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【单选题】

调制解调器的作用是

A.
计算机信号和模拟信号互相转换
B.
把计算机信号转换为模拟信号
C.
把模拟信号转换为计算机信号
D.
防止外部病毒进入计算机中
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参考解析:
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【单选题】Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply a...

A.
Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called "dumb" terminals (i. e., those without processing capability)simply access the information base via programs stored on the system. Personal computer (PC) users typically access the host through a modem (调制解调器). A PC software program serves as an interface (接口)between the server and a PC, allowing the user to operate through the online system and select different databases using a keyboard or a mouse.
B.
National and regional online systems usually have local telephone numbers that PC modems can call to access either a local information base or an indirect long-distance connection, thus reducing long-distance telephone fees. Some online systems allow users ’to copy large volumes of information onto a local memory storage device, which also reduces the time the user is connected to the online system.
C.
Besides offering a great number of different information based, ranging from full-text journal li- braries to reports of missing children, online services allow users to, for example, reserve airline tick- ets, buy stocks, purchase goods, and communicate with other users. In exchange for the service, users usually pay a monthly membership fee. They may also pay to connect to various databases on the service or to download information.

【单选题】● 调制解调器(MODEM)的主要功能是 (5) 。

A.
模拟信号的放大
B.
数字信号的整形
C.
模拟信号与数字信号的转换
D.
数字信号的编码

【单选题】ITU V90调制解调器(MODEM)______。

A.
下载速率是56kb/s,上传速率是33.6kb/s
B.
上下行速率都是56kb/s
C.
与标准X.25公用数据网连接,以56kb/s的速率交换数据
D.
时刻与ISP连接,只要开机,永远在线

【多选题】关于药物作用机制的描述,正确的是()

A.
药物可作为生命代谢物质的补充剂,参与或干扰细胞代谢过程
B.
抗酸药中和胃酸治疗溃疡病,主要是影响生理物质的转运过程
C.
新斯的明竞争性抑制胆碱脂酶,是药物对酶的影响作用所致
D.
药物可直接作用于细胞膜的离子通道

【单选题】调制解调器(modem)的主要功能是

A.
模拟信号的放大
B.
数字信号的编码
C.
模拟信号与数字信号的转换
D.
数字信号的放大

【单选题】调制解调器(Modem)的功能是。

A.
将数字信号转换成模拟信号
B.
将模拟信号转换成数字信号
C.
兼有A和B的功能
D.
使用不同频率的载波将信号变换到不同的频率范围

【单选题】奎尼丁的主要作用机制是()

A.
抑制钠内流
B.
抑制钙内流
C.
抑制钾内流
D.
阻断β受体
E.
延长动作电位时间