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   89046篇
  免费   1226篇
  国内免费   1095篇
安全科学   3728篇
废物处理   3185篇
环保管理   13790篇
综合类   21020篇
基础理论   26138篇
环境理论   72篇
污染及防治   13935篇
评价与监测   5373篇
社会与环境   3589篇
灾害及防治   537篇
  2022年   795篇
  2021年   797篇
  2020年   643篇
  2019年   853篇
  2018年   1104篇
  2017年   1158篇
  2016年   2124篇
  2015年   1819篇
  2014年   2560篇
  2013年   9218篇
  2012年   2148篇
  2011年   2343篇
  2010年   3218篇
  2009年   3387篇
  2008年   1890篇
  2007年   1738篇
  2006年   2199篇
  2005年   2175篇
  2004年   2473篇
  2003年   2329篇
  2002年   1865篇
  2001年   2094篇
  2000年   1897篇
  1999年   1473篇
  1998年   1360篇
  1997年   1349篇
  1996年   1471篇
  1995年   1566篇
  1994年   1459篇
  1993年   1310篇
  1992年   1308篇
  1991年   1274篇
  1990年   1229篇
  1989年   1197篇
  1988年   1034篇
  1987年   965篇
  1986年   991篇
  1985年   1060篇
  1984年   1151篇
  1983年   1174篇
  1982年   1174篇
  1981年   1096篇
  1980年   941篇
  1979年   929篇
  1978年   818篇
  1977年   720篇
  1976年   638篇
  1975年   610篇
  1973年   637篇
  1972年   650篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
Changes in the autotrophic pico- (0.2–2 μm), nano- (2–20 μm), and microplankton (>20 μm) biomass (chlorophyll a) and primary production were measured in the estuarine and coastal waters off Cochin, southwest coast of India during the onset and establishment of a monsoon. During this period, the estuary was dominated by nutrient-rich freshwater, whereas the coastal waters were characterized with higher salinity values (>30 psu) and less nutrients. The average surface chlorophyll a concentrations and primary production rates were higher in the estuary (average 13.7 mg m???3 and 432 mgC m???3 day???1) as compared to the coastal waters (5.3 mg m???3 and 224 mgC m???3 day???1). The nanoplankton community formed the major fraction of chlorophyll a and primary production, both in the estuary (average 85 ± SD 8.3% and 81.2 ± SD 3.2%) and the coastal waters (average 73.2 ± SD 17.2% and 81.9 ± 15.7%). Nanoplankton had the maximum photosynthetic efficiency in the coastal waters (average 4.8 ± SD 3.9 mgC mgChl a m???3 h???1), whereas in the estuary, the microplankton had higher photosynthetic efficiency (average 7.4 ± 7 mgC mgChl a m???3 h???1). The heavy cloud cover and increased water column turbidity not only limit the growth of large-sized phytoplankton in the Cochin estuary and coastal waters but also support the proliferation of nanoplankton community during the monsoon season, even though large variation in nanoplankton chlorophyll a and production exists between these two areas.  相似文献   
832.
The construction industry is now putting greater emphasis than ever before on increasing recycling and promoting more sustainable waste management practices. In keeping with this approach, many sectors of the industry have actively sought to encourage the use of recycled concrete aggregate (RCA) as an alternative to primary aggregates in concrete production. The results of a laboratory experimental programme aimed at establishing chemical and mineralogical characteristics of coarse RCA and its likely influence on concrete performance are reported in this paper. Commercially produced coarse RCA and natural aggregates (16-4 mm size fraction) were tested. Results of X-ray fluorescence (XRF) analyses showed that original source of RCA had a negligible effect on the major elements and a comparable chemical composition between recycled and natural aggregates. X-ray diffraction (XRD) analyses results indicated the presence of calcite, portlandite and minor peaks of muscovite/illite in recycled aggregates, although they were directly proportioned to their original composition. The influence of 30%, 50%, and 100% coarse RCA on the chemical composition of equal design strength concrete has been established, and its suitability for use in a concrete application has been assessed. In this work, coarse RCA was used as a direct replacement for natural gravel in concrete production. Test results indicated that up to 30% coarse RCA had no effect on the main three oxides (SiO2, Al2O3 and CaO) of concrete, but thereafter there was a marginal decrease in SiO2 and increase in Al2O3 and CaO contents with increase in RCA content in the mix, reflecting the original constituent's composition.  相似文献   
833.
