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81.
82.
Nancy I. Rivera Rivera Thomas E. Gill Max P. Bleiweiss Jenny L. Hand 《Atmospheric environment (Oxford, England : 1994)》2010,44(20):2457-2468
The Chihuahuan Desert region is an important contributor to atmospheric dust loading and transport in North America; however, specific dust sources in this region are poorly characterized. Major dust events frequently are characterized by multiple dust plumes developing nearly simultaneously over a large region. Remote sensing data were used to identify the source locations and associated land cover for the most extreme dust events in the Chihuahuan Desert since 2002. Analysis of infrared channels utilizing brightness temperature differences was used to analyze data from geostationary and polar-orbiting satellites, from which dust sources were determined and located. This methodology was applied to the five dust events in the region that resulted in “hazardous” PM10 levels in Texas per the USEPA’s Air Quality Index. Source locations determined from satellite images were used in conjunction with LANDSAT data and Google Earth? images to determine the corresponding land-surface features. Agricultural lands, playas, and their edges are pointed out as focus areas for dust emission, at least during the most intense events. The 130 dust plume initiation sites were relatively uniformly spaced over the landscape, not clumped into a few “hotspots,” suggesting the role of spatiotemporally random meteorological factors in determining major points of emission within and between dust storms. These findings provide an initial characterization of Chihuahuan Desert dust source locations and establish a baseline for continued research in determining potential locations for future dust outbreaks in the southwestern U.S. and northwestern Mexico. 相似文献
83.
Mohammadkazem Ramezani Danielle P. Oliver Rai S. Kookana Gurjeet Gill Christopher Preston 《Journal of environmental science and health. Part. B》2013,48(2):105-112
The abiotic degradation of the imidazolinone herbicides imazapyr, imazethapyr and imazaquin was investigated under controlled conditions. Hydrolysis, where it occurred, and photodegradation both followed first-order kinetics for all herbicides. There was no hydrolysis of any of the herbicides in buffer solutions at pH 3 or pH 7; however, slow hydrolysis occurred at pH 9. Estimated half-lives for the three herbicides in solution in the dark were 6.5, 9.2 and 9.6 months for imazaquin, imazethapyr and imazapyr, respectively. Degradation of the herbicides in the light was considerably more rapid than in the dark with half lives for the three herbicides of 1.8, 9.8 and 9.1 days for imazaquin, imazethapyr and imazapyr, respectively. The presence of humic acids in the solution reduced the rate of photodegradation for all three herbicides, with higher concentrations of humic acids generally having greater effect. Photodegradation of imazethapyr was the least sensitive to humic acids. The enantioselectivity of photodegradation was investigated using imazaquin, with photodegradation occurring at the same rate for both enantiomers. Abiotic degradation of imidazolinone herbicides on the soil surface only occurred in the presence of light. The rate of degradation for all herbicides was slower than in solution, with half-lives of 15.3, 24.6 and 30.9 days for imazaquin, imazethapyr and imazapyr, respectively. Abiotic degradation of these herbicides is likely to be slow in the environment and is only likely to occur in clear water or on the soil surface. 相似文献
84.
A routine, automated analytical method for simultaneous determination of total and inorganic mercury by cold vapour atomic absorption spectrometry in multimedia is described. Excellent accuracy and precision results were obtained with human hair certified reference materials namely, BCR-397 and IAEA-086. The reproducibility relative standard deviation for total mercury was 4% and 22%, respectively. The limit of detection for total and inorganic mercury was 0.2 μg/g hair. The described method has been successfully applied in determination of total and inorganic mercury as well as organic mercury in human hair, urine and fish tissue samples. 相似文献
85.
We evaluated wheat straw biochar produced at 450 °C for its ability to influence bioavailability and persistence of two commonly used herbicides (atrazine and trifluralin) with different modes of action (photosynthesis versus root tip mitosis inhibitors) in two contrasting soils. The biochar was added to soils at 0%, 0.5% and 1.0% (w/w) and the herbicides were applied to those soil-biochar mixes at nil, half, full, two times, and four times, the recommended dosage (H4). Annual ryegrass (Lolium rigidum) was grown in biochar amended soils for 1 month. Biochar had a positive impact on ryegrass survival rate and above-ground biomass at most of the application rates, and particularly at H4. Within any given biochar treatment, increasing herbicide application decreased the survival rate and fresh weight of above-ground biomass. Biomass production across the biochar treatment gradient significantly differed (p < 0.01) and was more pronounced in the case of atrazine than trifluralin. For example, the dose-response analysis showed that in the presence of 1% biochar in soil, the value of GR50 (i.e. the dose required to reduce weed biomass by 50%) for atrazine increased by 3.5 times, whereas it increased only by a factor of 1.6 in the case of trifluralin. The combination of the chemical properties and the mode of action governed the extent of biochar-induced reduction in bioavailability of herbicides. The greater biomass of ryegrass in the soil containing the highest biochar (despite having the highest herbicide residues) demonstrates decreased bioavailability of the chemicals caused by the wheat straw biochar. This work clearly demonstrates decreased efficacy of herbicides in biochar amended soils. The role played by herbicide chemistry and mode of action will have major implications in choosing the appropriate application rates for biochar amended soils. 相似文献
86.
