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51.
茶多酚中儿茶素类的HPLC分析方法学考察 总被引:25,自引:0,他引:25
本文建立了一种非梯度洗脱的儿茶素HPLC定性定量分析方法 ,同时对茶多酚中的四种主要儿茶素(EC ,EGCG ,ECG ,EGC)考察了其方法学。得到最佳色谱条件为 :ODS (5 μm ,4 6× 2 5 0mm)柱 ,以重蒸水∶乙睛∶乙酸乙酯 =86∶12∶2 (v v v)为流动相 (浓硫酸调pH值至 3 0~ 4 0 ) ,流速为 1 0ml min ,UV检测波长 2 80nm。探讨了分离测定条件并验证其精密度及方法的稳定性 相似文献
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Determination of gross N mineralization rate in soil, by use of the isotopic pool dilution approach implies that 15NH4+ is applied homogeneously to soil. Since the labeling is applied to the product of the mineralization, the application of 15NH4+ should in theory not alter the mineralization rate. However, recent studies have indicated inverse relation between the amounts of 15NH4+ applied and the determined gross N mineralization rates, due to overestimated rates when ‘low’ amounts of 15NH4+ were added, as a result of preferential 15NH4+ consumption. We present here results from a similar study. We observed no effect from the amount of applied NH4+ on the measured gross N mineralization rates. Our results indicate, that the inverse relation as described earlier, probably was due to underestimated rates when ‘high’ amounts of 15NH4+ were added, as a result of preferential 14NH4+ consumption, when the applied 15NH4+ was incomplete distribution in the soil. 相似文献
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中国小麦产业发展与科技进步 总被引:24,自引:2,他引:24
文章总结分析了新中国成立以来中国小麦生产发展和品种选育与栽培技术研究的历史进程。小麦生产发展分为4个阶段,即1949—1957年恢复性增长、1958—1978年稳定增长、1979—1999年单产快速增长和2000—2016年产量质量同步提升。简要介绍了1949年前的育种起步历史,1950年以后小麦育种取得了巨大进展,经历了抗病稳产早熟、矮化抗倒高产和高产优质高效3个阶段,矮秆基因和1B/1R易位系利用与株型改良起到关键作用,育成了碧蚂1号、泰山4号、扬麦158、豫麦21、济麦22等突破性品种,主产麦区经历了8~9次品种更新换代。黄淮麦区的矮秆高产育种和长江中下游麦区的抗赤霉病育种在国际上产生重要影响。概括了种质资源、远缘杂交、矮败小麦、品质改良、兼抗型成株抗性育种、基因组学等领域的新进展。小麦栽培研究经历了4个阶段,20世纪50年代以合理密植为核心,20世纪六七十年代重点研究不同麦区小麦生长发育规律与高产栽培历程,20世纪80年代提出了各主要麦区栽培技术模式包括精播高产、节水高产等技术,20世纪90年代以优质和信息技术应用为主。未来产业发展面临提升质量、降低成本和保护环境三大挑战,气候变化、病害加重、缺乏优质高效抗病品种制约生产发展,建议加强优质抗病高效品种选育与新技术应用研究,实现栽培研究与植保、土肥、农机等有机结合,以全面提高小麦产业的竞争力。 相似文献
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J.M. Sargeant A. Thompson J. Valcour R. Elgie J. Saint-Onge P. Marcynuk K. Snedeker 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2010,24(1):44-50
Background: To address concerns about the quality of reporting of randomized controlled trials, and the potential for biased treatment effects in poorly reported trials, medical journals have adopted a common set of reporting guidelines, the Consolidated Standards of Reporting Trials (CONSORT) statement, to improve the reporting of randomized controlled trials.
Hypothesis: The reporting of clinical trials involving dogs and cats might not be ideal, and this might be associated with biased treatment effects.
Animals: Dogs and cats used in 100 randomly selected reports of clinical trials.
Methods: Data related to methodological quality and completeness of reporting were extracted from each trial. Associations between reporting of trial features and the proportion of positive treatment effects within trials were evaluated by generalized linear models.
