The phrase "are only maintained" is correct and usable in written English.
It can be used when discussing the condition or status of something that is kept or preserved in a limited or specific manner.
Example: "The records are only maintained for a period of five years before they are archived."
Alternatives: "are solely kept" or "are just preserved".
Green spaces are only maintained, which means that they look similar for decades.
It is sometimes claimed that the village's traditions are only maintained for the visitors - that Olymbos has become a kind of theme-park.
Often, food supplies are only maintained at the expense of literally emptying some of the world's great rivers, such as the Indus in Pakistan, the Yellow River in China and the Nile in Egypt.
Of course, the bill's popularity and the demonization of LGBT people are only maintained through artificial means.
However, senescence features are only maintained in the p53ts-Ras cells incubated at 32°C (Figure 3B).
This is in agreement with the assumption that secondary metabolite gene clusters, once acquired, are only maintained, if natural selection favors their presence [55].
The two old parties whose stranglehold on Westminster is only maintained by the first past the post electoral system – though Labour has always had some reformers, and John Denham spoke for them.
Conservation is only maintained at the truncation error level at grid resolution changes and during grid adaptation, but our numerical tests indicate that the results are still very accurate.
For a general block with multiple discontinuity planes, it is assumed that contact is only maintained on a single plane (single-plane sliding) or two intersecting planes (double-plane sliding) in block theory analysis.
The aspect ratio of an imaged object is only maintained when considering planar rigid objects that move without rotating.
