few表示没有几个（否定含义），后面跟可数名词复数
only a few也表示同样的意思，后面也是跟可数名词复数
only 修饰 few 或 little 时，通常要与 a 连用。
Only a few children have read this book.
只有几个孩子看过这本书。
所以only a few就是few
另外：
only a little 和little也是同一个意思
表示没有几个（也是否定的），但后面跟不可数名词
[辨与析] few, a few, little, a little
虽然都表示“少”，但
（1）few, a few是可数的, little, a little是不可数的。
（2）a few, a little含肯定意味，few, little含否定意味。这里所谓的“肯定意味”和“否定意味”应该这样来理解：同样是半杯水，口渴者会认为：There is little water in the glass. 而不口渴的人则会认为：There is a little water in the glass.
再看看其他用法
few修饰可数名词复数。
2．few (= not many; hardly any)含否定意义；a few (= some; several; a small
number of) 含肯定意义。
3． not a few = no few = quite a few = a good few = many。
4． 当 few受 every, last, past, next, some, very等词所修饰时，表示肯定意义，few之前不再有冠词。如：
In the last few minutes, he checked up his paper again.
It took us some few days to repair the machine.
They are very few in number.
There were too few of them.
He goes to see his grandma every few weeks.
。