SFX offers a way of navigating between and within electronic resources.
SFX allows students and researchers to link from a citation in a database to a list of different services available for that item including

Only services directly related to the citation of interest will be offered.

SFX buttons not only appear in the UNSW Catalogue and Sirius but can also be found when you search other resources including Science Direct, ProQuest and most OVID, CSA, Galegroup, HW Wilson, ISI, Biblioline, RLG, Silverplatter databases & electronic journal collections from JSTOR & Swetsnet.

When you click on SFX, an SFX window opens listing all the services available for that citation. When you select one of these services, another window opens. There will generally only be three windows open for any article you are looking at.

SFX services are determined by the information available in the record you started with, as well as the library resources that are available to you.

Possible reasons why the article is missing:

SFX will get you to the full text as close as it can, given the structure of the publisher site and how well their citation records have been catalogued. Sometimes you will go straight to the full text or an abstract with a full text link, sometimes the best that SFX can do is take you to the journal issues table of contents or home page, and you will have to navigate the publisher site yourself to get to the full text. There is a note on the SFX services screen under the data boxes that indicates how close SFX can initially get you to the full text.
Essentially a full text link in SFX means that full text is available -- but you may have to do some of the work of getting to it yourself.

Use the Report a Problem link which is found at the top of the SFX Services page and also in the blue Electronic Access and Support bar which appears at the top of most electronic resource screens.