共查询到20条相似文献,搜索用时 140 毫秒
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《中国生物工程杂志》1988,8(Z1):17-41
美国的科技研究开发投资,主要来自两方面:一是政府的研究发展(R&D)预算,二是工业界的研究开发投资。政府的研究预算支出,主要是用于基础研究和一部分基础应用研究。这些研究大部分是通过大学来进行。至于应用研究,则主要是靠工业界自己的投资和研究。美国公私这两方面的投资比例,以1985年前后生物技术的数字说,大体上各占一半。 相似文献
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中国蜘蛛生态学研究概况 总被引:20,自引:3,他引:20
简要综述我国蜘蛛生态学研究,包括生态因子的研究;蜘蛛种群研究:蜘蛛群落及其多样性研究;蜘蛛的捕食以及运用血清学方法研究以及蜘蛛的生物学特性及生活史研究。 相似文献
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通过对6种藓类植物,即褶叶青藓(Brachythecium salebrosum(Web.et Mohr.)B.S.G.)、湿地匐灯藓(Plagiomnium acutum(Lindb.)Kop.)、侧枝匐灯藓(Plagiomnium maximoviczii(Lindb.)Kop.)、大凤尾藓(Fissidensnobilis Griff.)、大羽藓(Thuidium cymbifolium(Doz.et Molk.)B.S.G.)和大灰藓(Hypnum plumaeforme Wils.)嫩茎和老茎的石蜡切片和显微观察发现,同一藓类植株的嫩茎和老茎,茎结构稳定,不同种藓类植物茎横切面具有不同特征.植物体茎横切面形状、表层细胞的层数、细胞大小和细胞壁厚薄、皮层细胞大小和形状、中轴的有无以及比例等特征可以作为藓类植物的分科分类依据之一. 相似文献
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目的 针对医疗机构的合理用药水平进行评价研究。方法 根据医疗机构合理用药的具体要求,构建医疗机构合理用药评价指标体系,采用基于模糊群决策的方法和多指标评价分析法构建医疗机构合理用药评价模型。结果 构建了基于模糊群决策的医疗机构合理用药评价模型,并通过实例分析证明了评价模型的可行性。结论 建立的基于模糊群决策的医疗机构合理用药评价模型能够对医疗机构的合理用药水平进行科学评价,为提高医疗机构合理用药水平奠定基础。 相似文献
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The levels of endogenous phytohormones and respiratory rate in nine sorts of flowers such as Cymbidium faberi Rolfe, Nopalxochia ackermannii Kunth and others were investigated both at full bloom and senescence and meanwhile the effect of exogenous phytohormones on prolonging the blossoms and promoting ethylene production were tested. There is a high content of endogenous ethylene in all the long-lived flowere, about 3–16 folds higer than the short-lived ones. There is a high level of ABA at full blooming flowers of short-lived flowers, in which there is no or only some cytokinins in it, but the ratio of CTK (6BA+zeatin)/ABA is smaller(l.7). The endogenous ABA reached a much higher level at senescence in all nine sorts of flowers, so it is reasonable to consider that it is ABA which plays an important role of regulation in controlling flower's senescence. There is a much higher level of GA3 and zeatin in the long-lived flowers which is not demonstrated in the shortlived ones. The respiratory rate is one of the factors controtling the longevity of flowers, but it does not play a decided role. Application of 6BA and zeatin prolongs distinctly orchid’s longevity, however exogenous IAA through the promotive action on ethylene production, evidently extends the longevity of the flowers of the Nopalxochia ackermannii Kunth. 相似文献
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龙胆科药用植物化学成分的研究现状 总被引:16,自引:0,他引:16
龙胆科植物在我国的分布范围很广,且多数为药用植物,其多数种属的药用植物,至今其化学成分尚未被系统研究。综述了目前龙胆科药用植物的化学成分的研究现状及一般提取方法,对近年来发现的环烯醚萜及裂环烯醚萜类化合物进行了总结,为本科药用植物的更深入研究提供了参考。 相似文献
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真菌类遗传学分析的知识结构教学 总被引:3,自引:2,他引:3
本文以认知结构理论为指导,讨论了真菌类遗传分析与高等动植物遗传分析的内在联系,认为利用这种内在联系进行教学可收到好的效果并说明了作者的具体教学过程。
Abstract:In the paper, the relationship between genetic analysis of Fungi and genetic analysis of high animal and plant was discussed.A good results were obtained when we adopted this method in the teaching. 相似文献
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The main purpose of this study was to determine whether the magnitude effect is present in cases where delayed sequences of rewards are discounted. The magnitude effect refers to the inverse relationship between the amount of a reward and the steepness of temporal discounting. This study was conducted with a computer program to estimate the indifference points, which served as indicators of the present subjective value of delayed sequences of small and large rewards. In the indifference point the subjective value of a single, immediate reward was equal to the subjective value of the delayed sequence (or to the value of a single delayed reward). As a control condition, we added an experimental task involving choices between single immediate and single delayed rewards. The experiment showed that the sequences of large rewards are discounted less steeply than are the sequences of small rewards. This finding suggests that the magnitude effect is present within