共查询到20条相似文献，搜索用时 62 毫秒
1.
本文采用微分方程的李群方法，研究了外噪声影响下的Ｓｃｈｌｏｇｌ二级相变模型对应的Ｆ－Ｐ几率密度Ｐ（ｘ，ｔ）的严格表达式；讨论了最可几值ｘ随时间的变化。在时间ｔ→∞时，给出了几率密度的定态解Ｐｓｔ（ｘ）以及此时的最可几值ｘ与确定性描述的区别。 相似文献
2.
本文采用微分方程的李群方法,求解了外噪声影响下的非平衡二级相变模型对应的F—P方程,得出含时概率密度P（x.t）的严格表达式,讨论了最概然值x随时间的变化。在时间t→∞时,给出概率的定态解Pst(x)以及此时的最概然值;得出了它与确定性描述的差别。 相似文献
3.
水平基因转移与物种演化 总被引：2，自引：0，他引：2
周国庆 《湖州师范学院学报》2003,25(3):66-70
遗传学、基因组学和生物信息学业已证明，由病毒、类病毒、质粒等介导的细胞、个体和物种之间的水平基因转移广泛地存在于细菌、古生菌和真核生物中，水平基因转移可能造成同一生境中物种分化的抑制，种群的快速协同进化，不同物种的趋同进化、返祖遗传、获得性状(基因)遗传和家族成员的性状趋同等。因此，水平基因转移是物种进化的一个重要驱动力。 相似文献
4.
Two ancient rounds of polyploidy in rice genome 总被引：10，自引：0，他引：10
An ancient genome duplication (PPP1) that predates divergence ofthe cereals has recently been recognized. We report here another potentially older large-scale duplication (PPP2) event that predates monocot-dicot divergence in the genome of rice(Oryza saliva L.), as inferred from the age distribution of pairs of duplicate genes based on recent genome data for rice. Our results suggest that paleopolyploidy was widespread and played an important role in the evolution of rice. 相似文献
5.
An ancient genome duplication (PPP1) that predates divergence of the cereals has recently been recognized. We report here another potentially older large-scale duplication (PPP2) event that predates monocot-dicot divergence in 相似文献
6.
In order to share multimedia transmissions in mesh networks and optimize the utilization of network resources, this paper presents a Two-stage Evolutionary Algorithm （TEA）, i.e., unicast routing evolution and multicast path composition, for dynamic multicast routing. The TEA uses a novel link-duplicate-degree encoding, which can encode a multicast path in the link-duplicate-degree and decode the path as a link vector easily. A dynamic algorithm for adding nodes to or removing nodes from a multicast group and a repairing algorithm are also covered in this paper. As the TEA is based on global evaluation, the quality of the multicast path remains stabilized without degradation when multicast members change over time. Therefore, it is not necessary to rearrange the multicast path during the life cycle of the multicast sessions. Simulation results show that the TEA is efficient and convergent. 相似文献
7.
欧阳国亮 《桂林师范高等专科学校学报》2012,26(3):14-18
古入声在方言中的分化一直是方言界十分关注的问题,它对方言音韵比较研究及方言归属都具有积极意义。桂阳土话作为湘南土话的一部分,在入声的发展演变上有自己的一些特点。通过比较研究,桂阳土话入声分化的类型有四种:敖泉型、流峰型、燕塘型、荷叶型。 相似文献
8.
李杰 《廊坊师范学院学报》2012,28(3):37-39
＂针＂的古字＂箴＂与＂鍼＂在《说文解字》中有音同义近的现象,部分典籍中也提及＂箴＂与＂鍼＂字的同源关系,但辅证的资料极为匮乏。随着科技文化的发展,考古发现、古代文献典籍的整理以及现代研究成果,已经为＂针＂与＂箴＂和＂鍼＂的流变与替换提供了丰富的材料,＂针＂字的流变过程是汉字承载中国文化的典型代表。 相似文献
9.
