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91.
根据珠江口东四口门(虎门、蕉门、洪奇门、横门)海域的调查资料,对营养盐含量和比值与浮游植物生长和种群结构的关系进行分析。结果表明:调查海域浮游植物的生长与海水中营养盐的浓度及营养盐之间的比例均有关,丰富的氮、磷、硅和较高的N:P、Si:P、Si:N比,可能是形成目前调查海域浮游植物群落以硅藻类占优势的种群结构的主要原因;但是在像深圳湾这样的半封闭海湾,营养盐含量及其之间的比例发生变化(尤其是N:P),将对浮游植物种群结构产生相应的影响。 相似文献
92.
93.
Mountain lakes are usually sensitive to the effects of global and regional environmental changes. Since the second half of the 20th century, surface-water acidification has become a significant ecological problem, and many lakes in Europe and North America have anthropogenically acidified. Additionally, following reduction in emissions of sulfur (S) and nitrogen (N) compounds, recovery from acidification has been observed in many lakes. In this study, we used changes in diatom communities to reconstruct the pH histories based on changes recorded in nine Tatra lakes (Western Carpathians, Poland) since approximately 1850 AD. Overall, results indicate that acidic precipitation had little influence on lake-water pH in the Tatra Mountain lakes. Changes in diatom-inferred pH (DI-pH) generally were small and showed little evidence of acidification during the time of the highest air pollution (since the 1960s), and have shown little change since the reduction of acidic deposition since the 1990s. Lakes that showed some evidence of acidification included dystrophic lakes with low acid neutralizing capacity. However, as illustrated by the PCA trajectories of the diatom assemblages, the majority of the lakes currently contain diatom assemblages that are unlike the diatom floras that existed ca. 1850. 相似文献
94.
Xiyun Cai Jing Ye Guangyao Sheng Weiping Liu 《Environmental science and pollution research international》2009,16(4):459-465
Background, aim, and scope As emerging contaminants, transformation products of the pollutants via various environmental processes are rather unknown,
and some may predominately contribute to the environmental risks of the parent compounds. Hence, studies on transformation
products complement the assessment of the environmental safety of the parent compounds. In this study, degradation experiments
and toxicity tests using diclofop-methyl (DM), a widely used herbicide, and selected major transformation products were carried
out in algal cultures to assess the time course of DM toxicity and its relevance in the formation of new breakdown products.
Methods The alga Chlorella vulgaris was maintained in the algal growth medium HB IV. The inhibition of algal growth was determined by measuring optical density
at 680 nm (OD680). Initially, DM and two selected breakdown products were added to the algal cultures, and following degradation experiments
analyses were carried out by high performance liquid chromatography. In addition, the possible relationship between DM degradation
and toxicity was assessed, based on physico-chemical properties of the compounds and their toxicity.
Results DM was rapidly absorbed onto the surface of the algal cells where it was hydrolyzed to diclofop (DC). Further degradation
to 4-(2, 4-dichlorophenoxy) phenol (DP) occurred in the cells. However, only a minor amount of DC was degraded to DP under
the same conditions when DC was initially added to the algal culture. When C. vulgaris was exposed to these compounds for 96 h, the determined EC50 showed that DC was about ten times less toxic than DM (EC50 = 0.42 mg/L) and that DP (EC50 = 0.20 mg/L) was the most toxic.
Discussion Due to strong hydrophobicity and rare dissociation, DM has tendency toward absorption as compared to DC. The higher average
degradation rates of DC initially treated by DM revealed the damage of the cell membranes caused by the DM and, thus, enhanced
movement of DC into the cells. Following occurrence of phenolic breakdown products, DP suggested that DC should be intracellularly
degraded to DP, which had a more potent mode of action and a higher acute toxicity. Moreover, the results for EC50 at various intervals were in accordance with degradation processes of the initial compounds, in which rapid formation of
DP was attributed to an increasing toxicity of DM.
Conclusions The toxicity of DM in algal suspensions increased with time due to its degradation to DP, which contributed significantly
to the determined toxicity. These results indicate that the toxicity of the pesticide probably depends significantly on degradation.
It is thus important to consider the time-dependent environmental processes when evaluating the toxicological effects of pesticides
for proper risk assessment.
Recommendations and perspectives Increasing transformation products of these contaminants are identified in the environment, although they seem to be unknown
in terms of the lacking studies on environmental behavior and ecotoxicity concerning them. Certain breakdown products probably
greatly contribute to the apparent toxicity of the parent compounds, which is ascribed to the parent compounds in general
studies ignoring the dependence of their toxicity on various transformation pathways. These studies that identify new intermediates
and assess their toxicity via the environmental processes will be helpful to distinguish the nature of toxicity of the parent
contaminants. 相似文献
95.
