问题 问答题 简答题

齿轮传动杆工作条件的不同有哪三种传动形式?各种传动形式的应用场合如何?

答案

参考答案:

按照齿轮工作条件的不同,齿轮传动可分为开式传动、半开式传动和闭式传动三种形式。开式传动中,齿轮是外露的,由于灰沙容易落入齿面,润换不完善,故齿轮易磨损。优点是结构简单,适用于圆周速度较低和精度要求不高的场合。半开式齿轮传动中,齿轮的下部浸入润滑油池内,有简单的防护罩,当仍没有完全克服开式传动的缺点,一般用于叫低速的传动。闭式齿轮传动中,齿轮和轴承等均装在刚性很大的箱体内,润滑良好,封闭严密,安装精确,可保证良好的工作,因此广泛应用于各种场合。

阅读理解

阅读理解。

     The Parthenon in Athens is a building with a long and complex history.Built nearly 2,500 years ago

as a temple celebrating the Greek goddess Athena, it was for thousands of years the church of the

Virgin Mary of the Athenians, then a mosque (清真寺), and finally a ruin.The building was changed

and the sculptures were much damaged over the centuries.By 1800 only about half of the original

sculptural decoration remained.

     Between 1801 and 1805, Lord Elgin, the British ambassador to the Ottoman Empire, which

controlled Athens, acting with the full knowledge and permission of the Ottoman authorities, removed

about half of the remaining sculptures from the fallen ruins and from the building itself.Lord Elgin loved

Greek history and transported the sculptures back to Britain.The arrival of the sculptures in London

had a huge effect on the European public, greatly increasing interest in ancient Greek culture and

influencing contemporary artistic trends.These sculptures were acquired from Lord Elgin by the British

Museum in 1816 and since then they have all been on display to the public, free of charge.

     Since the early 1980s, however, the Greek government has argued for the permanent removal to

Athens of all the Parthenon sculptures in the British Museum.They have also challenged the British

Museum Board of Trustees' legal title to the sculptures.

     The British Museum, however, insists that it exists to tell the story of cultural achievement throughout

the world, from the dawn of human history over two million years ago until the present day.The museum

considers itself an important resource for the world: the breadth and depth of its collection allows the world public to reexamine cultural identities and explore the complex network of interconnected world cultures.

     It also says that, within the context of this unparalleled collection, the Parthenon sculptures are an

important representation of ancient Athenian civilization.Each year millions of visitors admire the artistry

of the sculptures and gain insights on how ancient Greece influenced-and was influenced by the other

civilizations that it encountered(遭遇).

1.For most of its history people went to the Parthenon to________.

A.admire the goddess Athena

B.pray to their god

C.search for sculptures

D.learn about its complex history

2.The underlined "it" (in Paragraph 4) refers to "________".

A.the British Museum

B.the Greek government

C.the Parthenon

D.the British Museum Board of Trustees

3.What can we learn about Lord Elgin from the passage?

A.He is greatly admired in Greece.

B.He worked for the Ottoman Empire.

C.He saved the Parthenon sculptures from being destroyed.

D.He had a deep interest in Greek culture.

4.The author's main intention in writing this passage is to tell________.

A.the history of the Parthenon and its sculptures

B.what people can see in the British Museum

C.why the British Museum refuses to return the sculptures

D.the influence of Greece on British culture

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