中国上市公司多元化经营绩效的实证分析

通过随机抽样,计算我国57家上市公司1998年-2002年的平均盈利指标和风险指标,根据各公司多元化熵值的大小对样本总体进行分组,分析多元化程度对企业绩效的影响.研究发现1.多元化程度越高,公司的平均净资产收益率越高;2.多元化经营降低了公司收益率的波动水平;3.资产规模越小的公司越倾向于选择多元化经营.     

加快凉山绿色肉羊基地建设的思考

本文根据当前畜牧业生产形势结合凉山实际,就凉山绿色肉羊基地建设问题进行了一些思考,并提出了相应对策建议.     

高效液相色谱法测定齿毛芝中的碱基

采用250SS4.6-ODSZ-8/5色谱柱,体积分数20%的甲醇为流动相,紫外260nm检测,尿嘧啶,尿苷,腺嘌呤腺苷的保留时间分别为2.23min,2.97min,4.13min和6.74min,检测齿毛芝中碱基的摩尔比依次为1`.24:0.41:2.29:2.05.     

汽车运材费用的多因素分析

本文应用多元统计分析方法对汽车运材费用进行分析，影响运材费用的主要因素按其对单位成本影响的贡献大小排序，依次是单位养路费、单位燃润费、单位保修费和单位大修费．     

云和县雪梨产业化建设进展与思考

分析了云和雪梨产业化建设的提出背景,总结了雪梨产业化建设进程中取得的经验与方法,同时在建立土地流转机制、发挥政府在雪梨产业化进程中的作用、培植龙头企业、科技创新与推广树立精品意识等方面进行了深入的思考.     

C_R704玉米与S_C704玉米过氧化物酶同工酶及生理指标分析

C_R704玉米与S_C704玉米各时期的过氧化物酶同功酶谱无明显差别,二者遗传基础一致,但酶活性C_R704玉米高于S_C704玉米。经测定三系杂种C_R704玉米在叶绿素、糖、淀粉及蛋白质含量均优于单交种S_C704玉米。     

暴发高致病禽流感疫区鸟类禽流感的血清学调查

本研究应用血凝抑制试验(H I),2004年初H 5亚型禽流感在中国内地发生前后,于湖北、广西二疫区市县的生态系中,自健康的鹰、鸽子、野鸭和鹌鹑中采集了54份血清,对其进行了血清学检测,并将获得的血清学检测数据进行了统计学分析。分析结果显示,在总共采集的54份血清样品中,抗H 6亚型禽流感病毒(H 6)抗体、抗H 9亚型禽流感病毒(H 9)抗体、抗H 5亚型禽流感病毒(H 5)抗体阳性率分别为64.8%、75.9%、29.6%。推断,这一时期,H 6亚型禽流感病毒(H 6)、H 9亚型禽流感病毒(H 9)和H 5亚型禽流感病毒(H 5)共循环于该生态系中,其中H 9、H 6亚型禽流感病毒长期、稳定循环于该生态系中,为该生态系禽流感主要流行血清型。血凝抑制试验检测结果发现,H 5亚型禽流感病毒抗体滴度较低,最高仅为640×,其阳性率为29.6%,推断其可能为新近传入的病毒或新近重组变异出现的新病毒,可能为与该次禽流感暴发相关的新病毒,这一推断还有待于通过对病毒基因序列的分析而做进一步验证。     

Serum 5'nucleotidase activity in rats: a method for automated analysis and criteria for interpretation

A manual kit for determining serum 5'nucleotidase (5'NT, EC 3.1.3.5) activity was adapted for use with rat samples on a large discrete clinical chemistry analyzer. The precision of the method was good (within-run C.V. = 2.14%; between-run C.V. = 5.5%). A comparison of the new automated method with a manual and semi-automated method gave regression statistics of y = 1.18X -3.66 (Sy. x = 4.54), and y = 0.733X + 1.97 (Sy. x = 1.69), respectively. Temperature conversion factors provided by the kit manufacturer for human samples were determined to be inaccurate for converting results from rat samples. Analysis of components contributing to normal variation in rat serum 5'NT activity showed age and sex to be major factors. Increased serum 5'NT activity was observed in female rats when compared to male rats beginning at about 5 to 6 weeks of age. An analysis of variance of serum 5'NT, alkaline phosphatase, and GGT activities observed over a 9-week period in normal rats suggests several advantages for 5'NT as a predictor of biliary lesions in rats.     

Predicting the spatial distribution of ground flora on large domains using a hierarchical Bayesian model

Accomodation of important sources of uncertainty in ecological models is essential to realistically predicting ecological processes. The purpose of this project is to develop a robust methodology for modeling natural processes on a landscape while accounting for the variability in a process by utilizing environmental and spatial random effects. A hierarchical Bayesian framework has allowed the simultaneous integration of these effects. This framework naturally assumes variables to be random and the posterior distribution of the model provides probabilistic information about the process. Two species in the genus Desmodium were used as examples to illustrate the utility of the model in Southeast Missouri, USA. In addition, two validation techniques were applied to evaluate the qualitative and quantitative characteristics of the predictions.This revised version was published online in May 2005 with corrections to the Cover Date.     

Role of polymerase β in DNA metabolism and genomic instability

The major role of DNA polymerase β was thought to be limited in its involvement in short patch base excision repair by removing 5’-deoxyribose phosphate and base insertion. However, the recent researches indicate that polymerase β might take part in a wide spectrum of DNA metabolism reactions, including long patch base excision repair, DNA replication, recombination, meiosis and transleisional DNA synthesis. Because of its wide and important cellular function, an inappropriate intracellular polymerase β level might be associated with genomic instability. Down-regulation or mutation of polymerase β is mutagenic due to deficient in DNA repair, while overexpression of this error-prone β polymerase might perturb the normal function of other accurate polymerases and cause genomic instability as well.