Perhaps you should try some spelling variations:
"toc sach thieu nghiem vi hoc" » "toc sach thi nghiem vi hoc", "toc sach thu nghiem vi hoc", "toc sach thieu nhi vi hoc", "toc sach thieu nghiem va hoc", "toc sach thieu nghiem thi hoc", "toc sach thieu nghiem van hoc", "hoc sach thieu nghiem vi hoc", "doc sach thieu nghiem vi hoc", "thuoc sach thieu nghiem vi hoc", "toc sach thieu nghiem li hoc"
"tu sach trach nhiem te hoc" » "tu sach trac nghiem te hoc", "tu sach tranh nhiem te hoc", "tu sach truc nhiem te hoc", "tu sat trach nhiem te hoc", "tu sach trach nghiem te hoc", "tu sach trach nhiem ve hoc", "tu sach trach nghiem de hoc", "thu sach trach nhiem te hoc", "su sach trach nhiem te hoc", "te sach trach nhiem te hoc"

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: (("toc sach thieu nghiem vi hoc") or ("tu sach trach nhiem te hoc"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("toc sach thieu nghiem vi hoc") OR ("tu sach trach nhiem te hoc")).
• Removing quotes may allow a broader search: (( toc sach thieu nghiem vi hoc ) or ( tu sach trach nhiem te hoc )).
• Adding a wildcard symbol may retrieve word variants: (("toc sach thieu nghiem vi hoc") or ("tu sach trach nhiem te hoc"))*.