搜题请搜索小程序“爱下问搜题”
问题 选择题

下图为原子结构模型的演变图，

⑴为道尔顿实心球式原子模型

⑵为卢瑟福行星运转式原子模型

⑶为汤姆生葡萄干面包式模型

⑷为近代量子力学原子模型

⑸为玻尔轨道式原子模型。其中合历史演变顺序的一组排列是

A．⑴⑶⑵⑸⑷

B．⑴⑵⑶⑷⑸

C．⑴⑸⑶⑵⑷

D．⑴⑶⑸⑷⑵

答案

答案：A

1803年，道尔顿提出了了世界上第一个原子的理论模型:实心球式；

1904年，汤姆生提出了葡萄干面包式模型：原子是一个带正电荷的球，电子镶嵌在里面，原子好似一块“蛋糕”；

1911年卢瑟福提出行星运转式模型：原子的大部分体积是空的，电子按照一定轨道围绕着一个带正电荷的很小的原子核运转

1913年玻尔提出轨道式原子模型：电子不是随意占据在原子核的周围，而是在固定的层面上运动，当电子从一个层面跃迁到另一个层面时，原子便吸收或释放能量

20世纪20年代以来提出了近代量子力学原子模型（电子云模型）

故答案为A

单项选择题

A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually hooked their TVs up to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry.

Some of the HDTVs weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to work to get the digital signals to their systems. Most of the industry’s cable providers do not yet offer high~definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them.

According to the passage, which of the following offers most of the HDTV programmes so far().

A. Retailer delivery services.

B. Cable providers.

C. Commercial television stations.

D. HDTV set manufacturers.
查看答案
选择题

甲、乙、丙三人共同开办了一家注册资本为60万的公司，甲以土地的使用权折价20万元、乙投资20万元人民币、丙以自己的专利技术折价20万元，从事科技开发。该公司属于（   ）

A．有限责任公司

B．股份有限公司

C．混合所有制企业

D．集体企业
查看答案