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61.
A generalised sorption model for the concentration dependent uptake of caesium by argillaceous rocks
A three-site cation exchange model is proposed to describe the concentration dependent uptake of Cs on natural argillaceous rock systems. Major premises in the model are that the sorption of Cs is dominated by the illite mineral component in the rock and that there is a fixed relationship between the site capacities of the three site types denoted as frayed edge, type II and planar sites. The definition of a “reference illite” with a cation exchange capacity of 0.2 equiv. kg-1 allows the three site capacities to be fixed in the model calculations over the weight fraction of illite in the argillaceous rocks. Up to Cs equilibrium concentrations of 10-3 M sorption occurs predominantly on the frayed edge and type II sites (higher affinity sites), with the planar site type playing only a minor role. Competition with Cs for sorption on the former two site types arises predominantly from monovalent cations such as K, Rb and NH4 which have low hydration energies. H and Na (except at high concentrations) are considerably less competitive and bivalent cations such as Mg, Ca and Sr are effectively non-competitive. A consistent set of selectivity coefficients for Cs with respect to K, Rb, NH4 and Na was derived from analyses and modelling of a wide range of Cs sorption data available in the open literature on pure illites from many different sources. The model was tested against four Cs sorption isotherm data sets determined on argillaceous rocks: Boom clay, Oxford clay, Palfris marl and Opalinus clay. The water chemistries and illite contents given in these experiments allowed the Cs sorption isotherms to be predicted. It is concluded that the Cs sorption model presented here, in which there are no free parameters, can be used to predict the uptake of Cs at equilibrium concentrations below 10-3 M to within a factor of 2 to 3 in natural argillaceous rock systems. 相似文献
62.
Transport of aquatic invasive species (AIS) by boats traveling up rivers and streams is an important mechanism of secondary
spread of AIS into watersheds. Because physical barriers to AIS movement also prevent navigation, alternate methods for preventing
spread are necessary while allowing upstream navigation. One promising approach is to lift boats over physical barriers and
then use hot water immersion to kill AIS attached to the hull, motor, or fishing gear. However, few data have been published
on the acute upper thermal tolerance limits of potential invaders treated in this manner. To test the potential effectiveness
of this approach for a planned boat lift on the Fox River of northeastern WI, USA, acute upper thermal limits were determined
for three AIS, adult zebra mussels (Dreissena polymorpha), quagga mussels (Dreissena rostriformis bugensis), and spiny water fleas (Bythotrephes longimanus) from the local area employing temperatures from 32 to 54°C and immersion times from 1 to 20 min. Mortality was determined
after immersion followed by a 20-min recovery period. Immersion at 43°C for at least 5 min was required to ensure 100% mortality
for all three species, but due to variability in the response by Bythotrephes a 10 min immersion would be more reliable. Overall there were no significant differences between the three species in acute
upper thermal limits. Heated water can be an efficient, environmentally sound, and cost effective method of controlling AIS
potentially transferred by boats, and our results should have both specific and wide-ranging applications in the prevention
of the spread of aquatic invasive species. 相似文献
63.
64.
65.
