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901.
Weichuan Qiao Rong Li Tianhao Tang Achuo Anitta Zuh 《Frontiers of Environmental Science & Engineering》2021,15(2):20
902.
Effects of Stonewalled Terracing Techniques on Soil-Water Conservation and Wheat Production Under Mediterranean Conditions 总被引:2,自引:0,他引:2
A field plot experiment was conducted in the Palestinian Autonomous Areas to study the effect of stonewalled terracing on soil and water conservation as compared to the nonterraced areas. Effects of the wheat canopy were considered as a second treatment. The experiment was undertaken over a period of two seasons (2000 and 2001). The results of the experiment found that the mean soil erosion was significantly lower (P < 0.05) in the terraced plots than in those that were nonterraced (182 kg/ha and 3525 kg/ha during the first season, 1769 kg/ha and 5057 kg/ha during the second season for terraced and nonterraced plots, respectively). A similar trend was observed with respect to runoff in areas under the same treatments. The wheat canopy showed lower, but not significant runoff and erosion in most of the cases for both seasons. Due to better soil and water conservation, the terraced plots obtained significantly higher total plant dry matter than nonterraced plots (1570 and 630 kg/ha in 2000, 2545 and 889 kg/ha in 2001 for terraced and nonterraced treatment, respectively). The runoff coefficient was 20% and 4% for the nonterraced and terraced plots, respectively. Rainstorms with intensity ≥4 mm/hand rainfall ≥10 mm are more likely to cause runoff and erosion. 相似文献
903.
Tijuana Childhood Lead Risk Assessment Revisited: Validating a GIS Model with Environmental Data 总被引:3,自引:0,他引:3
The objective of this research was to determine the spatial distributions of childhood lead poisoning and soil lead contamination
in urban Tijuana. The Bocco–Sanchez model of point-source emissions was evaluated in terms of validity and reliability. We
compared the model's predicted vulnerable populations with observed cases of childhood lead poisoning in Tijuana, identified
fixed point sources in the field, and analyzed 76 soil samples from 14 sites. The soil lead results were compared to the blood
lead analyses performed on Tijuana children whose blood lead levels were ≥10 μg/dL, who reported that they did not use lead-glazed
ceramics for cooking or storing food (n = 63). Using GIS, predicted vs observed risk areas were assessed by examining spatial patterns, including the distribution of cases
per designated risk area. Chi-square analysis of expected vs observed values did not differ significantly at the p = 0.02 level, showing that the model was strikingly accurate in predicting the distribution of subjects with elevated blood lead.
Results reveal that while point sources are significant, other sources of lead exposure are also important. The relative public
health risk from exposure to lead in an urban setting may be assessed by distinguishing among sources of exposure and associating
concentrations to blood lead levels. The results represent an iterative approach in environmental health research by linking
environmental and human biomarker lead concentrations and using these results to validate an environmental model of risk to
lead exposure. 相似文献
904.
In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0–5 cm and 5–20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0–5-cm topsoil in both C. microphylla and A. halodendron. At the 5–20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla. 相似文献
905.
RESEARCH: Managing Mountainous Degraded Landscapes After Farmland Abandonment in the Central Spanish Pyrenees 总被引:1,自引:0,他引:1
Genista scorpius. Under a dense shrub cover both runoff and sediment yield are strongly controlled. As the shrub cover becomes open, sediment
yield and runoff increase greatly. A dense herbaceous cover yields high runoff coefficients but moderate soil losses. From
the results obtained, the possibility of abandoned field reclamation by means of selective clearing of scrub is discussed. 相似文献
906.
Carlos Garcia Teresa Hernandez Ascension Barahona Francisco Costa 《Environmental management》1996,20(1):133-141
Twenty-one severely eroded soils of SE Spain (Torriorthent xeric soils) were studied. These soils form a fragile system characterized
by soils with a low density of plant cover (<5%), are loamy and occur in a semiarid climate. The soils formerly were used
for agricultural purposes but were abandoned at least 15 years ago. These eroded soils had a low total organic carbon content,
and their humic substances, humic acid carbon, and carbohydrates were lower compared with soils that had never been cultivated
(natural soils). The variables in which the effects of erosion were particularly noted were those related with the active
organic matter (respiration and water-soluble organic matter). Those eroded soils with higher salt content showed lower organic
matter and carbohydrate contents. Only total nitrogen was correlated with the carbon fractions in the eroded soils. 相似文献
907.
This article describes an approach to assessing spatial and temporal land-use and land-cover changes in and adjacent to protected
areas and to the measurement of landscape stability within a protected area. Methods employed include aerial photographic
interpretation and GIS technology. Odum's four-compartment ecosystem model provides the conceptual framework for assessing
landscape stability. The study area is a selected sample of the Upper San Pedro National Riparian Conservation Area in the
high desert grassland of southeastern Arizona. Significant changes were observed in the landscape matrix and riparian ecosystem.
