科技英語(yǔ)入門

內(nèi)容概要

本教材共分10單元，內(nèi)容包含數(shù)學(xué)、物理學(xué)、生物學(xué)、化學(xué)、通信、電子、計(jì)算機(jī)及機(jī)械等理工科題材。 本教材最大的特色就是在口語(yǔ)方面做了較多嘗試，編者在每章都配備了針對(duì)本單元主題和文章內(nèi)容的口語(yǔ)題目，供老師在上課時(shí)選擇性進(jìn)行師生、生生等口語(yǔ)交流練習(xí)。

書籍目錄

Unit One Mathematics and PhysicsUnit Two Computer SoftwareUnit Three Computer NetworksUnit Four Analog ElectronicsUnit Five Digital Logic CircuitsUnit Six An Important Communication TooI--MATLABUnit Seven Communication ModulationUnit Eight MechanicsUnit Nine ChemistryUnit Ten Biology

章節(jié)摘錄

　　The modulation is the trapezoidal wave shown in Fig. 7-2 （a）, while thecarrier is the cosine wave shown in Fig. 7-2 （b）. In the amplitude modulatedcase, Fig. 7-2 （c）, the modulation forms the envelope of the modulatedcarrier. That is, both the positive and negative excursions of the modulatedcarrier are determined by the magnitude of the modulation waveform.Notice that in the AM case neither the frequency nor the phase of the wavechange with time.　　In the frequency-modulated wave,　Fig. 7-2（d）,　the amplitude isconstant but the frequency varies.　The frequency is lowest when themodulation is least positive. One can view the frequency-modulated wave asone in which the sinusoids bunch up or spread out according to themagnitude of the modulating wave.　　The phase-modulated wave, Fig. 7-2 （e）, also exhibits bunching andspreading of sinusoids, but in a different way than for frequency modulation.During the flat portions of the modulation （constant phase）, the PM wavelooks just like the carrier except that its phase is different.

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