One difference between the language in fiction and science is that science would more likely use a specific kind of vocabulary that might not be known to the average reader.
Another difference is that the language used in fiction is often full of 'literary devices' such as figurative language (alliteration, personification for example) and might use irony or sarcasm. An article written for science would not use figurative language or other rhetorical devices.
Finally, a difference would be that papers written for a science publication are usually written in the passive tense and in third person. A work of fiction can be either in first, second (rare) or third person and usually active.