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排序方式: 共有355条查询结果,搜索用时 203 毫秒
291.
292.
We examined trends in sea ice cover between 1979 and 2002 in four months (March, June, September, and November) for four large (approximately 100,000 km2) and 12 small (approximately 10,000 km2) regions of the western Arctic in habitats used by bowhead whales (Balaena mysticetus). Variation in open water with year was significant in all months except March, but interactions between region and year were not. Open water increased in both large and small regions, but trends were weak with least-squares regression accounting for < or =34% of the total variation. In large regions, positive trends in open water were strongest in September. Linear fits were poor, however, even in the East Siberian, Chukchi, and Beaufort seas, where basin-scale analyses have emphasized dramatic sea ice loss. Small regions also showed weak positive trends in open water and strong interannual variability. Open water increased consistently in five small regions where bowhead whales have been observed feeding or where oceanographic models predict prey entrainment, including: (1) June, along the northern Chukotka coast, near Wrangel Island, and along the Beaufort slope; (2) September, near Wrangel Island, the Barrow Arc, and the Chukchi Borderland; and (3) November, along the Barrow Arc. Conversely, there was very little consistent change in sea ice cover in four small regions considered winter refugia for bowhead whales in the northern Bering Sea, nor in two small regions that include the primary springtime migration corridor in the Chukchi Sea. The effects of sea ice cover on bowhead whale prey availability are unknown but can be modeled via production and advection pathways. Our conceptual model suggests that reductions in sea ice cover will increase prey availability along both pathways for this population. This analysis elucidates the variability inherent in the western Arctic marine ecosystem at scales relevant to bowhead whales and contrasts basin-scale depictions of extreme sea ice retreats, thinning, and wind-driven movements. 相似文献
293.
Population frequencies of alternative male phenotypes in tree lizards: geographic variation and common-garden rearing studies 总被引:2,自引:0,他引:2
Diana K. Hews Christopher W. Thompson Ignacio T. Moore Michael C. Moore 《Behavioral ecology and sociobiology》1997,41(6):371-380
Tree lizards (Urosaurus ornatus) vary in throat fan (dewlap) color. Earlier, we described five dewlap types (Orange, Orange-Blue, Yellow, Yellow-Blue, and
Blue), and reported that only males had blue in the dewlap and that presence or absence of a discrete blue patch was correlated
with male alternative reproductive phenotypes in a central Arizona population. Here, with a modified scheme characterizing
two dewlap elements, background color (orange, yellow, blue) and blue patch occurrence, we assessed: (1) sexual, annual, and
geographic variation in the frequencies of dewlap elements; (2) simple habitat correlates; and (3) the effects of laboratory
rearing regime on dewlap type. Within a population, frequencies of males and females expressing orange or yellow backgrounds
did not differ, suggesting that control of background is similar in the sexes. Within several populations, frequencies of
the dewlap elements did not differ across years (and probably generations), indicating that phenotype frequencies are relatively
stable. Among five populations frequencies of background colors varied, as did frequencies of male types (blue patch present
or absent). Dewlap frequencies did not correlate with habitat (boulders or mesquite trees), although few populations were
sampled. In male and female offspring reared from eggs to sexual maturity in a common-garden laboratory study, background
color frequencies in both sexes and blue patch frequencies in males differed among offspring from different populations. Offspring
frequencies matched respective parental population frequencies. Results suggest that among-population variation in frequencies
of the two dewlap elements are mediated by differences in genetics, in maternal effects, or both. Thus, differences in male
behavior functionally linked to the blue patch also may be controlled by genetic or maternal effects.
Received: 17 January 1997 / Accepted after revision: 30 August 1997 相似文献
294.
A. Viarengo M. N. Moore G. Mancinelli A. Mazzucotelli R. K. Pipe S. V. Farrar 《Marine Biology》1987,94(2):251-257
It has been confirmed that metallothioneins play an important role in the accumulation of cadmium (Cd) in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.). The content of Cd in the tissue of mussels exposed for 9 d to the metal (estimated dosage of 180 g Cd mussel-1 d-1) was 66.2 ppm. This value is about the same as the metal content found in the digestive gland of Cd-exposed mussels kept in clean water for a recovery period of 28 d. At the end of the recovery period, however, the Cd bound to thionein had increased by approximately 250%. Our data demonstrate that the stability of lysosomes, a biological parameter adopted as a cellular stress index, is extremely low in mussels exposed to Cd for 9 d, but returns to control values in the digestive gland cells of mussels allowed to recover for 28 d in uncontaminated sea water. At this point most of the Cd present in the cytosol is bound to thionein. These data demonstrate the importance of metallothionein induction in the reduction of the cytotoxic effects exerted by high levels of Cd accumulation. The results of tests designed to clarify the reasons for the long biological half-life of Cd demonstrated that, in the digestive gland of mussels, the lysosomes are not able to eliminate Cd either bound to insoluble thionein polymers or to lipid peroxidation products such as lysosomal lipofuscin, both of which are apparently involved in the elimination of copper. The absence of these two mechanisms of metal sequestration and elimination via excretion of residual bodies (tertiary lysosomes) is in agreement with the persistence of cadmium in the digestive gland of mussels. Finally, the results also demonstrate that simultaneous exposure of mussels to Cd and phenanthrene, an established lysosomal membrane destabilizer, did not significantly alter the accumulation of Cd or the kinetics of the metal in mussels. 相似文献
295.
