Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van tham » van thanh, van tuan, van chat
van hanh » van thanh, ban hanh, van anh
nuoc van » nuoc va, nuoc san, luoc van
cua viet » ca viet, hoa viet, cua vat
va tham » va cham, va thanh, va thuat
sach ky » sac ky, sach y, sach ty
dang ha » dong ha, dung ha, lang ha
ky dang » ky nang, ky danh
cua tre » cua te, cuu tre, cua triet
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 ky dang ha hoi. hieu ((va tham) OR (van tham)) nuoc van hanh vi ((cua tre) or (cua viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky dang ha hoi. hieu ((va tham) OR (van tham)) nuoc van hanh vi ((cua tre) OR (cua viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky dang ha hoi. hieu ((va tham) OR (van tham)) nuoc van hanh vi ((cua tre) or (cua viet))".
• Adding a wildcard symbol may retrieve word variants: toc sach ky dang ha hoi. hieu ((va tham) OR (van tham)) nuoc van hanh vi ((cua tre) or (cua viet))*.