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991.
This study was undertaken to ascertain optimal methods of sampling, preserving, separating, and analyzing arsenic species
in potentially contaminated waters. Arsenic species are readily transformed in nature by slight changes in conditions. Each
species has a different toxicity and mobility. The conventional field sampling method using filters of 0.45 μm in size could
overestimate the dissolved arsenic concentrations, as passing suspended particles that can act as a sink or source of arsenic
depending on the site condition. For arsenic species in neutral pH and iron-poor waters, the precipitation can be stable for
up to 3 days without any treatment, but for longer periods, a preservative, such as phosphoric acid, is required. Also, the
analytical procedure must be selected carefully because the levels and hydride generation efficiencies of arsenic in different
species can vary, even for the same amount of arsenic. For arsenic speciation in samples that also include organic species,
a hybrid high-performance liquid chromatography (HPLC) column and inductively coupled plasma mass spectrometry (ICP-MS) gave
the best resolution and lowest detection limits. However, the procedure using a solid phase extraction (SPE) cartridge can
be used economically and conveniently for analyzing samples containing only inorganic arsenic species, such as groundwater,
especially that related to mine activity. 相似文献
992.
993.
Stefan M. Klose Justin A. Welbergen Anne W. Goldizen Elisabeth K. V. Kalko 《Behavioral ecology and sociobiology》2009,63(3):371-380
The social structure of animal aggregations may vary considerably in both space and time, yet little is known about how this
affects vigilance. Here, we investigate the vigilance architecture of a colony of wild-living grey-headed flying-foxes (Pteropus poliocephalus) in Australia and examine how spatial as well as temporal variation in social organization influences social and environmental
vigilance. We sampled color-marked individuals at different stages of the reproductive cycle and the year and at different
locations in the colony to examine the effects of temporal and spatial factors on social and environmental vigilance. We found
that vigilance architecture reflected the social structure of the colony, with the highest environmental vigilance being displayed
by bats at the periphery of the colony, and the highest social vigilance by bats that roosted at intermediate distances from
the colony’s edge. Furthermore, we found that vigilance levels reflected changes in reproductive state, with social vigilance
increasing toward the mating season, particularly in males. Our findings show that spatial and temporal variation in social
structure can have differential effects on social and environmental vigilance. This highlights the necessity to differentiate
between functions of vigilance to understand fully vigilance architecture in aggregations of social animals. 相似文献
994.
Edeltrauda Helios Rybicka Michael Jefferson Wilson 《Environmental science and pollution research international》2000,7(1):7-13
The examinations of selected wastes and stream sediments from the vicinity of a chemical plant by sequential extraction procedures
and direct methods, SEM/EDX and XRD, were carried out in order to identify the different forms of chromium, particularly as
they are released to potential mobility. The results show that the top and bottom waste samples contain 37,756 and 53,650
μg g1 Cr, respectively, but about 7% and 2% of the total chromium type Cr(VI). The chemical extraction results show that the mobility
of Cr in the upper part of the waste pile is significantly higher than in the bottom section; the exchangeable form of Cr
accounts for 25% and < 1%, respectively, the last one irrespective of redox conditions. About 50% of Cr is associated with
the reducible fraction of the top waste, and similar with the residual fraction in the bottom waste. Oxidation of the bottom
waste shift some portion of Cr from residual to the moderately reducible fraction. The major Cr-forms in the river sediments
are compounded with Fe-oxides. The < 2 μm size fraction of the selected sediment sample, particular enriched in chromium contained
up to 73,000 μg g1 Cr with about 95% of this in the moderately reducible fraction, predominantly bound with oxyhydroxides. SEM/EDX and XRD analysis
of wastes and river sediment indicate that the main insoluble Cr-phase is ferroan — (Mg, Fe) (Cr, Al)2O4 which would be dissolved mainly in the residual fraction. 相似文献
995.
Realistic models of contaminant transport in groundwater demand detailed characterization of the spatial distribution of subsurface hydraulic properties, while at the same time programmatic constraints may limit collection of pertinent hydraulic data. Fortunately, alternate forms of data can be used to improve characterization of spatial variability. We utilize a methodology that augments sparse hydraulic information (hard data) with more widely available hydrogeologic information to generate equiprobable maps of hydrogeologic properties that incorporate patterns of connected permeable zones. Geophysical and lithologic logs are used to identify hydrogeologic categories and to condition stochastic simulations using Sequential Indicator Simulation (SIS). The resulting maps are populated with hydraulic conductivity values using field data and Sequential Gaussian Simulation (SGS). Maps of subsurface hydrogeologic heterogeneity are generated for the purpose of examining groundwater flow and transport processes at the Faultless underground nuclear test, Central Nevada Test Area (CNTA), through large-scale, three-dimensional numerical modeling. The maps provide the basis for simulation of groundwater flow, while transport of radionuclides from the nuclear cavity is modeled using particle tracking methods. Sensitivity analyses focus on model parameters that are most likely to reduce the long travel times observed in the base case. The methods employed in this study have improved our understanding of the spatial distribution of preferential flowpaths at this site and provided the critical foundation on which to build models of groundwater flow and transport. The results emphasize that the impacts of uncertainty in hydraulic and chemical parameters are dependent on the radioactive decay of specific species, with rapid decay magnifying the effects of parameters that change travel time. 相似文献
996.
