机械制图弹簧画法:初二英语：谁给讲解一下现在完成时

现在完成时的用法
have(has)+过去分词
1.现在完成时用来表示现在之前已发生活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.
I haven't seen much of him recently (lately).
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, 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.
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, 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 bee 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.
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.
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现在完成时的“完成用法”和“未完成用法”

1.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？

2.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。

(2)现在完成时常见两种句型：

①主语＋have / has been＋for短语

②It is＋一段时间＋ since从句

例如：He has been in the League for three years.或It is three years since he joined the League. 他入团已三年了

买一本语法书
好好啃
这很难讲透

你可以买高中的
讲得很详细

需要真题练习
这须自己领悟
别人很难讲清楚
要讲也只有皮毛
你应该根据你的实际情况学习完成时

推荐一本书
《高中英语语法》

做完了
就通了

现在完成时是英语学习中的一种很重要的时态
现在完成时表示：1、过去发生的某一件事或某一个动作对现在造成的影响。
2、过去发生的某一件事或某一个动作意一直持续到现在并且还有可能延续下去。
在句中一般都有标志性词语。for example : since, for + 一段时间，等等