现在完成时主要用于哪几种情况？

现在完成时主要用于哪几种情况？

1.现在完成时不能单独与准确时间连用，(如表示过去的时间状语） 　　如yesterday(morning、afternoon),last(morning、afternoon)等，除非与for,since连用. 　　2.现在完成时往往同表示不确定的过去时间状语连用 　　,如already（肯定）, yet（否定，疑问）, just, before, recently,still, lately,never等: 　　He has already obtained a scholarship. 　　I haven't seen much of him recently (lately). 　　We have seen that film before. 　　Have they found the missing child yet ? 　　3. 现在完成时常常与表示频度的时间状语连用, 　　如often, sometimes, ever, never, twice, on several occasion等: 　　Have you ever been to Beijing 　　I have never heard Bunny say anything against her. 　　I have used this pen only three times. It is still good. 　　George has met that gentleman on several occasions. 　　4. 现在完成时还往往可以同包括现在时间在内的时间状语连用, 　　　如now, up to these few days/weeks/months/years, this morning/week/month/year, just, today, up to present, so far等: 　　Peter has written six papers so far. 　　Man has now learned to release energy from the nucleus of the atom. 　　There has been too much rain in San Francisco this year. 　　The friendly relations and cooperation between our two countries have been enhanced in the past few years. 　　Up to the present everything has been successful. 　　5. 现在完成时还可以用来表示过去的一个时间到现在这段时间内重复发生的动作. 　　　We have had four texts this semester. 　　6.现在完成时的"完成用法" 　　现在完成时的"完成用法"指的是动作发生在过去某一时刻并已结束，但该动作对现在产生了影响，与现在情况具有因果关系。 　　例如：He has turned off the light.他已把灯关了。(动作结束于过去，但说明的是现在的情况--灯现在不亮了。) 　　现在完成时"完成用法"的特点是动作不延续，因此，该时态只能与表示不定的过去时间状语(如：already，yet，before，recently等)、频度时间状语(如：never，ever，once等)、包括现在时刻在内的时间状语(如：this morning / month /year...，today等)连用。 　　例如： Have you found your pen yet？你已找到你的钢笔了吗？ 　　7.现在完成时的"未完成用法" 　　现在完成时的"未完成用法"指的是动作开始于过去某一时刻，一直延续到现在，或可能还要继续下去。 　　例如：He has lived here since 1978.自从1978年以来，他一直住在这儿。(动作起始于1978年，一直住到现在，可能还要继续住下去。) 　　I have been in the army for more than 5 years.我在部队已经呆了五年多了。(动作开始于5年前，一直延续至今，有可能还要继续下去。) 　　此种用法的句中常需一个表示一段时间的状语(由since或for引导)，或表示与现在时刻相连的时间状语(如：up to now，so far)等。 　　例如：I have heard nothing from him up to now.到目前为止我没有他的任何消息。 　　注意：(1)现在完成时的未完成用法只适用于延续性动词，不可用于终止性动词，即瞬间完成或延续时间很短的动词。如：come，go，arrive，leave，join，become，die等。 　　8.一段时间+has passed+since从句 　　　9. 现在完成时常和短语 "up to now /till now", "so far" (意思是从过去某一确定的时间一直延续到现在.) 　　　Up to/till now he's read many story books. 至今他已读过好多故事书。 　　I've been to New York three times so far. 至今我已到纽约去过三次。 　　10 has gone (to),has been (to), has been (in) 的区别 　　gone:去了没回 　　been to :去过 　　been in：呆了很久 　　10.不能与when连用