this week 不是介词短语，而是名词短语，但它在此具有副词性质，在句中用作状语（表时间）。其前并没有省略介词。像 this week, this year, this month, this morning, this evening, this afternoon 这类名词短语，通常都是直接用作状语（其前不用介词的）。如：

The company made a fat profit this year. 公司今年获利丰厚。

My birthday is on a Friday this year. 今年我的生日是在一个星期五。

Did you remember to take your pills this morning? 你今天早上记得服约了吗?

Peggy dropped by the office this afternoon. 佩吉今天下午顺路来了一下办公室。

但也不是说绝对不能用介词，若语义需要，也可以用 until, after, during 之类的介词。如：

Until this week, every attempt to tighten up the law had failed. 到本周为止，一切严格执法的努力都失败了。

Orders had come from on high that extra care was to be taken during this week. 上头传来话说这个星期要格外小心。

I asked the shop to hold the dress for me until this afternoon. 我要那家商店帮我把那件衣服留到今天下午。

Until this evening I had never so much as exchanged a word with him. 在今天晚上之前，我甚至连一句话都没跟他说过。