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   880781篇
  免费   89874篇
  国内免费   3609篇
  974264篇
  2018年   17646篇
  2017年   16060篇
  2016年   16118篇
  2015年   14369篇
  2014年   16486篇
  2013年   22408篇
  2012年   29122篇
  2011年   37026篇
  2010年   27679篇
  2009年   22901篇
  2008年   30853篇
  2007年   32920篇
  2006年   21818篇
  2005年   21153篇
  2004年   21393篇
  2003年   20271篇
  2002年   19668篇
  2001年   33892篇
  2000年   34192篇
  1999年   27351篇
  1998年   9882篇
  1997年   10143篇
  1996年   9547篇
  1995年   9124篇
  1994年   8812篇
  1993年   8783篇
  1992年   22530篇
  1991年   22127篇
  1990年   21563篇
  1989年   20840篇
  1988年   19520篇
  1987年   18554篇
  1986年   17569篇
  1985年   17568篇
  1984年   14541篇
  1983年   12523篇
  1982年   9676篇
  1981年   8959篇
  1980年   8195篇
  1979年   13850篇
  1978年   11266篇
  1977年   10160篇
  1976年   9551篇
  1975年   10934篇
  1974年   11959篇
  1973年   11769篇
  1972年   10984篇
  1971年   10087篇
  1970年   8427篇
  1969年   8294篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Systematic analysis of the long-chain components of Eubacterium lentum   总被引:1,自引:0,他引:1  
The cellular long-chain component patterns of 33 strains of Eubacterium lentum were determined by gas chromatography. Two main types of long-chain component patterns were distinguished. The first (26 strains) was characterized by saturated branched-chain fatty acids (br14:0, br15:0, br16:0 and br17:0). The second (7 strains) did not contain branched-chain fatty acids and was characterized by saturated straight-chain fatty acids (11:0, 12:0, 14:0 and 16:0). Both types contained fatty aldehydes and their respective dimethyl acetals (14ald and 14dma, 16ald and 16dma). br16dma was only found in the first type. The G + C content of the DNA (Tm) of the 33 strains varied between 63.7 and 69.1 mol %. Canonical correlation analysis distinguished three subtypes within the first main type.  相似文献   
132.
133.
Antibodies to calcitonin, parathyroid hormone and cortisol are detected in acute stage of infection-caused bronchial asthma. The appearance of antibodies is paralleled by marked hypercalcaemia. The antibodies may bind excessive hormones in the blood, preventing further hormonal imbalance. Ten-day treatment with glucocorticoids decreased the amount of antibodies possibly due to normalization of hormonal secretion and restoration of their balance. As a result, calcium blood levels returned to normal.  相似文献   
134.
135.
136.
137.
Neurospora grows vegetatively as a syncytium in which multiple nuclei exist within a connected cytoplasm. Because of the ability of separate and distinct mycelia to fuse, the possibility exists of generating heterocaryotic cultures in which the nuclei and cytoplasms of two different strains are comingled into the same syncytium. We have used such heterocaryons, in which the component parts differed with respect to their circadian clock phase, to examine whether or not clock-dominant phases exist in the circadian cycle. To this end, the phase subsequent to the formation of heterocaryons by pairs of mycelial discs that are initially at different circadian phases was examined in Neurospora crassa. The resulting phase was an average of the parent phases in many cases, but was sometimes observed to correspond more closely to just one of the original parental phases. In these cases, we did not observe any dominant phases in the circadian cycle; the phase of a particular parent disc was more dominant in the heterocaryon when the proportion of the nuclei from that parent was greater in the heterocaryon. In some instances, which occurred mostly when the difference in phase of the parental discs was large, the resultant phase could not be related in a simple way to the parental phases. An interpretation based on a limit cycle model of the circadian oscillation is possible.  相似文献   
138.
139.
140.
A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.  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