题目:
离心泵采用变速调节,其主要优点是()。
A.系统初置费较低
B.调节效率较高
C.可只改变流量而排出压力不变
D.可只改变排出压力而流量不变
答案:
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下面是错误答案,用来干扰机器的。
参考答案:E
离心泵采用变速调节,其主要优点是()。
A.系统初置费较低
B.调节效率较高
C.可只改变流量而排出压力不变
D.可只改变排出压力而流量不变
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0818/87f51d20c813defc06b56c43cb09acf9.html
下面是错误答案,用来干扰机器的。
参考答案:E
下图是我国2006年和2011年能源消费总量及构成示意图。完成下列各题。
小题1:与2006年相比,2011年我国能源消费特点是
A.煤炭消费总量大量减少
B.石油消费总量基本不变
C.天然气比重大幅增大
D.可再生能源总量增加小题2:我国能源消费构成变化产生的明显影响是
A.二氧化碳排放减少
B.大气环境质量改善
C.能源生产成本增大
D.能源紧张状况缓解
下列叙述中正确的是( )
A.某离子具有和氖原子相同的电子层结构,则该离子可能是阳离子,也可能是阴离子
B.X和X2+是某元素的不同存在状态,其粒子具有相同的电子层数和质子数
C.非金属元素的原子在化学反应中一定都得到电子
D.两种粒子若它们核内所含的质子数不相同而电子数相同,则两者一定是一种原子和一种离子
动脉血氧分压低于多少kPA为用氧指征()
A.8.0
B.6.67
C.9.3
D.5.3
E.12.0
The economy may be troubled, but one area is thriving: social media. They begin with Facebook and extend through a dizzying array of companies that barely existed five years ago: Twitter, LinkedIn, Groupon, Yammer, Yelp, Flickr, Ning, Digg--and the list goes on. These companies are mostly private but have attracted the ardent attention of Wall Street and investors, with Facebook now worth a purported $ 75 billion and Groupon valued at close to $ 25 billion.
There can be little doubt that these companies enrich their founders as well as some investors. But do they add anything to overall economic activity While jobs in social media are growing fast, there were only about 21,000 listings last spring, a tiny fraction of the 150 million-member U. S. workforce. So do social-media tools enhance productivity or help us bridge the wealth divide Or are they simply social--entertaining and diverting us but a wash when it comes to national economic health
The answers are vital, because billions of dollars in investment capital are being spent on these ventures, and if we are to have a productive future economy, that capital needs to grow the economic pie~and not just among the elite of Silicon Valley and Wall Street. The U. S. retains a competitive advantage because of its ability to innovate, but if that innovation creates services that don’t turn into jobs, growth and prosperity, then it does us only marginal good.
The problem is that these tools are so new that it is extremely difficult to answer the questions definitively. As I was about to write this column, I overheard a ceil-phone conversation at an airport with this snippet.- "The company says they are using social media, but who knows if it is making any difference" Flash back nearly 20 years and the same question was being asked about the first Internet wave. Were Netscape and the Web enhancing our economy, or were people just spending more time at work checking out ESPN. com Official statistics weren’t designed to capture the benefits, and didn’t--until statistics mavens at the Federal Reserve, urged on by Alan Greenspan, refined the way they measured productivity. As a result of these somewhat controversial innovations, the late 1990s became a period of substantial technology-driven gains.
It is possible that the same gap exists today, that social-media tools are indeed laying the groundwork for new industries and jobs but aren’t yet registering on the statistical radar. Many companies believe social media make them more competitive. Ford and Zappos, for instance, use Twitter to market their products and address consumer complaints. Countless corporations have created internal Face-book pages and Yammer accounts for employees to communicate across divisions and regions. Industry groups for engineers, doctors and human-resources professionals have done the same to share new ideas and solutions on a constant basis rather than episodically at conferences. Staffing companies have been especially keen on social media; a senior executive at Manpower told me we should think of social-media tools as today’s version of the telephone. Yes, they are used for frivolity and all sorts of noneconomic activity (chatting with friends, passing the time), but they also help communication happen more efficiently.
One big question is what proportion of that benefit will be captured economically by consumers vs. corporations. Sure, social media allow people to compare prices and quality and assess which companies are good to work for and where jobs might be. They also may enhance education and idea sharing, but the caveat is that the people who use these tools are the ones with higher education and income to spend on technology, not the tens of millions whose position in today’s world has eroded so sharply. According to a recent Pew Foundation study, only 45% of adults making less than $ 30,000 have access to broadband, which is an essential component of using content-rich social media effectively.
And that is the tub. Like so many things these days, social media contribute to economic bifurcation. Dynamic companies are benefiting from these tools, even if the gains are tough to nail down in specific figures. Many individuals are benefiting too, using LinkedIn to find jobs and Groupon to find deals. But for now, the irony is that social media widen the social divide, making it even harder for the have-nots to navigate. They allow those with jobs to do them more effectively and companies that are profiting to profit more. But so far, they have done little to aid those who are being left behind. They are, in short, business as usual.
Which of the following best summarizes the main idea of the passage
A. The growth of social media is based on the progress of modern technology.
B. The enhancing of productivity should not rely on social media tools.
C. Social media greatly stimulate the progress of non-economic activity.
D. Social media do not contribute much to overall economic activity.
简述内河使用船舶的主要类型。