1. A computer-implemented method for text processing, comprising: processing at least one body of text comprising semantic elements; recognizing respective syntactic roles of the semantic elements, wherein syntactic roles of the different semantic elements are represented by a given sentence as a hierarchical structure such as a tree, having subordinate and superordinate branches connected at nodes; segmenting the body of text into individual semantic constructs; removing at least one selected semantic element from the semantic constructs, so as to produce respective nuclear semantic constructs; computing respective occurrence frequencies of the nuclear semantic constructs; aggregating similar nuclear constructs, so that frequently occurring nuclear constructs are given high statistical significance; and invoking an action with respect to one or more of the nuclear semantic constructs whose occurrence frequencies meet a predefined condition, wherein removing the at least one selected semantic elements comprises predefining a nuclearization depth, and determining the selected semantic elements to be removed responsively to the predefined nuclearization depth, wherein computing the occurrence frequencies comprises assigning respective weights to occurrences of the nuclear semantic constructs, and computing the occurrence frequencies responsively to the weights.