Comparison and ranking of different modelling techniques for prediction of site index in Mediterranean mountain forests 总被引:3,自引:0,他引:3
Forestry science has a long tradition of studying the relationship between stand productivity and abiotic and biotic site characteristics, such as climate, topography, soil and vegetation. Many of the early site quality modelling studies related site index to environmental variables using basic statistical methods such as linear regression. Because most ecological variables show a typical non-linear course and a non-constant variance distribution, a large fraction of the variation remained unexplained by these linear models. More recently, the development of more advanced non-parametric and machine learning methods provided opportunities to overcome these limitations. Nevertheless, these methods also have drawbacks. Due to their increasing complexity they are not only more difficult to implement and interpret, but also more vulnerable to overfitting. Especially in a context of regionalisation, this may prove to be problematic. Although many non-parametric and machine learning methods are increasingly used in applications related to forest site quality assessment, their predictive performance has only been assessed for a limited number of methods and ecosystems.In this study, five different modelling techniques are compared and evaluated, i.e. multiple linear regression (MLR), classification and regression trees (CART), boosted regression trees (BRT), generalized additive models (GAM), and artificial neural networks (ANN). Each method is used to model site index of homogeneous stands of three important tree species of the Taurus Mountains (Turkey): Pinus brutia, Pinus nigra and Cedrus libani. Site index is related to soil, vegetation and topographical variables, which are available for 167 sample plots covering all important environmental gradients in the research area. The five techniques are compared in a multi-criteria decision analysis in which different model performance measures, ecological interpretability and user-friendliness are considered as criteria.When combining these criteria, in most cases GAM is found to outperform all other techniques for modelling site index for the three species. BRT is a good alternative in case the ecological interpretability of the technique is of higher importance. When user-friendliness is more important MLR and CART are the preferred alternatives. Despite its good predictive performance, ANN is penalized for its complex, non-transparent models and big training effort. 相似文献
66.
Previous studies of interference competition have shown an asymmetric effect on intake rate of foragers on clumped resources,
with only subordinate individuals suffering. However, the food distributions in these studies were uniform or highly clumped,
whereas in many field situations, food aggregation is intermediate. Here we investigated whether food distribution (i.e.,
uniform, slightly clumped, and highly clumped) affects the behavioral response of mallards foraging alone or competing with
another. Although the amount of food was the same in all distributions, the mallards reached higher intake rates, visited
fewer patches, and showed longer average feeding times in the highly clumped distribution. Competing mallards had lower intake
rates on the slightly clumped than on the uniform or highly clumped food distributions. Subordinates generally visited more
patches and had shorter feeding times per patch, but their intake rates were not significantly lower than those of dominants.
Therefore, we propose that subordinates do not necessarily suffer from interference competition in terms of intake rate, but
do suffer higher search costs. In addition, although dominants had significantly higher average feeding times on the best
quality patches of the highly clumped food distribution, such an effect was not found in the slightly clumped distribution.
These findings indicate that in environments where food is aggregated to a lesser extent, monopolization is not the best strategy
for dominants. Our results suggest that interference experiments should use food distributions that resemble the natural situation
animals are faced with in the field. 相似文献
67.
Arild?Johnsen Kim?L.?Carter Kaspar?Delhey Jan?T.?Lifjeld Raleigh?J.?Robertson Bart?KempenaersEmail author 《Behavioral ecology and sociobiology》2012,66(2):181-190
In birds, the number of sperm trapped between the perivitelline membranes around the ovum is an estimate of sperm numbers
present at the time and place of fertilisation in the female reproductive tract. Sperm numbers may vary among species and
between eggs in a clutch and can provide information about sperm utilisation and mechanisms of sperm competition. Here, we
describe patterns of variation in sperm numbers through the egg-laying sequence in three passerines in which extra-pair paternity
is common, but copulation behaviour differs. Sperm numbers showed no systematic change across the laying sequence in blue
tits (Cyanistes caeruleus), but decreased significantly with laying order in bluethroat (Luscinia svecica) and tree swallow (Tachycineta bicolor) clutches. This is consistent with observations that blue tits regularly copulate throughout the laying sequence, while bluethroats
stop mate guarding and tree swallows reduce their copulation frequency once the first egg is laid. Nevertheless, cases of
a sudden increase in sperm numbers in clutches of bluethroats and tree swallows suggest that successful inseminations also
occurred after laying started. In blue tits and bluethroats, sperm numbers were not higher on extra-pair sired eggs than on
eggs sired by the social male, suggesting that extra-pair copulations are not timed to the period of peak fertility for each
egg. More extra-pair offspring originated from eggs laid early in the sequence in blue tits, while there was no systematic
bias in bluethroats. Our results suggest that copulations during the laying sequence are predominantly performed by within-pair
males in our study species. 相似文献
68.
