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411.
412.
Zeping Gu Jialiang Feng Wenliang Han Li Li Minghong Wu Jiamo Fu Guoying Sheng 《环境科学学报(英文版)》2010,22(3):389-396
Forty-eight daily time interval PM2:5 samples were collected from December 2006 to January 2008 in an urban site in Shanghai,
China. Concentrations and compositions of polycyclic aromatic hydrocarbons (PAHs) were analyzed with GC-MS to study the diurnal
and seasonal variations and to identify the main emitting sources. The diurnal variation of the PAHs concentrations was greater in
the late autumn and winter sampling days, and was greatly influenced by meteorological conditions such as wind speed and ambient
temperature. The concentration of PAHs in the mornings (6:30–10:00) increased distinctly, and was high in the late autumn and winter
sampling days, indicating the contribution from vehicle emissions during rush hours. The diurnal variation of the high molecular weight
PAHs did not seem to be controlled by the shift of gas-particle partitioning due to temperature variation, instead, it could be indicative of
the variation in the source. Statistical analyses showed that the concentrations of PAHs were negatively correlated with temperature and
wind speed, and positively correlated with relative humidity. Diagnostic ratios of PAHs suggested mixed emission sources of petroleum
and coal/biomass combustion for PAHs in the PM2:5 in Shanghai. 相似文献
413.
Taihu Lake, the largest freshwater shallow lake in eastern China, has suffered from severe eutrophication over the past two decades. This research developed a three-dimensional eutrophication model to investigate the eutrophication dynamics. The model fully coupled the biological processes and hydrodynamics, and also took into account the effects of sediment release and the external loads from the tributaries. After sensitivity analyses, the key parameters were defined and then calibrated by the field observation data. The calibrated model was applied to study the seasonal primary productions and its regional differences. The comparisons between model results and field data in year 2000 indicated that the model is able to simulate the eutrophication dynamics in Taihu Lake with a reasonable accuracy. From the simulation experiments, it was found that the meteorological forcing have significant influences on the temporal variations of the eutrophication dynamics. The wind-induced circulation and sediment distribution play an important role in the spatial distribution of the algae blooms. 相似文献
414.
415.
天然沸石吸附氨氮和磷的研究 总被引:9,自引:0,他引:9
选用浙江缙云产颗粒状天然沸石为材料对氨氮和磷进行吸附动力学和吸附等温试验,考察初始浓度、振荡时间对吸附量、去除率的影响。试验结果表明:沸石对氨氮和磷吸附显示出"快速吸附,缓慢平衡"的特点;吸附动力学过程符合准二级动力学模型;吸附等温线更符合Freundlich方程;氨氮初始浓度小于7 mg/L、振荡时间在1h内和磷初始浓度小于30 mg/L、振荡时间在15 min内,吸附量、去除率随初始浓度、振荡时间增加而增加,当超过此阶段后,吸附量增加缓慢、去除率下降。 相似文献
416.
The effects of noise on neuronal dynamical systems are of much current interest. Here, we investigate noise-induced changes
in the rhythmic firing activity of single Hodgkin–Huxley neurons. With additive input current, there is, in the absence of
noise, a critical mean value μ = μ
c above which sustained periodic firing occurs. With initial conditions as resting values, for a range of values of the mean
μ near the critical value, we have found that the firing rate is greatly reduced by noise, even of quite small amplitudes.
Furthermore, the firing rate may undergo a pronounced minimum as the noise increases. This behavior has the opposite character
to stochastic resonance and coherence resonance. We found that these phenomena occurred even when the initial conditions were
chosen randomly or when the noise was switched on at a random time, indicating the robustness of the results. We also examined
the effects of conductance-based noise on Hodgkin–Huxley neurons and obtained similar results, leading to the conclusion that
the phenomena occur across a wide range of neuronal dynamical systems. Further, these phenomena will occur in diverse applications
where a stable limit cycle coexists with a stable focus. 相似文献
417.