In order to reduce the environmental impact due to land disposal of oil fly ash from power plants and to valorize this waste material, the removal of vanadium was investigated using leaching processes (acidic and alkaline treatments), followed by a second step of metal recovery from leachates involving either solvent extraction or selective precipitation. Despite a lower leaching efficiency (compared to sulfuric acid), sodium hydroxide was selected for vanadium leaching since it is more selective for vanadium (versus other transition metals). Precipitation was preferred to solvent extraction for the second step in the treatment since: (a) it is more selective; enabling complete recovery of vanadate from the leachate in the form of pure ammonium vanadate; and (b) stripping of the loaded organic phase (in the solvent extraction process) was not efficient. Precipitation was performed in a two-step procedure: (a) aluminum was first precipitated at pH 8; (b) then ammonium chloride was added at pH 5 to bring about vanadium precipitation.  相似文献   
834.
This work presents an analysis on the suitability of mechanical biological treatment of municipal solid waste in South America, based on two previous experimental investigations carried out in two different countries. The first experiment was performed for determining the mass and volume reduction of MSW in the province of Concepción (Chile). The implemented bench-scale process consisted of a manual classification and separation stage, followed by an in-vessel biological degradation process. The second experiment consisted of a full-scale experiment performed in the city of Estrela (Brazil), where the existing municipal waste management facility was adapted to enhance the materials sorting and separation. Expressed in wet weight composition, 85.5% of the material input in the first experiment was separated for biological degradation. After 27 days of processing, 60% of the initial mass was reduced through degradation and water evaporation. The final fraction destined for landfilling equals 59% of the total input mass, corresponding to about 50% of the initial volume. In the second experiment, the fraction destined to landfill reaches 46.6% of the total input waste mass, whilst also significantly reducing the total volume to be disposed. These results, and the possible recovery of material streams suitable for recycling or for preparing solid recovered fuels, are the main advantages of the studied process.  相似文献   
835.
Hospital waste management and toxicity evaluation: a case study   总被引:1,自引:0,他引:1  
Hospital waste management is an imperative environmental and public safety issue, due to the waste's infectious and hazardous character. This paper examines the existing waste strategy of a typical hospital in Greece with a bed capacity of 400-600. The segregation, collection, packaging, storage, transportation and disposal of waste were monitored and the observed problematic areas documented. The concentrations of BOD, COD and heavy metals were measured in the wastewater the hospital generated. The wastewater's toxicity was also investigated. During the study, omissions and negligence were observed at every stage of the waste management system, particularly with regard to the treatment of infectious waste. Inappropriate collection and transportation procedures for infectious waste, which jeopardized the safety of staff and patients, were recorded. However, inappropriate segregation practices were the dominant problem, which led to increased quantities of generated infectious waste and hence higher costs for their disposal. Infectious waste production was estimated using two different methods: one by weighing the incinerated waste (880 kg day(-1)) and the other by estimating the number of waste bags produced each day (650 kg day(-1)). Furthermore, measurements of the EC(50) parameter in wastewater samples revealed an increased toxicity in all samples. In addition, hazardous organic compounds were detected in wastewater samples using a gas chromatograph/mass spectrograph. Proposals recommending the application of a comprehensive hospital waste management system are presented that will ensure that any potential risks hospital wastes pose to public health and to the environment are minimized.  相似文献   
836.
This paper describes the feasibility of an aerobic system (rotating biological contactor, RBC) and a biological anaerobic system (upward-flow anaerobic sludge bed reactor) at small scale for the treatment of a landfill leachate. In the first phase of the aerobic system study, a cyclic-batch RBC system was used to select perforated acetate discs among three different acetate disc configurations. These discs were chosen on the basis of high COD removal (65%) and biological stability. In the second phase, the RBC system (using four stages) was operated continuously at different hydraulic retention times (HRT), at different rotational speeds, and with varying organic concentrations of the influent leachate (2500-9000mgL(-1)). Forty percent of the total surface area of each perforated disc was submerged in the leachate. A COD removal of about 52% was obtained at an HRT of 24h and a rotational speed of 6rpm. For the anaerobic system, the reactor was evaluated with a volumetric organic load of 3273g-COD m(-3) day(-1) at an HRT of 54, 44, 39, 24 and 17h. At these conditions, the system reached COD removal efficiencies of 62%, 61%, 59%, 44% and 24%, respectively.  相似文献   
837.