We develop regional-scale eutrophication models for lakes, ponds, and reservoirs to investigate the link between nutrients and chlorophyll-a. The Bayesian TREED (BTREED) model approach allows association of multiple environmental stressors with biological responses, and quantification of uncertainty sources in the empirical water quality model. Nutrient data for lakes, ponds, and reservoirs across the United States were obtained from the Environmental Protection Agency (EPA) National Nutrient Criteria Database. The nutrient data consist of measurements for both stressor variables (such as total nitrogen and total phosphorus), and response variables (such as chlorophyll-a), used in the BTREED model. Markov chain Monte Carlo (McMC) posterior exploration guides a stochastic search through a rich suite of candidate trees toward models that better fit the data. The Bayes factor provides a goodness of fit criterion for comparison of resultant models. We randomly split the data into training and test sets; the training data were used in model estimation, and the test data were used to evaluate out-of-sample predictive performance of the model. An average relative efficiency of 1.02 between the training and test data for the four highest log-likelihood models suggests good out-of-sample predictive performance. Reduced model uncertainty relative to over-parameterized alternative models makes the BTREED models useful for nutrient criteria development, providing the link between nutrient stressors and meaningful eutrophication response. 相似文献
997.
Klaus G. Heumann 《毒物与环境化学》2013,95(2):111-129
The application of mass spectrometric isotope dilution analysis in environmental analytical chemistry is described. Different ionization methods used in mass spectrometry for isotope dilution analysis and the advantage of isotope dilution analysis owing to its accuracy are discussed. The principle of the isotope dilution technique is explained using thallium analysis as an example. Possible methods of sample decomposition for organic and inorganic matrices and of element separation are given. Using lead, cadmium and thallium analyses as examples the application of mass spectrometric isotope dilution analysis for determination of toxic metals in environmental samples is shown. The determination of chloride and bromide traces in snow is given as an example of non‐metal analysis. The possibility of determining pure elements by the isotope dilution technique using a long‐lived radioactive isotope as a spike is discussed. 相似文献
998.
Ilija Vukadin 《毒物与环境化学》2013,95(1):209-215
Chemical hydrography, nutrients and trace metals in water, sediments and marine organisms were studied in the Bay of Mali Ston and their role in terms of pollution discussed. Results show that the entire study area is very strongly affected by the adjacent land. The overall area is well aerated so that no dangerous accumulation of nutrients with oxygen content reduction was recorded. Results of analyses of trace metals show that the water and sediments of the bay contain high levels of some metals significantly higher than those from the open sea. This may be attributed to the natural sedimentation processes and the Neretva River and submarine spring runoffs carrying constituents of ignous and limestone rocks. 相似文献
999.
Assessment of heavy metals contamination in soils surrounding a gold mine: comparison of two digestion methods 总被引:1,自引:0,他引:1
This study investigated two digestion methods (USEPA 3051: microwave, HNO3 or Hossner: hot plate, HF–H2SO4–HClO4) for heavy metals analysis in contaminated soil surrounding Mahad AD'Dahab mine, Saudi Arabia. Moreover, contamination metal levels were estimated. The Hossner and USEPA 3051 methods showed, respectively, average total contents of 17.2 and 18.1 mg kg?1 for Cd, 11.6 and 10.6 mg kg?1 for Co, 45.7 and 34.7 mg kg?1 for Cr, 1030 and 1100 mg kg?1 for Cu, 33,300 and 27,400 mg kg?1 for Fe, 963 and 872 mg kg?1 for Mn, 33.2 and 22.8 mg kg?1 for Ni, 791 and 782 mg kg?1for Pb, and 6320 and 2870 mg kg?1 for Zn. A lack of significant differences and a high correlation coefficient (>90%) for Cd, Pb and Cu between the two digestion methods suggest that the total-recoverable method (USEPA 3051) may be equivalent to the total-total digestion method (Hossner) for determining these metals in the studied soil. However, significantly higher concentrations of Cr, Fe, Ni and Zn were found by the Hossner method comapred with the USEPA 3051 method. The soil samples have very or extremely high levels of Zn, Cu, Cd and Pb contamination, indicating very high potential ecological risk. 相似文献
1000.
Michael J. Burtscher 《Safety Science》2012,50(5):1344-1354
The importance of team mental models (TMMs) - team members’ shared and organized understanding of relevant knowledge - for teamwork and team-performance, particularly in high-risk industries, has been recognized for almost two decades. In healthcare, however, systematic investigations on the influence of TMM on teamwork and team-performance had yet to be conducted at the time of this review, despite many authors considering the concept to be useful for medical teams. The lack of measurement procedures appropriate for settings as complex and dynamic as, for example, the operating room, represents a major obstacle for empirical research in healthcare. We systematically reviewed empirical studies on TMMs aiming to identify methods that could be applied in healthcare. In particular, we analyzed the methods used, and situations in which TMMs have been investigated. The reviewed studies were sorted according to task and team characteristics. We discuss the results of this review with regard to characteristics of healthcare teams including anaesthesia teams and teams of ward nurses. Each of these examples represents a distinct teamwork setting (e.g. long- vs. short-lived teams) and hence requires a different approach to TMM measurement (e.g. focus on task-model vs. focus on team-model). Implications for study design, feasible measurement approaches, and questions for future research on TMMs in healthcare are discussed. In sum, our findings highlight the possible significance of TMM research in healthcare and its potential benefits for team-performance and, ultimately, patient safety. 相似文献