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41.
Ernesto Bosatta 《Ecological modelling》1981,13(4):223-236
This paper demonstrates that if soil microorganisms are devoted suppliers of nitrogen, plant roots can coexist with them in the soil, i.e. if nitrogen net-mineralization is positive, the root-decomposer system is asymptotically stable. On the other hand, if net mineralization is negative, the system evolves in time towards the annihilation of the roots.Available data from an old pine stand system show that net mineralization is sometimes positive and sometimes negative during the course of a year. It is shown here that this situation is compatible with a state of dynamic stability in the root-decomposer system. The restrictions imposed on the validity of this analysis are also deduced. 相似文献
42.
Satellite telemetry and prey sampling reveal contaminant sources to Pacific Northwest Ospreys. 总被引:1,自引:0,他引:1
John E Elliott Christy A Morrissey Charles J Henny Ernesto Ruelas Inzunza Patrick Shaw 《Ecological applications》2007,17(4):1223-1233
Migratory behavior can be an important factor in determining contaminant exposure in avian populations. Accumulation of organochlorine (OC) pesticides while birds are wintering in tropical regions has been cited often as the reason for high concentrations in migrant populations. To explore this issue, we satellite tracked 16 Ospreys (Pandion haliaetus) over the period 1996-2003 from breeding sites in British Columbia, Canada, and integrated the results into a database on 15 Ospreys that were satellite tracked over the period 1995-1999, from breeding locations in Washington and Oregon, USA. Data on wintering sites of 31 Ospreys in Mexico and Central America were used for spatially targeted sampling of prey fish. Concentrations of the main organochlorine contaminant, p,p'-dichloro-diphenyl-dichloroethylene (DDE), in fish composites from Mexico ranged from 0.005 to 0.115 nicrog/g wet mass. Significant differences existed among fish families in p,p'-DDE, total dichloro-diphenyl-trichloroethane (sigmaDDT), sigmachlordanes, and total polychlorinated biphenyls (sigmaPCBs). Catfish (family Ariidae) generally had significantly higher levels of DDT metabolites and other organochlorine contaminants compared to other fish families collected. Differences in prey contaminant levels were detected among the collection sites around coastal Mexico, with fish from Veracruz State generally having higher levels of DDT metabolites, sigmachlordanes, sigmaPCBs, and hexachlorobenzene. Eggs collected from 16 nests throughout the Pacific Northwest (nine from British Columbia, seven from Oregon and Washington) where Ospreys had been satellite tagged, showed marked variation in levels of DDT metabolites (p,p'-DDE; range 0.02-10.14 microg/g). Wintering site had no significant effect on contaminant concentrations in sample eggs from those specific Ospreys; rather concentrations of p,p'-DDE, were predicted by breeding sites with highest levels in eggs of Ospreys breeding in the lower Columbia River, consistent with published reports of continued high concentrations of DDT and related compounds in that system. 相似文献
43.
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
44.
Fernando Bonilla-Musoles Luis E. Machado Newton G. Osborne Elkin A. Muñoz Francisco Raga Javier Blanes Francisco Bonilla Jr 《黑龙江环境通报》2001,21(8):622-626
A comparison between two-dimensional (2D), and three-dimensional (3D) ultrasonography was made in four fetuses diagnosed with neural tube defect (NTD) in the first half of pregnancy. 3D ultrasonography (orthogonal and multiplanar systems) proved to be an excellent complement to 2D, particularly when using orthogonal planes. When using the 3D multiplanar surface imaging system, excellent images of the malformations can be rapidly obtained. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
45.
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
46.
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
47.
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
48.
M. D. Herrero-Pérezrul H. Reyes Bonilla F. García-Domínguez C. E. Cintra-Buenrostro 《Marine Biology》1999,135(3):521-532
The reproduction and growth of Isostichopus fuscus (Ludwig, 1875) at Isla Espíritu Santo, Baja California Sur, México from July 1992 to September 1993 and from August 1996
to July 1997 were analyzed. The reproductive cycle was monitored by using histological analysis. Five gonadal stages were
described according to cell types present in the gonad; undetermined, gametogenesis, maturity, spawning and post-spawning.
This holothurian reproduces annually during summer (July to September), when sea surface temperature reaches 27 °C. The gonad
index is related to the gonadal stages. The first sexual maturity for I. fuscus was calculated at 367 g (4 to 5 years old) according to the von Bertalanffy equation, and nearly all the specimens at Isla
Espíritu Santo were 5 to 7 years old (including some individuals over 35 years old). Data of the length–weight relationship
showed that I. fuscus grows allometrically at the studied site (b = 1.83). The mortality rate was relatively high (M = 0.51), indicating that in a typical cohort, 40% of the recruits does not survive the first year, and less than 20% reaches
maturity.
Received: 15 July 1998 / Accepted: 19 August 1999 相似文献
49.
50.
Dissolved oxygen (DO) left in the voids of buffer and backfill materials of a deep geological high level radioactive waste (HLW) repository could cause canister corrosion. Available data from laboratory and in situ experiments indicate that microbes play a substantial role in controlling redox conditions near a HLW repository. This paper presents the application of a coupled hydro-bio-geochemical model to evaluate geochemical and microbial consumption of DO in bentonite porewater after backfilling of a HLW repository designed according to the Swedish reference concept. In addition to geochemical reactions, the model accounts for dissolved organic carbon (DOC) respiration and methane oxidation. Parameters for microbial processes were derived from calibration of the REX in situ experiment carried out at the Asp? underground laboratory. The role of geochemical and microbial processes in consuming DO is evaluated for several scenarios. Numerical results show that both geochemical and microbial processes are relevant for DO consumption. However, the time needed to consume the DO trapped in the bentonite buffer decreases dramatically from several hundreds of years when only geochemical processes are considered to a few weeks when both geochemical reactions and microbially-mediated DOC respiration and methane oxidation are taken into account simultaneously. 相似文献