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   1013篇
  免费   44篇
  国内免费   59篇
耳鼻咽喉   1篇
儿科学   61篇
妇产科学   110篇
基础医学   62篇
口腔科学   14篇
临床医学   213篇
内科学   231篇
皮肤病学   17篇
神经病学   12篇
特种医学   231篇
外科学   33篇
综合类   27篇
预防医学   44篇
眼科学   8篇
药学   29篇
中国医学   2篇
肿瘤学   21篇
  2022年   3篇
  2021年   9篇
  2020年   3篇
  2019年   3篇
  2018年   12篇
  2017年   3篇
  2015年   13篇
  2014年   13篇
  2013年   24篇
  2012年   10篇
  2011年   8篇
  2010年   20篇
  2009年   20篇
  2008年   15篇
  2007年   51篇
  2006年   9篇
  2005年   18篇
  2004年   21篇
  2003年   15篇
  2002年   16篇
  2001年   16篇
  2000年   15篇
  1999年   20篇
  1998年   54篇
  1997年   37篇
  1996年   60篇
  1995年   45篇
  1994年   45篇
  1993年   55篇
  1992年   23篇
  1991年   31篇
  1990年   33篇
  1989年   45篇
  1988年   52篇
  1987年   45篇
  1986年   34篇
  1985年   40篇
  1984年   26篇
  1983年   17篇
  1982年   14篇
  1981年   27篇
  1980年   19篇
  1979年   10篇
  1978年   11篇
  1977年   18篇
  1976年   9篇
  1975年   15篇
  1973年   2篇
  1972年   4篇
  1891年   1篇
排序方式: 共有1116条查询结果,搜索用时 15 毫秒
1.
2.
3.
Data from 4,300 consecutive cases following prenatal diagnosis by transcervical (TC) CVS (n = (1,570) and transabdominal (TA) CVS (n = 2,370) were evaluated. In the follow-up study only infants examined by a physician were included. Gestational age varied between 8.5 and 11.6 weeks (mean 10.3 weeks) for TC-CVS and between 9.3 and 20 weeks (mean 12.3 weeks) for TA-CVS 98% of TC-CVS was performed at 9–10 weeks, 80.7% of TA-CVS procedures were carried out at 12–15 weeks. Selective termination took place in 97 cases of TC-CVS (6.1%) and in 72 cases of TA-CVS (2.6%). Another 8 Women had a termination for psychosocial reasons, resulting in 4,123 (1,469 TC, 2,645 TA) continuing pregnancies. The overall fetal loss rare <28 weeks was 5.4% (n = 80) for TC-CVS and 2.6% (n = 70) for TA-CVS. The overall incidence of congenital abnormalities after birth was 0.9%. Two terminal transversal limb defects were detected in the TC-CVS group (0.14%) against one (0.04%) in the TA-CVS group. © 1993 Wiley-Liss, Inc.  相似文献   
4.
5.
6.
Inversion recovery (IR), commonly considered a pulse sequence capable of producing T1-weighted images with excellent display of normal anatomy, is versatile: The null point and peak time provide a useful, succinct summary of the properties of IR and its capacity for producing both T1- and T2-weighted images. Shortening of the inversion time (TI) and creation of a short-TI inversion-recovery (STIR) pulse sequence increases sensitivity to malignancy and other abnormalities by making the effects of prolonged T1 and T2 on signal intensity additive and by nulling the signal from fat. The authors examined over 300 patients with various malignancies and compared STIR images with T1- and T2-weighted images obtained at 0.5 T. In 43 cases, signal-difference-to-noise ratios (SD/Ns) were calculated between tumor, fat, and muscle. In general, STIR images demonstrated tumor as a conspicuously high-intensity area in a background of muted, discernible anatomic detail. The good contrast achieved with STIR sequences between tumor and fat (SD/N = 18.1) and tumor and muscle (SD/N = 12.9) consolidated into a single image the information contained separately on T1- and T2-weighted images, which facilitates efficient detection and localization of malignancy.  相似文献   
7.
Goei  R; Baeten  C; Arends  JW 《Radiology》1988,168(2):303-306
Sixteen cases of histopathologically proved solitary rectal ulcer syndrome were encountered. Fifteen patients underwent barium enema study; in nine cases the findings--including rectal stricture, granularity of the mucosa, and thickened rectal folds-were nonspecific. In six cases the study was normal. All patients had a long history of defecation disorders, and defecography was performed in all. In seven cases, intussusception of the rectal wall was seen; in another case the intussusception was accompanied by a rectocele. One case showed rectal prolapse. In four cases, failed relaxation of the puborectalis occurred and prevented the passage of the bolus; in another case there was abnormal perineal descent. In two patients studies were normal. In patients with defecation disorders, the possibility of this syndrome should be considered. Defecography is the method of choice for establishing the diagnosis.  相似文献   
8.
OBJECTIVES: To study heart rate and umbilical artery blood flow velocity variability in growth-restricted fetuses and investigate the influence of the autonomic nervous system on these parameters. METHODS: Doppler velocity waveforms were collected from long-lasting umbilical artery recordings in 15 fetuses with growth restriction and 15 normal age-matched controls at 23-35 weeks of gestation. Absolute heart rate and umbilical artery blood flow velocity as well as the coefficient of variation were determined. Using power spectral analysis the low- and high-frequency bands of heart rate variability and blood flow velocity variability were calculated. The low-to-high (LH) ratio of heart rate variability and blood flow velocity variability were examined as a measure of sympathovagal balance. RESULTS: In growth-restricted fetuses umbilical artery velocities were significantly reduced. Heart rate variability was significantly reduced in the presence of growth restriction, but no significant difference was demonstrated for blood flow velocity variability. The LH ratio for heart rate variability was significantly decreased in growth restriction, but no difference in LH ratio was demonstrated for blood flow velocity variability. CONCLUSION: Flow velocity variability in growth restriction seems not to be predominantly influenced by the autonomic nervous system, whereas the decreased heart rate variability seems to be influenced by altered sympathetic-parasympathetic balance.  相似文献   
9.
10.
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