共查询到20条相似文献，搜索用时 46 毫秒
1.
文耀智 《邵阳学院学报(社会科学版)》2001,23(2):42-48
上世纪初发现自由基反应,其特点有三引发、传递和终止;分为单分子和双分子反应.共振杂化体越多的自由基越稳定,对自由基稳定有利的空间构型其反应易进行,溶剂化作用、氢键的形成、过渡态活化能等对自由基反应都有影响. 相似文献
2.
研究了用电子自旋顺磁共振(ESR)法对香烟烟气中的自由基进行分析的样品处理方法及ESR检测方法.对四种英国产香烟样品中的粒相及气相自由基进行了分析检测并对检测结果进行了讨论.结论:大多数英国产的检测样品香烟中,含有1.5～3倍于国产对照香烟样品的气相自由基;而国产对照样品香烟的粒相自由基的含量水平则处于较高水平.实验结果还显示:同品牌的Sobranie香烟中,不同型号样品中粒相自由基含量与焦油含量具有负相关性,但不同品牌则不同;对于检测样品而言,气相自由基的含量与焦油含量有正相关性. 相似文献
3.
We investigated the effects of enhancing orthographic knowledge on the spelling of Chinese characters and words in 131 eight-year-old
Chinese children at risk for dyslexia. The traditional approach (37 children) emphasizing memory and repeated writing was
the control condition. The analytic and synthetic approach (ASA, 33 children) stressed insight into character structure. The
integrated analytic and synthetic approach added to ASA self-correction and metacognitive activities (INA, 61 children). The
children were first asked to write down as many words as possible associated with pictures of home, school, and community;
the correctly written words formed the baseline information. The children were then instructed by their classroom teachers
in six especially designed short texts and assessed in eight measurable bujian or radical tasks subserving three constructs: morpheme completion, bujian analysis and synthesis and bujian compounding.
Multivariate analyses of variance showed that the children in the INA condition outperformed those in the other conditions
in three of the measurable bujian tasks. A confirmatory factor analysis verified the stability of the eight tasks and their
clustering into three constructs. From these results, we tentatively propose a “bujian sensitivity hypothesis” as a means
of helping young Chinese children at risk for spelling disorders. 相似文献
4.
不同形态SiO_2的性质研究 总被引：2，自引：0，他引：2
温和瑞 《赣南师范学院学报》1994,(5)
本文比较了晶态ＳｉＯ＿２和无定形ＳｉＯ＿２的性质。结果表明，无定形ＳｉＯ＿２的溶解度大于α－石英。在ｐＨ＞３的范围内，ＳｉＯ＿２粒子表面带负电荷，α－石英粒子表面ξ电位高于无定形ＳｉＯ＿２粒子，ＥＳＲ谱表明，α－石英晶体被研磨后，粉尘粒子表面产生了自由基，而研磨无定形ＳｉＯ＿２则无自由基产生。α－石英粉尘粒子表面ξ电位大，粒子表面存在自由基与它的细胞毒性大是相一致的。 相似文献
5.
用自由基捕捉剂 1 ,1 -二苯基 -2 -三硝基苯肼 (DPPH)对等离子体引发水溶液体系聚合时体系中的自由基浓度进行了测定。发现在等离子体引发水溶液聚合体系中 ,自由基浓度随放电功率、放电时间的增加而增加 ,而且当体系中加入单体后 ,在同样的条件下体系中的自由基浓度比未加单体时的浓度高。 相似文献
6.
以丙烯酰胺(AM)和二甲基二烯丙基氯化铵(DMDAAC)为原料,在紫外灯照射和光引发剂作用下,通过水溶液自由基共聚法合成了水溶性好的阳离子型聚丙烯酰胺。研究了光引发剂用量、单体配比、pH值以及单体总浓度等对产物性能的影响规律,并通过对合成产物固含量、特性粘数、阳离子度等性能指标的测试,确定了本聚合反应体系的最佳工艺条件。用红外光谱和核磁共振氢谱对共聚物进行了结构表征。 相似文献
7.
A novel cyclodextrin-containing polymer was prepared by graftingβ-cyclodextrin onto the backbone of poly(D,L-lactic acid)(PLA).First,mono(6-(2-aminoethyl)amino-6-deoxy)-β-cyclodextrin(β-CD-6-en)was prepared by sulfonylation and amination ofβ-cyclodextrin and modified poly(D,L-lactic acid)(MPLA)was prepared by free radical polymerization of maleic anhydride and PLA.Then,grafting ofβ-cyclodextrin derivative to MPLA backbone was carried out by N-acylation reaction of MPLA andβ-CD-6-en in dimethyl formamide.The... 相似文献
8.
The effects of semantic and phonetic radicals on Chinese character decoding were examined. Our results suggest that semantic
and phonetic radicals are each available for access when a corresponding task emphasizes one or the other kind of radical.
