共查询到20条相似文献，搜索用时 31 毫秒
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1/4>( )>1/5,这类题目常见。一些资料都是把分数化成同分母分数或是同分子分数进行比较,然后得出答案。这种解法学生虽然能够理解和掌握,但较麻烦,特别是要填的空多了就更麻烦。 这里介绍一种既简便,又容易被学生理解和掌握的方法。如: 相似文献
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小学《数学》第十册第１２０页有这样一道真空题： 。一般人们常用的是下面两种解法。 解法１：先化成同分母分数,将 与 通分,取公分母４０,则 ＝ , ＝ ,取中间数 ,定有 ＞ ＞ 。解法２：先化成同分子分数： ＝ , ＝ ,取中间数 ,定有 ＞ ＞ 。 除以上两种一般解法外,我还总结出下面几种方法,并且比较简便。 解法１：取 与 的平均数,得 （ ＋ ）÷２＝ × ＝ ＞ ＞ 解法２：把分数化成小数,得： ＝０．０５, ＝０．２,取０．２４,必有 ＞０． ２４＞ 。 因为０．２４＝ ,所以 ＞… 相似文献
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M. G. Narasimhan 《Resonance》2011,16(6):529-539
Damodar Dharmananda Kosambi (1907–1966) was an eminent mathematician, scientist, innovative Marxist, a maverick scholar, and
historian of contemporary India. Combining both versatility and a certain sense of virtuosity Kosambi made seminal contributions
to a wide variety of disciplines spread across from pure and applied mathematics to archaeology and Indology. In the course
of these writings he provided an incisive analysis of various developments in science and technology and novel perspectives
onmany topics related to mathematics (especially in number theory and statistics), genetics and India’s past history, present
concerns, and future growth. 相似文献
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When it was first enunciated, Ehrenfest’s Theorem provided a necessary and important link between classical mechanics and
quantum mechanics. Today, the content of the theorem is understood to be a natural and immediate consequence of the equation
of motion for operators when quantum mechanics is formulated in the Heisenberg picture. Nevertheless, the theorem leads to
useful approximations when systems with Hamiltonians of higher than quadratic order in the dynamical variables are considered.
In this two-part article, we use it to provide a convenient illustration of the differences between so-called classical and
nonclassical states of radiation. 相似文献
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MicroRNAs (miRNAs or miRs) are endogenous non-coding RNAs that negatively regulate gene expression by binding to the 3′ non-coding regions of target mRNAs, resulting in their cleavage or blocking their translation. miRNAs may have an impact on cell differentiation, proliferation, and survival, and their deregulation can be inclined to diseases and cancers, including thyroid tumors. The purpose of this review is to summarize the existing findings of deregulated miRNAs in different types of thyroid tumors and to exhibit their potential target genes, especially to demonstrate those involved in tumor invasion and metastasis. In addition, new findings of circulating miRNA expression profiles, single nucleotide polymorphism (SNP) in thyroid tumors, and the correlation of somatic mutations with deregulated miRNA expression in thyroid tumors were all included in this review. 相似文献
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设计理念:这是一节学习辅音字母P音标读音的语音课。主要围绕/P/的正确发音和在字母中的不同位置展开,使学生能够看到字母P时,就会对应其发音/P/,听到/P/时,能写出字母P。为了顺利完成以上教学目标,更好地突出重点,突破难点,在整个 相似文献
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Evolution of Surface Oxide Film of Typical Aluminum Alloy During Medium-Temperature Brazing Process简 总被引：1，自引：0，他引：1
The evolution of the surface oxide film along the depth direction of typical aluminum alloy under medium-temperature brazing was investigated by means of X-ray photoelectron spectroscopy （XPS）. For the alloy with Mg content below 2.0wt%, whether under cold rolling condition or during medium-temperature brazing process, the en-richment of Mg element on the surface was not detected and the oxide film was pure Al2O3. However, the oxide film grew obviously during medium-temperature brazing process, and the thickness was about 80 nm. For the alloy with Mg content above 2.0wt%, under cold rolling condition, the original surface oxide film was pure Al2O3. However, the Mg element was significantly enriched on the outermost surface during medium-temperature brazing process, and MgO-based oxide film mixed with small amount of MgAl2O4 was formed with a thickness of about 130 nm. The alloy-ing elements of Mn and Si were not enriched on the surface neither under cold rolling condition nor during medium-temperature brazing process for all the selected aluminum alloy, and the surface oxide film was similar to that of pure aluminum, which was almost entire Al2O3. 相似文献
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这是一节学习辅音字母P音标读音的语音课。主要围绕／P／的正确发音和在字母中的不同位置展开,使学生能够看到字母P时,就会对应其发音/P／,听到／P／时,能写出字母P。为了顺利完成以上教学目标,更好地突出重点,突破难点,在整个教学过程中,教师引导学生通过观察、思考、发现、归纳、 相似文献
