首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   16630篇
  免费   2183篇
  国内免费   8篇
  18821篇
  2021年   208篇
  2019年   170篇
  2018年   199篇
  2017年   177篇
  2016年   301篇
  2015年   476篇
  2014年   549篇
  2013年   661篇
  2012年   768篇
  2011年   835篇
  2010年   542篇
  2009年   515篇
  2008年   671篇
  2007年   650篇
  2006年   564篇
  2005年   597篇
  2004年   615篇
  2003年   564篇
  2002年   525篇
  2001年   510篇
  2000年   555篇
  1999年   466篇
  1998年   207篇
  1997年   212篇
  1996年   192篇
  1995年   195篇
  1994年   198篇
  1993年   181篇
  1992年   389篇
  1991年   386篇
  1990年   381篇
  1989年   338篇
  1988年   323篇
  1987年   297篇
  1986年   250篇
  1985年   271篇
  1984年   228篇
  1983年   214篇
  1982年   168篇
  1981年   168篇
  1980年   154篇
  1979年   236篇
  1978年   199篇
  1977年   184篇
  1976年   179篇
  1975年   177篇
  1974年   170篇
  1973年   188篇
  1972年   176篇
  1971年   166篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
The skeletal age of each individual bone of the hand-wrist was assessed in serial radiographs of 169 Melbourne children. Seven different methods were used to obtain area skeletal ages from these bone skeletal ages. Methods employing arithmetic means of all the bone skeletal ages, excluding only extreme values, excluding those derived from the carpals or from other selected bones yielded similar means during the age range studied in each sex. There were large, but not significant, differences between the means derived from averages of the skeletal ages of the most and least mature bones and those derived from all the bone skeletal ages. A system of weighting and exclusion of bone skeletal ages led to the recording of area skeletal ages that differed from the others and fluctuated markedly for individuals until ossification had occurred in every carpal bone. The findings suggest that the exclusion of the skeletal ages of the carpal bones or the use of selected skeletal ages could lead to quicker assessments without real changes in means and variability.  相似文献   
85.
86.
87.
Radioactive glutamic acid and N-acetylglutamic acid have been incubated with normal and wilted leaf discs and radioactivity recovered in uncombined proline. The discs which had been placed under moisture stress incorporated considerably more label in uncombined proline than did normal discs.  相似文献   
88.
89.
Studies with N-methyl emetine   总被引:1,自引:0,他引:1  
  相似文献   
90.
Summary Quantitation of synapses at different postnatal ages has been undertaken in the cerebral cortex of the rat. In this study axial ratios of presynaptic bags, proportion of cortex occupied by presynaptic bags and numbers of synapses per unit volume of cortex have been estimated. Observations on synaptic vesicle packing densities have also been made.Synaptic bags become increasingly spherical up to 7 days of age and become more elongated thereafter. The proportion of cortex occupied by presynaptic bags increases rapidly up to 7 days of age and then at a decelerated rate up to maturity. The number of synapses per unit volume increases slowly over the first four days after which there is a rapid increase to 14 days, followed by a decelerated rate.The average presynaptic bag shows marked changes in volume with increasing age which indicate the probability of two stages of synaptic development. This two stage development is further reflected in the estimates on vesicle packing densities. The implications of the results are discussed in relationship to changes in functional activity of the cortex during postnatal development.The authors wish to express their thanks to Mr. R. Birchenough and Mr. J. Manston for much technical assistance.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号