Support FAQ - When searching some words in the portal no results are found
Words like "a", "and", "is", "for" are examples of stop words. To keep full-text from becoming so large that it becomes unusable, Microsoft puts certain words that are deemed “useless” to a query into an 'ignore' list
You can refer to the following link:
https://msdn.microsoft.com/en-us/library/ms142551(v=sql.100).aspx