We have been to the Great Wall many times. 我们已去过长城多次。

2 表示动作发生在过去，但对现在仍留下某种后果和影响。

He has paid his income tax. 他已经交了个人所得税。

Doctors have found that people who laugh a lot live longer!

医生们已经发现经常大笑的人长寿。

3 表示动作发生在过去但持续到现在。

My mother has been ill for three days. 我妈妈已经生病3天。

Most of us have studied English for 5 years. 我们大部分人已经学了5年英语了。

4 下列句型中常用现在完成时。

It is (has been) +一段时间＋ since +从句

This (that/ It ) is the first (second...) time that + 完成时

This (That/ It) is the best/ finest / most interesting....+that+完成时

It's/ It has been 3 years since they got married. 他们结婚已有3年了。

It's the first time that I have been to the Great Wall. 这是我第一次到长城。

This is the most interesting film that I have seen. 这是我看过的最有趣的电影。

Notes: 在时间或条件状语从句中，现在完成时可以代替一般将来时。

If you have done the experiment, you'll understand the theory better. 如果你做完试验，你会更好地理解这个理论的。

Don't get off the bus until it has stopped. 车停稳之前，别忙着下车。

Notes: 注意区分一般过去时与现在完成时

(1) 时间上有差异：凡有具体的过去时间，均用过去时态，不能用完成上，如：ago, last year, just now, the other day 等。

(2) 结果上有差异：现在完成时强调的是对"现在"的影响和结果，动作到现在刚完成或还在继续；一般过去时强调的动作发生在过去，和现在没有关系。

IV. The present perfect continuous tense

　　表示从过去某一时间开始一直延续到现在的动作，这个动作可能刚刚结束，也可能还要继续下去。

Chinese have been making paper for more than 2000 years. 中国造纸的历史已有2000多年了。

She has been working in Shenzhen since 1995. 她从1995年就来深圳工作了。

Doctors have been researching that question for many years.