Words are handled differently by different search tools. Many search tools such as Google & Summon assume AND -- so if you enter nursing ethics, you'll retrieve items that contain both words in any order, and perhaps separated by other words.
Do you want a phrase? Use "quotation marks" to indicate a phrase.
For example, in Summon:
|Caution using quotations in PubMed as it turns OFF automatic mapping to MeSH terms|