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61.
Gareth K. Phoenix Jonathan R. Leake David J. Read J. Philip Grime John A. Lee 《Water, Air, & Soil Pollution: Focus》2004,4(6):159-167
Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha–1 year–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing 15N labelled ammonium nitrate (+35 kg N ha–1 year–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of 15N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study. 相似文献
62.
George Yu. Sofronov Gareth E. Evans Jonathan M. Keith Dirk P. Kroese 《Environmental Modeling and Assessment》2009,14(5):577-584
The genomes of complex organisms, including the human genome, are highly structured. This structure takes the form of segmental
patterns of variation in various properties and may be caused by the division of genomes into regions of distinct function,
by the contingent evolutionary processes that gave rise to genomes, or by a combination of both. Whatever the cause, identifying
the change-points between segments is potentially important, as a means of discovering the functional components of a genome,
understanding the evolutionary processes involved, and fully describing genomic architecture. One property of genomes that
is known to display a segmental pattern of variation is GC content. The GC content of a portion of DNA is the proportion of
GC pairs that it contains. Sharp changes in GC content can be observed in human and other genomes. Such change-points may
be the boundaries of functional elements or may play a structural role. We model genome sequences as a multiple change-point
process, that is, a process in which sequential data are separated into segments by an unknown number of change-points, with
each segment supposed to have been generated by a different process. We consider a Sequential Importance Sampling approach
to change-point modeling using Monte Carlo simulation to find estimates of change-points as well as parameters of the process
on each segment. Numerical experiments illustrate the effectiveness of the approach. We obtain estimates for the locations
of change-points in artificially generated sequences and compare the accuracy of these estimates to those obtained via Markov
chain Monte Carlo and a well-known method, IsoFinder. We also provide examples with real data sets to illustrate the usefulness
of this method. 相似文献
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64.
Thomas GO Farrar D Braekevelt E Stern G Kalantzi OI Martin FL Jones KC 《Environment international》2006,32(1):34-40
Chlorinated paraffins (also called polychlorinated n-alkanes -- PCAs) are a class of industrial chemicals comprising chlorinated straight chain hydrocarbons. They have a wide range of applications and are now found in a range of environmental compartments. We analysed a total of 25 human milk-fat samples, donated by 18 individuals from the urban London and more rural Lancaster areas in the UK, for short chain PCAs (C(10)-C(13) sPCAs) and medium chain PCAs (C(14)-C(17) mPCAs), using gas chromatography-ECNI high-resolution mass spectrometry. Our study confirms that trace quantities of PCAs can reach human milk-fat. sPCAs were detected in all but four samples, while mPCAs were detected in all samples. The median sPCA concentration was 180 ng/g fat (range of 49 to 820 ng/g fat -- detected values only) and the median mPCA concentration was 21 ng/g fat (range of 6.2 to 320 ng/g fat). No differences were noted in ranges of observed values for either sPCAs or mPCAs between samples from London and Lancaster. Most samples also exhibited similar patterns of sPCAs and mPCAs. One sample exhibited a different pattern for sPCAs and mPCAs, an observation that may be related to differences in exposure or biological factors for this individual. 相似文献
65.
Hansen HR Raab A Price AH Duan G Zhu Y Norton GJ Feldmann J Meharg AA 《Journal of environmental monitoring : JEM》2011,13(1):32-34
Tetramethylarsonium has for the first time been identified in a commercially grown food product, rice, constituting up to 5.8% of the total arsenic in the rice. 相似文献
66.
Wildfires are a common feature of peatland environments, but the carbon balance of these wildfires is often not considered and the production of refractory black carbon in these wildfires could be an important addition to carbon accumulation and mitigate losses of biomass during the fire. This study investigates the biomass and carbon losses during a moorland wildfire. Changes in above-ground carbon stocks were calculated using a combination of field data, laboratory measurements and literature values. The results show that approximately 14% of the carbon in the original above-ground biomass remained on the site after the burn. Black carbon production was approximately 6 gC m(-2) which constituted 4.3% of the biomass lost. The survival of biomass and black carbon may help to mitigate the loss of carbon during the fire. 相似文献
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69.
Disease resistance: a benefit of sociality in the dampwood termite Zootermopsis angusticollis (Isoptera: Termopsidae) 总被引:1,自引:0,他引:1
Rebeca B. Rosengaus Amy B. Maxmen Laran E. Coates James F. A. Traniello 《Behavioral ecology and sociobiology》1998,44(2):125-134
The benefit of sociality in relation to disease susceptibility was studied in the dampwood termite Zootermopsis angusticollis. Although contact with high concentrations of fungal conidia is lethal, the survivorship of nymphs exposed to spore suspensions
ranging from 6 × 106 to 2 × 108 spores/ml of the fungus Metarhizium anisopliae increased with group size. The survivorship (measured as LT50) of isolated individuals ranged from 3.0 to 4.8 days, but infected nymphs living in groups of 10 and 25 individuals survived
significantly longer (5.6–8.3 and 5.6–9.1 days, respectively). In most cases, there were no significant differences in the
survival distributions of the 10- and 25-termite groups. When nymphs were infected with concentrations of 7 × 101–7 × 104 spores/ml and allowed to interact with healthy nestmates, fungal infections were not contracted by the unexposed termites.
Moreover, infected termites benefitted from social contact with unexposed nestmates: their survival rates were significantly
higher than those of infected termites living with similarly infected nestmates. Allogrooming, which increased in frequency
during and after exposure to conidia, appeared to remove potentially infectious spores from the cuticle, thus increasing termite
survivorship. These results suggest that allogrooming plays a crucial role in the control of disease and its death hazard
in termites. The infection-reducing advantage of group living may have been significant in the evolution of social behavior
in the Isoptera.
Received: 18 March 1998 / Accepted after revision: 31 May 1998 相似文献
70.