首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   915篇
  免费   8篇
  国内免费   15篇
安全科学   27篇
废物处理   53篇
环保管理   93篇
综合类   142篇
基础理论   204篇
环境理论   2篇
污染及防治   302篇
评价与监测   55篇
社会与环境   58篇
灾害及防治   2篇
  2023年   2篇
  2022年   15篇
  2021年   17篇
  2020年   8篇
  2019年   8篇
  2018年   29篇
  2017年   36篇
  2016年   36篇
  2015年   31篇
  2014年   29篇
  2013年   93篇
  2012年   47篇
  2011年   73篇
  2010年   56篇
  2009年   55篇
  2008年   66篇
  2007年   53篇
  2006年   47篇
  2005年   31篇
  2004年   29篇
  2003年   31篇
  2002年   19篇
  2001年   8篇
  2000年   6篇
  1999年   6篇
  1998年   8篇
  1997年   9篇
  1996年   4篇
  1995年   12篇
  1994年   2篇
  1993年   4篇
  1991年   4篇
  1990年   3篇
  1987年   2篇
  1981年   3篇
  1965年   7篇
  1964年   3篇
  1963年   4篇
  1962年   9篇
  1961年   11篇
  1960年   1篇
  1958年   2篇
  1957年   1篇
  1956年   1篇
  1954年   1篇
  1947年   1篇
  1942年   1篇
  1941年   2篇
  1938年   1篇
  1932年   1篇
排序方式: 共有938条查询结果,搜索用时 31 毫秒
891.
This paper explores the characteristics of 238 patents on 90 inventions contributed by major multinational innovators to the “Eco-Patent Commons”, which provides royalty-free access to third parties to patented innovations on green technologies. We compare the pledged patents to other patents in the same technologies or held by the same multinationals to investigate the motives of the contributing firms as well as the potential for such commons to encourage innovation and diffusion of climate change related technologies. We find pledged patents to protect environmentally friendly technologies and to be of similar value as the average patent in a pledging firm's patent portfolio but of lower value than other patents in their class. Our analysis of the impact of the patent commons on diffusion of patented technologies suggests that making patents accessible royalty-free did not result in any significant increase in diffusion as measured by citing patents. This study, therefore, indirectly provides evidence on the role of patents in the development and diffusion of green technologies.  相似文献   
892.
Several air toxics are emitted from mobile sources on roadways and these emissions account for a significant fraction of the health risks to the population. In addition, health effect studies are now becoming more comprehensive and some account for the spatial heterogeneities of air pollutant concentration fields (as is the case near roadways). Standard models can simulate either the near-source concentration fields or the urban background, but no model can handle both spatial scales in the vicinity of roadways in a coherent and scientifically correct manner. Here, we present a model that provides such an integrated treatment by combining a grid-based air quality model of the urban background with a plume-in-grid representation of roadway emissions. The model is applied to simulate near-roadway concentrations due to emissions from a busy interstate highway in New York City. Qualitative comparisons with typical measured concentration profiles show that the model captures the observed features of toxic air pollutant concentrations near roadways.  相似文献   
893.
Biosolids spread onto agricultural soils are potential sources of steroidal hormones that are able to adversely affect the soil ecosystem. Here we studied the fate of the [4-14C]-17-β-estradiol hormone in laboratory experiments. First, our results show that only 2.9% of the hormone was mineralized in the soil from a French vineyard. By contrast, the mineralization increased to 7.1% when the hormone was provided in composted biosolids. Second, we found that only a minor part of the estradiol-derived 14C was mobile and partly transferred to soil leachates. Indeed, the hormone was mainly stabilized in the soil as non-extractable residues. Overall, our findings show that estradiol undergoes two main processes, complete degradation and stabilisation. We therefore conclude that the environmental risk of hormones provided to the soil through composted biosolids is negligible under the conditions of our experiments.  相似文献   
894.

Background

Due to the rising number of type 2 diabetes patients, the antidiabetic drug, metformin is currently among those pharmaceuticals with the highest consumption rates worldwide. Via sewage-treatment plants, metformin enters surface waters where it is frequently detected in low concentrations (µg/L). Since possible adverse effects of this substance in aquatic organisms have been insufficiently explored to date, the aim of this study was to investigate the impact of metformin on health and development in brown trout (Salmo trutta f. fario) and its microbiome.

