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1.
多环芳烃(PAHs)与纳米材料污染已对沉积物生态系统和人类生存环境构成严重威胁,其复合污染的毒性效应环境危害可能更大。为了深入探讨PAHs与纳米材料对近岸表层沉积物反硝化作用的复合毒性效应,本文选取位于胶州湾(JZB)的大沽河河口区(DRE)E站和湾内S站,分别以菲和纳米银代表PAHs和纳米材料,通过测定不同剂量单一及复合污染下沉积物反硝化潜势(PDA)的变化,结合浓度相加模型(CA)、独立作用模型(IA)和中效/联合指数等效图法(CI)三种复合毒性评价方法,评价菲和纳米银对沉积物反硝化潜势的复合毒性效应,并对评价方法进行了优选。结果表明,两种污染物浓度越高,对研究区域反硝化潜势的抑制作用越大。菲、纳米银单一及复合作用下对河口区沉积物反硝化潜势的EC50值分别为44.62、112.49和64.86 mg·kg-1,对湾内分别为61.79、147.05和96.18 mg·kg-1。菲单一作用对反硝化潜势的抑制效应强于纳米银,但复合污染的抑制效应更强。两种污染物对河口区的沉积物反硝化潜势抑制效应强于湾内,可能与河口区具有较高Eh和沉积物颗粒度及较低的pH、盐度和有机质含量有关。三种毒性效应评价方法的结果表明,菲和纳米银的复合污染对2个站位反硝化潜势的毒性效应均为协同作用,且对大沽河河口区的协同作用更强。此外,CI法对复合效应的预测结果比CA和IA法更为接近实际观测值,且CI不需要考虑污染物作用模式的限制,因此认为CI法更适用于评价混合污染对沉积物反硝化作用复合影响的效果。本研究结果表明,菲和纳米银会增强彼此对反硝化菌及反硝化功能的毒性效应,由此推断,PAHs和纳米材料在环境中同时存在时比其单独存在对沉积环境的危害更大。  相似文献   
2.
Indirect nitrous oxide (N2O) emissions produced by nitrogen (N) leaching into surface water and groundwater bodies are poorly understood in comparison to direct N2O emissions from soils. In this study, dissolved N2O concentrations were measured weekly in both lowland headwater streams and subsurface agricultural field drain discharges over a 2‐year period (2013–2015) in an intensive arable catchment, Norfolk, UK. All field drain and stream water samples were found to have dissolved N2O concentrations higher than the water–air equilibrium concentration, illustrating that all sites were acting as a net source of N2O emissions to the atmosphere. Soil texture was found to significantly influence field drain N2O dynamics, with mean concentrations from drains in clay loam soils (5.3 μg N L?1) being greater than drains in sandy loam soils (4.0 μg N L?1). Soil texture also impacted upon the relationships between field drain N2O concentrations and other water quality parameters (pH, flow rate, and nitrate (NO3) and nitrite (NO2) concentrations), highlighting possible differences in N2O production mechanisms in different soil types. Catchment antecedent moisture conditions influenced the storm event mobilisation of N2O in both field drains and streams, with the greatest concentration increases recorded during precipitation events preceded by prolonged wet conditions. N2O concentrations also varied seasonally, with the lowest mean concentrations typically occurring during the summer months (JJA). Nitrogen fertiliser application rates and different soil inversion regimes were found to have no effect on dissolved N2O concentrations, whereas higher N2O concentrations recorded in field drains under a winter cover crop compared to fallow fields revealed cover crops are an ineffective greenhouse gas emission mitigation strategy. Overall, this study highlights the complex interactions governing the dynamics of dissolved N2O concentrations in field drains and headwater streams in a lowland intensive agricultural catchment.  相似文献   
3.
纳米铁还原脱氮动力学及其影响因素   总被引:3,自引:1,他引:2  
饮用水中硝酸盐(NO3-)对人体健康有危害。为了去除水溶液中NO3-,在实验室制得纳米铁颗粒。它的粒径为20~40 nm,比表面积(BET)为49.16 m2/g。本研究通过批实验考察了纳米铁对NO3-还原脱氮动力学性质和影响NO3-脱氮快慢的主要因素,如反应pH、纳米铁投加量和NO3-起始浓度。实验结果表明,pH越低越有利于NO 3-还原。在一定范围内,NO 3-还原速率随纳米铁投加量增加而增大,而随NO 3-起始浓度升高而降低,反应遵循准一级反应动力学方程,表面吸附和氧化还原反应是纳米铁对NO3-脱氮的主要去除机理。纳米铁对NO3-还原过程中可能反应的途径进行了讨论,NO3-还原产物取决于反应条件。在本研究条件下,纳米铁对NO3-脱氮的最终产物主要为NH4+-N而不是N2,必须进行更多的研究来解决这一问题。  相似文献   
4.
氧化亚氮(N2O)是大气中重要和微量的温室气体,且在平流层N2O形成NO自由基与O3发生反应破坏臭氧层.海洋是大气中N2O净源,但由于海洋中生物化学过程的复杂性,有关N2O形成机制至今是人们研究的重点和难点.应用稳定同位素分馏原理对海洋中N2O形成机制的研究,区分海洋中通过硝化和反硝化过程不同途径产生的N2O过程,为深入研究海洋中N2O循环、估算将来大气中N2O浓度变化提供有用工具.  相似文献   
5.
