共查询到19条相似文献，搜索用时 578 毫秒
1.
综合气象干旱指数(Ci指数)是以标准化降水指数、湿润度指数及近期降水量为基础,同时考虑了降水和潜在蒸散两项因子而设计的干旱指标。通过对衡阳市各区域1960—2012年逐日Ci指数统计,运用非参数Mann-Kendall检验(MK检验),分析了近53年来Ci指数的年代际、年及季节变化特点。结果表明:衡阳市干旱日、重旱日及特旱日出现频率分别为24.6%、3.1%和1.2%,其中有94.3%和77.4%年份出现了重、特旱日,进入21世纪以后,特旱日出现频率略有增大;Pd值在冬、夏季呈减少变化,而在春、秋季则有增大趋势,且在Pd值较高的季节,其倾向率增大(减小)更为明显;Pd值在8～9月达到高点,而Pz和Pt则在10～11月达到较高水平,9月份Pz、Pt偏低是由于8月降水较7月偏多所致。 相似文献
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为了有效控制陀螺驱动模态的工作状态,从原理上分析了微机械陀螺的驱动特性,提出了一个新型的微机械陀螺闭环驱动数字控制电路,即采用数字锁相环和自动增益控制方法分别控制驱动频率和振荡幅度.设计了带有现场可编程门阵列的数字处理电路,并进行了实验.结果表明:当温度变化时,驱动频率能够自动跟踪陀螺驱动模态的谐振频率,并且振荡幅值始终保持在设定值.在常温下驱动频率相对偏差为0.624×10-6,振荡幅值相对偏差为8.0×10-6,分别是模拟控制方案的0.094%和18.39%.因此,基于数字锁相环和自动增益控制的频率和幅值闭环驱动控制方案是可行的. 相似文献
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以风干野草香茎、叶、花序为供体,种子为受体,研究了野草香地上部器官水浸液的自毒作用.采用A×B=3×5二因素完全随机试验设计,室内生物测定法,测定了受体的发芽势、发芽指数、发芽率、成苗率、胚轴长度、胚根长度6项指标,并计算化感效应指数和化感综合效应(SE).结果表明:A因素(野草香的地上器官叶、花序、茎)3个水平的SE值分别为-0.52、-0.64、-0.61,表现出叶>花序>茎的自毒作用强弱顺序;B因素(供体水浸液的浓度)5个水平的SE值分别为0、-0.18、-0.78、-0.99、-1.00,说明随供体水浸液浓度的升高自毒作用增强;受体6项指标的SE值分别为-0.53、-0.58、-0.58、-0.59、-0.54、-0.73,表明供体对受体6项指标的自毒作用强弱顺序为胚根长度>成苗率>发芽指数=发芽率>胚轴长度>发芽势. 相似文献
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在B3LYP/6-31G理论水平上对环氧乙烷、乙烯和乙醛分子进行了构型优化,计算了三个分子在Titan大气条件下的频率、绘制分子的红外振动光谱.对环氧乙烷分子的红外振动频率进行了理论归属,与Titan大气模拟实验的结论相比较,发现量子化学理论计算结果与模拟实验结果基本一致,而且,量子化学理论计算结果与环氧乙烷红外光谱的实验值也符合较好.并进一步分析比较了与环氧乙烷分子的红外谱线很相似的乙烯分子的谱带特征和频率归属以及环氧乙烷的异构体乙醛分子的谱带特征和频率归属.结果表明Titan大气中存在环氧乙烷分子的可能性是很大的. 相似文献
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对 2 67例湖南侗族正常人的鼻部进行了 1 1项观察和 4项测量研究 计算了鼻指数 ,并按鼻指数划分鼻型 ,表明湖南侗族以中鼻型为主 对鼻高度值与鼻宽度值列出了综合表 ,根据此表将鼻分为 9种类型 ,其中低窄型是一种最常见、最理想的鼻型 相似文献
6.
