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991.
新鲜海带中碘的含量与分布 总被引:1,自引:0,他引:1
海带中含有高浓度的碘是其独特的化学组成特点,历来被海藻学家所重视(Tang and Chang, 1935, 1936; Black, 1948, 1949; Klemperer, 1957; Fernandez et al., 1964:Dave et al., 1973; Law, 1975; Solimabi and Das, 1977; Yamamoto et al., 1984:Doshi and Joshi,1989; Mairh et al.,1989),但是几乎所有的有关研究方法都基于化学滴定,在材料上局限于海藻干品,另外海带样品含有大量的褐藻多糖以及多酚类化合物,能够包溶部分碘离子及碘单质,因此用常规的化学滴定法误差较大,从而导致试验结果的非重复性和非可靠性。本文利用碘离子选择电极法,直接在样品溶液中测定,不必经过离心、氧化还原等一系列复杂的步骤,测定了新鲜海带中不同部位碘的含量和分布,为进一步研究海带中碘的化学存在形态提供了理论数据。 相似文献
992.
为了评价GPS与VLBI这两种空间技术测定的地心坐标的真正实现精度,选择使用它们的并置站坐标数据,在进行了历元改正和偏心改正后,计算了这两种技术实现的参考架的转换参数,并分析了它们坐标不符值的中误差,得出GPS与VLBI这两种技术实现的参考架的外符合精度在1cm之内,表明了GPS与VLBI这两种技术测定的地心坐标精度已经达到毫米量级。 相似文献
993.
994.
995.
基于渗透原理的农民工城市空间融入变化规律研究 总被引:2,自引:2,他引:0
根据2015~2016年对西安市区农民工调查和访谈的1 200份问卷为基础,结合渗透原理,借助数理统计方法,构建城市空间网络节点模型,分析城市融入动态变化规律。研究得出:①农民工城市空间融入具有渗透和排斥规律,其影响因素涉及软差异实力与硬差异实力在城市空间网络节点上渗透力与排斥力相互作用;②该综合作用的阈值决定农民工在城市空间网络节点上的迁移与逗留时间;③理论数据仿真测试表明基于同心圆理论的城市空间网络节点模型(Logistic)符合农民工城市融入动态位移特征,对城市空间和谐发展有着积极的启示意义。 相似文献
996.
腾格里沙漠东南缘生物土壤结皮对土壤理化性质的影响 总被引:3,自引:1,他引:2
生物土壤结皮是荒漠生态系统地表景观的重要组成部分,在沙化土地恢复和流沙固定中起着重要作用。研究了腾格里沙漠东南缘固沙植被区不同类型生物土壤结皮理化性质及结皮发育对下层土壤性质的影响。结果表明:结皮层厚度、孔隙度、黏粉粒和田间持水量以及有机碳、无机碳、全氮、碱解氮、速效磷、速效钾含量和电导率均表现为藓类结皮 > 混生结皮 > 地衣结皮 > 藻类结皮;砂粒含量和容重表现为藻类结皮 > 地衣结皮> 混生结皮 > 藓类结皮。结皮下0~2 cm和2~5 cm土层理化性质表现出与结皮层相同的变化规律。总体上,生物土壤结皮对下层土壤理化性质的影响表现为藓类结皮和混生结皮大于地衣结皮和藻类结皮;而结皮对下层土壤理化性质的影响随土壤深度的增加而减小。生物土壤结皮的拓殖和发育是荒漠生态系统成土过程和土壤质量的关键影响因素。 相似文献
997.
998.
Based on the NCEP/NCAR daily reanalysis data and the daily rainfall data of ground observation at 164 weather stations in the middle and lower reaches of the Yangtze River from 1960 to 2013, the relationship between South Asia high low frequency oscillation and the drought and flood in the middle and lower reaches of the Yangtze River were analyzed using a composite analysis, wavelet analysis and band-pass filtering analysis method. The results indicated that in the typical drought and flood years, the Qinghai-Tibet Plateau 200 hPa atmosphere u, v low-frequency primary cycle and the summer rainfall cycle over the middle and lower reaches of the Yangtze River were the same. In more summer rainfall, from the Qinghai-Tibet Plateau to east China and west Pacific coast, there existed a cycle-anticyclone-cycle low frequency wave train. Low-frequency anticyclone controlled eastern China and the low-frequency cyclone controlled the northern Qinghai-Tibet Plateau. In drought years, results were opposite. In flood years, the precipitation of low frequency over the middle and lower reaches of the Yangtze River and that of 200 hPa atmospheric low frequency change of the Qinghai-Tibet Plateau was closely related. When the northerly wind in the northeast part of the the Qinghai-Tibet Plateau and in the middle and lower reaches of the Yangtze River was strong, and Lake Baikal southerly wind was strong, there was more precipitation. On the contrary, precipitation was less. The low frequency oscillation wave train was mainly spread from the northeast of China and Japan's southern to China’s southwest. However, in drought years, the relationship between them was not clear and needed to be further studied. 相似文献
999.
