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991.
Grulke NE Preisler HK Fan CC Retzlaff WA 《Environmental pollution (Barking, Essex : 1987)》2002,119(2):163-175
In highly polluted sites, stomatal behavior is sluggish with respect to light, vapor pressure deficit, and internal CO2 concentration (Ci) and poorly described by existing models. Statistical models were developed to estimate stomatal conductance (gs) of 40-year-old ponderosa pine at three sites differing in pollutant exposure for the purpose of calculating O3 uptake. Gs was estimated using julian day, hour of day, pre-dawn xylem potential and photosynthetic photon flux density (PPFD). The median difference between estimated and observed field gs did not exceed 10 mmol H2O m(-2) s(-1), and estimated gs within 95% confidence intervals. 03 uptake was calculated from hourly estimated gs, hourly O3 concentration, and a constant to correct for the difference in diffusivity between water vapor and 03. The simulation model TREGRO was also used to calculate the cumulative 03 uptake at all three sites. 03 uptake estimated by the statistical model was higher than that simulated by TREGRO because gas exchange rates were proportionally higher. O3 exposure and uptake were significantly correlated (r2>0.92), because O3 exposure and gs were highly correlated in both statistical and simulation models. 相似文献
992.
The codisposal of toxic metals and radionuclides with organic chelating agents has been implicated in the facilitated transport of the inorganic contaminants away from primary waste disposal areas. We investigated the transport of Co(II)NTA through undisturbed cores of fractured shale saprolite. Experiments were conducted across the pH range 4 to 8 by collecting cores from different locations within the weathering profile. Aqueous complexation, adsorption, dissociation and oxidation reactions influenced Co(II)NTA transport. The suite of reaction products identified in column effluent varied with experimental pH. At low pH and in the presence of abundant exchangeable aluminum, Co transport occurred predominantly as the Co2+ ion. At higher pH, Co was transported primarily as Co(II)NTA and the Co(III) species Co(III)(HNTA)2 and Co(III)(IDA)2. The formation of the geochemical oxidation products (Co(III) species) has far reaching implications as these compounds are kinetically and thermodynamically stable, are transported more rapidly than Co(II)NTA, and are resistant to biodegradation. These results demonstrate that natural minerals, in the physical structure encountered naturally, can be more important in the formation of mobile, stable contaminant forms than they can be for the retardation and dissociation of the contaminants. 相似文献
993.
Beekman M Good G Allsopp MH Radloff S Pirk CW Ratnieks FL 《Die Naturwissenschaften》2002,89(10):479-482
In the Cape honey bee Apis mellifera capensis, workers lay female eggs without mating by thelytokous parthenogenesis. As a result, workers are as related to worker-laid eggs as they are to queen-laid eggs and therefore worker policing is expected to be lower, or even absent. This was tested by transferring worker- and queen-laid eggs into three queenright A. m. capensis discriminator colonies and monitoring their removal. Our results show that worker policing is variable in A. m. capensis and that in one colony worker-laid eggs were not removed. This is the first report of a non-policing queenright honey bee colony. DNA microsatellite and morphometric analysis suggests that the racial composition of the three discriminator colonies was different. The variation in policing rates could be explained by differences in degrees of hybridisation between A. m. capensis and A. m. scutellata, although a larger survey is needed to confirm this. 相似文献
994.
Response of Ceriodaphnia dubia to ionic silver: discrepancies among model predictions, measured concentrations and mortality 总被引:1,自引:0,他引:1
Silver thiosulfate, often a waste product of photoprocessing, is less bioavailable or toxic to aquatic organisms than is ionic silver. We conducted duplicate 48-h Ceriodaphnia dubia tests in reconstituted laboratory water using treatments of 92.7 nM Ag+ with various concentrations of thiosulfate. Expected Ag+ concentrations were generated for thiosulfate treatment levels using MINEQL + chemical equilibrium modeling. Ag+ concentrations in treatments were determined using a novel silicon-based sensor. Based on predicted Ag+ and published 48-h LC50 values for C. dubia, we did not expect to observe adverse effects. Yet, 100% mortality was observed at low thiosulfate treatments, whereas > 85% and > 95% survival was observed at higher thiosulfate treatment levels, respectively. Our results indicate that biotic responses match the sensor-based Ag+ concentrations. However, there is a discrepancy between these empirical results and responses expected to occur with Ag+ concentrations as predicted by MINEQL + chemical modeling. By correlating silicon sensor data with toxicity results obtained from our laboratory, our work clearly relates a specific chemical form (Ag+) to toxicity results. 相似文献
995.
The hydrogeomorphic (HGM) approach to wetland classification and functional assessment is becoming more widespread in the
United States but its use has been limited by the length of time needed to develop appropriate data sets and functional assessment
models. One particularly difficult aspect is the transferability among geographic regions of specific models used to assess
wetland function. Sharing of models could considerably shorten development and implementation of HGM throughout the United
States and elsewhere. As hydrology is the driving force behind wetland functions, we assessed the comparability of hydrologic
characteristics of three HGM subclasses (slope, headwater floodplain, mainstem floodplain) using comparable long-term hydrologic
data sets from different regions of the United States (Ridge and Valley Province in Pennsylvania and the Willamette Valley
in Oregon). If hydrology by HGM subclass were similar between different geographic regions, it might be possible to more readily
transfer extant models between those regions. We found that slope wetlands (typically groundwater-driven) had similar hydrologic
characteristics, even though absolute details (such as depth of water) differed. We did not find the floodplain subclasses
to be comparable, likely due to effects of urbanization in Oregon, regional differences in soils and, perhaps, climate. Slight
differences in hydrology can shift wetland functions from those mediated by aerobic processes to those dominated by anaerobic
processes. Functions such as nutrient cycling can be noticeably altered as a result. Our data suggest considerable caution
in the application of models outside of the region for which they were developed. 相似文献
996.