In a chemical sense, the positive muon is a light proton. It is obtained at the ports of accelerators in beams with a spin
polarization of 100%, which makes it a highly sensitive probe of matter. The muonium atom is a light hydrogen isotope, nine
times lighter than H, with a muon as its nucleus. It reacts the same way as H, and by addition to double bonds it is implemented
in free radicals in which the muon serves as a fully polarized spin label. It is reviewed here how the muon can be used to
obtain information about muonium and radical reaction rates, radical structure, dynamics, and local environments. It can even
tell us what a fragrance molecule does in a shampoo. 相似文献
418.
梭鱼草净化黑臭河水的日变化试验研究 总被引:4,自引:0,他引:4
测定了曝气和非曝气的2个植物净化槽在1 d中7个不同时间点的出水水质理化指标(pH、DO、COD、NH_4~+-N、TP)及植物叶片的叶绿素(Chla)、可溶性蛋白(SP)含量及过氧化物酶(POD)活性,另设空白槽为对照;试验目的是研究各指标的日变化情况及相互关系,为提高梭鱼草净化黑臭河水的处理效率及其植物净化槽的合理优化运行提供科学依据.结果表明,各水槽内所测指标的变化均在一定程度上与光强变化相关,对非曝气植物槽的分析发现,在出水理化指标中TP浓度与光强的相关性最好(r=0.93,p<0.01),而在植物生理指标中SP含量与光强相关性最好(r=0.91,p<0.01);植物处理使出水的DO日均值增加了0.13 mg/L,而曝气植物处理则使其增加了1.8 mg/L,曝气是对城市黑臭河水进行植物净化修复的必要辅助手段;曝气植物槽对黑臭河水中COD和NH_4~+-N的去除率日均值比植物槽升高了7.1%和6.3%(p<0.01),TP去除率却相应下降了38%(p<0.01);与非曝气槽植物相比,曝气槽植物体内Chla、SP日平均含量显著降低(p<0.05)而POD活性显著升高(p<0.05);光强和曝气的变化能迅速而显著地影响梭鱼草的生理特性从而改善其净化槽出水水质,是构建和优化黑臭河水植物净化槽时值得考虑的重要调控因素. 相似文献
419.
广州森林大气中VOCs昼夜变化特征及对O_3的影响 总被引:1,自引:0,他引:1
挥发性有机物化合物(VOCs)是大气光化学过程的重要前驱物,对大气中的臭氧(O)3有重要影响。文章对广州市花都区王子山森林公园大气中VOCs的昼夜变化特征进行了分析,并且评估了其对大气中O3的相对贡献。共定性和定量了21种VOCs,其中1,2,4-三甲基苯(21.50±32.90)μg/m3、甲基环戊烷(20.40±23.30)μg/m3和异戊二烯(14.90±39.20)μg/m3浓度最高。对于大多数VOCs来说,活性VOCs与相对惰性的VOCs表现出相反的昼夜变化特征,这反映了大气光化学反应对于VOCs的影响。采用Propy-Equiv浓度对大气VOCs对O3的影响评估结果表明,该地区大气VOCs对O3贡献的大小为:烯烃>苯系物>烷烃。 相似文献
420.
为识别高校消防安全管理的影响因素,有效预防高校火灾事故,本文结合实际案例和调研情况,建立高校消防安全管理系统动力学模型,仿真分析不同消防安全投入比例对高校消防安全管理水平的提升效果和影响趋势。结果表明:高校消防安全管理系统中采用平均分配的投入方案并不理想,且侧重单一分支的投入方案不能有效提升高校整体消防安全管理水平;与之相对应的,采取分散却有所侧重的投入策略是高校消防安全管理投入的最佳选择,消防管理及检查、设备维保更新和消防宣传教育是高校消防安全管理的重点需求与亟需方向;构建的高校消防安全管理系统动力学模型符合实际,能够识别高校消防安全管理中各要素间的相互作用和影响机制,并能有效预测高校消防安全管理水平的变化趋势。 相似文献