慕泽刚 《数学爱好者(高二版)》2007,(4)
解答与二项展开式的项的系数有关的问题,常规的解法是根据(a b)n的二项展开式的通项公式Tr 1=Cnran-rbr,整理为有关字母的指数形式,再令指数为满足条件的次数,求出r的值进行解答.但其过程 相似文献
7.
对267例湖南侗族正常人的鼻部进行了11项观察和4项测量研究，计算了鼻指数，并按鼻指数划分鼻型，表明湖南侗族以中鼻型为主，对鼻高度值与鼻宽度值列出了综合表，根据此表将鼻分为9种类型，其中低窄型是一种最常见、最理想的鼻型。 相似文献
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文章对含源项一维非定常对流扩散方程进行分析.对微分方程进行半离散,对半离散后的方程作指数变换消去一阶对流项,构造变换后方程的一种2m阶(m为任意正整数)的指数型差分格式,作指数变换的逆变换得到原一维非定常对流扩散方程的2m阶指数型差分格式.分析此格式的稳定性,用数值例子验证提出格式的有效性. 相似文献
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以＂晋燕14号＂裸燕麦为研究对象,进行人工盆栽,在第四子叶期进行生长指标测量,对其苗期叶片进行抗旱性研究。测定裸燕麦幼苗叶片在干旱胁迫下叶绿素含量、电导率、游离脯氨酸含量、株高、干重以及鲜重的变化情况。结果表明,与对照组相比,在干旱胁迫条件下,裸燕麦的电导率逐渐上升,叶绿素a、叶绿素b和叶绿素a＋b含量具有上升的趋势,游离的脯氨酸含量也逐渐上升,但其株高和鲜重以及干重却呈下降趋势。因此对叶片的叶绿素含量、电导率、游离脯氨酸的测定可以作为裸燕麦抗旱鉴定的生理生化指标。 相似文献
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研究了0、0.15,0.20和0.25 mg/L HgCl2溶液0、1、2、48、d对黄鳝外周血红细胞微核及白细胞的影响.结果表明,不同暴露时间、不同浓度的Hg2 不同程度地引起黄鳝红细胞微核率和核异常率等遗传指标的上升,并引起白细胞数量及各类白细胞比例的变化,与对照组相比几乎都达到显著差异(p<0.05)或极显著差异(p<0.01). 相似文献
13.
Dixie Lee Charbonneau-Lyons Pearl M. Mosher-Ashley Meredith Stanford-Pollock 《Educational gerontology》2013,39(10):823-833
This study compared opinions of successful aging among college students and older independent-living adults. Participants were 226 undergraduate students, 44 graduate students, and 59 independent-living older adults subjects. The participants were asked to rate the level of importance of 29 items in relation to their contribution to successful aging. The 29 items were divided into seven categories. Social and familial relationships, intrinsic values, financial concerns, accomplishments, and cognitive functioning were viewed as contributing the most to successful aging. Independence was reported to be somewhat important, while physical appearance was reported as being least important. There were few differences between how young and old viewed successful aging. Only the categories of financial concerns and physical appearance showed age-related differences, with older adults attributing a higher level of importance to financial concerns and physical appearance than did the younger participants. 相似文献
14.
