首页 | 官方网站   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   1700051篇
  免费   123854篇
  国内免费   3807篇
医药卫生   1827712篇
  2021年   12889篇
  2019年   13619篇
  2018年   20058篇
  2017年   15288篇
  2016年   16685篇
  2015年   19040篇
  2014年   26342篇
  2013年   38091篇
  2012年   52974篇
  2011年   55672篇
  2010年   32905篇
  2009年   30809篇
  2008年   51729篇
  2007年   55030篇
  2006年   55465篇
  2005年   52788篇
  2004年   50936篇
  2003年   48353篇
  2002年   46557篇
  2001年   91911篇
  2000年   93731篇
  1999年   77057篇
  1998年   19772篇
  1997年   17313篇
  1996年   17423篇
  1995年   16780篇
  1994年   15327篇
  1993年   14097篇
  1992年   57487篇
  1991年   55364篇
  1990年   53049篇
  1989年   50853篇
  1988年   46217篇
  1987年   45006篇
  1986年   42280篇
  1985年   40057篇
  1984年   29417篇
  1983年   24952篇
  1982年   13922篇
  1979年   25568篇
  1978年   17601篇
  1977年   14925篇
  1976年   13902篇
  1975年   14587篇
  1974年   17663篇
  1973年   16984篇
  1972年   15699篇
  1971年   14475篇
  1970年   13457篇
  1969年   12546篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Experiments were performed to determine the effect of pin channel preparation with standard and reduction speed handpieces, and pin seating by hand and with motor drive. The greatest retention was achieved by preparation with a standard handpiece at 6000 rpm, and manual pin placement with a hand driver. The most consistent retention values were achieved using the reduction handpiece. All preparation and placement combinations examined produced a clinically acceptable result.  相似文献   
992.
A prospective blinded study was performed on 191 high-risk patients with pregnancies ranging from 25 to 42 weeks gestation to investigate the value of a single Doppler analysis of the umbilical artery blood flow waveform (systolic-to-diastolic ratio, S/D) for predicting poor perinatal outcome. This was defined as the presence of heavy meconium, delivery of a growth-retarded infant, an umbilical cord arterial pH less than 7.2, or a 5-minute Apgar score less than 7. The interval between Doppler examination and delivery ranged from 12 hours to 15 weeks. No clinical data were available to the examiner performing the Doppler study. Moreover, the Doppler measurements were unknown to the attending physicians. The sensitivity, specificity, and positive and negative predictive values of the Doppler study in predicting outcome were 30.4%, 92.9%, 36.8%, and 92.6%, respectively, with an adverse outcome prevalence of 12%. These results indicate that a single random S/D ratio from the umbilical artery is not an adequate screening test for the risk of perinatal complications.  相似文献   
993.
1. alpha 2-Adrenoceptors on platelet membranes and beta 2-adrenoceptors on lymphocytes were studied in 24 patients with primary Raynaud's phenomenon and in 24 age- and sex-matched control subjects. In two subgroups, a standardized mental arithmetic test and a finger-cooling test were performed. 2. Baseline blood pressure, heart rate and forearm blood flow did not differ between the two groups. 3. Baseline skin microcirculation (laser Doppler flux) was decreased in primary Raynaud's phenomenon (19 +/- 15 arbitrary units) compared with control subjects (33 +/- 14 arbitrary units) (P less than 0.01). 4. Baseline plasma noradrenaline concentration (2.00 +/- 1.44 versus 1.16 +/- 0.36 nmol/l) and alpha 2-adrenoceptor density (301 +/- 119 versus 210 +/- 82 fmol/mg) were increased in patients with primary Raynaud's phenomenon in comparison with the control subjects. The alpha 2-adrenoceptor density/beta 2-adrenoceptor density ratio in patients with primary Raynaud's phenomenon was, with a value of 0.37 +/- 0.04, higher than in the control subjects, where a value of 0.25 +/- 0.02 was measured (P less than 0.001). Plasma adrenaline concentration, beta 2-adrenoceptor density and the antagonist affinity to both receptor subtypes did not differ between both groups under baseline conditions. 5. Whereas during the finger-cooling test no differences were seen in the responses of the parameters measured, the mental arithmetic test induced an increase in laser Doppler flux in patients with primary Raynaud's phenomenon and a decrease in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
994.
Using the indirect immunofluorescent assay, we observed the variation of T-lymphocyte subsets of peripheral blood in 100 patients of primary bronchogenic carcinoma and 31 cases with active pulmonary tuberculosis. Serum CEA were measured simultaneously. The decrease of OKT3+, OKT4+, OKT8+ lymphocytes were significant in patients with lung cancer than that in healthy controls (P less than 0.01). The ratio of OKT4+/OKT8+ increased. It suggested that both cellular immunoincompetence and immunoregulatory abnormality were present in patients with lung cancer. After the resection of tumors 65 cases, the percentage of OKT4+ cells increased at the first week. Fourty seven cases were observed continuously for six months, it was found that OKT8+ cells increased (P less than 0.01). After anticancer chemotherapy, the patients with small cell carcinoma revealed a similar changes too. After operation and chemotherapy, serum CEA level decreased significantly too.  相似文献   
995.
Stylistic amendments to the original Penrose text have been made where necessary for further clarity  相似文献   
996.
Liver histopathology in clinical Reye syndrome   总被引:1,自引:0,他引:1  
Analysis of the liver histopathology in 19 children with clinical Reye syndrome (RS) revealed that nine had diffuse panlobular steatosis, one giant cell hepatitis, one a mild choledochal cyst with inflammation, two multifocal spotty necrosis and one multiple centrilobular necrosis, the other five being normal. Four of the nine patients with diffuse panlobular steatosis showed microvesicular fatty droplets with central nuclei, which was consistent with findings characteristic for typical RS. Two cases showed a periportal area dominant macrovesicular fatty change, which was highly suggestive for metabolic disorder. In the other three cases, the findings were so variable in terms of the size of lipid droplets and the location of nuclei in hepatocytes that it was not possible to provide any clue for defining a diagnosis. These results confirmed the legitimacy of the diagnostic criteria of RS which included a liver biopsy as one of the mandatory conditions. They also indicated that RS-mimicking clinical pictures can be presented by miscellaneous conditions in which liver histology does not necessarily helpful in establishing definite diagnosis.  相似文献   
997.
The ravelled sleeve of care. Managing the stresses of residency training   总被引:4,自引:0,他引:4  
J M Colford  S J McPhee 《JAMA》1989,261(6):889-893
  相似文献   
998.
999.
An understanding of factors which influence gastric emptying rate is important for anaesthetists. In the absence of pyloric stenosis or other mechanical obstruction to the gastric outlet, opioid drugs constitute the most important cause of delayed emptying in the perioperative period.  相似文献   
1000.
A prospective randomized study was carried out on a total of 686 patients who underwent vaginal or abdominal hysterectomy. Of these, 338 were given prophylactic cefotetan (2 g) and 348 piperacillin (2 g). Both drugs were administered as i.v. bolus 30 min before operation. Findings confirm the higher risk of infection with abdominal hysterectomy and the advantages of the long half-life cephalosporin, cefotetan.  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-23

京公网安备 11010802026262号