No it is not a research station.
Each country supports its own research station on Antarctica. All of Antarctica is "controlled" by the Antarctic Treaty.
There is no Antarctic postal service. Every research station uses its country's postal services, and each station has its own individual postal code.
You may be thinking of the US research station at the South Pole: the Amundsen- Scott Research Station.
San Martin Base is on Barry Island, Marguerite Bay, Antarctic Peninsula. The base is operated by Argentina as a research office.
The largest research station on the Antarctic continent is called McMurdo Station. It is supported by the National Science Foundation, which represents the United States of America's interests there.
You can refer to the map, below, to identify those stations that qualify for your definition of 'inland' as locations for research stations on the Antarctic continent.
There are no cities on the continent of Antarctica. There are research stations, and there are times when the largest station is McMurdo Station with a transient population of about 1,000 souls.
A fire in an Antarctic research station is possibly the most dangerous event possible. Because there are generally no huge amounts of liquid water available to fight a fire, and because of the extreme dryness of the continent and all its buildings, fire can be fatal and completely devastating to a research station.
Station buildings are fabricated from imported building materials, including wood, metals, glass and so forth.
The country with the most permanent -- year 'round operation -- research stations is Argentina, with six. An additional summer station is also supported by the Argentine Antarctic Institute. The Russian Antarctic Expedition supports seven stations, only four of which are permanent, and three of which operate in the summer. One of these is a joint-support venture with Belarus.
Casey Station is supported by the Australian Antarctic Division (AAD) of the Australian government.