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141.
Kenneth B. Raposa Marci L. Cole Ekberg David M. Burdick Nicholas T. Ernst Susan C. Adamowicz 《Regional Environmental Change》2017,17(2):389-397
Salt marshes persist within the intertidal zone when marsh elevation gains are commensurate with rates of sea-level rise (SLR). Monitoring changes in marsh elevation in concert with tidal water levels is therefore an effective way to determine if salt marshes are keeping pace with SLR over time. Surface elevation tables (SETs) are a common method for collecting precise data on marsh elevation change. Southern New England is a hot spot for SLR, but few SET elevation change datasets are available for the region. Our study synthesizes elevation change data collected from 1999 to 2015 from a network of SET stations throughout Rhode Island (RI). These data are compared to accretion and water level data from the same time period to estimate shallow subsidence and determine whether marshes are tracking SLR. Salt marsh elevation increased at a mean overall rate of 1.40 mm year?1 and ranged from ?0.33 to 3.36 mm year?1 at individual stations. Shallow subsidence dampened elevation gain in mid-Narragansett Bay marshes, but in other areas of coastal RI, subsurface processes may augment surface accretion. In all cases, marsh elevation gain was exceeded by the 5.26 mm year?1 rate of increase in sea levels during the study period. Our study provides the first SET elevation change data from RI and shows that most RI marshes are not keeping pace with short- or long-term rates of SLR. It also lends support to previous research that implicates SLR as a primary driver of recent changes to southern New England salt marshes. 相似文献
142.
Environmental Management - Restoration ecologists conduct both basic and applied research using a diversity of funding and collaborative models. Over the last 17 years we have assessed the... 相似文献
143.
The formation and fate of chlorinated organic substances in temperate and boreal forest soils 总被引:1,自引:0,他引:1
Nicholas Clarke Květoslava Fuksová Milan Gryndler Zora Lachmanová Hans-Holger Liste Jana Rohlenová Reiner Schroll Peter Schröder Miroslav Matucha 《Environmental science and pollution research international》2009,16(2):127-143
Background, aim and scope Chlorine is an abundant element, commonly occurring in nature either as chloride ions or as chlorinated organic compounds
(OCls). Chlorinated organic substances were long considered purely anthropogenic products; however, they are, in addition,
a commonly occurring and important part of natural ecosystems. Formation of OCls may affect the degradation of soil organic
matter (SOM) and thus the carbon cycle with implications for the ability of forest soils to sequester carbon, whilst the occurrence
of potentially toxic OCls in groundwater aquifers is of concern with regard to water quality. It is thus important to understand
the biogeochemical cycle of chlorine, both inorganic and organic, to get information about the relevant processes in the forest
ecosystem and the effects on these from human activities, including forestry practices. A survey is given of processes in
the soil of temperate and boreal forests, predominantly in Europe, including the participation of chlorine, and gaps in knowledge
and the need for further work are discussed.
Results Chlorine is present as chloride ion and/or OCls in all compartments of temperate and boreal forest ecosystems. It contributes
to the degradation of SOM, thus also affecting carbon sequestration in the forest soil. The most important source of chloride
to coastal forest ecosystems is sea salt deposition, and volcanoes and coal burning can also be important sources. Locally,
de-icing salt can be an important chloride input near major roads. In addition, anthropogenic sources of OCls are manifold.
However, results also indicate the formation of chlorinated organics by microorganisms as an important source, together with
natural abiotic formation. In fact, the soil pool of OCls seems to be a result of the balance between chlorination and degradation
processes. Ecologically, organochlorines may function as antibiotics, signal substances and energy equivalents, in descending
order of significance. Forest management practices can affect the chlorine cycle, although little is at present known about
how.
Discussion The present data on the apparently considerable size of the pool of OCls indicate its importance for the functioning of the
forest soil system and its stability, but factors controlling their formation, degradation and transport are not clearly understood.
It would be useful to estimate the significance and rates of key processes to be able to judge the importance of OCls in SOM
and litter degradation. Effects of forest management processes affecting SOM and chloride deposition are likely to affect
OCls as well. Further standardisation and harmonisation of sampling and analytical procedures is necessary.
Conclusions and perspectives More work is necessary in order to understand and, if necessary, develop strategies for mitigating the environmental impact
of OCls in temperate and boreal forest soils. This includes both intensified research, especially to understand the key processes
of formation and degradation of chlorinated compounds, and monitoring of the substances in question in forest ecosystems.
It is also important to understand the effect of various forest management techniques on OCls, as management can be used to
produce desired effects. 相似文献
144.
Harwell MC Surratt DD Barone DM Aumen NG 《Environmental monitoring and assessment》2008,147(1-3):445-462
Agricultural and urban runoff pumped into the perimeter canals of the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge), a 58,320-ha soft-water wetland, has elevated nutrients which impact the Refuge interior marsh. To best manage the Refuge, linkages between inflows to the perimeter canals and environmental conditions within the marsh need to be understood. Conductivity, which typically is high in the canals and lowest at the most interior sites, was used as a surrogate tracer to characterize patterns of constituent transport. The Refuge was initially classified into four zones based upon patterns and variability in conductivity data: Canal Zone; Perimeter Zone (canal to 2.5 km into the interior); Transition Zone (2.5 to 4.5 km from the canal); Interior Zone (>4.5 km from the canal). Conductivity variability declined from the Perimeter to the Interior Zone, with the highest variability in the marsh observed in the Perimeter Zone and the lowest variability observed in the Interior Zone. Analysis of other water quality parameters indicated that conditions in the Perimeter and Transition Zones were different, and more impacted, than in the Interior Zone. In general, there was a positive relationship between structure inflows and canal phosphorus concentrations, including discharges from treatment wetlands and bypasses of untreated water. This classification approach is applicable for stratified sampling designs, resolving spatial bias in water quality models, and in aiding in management decisions about resource allocation. 相似文献
145.