曝气对人工湿地氮去除效果的影响   总被引:5,自引:0,他引:5  
选择不同的植物组合,分别在6组复合垂直流人工湿地的下行池、上行池种植金边石菖蒲(Acorus gramineus)、宽叶泽苔(Caldesia renif ormis);慈姑(Sagittaria sagittif olia)、水葱(Scirpus validus);灯芯草(Juncus effuses)、梭鱼草(Po...  相似文献   
6.
Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L−1), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L−1, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m−2 d−1 in the hypoxic western LSLE to 100 μmol m−2 d−1 in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m−2 d−1, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 106 t N, yielding an almost balanced N budget for the SL marine system.  相似文献   
7.
Groundwater that bypasses the riparian zone by travelling along deep flow paths may deliver high concentrations of fertilizer‐derived NO3? to streams, or it may be impacted by the NO3? removal process of denitrification in streambed sediments. In a study of a small agricultural catchment on the Atlantic coastal plain of Virginia's eastern shore, we used seepage meters deployed in the streambed to measure specific discharge of groundwater and its solute concentrations for various locations and dates. We used values of Cl? concentration to discriminate between bypass water recharged distal to the stream and that contained high NO3? but low Cl? concentrations and riparian‐influenced water recharged proximal to the stream that contained low NO3? and high Cl? concentrations. The travel time required for bypass water to transit the 30‐cm‐thick, microbially active denitrifying zone in the streambed determined the extent of NO3? removal, and hydraulic conductivity determined travel time through the streambed sediments. At all travel times greater than 2 days, NO3? removal was virtually complete. Comparison of the timescales for reaction and transport through the streambed sediments in this system confirmed that the predominant control on nitrate flux was travel time rather than denitrification rate coefficients. We conclude that extensive denitrification can occur in groundwater that bypasses the riparian zone, but a residence time in biologically active streambed sediments sufficient to remove a large fraction of the NO3? is only achieved in relatively low‐conductivity porous media. Instead of viewing them as separate, the streambed and riparian zone should be considered an integrated NO3? removal unit. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
8.
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3 pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification on the change in the δ15N in the water column. The δ15N of NO3 in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion from NH4 + to NO3 . The significantly 15N-depleted NO3 in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3 from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small.  相似文献   
9.
Samples of sediments and the overlying water were collected in the Qi'ao Island coastal zone, the Zhujiang (Pearl River) Estuary (ZE). Denitrification rates, sediment oxygen demand (SOD) , and fluxes of inorganic nitrogen compounds were investigated with N2 flux method, using a self-designed continuous flow through and auto-sampling system. The results indicate that the denitrification rates varied between 222 and 908 μmol/(m2·h) with an average of 499 μmol/(m2·h). During incubation, the sediments absorbed dissolved oxygen in the overlying water with SOD ranging from 300 to 2 363 μmol/(m2·h). The denitrification rates were highly correlated with the SOD (r2 =0.77) regardless of the NO3- + NO2- concentrations in the overlying water, organ- ic carbon contents in sediments and water temperature, suggesting that the SOD was probably the main environ-mental factor controlling the denitrification in the Qi'ao Island coastal zone. There was a net flux of NO3- + NO2-into the sediments from the overlying water. The NH4+ flux from sediments into water as the result of mineraliza-tion was between 12. 3 and 210. 3 μmol/(m2·h) ,which seems limited by both organic carbon content in sedi-ment and dissolved oxygen concentration in the overlying water.  相似文献   
10.
An integrated mass balance and modelling approach for analysis of estuarine nutrient fluxes is demonstrated in the Swan River Estuary, a microtidal system with strong hydrological dependence on seasonal river inflows. Mass balance components included estimation of gauged and ungauged inputs to the estuary and losses to the ocean (outflow and tidal exchange). Modelling components included estimation of atmospheric (N fixation, denitrification) and sediment–water column nutrient exchanges. Gross and net denitrification derived using two independent methods were significantly correlated (r2 = 0.49, p < 0.01) with net rates averaging 40% of gross. Annual nitrogen (N) and phosphorus (P) loads from major tributaries were linearly correlated with annual freshwater discharge and were 3-fold higher in wet years than in dry years. Urban drains and groundwater contributed, on average, 26% of N inputs and 19% of P inputs, with higher relative contributions in years of low river discharge. Overall, ungauged inputs accounted for almost 35% of total nitrogen loads. For N, elevated loading in wet years was accompanied by large increases in outflow (7x) and tidal flushing (2x) losses and resulted in overall lower retention efficiency (31%) relative to dry years (70%). For P, tidal flushing losses were similar in wet and dry years, while outflow losses (4-fold higher) were comparable in magnitude to increases in loading. As a result, P retention within the estuary was not substantially affected by inter-annual variation in water and P loading (ca. 50% in all years). Sediment nutrient stores increased in most years (remineralisation efficiency ca. 50%), but sediment nutrient releases were significant and in some circumstances were a net source of nutrients to the water column.  相似文献   
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