But in a more neutral lexical recognition task, the semantic radical is more informative. Semantic radicals that correctly
pertain to character meaning facilitated reaction time in semantic categorization tasks (Experiment #1), while radicals that
had no immediately interpretable relation to character meaning had a strong inhibitory effect. Likewise, phonetic radicals
that accurately indicated a character’s pronunciation facilitated a homonym recognition task (Experiment #2), whereas phonetic
radicals that differed significantly in pronunciation from their character inhibited homonym recognition. In a lexical decision
task (Experiment #3) where each character had either a blurred semantic radical or a blurred phonetic radical, the characters
with a blurred semantic radical elicited a significantly higher error rate and a trend for longer response times. These results
are interpreted to indicate that while educated native Chinese speakers have full use of both semantic and phonetic paths
to character decoding, there is a slight predisposition to semantic decoding strategies over phonetic ones indicating that
the semantic path is the default means of character recognition. 相似文献
9.
自由基是含有外层未配对电子的具有强氧化反应能力的中间物质 .它通过氧化作用攻击机体内生物大分子 ,从而引起细胞及细胞器特别是供能的线粒体结构和机能的破坏 .急性剧烈运动使运动员体内产生大量的自由基 ,引发机体疲劳和组织细胞的损伤 .因此 ,如何有效地提高自由基的清除能力和预防产生过量的自由基 ,对提高运动员的运动水平具有十分重要的意义 . 相似文献
10.
The whole Marxist theory centers on the emancipation and freedom of human beings, the naming of his highest ideal as ‘association
of free individuals’ being the clear proof. However, it would be superficial to announce Marxism as humanism of individualism
according to Marx’s pursuit of ‘free development of each’. The ‘free development of each’ put forward by Marx when describing
the ‘association of free individuals’ refers to individuals’ re-subjecting their social relations that have been changed into
material powers owing to private ownership and alienation. In this sense, the free development of each is the condition for
the free development of all. In this very sense, too, the foundation of the real community is required as the presupposition
so as to relate his theory of freedom to the theory on the elimination of private ownership and the alienation and elimination
of class and state finally.
Project supported by National Social Science Foundation of China(No. 00BZZ001) and the Excellent Young Teachers Program of
Ministry of Education, China. 相似文献
11.
目的:探讨绵地花菌黄酮类化合物的抗氧化活性。方法:采用有机溶剂萃取的方法,获取绵地花菌子实体黄酮类化合物,以VC作为对照,测定清除DPPH·、羟基自由基、亚硝酸盐、超氧阴离子的能力等指标。结果:绵地花菌黄酮类化合物能有效的清除DPPH·、羟自由基、亚硝酸盐和超氧阴离子,其清除能力的大小与浓度呈正相关。结论:绵地花菌黄酮类化合物具有较强的体外抗氧化活性。 相似文献
12.
G Nagendrappa 《Resonance》2005,10(9):79-84
In the previous five parts, we have seen how the ubiquitous free radicals touch our lives in many ways. In this part, four
experiments involving free radical intermediates are described. They are very simple, economical and practical, and can be
easily carried out in laboratories with meagre resources. They can, therefore, be adapted for MSc chemistry practicals as
part of free radical chemistry course. 相似文献
13.
为评价泉州湾底栖生物可口革囊星虫对有机污染物BaP的暴露风险,研究了BaP对可口革囊星虫体壁中氧自由基和丙二醛含量等因子的影响．结果表明：BaP对可口革囊星虫产生的氧自由基及膜脂过氧化伤害受暴露剂量和时间的双重影响．在20～500ng／gBaP浓度范围,超氧阴离子自由基含量随着BaP浓度以及暴露时间的延长呈显著上升变化,可口革囊星虫体壁丙二醛含量和羟自由基含量在BaP暴露1～4d内随暴露浓度的升高而显著增高;在暴露时间达7d时,各处理组丙二醛含量与BaP暴露4d之间无显著性差异,羟自由基含量则下降到与空白对照含量相当的水平．可口革囊星虫氧自由基和丙二醛含量可作为海洋环境BaP污染的早期预警生物标志物． 相似文献
14.
In this research, an implicit test using a lexical-decision task, in which words were discriminated from homophonic pseudo-words,
was developed to detect the phenomenon of Chinese orthographic satiation. The phenomenon is defined as a sense of uncertainty of the composition of a well-learned Chinese character through a prolonged
visual inspection of the character. A statistic, β, was developed as a measure of the rate of orthographic satiation. Results show that the characters consisting of two radicals
resulted in a higher value of β than did those consisting of a single radical. The results also showed that characters semantically dissimilar to its radical
resulted in a higher rate of satiation than did those semantically similar to its radical. These results are discussed in
terms of the link between orthography and sound of Chinese characters and its relation to orthographic satiation. 相似文献
15.
以铁尾矿砂为原料,用NaOH,HNO3调节pH值,采用熔融-水热两步法制备了铁尾矿砂光催化剂。利用X射线衍射仪、紫外/可见/近红外光谱仪等对铁尾矿砂光催化剂的结构性能进行表征;以罗丹明B溶液为标准降解物,汞灯为光源,探讨在不同pH条件下合成的铁尾矿砂光催化剂的光催化活性。结果表明,铁尾矿砂光催化剂的主要成分为Fe2.35Si0.65O4和NaNO3,且具有良好的光催化效果;在pH 8.5条件下制备的样品具有多孔结构,光催化性能最强;光照120 min时此样品可降解95.1%的罗丹明B溶液;·O2-是光催化反应过程中最主要的氧化活性自由基。 相似文献
16.
