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   17294篇
  免费   1303篇
  国内免费   77篇
医药卫生   18674篇
  2023年   122篇
  2022年   104篇
  2021年   635篇
  2020年   371篇
  2019年   505篇
  2018年   606篇
  2017年   440篇
  2016年   490篇
  2015年   479篇
  2014年   641篇
  2013年   821篇
  2012年   1187篇
  2011年   1195篇
  2010年   679篇
  2009年   600篇
  2008年   925篇
  2007年   1015篇
  2006年   947篇
  2005年   869篇
  2004年   819篇
  2003年   709篇
  2002年   622篇
  2001年   273篇
  2000年   249篇
  1999年   255篇
  1998年   148篇
  1997年   91篇
  1996年   88篇
  1995年   78篇
  1994年   79篇
  1993年   77篇
  1992年   133篇
  1991年   154篇
  1990年   139篇
  1989年   143篇
  1988年   115篇
  1987年   117篇
  1986年   127篇
  1985年   127篇
  1984年   111篇
  1983年   89篇
  1982年   88篇
  1981年   102篇
  1980年   75篇
  1979年   86篇
  1978年   81篇
  1977年   67篇
  1975年   46篇
  1974年   55篇
  1972年   49篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
Background: During labor, ephedrine is widely used to prevent or to treat maternal arterial hypotension and restore uterine perfusion pressure to avoid intrapartum fetal asphyxia. However, the effects of ephedrine on uterine blood flow have not been studied during uterine contractions. The purpose of the study was to assess the effects of ephedrine on uterine artery velocities and resistance index using the Doppler technique during the active phase of labor.

Methods: Ten normotensive, healthy parturients with uncomplicated pregnancies at term received intravenous ephedrine during labor to increase mean arterial pressure up to a maximum of 20% above their baseline pressure. Peak systolic and end-diastolic Doppler flow velocities and resistance indices were measured in the uterine artery before and immediately after administration of bolus intravenous ephedrine and after ephedrine washout. Umbilical and fetal middle cerebral arterial resistance indices and fetal heart rate were also calculated.

Results: After ephedrine administration, mean arterial pressure increased by 17 +/- 4%. End-diastolic flow velocity in the uterine artery at peak amplitude of uterine contraction was restored to 74% of the value observed in the absence of contraction. The systolic velocity was totally restored, and the uterine resistance index was significantly decreased, compared with the values in the absence of contraction. Between uterine contractions, ephedrine induced similar but less marked effects. Fetal hemodynamic parameters were not altered by ephedrine administration.  相似文献   

42.
43.

Background:   