However, when these changes were assessed in the context of Odum's model, the change was nonsignificant. Implications of the
approach and potential applications in protected area management are discussed. 相似文献
908.
Ground flora trampling studies: Five years after closure 总被引:8,自引:1,他引:8
Trampling as an ecological factor is a major concern of the management of park, forest, nature preserves, and wilderness areas
as recreational resources. Of particular importance to the management concept of carrying capacity is the relative resistance
of native plant communities, to trampling and the resilience or the capacity of impacted communities to recover. This information
can be used by management to establish seasonal use limits to prevent irreversible degradation of these resources. The purpose
of this study was to follow the recolonizaton of experimental trail surfaces barren of vegetative cover and hiked at three
levels of use intensity. Results of this study indicate that soil compaction as measured by soil penetration resistance increased
progressively with use level while the total number of species, species diversity, and dominant index scores declined. A major
finding was that the greatest degree of change occurred at the first level of hiking, indicating that major floristic measures
were most affected by the least amount of hiking. Recolonization of impacted areas that received 100 trampling passes as measured
by plant cover, dominant indices, floristic dissimilarity, and species diversity was similar to areas receiving four and eight
times more trampling, despite major differences in soil penetration resistance. These data suggest limited use delivered at
one time can be as damaging as increasing levels of use delivered at over time. 相似文献
909.
Robert H. Webb H. Craig Ragland William H. Godwin Oennis Jenkins 《Environmental management》1978,2(3):219-233
The effects of off-road vehicles (ORVs) on the physical and chemical properties of 6 soil series were measured at Hollister Hills State Vehicular Recreation Area in central California. Accelerated soil erosion and the alteration of surface strength, bulk density, soil moisture, temperature, and soil nutrients were quantified to gain an insight into the difficulty of revegetating altered, or modified, areas.Erosion is severe at Hollister Hills, particularly in coarse grained soils on steep slopes. Erosion displaced 0.5 and 3.0 metric tons per square meter on 2 trails on gravelly sandy loam, and 0.3 metric tons/m2 from a trail on sandy loam. The surface strength and bulk density increased while the soil moisture decreased in gravelly sandy loam, coarse sandy loam, sandy loam, and clay. Clay loam had an increased surface strength with variably increased bulk density and no decrease in soil moisture. Diurnal temperature fluctuations increased and organic material and soil nutrients decreased in soil modified by vehicles.These property changes increase the erosion potential of the soil, impede germination of seedlings, and slow natural revegetation. Management methods in ORV-use areas should include planning trails by prior application of the universal soil loss equation and soil surveys, trail closure before complete loss of the soil mantle, and revegetation of closed areas. 相似文献
910.
Charles P. Newcombe 《Journal of the American Water Resources Association》2003,39(3):529-544
ABSTRACT: A new type of empirical model described here enables real time assessment of impacts caused by excessive water cloudiness as a function of (a) reduced visual clarity (excessive cloudiness) and (b) duration of exposure to cloudy conditions, in fisheries or fish life stages adapted to life in clear water ecosystems. This model takes the familiar form used in earlier suspended sediment dose effect models where z is severity of ill effect (SEV), x is duration of exposure (h), y is black disk sighting range (y BD, m)—a measure of water clarity, a is the intercept, and b and c are slope coefficients. As calibrated in this study the model is Severity of ill effect is ranked on a 15‐step scale that ranges from 0 to 14, where zero represents nil effect and 14 represents 100 percent mortality. This model, based on peer consultation and limited meta analysis of peer reviewed reports, accomplishes the following: (a) identifies the threshold of the onset of ill effects among clear water fishes; (b) postulates the rate at which serious ill effects are likely to escalate as a function of reduced visual clarity and persistence; (c) provides a context (the “visual clarity” matrix, with its cell coordinates) to share and compare information about impacts as a function of visual clarity “climate” (d) demonstrates changes in predator prey interactions at exposures greater than and less than the threshold of direct ill effects; (e) calibrates trout reactive distance (cm) as function of water clarity in the form where y represents reactive distance (cm) and x represents visual clarity (black disk sighting range, cm), and where a and b are intercept and slope respectively, such that (f) identifies black disk sighting range, in meters, and its reciprocal, beam attenuation, as preferred monitoring variables; and (g) provides two additional optical quality variables (Secchi disk extinction distance and turbidity) which, suitably calibrated as they have been in this study, expand the range of monitoring options in situations in which the preferred technology—beam attenuation equipment or black disk sighting equipment—is unavailable or impractical to use. This new model demonstrates the efficacy of peer collaboration and defines new research horizons for its refinement. 相似文献