Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cam thuc » am thuc, nam thuc, cam thu
cau tren » cu tren, dau tren, ca tren
ky tang » ky nang, kho tang, ky trong
ky dang » ky nang, ky danh
so sanh » do sanh
hieu ve » hieu va, hieu van
thuc va » thuc vat, thuc dan, thuc day
va hang » van hang, va nang, va lang
hang di » hang doi, hang vi, hang dien
ve cam » ve cham, ve cac, va cam
di cau » da cau, diem cau
ha hoi » hoa hoi, ha noi, xa hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (so sanh)) ((ky tang) or (ky dang)) ha hoi. hieu ve cam thuc va hang di cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (so sanh)) ((ky tang) OR (ky dang)) ha hoi. hieu ve cam thuc va hang di cau tren.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (so sanh)) ((ky tang) or (ky dang)) ha hoi. hieu ve cam thuc va hang di cau tren*.