A simultaneous model describing the demand for and supply of wastepaper in the USA during 1952-74 has been estimated using the three stage least squares procedure. In our analysis, a low supply elasticity coupled with a zero price elasticity of demand explains the volatile nature of wastepaper prices. The structural estimates indicate that neither the elimination of differential rail freights nor the elimination of preferential tax treatment of stumpage profits will have a significant effect in stimulating the recycling effort. 相似文献
87.
M. Kashif Gill Tirusew Asefa Mariush W. Kemblowski Mac McKee 《Journal of the American Water Resources Association》2006,42(4):1033-1046
ABSTRACT: Herein, a recently developed methodology, Support Vector Machines (SVMs), is presented and applied to the challenge of soil moisture prediction. Support Vector Machines are derived from statistical learning theory and can be used to predict a quantity forward in time based on training that uses past data, hence providing a statistically sound approach to solving inverse problems. The principal strength of SVMs lies in the fact that they employ Structural Risk Minimization (SRM) instead of Empirical Risk Minimization (ERM). The SVMs formulate a quadratic optimization problem that ensures a global optimum, which makes them superior to traditional learning algorithms such as Artificial Neural Networks (ANNs). The resulting model is sparse and not characterized by the “curse of dimensionality.” Soil moisture distribution and variation is helpful in predicting and understanding various hydrologic processes, including weather changes, energy and moisture fluxes, drought, irrigation scheduling, and rainfall/runoff generation. Soil moisture and meteorological data are used to generate SVM predictions for four and seven days ahead. Predictions show good agreement with actual soil moisture measurements. Results from the SVM modeling are compared with predictions obtained from ANN models and show that SVM models performed better for soil moisture forecasting than ANN models. 相似文献
88.
Our comparative study of the knees of horses and cows (paraphrased as highly evolved joggers and as domesticated couch-potatoes, respectively) demonstrates significant differences in the posterior sections of bovine and equine tibial cartilage, which are consistent with specialisation for gait. These insights were possible using a novel analytical measuring technique based on the shearing of small biopsy samples, called dynamic shear analysis. We assert that this technique could provide a powerful new tool to precisely quantify the pathology of osteoarthritis for the medical field. 相似文献
89.
Peter H. Kahn Jr. Batya Friedman Brian Gill Jennifer Hagman Rachel L. Severson Nathan G. Freier Erika N. Feldman Sybil Carrre Anna Stolyar 《Journal of environmental psychology》2008,28(2):192-199
Humans will continue to adapt to an increasingly technological world. But are there costs to such adaptations in terms of human well being? Toward broaching this question, we investigated physiological effects of experiencing a HDTV quality real-time view of nature through a plasma display “window.” In an office setting, 90 participants (30 per group) were exposed either to (a) a glass window that afforded a view of a nature scene, (b) a plasma window that afforded a real-time HDTV view of essentially the same scene, or (c) a blank wall. Results showed that in terms of heart rate recovery from low-level stress the glass window was more restorative than a blank wall; in turn, a plasma window was no more restorative than a blank wall. Moreover, when participants spent more time looking at the glass window, their heart rate tended to decrease more rapidly; that was not the case with the plasma window. Discussion focuses on how the purported benefits of viewing nature may be attenuated by a digital medium. 相似文献
90.
Efficient cooperation in eusocial insect colonies requires effective communication, and there is abundant evidence of non-volatile
chemicals playing a role in regulating reproduction within colonies. In contrast, there have been fewer studies investigating
the role of volatile chemicals. This study investigated the potential role of volatile chemicals in regulating queen reproduction
either by directly inhibiting queen reproduction or by honestly signalling queen fecundity to workers. We tested this using
multiple queen colonies of the ant (Leptothorax acervorum) from a functionally monogynous population where one queen monopolizes all reproduction. Nine colonies, each with an established
laying queen, were split to produce two colony fragments—one containing the reproducing queen (group 1) and one containing
only previously non-reproducing queens (group 2). Each group was separated by a fine wire mesh preventing physical contact,
but allowing volatile chemical contact. In each group 2 fragment, we found that a single formerly non-reproductive queen commenced
reproduction and that the rate of egg laying and maximum number of eggs recorded did not significantly differ between groups
1 and 2, results that do not support volatile chemicals as playing a role in regulating queen reproduction. Instead, our findings
suggest that physical contact is necessary to maintain functional monogyny. 相似文献