Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
hieu cua » hieu qua, dieu cua, bieu cua
tu sach » su sach, te sach, tu cach
tu nang » tru nang, tu nong, tu nano
nang ma » tang ma, sang ma, nang cao
doan vi » doan va, don vi, doan thi
vi cua » vai cua, di cua
cua te » cua tu

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (thu sach)) tu nang ma hoa. hieu cua cac ((duc va) or (tuc xa)) doan vi cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) tu nang ma hoa. hieu cua cac ((duc va) OR (tuc xa)) doan vi cua te.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thu sach)) tu nang ma hoa. hieu cua cac ((duc va) or (tuc xa)) doan vi cua te*.