Elofsson K 《Environmental management》2006,37(1):54-68
Excess nutrient loads to coastal waters lead to increased production of algae, which when decaying cause oxygen depletion
in bottom sediments, which in turn leads to major changes in marine ecosystems. A cost-minimization model was investigated
in which nitrogen and phosphorus were assumed to interact with respect to algae production. It was investigated under what
conditions only a single nutrient should be decreased and when it is cost-effective to decrease both nutrients. The model
was applied to the Baltic Proper, which is the largest of the seven major basins in the Baltic Sea. Results showed that the
stringency of the environmental target, as well as assumptions regarding substitutability between nutrients, are important
factors to determine the nutrient on which to focus. Uniform decrease rates for emissions are often used in international
agreements, and the results of this model showed that the costs of making such proportional decreases could be substantial. 相似文献
96.
Microbial Removal of Arsenic 总被引:1,自引:0,他引:1
Kauser Jahan Patricia Mosto Crystal Mattson Erin Frey Lara Derchak 《Water, Air, & Soil Pollution: Focus》2006,6(1-2):71-82
Bangladesh is currently the subject of the world's largest mass arsenic poisoning in history. Groundwater throughout Bangladesh
and West Bengal is contaminated with naturally occurring arsenic from the alluvial and deltaic sediments that form the region's
aquifers. It has been estimated that 75 million people are at risk of developing health effects associated with the ingestion
of arsenic. This project focuses on the use of microorganisms such as bacteria and algae to remove arsenic from water. Arsenic
in the arsenite form was used in the studies. Experiments were conducted with a common alga and wastewater bacteria. A common
green algae Scenedesmus abundans was used for determining arsenic uptake in batch experiments. Results of the experiments indicated that the algae biosorption
could be modeled by the conventional Langmuir isotherm model. Algae morphology studies indicated that the algae cells were
impacted due to the presence of arsenic as evidenced by clumping or loss of cell clusters. The wastewater bacteria also were
capable of high percent of arsenic removal. Results indicate that microbial uptake of arsenic may be a viable method of pretreatment
of arsenic contaminated water. However algae and sludge disposal would pose a problem and will have to be dealt with accordingly. 相似文献
97.
Which group is best? Attributes of different biological assemblages used in freshwater biomonitoring programs 总被引:3,自引:0,他引:3
Resh VH 《Environmental monitoring and assessment》2008,138(1-3):131-138
Of the many groups of organisms proposed for use in biomonitoring, assemblages of fish, algae, and benthic macroinvertebrates
are the most commonly selected. Purported advantages and disadvantages of using these groups, along with those of zooplankton,
were assembled from 65 different publications and websites. From these, 13 categories of advantages and nine of disadvantages
were created. The diversity of the assemblage and its importance to the ecosystem were reported as advantages in >20% of citations
for each group; these similarities suggest that some redundancy exists among the different groups in terms of these features.
Likewise, sampling difficulties and lack of analytic metrics were disadvantages listed in >20% of citations for each group.
Few reported advantages (e.g. recreational value of fish) or disadvantages (e.g. short generation time of algae) were unique
for a particular assemblage. The validity of reported advantages and disadvantages were sometimes region specific, other times
incorrect. The choice of which assemblage is most appropriate for a biomonitoring program ultimately depends on the characteristics
of the area to be studied and the program objectives. 相似文献
98.
99.
聚合氯化铝铁的形态分布对微污染源水混凝效果的影响 总被引:2,自引:0,他引:2
针对微污染源水中浊度、叶绿素a等的强化去除问题,研究了碱化度、铝铁比和加碱方式等对聚合氯化铝铁形态分布的影响,并考察了形态分布与混凝除污效率和混凝沉淀出水中残铝浓度的关系.结果表明:在铁摩尔分数一定时,混凝剂中单体、中等聚合物和无定形凝胶含量与碱化度存在线性相关性,并推导出中等聚合物含量的计算公式;在碱化度一定时,混凝剂中单体、中等聚合物和无定形凝胶含量与铁摩尔分数也存在线性相关性;增加碱化度或降低铁摩尔分数,可以增加中等聚合物含量、降低单体含量,从而影响混凝除污效率和混凝沉淀后出水中残铝浓度.混凝实验结果表明,混凝过程中叶绿素a去除率和浊度去除率均与混凝剂中中等聚合物含量存在线性相关性,但两者相关系数不同.混凝沉淀后出水中残铝浓度与混凝剂中单体含量存在线性相关性.因此,预聚合的无机高分子混凝剂对提高混凝过程中的除浊、除藻效率,降低混凝沉淀后出水中残铝浓度具有重要的意义. 相似文献
100.
汉江“水华”成因分析及防治 总被引:10,自引:0,他引:10
汉江是长江的最大支流,是陕西、湖北两省沿岸居民生活用水和工业用水的重要水源。随着沿岸人口的增加,工业的发展,排污量不断增加,使汉江水质逐年下降,于近几年多次出现水华。本文在调查的基础上,对汉江水华成因进行了分析并提出了防治措施,供有关部门参考。 相似文献