Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach thu » sach thue, sach thieu, sach tham
thu nang » thi nang, thu hang, thu bang
hieu cua » hieu qua, bieu cua, hieu ca
dieu cua » dieu tra
nhan tuc » nhan thuc, nhan luc, nhanh thuc
han thai » han tai, ban thai, van thai
thai cua » than cua, tai cuc, tri cua
tuc va » thuc va, truc va, tuc xa
va han » va phan, van han, va hanh
cua tu » cua tuc, cua su, cua cu
x hoi » xa hoi, o hoi, 5 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 thu nang ((x hoi) or (x ho)). ((hieu cua) or (dieu cua)) nhan tuc va han thai cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach thu nang ((x hoi) OR (x ho)). ((hieu cua) OR (dieu cua)) nhan tuc va han thai cua tu.
• Adding a wildcard symbol may retrieve word variants: toc sach thu nang ((x hoi) or (x ho)). ((hieu cua) or (dieu cua)) nhan tuc va han thai cua tu*.