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什么是核心期刊？怎样判别核心期刊？

答案

参考答案：核心期刊又称重点期刊，它是指那些内容中信息密度大，代表学科发展水平，所刊载的论文使用寿命长，利用率和被引用率都比较高的期刊。各个学科都有自己的核心期刊。一般来说，只要掌握了核心期刊，就可以用较少的花费获得较多的信息。核心期刊的判别标准是：

（1）期刊中论文的被摘率。主要指期刊中的论文被有关权威的文摘刊物摘录的情况。通常核心期刊中论文被摘录的机会高于一般期刊。

（2）期刊中论文的被引用率。主要指其他作者在论文写作过程中参考引用文献的来源，通常核心期刊中的论文被别人引用的频率要比一般期刊论文高。

（3）期刊流通过程中的读者利用率。信息量大，情报价值或艺术价值高的期刊，通常读者的利用率也高。核心期刊的利用率总是高于一般期刊。

填空题

Part 1


·Read the following passages, eight sentences have been removed from the article.
·Choose from the sentences A-H the one which fits each gap.
·For each gap (1-8) mark one letter (A-H) on the Answer Sheet.
Buzz Aldrin, the second man to walk on the Moon, is a long-time fan of space tourism. Aldrin climbed out of Apollo11 hot on the heels of Neil Armp in 1969. (1)
Together with scientists from Purdue University, the Massachusetts Institute of Technology, and the University of Texas, Aldrin is designing spacecrafts that would perpetually cruise between Earth and Mars. (2) "Some day, people will go to Mars on a regular basis," says team member James Longuski, a professor at Purdue. (3)
The average distance between Mars and Earth is 48 million miles. (4)
It sounds like a trip that would require a lot of fuel. According to the engineers, the cyclers may have a natural, renewable "fuel" supply: from the gravitational forces of the Sun, the planets, and their moons.
As a spacecraft travels close to a planet, its flight path is bent, causing it to whip around the planet and significantly increasing its speed (it’s as if the planet’s gravity gives the passing spacecraft a kick into space). (5) It’s not just science fiction: it might help us get Mars with very little fuel on board, in a journey that would take as little as six to eight months.
"The cycler is essentially in orbit around the Sun and makes regular flybys of Earth and Mars," says James Longuski. "Once you put your vehicle into a cycler orbit, it continues on its own momentum, going back and forth between Earth and Mars. (6)
When the cycler flies by Earth, it will be traveling at a speed of about 13,000 miles per hour.
(7) This is sort of like a bus that doesn’t stop," Longuski says. "When it comes by, you have to run alongside of it and grab on."
AIdrin and his group think that the first cycler could be on its way by as soon as 2018. (8) (It seems a long way off now, but it’s closer than you think!)
Fasten your seatbelts and make sure your seatback is in its upright position. Your flight to space may be departing soon.
  • A. These crafts, known as "cyclers", would ferry people and supplies between the two planets, enabling humans to colonize Mars — something that has long been dreamed about in science fiction.
  • B. Most people are convinced that we are going to do this; the only question is when.
  • C. So, if you’re in middle school now, you could be taking a trip to Mars by the time you’re in your thirties.
  • D. To get a sense of just how far this is, try doing this calculation: Given that there are 2,500 miles between New York and Los Angeles, how many times would you have to travel from NY to LA and back to cover the same distance’
  • E. Now, at the age of 72, Aldrin is working on a new project that could put more of his fellow humans in space — namely, on journeys to one of our most fascinating neighbors, Mars.
  • F. This is the "slingshot" trajectory that you may have seen in movies.
  • G. Space taxis will be needed to bring people from the surface of the planet to intercept the cycler.
  • H. You may need to carry some propellant for an occasional boost, but it’s pretty much a free trip after that.
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实验题

某同学设计了如图（a）所示电路研究电源输出功率变化情况。电源E电动势、内电阻恒定，R1为滑动变阻器，R2、R3为定值电阻，A、V为理想电表。

（1）若滑动片P由a滑至b时A示数一直变小，则R1和R2必须满足的关系是___________。

（2）若R1＝6 Ω，R2＝12 Ω，电源内电阻r＝6 Ω，当滑动片P由a滑至b时，电源E的输出功率P随外电路总电阻R的变化关系如图（b）所示，则R3的阻值应该选择___________。 

A．2 Ω

B．4 Ω

C．6 Ω

D．8 Ω

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