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Molecular data and methods have become centrally important to evolutionary analysis, largely because they have enabled global phylogenetic reconstructions of the relationships between organisms in the tree of life. Often, however, molecular stories conflict dramatically with morphology-based histories of lineages. The evolutionary origin of animal groups provides one such case. In other instances, different molecular analyses have so far proved irreconcilable. The ancient and major divergence of eukaryotes from prokaryotic ancestors is an example of this sort of problem. Efforts to overcome these conflicts highlight the role models play in phylogenetic reconstruction. One crucial model is the molecular clock; another is that of ‘simple-to-complex’ modification. I will examine animal and eukaryote evolution against a backdrop of increasing methodological sophistication in molecular phylogeny, and conclude with some reflections on the nature of historical science in the molecular era of phylogeny.  相似文献   
33.
《泪珠缘》是晚清典型的“仿红小说”,叙事艺术上采用家族———社会立体网络式结构,在故事情节上运用线式情节结构,在人物形象上也借鉴了《红楼梦》,并融合了晚清特有的时代特色,是一部优秀的家庭小说。  相似文献   
34.
Zhang  Xu  Liu  Jia  Chen  ChuangYe  Liu  Wei  Liu  JingBin  Li  BaoHui  He  Ming  Zhou  TieGe  Zhao  XinJie  Yan  ShaoLin  Fang  Lan 《科学通报(英文版)》2011,56(35):3884-3887
A new circuit model for designing and manufacturing an S-band low noise amplifier(LNA) with the software,Advanced Design System(ADS),is introduced in this paper.The proposed model involves shunted impedance at the grid to achieve a stable LNA without measuring the S-parameters of transistors at low temperatures.The LNA was measured over the operation band of 2.2-2.3 GHz,which has input and output standing wave ratios below 1.2.The noise figure of the manufactured LNA was about 0.2 dB and the gain was above 22 dB,which indicated that our LNA worked well at 77 K.  相似文献   
35.
笛卡尔的解析几何与欧几里得的《几何原本》在点、线和空间等基本概念上有较大差异。相对于《几何原本》:解析几何中的点可相互区分,且依赖于与其它点的关系而存在;曲线的存在依赖坐标空间整体,同时是点的运动轨迹,与物理运动的可能路径相关;坐标系通过量化空间,提供了对于空间的完整构造。从图形实体到几何存在,是笛卡尔对于数学实在和存在方式所作的区分。  相似文献   
36.
Many types of experiments have been recognized in the literature. One important type we discuss in this article is the orientation experiment. While orientation experiments are like other types of experiments in that they are tests for causal relevance, they also have other qualities. One important (but not the only) goal of these experiments is to offer a rough, qualitative characterization of the mechanism responsible for a capacity of interest, effectively constraining future research. This makes them particularly useful during the early stages of investigation, when an explanandum-phenomenon has just been identified and several (often competing) hypotheses as to the qualitative character of the mechanism responsible for it are proposed. We illustrate our claims, and explicate a number of additional aims that orientation experiments can sometimes serve, by considering three case studies from different era's, namely the discovery of the mechanisms responsible for i) the capacity of eels to produce numbing sensations (17th and 18th century), ii) puerperal fever in Semmelweis' Vienna Maternity Hospital (19th century), and iii) the capacity of pigeons to home (20th century).  相似文献   
37.
现代工笔人物画造型大多采用西方素描再现方法,而忽视了我国传统绘画的意象表现,本文从绘画理论和美学思想方面入手,探讨了我国工笔人物传统绘画重意轻形的美学理念,我们只有对传统文化深入了解,才能真正做到对我国绘画艺术的创新和发展。  相似文献   
38.
In natural kind debates, Boyd's famous Homeostatic Property Cluster theory (HPC) is often misconstrued in two ways: Not only is it thought to make for a normative standard for natural kinds, but also to require the homeostatic mechanisms underlying nomological property clusters to be uniform. My argument for the illegitimacy of both overgeneralizations, both on systematic as well as exegetical grounds, is based on the misconstrued view's failure to account for functional kinds in science. I illustrate the combination of these two misconstruals with recent entries into the natural kind debate about emotions. Finally, I examine and reject Stich's “Kornblith-Devitt method” as a potential justification of these misconstruals.  相似文献   
39.
This paper examines the justification for the hypothesis of extended cognition (HEC). HEC claims that human cognitive processes can, and often do, extend outside our head to include objects in the environment. HEC has been justified by inference to the best explanation (IBE). Both advocates and critics of HEC claim that we can infer the truth value of HEC based on whether HEC makes a positive or negative explanatory contribution to cognitive science. I argue that IBE cannot play this epistemic role. A serious rival to HEC exists with a differing truth value, and this invalidates IBEs for both the truth and the falsity of HEC. Explanatory value to cognitive science is not a guide to the truth value of HEC.  相似文献   
40.
The considerations set out in the paper are intended to suggest that in practical contexts predictive power does not play the outstanding roles sometimes accredited to it in an epistemic framework. Rather, predictive power is part of a network of other merits and achievements. Predictive power needs to be judged differently according to the specific conditions that apply. First, predictions need to be part of an explanatory framework if they are supposed to guide actions reliably. Second, in scientific expertise, the demand for accurate predictions is replaced with the objective of specifying a robust corridor of estimates. Finally, it is highly uncertain to predict the success of research projects. The overall purpose of the paper is to enlarge the debate about predictions by addressing specifically the roles of predictions in application-oriented research.  相似文献   
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