The phrase "attempts were then" is correct and usable in written English.
It can be used to indicate that attempts were made at a specific point in time, often following a previous action or event.
Example: "After the initial failure, attempts were then made to rectify the situation and improve the outcome."
Alternatives: "efforts were subsequently" or "attempts were subsequently".
Attempts were then made to return to business as usual as quickly as possible.
The state has refused to say whether, as required by its execution protocol, any attempts were then made to revive Lockett.
As these heat exchangers were not specifically designed for this application, attempts were then made to improve the overall performance of the exhaust heat recovery system by optimizing the design of the heat exchangers.
Attempts were then made to analyze the data using GridQTL, version 1.4.1.
However, the symptoms were confused with those of malaria, and attempts were then made to treat the patients with quinine.
Virus isolation attempts were then terminated because the cultivation of C-CHFV (the presumptive cause) requires biosafety level 4 facilities.
The increase or decrease ratio for the scores of the observed peak positions with respect to the expected value for the null hypothesis (the average score of random attempts) was then calculated, and the P-value for the drift was estimated as Standard Normal CDF of (actual − mean) / deviation.
The Sensitivity (Sen) and Specificity (Sp) diagnostic values for each examiner attempt were then calculated (Table 2).
Blair's attempt was then.
Although an attempt is then made to find a foundation for the human sciences (Geisteswissenschaften) by means of experimental psychology, it proves to be impossible, because in so doing one is unable to grasp precisely what is at stake in knowledge as found in the natural sciences.
An attempt was then made to correlate the amount of tightly bound rubber with the carbon surface chemistry in CB.
