電是什么?

在大自然中,電以形形色色的姿態出現。其中最顯著、最普遍的,就是閃電。鄰近北極地帶(如蘇聯的北方)的居民很熟悉這些雄偉的現象:有時候,在夜間的天空上出現了紅、紫、黄、綠各種顏色的寬闊的、明亮的帶子。它們形成火燄般的帷幕,它們離奇地捲起而又展開。這是“北極光”,它的產生就是由於電。在高山上,當空氣相當乾燥的時候,可以看到“電光”。它們表現爲在金屬物體的尖端上的小小的火燄。古     

等待胜利

阿拉斯加湾将会复原，但是复原速速度不会太快。今年3月24日凌晨，埃克森公司的瓦尔德兹号油轮运载着120万桶原油驶向公海，在威廉王子湾的暗礁上搁浅，而阿拉斯加湾从那时起要从生态恶梦中恢复过来得花多长时间呢?该地区的动植物是否能够恢复其原有面貌呢?     

令人窒息的飞行竞赛

这是世界上速度最快、最富有激情的运动。比赛过程可能只持续几分钟．但选手在场下所付出的艰辛却是我们难以想象的。     

西点怎样培养领导者?

美国西点陆军学校一向以培养最优秀的领导人才为己任。西点自1802年创校以来,建立了一套独特的教学体系,为国家社会栽培最杰出的领导人才。西点的独特之处是"教给人品德。"一个有品德的领导人,具有一般领导人物所应具有的特质、     

爱因斯坦在长岛的那个夏天

1939年夏天,爱因斯坦到位于纽约东部的长岛度假.而我的祖父--大卫·罗斯曼,在那里经营着罗斯曼百货公司.6月的一天,爱因斯坦走进店里.尽管祖父一眼就认出了他,但还是把他当作一名普通顾客对待.     

德国的大学和科学

你们已经听说我是一个数学家。我的兴趣一直集中于科学本身，而不是它的科学机构和科学组织。不过，今晚我要谈的主要内容是关于德国的大学和科学研究机构，所以我恳求诸位理解我不是谈论这一主题的专家。我是通过我     

Newborn irritability moderates the association between infant attachment security and toddler exploration and sociability

This longitudinal investigation of 84 infants examined whether the effect of 12-month attachment on 18- and 24-month exploration and sociability with unfamiliar adults varied as a function of newborn irritability. As expected, results revealed an interaction between attachment (secure vs. insecure) and irritability (highly irritable vs. moderately irritable) in predicting both exploration and sociability with unfamiliar adults. For exploration, results supported a dual-risk model; that is, toddlers who had been both highly irritable and insecurely attached were less exploratory than other toddlers. For sociability, results supported the differential-susceptibility hypothesis; that is, highly irritable infants, compared to moderately irritable infants, were both less sociable as toddlers when they had been insecurely attached and more sociable when they had been securely attached.     

A longitudinal examination of African American adolescents' attributions about achievement outcomes

Developmental, gender, and academic domain differences in causal attributions and the influence of attributions on classroom engagement were explored longitudinally in 115 African American adolescents. In Grades 8 and 11, adolescents reported attributions for success and failure in math, English and writing, and science. In Grade 11, English and mathematics teachers rated students' classroom engagement. Boys were more likely than girls to attribute math successes to high ability and to attribute English failures to low ability. Both genders' ability attributions for math became more negative from eighth to eleventh grades. Grade 8 attributions of math failure to lack of ability were negatively related to Grade 11 math classroom engagement. Results illustrate the gendered nature of motivational beliefs among Black youth.     

Dynamic and static assessment of phonological awareness in preschool: a behavior-genetic study

The genetic and environmental overlap between static and dynamic measures of preschool phonological awareness (PA) and their relation to preschool letter knowledge (LK) and kindergarten reading were examined using monozygotic and dizygotic twin children (maximum N = 1,988). The static tests were those typically used to assess a child's current level of PA such as blending and elision, and the dynamic test included instruction in phoneme identity to assess the child's ability to respond to this instruction. Both forms were influenced by genes and by shared and nonshared environment. The static and dynamic versions were influenced by the same genes, and part of the total genetic influence was shared with LK. They were subject to both overlapping and independent shared environment influences, with the component in common also affecting LK. Nonshared environment influences were mostly independent. Scores from dynamic assessment added only minimally to variance explained in kindergarten reading after LK and static assessment had been factored in. Although one of the genetic factors that influenced both forms of PA also affected kindergarten reading, it was only the one shared with LK. The authors conclude that dynamic assessment of PA in preschool offers little advantage over the more commonly used static forms, especially if LK scores are available, although they acknowledge its potential in cases of preschool educational disadvantage.