Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
doan thi » dan thi, doanh tai, hoang thi
dau tren » dau tien, dat tren, dau tieng
tu sach » thu sach, su sach, te sach
qua cau » quan cau, qua cac, qua ca
cau duc » cao duc, cau luc, chu duc
va doan » va doanh, van doan, va dan
thi dau » thi dai, phi dau, thi dan

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 (toc sach)) ky nang x ho. hieu qua cau duc va doan thi dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky nang x ho. hieu qua cau duc va doan thi dau tren.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky nang x ho. hieu qua cau duc va doan thi dau tren*.