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   26499篇
  免费   2906篇
  国内免费   5篇
  29410篇
  2022年   191篇
  2021年   384篇
  2020年   186篇
  2019年   257篇
  2018年   337篇
  2017年   296篇
  2016年   579篇
  2015年   832篇
  2014年   927篇
  2013年   1142篇
  2012年   1525篇
  2011年   1505篇
  2010年   1036篇
  2009年   974篇
  2008年   1339篇
  2007年   1340篇
  2006年   1159篇
  2005年   1209篇
  2004年   1196篇
  2003年   1128篇
  2002年   1061篇
  2001年   559篇
  2000年   537篇
  1999年   504篇
  1998年   318篇
  1997年   282篇
  1996年   268篇
  1995年   237篇
  1994年   259篇
  1993年   231篇
  1992年   413篇
  1991年   407篇
  1990年   419篇
  1989年   379篇
  1988年   363篇
  1987年   319篇
  1986年   298篇
  1985年   318篇
  1984年   308篇
  1983年   322篇
  1982年   264篇
  1981年   202篇
  1980年   217篇
  1979年   259篇
  1978年   238篇
  1977年   219篇
  1976年   197篇
  1975年   197篇
  1974年   204篇
  1973年   205篇
排序方式: 共有10000条查询结果,搜索用时 66 毫秒
101.
102.
The velo-cardio-facial syndrome is one of the most common syndromes of clefting. Previous reports have shown vertical pedigree transmission, but in all cases the gene was maternally transmitted. The genetics of this syndrome had been suspected as autosomal dominant, but X-linked dominant inheritance could not be ruled out. This report describes an instance of male-to-male transmission of the velo-cardio-facial syndrome. In addition, the clinical findings in 60 cases are reported to further delineate the phenotypic spectrum of the syndrome.  相似文献   
103.
104.
The introduction of the new immigration rules will considerably reduce the number of overseas doctors available for junior hospital appointments over the next five years. To offset this sponsorship schemes should be offered by universities and colleges comprising training courses, entry to examinations, and hospital appointments, and training programmes should be adapted to make objectives attainable in the four years available to overseas doctors. Employment of overseas doctors can ease the transition within the staffing structure to fewer juniors and more consultants, but planning is urgently required, and in particular the service and manpower needs of the National Health Service must be considered.  相似文献   
105.
Rumen holotrich ciliate protozoa.   总被引:8,自引:0,他引:8       下载免费PDF全文
  相似文献   
106.
A technique for differentiating high-resolution NMR signals from different regions of small objects is outlined and some initial results on model systems are given. This method uses inorganic paramagnetic or diamagnetic ions to create magnetic field gradients at phase boundaries.  相似文献   
107.
108.
Non-mydriatic retinal photography with later interpretation of the photographs was assessed as a screening method for the detection of diabetic retinopathy; when compared with an ophthalmologist''s clinical assessment in a random group of 62 diabetic patients it was accurate (false negative 6.8%, false positive 2%) and sensitive (sensitivity 96%, specificity 98%). The assessment of further management required based on analysis of the photographs was 96.5% in agreement with the further management suggested by the ophthalmologist after direct clinical assessment of the patient. If this technique were used to screen patients in a typical diabetic clinic the predicted positive accuracy rate would be 84% and the predicted negative accuracy rate 99.5%.  相似文献   
109.
Meiofauna were collected from adjacent areas with and without Spartina alterniflora Loisel culms. Environmental complexity resulting from root structure cannot be determined by simply observing S. alterniflora culm distribution. There were no significant differences between the two areas with respect to root density or root sizes; however, the number of live roots was significantly higher in the area containing Spartina culms. Nematodes, the most abundant taxon were positively correlated with live root density. In contrast, the number of dead roots and harpacticoid copepods were higher in the area without culms. This study suggests that nematodes are positively associated with micro-oxygenated zones produced by live S. alterniflora roots. Other measures of biogenic structure, such as total root density or root size fractions are not important in affecting nematode abundance.  相似文献   
110.
The murine E alpha immune response gene   总被引:26,自引:0,他引:26  
  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