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221.
As well known, risk is a combination of probability and consequences of an accident. In analyzing the consequence of accidental hydrocarbon fires and the potential for domino effects, the evaluation of the flame extent and temperature are of the utmost importance. Since the primary effects of pool fires are connected to thermal radiation and issues of interplant/tank spacing employees’ safety zones, firewall specifications are to be addressed on the basis of a proper consequence analysis. By means of real scale experimental tests it was verified that both the thermal power and the flame temperature, Tf, increase as the pool area increases, up to reach maximum values in connection with a “critical pool dimension”. Dealing with pool areas higher than the critical one, experimental results, performed by different researchers at different scales, show a decrease of Tf. An in-depth analysis of the different concurring phenomena connected to a pool fire development allowed identifying the limiting step controlling the flame temperature. In fact, the trend of Tf is mainly determined by the increasing difficulty of oxygen diffusion within the internal bulk of gaseous hydrocarbons. In this article, we propose a novel pool fire modelling approach based on the simplified physical phenomena occurring in a circular turbulent diffusion fire and suitable to provide a theoretical insight into the above-mentioned experimental trends and to obtain the maximum values of the flame temperature and of the thermal power.The geometry of the pool is dictated by the surroundings (i.e., diking) and the analytical models here presented were successfully applied to the common situation of circular pools.However, it must be remarked that the developed model, matching fairly well experimental data for different hydrocarbons, can be applied in modelling similar scenarios characterized by different geometric or environmental conditions (e.g. road and rail tunnel fires). 相似文献
222.
为表征建筑物火灾环境下人员疏散预动作时间随机性,提出累积分布函数表征法,并给出根据已知累积分布曲线产生随机预动作时间的方法和步骤。对1993年发生在美国纽约2幢世贸中心双子大楼(WT1和WT2)的火灾案例进行分析。结果表明,前人提出的正态分布、威布尔分布等概率分布表征人员疏散预动作时间,具有一定的局限性,对WT1的数据比较适用,对于WT2数据完全失效。而应用累积分布函数法分别对WT1和WT2的数据进行表征,结果表明,模拟生成随机预动作时间的累积分布与原始数据的累积分布曲线完全吻合。同时,随机预动作时间的均值和标准差几乎与样本大小无关。 相似文献
223.
光纤光栅感温火灾报警系统在石油化工行业储罐区等易燃易爆场所得到应用,但目前尚没有相关的国家级设计规范,且安徽省和湖北省地方设计规范关于感温探测器敷设间距的要求存在较大差异,有必要开展深入研究。以外浮顶原油罐为例进行研究,获得了差温和定温两种探测方式在两种敷设高度下,其敷设间距与罐径之间的关系表达式,二者呈正相关。研究结果表明,初起阶段火源功率与罐径呈线性关系且火源功率较小,按照地方规范设置敷设间距时,难以对其进行及时探测,应加大敷设密度;差温探测比定温探测方式具有更为快速探测报警优势且可以设置较大的敷设间距。 相似文献
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利用FDS(Fire Dynamics Simulator)分别对自然排烟和机械排烟作用下的中庭火灾烟气控制效果进行了数值模拟研究,自然排烟口的面积分别为中庭地面面积的5.6%、11.3%和22.5%,机械排烟量分别为43182m3/h和102000m3/h,同时改变机械排烟口的位置。通过对比各工况下的竖向温度分布、中庭内温度场、烟气层界面高度来判断不同工况下的排烟效果,并计算得到了相应排烟效率来判断各排烟模式下的排烟有效性。结果显示,中庭内的温度和排烟效率都随排烟量的增大而减小,自然排烟的排烟效率最低,仅为17.9%~21.3%,机械排烟量43182m3/h时的排烟效率最高,可达45%左右。 相似文献
227.
处理城市污水的好氧颗粒污泥培养及形成过程 总被引:2,自引:0,他引:2
在中试序列间歇式活性污泥法(SBR)反应器中采用有机物浓度低的城市污水培养好氧颗粒污泥. 运行过程中考察了污泥性能,并通过调整、优化沉淀时间和排水比等运行参数,培养出了高性能且稳定的好氧颗粒污泥. 活性污泥接种40 d后反应器内开始出现细小颗粒,160 d后颗粒污泥趋于成熟,粒径可达0.8 mm,且其周围有大量的原生动物. 颗粒化过程中,污泥密度、沉降速率和ρ(MLSS)分别从初期的1.004 0 g/cm3,6.8 m/h和4 000 mg/L升至1.010 5 g/cm3,38.5 m/h和8 000 mg/L,污泥容积指数(SVI30)则从75 mL/g降至40 mL/g. 形成后的颗粒污泥对城市污水中CODCr和NH4+-N有很好的去除效果,出水中ρ(CODCr)和ρ(NH4+-N)分别在50和5 mg/L以下. 相似文献
228.
Temporal scaling behavior of human-caused fires and their connection to relative humidity of the atmosphere 总被引:1,自引:0,他引:1
It has been found that many natural systems are characterized by scaling behavior. In such systems natural factors dominate the event dynamics. But in countries with high population density such as China and Japan, more than 95% of the forest fire disasters are caused by human activities. Furthermore, with the development of society, the wildland-urban interface (WUI) area is becoming more and more populated, and the forest fire is much connected with urban fire. Therefore exploring the scaling behavior of fires dominated by human-related factors is very challenging. The present paper explores the temporal scaling behavior of forest fires and urban fires in Japan. Our findings point out that although the human factors are the main cause, both the forest fires and urban fires exhibit time-scaling behavior. Similar distribution law characterizes the relative humidity. 相似文献
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《Atmospheric environment (Oxford, England : 1994)》1999,33(27):4413-4419
Conductometry was used to study the kinetics of the oxidation of hydrogen sulfite, HSO−3, by hydrogen peroxide in aqueous non-buffered solution at the low concentration level of 10−5–10−6 M, typically found in cloud water. The kinetic data confirm that the rate law reported for the pH range 3–6 at higher concentration levels, rate=kH·[H+]·[HSO−3]·[H2O2], is valid at the low concentration level and at low ionic strength Ic. At 298 K and Ic=1.5×10−4 M, third-order rate constant kH was found to be kH=(9.1±0.5)×107 M−2 s−1. The temperature dependence of kH led to an activation energy of Ea=29.7±0.9 kJ mol−1. The effect of the ionic strength (adjusted with NaCl) on rate constant kH was studied in the range Ic=2×10−4–5.0 M at pH=4.5–5.2 by conductometry and stopped-flow spectrophotometry. The dependence of kH on Ic can be described with a semi-empirical relationship, which is useful for the purpose of comparison and extrapolation. The kinetic data obtained are critically compared with those reported earlier. 相似文献