Copy number variants (CNVs) are pieces of genomic DNA of 1000 base pairs or longer which occur in a given genome at a different frequency than in a reference genome. Their importance as a source for phenotypic variability has been recognized only in the last couple of years. Chromosomal deletions can be seen as a special case of CNVs where stretches of DNA are missing in certain lines when compared to the reference genome of the mouse line C57BL/6, for example. Based upon more than 8 million single nucleotide polymorphisms (SNPs) in the fifteen inbred mouse lines which were determined in a whole genome chip based resequencing project by Perlegen Sciences, we detected 20166 such long chromosomal deletions. They cover altogether between 4.4 million and 8.8 million base pairs, depending on the mouse line. Thus, their extent is comparable to that of SNPs. The chromosomal deletions were found by searching for clusters of missing values in the genotyping data by applying bioinformatics and biostatistical methods. In contrast to isolated missing values, clusters are likely the consequence of missing DNA probe rather than of a failed hybridization or deficient oligos. We analyzed these deletion sites in various ways. Twenty-two percent of these deletion sites overlap with exons; they could therefore affect a gene's functioning. The corresponding genes seem to exist in alternative forms, a phenomenon that reminds of the alternative forms of mRNA generated during gene splicing. We furthermore detected statistically significant association between hundreds of deletion sites and fat weight at the age of eight weeks. 相似文献
10.
新取代苯并冠醚的合成 总被引：2，自引：0，他引：2
张来新 《安阳师范学院学报》2001,(5):13-14
以多聚磷酸(PPA)为催化剂和反应溶剂，氯乙酸为酰化剂，对苯并-12-冠-4进行酰化，成功地合成了氯乙酰取代苯并-12-冠-4。产物由IR、MS和元素分析鉴定了其结构。 相似文献
11.
清代训诂巨著《经籍纂诂》是今人阅读古籍的必备工具书。然今人诸多论及此书的著作多将书名中的“纂”误作“纂”。从历史演变渊源来看,“纂”与“撰”同,有创作义。“纂”为“缵”之假借,乃汇集义。“籑”与“纂”二字在原始义、语法义、比喻义诸方面存在显著区别,因此《经籍纂诂》使用“纂”是不宜替代的。 相似文献
12.
María Domínguez Maria-José Vieira 《Assessment in Education: Principles, Policy & Practice》2012,19(4):393-409
The aim of this study is to assess the impact of PISA (Programme for International Student Assessment) on international scientific journals. A bibliometric analysis was conducted of publications included in three main scientific publication databases: Eric, EBSCOhost and the ISI Web of Knowledge, from 2002 to 2010. The paper focused on four main questions: who carried out these studies, in which academic journals have the articles been published, what has been the evolution of these publications and what were the main article topics? The study concludes that PISA has had a considerable impact on the scientific research, reflected primarily by university-based authors from the areas of education and social sciences analysing student performance. The evolution since 2007 seems to indicate that more articles will be published in coming years through the initiative of researchers (rather than the editorial boards), even from other scientific areas, thus increasing the number of topics of analysis. 相似文献
13.
With the rapid growth of service scale, there are many services with the same functional properties but different non-functional
properties on the Internet. There have been some global optimizing service selection algorithms for service selection. However,
most of those approaches cannot fully reflect users’ preferences or are not fully suitable for large-scale services selection.
In this paper, an ant colony optimization (ACO) algorithm for the model of global optimizing service selection with various
quality of srevice (QoS) properties is employed, and a user-preference based large-scale service selection algorithm is proposed.
This algorithm aims at optimizing user-preferred QoS properties and selecting services that meet all user-defined QoS thresholds.
Experiment results prove that this algorithm is very efficient in this regard. 相似文献
14.
Josef Guggemos Sabine Seufert Stefan Sonderegger 《British journal of educational technology : journal of the Council for Educational Technology》2020,51(5):1864-1883
This study investigates the acceptance of social robots by higher education students in the social sciences. Pepper, a humanoid social robot from SoftBank Robotics, provided a sample of its capabilities during a first semester, large-scale, university course, “Introduction to academic writing.”From this course, 462 freshmen participated in our survey. The unified theory of acceptance and use of technology (UTAUT) acts as the conceptual framework, and partial least squares structural equation modelling (PLS-SEM) as the method for data analysis. The four perceived characteristics—trustworthiness, adaptiveness, social presence and appearance—all predict the intention to use the robot for learning purposes; anxiety regarding making mistakes in handling the robot and about privacy issues are not significant predictors. An importance-performance map analysis indicated adaptiveness as the robot’s most important characteristic for predicting student behavioural intention. Overall, however, the study shows that students do not have the intention to rely on social robots for learning purposes at the current level of state-of-the-art technology: behavioural intention reaches only 36.6% of the theoretical maximum. 相似文献
15.
刘德华 《南阳师范学院学报》2005,4(12):111-113
在高校公共体育课乒乓球选项课教学中，同质搭配和异质搭配练习有着特殊的意义和作用，它能培养兴趣，充分发挥个性，扩大学生之间的信息交流，使得体育教学实现因材施教，教学效果明显提高。 相似文献
16.
