Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
cam thuc » nam thuc, cam thu, can thuc
sach hay » sach han, sach ha, sach nay
hieu van » hieu va, thien van, lieu va
nang ma » tang ma, sang ma, nang cao
sach ty » sach y, sach tu, sach thu
dan hai » doan hai, dang hai, dan khai
hai cau » hai chau, hai chu, hai hau
va dan » ca dan, va dao, va dau

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach hay) or (sach ty)) nang ma hoa. hieu van ((cam thuc) or (am thuc)) va dan hai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach hay) OR (sach ty)) nang ma hoa. hieu van ((cam thuc) OR (am thuc)) va dan hai cau tren.
• Adding a wildcard symbol may retrieve word variants: su ((sach hay) or (sach ty)) nang ma hoa. hieu van ((cam thuc) or (am thuc)) va dan hai cau tren*.