题干

我国社会主义初级阶段的基本经济制度是   (     )

A:以公有制为主体,多种所有制经济共同发展

B:以国有经济为主体,多种所有制经济共同发展

C:以公有制为主导,多种所有制经济共同发展 

D:以国有经济为主导,多种所有制经济共同发展

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答案(点此获取答案解析)

A

同类题1

阅读理解

    Mobile technology has created new ways for all types of learning styles to help discover new information. If you want to teach yourself things, here are some apps that will help you.

    Coursera

    Perhaps one of the biggest advancements in the history of e-learning, Coursera has teamed up with top school like Duke, Stanford, and John Hopkins to bring you direct access to real college courses in psychology, computer science, business, and technology. Each course features pre-recorded videos, projects, and quizzes, just like you'd receive inside the classroom.

    Lumosity

    This app features three-day sessions that target many different areas of brain activity: memory, speed, problem solving, and thinking flexibility. Each day you can participate in a timed session to sharpen mental intelligence and keep track of your progress over time.

    Duolingo

    If you've ever wanted to learn a new language but didn't know where to start or couldn't afford expensive apps, you need to check out Duolingo. This app teaches more than a dozen languages by breaking up exercises into mini games. The developer of Duolingo claims that 34 hours of learning in this app equals a full term's worth of school.

    EarthViewer

    Ever wonder what Earth looked like a million years ago? There's no better way to know than to look for yourself. Earth Viewer takes you on a digital journey to see how the landscape(地貌) and face of the planet has developed over the past 4.5 billion years, and view climate changes, sea level adjustments, or the evolution of famous cities.

同类题5

阅读下文,完成下列小题。

圆珠笔头的制造难度有多大

任志方

    ①圆珠笔头分为笔尖上的球珠和球座体。油性圆珠笔头的圆珠由黄铜、钢或者碳化钨制成;水性圆珠笔头的圆珠则采用不锈钢、硬质合金或氧化铝等材料制成。由这些材料制成的圆珠笔,要满足在同一个角度下,连续不断地书写800米且不出现断线的情况才算合格。

    ②其中,球珠用的碳化钨的硬度比钢的硬度高数倍,仅比金刚石的稍微差一点。其制造工艺和轴承滚珠的类同,主要是采用滚珠旋压成型技术,用钢丝冲剪,或成型锻压成小方块,再磨成圆珠,需要专用的滚珠凹模座,它的精度与旋压力、转速有关。

    ③这一产品真正的设计难点在于怎样把这么小的圆球,在极大的生产数量下,做到相同的尺寸。这里的高精度、高互换性是基于整个制造体系的严谨得到的。

    ④笔头的另外一部分,直径仅有2.3毫米的球座体,无论是生产设备还是原材料,此前都长期掌握在瑞士、日本等国家手中。关键部位的尺寸精度要求在两微米之内,表面粗糙度要求为0.4微米,在笔头最顶端的地方,也就是放小圆珠的地方,厚度仅有0.3毫米到0.4毫米。由于后期要进行高精度的加工,既要容易切削,加工时又不能开裂,对不锈钢原材料提出了极高的性能要求。

    ⑤圆珠笔头对加工精度的要求极高,由于笔头上不仅有小球珠,里面还有5条引导墨水的沟槽,生产加工中一个小小的偏差都会影响书写的流畅度和笔的使用寿命,笔尖的开口厚度不到0.1毫米,还要考虑到书写角度和压力,球珠与笔头、墨水沟槽位必须搭配得“天衣无缝”,加工误差不能超过0.003毫米。以来自瑞士公司的笔头一体化生产设备为例,生一产个小小的圆珠笔头需要20多道工序

(摘自《齐鲁晚报》2017年1月12日 有删节)