Results

Brown trout embryos were exposed to 0, 1, 10, 100 and 1000 µg/L metformin over a period from 48 days post fertilisation (dpf) until 8 weeks post-yolk sac consumption at 7 °C (156 dpf) and 11 °C (143 dpf). Chemical analyses in tissues of exposed fish showed the concentration-dependent presence of metformin in the larvae. Mortality, embryonic development, body length, liver tissue integrity, stress protein levels and swimming behaviour were not influenced. However, compared to the controls, the amount of hepatic glycogen was higher in larvae exposed to metformin, especially in fish exposed to the lowest metformin concentration of 1 µg/L, which is environmentally relevant. At higher metformin concentrations, the glycogen content in the liver showed a high variability, especially for larvae exposed to 1000 µg/L metformin. Furthermore, the body weight of fish exposed to 10 and 100 µg/L metformin at 7 °C and to 1 µg/L metformin at 11 °C was decreased compared with the respective controls. The results of the microbiome analyses indicated a shift in the bacteria distribution in fish exposed to 1 and 10 µg/L metformin at 7 °C and to 100 µg/L metformin at 11 °C, leading to an increase of Proteobacteria and a reduction of Firmicutes and Actinobacteria.

Conclusions

Overall, weight reduction and the increased glycogen content belong to the described pharmaceutical effects of the drug in humans, but this study showed that they also occur in brown trout larvae. The impact of a shift in the intestinal microbiome caused by metformin on the immune system and vitality of the host organism should be the subject of further research before assessing the environmental relevance of the pharmaceutical.
  相似文献   
895.
This paper discusses the need for critically evaluating regional-scale (~200–2,000 km) three-dimensional numerical photochemical air quality modeling systems to establish a model’s credibility in simulating the spatio-temporal features embedded in the observations. Because of limitations of currently used approaches for evaluating regional air quality models, a framework for model evaluation is introduced here for determining the suitability of a modeling system for a given application, distinguishing the performance between different models through confidence-testing of model results, guiding model development and analyzing the impacts of regulatory policy options. The framework identifies operational, diagnostic, dynamic, and probabilistic types of model evaluation. Operational evaluation techniques include statistical and graphical analyses aimed at determining whether model estimates are in agreement with the observations in an overall sense. Diagnostic evaluation focuses on process-oriented analyses to determine whether the individual processes and components of the model system are working correctly, both independently and in combination. Dynamic evaluation assesses the ability of the air quality model to simulate changes in air quality stemming from changes in source emissions and/or meteorology, the principal forces that drive the air quality model. Probabilistic evaluation attempts to assess the confidence that can be placed in model predictions using techniques such as ensemble modeling and Bayesian model averaging. The advantages of these types of model evaluation approaches are discussed in this paper.  相似文献   
896.
Modelling nutrient uptake by crops implies considering and integrating the processes controlling the soil nutrient supply, the uptake by the root system and relationships between the crop growth response and the amount of nutrient absorbed. We developed a model that integrates both dynamics of maize growth and phosphorus (P) uptake. The crop part of the model was derived from Monteith's model. A complete regulation of P-uptake by the roots according to crop P-demand and soil P-supply was assumed. The soil P-supply to the roots was calculated using a diffusion equation and assuming that roots behave as zero-sinks. The actual P-uptake and crop growth were calculated at each time step by comparing phosphate and carbohydrate supply–demand ratios. Model calculations for P-uptake and crop growth were compared to field measurements on a long term P-fertilization trial. Three P-fertilization regimes (no P-fertilization, 42.8 kg P ha−1 year−1 and 94.3 kg P ha−1 year−1) have led to a range of P-supply. Our model correctly simulated both the crop development and growth for all P-treatments. P-uptake was correctly predicted for the two non-limiting P-treatments. Nevertheless, for the limiting P-treatment, P-uptake was correctly predicted during the early period of growth but it was underestimated at the last sampling date (61 day after sowing). Several arguments for under-prediction were considered. However, most of them cannot explain the observed magnitude in discrepancy. The most likely reason might be the fact that biomass allocation between shoot and root must be modelled more precisely. Despite this mismatch, the model appears to provide realistic simulations of the soil–plant dynamic of P in field conditions.  相似文献   