The effects of increasing salinity on the ultrastructural morphology of the lysosomal-vacuolar system in digestive cells of the common mussel Mytilus edulis were investigated in order to relate structural changes to previous biochemical and cytochemical observations. After 3 h of increased salinity, from 21 to 35%., the digestive cells showed an increase in numbers of heterolysosomes. There was some evidence of digestive cell breakdown, the contents forming membrane-bound bodies and being released into the tubule lumen. After 12 h of increased salinity, heterolysosomes were prevalent in the digestive cells. There was increased evidence for digestive-cell breakdown, many of the tubule lumina being packed with membrane-bound bodies. It is concluded that increasing salinity from 21 to 35%. stimulates the lysosomal-vacuolar system, as a result of autophagocytosis or apoptosis; this is consistent with the hypothesis that intracellular, lysosomally-mediated, catabolism of proteins is a source for free amino acids during the adaptation of mussels to increased salinity. 相似文献
296.
A. J. Moore 《Behavioral ecology and sociobiology》1994,35(4):235-241
The adaptive nature of female mate choice remains one of the most contentious issues in the study of sexual selection. Here, I provide evidence that mate choice by females of the ovoviviparous cockroach Nauphoeta cinerea influences the rate at which offspring develop and provides both direct and indirect benefits to the female. Males that are more attractive to females produce offspring with shorter development times than less preferred males. Development time is heritable and apparently unconstrained by antagonistic pleiotropy. Male attractiveness and rate of offspring development are genetically correlated. Offspring gain an indirect benefit from their mother's mate choice because, on average, individuals that hatch faster reach sexual maturity more quickly. Females that discriminate among males gain a direct benefit because N. cinerea is ovoviviparous and the time between clutches is decreased by producing offspring with shorter development. In addition to providing evidence for beneficial consequences of mate choice, this study highlights how genetic data provide insights into the process of sexual selection not gained in a purely phenotypic study.Communicated by P. Pamilo 相似文献
297.
William O'Neil Martin David Christina Moore Erhard Joeres 《Journal of Environmental Economics and Management》1983,10(4):346-355
Recent emphasis on reforms of environmental regulation has led to suggestions for strategies which maintain environmental standards but allow the needed flexibility and cost effectiveness. The transferable discharge permit (TDP) is one such strategy for water pollution control recently adopted in Wisconsin. In this article, the potential for substantial cost savings from trading TDPs is demonstrated using data on the Fox River in Wisconsin. A simulation model of water quality (Qual-III) and a linear programming model of abatement costs determine the optimum pattern of discharge. Reaching that optimum from proposed pollution abatement orders is shown to be feasible. Varying conditions of flow and temperature can be accommodated using trade coefficients which can be accurately estimated through interpolation. The calculations demonstrate the value and feasibility of flexible regulations governing water pollution abatement. 相似文献
298.
David P. Bick MD Daniel F. Schorderet Paul A. Price Leslie Campbell Robert W. Huff Larry J. Shapiro Charleen M. Moore 《黑龙江环境通报》1992,12(1):19-29
We report the prenatal diagnosis of a male fetus with X-linked recessive chondrodysplasia punctata (CDPX), steroid sulphatase (STS) deficiency, X-linked Kallmann syndrome (KAL), and a chromosome deletion at Xp22.31. Biochemical analysis of bone from this case indicates that CDPX is not a defect of vitamin K metabolism. Immunocytochemical study of the brain suggests that KAL is a defect in neuronal migration. 相似文献
299.
Flux chamber measurements made in a rainforest provide evidence that methyl chloride is emitted from rotting wood. However, its net flux was found to be into the soil, probably due to competing production and consumption processes within the soil. Evidence was found for a regional source, possibly vegetation, since its concentration above the canopy was substantially greater than reported average equatorial values. 相似文献
300.
Vegetative and structural characteristics of agricultural drainages in the Mississippi Delta landscapes 总被引:7,自引:0,他引:7
Bouldin JL Farris JL Moore MT Cooper CM 《Environmental pollution (Barking, Essex : 1987)》2004,132(3):403-411
Agricultural drainage ditches in the Mississippi Alluvial Delta landscape vary from edge-of-field waterways to sizeable drainages. Ditch attributes vary with size, location and maintenance and may aid in mitigation of contaminants from agricultural fields. The goal of this study was to better understand how vegetative characteristics affect water quality in conveyance structures in the context of ditch class and surrounding land use. Characterization of 36 agricultural ditches included presence of riparian buffer strips, water depth, surrounding land use, vegetative cover, and associated aqueous physicochemical parameters. Vegetation was assessed quantitatively, obtaining stem counts in a sub-sample of ditch sites, using random quadrat method. Physical features varied with ditch size and vegetative diversity was higher in larger structures. Polygonum sp. was the dominant bed vegetation and was ubiquitous among site sizes. Macrophytes varied from aquatic to upland species, and included Leersia sp. and upland grasses (Poaceae family) in all drainage size classes. Percent cover of bed and bank varied from 0 to 100% and 70 to 100%, respectively, and highest nutrient values were measured in sites with no buffer strips. These conveyance structures and surrounding buffer zones are being ranked for their ability to reduce excess nutrients, suspended solids, and pesticides associated with runoff. 相似文献