17.
This study assessed the representations of nature of science (NOS) in high school chemistry textbooks and the extent to which these representations have changed during the past four decades. Analyses focused on the empirical, tentative, inferential, creative, theory‐driven, and social NOS, in addition to the myth of “The Scientific Method,” the nature of scientific theories and laws, and the social and cultural embeddedness of science. A total of 14 textbooks, including five “series” spanning one to four decades, were analyzed. The textbooks commanded significant market shares in the United States and were widely used in some of the most populace states. Relevant textbook sections were scored on each of the target NOS aspects on a scale ranging from −3 to +3, which reflected the accuracy, completeness, and manner (explicit versus implicit) in which these aspects were addressed. The textbooks fared poorly in their representations of NOS. Additionally, with a few exceptions, textbook scores either did not change or decreased over the past four decades. These trends are incommensurate with the discourse in national and international science education reform documents, which has witnessed an increasing emphasis on the centrality of NOS to scientific literacy and pre‐college science education during the same time period. Assessment and evaluation strategies, and policies need to be targeted if substantial and desired changes in the ways NOS is addressed in science textbooks are to be effected. © 2008 Wiley Periodicals, Inc. J Res Sci Teach 45: 835–855, 2008 相似文献
18.
Type-dependent differential expression of neuropeptide Y in chicken hypothalamus （Gallus domesticus）
Chen GQ Hu XF Sugahara K Chen JS Song XM Zheng HC Jiang YQ Huang X Jiang JF Zhou WD 《Journal of Zhejiang University. Science. B》2007,8(11):839-844
Neuropeptide Y (NPY) is one of the most important orexigenic agents in central regulation of feeding behavior, body weight and energy homeostasis in domestic chickens. To examine differences in the hypothalamic NPY between layer-type and meat-type of chickens, which are two divergent kinds of the domestic chickens in feeding behavior and body weight, we detected mRNA levels of NPY in hypothalamic infundibular nucleus (IN), paraventricular nucleus (PVN) and lateral hypothalamic area (LHA) of these two types of chickens using one-step real time RT-PCR. The meat-type chicken had more food daily (about 1.7 folds) and greater body weights (about 1.5 folds) and brain weights than the layer-type chicken at the age of 14 d. In the meat-type of chicken, NPY mRNA levels of the IN and PVN were significantly greater than those of the LHA, and were not significantly different between the IN and PVN. However, in the layer-type of chicken, NPY mRNA levels were significantly greater in the IN than those in the LHA and PVN, and were not significantly different between the PVN and LHA. In all these hypothalamic regions, the layer-type of chicken had significantly higher NPY mRNA levels than the meat-type chicken did. These results suggest the expression of NPY in the hypothalamus has a type-dependent pattern in domestic chickens. 相似文献
19.
李春青 《北京师范大学学报(社会科学版)》2019,(4):46-55
"中"是儒学核心范畴之一,集中体现着儒家士人政治诉求和道德理想,也表征着儒学中的哲学之维。作为对君权的要求与约束,它具有政治性;作为儒家士人所追求的人格理想,它是一种道德境界;作为能使"天地位焉,万物育焉"的"大本"与"达道",它又具有哲学本体意味。但在具体的历史语境中,"中"的语义并不尽相同,一般而言,在先秦子学时代,"中"既有政治含义,也有伦理道德与哲学本体论的意义,在两汉的经学语境中侧重于政治规范意义,到了宋明时期则更多地成为一种道德哲学的概念,而在晚明的何心隐那里又重新成为一种直接指向君主的政治话语。"中"概念的意义演变与儒家士人与君权的关系以及他们的自我认同密切相关。 相似文献
20.
朱俊林 《湖南师范大学社会科学学报》2008,37(4):27-31
转基因技术是现代科技发展的前沿领域,它的出现在给人类带来福祉的同时,也会给自然生态环境造成不良的影响。正因为如此,人类中心主义和自然中心主义对转基因技术及其应用持不同的伦理立场——支持或否定。当然,两者都没有足够的理由。要摆脱这一困境,有必要超越人类中心主义和自然中心主义,建构一种新的自然观。这种新自然观的基本立场是：立足于人类是自然大家庭中的成员这一科学事实,把人类的活动纳入自然演化的一个重要环节来加以考察,同时充分考虑到人类活动的自由自觉性特点。尊重自然和尊重人类权利两者的有机结合,是我们对待转基因技术及其应用所应持的基本的伦理维度。 相似文献