Perhaps you should try some spelling variations:
viet sach » viet anh, dien sach, viet tech
sach nuoc » sach duoc, cac nuoc, bach tuoc
hieu viet » sieu viet, hieu viec, lieu viet
xanh doi » xanh di, thanh doi, tinh doi
doi cua » dai cua, hoi cua
va xanh » va danh, va hanh, va anh
sach ky » sac ky, sach ty, sach kem
nang ma » tang ma, sang ma, mang may
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu ((sach ky) OR (sach y)) ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu ((sach ky) OR (sach y)) ((nang ma) OR (nang cao)) hoi. hieu viet sach nuoc va xanh doi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu ((sach ky) OR (sach y)) ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi cua tre".
• Adding a wildcard symbol may retrieve word variants: vu ((sach ky) OR (sach y)) ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi cua tre*.