问题 问答题 简答题

发电机线棒的“电腐蚀”产生的原因

答案

参考答案:

发电机定子线棒内部绝缘表面,包括防晕层表面,常有一种蚀伤现象,轻则变色,重则防晕层变酥,主绝缘出现麻点。这种现象叫“电腐蚀”,根据其发生的部位不同又分为内腐蚀和外腐蚀,外腐蚀是指定子线棒防晕层外表面的腐蚀,它是由防晕层的外表面与定子铁芯槽壁间的放电引起的。内腐蚀是指防晕层表面腐蚀,它是由定子线棒的防晕层和主绝缘之间放电引起的。

单项选择题

In 1998 consumers could purchase virtually anything over the Internet. Books, compact discs, and even stocks were (1) from World Wide Websites that seemed to (2) almost daily a few years earlier, some people had predicted that consuners accustomed to shopping in stores would be (3) to buy things that they could not see or touch (4) . For a growing number of time-starved consumers, however, shopping from their home computer was proving to be a convenient (5) to driving to the store.

A research estimated that in 1998 US consumers could purchase $ 7.3 billion of goods over the Internet, double the 1997 total. Finding a bargain was getting easier, (6) the rise of online auctions and Websites that did comparison shopping on the Internet for the best (7) .

For all the consumer interest, (8) in eyberspaee was still a largely (9) business, however. Internet pioneer Amazon. eom, which began selling books in 1995 and later (10) into recorded music and videos, posted (11) of $ 153.7 million in the third quarter, up from $ 37.9 million in the same period of 1997. Overall, (12) , the company’ s loss widened to $ 45.2 million from $9.6 million, and analysts did not expect the company to turn a profit (13) 2001. (14) the great loss, Amazon. tom had a stock market value of many billions, reflecting investors’ (15) about the future of the industry.

Internet retailing appealed (16) investors because it provided an efficient means for reaching millions of consumers without having the cost of operating (17) stores with their armies of salespeople. Selling online carried its own risks, however, (18) so many companies competing tor consumers’ attention, price competition was (19) and profit (20) thin or nonexistent.

7()

A.trade

B.exchange

C.commerce

D.deal

判断题