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   1282886篇
  免费   109867篇
  国内免费   1454篇
  2021年   17863篇
  2020年   12653篇
  2019年   16218篇
  2018年   17377篇
  2017年   16153篇
  2016年   27924篇
  2015年   42441篇
  2014年   50504篇
  2013年   76792篇
  2012年   34978篇
  2011年   22837篇
  2010年   42809篇
  2009年   44519篇
  2008年   22165篇
  2007年   19711篇
  2006年   25482篇
  2005年   26449篇
  2004年   25714篇
  2003年   23403篇
  2002年   21549篇
  2001年   29087篇
  2000年   26134篇
  1999年   27413篇
  1998年   24916篇
  1997年   24719篇
  1996年   24350篇
  1995年   22375篇
  1994年   22325篇
  1993年   21323篇
  1992年   24262篇
  1991年   22843篇
  1990年   21419篇
  1989年   22558篇
  1988年   20554篇
  1987年   19560篇
  1986年   18592篇
  1985年   20628篇
  1984年   20905篇
  1983年   18524篇
  1982年   19643篇
  1981年   19065篇
  1980年   17752篇
  1979年   17040篇
  1978年   16408篇
  1977年   16065篇
  1976年   15276篇
  1975年   14587篇
  1974年   15029篇
  1973年   15385篇
  1972年   12889篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
155.
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   
156.
When cotyledonary tissue of G., barbadense cotton are treated with the mutagen ethyl methanesulfonate and then germinated, an enhanced, unscheduled DNA synthesis response is observed, along with a concomitant increase in the thymidine triphosphate precursor pool size. The implications of these results are discussed in this paper.  相似文献   
157.
158.
159.
Nitrogen fertigation of greenhouse-grown cucumber   总被引:2,自引:0,他引:2  
Summary This greenhouse study investigated the response of trickle-irrigated cucumber (Cucumis sativa cv. ‘Petita’) to three N levels applied with every irrigation via the irrigation stream. The plants were grown in pots filled with 12 kg of soil. Water containing 5.8, 11.8, or 17.8 mmol N/l, and uniformly supplied with 2.0 and 3.9 mmol/l of P and K, respectively, was applied two to three times daily. In all treatments of 0.3 leaching fraction was allowed. The resulting total N applications were 15.7, 31., and 47.2 g N/plant. The total amount of water applied was 1851/plant. Total N and NO3-N, in lajinae and petioles, increased with increasing N level whereas P and K in generated decreased. Although different NO3/NH4 ratios in the treatments may have influeced the response to N, it could be concluded that the highest yield was obtained with 11.8 mmol N/1 due to increased number of fruit. In the root volume of this treatment the NO3-N concentration in the soil solution was aroun 7 mmol/1 for most of the growing season. The dry matter concentration of fruits was not affected by the N levels. It was concluded that 11.8 mmol N/1 applied with every irrigation via the irrigation stream is adequate to cover the needs of greenhous-grown cucumber for higher yield (9.42 kg/plant over a harvesting period of 93 days).  相似文献   
160.
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   
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