Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
vien cac » vien dai, vien da, gian cac
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
sang ma » tang ma, nang ma, sang tao
ma hoi » mai hoi, xa hoi, ma hoa
ve cac » va cac
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cau » va cau, ve cau, di cau

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 sang ma hoi. hieu ((ve cac) or (((vien cac) OR (vien bach)))) nuoc va dan vi cau tao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky sang ma hoi. hieu ((ve cac) OR (((vien cac) OR (vien bach)))) nuoc va dan vi cau tao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky sang ma hoi. hieu ((ve cac) or (((vien cac) OR (vien bach)))) nuoc va dan vi cau tao".
• Adding a wildcard symbol may retrieve word variants: toc sach ky sang ma hoi. hieu ((ve cac) or (((vien cac) OR (vien bach)))) nuoc va dan vi cau tao*.