New composite materials based on an alkali-resistant glass-fibre reinforced cement (AR-GRC) system are being developed by using fly ash (FA) produced at coal thermoelectric power plants, and fluid catalytic cracking catalyst residue (FC3R) from the petrol industry as cement replacement materials. These wastes are reactive from the pozzolanic viewpoint, and modify the nature and the microstructure of the cement matrix when a part of the Portland cement is replaced in the formulation of GRC. Several microstructural and mechanical aspects are being studied for AR-GRC systems. The behaviour of composites exposed to ageing shows that the pozzolanic activity of the ground FA added in high amounts and its mixture with the FC3R increase the flexural strength and no evidences of strength decay are observed. Additionally, the fibres due to the high alkalinity of the cementing matrix can be deteriorated. Fibres in the control (only Portland cement) and FC3R containing composites were attacked, whereas composites with FA and their mixture with FC3R show that the fibres have not been attacked, due to the pozzolanic activity of replacing materials that reduce the calcium hydroxide content in the cementing matrix.  相似文献   
838.
Sorbitol and glycerol were used to plasticize sugar beet pulp-poly(lactic acid) green composites. The plasticizer was incorporated into sugar beet pulp (SBP) at 0%, 10%, 20%, 30% and 40% w/w at low temperature and shear and then compounded with poly(lactic acid) (PLA) using twin-screw extrusion and injection molding. The SBP:PLA ratio was maintained at 30:70. As expected, tensile strength decreased by 25% and the elongation increased. Acoustic emission (AE) showed correlated debonding and fracture mechanisms for up to 20% w/w plasticizer and uncorrelated debonding and fracture for 30–40% sorbitol and 30% glycerol content in SBP–PLA composites. All samples had a well dispersed SBP phase with some aggregation in the PLA matrix. However, at 40% glycerol plasticized SBP–PLA composites exhibited unique AE behavior and confocal microscopy revealed the plasticized SBP and PLA formed a co-continuous two phase system.
V. L. FinkenstadtEmail:
  相似文献   
839.
The concentrations of 41 phenols in leachates from 38 municipal solid waste (MSW) landfill sites in Japan were measured. The main phenols detected in leachates were phenol, three cresols, 4-tert-butylphenol, 4-tertoctylphenol, 4-nonylphenol, bisphenol A, and some chlorophenols. The concentration levels of phenols were affected by the pH values of the leachates and the different types of landfill waste. The origins of phenol and p-cresol were considered to be incineration residues, and the major origin of 4-tert-butylphenol, bisphenol A, and 2,4,6-trichlorophenol was considered to be solidified fly ash. In contrast, the major origins of 4-tert-octylphenol and 4-nonylphenol were considered to be incombustibles. The discharge of leachates to the environment around MSW landfill sites without water treatment facilities can cause environmental pollution by phenols. In particular, the disposal of incineration residues including solidified fly ash and the codisposal of solidified fly ash and incombustibles might raise the possibility of environmental pollution. Moreover, the discharge of leachates at pH values of 9.8 or more could pollute the water environment with phenol. However, phenol, 4-nonylphenol, and bisphenol A can be removed to below the con centration levels that impact the environment around landfill sites by a series of conventional water treatment processes.  相似文献   
840.
In Europe, the use of direct methods using lysimeters for measuring water and solute flow in soils increased in recent years. Large weighable lysimeters are best suitable for obtaining reliable data about seepage water quantity and quality. Field lysimeters – lysimeters built in directly in agriculturally used areas – of high technical standard allow a precise determination of the influence of different cropping systems on groundwater quality. They combine the advantages of true field conditions and laboratory possibilities of varying parameters, handling and maintenance. Due to the specific needs of each application the instrumentation varies. Based on general remarks on the advantages of precise weighing lysimeters four standardized lysimeter configurations are presented. Beside the specific needs of design and setup of lysimeter stations, there is need to define general requirements to enable comparable results based on standardized basic design and to reduce individual mistakes.  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