yet already in the last five/few years for + 一段时间 since every never up to/till now so far Up to the present once recently lately 1.现在完成时用来表示现在之前已发生过或完成的动作或状态,但其结果却和现在有联系,也就是说,动作或状态发生在过去但它的影响现在还存在. I have lost my wallet.(含义是:现在我没有钱花了.) Jane has laid the table.(含义是:已可以吃饭了.) Michael has been ill.(含义是:现在仍然很虚弱) He has returned from abroad. (含义是:现在已在此地) 2. 现在完成时可以用来表示发生在过去某一时刻的,持续到现在的情况,常与for,since连用. Mary has been ill for three days. I have lived here since 1998. 3. 现在完成时往往同表示不确定的过去时间状语连用,如already, yet, just, before, recently, lately等: He has already obtained a scholarship. We have seen that film before. Have they found the missing child yet 4. 现在完成时常常与表示频度的时间状语连用,如often, sometimes, twice, on several occasion等: Have you ever been to Beijing George has met that gentleman on several occasions. 5. 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, now, just, today, . 6. 现在完成时表示现在之前业已完成的动作,虽然其效果或影响仍然存在但已不再继续,但是有一些现在完成时的句子,在后面加上for+一段时间,则现在完成时的动作就表示延续性. Thomas has studied Russian. (现在不再学俄语) Thomas has studied Russian for three years. (=Thomas began to study Russian three years ago, and is still studying it now.(同第2点用法第一个例句) 7. 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. 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？ 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 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。
温馨提示：答案为网友推荐，仅供参考