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   1273836篇
  免费   109218篇
  国内免费   1452篇
  2021年   17723篇
  2020年   12572篇
  2019年   16126篇
  2018年   17234篇
  2017年   16005篇
  2016年   27717篇
  2015年   42146篇
  2014年   50161篇
  2013年   76357篇
  2012年   34003篇
  2011年   21829篇
  2010年   42397篇
  2009年   44164篇
  2008年   21379篇
  2007年   18869篇
  2006年   24801篇
  2005年   25827篇
  2004年   25155篇
  2003年   22836篇
  2002年   20994篇
  2001年   29021篇
  2000年   26093篇
  1999年   27363篇
  1998年   24835篇
  1997年   24679篇
  1996年   24316篇
  1995年   22338篇
  1994年   22284篇
  1993年   21283篇
  1992年   24227篇
  1991年   22816篇
  1990年   21393篇
  1989年   22543篇
  1988年   20540篇
  1987年   19550篇
  1986年   18576篇
  1985年   20616篇
  1984年   20891篇
  1983年   18511篇
  1982年   19640篇
  1981年   19060篇
  1980年   17747篇
  1979年   17036篇
  1978年   16403篇
  1977年   16062篇
  1976年   15274篇
  1975年   14581篇
  1974年   15024篇
  1973年   15385篇
  1972年   12887篇
排序方式: 共有10000条查询结果,搜索用时 281 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