The formation and development of debris flows in large watersheds after the 2008 Wenchuan Earthquake 总被引:2,自引:0,他引:2
The Wenchuan earthquake has caused abundance of loose materials supplies for debris flows. Many debris flows have occurred in watersheds in area beyond 20 km2, presenting characteristics differing from those in small watersheds. The debris flows yearly frequency decreases exponentially, and the average debris flow magnitude increases linearly with watershed size. The rainfall thresholds for debris flows in large watersheds were expressed as I?=?14.7 D ?0.79 (2 h?<?D?<?56 h), which is considerably higher than those in small watersheds as I?=?4.4 D ?0.70 (2 h?<?D?<?37 h). A case study is conducted in Ergou, 39.4 km2 in area, to illustrate the formation and development processes of debris flows in large watersheds. A debris flow develops in a large watershed only when the rainfall was high enough to trigger the wide-spread failures and erosions on slope and realize the confluence in the watershed. The debris flow was supplied by the widely distributed failures dominated by rill erosions (14 in 22 sources in this case). The intermittent supplying increased the size and duration of debris flow. While the landslide dam failures provided most amounts for debris flows (57 % of the total amount), and amplified the discharge suddenly. During these processes, the debris flow velocity and density increased as well. The similar processes were observed in other large watersheds, indicating this case is representative. 相似文献
1000.
SCOTT ELLIOTT MEI SHEN DONALD R. BLAKE RONG LU ARMISTEAD G. RUSSELL C. Y. J. KAO GERALD E. STREIT XUE PENG ZHAO EDWARD IAIN McCREARY F. SHERWOOD ROWLAND MICHAEL J. BROWN RICHARD P. TURCO 《Journal of Atmospheric Chemistry》1997,27(1):31-70
Local surface travel needs in the Peoples Republic of China (mainlandChina) have traditionally been met largely by nonpolluting bicycles. A majorautomobile manufacturing/importing effort has begun in the country over thelast decade, and planning documents indicate that the Chinese may strive toacquire more than 100 million vehicles early in the next century. By analogywith large automotive fleets already existing in the western world, bothregional and global scale pollution effects are to be expected from theincrease. The present work adopts the latest projections of Chinese automobilemanufacture and performs some quantitative assessments of the extent ofpollution generation.Focus for the investigation is placed upon the oxidant ozone. Emissions of theprecursor species nitrogen oxides and volatile organics are constructed basedon data for the current automotive sector in the eastern portion of the UnitedStates. Ozone production is first estimated from measured values forcontinental/oceanic scale yields relative to precursor oxidation. Theestimates are then corroborated through idealized two dimensional modeling ofthe photochemistry taking place in springtime air flow off the Asian land massand toward the Pacific Ocean. The projected fleet sizes could increase coastaland remote oceanic ozone concentrations by tens of parts per billion (ppb)in the lower troposphere. Influences on the tropospheric aerosol system andon the major greenhouse gas carbon dioxide are treated peripherally. Nitrogenoxides created during the vehicular internal combustion process willcontribute to nitrate pollution levels measured in the open Pacific. Thepotential for soot and fugitive dust increases should be considered as theautomotive infrastructure develops. Since the emerging Chinese automotivetransportation system will represent a substantial addition to the globalfleet and all the carbon in gasoline is eventually oxidized completely, asignificant rise in global carbon dioxide inputs will ensue as well.Some policy issues are treated preliminary. The assumption is made thatalterations to regional oxidant/aerosol systems and to terrestrial climate areconceivable. The likelihood that the Chinese can achieve the latest vehiclefleet goals is discussed, from the points of view of new production, positivepollution feedbacks from a growing automobile industry, and known petroleumreserves. Vehicular fuel and maintenance options lying before the Chinese areoutlines and compared. To provide some perspective on the magnitude of theenvironmental changes associated with an Asian automotive buildup, recentestimates of the effects of future air traffic over the Pacific Rim aredescribed. 相似文献