Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
sach ky » sac ky, sach y, sach ty
dat tai » dat dai, dai tai, tat tai
dau tai » dai tai, da tai, dan tai
thuc va » thuc vat, thuc dan, thuc day
buu tre » cuu tre
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
va nam » van nam, ha nam
va nay » va ngay, va cay

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky lang xa hoi. hieu ((va nam) or (va nay)) thuc va ((dau tai) OR (dat tai)) buu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky lang xa hoi. hieu ((va nam) OR (va nay)) thuc va ((dau tai) OR (dat tai)) buu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky lang xa hoi. hieu ((va nam) or (va nay)) thuc va ((dau tai) OR (dat tai)) buu tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky lang xa hoi. hieu ((va nam) or (va nay)) thuc va ((dau tai) OR (dat tai)) buu tre*.