中文网页自动分类新算法

为了有效地组织因特网上极其丰富的信息资源 ,通过分析中文和中文网页的特点 ,提出了一种新的中文网页的自动分类算法。这种算法主要利用字间的相关信息、词频以及页面的标记信息等 ,提取网页特征 ,并计算可调的词频加权参数 ,然后通过本类和非本类训练 ,建立专家数据库。实验表明 ,该算法可以获得 80 %以上的网页分类准确率     

Discovery of carbonaceous compressions and their multicellular tissues from the Changzhougou formation (1800 Ma) in the Yanshan range, North China

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.     

Global pollution shown by lead and cadmium contents in precipitation of polar regions and Qinghai-Tibetan Plateau

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.     

Simulation for the primary electronic donor of photosystem IIin vitro

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.     

子长油矿4207裸眼井"压胀松动"增产技术现场试验

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．     

A Review of The Road Not Taken

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.     

陈子昂:有实力,也要有机会

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。     

重塑直销行业语言

2020年,美国80%的直销公司销售额实现增长,30家直销公司收入增长超过1亿美元。2020年,直销行业又一次创下了销售纪录。尽管直销行业在2020年面临着诸多挑战,但与2019年相比,美国约80%的直销公司实现收入增长,其中30家公司的收入增长超过1亿美元,至少10家公司的年收入翻了一番。包括蒙纳特、香榭丽在内的几家私营企业增长超过4亿美元,以康宝莱为代表的上市公司也在稳健增长。值得注意的是,在新冠疫情爆发后的每一个月,这些企业的业绩都实现了持续增长,这很了不起。