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881.
本文以北京市城市绿地系统为研究对象,对其发展现状及其生态和社会功能进行了分析,并就目前城市绿地发展中存在的一些问题进行了探讨,最后提出了一些相应的发展对策。  相似文献   
882.
珠江澳门河口沉积物柱样中有机氯农药的垂直分布特征   总被引:34,自引:6,他引:28  
以GC/ECD内标法定量测定了沉积物柱样品中有机氯农药含量 ,以便探讨柱样中有机氯农药的垂直变化特征及可能的来源 .样品采自珠江澳门河口 ,柱样以2 10 Pb同位素法定年 .定量测定结果表明以BHCs、DDTs总量计算时 ,样品中含量分别为 0 4 8~ 2 6 2 8ng/ g、1 92~ 39 1 3ng/ g .柱样中农药含量随深度变化和珠江口区的水域水流量随年份的变化有着很好的对应性 .有机氯农药主要是来源于施用农药长期风化后的土壤 .样品中DDTs的浓度超过了河口沉积物化学品风险评价最低值标准 .  相似文献   
883.
The quality of cultivated consumed vegetables in relation to environmental pollution is a crucial issue for urban and peri-urban areas, which host the majority of people at the global scale. In order to evaluate the fate of metals in urban soil–plant–atmosphere systems and their consequences on human exposure, a field study was conducted at two different sites near a waste incinerator (site A) and a highway (site B). Metal concentrations were measured in the soil, settled atmospheric particulate matter (PM) and vegetables. A risk assessment was performed using both total and bioaccessible metal concentrations in vegetables. Total metal concentrations in PM were (mg kg?1): (site A) 417 Cr, 354 Cu, 931 Zn, 6.3 Cd and 168 Pb; (site B) 145 Cr, 444 Cu, 3289 Zn, 2.9 Cd and 396 Pb. Several total soil Cd and Pb concentrations exceeded China’s Environmental Quality Standards. At both sites, there was significant metal enrichment from the atmosphere to the leafy vegetables (correlation between Pb concentrations in PM and leaves: r = 0.52, p < 0.05) which depended on the plant species. Total Cr, Cd and Pb concentrations in vegetables were therefore above or just under the maximum limit levels for foodstuffs according to Chinese and European Commission regulations. High metal bioaccessibility in the vegetables (60–79 %, with maximum value for Cd) was also observed. The bioaccessible hazard index was only above 1 for site B, due to moderate Pb and Cd pollution from the highway. In contrast, site A was considered as relatively safe for urban agriculture.  相似文献   
884.
Phenol removal by n/m Fe in the presence of H2O2 was highly effective. Increasing the amounts of n/m Fe and H2O2?increased the phenol removal rate. Phenol removal was decreased with an increase in the concentration of phenol. The natural pH (6.9) of the solution was highly effective for phenol removal. The pseudo-first-order kinetics was best fitted for the degradation of phenol. The study investigates the magnetic separation of Fe from automobile shredder residue (ASR) (<0.25 mm) and its application for phenol degradation in water. The magnetically separated Fe was subjected to an ultrasonically assisted acid treatment, and the degradation of phenol in an aqueous solution using nano/micro-size Fe (n/m Fe) was investigated in an effort to evaluate the possibility of utilizing n/m Fe to remove phenol from wastewater. The prepared n/m Fe was analyzed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The effects of the dosages of n/mFe, pH, concentration of phenol and amount of H2O2 on phenol removal were evaluated. The results confirm that the phenol degradation rate was improved with an increase in the dosages of n/mFe and H2O2; however, the rate is reduced when the phenol concentration is higher. The degradation of phenol by n/mFe followed the pseudo-first-order kinetics. The value of the reaction rate constant (k) was increased as the amounts of n/m Fe and H2O2 increased. Conversely, the value of k was reduced when the concentration of phenol was increased. The probable mechanism behind the degradation of phenol by n/m Fe is the oxidation of phenol through hydroxyl radicals which are produced during the reaction between H2O2 and n/m Fe.  相似文献   
885.
Water-dissolved oxygen was supplied into anaerobic aquifer , which oxidized Fe(II), Mn(II) and trivalent arsenic and changed them into undissolved solid matter through hydrolysis, precipitation, co-precipitation and adsorption processes. The experiment was carried out on the column imitated a bore core of anaerobic aquifer with water phase containing Fe(II), Mn(II), As(III) concentration of 45.12 mg/L, 14.52 mg/L, 219.4 μg/L, respectively and other ions similarly composition in groundwater. After 6 days of air supply, concentration of iron reduced to 0.38 mg/L, manganese to 0.4 mg/L, arsenic to 9.8 μg/L (equivalent 99.16% of iron, 97.25% of manganese and 95.53% of arsenic fixed), and for other ions, the concentration changed almost according to general principles. Ion phosphate and silicate strongly influenced on arsenic removal but supported iron and manganese precipitation from water phase. Based on the experimental results, new model of groundwater exploitation was proposed.  相似文献   
886.
北方旱农区玉米自然降水生产潜力研究   总被引:12,自引:2,他引:10  
针对我国北方水资源匮乏日益严重的状况,利用CERES-Maize作物模型模拟分析了北方旱区玉米自然降水生产潜力及其时空分布规律。研究表明,我国北方旱区玉米的水分生产潜力大小排序依次是半湿润区>半干旱区>干旱区,半湿润区的玉米自然降水生产潜力大约为11000kg/hm2,干旱区大约在5000kg/hm2,但同时半湿润区潜力的年际间波动性也最显著,干旱区则相对较为稳定。我国北方旱区东部的玉米生产潜力高于西部,但南北方向潜力差异不明显。  相似文献   
887.
