Perhaps you should try some spelling variations:
cam thuc » am thuc, nam thuc, can thuc
vat hanh » vat thanh, van hanh, va hanh
cam thu » nam thu, cac thu, ca thu
tu sach » thu sach, su sach, tu cach
sang ma » tang ma, nang ma, sang tao
ky sang » ky nang, ky dang, ky tang
te sach » toc sach
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (te sach)) ky sang ma hoi. lieu va ((cam thuc) OR (cam thu)) vat hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (te sach)) ky sang ma hoi. lieu va ((cam thuc) OR (cam thu)) vat hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (te sach)) ky sang ma hoi. lieu va ((cam thuc) OR (cam thu)) vat hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (te sach)) ky sang ma hoi. lieu va ((cam thuc) OR (cam thu)) vat hanh vi cua tre*.