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   669968篇
  免费   78718篇
  国内免费   487篇
  2018年   5561篇
  2016年   7877篇
  2015年   11574篇
  2014年   13007篇
  2013年   18783篇
  2012年   21046篇
  2011年   21359篇
  2010年   14180篇
  2009年   13145篇
  2008年   18969篇
  2007年   19523篇
  2006年   18021篇
  2005年   17650篇
  2004年   17321篇
  2003年   16538篇
  2002年   15923篇
  2001年   29817篇
  2000年   30057篇
  1999年   24083篇
  1998年   8819篇
  1997年   9303篇
  1996年   8988篇
  1995年   8093篇
  1994年   8130篇
  1993年   8008篇
  1992年   19620篇
  1991年   18956篇
  1990年   18410篇
  1989年   18254篇
  1988年   16523篇
  1987年   15945篇
  1986年   14645篇
  1985年   14588篇
  1984年   12340篇
  1983年   10567篇
  1982年   8327篇
  1981年   7595篇
  1980年   7092篇
  1979年   11733篇
  1978年   9089篇
  1977年   8528篇
  1976年   7934篇
  1975年   8532篇
  1974年   9310篇
  1973年   9149篇
  1972年   8210篇
  1971年   7639篇
  1970年   6580篇
  1969年   6432篇
  1968年   5784篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked.  相似文献   
82.
83.
84.
OBJECTIVE--To test the hypothesis that farmers are at high risk of hip osteoarthritis and to investigate possible causes for such a hazard. DESIGN--Cross sectional survey. SETTING--Five rural general practices. SUBJECTS--167 male farmers aged 60-76 and 83 controls from mainly sedentary jobs. All those without previous hip replacement underwent radiography of the hip. MAIN OUTCOME MEASURES--Hip replacement for osteoarthritis or radiological evidence of hip osteoarthritis. RESULTS--Prevalence of hip osteoarthritis was higher in farmers than controls and especially in those who had farmed for over 10 years (odds ratio 9.3, 95% confidence interval 1.9 to 44.5). The excess could not be attributed to any one type of farming, and heavy lifting seems the likely explanation. CONCLUSIONS--Manual handling in agriculture should be limited where possible. Consideration should be given to making hip osteoarthritis a prescribed industrial disease in farmers. There may be wider implications for the prevention of hip osteoarthritis in the general population.  相似文献   
85.
86.
87.
88.
An earlier report (1) of an adverse effect of high doses of oxytocin on human memory included results of studies on women receiving oxytocin as part of the treatment to induce 2nd trimester therapeutic abortion. These women served as their own controls. We have now been able to study a group of women who have been treated in all ways like the original group, with the exception that they did not receive oxytocin. The results from this external control corroborate the finding that oxytocin affected memory.  相似文献   
89.
90.
β-Xylosidases are hydrolytic enzymes which play an important role in xylan degradation, hydrolyzing xylobiose and xylooligosaccharides to xylose from the non-reducing end. Filamentous fungi are particularly interesting producers of this enzyme from an industrial point of view, due to the fact that they secrete β-xylosidases into the medium. Besides, fungal β-xylosidases are highly advantageous for their elevated activity levels and specificity. Interest in xylanolytic enzymes has been increasing, for their possible application in many biotechnological processes. This fact has driven the isolation, purification and characterization of several β-xylosidases. In this review, the mechanisms of action, substrate specificities, physicochemical characteristics, regulation at molecular level, molecular cloning and classification of filamentous fungal β-xylosidases are described. The potential industrial applications of fungal β-xylosidases will also be presented.  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