A study was conducted in southern Ethiopia to evaluate the nutrient status on smallholder farms with respect to land use class
(garden, grassland, and outfield) and slope position (upper, middle, and lower). Soil physical and chemical properties were
quantified using soil samples collected at two depths (0–15 and 15–30 cm). Available phosphorous was significantly different
among the three land use classes. However, organic carbon and total nitrogen were lower in the outfield compared to the garden
and grass land but not significantly different. The lower than expected nutrient status of the garden and grassland, which
receive almost all available organic supplements, was attributed to the overall low availability of these inputs. Similarly,
pH and cation exchange capacity were not significantly different among the different land use classes. However, the sum of
the exchangeable cations was significantly higher in the garden compared to the outfields. Comparison at landscape level revealed
that the sand fraction was significantly greater, whereas the silt fractions were significantly smaller, on the lower slopes
relative to the middle slopes. Moreover, the organic carbon, total nitrogen, cation exchange capacity, Ca, and Mg values were
significantly less on lower slopes than upper and middle slopes. Perhaps this is because of leaching and the effect of deposition
of coarser sediments from the prevailing gully system. Overall, the fertility of the soil was adequate for supporting smallholder
farming, but consideration must be given to reducing pressure on the land resources, addressing erosion problems, and providing
a line of credit for purchasing inputs. 相似文献
146.
147.
148.
Nicholas J. Wald Jonathan P. Bestwick Wayne J. Huttly Jonathan Aldis Antoni Borrell Sandy Goodburn Ian Mills 《黑龙江环境通报》2018,38(13):1079-1085
The aims of this study were to determine whether assumptions used in prenatal screening for Down syndrome in twin pregnancies are valid and derive estimates of risk and screening performance in twin pregnancies using observed data. Data were collected on nuchal translucency, chorionicity, pregnancy associated plasma protein-A (PAPP-A), and free ß human chorionic gonadotrophin (free ß-hCG) from 61 twin pregnancies with Down syndrome and 7302 unaffected twin pregnancies. Distribution parameters were determined and used to estimate screening performance. The assumption that proportional differences in serum marker levels in affected and unaffected singleton pregnancies apply to twin pregnancies was not confirmed. Median free β-hCG value in monochorionic affected twin pregnancies (2.63 multiples of the median [MoM]; 95% CI, 1.79-3.22 MoM) was lower than that assuming proportionality (3.76 MoM), and the median PAPP-A value in dichorionic affected twin pregnancies (1.88 MoM; 95% CI, 1.60-2.17 MoM) was higher than that based on proportionality (1.33 MoM). The detection rate was 87% for a 3% false-positive rate in monochorionic twin pregnancies and 74% in dichorionic twin pregnancies compared with 86% in singleton pregnancies. Estimates of screening performance in Down syndrome twin pregnancies do not need to rely on assumptions and can take account of chorionicity and gestational age. 相似文献
149.
A model is described that may help to resolve uncertainty and controversy over the long-term consequences of sludge applications to arable land, especially with regard to the effects of sludge adsorption characteristics on trace metal solubility and bioavailability (e.g., the sludge "time bomb" or sludge "protection" hypotheses). Mass balances of organic and inorganic material derived from sludge and crop residues are simulated. Each pool has a potentially different adsorption affinity for trace metals, and this leads to changes in the adsorption capacity of sludge-amended soil that influence leaching and crop uptake. Model simulations were compared with measured changes in organic carbon and ethylenediaminetetraacetic acid (EDTA)-extractable cadmium contents in a clay loam soil following 41 years of sludge applications. The model adequately reproduced the data, although discrepancies in the vertical distribution of Cd were attributed to the effects of macropore transport and root-uptake driven recirculation. A Monte Carlo sensitivity analysis demonstrated that the most important parameters affecting leaching and crop uptake were the Cd loading and parameters controlling adsorption, especially the partition coefficient for sludge-derived inorganic material and the exponent regulating the effect of pH on sorption. Scenario simulations show that no general conclusions can be drawn with respect to the validity of the sludge "time bomb" and sludge "protection" hypotheses. Either may occur, or neither, depending on three key system parameters: the ratio of sludge adsorption capacity to the initial adsorption capacity of the soil, the proportion of the sludge adsorption capacity contributed by the inorganic fraction, and the sludge Cd loading. 相似文献
150.
Cynthia S. Loftin Wiley M. Kitchens Nicholas Ansay 《Journal of the American Water Resources Association》2001,37(4):935-956
ABSTRACT: :The model described herein was used to assess effects of the Suwannee River sill (a low earthen dam constructed to impound the Suwannee River within the Okefenokee National Wildlife Refuge to eliminate wildfires) on the hydrologic environment of Okefenokee Swamp, Georgia. Developed with Arc/Info Macro Language routines in the GRID environment, the model distributes water in the swamp landscape using precipitation, inflow, evapotranspiration, outflow, and standing water. Water movement direction and rate are determined by the neighborhood topographic gradient, determined using survey grade Global Positioning Systems technology. Model data include flow rates from USGS monitored gauges, precipitation volumes and water levels measured within the swamp, and estimated evapotranspiration volumes spatially modified by vegetation type. Model output in semi‐monthly time steps includes water depth, water surface elevation above mean sea level, and movement direction and volume. Model simulations indicate the sill impoundment affects 18 percent of the swamp during high water conditions when wildfires are scarce and has minimal spatial effect (increasing hydroperiods in less than 5 percent of the swamp) during low water and drought conditions when fire occurrence is high but precipitation and inflow volumes are limited. 相似文献