Should publishers of scientific papers such as Elsevier be regulated by the government? To get a pdf copy of a paper published in Elsevier is quite difficult. You need to pay a high price. Publishers like Elsevier used to have good reasons to charge people a lot: before the invention of internet it was expensive to make those papers accessible.

However, now the cost to make those papers accessible is very low. The marginal cost of sending out a pdf copy is zero. The fixed cost of administration expense is extremely low compare to the publishers' stunningly high profit. What's worse is that the creators of those research papers do not get paid from publishers at all most of the time.

According to the most basic theory of economics, the consumer surplus is maximized if and only if the price is equal to the marginal oppotunity cost. So if we want to benifit the society as a whole, we should set the price of those pdf papers to nearly zero. So the copyright laws today actually unfairly benefit Publishers at the cost of the interest of the whole society.

So should the government force publishers of research papers to make their price more reasonable? Is there any other solution to this problem?

I am an ESL learner. please condone my error if it was a language problem. Thank you.
According to the most basic theory of economics, the consumer surplus
  is maximized if and only if the price is equal to the marginal
  opportunity cost.


You are mixing agents in using these concepts. Consumer's surplus (or utility) is independent of the producer's marginal cost. Paraphrasing Investopedia's explanation, the consumer surplus or utility is maximized when the purchase of an additional unit equals the marginal benefit the consumer obtains from that additional unit.


  Should publishers of scientific papers such as Elsevier be regulated
  by the government?


No. Doing so could prompt the publisher to reduce the quality of its product or --in an extreme scenario-- close operations altogether. The existence substitute publications which are available for free further weakens the need for governmental intrusion in a private entity's decision-making.