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131.
Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme
vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The
aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency
distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth
function were estimated (K=0.281 year−1; t
0=0.043; C=0.103; and t
s=0.268) assuming a L
∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously
for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled
off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year−1(99.4% year−1) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic
bottleneck appears to limit the number of juveniles on some shores. 相似文献
132.
Derek P. Manning Carla Jones Frederick James Rowland Martin Roff 《Journal of Safety Research》1998,29(4):275-283
For more than a decade, evidence has been accumulating that points to the fact that the microscopic roughness of the footwear soling surface is a major determinant of slip-resistance on lubricated surfaces, but conclusive experimental proof has been lacking. This article describes an experiment in which five pairs of shoes were soled with the same rubber compound. Four of the pairs were abraded by different grades of grit to produce a range of roughness values. The coefficient of friction (CoF) of the five solings was then measured repeatedly by the walking traction method on wet surfaces including glazed wall tiles, vinyl asbestos coated with the wax floor polish, and both sides of a sheet of float glass. The Kruskal-Wallis statistical test proved beyond doubt that the soling roughness is a major factor in determining the CoF of this rubber soling material; p < 10−5. Nearly all of the grip was due to surface roughness of the soling material on these atypically smooth floors, although the surface roughness of the floors also had a significant effect on CoF; p < 0.003. Float glass is shown to be a promising reference floor material for the measurement of CoF of footwear; there was no statistical difference between results for the two sides of the glass sheet. Float glass could be used in the development of a standard CoF test method because new sheets of glass from the same manufacturer are identical and extremely smooth. The specification of CoF values for solings/floors combinations in lubricated conditions is of little value unless associated with roughness measurements and knowledge of how wear will affect the surface roughness of the sole. This article reports the first evidence that any specification of flooring by measuring CoF based on dry surfaces could lead to an increase in the number of injuries caused by slipping on the wet surfaces. Published by Elsevier Science Ltd 相似文献
133.
A congener-specific PCDD/F emissions inventory for the UK: do current estimates account for the measured atmospheric burden? 总被引:2,自引:0,他引:2
Considerable effort has been expended in the UK and elsewhere to quantify and rank PCDD/F primary sources and emissions to the environment, principally the atmosphere, so that cost-effective source reduction measures can be taken. Here, we predict a congener-specific emissions inventory for primary and secondary nondioxin-regulated sources to the UK atmosphere, estimated to have ranged from 3 to 22 kg in 1996. The inventory profile is dominated by OCDD (approximately 30-40%), 1,2,3,4,6,7,8-HpCDD (approximately 15-19%) and 1,2,3,4,6,7,8-HpCDF (approximately 14-19%). Congeners 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD dominate the sigmaTEQ composition. Mass balance modelling suggests that the predicted congener pattern in UK air (based on the emission inventory) is similar to observed measurements, with absolute concentrations being estimated within a factor of 2 for most congeners. Calculations taking into account atmospheric weathering processes and long range (advective) transport suggest that PCDD/F sources to ambient air are primarily ongoing and that atmospheric mixing will mask individual emission source profiles/identities. This supports measured evidence for the consistency of PCDD/F air profiles observed around the UK throughout the year. 相似文献
134.
Mechanism of effective nocardioform foam control measures for non-selector activated sludge systems.
Domènec Jolis Chu-Fei H Ho Paul A Pitt Bonnie M Jones 《Water environment research》2006,78(9):920-929
Solids retention time (SRT), biological scum trapping and recycle, and the dynamic equilibrium between Nocardioform populations in the foam and the mixed liquor are the controlling factors in activated sludge foaming events caused by Nocardioform bacteria. For the operating modes described in this paper, a cured mixed liquor foaming condition (filament counts of approximately 10(5) intersections/g volatile suspended solids) was only achieved when SRT control, selective wasting, and polymer addition were in effect. Solids retention time control, with the SRT remaining below 1.5 days, and selective wasting will cure a severely foaming mixed liquor, but effects will only be observed after 3 or 4 months after implementation. The combined wastage of Nocardioform bacteria from selective wasting and SRT control can ensure long-term foam control to the operation of a pure-oxygen activated sludge system with foam-trapping features. An SRT of 0.3 days will result in the complete washout of Nocardioform bacteria from the activated sludge system, which can then operate at an SRT of 3 days free of Nocardioform. Polymer addition to mixed liquor is only effective for foam control when a large portion of the system biomass exists as a heavy layer of foam above the mixed liquor. 相似文献
135.
