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61.
62.
G. Vredeveld R. Bullard M. Sells S. Sims J. West 《Agriculture, ecosystems & environment》1983,9(1):51-56
The deletrious effects of chemical pesticides on many plant and animal populations have been described. Rapidly increasing costs of convenient energy sources have increased cost-benefit ratios of chemical pesticides used. We compared biological control techniques versus chemical pesticides for inputs of human labor, machinery, and fuel per hectare at each pertinent step of the production procedure. Three pest-crop systems were selected and all applicable factors converted into kilocalories of energy required. These were: (1) citrus-red scale (Aonidiella aurantii), using oil as a chemical and the predator wasp, Aphytis melinus as a biological control; (2) greenhouse cucumbers-white fly (Trialeurodes vaporariorum), using Orthene or the wasp, Encarsia formosa; (3) tomato-hornworm (Manduca quinquemaculata) using Sevin or the bacterium, Bacillus thurengiensis.For citrus-red scale, the pesticide required 5 248 405 kcal, the use of A. melinus 100 793 kcal; for cucumber-white fly the pesticide required 29 300 kcal, E. formosa 154 500 kcal; for tomato-hornworm the pesticide 26 693, B. thurengiensis 207 240 kcal. 相似文献
63.
Size regulation in larvae of the crustacean Balanus eburneus (Cirripedia: Thoracica) 总被引:1,自引:0,他引:1
We tested the hypothesis that larval size in the acorn barnacle Balanus eburneus Gould (Cirripedia Thoracica) varies in relation to food availability. In March–November 1980, and March–July 1981, larvae were obtained from adult Balanus eburneus collected in the Newport River, North Carolina, USA. Carapace length and width of larvae reared at three different food concentrations were measured. Mean naupliar instar size was independent of food concentration. Mean size of the cypris instar increased with increasing food level. Greater cypris size could be attributed to increased food reserves in the preceding naupliar stage, and was coinciden with inmarked increase in metamorphic success. Variation in instar size remained constant or declined during naupliar development, but increased sharply at the molt to the cyprid. Naupliar size regulation involved: (1) conservation of a molt increment specific for each naupliar-naupliar molt, (2) an inverse relationship between premolt size and the molt increment during the first five naupliar instars, and (3) an increase in the precision of the molt increment at the molt to the sixth naupliar instar. Experimental evidence implies that size regulation in Balanus eburneus limits variation about a fixed final naupliar size (e.g. volume). Measurement of naupliar size, accumulated energy reserves, survival and development time, and cypris metamorphic success indicated that naupliar cuticular growth is the most conservative feature of larval development. The data suggest that maximum naupliar size is limited by escalating metabolic costs during development, while minimum naupliar size is limited by size-related feeding effectiveness. 相似文献
64.
Yuping Wu Walter W. Piegorsch R. Webster West Dengfang Tang Maureen O. Petkewich Wei Pan 《Environmental and Ecological Statistics》2006,13(1):125-141
We develop and study multiplicity adjustments for low-dose inferences in environmental risk assessment. Application is intended
for risk analysis studies where human, animal, or ecological data are used to set safe levels of a hazardous environmental
agent. A modern method for making inferences in this setting is known as benchmark analysis, where attention centers on the
dose at which a fixed benchmark level of risk is achieved. Both upper confidence limits on the risk and lower confidence limits
on the “benchmark dose” are of interest. In practice, a number of possible benchmark risks may be under study; if so, corrections
must be applied to adjust the limits for multiplicity. In this note, we discuss approaches for doing so with continuous, nonquantal
response data. 相似文献
65.
Martha L. Sykes Hsueh-Wen Yeh Ian F. West R. W. Gauldie Charles E. Helsley 《Journal of Polymers and the Environment》1994,2(3):201-209
A new method for evaluating biodegradability of starch-based and certain other polymer blends uses the pre- and postexposure stable carbon isotope composition of material coupled with weight loss data to determine which components have degraded. The naturally occurring stable isotope of carbon.13C, is enriched in corn starch (13C, approx. –11) compared to petroleum-derived synthetic polymers (13C, approx. –32). Results on starch-synthetic polymer blends indicate that the 13C signatures of these blends are near-linear mixtures of their component 13C. Values of a 13C for starch-synthetic polymer blends exposed to biologically active laboratory soil and artificial seawater conditions are depleted in13C compared to unexposed samples, suggesting loss of the starch component. Combined with weight loss data for the exposed samples, the 13C values are statistically consistent with models requiring loss of the soluble component glycerin, followed by loss of starch, then petrochemical polymer, or simultaneous loss of starch and petrochemical polymer. Replicate 13C analyses of starch-synthetic polymer blends increase the statistical power of this relatively inexpensive, accessible technique to discriminate between degrading components. 相似文献
66.