连翘苷对氧自由基清除作用的研究 总被引：1，自引：0，他引：1
研究连翘苷对氧自由基（包括超氧阴离子自由基及羟自由基）的清除作用．通过甲醇回流法提取、纯化连翘苷,再分别采用H2O2／Fe^2＋体系法、AP—TEMED体系法以及AAPH·自由基致DNA损伤测定法,研究连翘苷在清除羟自由基、超氧阴离子自由基和抑制AAPH·自由基的能力．结果显示,连翘苷能有效清除超氧阴离子自由基、羟自由基,在连翘苷浓度达4．5mg／mL时,其清除率分别为18．18％和33．99％,均超过阳性药物BHT;同时,电泳结果表明,连翘苷对AAPH·自由基引起DNA氧化损伤有一定的修复作用,提示连翘苷具有明显的抗氧化作用． 相似文献
17.
山莨菪碱对Fenton反应生成的·OH具育较强的直接清除作用,其IC_(50)为276mg.L~(-1),作用比·OH特异性清除剂甘露醇(IC_(50)为1349mg·L~(-1)强。对黄嘌呤-黄嘌呤氧化酶系统产生的O(?)也有较强的清除作用,其IC_(50)126mg·L~(-1)。山莨菪碱对自由基发生系统(FRGS)诱导离体大鼠心肌匀浆组织产生的脂质过氧化(LPO)作用有明显的抑制效应。对FRGS诱导离体大鼠心肌线粒体膜LPO也有一定的抑制作用。结果提示山莨菪碱的抗脂质过氧化作用与清除氧自由基作用有关。 相似文献
18.
Gerald Wangenge-Ouma 《Higher Education》2012,64(6):831-844
The funding of higher education in South Africa has in the recent past been a subject of animated debate. This debate has ranged from the adequacy of government funding of higher education, the suitability of the funding framework, to protestations against frequent tuition fee increases. At present, the debate is mainly about “free” higher education. Unlike most African countries, South Africa has an established history of cost sharing. But, for a while now, students, especially Black students, have been demanding tuition free higher education even though the country has a student financial aid scheme to support talented but poor students. The demands for tuition free higher education suggest, among others, the possible existence of financial barriers to higher educational opportunities. This paper is a sequel to the debate on free higher education in South Africa. It seeks, in the main, to understand and examine the rationale and drivers for the students’ demand for “free” higher education. What are the financial barriers to higher educational opportunities that the current funding architecture has failed to address? Secondly, why are students demanding free higher education when there is a scheme to support talented but poor students? Is cost sharing inconsistent with the country’s post-apartheid transformation policy in higher education? Finally, is “free” higher education the panacea to the access and participation challenges facing Black students? 相似文献
19.
具有很高隔离度的双极化缝隙耦合微带天线 总被引：3，自引：0，他引：3
A wideband dual-polarized slot-coupled stacked microstrip antenna with very high isolation and low cross-polarization is presented. To improve isolation between two poiarization ports, the stacked patches are excited by an open-ended and a T-shaped microstrip lines both via two H-shaped slots placed in a ＂T＂ configuration. The measured isolation is better than 40.5 dB over the bandwidth from 8.8 to 9.8 GHz with cross-polarization level less than - 28.5 dB. The measured VSWR ≤ 2 bandwidths reach 20.7 96 and 19.196 at the verrical and horizontal polarization ports, respectively. This antenna is suitable to be used as array elements in spacebome synthetic aperture radars （SAR） and active phased array radars. 相似文献
20.
Evaluation of the antioxidant effects of four main theaflavin derivatives through chemiluminescence and DNA damage analyses 总被引：1，自引：0，他引：1
Theaflavins (TFs) are the dimers of a couple of epimerized catechins, which are specially formed during black tea fermentation.
To explore the differences among four main TF derivatives (theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3′-gallate (TF2B), and theaflavin-3,3′-digallate (TF3)) in scavenging reactive oxygen species (ROS) in vitro, their properties of inhibiting superoxide, singlet oxygen, hydrogen
peroxide, and the hydroxyl radical, and their effects on hydroxyl radical-induced DNA oxidative damage were systematically
analyzed in the present study. The results show that, compared with (−)-epigallocatechin gallate (EGCG), TF derivatives were
good antioxidants for scavenging ROS and preventing the hydroxyl radical-induced DNA damage in vitro. TF3 was the most positive in scavenging hydrogen peroxide and hydroxyl radical, and TF1 suppressed superoxide. Positive antioxidant capacities of TF2B on singlet oxygen, hydrogen peroxide, hydroxyl radical, and the hydroxyl radical-induced DNA damage in vitro were found.
The differences between the antioxidant capacities of four main TF derivatives in relation to their chemical structures were
also discussed. We suggest that these activity differences among TF derivatives would be beneficial to scavenge different
ROS with therapeutic potential. 相似文献