Cases of extrahepatic biliary tree trauma are not as common as other intraabdominal injuries and may pose a diagnostic and therapeutic challenge.  相似文献   
44.
BACKGROUND CONTEXT: Diastematomyelia is uncommon and rarely presents in adulthood. This report draws attention to the fact that patients who underwent spinal fusion for deformity before the widespread use of computed tomography (CT) and magnetic resonance imaging (MRI) may have unrecognized spinal cord abnormalities. This should be considered if revision surgery is contemplated. PURPOSE: This case report focuses on the late presentation of lower-extremity weakness in a 44-year-old woman with a split cord malformation (diplomyelia), diastematomyelia and tethered cord syndrome. STUDY DESIGN/SETTING: METHODS: The patient underwent instrumented posterior spinal fusion with a Harrington rod as a child for progressive thoracolumbar scoliosis. As an adult, she developed paraparesis after a traumatic event.The patient underwent decompressive laminectomy, subtotal resection of the old fusion mass and resection of the osseous septum. Postoperatively, an anterior spinal fluid leak in the lower thoracic region required repeated fascial grafting, resection of a pseudomeningocele and reverse left latissimus dorsi flap transfer. The leak was controlled, and the patient had near complete resolution of her paraparesis 1 year after her surgery. RESULTS: The case described herein is unusual in that patients with diplomyelia and diastematomyelia rarely are symptomatic in adulthood. However, trauma may precipitate the onset of neurologic symptoms. This patient underwent spinal surgeries to address deformity, pain and progressive lower-extremity weakness. Preoperative CT and MRI studies showed a split cord malformation and diastematomyelia at L1-L2 with spinal stenosis and tethering of both hemicords. CONCLUSIONS: Progressive weakness without any previous neurologic deficit or neurocutaneous stigmas of an underlying spinal cord abnormality may develop in the adult with unrecognized diastemotomyelia. This case demonstrates that a thorough preoperative workup of patients with complex spinal deformities is imperative.  相似文献   
45.
46.
47.
The relationship between the amount of inhaled steroids delivered from pressurized metered-dose inhalers used with their recommended holding chambers and age of the patients using these devices was studied in an open randomised cross-over filter study. We recruited 1-2-month-old healthy infants (n = 21), 2-3-year-old asthmatics (n = 13), 4-6-year-old asthmatics (n = 15), and 10-15-year-old asthmatics (n = 20). Each child inhaled two puffs, administered by a single investigator, of both budesonide through Nebuchamber and fluticasone propionate through Babyhaler, on two occasions. Moreover, the 4-6-year-old group inhaled via both facemask and mouthpiece. Drug, collected on a filter interposed between holding chamber and patient, was analysed by high performance liquid chromatography. Filter dose, expressed in percent of the nominal dose, was analysed in a mixed effect linear regression model with age group, holding chamber and inhalation interface (facemask or mouthpiece) as fixed effects and subject as random effect. Filter dose from both holding chambers increased significantly with age, from 3% with Babyhaler and 7% with Nebuchamber in the youngest children, to 40-41% with both holding chambers in adolescents. Nebuchamber delivered more drug than Babyhaler (p = 0.002), but variability in drug delivery (about 11%) was similar between holding chambers. Filter dose decreased from 35% to 22% with Babyhaler, and from 42% to 27% with Nebuchamber when using a mouthpiece rather than a facemask (p < 0.0001). Delivery of inhaled steroids used with their recommended holding chambers depends from age and holding chamber, but also from the inhalation interface. Lung deposition and clinical studies comparing inhalation from holding chambers with mouthpiece and facemask are urgently required.  相似文献   
48.
BACKGROUND: Identify risk factors for asthma in adolescents from S?o Paulo, Brazil. METHODS: total of 528 adolescents (141 asthmatics, 387 control subjects) from the ISAAC study (phase III) were submitted to a complementary questionnaire to evaluate risk factors, through response to questions regarding personal history, environment, and diet and an agreement to undergo the skin prick test (SPT) for aeroallergens. RESULTS: Positive SPT to at least one allergen occurred in 49.4% adolescents. The risk factors for asthma were: prematurity (OR: 3.84, 95% CI: 1.54-9.64), rhinitis (OR: 3.18, 95% CI: 1.71-5.91), positivity in the SPT (OR: 2.81, 95% CI: 1.48-5.32), eczema in characteristic skin-folds (OR: 2.86, 95% CI: 1.13-7.26), and an allergic mother (OR: 2.01, 95% CI: 1.02-3.93). The consumption of cooked vegetables was a protective factor for asthma (OR: 0.37, 95% CI: 0.18-0.79) CONCLUSIONS: Asthma is a multifatorial disease. An allergic mother, aeroallergen sensitization, rhinitis, eczema and prematurity were considered risk factors and the consumption of cooked vegetables was considered a protective factor for asthma in this population.  相似文献   
49.
50.
Endogenous ecotropic murine leukemia proviruses that were not present in the parental stock are acquired by the progeny of some SWR/J X RF/J hybrid females. We have made a stock of an ecotropic murine leukemia virus produced by such a hybrid female and inoculated newborn SWR/J females with it. We show that upon crossing of the inoculated females to SWR/J males, some of their progeny acquire ecotropic proviruses. Although most of these proviruses appear to be distributed in somatic tissues in a mosaic way, some are transmitted through the germ line. Thus an exogenous infection is able to mimic the phenomenon observed in SWR/J X RF/J hybrid mice. Available evidence suggests that this infection occurs during oogenesis in the recipient female. Our results document the conversion of an exogenous infectious ecotropic murine leukemia virus to an endogenous provirus without any manipulation of either eggs or embryos.  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