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   30919篇
  免费   3324篇
  国内免费   10篇
  34253篇
  2021年   358篇
  2019年   254篇
  2018年   343篇
  2017年   294篇
  2016年   580篇
  2015年   926篇
  2014年   987篇
  2013年   1288篇
  2012年   1572篇
  2011年   1551篇
  2010年   1137篇
  2009年   1012篇
  2008年   1365篇
  2007年   1458篇
  2006年   1319篇
  2005年   1318篇
  2004年   1267篇
  2003年   1247篇
  2002年   1216篇
  2001年   672篇
  2000年   624篇
  1999年   610篇
  1998年   387篇
  1997年   357篇
  1996年   330篇
  1995年   302篇
  1994年   314篇
  1993年   282篇
  1992年   512篇
  1991年   490篇
  1990年   506篇
  1989年   457篇
  1988年   442篇
  1987年   431篇
  1986年   395篇
  1985年   425篇
  1984年   432篇
  1983年   411篇
  1982年   385篇
  1981年   300篇
  1980年   295篇
  1979年   350篇
  1978年   318篇
  1977年   292篇
  1976年   283篇
  1975年   269篇
  1974年   292篇
  1973年   260篇
  1972年   260篇
  1971年   227篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
A technique for differentiating high-resolution NMR signals from different regions of small objects is outlined and some initial results on model systems are given. This method uses inorganic paramagnetic or diamagnetic ions to create magnetic field gradients at phase boundaries.  相似文献   
132.
133.
Non-mydriatic retinal photography with later interpretation of the photographs was assessed as a screening method for the detection of diabetic retinopathy; when compared with an ophthalmologist''s clinical assessment in a random group of 62 diabetic patients it was accurate (false negative 6.8%, false positive 2%) and sensitive (sensitivity 96%, specificity 98%). The assessment of further management required based on analysis of the photographs was 96.5% in agreement with the further management suggested by the ophthalmologist after direct clinical assessment of the patient. If this technique were used to screen patients in a typical diabetic clinic the predicted positive accuracy rate would be 84% and the predicted negative accuracy rate 99.5%.  相似文献   
134.
The murine E alpha immune response gene   总被引:26,自引:0,他引:26  
  相似文献   
135.
This study was designed to investigate the mitotic response to wounding in the rat thyroid. The spatial distribution of mitotic activity 48 hr after incision of the thyroid isthmus, or mere exposure of the gland (sham-operation), was assessed using a stathmokinetic technique. Incision resulted in a 66-fold increase over normal in metaphase index adjacent to the wound, falling over 2 mm to a stable 13-fold elevation. Sham-operation produced a smaller response with a complete return to normal levels over 1-1 X 5 mm. The results demonstrate that there is a dramatic localized mitotic response to wounding in the thyroid together with a smaller generalized response. Further, the response to sham-operation indicates that thyroid follicular cells respond to a diffusible 'wound hormone'. We suggest that this may be a major mechanism mediating reparative growth in this gland.  相似文献   
136.
Thermal shock is a form of hemolysis which occurs in human red cells exposed to greater than a critical level of osmotic stress of 1.4 Osm and subsequently cooled from above about 12 degrees C to below that temperature. Higher concentrations and higher cooling rates each increase the amount of hemolysis, within limits. Incubation for varying periods in hypertonic solutions and varying temperatures of incubation affect the amount of thermal shock. The effect of cooling rate on thermal shock is independent of the period of exposure to hypertonic solutions. Thermal shock is not the cause of freezing injury in human red cells, at least above -10 degrees C.  相似文献   
137.
The effect of continuous-wave ultrasound on the chromosomes of newborn infants has been investigated. Twenty-four women were studied during labour. The fetal heart was monitored by a Sonicaid FM2 monitor applied to the abdomen, and continuous monitoring undertaken for intervals varying from 1 hour 5 minutes to 9 hours 25 minutes. There was no increase in the number of chromosome aberrations in cultures of blood taken from the insonated babies when compared with controls.  相似文献   
138.
139.
In a series of 68 patients with gastric ulcer who were treated by vagotomy and pyloroplasty there were no operative deaths, though one patient who received massive transfusions died 14 weeks later from hepatic necrosis probably associated with serum hepatitis. Four patients developed recurrent peptic ulceration requiring further surgical treatment. The clinical condition of all but three of the remainder was satisfactory after an average follow-up period of three years and two months. Of the 14 patients who presented with an acutely bleeding gastric ulcer, one subsequently required gastrectomy for continued bleeding; in all the others the immediate and long-term results were satisfactory. Of 21 patients with a “high” ulcer and 29 with combined gastric and duodenal ulceration one (4·8%) and three (10%) respectively suffered recurrences. We conclude that vagotomy and pyloroplasty is a satisfactory form of treatment for a high or bleeding gastric ulcer, but that for all other gastric ulcers some form of gastric resection is preferable.  相似文献   
140.
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