Impact of consistent boundary layer mixing approaches between NAM and CMAQ   总被引:1,自引:0,他引:1  
Discrepancies in grid structure, dynamics and physics packages in the offline coupled NWS/NCEP NAM meteorological model with the U.S. Environmental Protection Agency Community Multiscale Air Quality (CMAQ) model can give rise to inconsistencies. This study investigates the use of three vertical mixing schemes to drive chemistry tracers in the National Air Quality Forecast Capability (NAQFC). The three schemes evaluated in this study represent various degrees of coupling to improve the commonality in turbulence parameterization between the meteorological and chemistry models. The methods tested include: (1) using NAM predicted TKE-based planetary boundary height, h, as the prime parameter to derive CMAQ vertical diffusivity; (2) using the NAM mixed layer depth to determine h and then proceeding as in (1); and (3) using NAM predicted vertical diffusivity directly to parameterize turbulence mixing within CMAQ. A two week period with elevated surface O3 concentrations during the summer 2006 has been selected to test these schemes in a sensitivity study. The study results are verified and evaluated using the EPA AIRNow monitoring network and other ozonesonde data. The third method is preferred a priori as it represents the tightest coupling option studied in this work for turbulent mixing processes between the meteorological and air quality models. It was found to accurately reproduce the upper bounds of turbulent mixing and provide the best agreement between predicted h and ozonesonde observed relative humidity profile inferred h for sites investigated in this study. However, this did not translate into the best agreement in surface O3 concentrations. Overall verification results during the test period of two weeks in August 2006, did not show superiority of this method over the other 2 methods in all regions of the continental U.S. Further efforts in model improvement for the parameterizations of turbulent mixing and other surface O3 forecast related processes are warranted.  相似文献   
888.
A sensitivity study is performed to examine the impact of lateral boundary conditions (LBCs) on the NOAA-EPA operational Air Quality Forecast Guidance over continental USA. We examined six LBCS: the fixed profile LBC, three global LBCs, and two ozonesonde LBCs for summer 2006. The simulated results from these six runs are compared to IONS ozonesonde and surface ozone measurements from August 1 to 5, 2006. The choice of LBCs can affect the ozone prediction throughout the domain, and mainly influence the predictions in upper altitude or near inflow boundaries, such as the US west coast and the northern border. Statistical results shows that the use of global model predictions for LBCs could improve the correlation coefficients of surface ozone prediction over the US west coast, but could also increase the ozone mean bias in most regions of the domain depending on global models. In this study, the use of the MOZART (Model for Ozone And Related chemical Tracers) prediction for CMAQ (Community Multiscale Air Quality) LBC shows a better surface ozone prediction than that with fixed LBC, especially over the US west coast. The LBCs derived from ozonesonde measurements yielded better O3 correlations in the upper troposphere.  相似文献   
889.
Kang N  Hua I  Rao PS 《Chemosphere》2006,63(10):1685-1698
The Fenton's system is applied to the destruction of perchloroethylene (PCE) present as a dense non-aqueous phase liquid (DNAPL) in soil slurry systems; the initial concentration of PCE was 45 times higher than its aqueous solubility. Studies were conducted in two matrices: Ottawa sand and soil from Warsaw, IN. In Ottawa sand, a 60-62% decrease in PCE concentration was observed, and Cl(-) recovery was 47-58%, whereas in Warsaw soil, a 44-49% decrease in PCE concentration and a Cl(-) recovery of 40-42% were observed after the addition of 600 mM H(2)O(2) and 10 mM dissolved iron. Significantly enhanced destruction resulted during application of N-(2-hydroxyethyl) iminodiacetic acid (HEIDA) to Warsaw soil. For example, in the absence of HEIDA in Warsaw soil, 36% PCE loss and 33% Cl(-) release were observed at 600 mM H(2)O(2) and 5 mM Fe(III), while 74% PCE loss and 63% Cl(-) release were achieved at 600 mM H(2)O(2) and 5 mM Fe(III)-HEIDA. For both soils, the catalytic activities of Fe(II) and Fe(III) were nearly equivalent. These findings clearly demonstrate that system design can be optimized with regard to process variables in Fenton's treatment of DNAPL in soils.  相似文献   
890.
在实验室条件下,研究了Shewanella oneidensis MR-1对磺胺甲噁唑(Sulfamethoxazole,SMX)的降解特性以及低分子有机酸强化Fe(Ⅲ)还原介导的S.oneidensis MR-1对SMX的降解.结果表明,S.oneidensis MR-1对不同浓度SMX的降解能力与体系中的有机酸和Fe(Ⅲ)密切相关.低浓度SMX对其生长影响不大,高浓度时细菌生长则受到抑制,进而抑制SMX的降解率.当低分子有机酸单独加入体系后,S.oneidensis MR-1对SMX的最大降解率为58.5%;Fe(Ⅲ)单独加入体系后,S.oneidensis MR-1对SMX的最大降解率为67.6%.此外,当柠檬酸和Fe(OH)3同时加入体系后,S.oneidensis MR-1对SMX生物降解和铁还原作用促进效果最显著,培养5 d后SMX降解率为90.3%.最后,采用液相色谱-质谱联用仪(LC-MS)对SMX的降解中间产物进行了分析,推测SMX的可能降解途径是由S-N键断裂引起的.本研究以期为地下水污染场地修复提供理论依据.  相似文献   
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