Perhaps you should try some spelling variations:
"toc sach ky thuat do khi" » "hoc sach ky thuat do khi", "doc sach ky thuat do khi", "thuoc sach ky thuat do khi", "toc sac ky thuat do khi", "toc sach y thuat do khi", "toc sach ty thuat do khi", "toc sach ky thuat doi khi", "toc sach ky thuat do thi", "toc sach ky thuat bo khi", "toc sach ky thuat dbo khi"
"su sach ki thuat o khi" » "so sach ki thuat o khi", "vu sach ki thuat o khi", "su sach kinh thuat o khi", "su sach bai thuat o khi", "su sach kem thuat o khi", "su sach ki thuat bo khi"
"tu sach ky thuat co khi" » "thu sach ky thuat co khi", "te sach ky thuat co khi", "tu cach ky thuat co khi", "tu sac ky thuat co khi", "tu sach y thuat co khi", "tu sach ty thuat co khi", "tu sach ky thuat cbo khi"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("su sach ki thuat o khi") or ((("tu sach ky thuat co khi") or ("toc sach ky thuat do khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("su sach ki thuat o khi") OR ((("tu sach ky thuat co khi") OR ("toc sach ky thuat do khi")))).
• Removing quotes may allow a broader search: (( su sach ki thuat o khi ) or ((( tu sach ky thuat co khi ) or ( toc sach ky thuat do khi )))).
• Adding a wildcard symbol may retrieve word variants: (("su sach ki thuat o khi") or ((("tu sach ky thuat co khi") or ("toc sach ky thuat do khi"))))*.