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991.
992.
ZHU Shixing SUN Shufen HUANG Xueguang HEYuzhen(Tianjin Institute of Geology Mineral Resources Chinese Academy of GeologicalSciences Tianjin China)ZHU Gengxin SUN Lixin & ZHANG Kuan(Regional Geological Survey Institute Hebei Bureau of Geology Exploration Langfang China)Correspondence should be addressed to Zhu Shixing 《科学通报(英文版)》2000,45(9):841-847
In 1997 and 1998, hundreds of specimens of megascopic carbonaceous compressions or algal fossils were found from ∼ 1800-million-year
old Changzhougou Formation, which is the lowermost unit of the latest Palaeoproterozoic Changcheng Group (∼1 600–1 800 Ma)
in the Xinglong-Kuancheng areas at the middle Yanshan Range, North China. They are discoid, ellipsoid and sausage-like, namely
shaped likeChuaria Shouhsiennia (Ellipsophyta) andTawuia. By adopting HF acid-resistant maceration coupled with scanning electron microscope and petrologic section, the authors made
a preliminary research on the histology for some circular and ellipsoid carbonaceous compressions, namelyChuaria- andShouhsienia-like forms, in addition to their morphology. The following three types of multicellular tissues have been found in the fragments
of them: colony-like, pseudoparenchyma-like and parenchyma-like. All of the new data about multicelluar tissues not only supply
a very important basis in histology to determine the biological affinity of multicellular algal remains for the Changzhougou
carbonaceous compressions newly found, but also provide reliable fossil evidence to prove that metaphytes originated at least
1 800 million years ago. 相似文献
993.
Global pollution shown by lead and cadmium contents in precipitation of polar regions and Qinghai-Tibetan Plateau 总被引:1,自引:1,他引:0
XIAO Cunde QIN Dahe YAO Tandong RENJiawen & LI Yuefang(Laboratory of Ice Core Cold Region Environment Lanzhou Institute of Glaciology andGeocryology Chinese Academy of Sciences Lanzhou China)Correspondence should be addressed to Ren Jiawen 《科学通报(英文版)》2000,45(9):847-853
The analysis of the major ions, lead and cadmium has been performed for snow-pit samples collected from the Arctic, the Qinghai-Tibetan
Plateau and the Antarctic Ice Sheet. These snow pits were excavated respectively from the snowpack in Canadian Northwest Territory
(NWT) and the central Arctic, three glaciers on the Qinghai-Tibetan Plateau and surface snow along the route of the International
Trans-Antarctic Expedition (ITAE). The source regions for the lead pollution of central Arctic have been identified by analyzing
of stable lead isotopic ratios, meteorological and atmospheric chemistry studies. It shows that the central Arctic is still
under intensive lead input, despite the fact that lead content in Greenland Ice Sheet displays a rapid decreasing since the
1970s due to US and some European countries’ campaigns to reduce lead-containing gasoline-additives. This is because there
are multiple lead sources for the central Arctic, including the countries that have not performed gasoline-additives reducing.
The backgrounds of atmospheric aerosol compositions, as well as the concentrations of lead and cadmium in precipitation of
the early 1990s, are contrasted among the Arctic, Antarctica and Qinghai-Tibetan Plateau. The measured lead content in the
snowfall at the typical sites of the three regions is divided into natural (background) and anthropogenic components. It is
found that natural lead concentration (mainly crustal and/or sea-salt lead) is roughly equal among the three regions (< 3×1012g · g1). However, the percentage of the natural lead to the measured lead is negligible in precipitation in the central Arctic and
the Qinghai-Tibetan Plateau, while it is considerable in Antarctic precipitation. The anthropogenic component of lead (>50%
in Antarctic precipitation, >97% in the Arctic and the Qinghai-Tibetan Plateau ) is mainly responsible for the lead input
to both polar regions and to the Qinghai-Tibetan Plateau. Lead pollution may have spread into the whole troposphere and the
most remote regions on earth. 相似文献
994.
Fig. The absorption 《科学通报(英文版)》2000,45(10):914-920
Histidine coordinated to Chi a is a distinct characteristic of Chl ain vivo. By using histidine analogue of 1-methylimidazole (C4H6N22) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C4H6N2 and Chl a in CCI4, we have obtained that: (i) In pure CCl4 solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong
coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two
oxygen atoms come from the C=O of C131 keto and C17 ester, respectively); (ii) when the molar ratio of C4H6N2/Chl a is 0.5 or 1 (corresponding to 2Chl a · 1C4H6N2 and 2Chl a · 2C4H6N2, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl
a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C4H6N2 replaces the ligation of C=O of C17 ester and C131 keto to Mg atoms sequentially. The two Chl a molecules linked by two weakly interacted Mg…O bonds form a relaxed-dimer. The
structure of the model is essentially similar to that of the primary electronic donor, P680, of photosystem II in high plants and algae. 相似文献
995.
为了研究“压胀松动”增产技术的增产效果和施工工艺,在延长石油管理局子长油矿对4207裸眼井进行了现场试验.介绍了裸眼井“压胀松动”增产技术的基本原理、该井现场试验所需岩石力学参数的测定、药量的计算及装药设计.并对施工工艺和实验结果进行了分析和研究,说明“压胀松动”增产技术对此井是有效的. 相似文献
996.
The Road Not Taken is one of the most important poems written byAmerican famous poet Robert Frost.The poem reflects his important life experi-ence,thought and emotions.Even today this poem is significant. 相似文献
997.
你叫陈子昂?是的。这是我的诗文我想向你家老爷请教。我家老爷没听说过你。你请回吧!唉,我又吃了闭门羹!我陈子昂自幼博览群书,自许才学过人,想不到在长安城却无人赏识。 相似文献
998.
999.
世界上有一个动听的词,它叫“妈妈”.妈妈很忙碌,是一名化验师,整天忙于工作。2020年年初,突如其来的新冠肺炎疫情打破了我家的平静。其他孩子跟爸爸妈妈在一起,可我的爸爸在隔离病房里、妈妈在实验室里。 相似文献
1000.