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381.
Richard D. Ashby Peter Cooke Daniel K. Y. Solaiman 《Journal of Polymers and the Environment》2007,15(3):179-187
Poly(hydroxyalkanoates) (PHAs) are a class of bacterially-derived polymers that are naturally biodegradable through the action
of extracellular depolymerase enzymes secreted by a number of different bacteria and fungi. In this paper we describe the
development of topographical imaging protocols (by both scanning electron microscopy; SEM, and confocal microscopy; CM) as
a means of monitoring the biodegradation of solution cast films of poly(3-hydroxybutanoate-co-3-hydroxyhexanoate) (P3HB/3HHx) and medium-chain-length (mcl-) PHA. Pseudomonas lemoignei and Comamonas P37C were used as sources for PHA depolymerase enzymes as these bacteria are known to degrade at least one of the polymers
in question. SEM revealed the bacterial colonization of the film surfaces while CM permitted the comparative assessment of
the roughness of the film surfaces upon exposure to the two bacterial strains. By dividing the total surface area of the film
(A′) by the total area of the scan (A) it was possible to monitor biodegradation by observing differences in the topography
of the film surface. Prior to inoculation, P3HB/3HHx films had an A′/A ratio of 1.06. A 24-h incubation with P. lemoignei increased the A′/A ratio to 1.47 while a 48- and 120-h incubation with Comamonas resulted in A′/A ratios of 1.16 and 1.33, respectively. These increases in the A′/A ratios over time demonstrated an increase
in the irregularity of the film surface, indicative of PHA polymer breakdown.
Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 相似文献
382.
Policymakers today are faced with a difficult task of planning for large scale infrastructure that can cater to the climatic and socio-economic changes that the future will bring. To address the deeply uncertain nature resulting from long-term changes, it is becoming necessary to develop strategies that support flexibility and react more strategically than traditional planning approaches. This paper applies the concept of adaptation tipping points and adaptation pathways to a case study in Singapore for the planning of long-term urban drainage infrastructure. Using conventional grey and sustainable green solutions in isolation and in combination, adaptation pathway maps are developed and compared across outlined climatic and landuse scenarios. To understand and justify if the imparted flexibility is worth its cost, economic assessments are performed. This is a valuable extension of the existing framework, helps to identify the preferred configuration of land use and sub-select adaptation actions that should be implemented at the current time frame. The main finding of this study is that the adaptation pathways map for the sustainable grey landuse scenario economically outperforms those of the other outlined land uses. This provides a valuable insight for policy makers, as it implies that if carefully planned development is undertaken, the requirements of storm water management can be met in a sustainable manner, while simultaneously freeing up land for other purposes. This is especially important in the context of highly dense urban areas such as Singapore, where land is a scare resource. 相似文献
383.
Björklöf K Salminen J Sainio P Jørgensen K 《Environmental geochemistry and health》2008,30(2):101-107
Evidence for on site biodegradation may be difficult to provide at heterogeneous sites without additional experiments in controlled
laboratory conditions. In this study, microbial activities measured as CO2 and CH4 production were compared in situ, in intact soil cores and in bottle microcosms containing sieved soils. In addition, biodegradation
rates were determined by measuring the decrease in petroleum hydrocarbon concentrations at 7°C in aerobic and anaerobic conditions.
Elevated concentrations of CO2 and CH4 in the soil gas phase indicated that both the aerobic and anaerobic microbial activity potentials were high at the contaminated
site. Aerobic and anaerobic microbial degradation rates in laboratory experiments of petroleum hydrocarbons were highest in
soils from the most contaminated point and degradation in the aerobic and anaerobic microcosms was linear throughout the incubation,
indicating mass-transfer-dependent degradation. Different results for microbial activity measurements were obtained in laboratory
studies depending on pretreatment and size of the sample, even when the environmental conditions were mimicked. These differences
may be related to differences in the gas exchange rates as well as in changes in the bioavailability of the contaminant in
different analyses. When predicting by modeling the behavior of an aged contaminant it is relevant to adapt the models in
use to correspond to conditions relevant at the contaminated sites. The variables used in the models should be based on data
from the site and on experiments performed using the original aged contaminant without any additions. 相似文献
384.
环境雌激素(Environmental Estrogens, EEs)种类繁多、来源多样且分布广泛,大量工业添加剂、食品添加剂和农药类物质已被证实具有雌激素活性。EEs对人体生殖、神经、免疫等系统生物毒性,已经引起了公众的普遍关注。近年来的研究表明,EEs不仅可以结合雌激素核受体(nuclear Estrogen Receptor, nER)干扰正常的雌激素基因组信号通路,还能活化雌激素膜受体(membrane Estrogen Receptor, mER)引发快速的雌激素非基因组信号转导途径。本文总结了EEs通过nER、mER介导的多种雌激素基因组和非基因组信号途径及其产生的生物学效应,综述了在其毒理学作用机理基础上发展的环境样品的雌激素活性评估和EEs混合物的联合作用研究,以期为该类污染物的筛查、风险评估和进一步的机制研究提供参考。 相似文献
385.
386.
387.
388.
Ecological network and emergy analysis of urban metabolic systems: Model development,and a case study of four Chinese cities 总被引:2,自引:0,他引:2
Analysis of the structure and function of urban metabolic systems is an important goal of urban research. We used network pathways and network utility analysis to analyze the basic network structure of the urban metabolic system and the complex ecological relationships within the system, providing a new way to perform such research. Using four Chinese cities as examples, we developed an ecological network model of the urban metabolic system. By using network pathway analysis, we studied the changing relationships between metabolic length and the number of metabolic pathways, and between metabolic length and reachability. Based on the distribution of the number of metabolic pathways, we describe the basic structure and intercompartment relationships of the system. By using the sign distribution in the network utility matrix, we determined the ecological relationships and degree of mutualism between the compartments of the system. The basic components of the system consisted of the internal environment, the external environment, and the agricultural, industrial, and domestic sectors. With increasing metabolic length, the ecological relationships among the components of the system became more diverse, and the numbers of metabolic paths and their reachability improved. Although the basic network structure of the four cities was identical, the mutualism index differed. Beijing's mutualism index was superior to that of Shanghai, and much higher than those of Tianjin and Chongqing. By analyzing the structure and function of the urban metabolic system, we provide suggestions for optimizing the structure and adjusting the relationships, and propose methods for the application of ecological network analysis in future urban system research. 相似文献
389.
As part of a project to determine the fate of contaminated milk in the marine environment (Elliott et al ., 2001), the Biochemical Oxygen Demand (BOD) of unprocessed natural milk in sea water was followed in standard BOD bottles and in an open system. The best estimate for the BOD was ¨ 170,000 r mg - l m 1 although measurable effects could still be seen with dilutions up to one in a million. If incubated in the light, simulating summer conditions, the algae produced oxygen and offset some of the loss through bacterial degradation thereby reducing any slump in oxygen. There was also a "nutrient effect" where the presence of milk increased the oxygen production at low concentrations in sea water. In an open system akin to a slick being dispersed, the change in BOD was exponential after an initial activation period. The length of this activation period was greater in more concentrated mixtures of milk and sea water. These results have been utilised in a model to determine the best strategy for disposing of contaminated milk (Elliott et al ., 2001). 相似文献
390.