Search mode errors occur because the descriptors are not searched in the [mesh] field, either explicitly or through automatic mapping; because they are not exploded (and, thus, their more specific terms are not retrieved) when searching in the text words [tw] field; because automatic mapping is disabled by truncating descriptors or enclosing MeSH phrases in double quotes; or because terms are not searched in free-text fields such as the title and abstract.
Note that searching all fields [all] is equivalent to automatic mapping, unless the terms are truncated or enclosed in double quotes, because they turn off automatic mapping.
* Truncating a term or phrase enclosed in double quotes has no effect.
The procedure for performing phrase searches in PubMed includes the following steps: (a) truncating the final term, (b) joining terms with a hyphen, (c) enclosing the phrase in double quotes, and (d) using a field tag.
Meanwhile, it should be taken into account that MeSH terms searched in the [tw] field are not exploded and do not retrieve more specific terms (lower recall), while terms searched in the [all] field are processed automatically unless truncated or enclosed in double quotes, in which case they are searched in all fields.
 (phrase final term to enclosed in search as a double quotes) phrase OS "decision support system" 2,731 CS decision support system * 10,394 Truncating Truncate Eddens L, et al.
Used in Google, the double quotes have no additional features.
It is for this reason that some Google search trainers now speak of the double quotes as exact search operators rather than as just for phrase searching.
Embase supports either single or double quotes for phrases.
While double quotes designate phrase searches in both the legacy and the new platform, how ProQuest interprets multiple-word queries without quotes has changed.
Phrase searching with double quotes typically gets around such differences and tries for an exact match of the phrase, but EBSCOhost does not search stop words even within quotation marks.