Results: There were substantive deficiencies in reporting of key trial features. An increased proportion of positive treatment effects within a trial was associated with not reporting: the method used to generate the random allocation sequence ( P < .001), the use of double blinding ( P < .001), the inclusion criteria for study subjects ( P = .003), baseline differences between treatment groups ( P = .006), the measurement used for all outcomes ( P = .002), and possible study limitations ( P = .03).
Conclusions and Clinical Importance: Many clinical trials involving dogs and cats in the literature do not report details related to methodological quality and aspects necessary to evaluate external validity. There is some evidence that these deficiencies are associated with treatment effects. There is a need to improve reporting of clinical trials, and guidelines, such as the CONSORT statement, can provide a valuable tool for meeting this need. 相似文献
Hypothesis: The reporting of clinical trials involving dogs and cats might not be ideal, and this might be associated with biased treatment effects.
Animals: Dogs and cats used in 100 randomly selected reports of clinical trials.
Methods: Data related to methodological quality and completeness of reporting were extracted from each trial. Associations between reporting of trial features and the proportion of positive treatment effects within trials were evaluated by generalized linear models.
Results: There were substantive deficiencies in reporting of key trial features. An increased proportion of positive treatment effects within a trial was associated with not reporting: the method used to generate the random allocation sequence ( P < .001), the use of double blinding ( P < .001), the inclusion criteria for study subjects ( P = .003), baseline differences between treatment groups ( P = .006), the measurement used for all outcomes ( P = .002), and possible study limitations ( P = .03).
Conclusions and Clinical Importance: Many clinical trials involving dogs and cats in the literature do not report details related to methodological quality and aspects necessary to evaluate external validity. There is some evidence that these deficiencies are associated with treatment effects. There is a need to improve reporting of clinical trials, and guidelines, such as the CONSORT statement, can provide a valuable tool for meeting this need. 相似文献
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[目的]通过紫外分光光度法建立氮肥中尿素含量的测定方法。[方法]利用紫外分光光度计,根据Ehrlich反应,二甲氨基苯甲醛可以与含氮的有机化学物发生显色反应,此物质在403 nm处有最大吸收峰,颜色的深浅与测定的尿素含量呈正比,因此通过测定反应液在403 nm处的吸光值来确定尿素溶液中尿素含量。[结果]得到尿素检测标准曲线为y=0.004 3x+0.009 9(R2=0.999 2),尿素浓度在3.75~210μg/ml之间呈良好线性关系,平均回收率为96.83%,RSD=0.2%。[结论]该方法准确度、精密度良好,可以用来测定尿素的含量。 相似文献
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W. Foissner 《Biology and Fertility of Soils》1997,25(4):317-339
This paper provides, for the first time, comprehensive data on alpha diversity of soil ciliates from evergreen tropical and
temperate rain forests. Thirty-three samples were collected in Australia, Tasmania, Amazonia and Costa Rica and analysed with
the non-flooded Petri dish method, which reactivates the ciliates’ resting cysts from air-dried samples. The 175 taxa found
contained 34 new species, 4 of which are described in this paper, viz. Platyophrya paoletti n. sp., Lamtostyla abdita n. sp., L. granulifera n. sp., and Apoamphisiella tihanyiensis (Gellért and Tamás 1958) n. gen., n. comb. Although this is a considerable number, it is much lower than one would expect.
The data would be even more perplexing if the four rich samples (up to 90 species/sample) from the Manaus floodplain were
excluded. We then would be confronted with about 90 taxa in 29 samples, of which 13 contained fewer than ten species. A hypothesis
is put forward that the non-flooded Petri dish method is inappropriate for studying soil ciliate diversity in evergreen rain
forests because most species have a reduced capacity to produce dry-resistant (protective) resting cysts due to the permanent
wetness of their habitats. This view is supported by a comparative analysis of a fresh (containing 40 species) and air-dried/rewetted
(2 species only) sample from a cloud rain forest near Merida (Venezuela), and the observation that the capacity of soil ciliates
to produce resting cysts often dramatically decreases after prolonged laboratory cultivation in liquid media. Direct microscopy
of fresh samples seems to be an appropriate alternative because specimens can be easily collected due to their considerable
abundance (≥1000 individuals/g wet mass of litter).
Received: 8 April 1997 相似文献
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