PCDD/Fs were quantified in samples of cattle, pig, sheep and chicken manure. TEQs ranged from 0.19 ng TEQ/kg dw for the pig manure to 20 ng TEQ/kg dw for one cattle manure sample. Exposure assessments were carried out to compare the effect of various sewage sludge and cattle manure land application scenarios on human PCDD/F exposure. Background exposure was estimated at 4.9 pg TEQ/kg bw/day and it was found that land application of sewage sludge and cattle manure at contemporary rates did not increase PCDD/F TEQ background exposure. It was concluded that the application of sewage sludge, under the new UK guidelines, and cattle manure to agricultural land, do not make a significant contribution to human exposure to PCDD/Fs. 相似文献
136.
137.
Polychlorinated biphenyls in digested UK sewage sludges 总被引:1,自引:0,他引:1
Twelve sewage sludges from rural, urban and industrial waste water treatment works in north west England were analysed for polychlorinated biphenyls by capillary GC-ECD. The total polychlorinated biphenyl content ranged between 106 to 712 μg/kg, with a mean of 292 μg/kg. Di- and penta-chlorinated congeners made the greatest contribution to the ΣPCB concentrations at most sites. The 6 IUPAC congeners were found in the following order of abundance, 101>180>153>138>52>28. Industrial inputs would appear to influence levels of ΣPCB in the sludge.
If these sludges were ploughed into arable land at typical rates only a slight elevation in soil ΣPCB levels would result. Alternatively, if the same quantity of sludge were applied to the surface of pasture grassland, significant elevations in the potential transfer of PCBs to grazing livestock may result. 相似文献
138.
A method was developed to determine trace concentrations of a range of individual PCB congeners in biological samples (serum, food and faeces) using GC-MS, to prepare a mass balance of PCBs in humans. A simple method for the analysis of PCBs in human serum, which excluded an extraction step, was first employed. Results indicated that the recoveries of 13C12 PCB spikes were variable. A soxhlet extraction step was added and was found to be efficient and reproducible. A quality control routine and method validation results are presented. In batch tests of the methods presented it was found that the serum analysis method gave within batch mean 13C12 spike recoveries of 98-120% and standard deviations between 6 and 20%. The food/faeces analysis method gave within-batch mean 13C12 spike recoveries of 88-100%, and within batch standard deviations between 4 and 12%. The batch to batch mean recovery for serum analysis was 100%, with an RSD of 9% for high spikes and 10% for low spikes. For food/faeces analysis the batch to batch average recovery was 110%, with an RSD of 5% for high spikes and 9% for low spikes. 相似文献
139.
140.
An inventory of the vascular plants, bryophytes, fungi and terricolous lichens recorded within the different sand-dune communities
in Wales has been compiled and a summary of the importance of these different taxonomic groups to the ecology and conservation
of sand dunes is provided. The total floristic assemblage amounted to 945 species, with vascular plants representing 439 of
these. Fungi unexpectedly formed the next most important group with ca. 289 species, followed by bryophytes (171 species)
and terricolous lichens (66 species). However, very few of these species are confined to sand dunes. Of the vascular plants
only ca. 7 % (32 species) could be classed as either wholly dependent or strongly associated with sand dunes, whereas up to
13% (22 species) of the bryophytes fell within this category. Of the fungi only 4% (10 species) appear to be restricted to
sand dunes, but none of the lichen species could be classed as being either limited to, or strongly associated with, this
habitat.
Over 9% (91 species) of the total flora are considered to be rare, scarce or endangered within the UK or Europe, and ca. 8%
of the vascular plant species are considered to be endemic or near-endemic to Europe. The inventory therefore not only provides
an insight in the overall plant diversity of dune systems in Wales, it also gives an indication of the proportion of species
that are under threat, and the numbers of species that are more-or-less totally dependent on sand dunes. In the discussion
various relevant sand-dune management issues are addressed. 相似文献