吴澎 《河南师范大学学报(哲学社会科学版)》2005,32(5):186-187
大学作为人类精神家园的象征,其空间形态和内涵因社会需求的变化而被不断地赋予新的内容。是大学理念变革的反映。本文回顾了大学校园规划理念的演进。分析了新形势下校园规划建设的思路与创新,结合近年来我国高校校园规划建设的经验,总结了新老校园建设中应注意的事项,并给出相应的对策与建议。 相似文献
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评分趋中性现象的初步分析 总被引：1，自引：0，他引：1
DING Wen PEI Yun 《中国考试》2008,(8)
各类大型考试中的主观题由于题目要求灵活和考生答案多种多样,因此很难根据评分标准确保评分的准确性。利用网上评卷可以在某种程度上解决评分的误差问题,但仍发现存在着评分趋中性现象。本文通过对评分趋中性现象成因的分析,提出技术上进一步补充引入指标参数、不断完善评卷质量评价体系、系统中借鉴并设立评卷"外卡"机制等对策和措施,从而保证"个性化"评分的正常显现,减少"保险分",加强对评卷人员的人文关怀,充分发挥评卷人员的主观能动性,避免或减少趋中现象的发生,最终达到提高评卷准确性(有效度)的目的。 相似文献
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FRED PYRCZAK 《Journal of Educational Measurement》1973,10(3):227-231
Numerous writers have suggested that the discrimination index may be helpful in identifying faulty test items. The purpose of this study was to investigate systematically the validity of the index for this purpose. To attain this objective, two forms of an arithmetic-reasoning test were written. In each form, the items were designed to vary in quality with respect to nine item-writing principles, and on the basis of the responses of 364 examinees, a discrimination index was computed for each item. Next, the items were rated independently for quality by three judges who used a check list of the nine item-writing principles. The average of their ratings for each item was used as the criterion for determining the validity of the indices. The results indicate that the discrimination index is a moderately valid measure of item quality. The implications of this finding are discussed. 相似文献
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Bloom Filter算法是一种高效多哈希算法,它使用紧凑的数据结构以极小且可控的误差率表达一个数据集合,支持查询特定元素是否在集合中出现文中．基于Bloom Filter,针对元素出现频率呈重尾分布的特定集合,提出一种标记多重嵌套Bloom Filter（SMNBF）算法,采用带标记的多重嵌套方式存储集合中元素出现频率的信息．通过对算法的时间和空间复杂度以及误差比例的分析,结果显示该算法以较小计算代价和误差率,大幅减小计算所需的存储空间．将SMNBF算法应用于频率服从重尾分布的集合的实验结果表明,该算法在基本不改变计算误差的基础上,性能明显优于其他类似算法． 相似文献
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《The Journal of educational research》2012,105(6):313-315
AbstractIn an attempt to identify some of the causes of answer changing behavior, the effects of four tests and item specific variables were evaluated. Three samples of New Zealand school children of different ages were administered tests of study skills. The number of answer changes per item was compared with the position of each item in a group of items, the position of each item in the test, the discrimination index and the difficulty index of each item. It is shown that answer changes were more likely to be made on items occurring early in a group of items and toward the end of a test. There was also a tendency for difficult items and items with poor discriminations to be changed more frequently. Some implications of answer changing in the design of tests are discussed. 相似文献
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OBJECTIVE: To determine whether child maltreatment is associated with obesity in preschool children. METHODS: Data were obtained from the Fragile Families and Child Wellbeing Study, a birth cohort study of 4898 children born between 1998 and 2000 in 20 large US cities. At 3 years of age, 2412 of these children had their height and weight measured, and mothers answered items on the Parent-Child Conflict Tactics Scales about three types of child maltreatment--neglect, corporal punishment, and psychological aggression. The frequency of each type of maltreatment behavior in the prior year was analyzed using categories--ever/never for neglect and quintiles for the other two types of maltreatment. Child obesity was defined as measured body mass index (kg/m(2)) > or =95th percentile. RESULTS: Eighteen percent of the children were obese, and the prevalence of any episode of neglect, corporal punishment, and psychological aggression was 11%, 84%, and 93%, respectively. The odds of obesity were increased in children who had experienced neglect (odds ratio 1.56, 95% confidence interval, 1.14-2.14), after controlling for the income and number of children in the household, the mothers' race/ethnicity, education, marital status, body mass index, prenatal smoking, and age, and the children's sex and birth weight. Neither the frequency of corporal punishment nor psychological aggression was associated with an increased risk of obesity. CONCLUSIONS: In a sample of preschool children from 20 large US cities, maternal self-report of neglectful behavior was associated with an increased risk of childhood obesity, after controlling for birth weight, maternal obesity, and multiple socioeconomic factors. 相似文献