Angela M. Leung D. Matthew McDonough C. David West 《Environmental monitoring and assessment》1998,50(1):85-94
The extent of contamination by endosulfans in soil samples collected from the Point Mugu watershed near Oxnard, California was determined using capillary gas chromatography/mass selective detection (GC/MSD). The study was designed to detect three organochlorinated pesticides: endosulfan , endosulfan and endosulfan sulfate. Thirteen sets of two soil samples each were taken from various sites in the region. Our results show that the endosulfan levels in these soils range from trace amounts to nearly 30 ppm, with endosulfan being the most abundant and endosulfan sulfate the least. Two sites of the study, Hueneme and Revolon and Farm and Revolon, showed high amounts of endosulfans and , with concentrations between 20 and 30 ppm. The majority of the other sites studied in this research produced concentrations of less than 10 ppm for each of the three endosulfans monitored. At five areas in particular, Pleasant Valley and Creek, Laguna and Creek, Etting and Creek, Road and Creek and Hueneme and Creek, less than 2 ppm or only trace amounts of endosulfans , and sulfate were detected. 相似文献
67.
D. Jones A.G. Scarlett C.E. West R.A. Frank R. Gieleciak D. Hager J. Pureveen E. Tegelaar S.J. Rowland 《Chemosphere》2013
‘Naphthenic acids’ (NAs) in petroleum produced water and oil sands process water (OSPW), have been implicated in toxicological effects. However, many are not well characterized. A method for fractionation of NAs of an OSPW was used herein and a multi-method characterization of the fractions conducted. 相似文献
68.
S. J. Rowland C. E. West A. G. Scarlett D. Jones M. Boberek L. Pan M. Ng L. Kwong A. Tonkin 《Environmental Chemistry Letters》2011,9(4):525-533
Characterisation of the complex mixtures of carboxylic acids (naphthenic acids) occurring in crude oils and in degraded oil
sands is environmentally important. Indeed some acids in waters from oil platforms are apparently hormonally active, and the
oil sands acids are said to be toxic to a wide range of biota. Previous attempts to identify monocyclic and monoaromatic naphthenic
acids have been hampered by the lack of authenticated synthetic reference compounds. Some studies have indicated that acids
with ethanoic acid side chains are present in the naphthenic acids mixtures, so in the present study, we synthesised and characterised
by mass spectrometry, a range (C8–14) of monoaromatic and monocyclic ethanoic acids. Using 2-D comprehensive gas chromatography–mass spectrometry, we then compared
the retention times and mass spectra of the synthetic acids with those of a commercial naphthenic acids mixture. Some alicyclic
and numerous aromatic acids were successfully identified. 相似文献
69.
Anwar Hussain Ian A. Munn Darren Hudson Ben West 《Journal of environmental management》2010,91(12):2565-2571
Understanding of hunter preferences for hunting lease attributes is important to landowners because such knowledge provides key information for managing and marketing fee-hunting in order to maximize revenues. Premised on this insight, we used attribute based modeling to investigate how hunter preferences for potential leases were influenced by lease and hunter-specific attributes. A mail survey of Mississippi licensed hunters provided the necessary data. Estimation results based on McFadden conditional logit regression suggested that lease attributes including game diversity, lease location relative to hunter residence, lease size, lease duration and lease rate influenced willingness to pay for additional units of lease attributes. Depending on the specific levels of these attributes, WTP could vary as much as $5.70 per acre. Of the hunter-specific attributes, age and income significantly influenced hunter decision to buy a lease or opt for status quo. Results of this study should assist landowners in increasing financial returns from fee-hunting endeavors through appropriate changes to their hunting access policies and wildlife management activities in response to hunter preferences regarding lease attributes. 相似文献
70.