a)如何指出当前研究的不足以及有目的地引导出自己的研究的重要性通常在叙述了前人成果之后，用However来引导不足，比如
However, little information..
      little attention...
      little work...
      little data
      little research
or     few studies
      few investigations...
      few researchers...
      few attempts...
or     no
      none of these studies
has (have) been less
        done on ...
        focused on
        attempted to
        conducted
        investigated
        studied
  (with respect to)
Previous research (studies, records) has (have)
    failed to consider
    ignored
    misinterpreted
    neglected to
    overestimated, underestimated
    misled
thus, these previous results are  inconclusive, misleading, unsatisfactory, questionable, controversial..
Uncertainties (discrepancies) still exist ...
这种引导一般提出一种新方法，或者一种新方向。如果研究的方法以及方向和前人一样，可以通过下面的方式强调自己工作的作用：
However, data is still scarce
              rare
              less accurate
      there is still dearth of
We need to
  aim to
  have to
      provide more documents
              data
              records
              studies
      increase the dataset
Further studies are still necessary...
            essential...
为了强调自己研究的重要性，一般还要在However之前介绍自己研究问题的反方面，另一方面等等
比如：
1)时间问题
如果你研究的问题时间上比较新，你就可以大量提及对时间较老的问题的研究及重要性，然后说(However)，对时间尺度比较新的问题研究不足
2)物性及研究手段问题
如果你要应用一种新手段或者研究方向，你可以提出当前比较流行的方法以及物质性质，然后说对你所研究的方向和方法，研究甚少。

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