897.
The success of reintroduction programs greatly depends on the amount of mortality and dispersal of the released individuals. Although local environmental pressures are likely to play an important role in these processes, they have rarely been investigated because of the lack of spatial replicates of reintroduction. In the present study, we analyzed a 25-year data set encompassing 272 individuals released in five reintroduction programs of Griffon Vultures (Gyps fulvus) in France to examine the respective roles of survival and dispersal in program successes and failures. We use recent developments in multi-strata capture-recapture models to take into account tag loss in survival estimates and to consider and estimate dispersal among release areas. We also examined the effects of sex, age, time, area, and release status on survival, and we tested whether dispersal patterns among release areas were consistent with habitat selection theories. Results indicated that the survival of released adults was reduced during the first year after release, with no difference between sexes. Taking into account local observations only, we found that early survival rates varied across sites. However when we distinguished dispersal from mortality, early survival rates became equal across release sites. It thus appears that among reintroduction programs difference in failure and success was due to differential dispersal among release sites. We revealed asymmetrical patterns of dispersal due to conspecific attraction: dispersers selected the closest and the largest population. We showed that mortality can be homogeneous from one program to another while, on the contrary, dispersal is highly dependent on the matrix of established populations. Dispersal behavior is thus of major interest for metapopulation restoration and should be taken into account in planning reintroduction designs.  相似文献   
898.
899.
The pH-dependent release of cadmium, copper, and lead from soil materials was studied by use of a stirred flow cell to quantify their release and release rates, and to evaluate the method as a test for the bonding strength and potential mobility of heavy metals in soils. Soil materials from sludge-amended and nonamended A horizons from a Thai coarse-textured Kandiustult and a Danish loamy Hapludalf were characterized and tested. For each soil sample, release experiments with steady state pH values in the range 2.9 to 7.1 and duration of 7 d were performed. The effluent was continuously collected and analyzed. Release rates and total releases were higher for the Hapludalf than the Kandiustult and higher for the sludge-amended soils than the nonamended soils. With two exceptions the relative release rates (release rate/total content of metal in soil) plotted vs. steady state pH followed the same curves for each metal, indicating similar bonding strengths. These curves could be described by a rate expression of the form: relative release rate = k[H+]a, with specific a (empirical constant) and k (rate constant) parameters for each metal demonstrating that metal release in these systems can be explained by proton-induced desorption and dissolution reactions. With decreasing pH, pronounced increases in release rates were observed in the sequence cadmium > lead > copper, which express the order of metal lability in the soils. The flow cell system is useful for comparison of metal releases as a function of soil properties, and can be used as a test to rank soils with respect to heavy metal leaching.  相似文献   
900.
The Oregon Department of Forestry is a designated management agency to provide a forestry program to assist in bringing the Tualatin River into complicance with pH and dissolved oxygen water quality standards. The Oregon Environmental Quality Commission set a total maximum daily load (TMDL) of 70 µg/l total phosphorus to control algae growth and meet these standards. The Department of Forestry has a basin effectiveness monitoring plan to determine that the Oregon Forest Practice Rules' BMPs are maintaining adequate control of phosphorus loadings from forest operations. Three sites monitored during May to October of 1990 were augmented by eight more sites in 1991. As laboratory methods were refined, the results became more accurate. The 1991 monitoring showed lower phosphorus levels that were consistent for each tributary. Mean total phosphorus levels ranged from 17 to 65 µg/l. Preliminary field reconnaissance suggests a correlation between phosphorus levels and underlying geology. Concentrations were lowest at sites underlain by tertiary intrusive basalts, next higher for sites with terrestrial basalt, next higher for one site with a basalt-sandstone bedrock mix, and highest for sites underlain predominately by sandstone. These results may be modified by 1992 monitoring and further analysis.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号