Perhaps you should try some spelling variations:
cach thuc » anh thuc, cac thu
toc sach » hoc sach, doc sach, thuoc sach
tang van » dang van, hoang van, trong van
cac thuc » cac thu, can thuc, cay thuc
su sach » so sach, vu sach
tinh va » tich va, trinh van, trinh vat
hieu ve » hieu va, hieu van
van hoi » van hoa, van hoc, van hoe
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua

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) or (toc sach)) ky tang van hoi. hieu ve ((cac thuc) OR (cach thuc)) may tinh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (toc sach)) ky tang van hoi. hieu ve ((cac thuc) OR (cach thuc)) may tinh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (toc sach)) ky tang van hoi. hieu ve ((cac thuc) OR (cach thuc)) may tinh va cua tre".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (toc sach)) ky tang van hoi. hieu ve ((cac thuc) OR (cach thuc)) may tinh va cua tre*.