laboratory and field using a clonally replicated design. Amoebocyte reaction time differed markedly between the lab (% amoebocyte surface area in tissue sections peaked at 2 days) and field (peak at 6 days). PPO activity decreased between 0 and 6 days after grafting in both ungrafted and grafted tissue, suggesting PPO is decoupled from other cellular components. The reaction norms of the fold induction in % amoebocyte area between disease-grafted and healthy-grafted tissue of each colony across time indicate high intercolony plasticity in cellular immune response. The plasticity between colonies was also evident in the magnitude of cellular immune response, ranging from a 0.88- to 1.60-fold increase in amoebocyte area between initial and 6 days for the disease-grafted tissue. With the demonstration of highly dynamic cnidarian cellular immune responses, our study expands understanding of the evolutionary ecology of metazoan immune defense mechanisms. 相似文献
50.
Norma A. Estrada Nestor Lagos Carlos García Alfonso N. Maeda-Martínez Felipe Ascencio 《Marine Biology》2007,151(4):1205-1214
Juvenile Pacific giant lions-paw scallops Nodipecten subnodosus were fed the toxic dinoflagellate Gymnodinium catenatum, a producer of paralytic shellfish poison (PSP), supplied with Isochrysis galbana (a nontoxic microalgae). Short-term (<24 h) experiments were performed to determine clearance and ingestion rates of G. catenatum. Kinetics of PSP was examined in longer-term experiments (>2 days). At high food concentrations, juvenile scallops showed
production of pseudofeces, partial shell valve closure, and reduction in feeding. According to HPLC analysis, the only toxins
present in the dinoflagellate G. catenatum and in the scallops were the gonyautoxins (GTXs), except in the labial palps and digestive gland, where trace amounts of
saxitoxin (STX) were present in scallops. These tissues could play an important role in toxin biotransformation. The ranking
of toxin concentration in tissues was: digestive gland > labial palps > intestine > gills > mantle > adductor muscle, where
the total contribution of viscera was more than 80% of the total toxin body burden. Juvenile scallops exhibited no apparent
detrimental physiological responses during the long-term feeding experiment. The dinoflagellate may contribute nutrients to
the scallop, in addition to the microalgae I. galbana. The dinoflagellate may enhance cell uptake and byssus production. Once PSP accumulated during the first 12 days, it was
slowly eliminated. The limited capacity for accumulating toxins in the adductor muscle favors domestic marketing of scallops. 相似文献