web scraping in R but in a search interface

I am using package rvest for web-scraping in R. This is a search site. I need to input some conditions to search the result I want, which is scraping data from a search interface site. But the url of the search result is same to the original website. So if I input

library(rvest) url<-html("http://....")

The content of url is from the search site but not the search result. On the search result site, of course I can view the page source. The question is how to input the search result into R.

Any one has experience in this type of scraping? Thank you in advance!