Logic Word
It is represented by "AND" and "*". It can be used to indicate the intersection of the two search terms connected, that is, the intersection. If you use AND to connect search term A and search term B, the search formula is: A AND B (or A*B): The system searches the information collection C that contains both the search term A and the search term B.
For example, the search formula for searching "insulin for diabetes" is: insulin (insulin)anddiabetes (diabetes).
It is represented by "OR" or "+". The search term used to connect the parallel relationship. Use OR to connect search term A and search term B, then the search formula is: AORB (or A+B). Means to let the system search for information that contains one of search terms A and B, or both search term A and search term B. For example, the search formula for searching for "tumor" is: cancer (cancer)or tumor (tumor)or carcinoma (cancer)or neoplasm (new Biology).
It is indicated by "NOT" or "—". Search terms used to connect exclusion relations, that is, concepts that exclude unnecessary and affect search results. Use NOT to connect search term A and search term B. The search formula is: A NOT B (or A-B). It means to search for information containing search term A but not search term B, that is, to exclude the information set containing search term B.
For example, the search formula for searching the literature of "animal hepatitis B virus (not human)" is: hepatitis B virus (hepatitis B virus) not human (human).
Operator
With
It is represented by "With". Used to indicate two words that appear in a field of the same document at the same time. Use With to connect search term A and search term B. The search formula is: "Awith B". It means that the search term A and the search term B must not only appear in a record at the same time, but also the documents that appear in the same field at the same time are the hit documents.
Such as: drug (drug) withabuse (abuse), the retrieved is the record where these two words appear in the same field at the same time.
Near
It is represented by "Near". Used to indicate that not only two words that must appear in the same field of a record at the same time, but also two words in the same subfield (one sentence), use Near to connect search term A and search term B. The search formula is: " A NearB". It means that the search term A and the search term B must not only appear in the same field in a record at the same time, but also the documents that appear in the same subfield (sentence) at the same time are the hit documents. For example: drug (drug) Near abuse (abuse), retrieved is the record of the two words appearing in the same sentence at the same time. (It can also be said to be a document without a full stop between two words).
Near#
It is represented by "Near#". Among them, "#" represents a constant. Use Near# to connect search term A and search term B. The search formula is: “A near# B” means documents with 0~# words between search term A and search term B (A And B are in the same record and same field). Add a number after near to specify how close the two words are, regardless of word order. Such as: information (information retrieval) near2 retrieval (data), which means that the search terms information and retrieval appear in a sentence at the same time, and the number of words between the two search terms does not exceed two The document is a hit document.
Order of operations
In a search formula, multiple logical operators can be used at the same time to form a compound logical search formula. In the compound logic search formula, the priority of operations is not, and, near, with, or from high to low. You can use parentheses to change the order of operations.
Such as: (A or B) and C first compute (A or B), then and C< /p>
The use of logical operators is the most frequent in search. The technique used by logical operators determines the satisfaction of search results. Using Boolean logic to express search requirements, in addition to grasping the relevant factors of the search subject, attention should also be paid to the influence of Boolean operators on the search results. In addition, for the same Boolean logic question formula, different operation orders will have different retrieval results.