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 sach kmy thuat do khi", "toc sach kkxy thuat do khi", "toc sach kki thuat do khi", "toc sac ky thuat do khi", "toc sach ty thuat do khi", "toc sach kem 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"
"so sach y thuat co khi" » "so sanh y thuat co khi", "bo sach y thuat co khi", "co sach y thuat co khi", "so sach my thuat co khi", "so sach kxy thuat co khi", "so sach ki thuat co khi", "so sach y thuat cbo khi"
"tu cach ky thuat o khi" » "tu cach kmy thuat o khi", "tu cach kkxy thuat o khi", "tu cach kki thuat o khi", "tu cac ky thuat o khi", "tu cach ky thuat bo 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: (("so sach y thuat co khi") or ((("tu cach ky thuat o khi") or ("toc sach ky thuat do khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("so sach y thuat co khi") OR ((("tu cach ky thuat o khi") OR ("toc sach ky thuat do khi")))).
• Removing quotes may allow a broader search: (( so sach y thuat co khi ) or ((( tu cach ky thuat o khi ) or ( toc sach ky thuat do khi )))).
• Adding a wildcard symbol may retrieve word variants: (("so sach y thuat co khi") or ((("tu cach ky thuat o khi") or ("toc sach ky thuat do khi"))))*.