Three mathematical models, the runoff curve number equation, the universal soil loss equation, and the mass response functions,
were evaluated for predicting nonpoint source nutrient loading from agricultural watersheds of the Mediterranean region. These
methodologies were applied to a catchment, the gulf of Gera Basin, that is a typical terrestrial ecosystem of the islands
of the Aegean archipelago. The calibration of the model parameters was based on data from experimental plots from which edge-of-field
losses of sediment, water runoff, and nutrients were measured. Special emphasis was given to the transport of dissolved and
solid-phase nutrients from their sources in the farmers' fields to the outlet of the watershed in order to estimate respective
attenuation rates. It was found that nonpoint nutrient loading due to surface losses was high during winter, the contribution
being between 50% and 80% of the total annual nutrient losses from the terrestrial ecosystem. The good fit between simulated
and experimental data supports the view that these modeling procedures should be considered as reliable and effective methodological
tools in Mediterranean areas for evaluating potential control measures, such as management practices for soil and water conservation
and changes in land uses, aimed at diminishing soil loss and nutrient delivery to surface waters. Furthermore, the modifications
of the general mathematical formulations and the experimental values of the model parameters provided by the study can be
used in further application of these methodologies in watersheds with similar characteristics. 相似文献
997.
Huntington HP Brown-Schwalenberg PK Frost KJ Fernandez-Gimenez M Norton DW Rosenberg DH 《Environmental management》2002,30(6):0778-0792
Traditional ecological knowledge (TEK) and the information and insights it offers to natural resource research and management
have been given much attention in recent years. On the practical question of how TEK is accessed and used together with scientific
knowledge, most work to date has examined documentation and methods of recording and disseminating information. Relatively
little has been done regarding exchanges between scientific and traditional knowledge. This paper examines three workshop
settings in which such exchanges were intended outcomes. The Barrow Symposium on Sea Ice, the Exxon Valdez Oil Spill Restoration Program Synthesis/Information Workshops, and the Alaska Beluga Whale Committee illuminate certain features
of the preparation, format, and context of workshops or series of workshops and their eventual outcomes and influence. The
examples show the importance of long-term relationships among participants and thorough preparation before the actual workshop.
Further research should look more systematically at the factors that influence the success of a given workshop and the various
ways in which participants perceive success. 相似文献
998.
We examined the impact of single-tree selective logging and fuel reduction burns on the abundance of hollow-nesting bird species
at a regional scale in southeastern Queensland, Australia. Data were collected on species abundance and habitat structure
of dry sclerophyll production forest at 36 sites with known logging and fire histories. Sixteen bird species were recorded
with most being resident, territorial, obligate hollow nesters that used hollows that were either small (<10 cm diameter)
or very large (>18 cm diameter). Species densities were typically low, but combinations of two forest management and three
habitat structural variables influenced the abundances of eight bird species in different and sometimes conflicting ways.
The results suggest that habitat tree management for biodiversity in production forests cannot depend upon habitat structural
characteristics alone. Management histories appear to have independent influence (on some bird species) that are distinguishable
from their impacts on habitat structure per se. Rather than managing to maximize species abundances to maintain biodiversity, we may be better off managing to avoid extinctions
of populations by identifying thresholds of acceptable fluctuations in populations of not only hollow-nesting birds but other
forest dependent wildlife relative to scientifically valid forest management and habitat structural surrogates. 相似文献
999.
A GIS/Simulation Framework for Assessing Change in Water Yield over Large Spatial Scales 总被引:1,自引:0,他引:1
Recent legislation to initiate vegetation management in the Central Sierra hydrologic region of California includes a focus
on corresponding changes in water yield. This served as the impetus for developing a combined geographic information system
(GIS) and simulation assessment framework. Using the existing vegetation density condition, together with proposed rules for
thinning to reduce fire risk, a set of simulation model inputs were generated for examining the impact of the thinning scenario
on water yield. The approach allows results to be expressed as the mean and standard deviation of change in water yield for
each 1-km2 map cell that is thinned. Values for groups of cells are aggregated for typical watershed units using area-weighted averaging.
Wet, dry, and average precipitation years were simulated over a large region. Where snow plays an important role in hydrologic
processes, the simulated change in water yield was less than 0.5% of expected annual runoff for a typical watershed. Such
small changes would be undetectable in the field using conventional stream flow analysis. These results suggest that use of
water yield increases to help justify forest-thinning activities or offset their cost will be difficult. 相似文献
1000.
Power line rights-of-way provide a major portion of the shrub habitat in New York. Since this habitat type is on the decline,
many of the birds dependent on shrub habitat are also declining. The methods used to control right-of-way vegetation could
therefore have serious impacts on several birds of conservation concern. Since New York is increasingly using selective herbicide
treatments in vegetation management, we sought to investigate the potential impacts of these treatments on nesting birds.
The study looked at plots in two adjacent rights-of-way before and after a selective herbicide treatment in one of the rights-of-way.
We investigated three bird species: alder flycatcher (Empidonax alnorum), chestnut-sided warbler (Dendroica pensylvanica), and gray catbird (Dumetella carolinensis). All three species exhibited a preference for shrub vegetation around nest sites. The selective herbicide treatment did
not significantly decrease that shrub vegetation, and neither the density nor the nesting success of the three species declined
following the treatment. We conclude that selective herbicide vegetation management encourages the development of shrub habitat
without negatively impacting the birds nesting in the habitat. 相似文献