Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dang xay » dang van, van xay
duc suu » duc suc, duoc sua, quoc suu
va dinh » van dinh, va kinh, va tinh
cam luc » cam xuc, cau luc
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
va cam » va cham, va cac, va cao
luc va » duc va, tuc va, loc va

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 xay) or (nang ma)) hoi. hieu va cam luc va dinh ((duc cuu) OR (duc suu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((dang xay) OR (nang ma)) hoi. hieu va cam luc va dinh ((duc cuu) OR (duc suu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((dang xay) or (nang ma)) hoi. hieu va cam luc va dinh ((duc cuu) OR (duc suu)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((dang xay) or (nang ma)) hoi. hieu va cam luc va dinh ((duc cuu) OR (duc suu)) tre*.