the delayed sequences of rewards. In addition, when outcomes are relatively large, the results suggest that a single reward is discounted less steeply than the sequence of a total nominal value equal to this single reward. However, for relatively small rewards, the difference is not statistically significant. The less steep discounting of sequences of large rewards may explain the reward-bundling effect, which refers to less steep discounting of longer sequences than of shorter ones: longer sequences usually have greater overall nominal value. The present study was conducted on hypothetical rewards, and the results should be validated using real rewards. 相似文献
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Scales of spatial patterns of distribution of intertidal invertebrates 总被引:15,自引:0,他引:15
Few comparative studies of spatial patterns at different scales have examined several species in the same habitat or the same species over a range of habitats. Therefore, variability in patterns among species or among habitats has seldom been documented. This study quantifies spatial patterns of a suite of intertidal snails and a species of barnacle using a range of statistical techniques. Variability in densities was quantified from the scale of adjacent quadrats (over a distance of centimeters) to tens of kilometers. Significant differences in abundances occurred primarily at two spatial scales. Small-scale differences were found at the scales of centimeters or 1–2 m and, for many species on many shores, these accounted for most of the variability in abundances from place to place. These are likely to be determined by behavioural responses to small-scale patches of microhabitat. Large-scale differences in abundance were also found in most species at the scale of hundreds of meters alongshore. These are likely to be due to variation in recruitment (and/or mortality) because of limited dispersal by adults of these species. There was little or no additional variation among shores, separated by tens of kilometers, than was shown among patches of shore separated by hundreds of meters. Identification of the scale(s) at which significant differences in abundance are found focus attention on the processes (and the scales at which these processes operate) that influence patterns of distribution and abundance. Some of the advantages and disadvantages of various procedures are discussed. 相似文献
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M. V. Kozlov V. V. Urnysheva L. N. Shishkina 《Journal of Evolutionary Biochemistry and Physiology》2008,44(4):470-475
A complex analysis of seasonal fluctuations of the mean group parameters of the system of regulation of lipid peroxidation has been performed in liver of Balb/c mice. Association of lipid characteristics and morphophysiological parameters is studied in the Balb/c mouse liver. An inter-connection is revealed between the liver index and the amount of lysoforms of phospholipids, the scale and character of the interconnection differing essentially depending on proportion of phos-phatidylcholine in mouse liver phospholipids. 相似文献
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Knowledge of the timing of perinatal transmission of HIV would be valuable for the determination and evaluation of preventive treatments and would shed light on the mechanism of transmission. Estimation of the distribution of the time of perinatal transmission is difficult, however, because tests of infection status can only be undertaken after birth. DNA and RNA polymerase chain reaction (PCR) assays and HIV culture have been the most commonly used diagnostic tests for perinatal HIV infection. Such tests have high sensitivity and specificity, except when they are given shortly after infection. In this paper we use the time-dependent sensitivity of these diagnostic tests to make nonparametric and semiparametric inferences about the distribution of the time of perinatal HIV transmission as well as the cumulative probability of perinatal transmission. The methods are illustrated with data from a clinical trial conducted by the AIDS Clinical Trials group. 相似文献