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81.
García R Rubio V Vegas I Frías M 《Environmental science and pollution research international》2009,16(3):274-277
Background, aim and scope One of the problems to affect Portland cement matrices is low resistance to aggressive agents, due principally to the presence
of a high content of portlandite in the hydrated cements. Pozzolanic materials have played an important role in the improving
the durability of cement-based materials for decades. This work studies the behaviour of cement mortar matrices blended with
10% calcined paper sludge (source for metakaolinite) and exposed to different environmental conditions (saline and non-saline
environments) after 6 and 12 months of exposure.
Materials and methods Two cements were studied: an ordinary Portland cement (CEM 1, 42.5R), acting as reference cement, and a blended cement formulated
by mixing 90% (by mass) of CEM 1, 42.5R with 10% (by mass) of paper sludge calcined at 700°C for 2 h. The specimens were exposed
1 year to saline and non-saline environments. All the mineralogy samples were studied through X-ray diffraction and scanning
electron microscopy (SEM) equipped with an energy dispersive X-ray analyser. The in-depth study on ionic mobility was performed
on samples subjected to natural exposure (coast and tableland) for 6 and 12 months.
Results Portland cement was composed of quartz, calcite, calcium hydroxide and tobermorite gels. The pozzolanic cement (10% calcined
paper sludge) is of the same composition but a high calcite concentration and barium carbonate. SEM analysis from coastline
show deposits of variable composition. The deposits are identified on the surface of different mineral components. The minerals
from tableland are much fractured, i.e. calcite and feldspars. Inside the fractures, the deposits and the ions are located
and trapped superficially.
Discussion SEM analysis of control cement Portland and 10% calcined paper sludge shows deposits on quartz and calcite with a very high
concentration of Pb, Zn, Cl and barium sulphate. A very porous aspect is due to the presence of the different aggregate types.
This porous configuration permits retention of the ion environment. The pozzolanic cement in environments subject to the saline
mist favours the retention and transport of ions observed. Something similar also happens with the increase in exposure to
outdoor weather. Non-saline samples show temperature changes (ice or thaw cycles). Barium retention is kept on the surface
in fracture lines by the gelification processes. In general, it may be inferred that an increase in exposure time increases
the diffusion of ions towards test piece interiors. The chemical composition profiles show that the ions present different
penetration speeds.
Conclusions The results indicate the better vulnerability of pozzolanic cements from calcined paper sludge in saline and non-saline environments.
The cements with a 10% addition of calcined paper sludge favour retention and transport of ion has been observed.
Recommendations and perspectives Today, projects are centred on a new recycling line for industrial waste of this kind, with special attention on its incorporation
in cement manufacture as a pozzolanic material, setting the most appropriate activation conditions of the mineralogical compound
in this waste (kaolinite and metakaolinite) and taking them as a starting point for this project. The use of pozzolanic cement
with 10% addition of calcined paper sludge is a system which favours ionic retention. 相似文献
82.
随着重庆市经济快速的发展,土地与生态环境的矛盾也越加尖锐。利用层次分析法,选择PSR(压力、状态、响应)指标模型对重庆市“一小时经济圈”2000和2006年的生态环境质量进行定量评价。结果发现:2000和2006年,整体上渝西地区的潼南、铜梁、大足、壁山、永川以及荣昌等区县生态环境都处于一个较差的水平,而涪陵均处于较高的水平。两年间研究区域生态质量均以优、良为主,所占面积比例分别为6096%和6256%;从2000年到2006年,研究区生态环境质量整体呈一个明显下降的趋势,显著变差的面积比例达到3171%,而显著变好的区域面积比例仅有524%;研究区生态环境下降区域面积比例达到5972%,而生态环境上升区域面积则仅有2702%,生态环境质量变化区域具有明显的空间差异性,显著变差区域基本分布于渝西南地区,即成渝交通干线辐射区域及主城大部分地区. 相似文献
83.
The psychological benefits of indoor plants: A critical review of the experimental literature 总被引:1,自引:0,他引:1
People have been bringing plants into residential and other indoor settings for centuries, but little is known about their psychological effects. In the present article, we critically review the experimental literature on the psychological benefits of indoor plants. We focus on benefits gained through passive interactions with indoor plants rather than on the effects of guided interactions with plants in horticultural therapy or the indirect effect of indoor plants as air purifiers or humidifiers. The reviewed experiments addressed a variety of outcomes, including emotional states, pain perception, creativity, task-performance, and indices of autonomic arousal. Some findings recur, such as enhanced pain management with plants present, but in general the results appear to be quite mixed. Sources of this heterogeneity include diversity in experimental manipulations, settings, samples, exposure durations, and measures. After addressing some overarching theoretical issues, we close with recommendations for further research with regard to experimental design, measurement, analysis, and reporting. 相似文献
84.
ICNIRP于2020年3月出版了2020年版《限制电磁场暴露的导则(100 kHz~300 GHz)》,为了准确掌握2020版导则在基本限值和导出限值方面与旧版导则的差异,通过对比新旧导则对应条款得到具体变化情况。2020版导则修订了全身暴露基本限值与导出限值、局部暴露基本限值、神经刺激基本限值、肢体感应电流导出限值,增加了局部暴露导出限值、短暂局部暴露基本限值与导出限值,删除了微波听觉效应基本限值、接触电流导出限值。2020版导则更新了限制射频电磁场暴露的科学基础,使限值更加匹配近年来的科学研究成果,提升了导则的科学性、严谨性和准确性。 相似文献