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241.
Methanol extracts of freshly harvested cells of the marine diatom Phaeodactylum tricornutum were found to produce a feeding deterrent effect in the copepod Tigriopus californicus. Bioassay guided fractionation of the methanol extracts led to the isolation of four compounds possessing feeding deterrent activity. The compounds were identified as apo-10-fucoxanthinal (1), apo-12-fucoxanthinal (2), apo-12-fucoxanthinal (3), and apo-13-fucoxanthinone (4) by detailed spectroscopic analysis and comparison with authentic compounds produced semi-synthetically from fucoxanthin. Compounds 1 to 4 exhibited feeding deterrent responses in T. californicus at concentrations of less than 20 ppm. 相似文献
242.
Michelle Casey Chris Gennings W Hans Carter Jr Virginia C Moser Jane Ellen Simmons 《Environmental and Ecological Statistics》2006,13(1):11-23
Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely
accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental
effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals.
When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays
of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a
response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple
fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper
is to address power and sample size issues related to the hypothesis of no interaction. 相似文献
243.
244.
Douglas T. Shaw David R. Maidment 《Journal of the American Water Resources Association》1987,23(6):1037-1046
ABSTRACT: Mandatory water conservation in the form of restrictions on outdoor watering, car washing, and recreation was implemented in the City of Austin, Texas, during the summers of 1984 and 1985. Three different stages of restrictions were implemented limiting the number of watering hours per day, as well as a restriction that allowed lawn watering once every five days according to the last digit of the street address, Intervention analysis using a transfer function-noise model of daily water use is applied to assess the impact of the restrictions. Compared to a peak water use rate of about 170 MGD, it is shown that mandatory restrictions in 1984 reduced water use by an average of 13.5 MGD, while similar restrictions during the summer of 1985 reduced usage by an average of 5.5 MGD. Lawn watering restrictions on a five-day cycle produced a corresponding five-day cycle in water use of more than 10 MGD in amplitude in 1985. An alternative lawn watering scheme that eliminates this cycle is prescribed. 相似文献
245.
A method is presented for calculating allowable use of tracked vehicles on the US Army's Pinon Canyon Maneuver Site in southeastern Colorado. The first step in this process is to determine the sheet and rill erosion rate on each soil series using the revised Universal Soil Loss Equation. Soil series are then ranked according to their trainability (e g., ranked based on how much vegetative cover can be lost without exceeding soil loss tolerance) Maximum onetime surface use, allowable surface use per year, usable hectares per year, and tracked vehicle days per year can then be calculated Examples are given to illustrate how these values can be manipulated to assist land managers and military trainers to better plan and match training missions to available land. Also, short- and long-term monitoring schemes are presented that can be used to verify or adjust estimates of allowable use. The methods presented can be converted to determine allowable use of other types of activities that disturb the vegetation and expose the soil surface to the erosive forces of wind and water (e g, recreational and off-road vehicles). 相似文献
246.
Christopher L. Shaw 《Natural resources forum》1991,15(2):123-131
Central governments are facing increasingly stringent demands to lead the clean-up of public resources. Historically, governments have chosen legislation and regulation to address these concerns and achieved mixed results, but another tool of public policy holds significant promise and is gaining ground in the policy debate: 'green' taxes. The potential of a tax system to mitigate environmental externalities is explored. The theory of pollution tax is reviewed and a comparison of two country cases where taxes have been designed explicitly to reduce industrial effluents and improve the quality of fresh water resources is presented. If structures to approximate social costs are federally mandated and regionally implemented, a comprehensive tax system can constitute an integral part of an effective response to private spoliation of the commons. 相似文献
247.
William Whipple Joseph V. Hunter Shaw L. Yu 《Journal of the American Water Resources Association》1978,14(2):288-301
ABSTRACT: Increasingly, residential development in urbanizing areas is accomplished by large housing projects, composed of clusters of townhouses or garden partments. It is hypothesized that the runoff from such developments should carry more pollution than that from the same number of housing units on separate plots, because the runoff is conveyed directly to drainage channels rather than being drained across lawns and gardens, which may absorb part of the pollutants. In order to evaluate this effect, storm event data were obtained from a planned unit development near Hightstown, N. J., using samples taken every 10 minutes throughout the storm at two different storm sewers. Results show heavy metals pollution about what had been anticipated, in accordance with the hypothesis given above, and BOD ammonia and phosphates higher than predicted. The results are significant for areawide water quality planning in metropolitan areas, where projections of future pollution loadings depends upon the land use. 相似文献
248.
249.
Soil contamination with radionuclides and potential remediation 总被引:5,自引:0,他引:5
Soils contaminated with radionuclides, particularly 137Cs and 90Sr, pose a long-term radiation hazard to human health through exposure via the foodchain and other pathways. Remediation of radionuclide-contaminated soils has become increasingly important. Removal of the contaminated surface soil (often up to 40 cm) or immobilization of radionuclides in soils by applying mineral and chemical amendments are physically difficult and not likely cost-effective in practicality. Reducing plant uptake of radionuclides, especially 137CS and 90Sr by competitive cations contained in chemical fertilizers has the general advantage in large scale, low-level contamination incidents on arable land, and has been widely practiced in central and Western Europe after the Chernobyl accident. Phytoextraction of radionuclides by specific plant species from contaminated sites has rapidly stimulated interest among industrialists as well as academics, and is considered to be a promising bio-remediation method. This paper examines the existing remediation approaches and discusses phytoextraction of radionuclides from contaminated soils in detail. 相似文献
250.
Prasad VK Ortiz A Stinner B McCartney D Parker J Hudgins D Hoy C Moore R 《Environmental monitoring and assessment》2005,110(1-3):141-169
Ohio is typical among the Midwestern and Eastern United States with high levels of water pollutants, the main sources being
from agriculture. In this study, we used a digital elevation model in conjunction with hydrological indices to determine the
role of landscape complexity affecting the spatial and temporal variation in pollutant levels, in one of the most impaired
headwater streams in Ohio. More than eighty five percent of the study area is dominated by agriculture. Spatial distribution
of slope (S), altitude and wetness index along with other watershed parameters such as flow direction, flow accumulation,
stream networks, flow stream orders and erosion index were used within a Geographic Information Systems framework to quantify
variation in nitrate and phosphate loads to headwater streams. Stream monitoring data for nutrient loads were used to correlate
the observed spatial and temporal patterns with hydrological parameters using multiple linear regressions. Results from the
wetness index calculated from a digital elevation model suggested a range of 0.10–16.39, with more than 35% having values
less than 4.0. A Revised Universal Soil Loss Equation (RUSLE) predicted soil loss in the range of 0.01–4.0 t/ha/yr. Nitrate
nitrogen levels in the study area paralleled precipitation patterns over time, with higher nitrate levels corresponding to
high precipitation. Atmospheric deposition through precipitation could explain approximately 35% of total nitrate levels observed
in streams. Among the different topographic variables and hydrological indices, results from the step-wise multiple regression
suggested the following best predictors, (1) elevation range and upstream flow length for nitrate, (2) flow direction and
upstream flow length for ammonia-nitrogen and slope, and (3) elevation range for phosphate levels. Differences in the landscape
models observed for nitrate, phosphate and ammonia-nitrogen in the surface waters were attributed partly to differences in
the chemical activity and source strengths of the different forms of these nutrients through agricultural management practices.
The results identify geomorphologic and landscape characteristics that influence pollutant levels in the study area. 相似文献