题干

国家统计局统计资料显示,2005年第一季度我国国内生产总值为31355.55亿元,用科学记数法表示为(   )元.(用四舍五入法保留3个有效数字)

A:3.13×1012

B:3.14×1012

C:3.14×1013

D:31355.5×108

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答案(点此获取答案解析)

B

同类题2

阅读短文,回答文中问题.

在现代战场上,精确制导武器的打击精度迅速提高,而为了提高兵器的生存能力,敌对双方又都想方设法隐蔽自己,同时千方百计地搜寻敌人,这种斗争愈演愈烈,形成了在高科技领域内一场隐身与现形的生死大较量.

所谓兵器隐身,通俗地讲,就是改变武器装备的电、光、声、磁等特征,使对方探测设备难以发现和识别.雷达是最常见和有效地探测设备之一,它在工作时,向一定空域发射____ ,遇到目标后会被____ ,雷达接收到该信号,就会发现目标.我国的“歼﹣20”第五代隐身重型歼击机的表面有多个小平面拼成,其尾翼间的夹角小于90°,呈“V”字形,大大提高了雷达隐身功能.

兵器有了雷达隐身的功能后,是否就高枕无忧了呢?绝非如此,军事侦查手段很多,除雷达外,红外探测也是发现目标的重要手段.物体辐射红外线能力与自身的温度密切相关,温度越高,其红外辐射就越____ (填“强”或“弱”).美国的F﹣117A用冷空气对尾气进行预冷,有效降低了尾气的温度.还有一种隐身,对于水面舰艇和潜艇而言至关重要,就是对声探测隐身.声呐是在水下发现目标的重要工具.它分为主动声呐和被动声呐两种,主动声呐是自己发出声波,并根据目标反射的回波来发现目标.若声波在水中速度为1500m/s,潜艇在发出声波4s后接收到回波,则目标距潜艇的距离为____ ,被动声呐是通过接收舰艇的噪声来发现目标,有些舰艇经常关闭发动机来躲避敌人追击,这是在____ 处减弱噪声.

随着科技的发展,隐身和反隐身的对抗将会愈演愈烈,未来战场必将是高潮迭起,好戏连台.

同类题5

阅读理解

    It was a cold night in Washington, D. C., and I was heading back to the hotel when a man approached me. He asked if l would give him some money so he could get something to eat. I'd read the signs "Don't give money to beggars." So I shook my head and kept walking.

    I wasn't prepared for a reply, but he said, "I really am homeless and I really am hungry! You can come with me and watch me eat!" But I kept on walking.

    The incident bothered me for the rest of the week. I had money in my pocket and it wouldn't have killed me to hand over a buck or two even if he had been lying. Flying back to Anchorage, I couldn't help thinking of him. I tried to rationalize (找借口)my failure to help by thinking government agencies, churches and charities were there to feed him. Besides, you're not supposed to give money to beggars.

    Somewhere over Seattle, I started to write my weekly garden column for The Anchorage Daily News. Out of the blue, I came up with an idea. Bean's Cafe, the soup kitchen in Anchorage, feeds hundreds of hungry Alaskans every day. Why not try to get all my readers to plant one row in their gardens dedicated to Bean's? Dedicate a row and take it down to Bean's. Clean and simple.

    The idea began to take off. Readers would fax or call me when they got something in their garden. Those who only grew flowers donated them. Food for the spirit.

    In 1995, the Garden Writers Association of America held their annual convention in Anchorage and after learning of Anchorage's program, Plant a Row for Bean's became Plant a Row for the Hungry. The original idea was to have every member of the Garden Writers Association of America write or talk about planting a row for the hungry sometime during the month of April.

    As more and more people started working with the Plant a Row idea, new changes appeared unexpectedly. Many companies gave free seed to customers and displayed the logo, which also appeared in national gardening publications. Row markers with the Plant a Row logo were delivered to gardeners to set apart their "Row for the Hungry."

    Garden editor Joan Jackson, supported by The San Jose Mercury News and California's nearly year-round growing season, raised more than 30,000 pounds of fruits and vegetables her first year, and showed GWAA how the program could really work. Texas fruit farms donated food to their local food bank after being inspired by Plant a Row. Today the program continues to thrive and grow.

    I am surprised that millions of Americans are threatened by hunger. If every gardener in America--and we're seventy million strong--plants one row for the hungry, we can make quite a decrease in the number of neighbors who don't have enough to eat. Maybe then I will stop feeling guilty about abandoning a hungry man I could have helped.