Perhaps you should try some spelling variations:
pham thuc » phap thuc, pham chuc, nham thuc
tham thuc » nham thuc, tam thuc, thai thuc
vanh dai » van dai, vanh tai, lanh dao
nang cai » nang cao, nang tai, nang cap
va vanh » va van, va danh, va hanh
hieu ve » hieu va, hieu van
sach ky » sac ky, sach y, sach kem
cai hoi » cau hoi, dai hoi, cai hoa
sach ty » sach y, sach tu, sach thu
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: su ((sach ky) OR (sach ty)) nang cai hoi. hieu ve ((tham thuc) or (pham thuc)) va vanh dai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) nang cai hoi. hieu ve ((tham thuc) OR (pham thuc)) va vanh dai cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) OR (sach ty)) nang cai hoi. hieu ve ((tham thuc) or (pham thuc)) va vanh dai cua te".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) OR (sach ty)) nang cai hoi. hieu ve ((tham thuc) or (pham thuc)) va vanh dai cua te*.