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   643335篇
  免费   65268篇
  国内免费   9998篇
  718601篇
  2021年   8655篇
  2020年   5939篇
  2019年   7326篇
  2018年   18136篇
  2017年   15868篇
  2016年   16445篇
  2015年   15337篇
  2014年   17256篇
  2013年   21492篇
  2012年   28391篇
  2011年   35215篇
  2010年   25987篇
  2009年   21395篇
  2008年   27489篇
  2007年   28754篇
  2006年   16983篇
  2005年   16076篇
  2004年   15728篇
  2003年   14996篇
  2002年   13862篇
  2001年   24658篇
  2000年   24573篇
  1999年   19704篇
  1998年   7444篇
  1997年   7703篇
  1996年   7452篇
  1995年   6705篇
  1994年   6684篇
  1993年   6316篇
  1992年   14879篇
  1991年   13954篇
  1990年   13405篇
  1989年   13137篇
  1988年   11688篇
  1987年   11240篇
  1986年   10212篇
  1985年   9982篇
  1984年   8370篇
  1983年   7272篇
  1982年   5630篇
  1981年   5101篇
  1979年   7760篇
  1978年   5960篇
  1977年   5487篇
  1976年   5116篇
  1975年   5409篇
  1974年   5847篇
  1973年   5705篇
  1972年   5364篇
  1971年   5002篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
In a multicentre, randomised, prospective trial 89 patients (67 children and 22 adults) with the minimal change nephrotic syndrome were treated with three intravenous pulses of methylprednisolone followed by low dose oral prednisone for six months (group given methylprednisolone) or with high dose oral prednisone for four weeks followed by low dose oral prednisone for five months (control group). Five patients in the group given methylprednisolone and one in the control group did not respond initially. The time to response was shorter in children treated with methylprednisolone. No significant differences between the two groups were observed in the number of patients who relapsed or number of relapses per patient per year. Patients given methylprednisolone tended to relapse earlier than patients in the control group. Side effects related to treatment were significantly fewer in the group given methylprednisolone than in the control group. These data suggest that a short course of methylprednisolone pulses followed by low dose oral prednisone is only marginally less effective than a regimen of high dose oral steroids but can improve the ratio of risk to benefit associated with treatment of the minimal change nephrotic syndrome.  相似文献   
62.
Monosomy 21: a new case confirmed by in situ hybridization   总被引:4,自引:0,他引:4  
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.  相似文献   
63.
A series of measurements of blood pressure in normotensive and hypertensive subjects showed that measurements made with a sphygmomanometer with the arm dependent by the side were consistently higher than those made with the arm horizontal at heart level. The mean difference in a group of 90 hypertensive outpatients was 11/12 mm Hg. Failure to appreciate the importance of arm position may lead to erroneous measurements of blood pressure. This has important implications for clinical practice and research.  相似文献   
64.
65.
Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402. Received 31 May 2001/ Accepted in revised form 09 July 2001  相似文献   
66.
67.
The heart rate and respiratory patterns in hypoxia are not well documented in unanaesthetized intact newborn animals. We studied heart rate and respiratory patterns during quiet sleep in 17% inspired O2 in 31 unanaesthetized newborns of five species: lamb, piglet, puppy, kitten, and rabbit. There was no significant change in mean heart rate and respiratory rate with hypoxia for any species. Brief apneas greater than 5 s were frequent (5-8/h), both in 21 and 17% O2 only in lambs and puppies. No sustained periodic breathing was induced by hypoxia. Thus, mild hypoxia has little steady-state effect on heart rate and respiratory rate and pattern in these unanaesthetized newborns. These findings are compatible with depressed chemoreceptor threshold, but indicate a remarkably mature respiratory pattern in full-term newborns of these species.  相似文献   
68.
69.
70.
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