/ In 1991 and 1992, temperature, salinity, and fluorescence were measured by automatic continuous registration using instrumentation on a ferry crossing the southern North Sea daily along a transect between Zeebrugge, Belgium, and Hull, United Kingdom. The temperature ranged between 4 and 21 degrees C off the Belgian coast and between 6 and 17 degrees C in the middle of the transect. Salinity varied between 34 and 35.5 PSU in the offshore part of the transect, but showed much larger variation along the Belgian and UK estuarine coasts. Fluorescence, which was used as a measure of phytoplankton biomass, was highest at the continental coast and lowest near the English coast. Spring blooms of phytoplankton were found along the continental coast and in the channel-influenced water; in 1991 the blooms were denser than in 1992. Some summer blooms were also recorded. Water masses could be distinguished on the basis of salinity and fluorescence patterns. The general patterns in the data are compared with the literature and discussed in relation to river discharge, light penetration, and wind speed and direction. Finally, the value of automatic and frequent measurements of fluorescence for monitoring phytoplankton is compared with less frequent observations at selected stations. It is concluded that accurate information about phytoplankton biomass can only be established from the high-frequency data. KEY WORDS: Monitoring; Sampling; North Sea; Ferry; Fluorescence; Salinity; Temperature 相似文献
69.
Motallebi N Taylor CA Croes BE 《Journal of the Air & Waste Management Association (1995)》2003,53(12):1517-1530
Geographic and temporal variations in the concentration and composition of particulate matter (PM) provide important insights into particle sources, atmospheric processes that influence particle formation, and PM management strategies. In the nonurban areas of California, annual-average PM2.5 and PM10 concentrations range from 3 to 10 microg/m3 and from 5 to 18 microg/m3, respectively. In the urban areas of California, annual-averages for PM2.5 range from 7 to 30 microg/m3, with observed 24-hr peaks reaching levels as high as 160 microg/m3. Within each air basin, exceedances are a mixture of isolated events as well as periods of elevated PM2.5 concentrations that are more prolonged and regional in nature. PM2.5 concentrations are generally highest during the winter months. The exception is the South Coast Air Basin, where fairly high values occur throughout the year. Annual-average PM2.5 mass, as well as the concentrations of major components, declined from 1988 to 2000. The declines are especially pronounced for the sulfate (SO4(2-)) and nitrate (NO3-) components of PM2.5 and PM10) and correlate with reductions in ambient levels of oxides of sulfur (SOx) and oxides of nitrogen (NOx). Annual averages for PM10-2.5 and PM10 exhibited similar downwind trends from 1994 to 1999, with a slightly less pronounced decrease in the coarse fraction. 相似文献
70.
van Ginneken V Ballieux B Antonissen E van der Linden R Gluvers A van den Thillart G 《Die Naturwissenschaften》2007,94(2):128-133
In birds and mammals, the thyroid gland secretes the iodothyronine hormones of which tetraiodothyronine (T4) is less active
than triiodothyronine (T3). The action of T3 and T4 is calorigenic and is involved in the control of metabolic rate. Across
all vertebrates, thyroid hormones also play a major role in differentiation, development and growth. Although the fish thyroidal
system has been researched extensively, its role in thermogenesis is unclear. In this study, we measured overall heat production
to an accuracy of 0.1 mW by direct calorimetry in a free-moving European eel (Anguilla anguilla L.) with different thyroid status. Hyperthyroidism was induced by injection of T3 and T4, and hypothyroidism was induced
with phenylthiourea. The results show for the first time at the organismal level, using direct calorimetry, that neither overall
heat production nor overall oxygen consumption in eels is affected by hyperthyroidism. Therefore, we conclude that the thermogenic
metabolism-stimulating effect of thyroid hormones (TH) is not present with a cold-blooded fish species like the European eel.
This supports the concept that TH does not stimulate thermogenesis in poikilothermic species. 相似文献