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Hypersonic vehicles subjected to strong aerodynamic forces and serious aerodynamic heating require more stringent design for an infrared window. In this paper, a finite element analysis is used to present the distributions of thermal and stress fields in the infrared window for hypersonic vehicles based on flowfield studies. A theoretical guidance is provided to evaluate the influence of aerodynamic heating and forces on infrared window materials. The aerodynamic heat flux from Mach 3 to Mach 6 flight at an altitude of 15 km in a standard atmosphere is obtained through flowfield analysis. The thermal and stress responses are then investigated under constant heat transfer coefficient boundary conditions for different Mach numbers. The numerical results show that the maximum stress is higher than the material strength at Mach 6, which means a failure of the material may occur. The maximum stress and temperatures are lower than the material strength and melting point under other conditions, so the material is safe. 相似文献
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The separation of ternary methanol/methyl butyl ether/1-butylchloride mixtures was investigated, which are the main components of the waste liquid. After preliminary studies on the ternary system, the integrated process of extraction and distillation was put forward to separate the ternary system. The results show that methanol carl be removed from the mixtures by extraction using water as the extracting agent. Through distillation of extract and dried raffinate respectively, methanol, methyl butyl ether and 1-butylchloride can be separated and recovered. In addition, the optimal volume for the extracting agent and effects of reflux ratio on the yield of product were also studied. The optimal volume ratio of the extracting agent to material is 1： 3.5, and the yield of the product increases with the increase of reflux ratio. 相似文献
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A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four curved surfaces formed from thin sheets of composite materials connected by hinges along the edges, and the reflective surface is provided by the front surface. The edge profiles of connecting lines were obtained through geometric analysis. A scaled model, including design and manufac- ture, was demonstrated to validate the process from the folded state to the fully deployed state. The non-contact synchronous vision measuring method was used to test the basic frequency of the scaled model, and the test results gave the verification of the analyses. Compared with the existing unidirectional deployable antenna, this new type of bidirectional deployable antenna can be applied to larger-size antennas and has better performance because the glass-woven tape connections were substituted with more reliable hinges. Static, modal, harmonic response, and transient response analyses of the full-sized reflector structure were mod- eled with the commercial finite element （FE） package ABAQUS. The modeling techniques were developed to predict the struc- tural dynamic behavior of the reflector and the results showed that the first natural frequency was 0.865 Hz, and the reflector structure had good stiffness in three directions. This proposed structure has very high stiffness-to-mass ratio because of its hollow solid construction. A preliminary simulation of radiation properties of the parabolic cylindrical antenna, fed by an off-set linear feed horn array, was conducted to obtain the radiation pattern of the feed and the reflector. 相似文献
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The copolymerization of CO and styrene catalyzed by Pd/C toward the formation of polyketones(PK)was studied in the N-valeronitrile-N'-methylimidazolium hexafluorophosphate([C4CNmim]+PF-6) medium. The synthesized PK was characterized by Fourier transform infrared(FTIR), elemental analysis, 13C-nuclear magnetic resonance(13C-NMR), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and gel permeation chromatography(GPC). The supported ionic liquid film on the surface of Pd/C catalyst can prevent the products from covering the hole of active carbon due to its chemical stability and weak coordination ability with metal ions, and thus efficiently improve the catalytic activity. The effects of different amounts of ionic liquid on the catalytic activity and reusability of the catalyst and the molecular weight of PK were discussed. When the usage of ionic liquid is 10wt%(0.1 g ionic liquid / 1 g active carbon carrier) and the theoretical content of Pd2+ is 5wt%(0.05 g Pd2+/ 1 g active carbon carrier), the highest catalytic activity 2 963.64 gSTCO/(gPd·h) is achieved with the molecular weight and polydispersity index of PK as Mn=9 684, Mw=13 452 and Mw /Mn=1.389. 相似文献