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   1030篇
  免费   55篇
  国内免费   13篇
耳鼻咽喉   4篇
儿科学   36篇
妇产科学   25篇
基础医学   132篇
口腔科学   70篇
临床医学   81篇
内科学   212篇
皮肤病学   18篇
神经病学   94篇
特种医学   42篇
外科学   116篇
综合类   22篇
一般理论   1篇
预防医学   51篇
眼科学   42篇
药学   92篇
中国医学   9篇
肿瘤学   51篇
  2024年   6篇
  2023年   9篇
  2022年   31篇
  2021年   39篇
  2020年   38篇
  2019年   36篇
  2018年   41篇
  2017年   44篇
  2016年   40篇
  2015年   44篇
  2014年   53篇
  2013年   71篇
  2012年   89篇
  2011年   84篇
  2010年   62篇
  2009年   52篇
  2008年   53篇
  2007年   62篇
  2006年   63篇
  2005年   39篇
  2004年   32篇
  2003年   20篇
  2002年   16篇
  2001年   4篇
  2000年   9篇
  1999年   4篇
  1998年   6篇
  1997年   3篇
  1996年   5篇
  1995年   5篇
  1994年   1篇
  1993年   4篇
  1992年   2篇
  1991年   2篇
  1990年   5篇
  1989年   8篇
  1988年   3篇
  1987年   1篇
  1986年   4篇
  1985年   2篇
  1982年   3篇
  1975年   1篇
  1966年   1篇
  1965年   1篇
排序方式: 共有1098条查询结果,搜索用时 0 毫秒
61.
62.
63.
BACKGROUND: Little is known about what specific cognitive functions are affected by elevated blood pressure (BP) and how orthostatic BP change is related to cognitive impairment. The aim of this study was to determine the effect of BP and its postural change on cognitive functions in otherwise healthy elders. METHODS: In 70 healthy persons (mean age, 72 +/- 4 years), supine systolic BP (SBP) was assessed 3 times using a sphygmomanometer, and the average values were obtained for the analysis. After 1, 3, and 5 minutes of standing, 3 BP measurements were obtained and the orthostatic SBP changes were determined by subtracting these values from the supine average. Neuropsychological tests were administered to assess short-term and long-term verbal and visual memory, visuospatial skills, and frontal-executive functions. Participants were considered impaired in the specific cognitive performance if their scores fell below the 25th percentile of the study population. Multiple logistic regression models were used to evaluate the relation of SBP and the magnitude of orthostatic SBP decline to risk for impairment in each of the cognitive tests. RESULTS: Controlling for potential confounders, each 10 mmHg increase in supine SBP was associated with a 2.31-fold increase (95% confidence interval, 1.14 to 4.66) in risk for impairment in psychomotor speed and set shifting as measured using the Trailmaking Part-B test. There was no significant association between cognitive functions and orthostatic SBP decline at 1, 3, and 5 minutes of standing. CONCLUSION: Elevation of BP is associated with a selective impairment in executive function in otherwise healthy community-dwelling elders.  相似文献   
64.
BACKGROUND: A parental history of cardiovascular disease has a strong relationship with risk factor clusters in the offspring. This study was performed to identify major cardiovascular risk factors in middle school-aged children and their parents in both high and low-risk families. DESIGN: A school-based, cross-sectional study. METHODS: The middle schools of the 6th district of Tehran were divided randomly into two groups. A total of 169 high-risk children with their families were recruited from the first group and 105 low-risk children with their families were recruited from the second group of schools. Anthropometric and metabolic measurements were performed. RESULTS: The means of the waist circumference and waist-to-hip ratio were significantly higher in high-risk fathers. The means of total and low-density lipoprotein (LDL) cholesterol were significantly higher in both parents and children of the high-risk group. The means of the fasting plasma glucose were significantly higher in fathers and offspring of high-risk families. More fathers in high-risk families were smokers. The prevalence of increased total cholesterol, LDL-cholesterol and hyperglycemia (> or = 100 mg/dl) were higher in high-risk parents and children. The prevalence of increased body mass index (> or = 25 kg/m for parents and 85th percentile for children) was higher in fathers and children of high-risk families. CONCLUSIONS: Cardiovascular risk factors are more prevalent and clustered in high-risk families. The screening of high-risk families is essential to prevent the progression of atherosclerosis from childhood and reduce the burden of cardiovascular disease in adulthood.  相似文献   
65.
BACKGROUND: In some patients GERD presents with heartburn and regurgitation symptoms but a relative paucity of endoscopic and clinical findings, while in others symptoms may be minor or absent yet there is significant mucosal damage on endoscopy including the presence of Barrett's esophagus. The initial injury of gastroesophageal reflux is to the squamous esophageal mucosa, but while substantial research has been devoted to determining which genes are involved in the progression of Barrett's to dysplasia and cancer, little is known about the gene expression alterations in the squamous mucosa of patients with reflux. We hypothesized that the expression of cyclooxygenase-2 (Cox-2) might be increased in the squamous esophageal mucosal of patients with reflux, and might be a molecular indicator of reflux injury. Further, we hypothesized that Cox-2 expression in the squamous mucosa would be reduced following the elimination of reflux with an antireflux operation. METHODS: Biopsies of the distal esophageal squamous mucosa were taken 3 cm above the squamocolumnar junction (SCJ) in 28 GERD patients before and after Nissen fundoplication. Following microdissection and RNA isolation, quantitative real-time PCR was used to measure Cox-2 gene expression in paraffin-embedded (N = 16) and fresh frozen (N = 12) tissue. Biopsies from patients (paraffin N = 15, frozen N = 14) with normal acid exposure and no evidence of mucosal injury were analyzed as controls. RESULTS: Median Cox-2 expression in the squamous epithelium from paraffin embedded biopsies in patients with reflux disease was significantly increased compared to controls (p = 0.04). The presence of esophagitis or Barrett's esophagus did not significantly alter the expression of Cox-2 compared to patients with nonerosive reflux disease (NERD). After antireflux surgery median Cox-2 expression values were significantly reduced (p = 0.0003) and were normalized to levels similar to controls without reflux (p = 0.74). Similar results were observed in the prospectively obtained fresh frozen tissue. CONCLUSIONS: Cox-2 gene expression is increased in the distal esophageal squamous mucosa of most patients with GERD, and the elevation was similar whether there was mucosal injury in the form of esophagitis or Barrett's or no visible mucosal injury. This suggests that increased Cox-2 expression may serve as a molecular marker of reflux disease. The increased Cox-2 expression in patients with reflux was usually normalized following antireflux surgery. These findings demonstrate for the first time that gene expression can be altered by surgical correction of reflux. Thus, in addition to symptom control and improvement in the quality of life, perhaps future studies assessing the efficacy of antireflux therapy should also focus on the impact of the therapy on gene expression in the esophageal squamous mucosa.  相似文献   
66.
Although thorough studies on the immune reponse to rubella have been performed, less attention has been given to the cellular mechanism and mediators that shape the process. Specifically, information concerning the nature ofcytokine patterns involved in the immune response to Rubella vaccination is not avaliable. This study deals with cytokine production patterns of spleen cells from Balb/c mice following vaccination with the Takahashi strain of Rubella vaccine. Mice were injected intraperitonealy with Rubella virus and PBS and 7, 10 or 14 days later, spleen cells were separated and cultured with varying doses of virus, con A or only the medium. ELISA assays were performed on supernatants for measurement of IL-4, INF-gamma and IL-5. LTT (Lymphocyte Transformation Test) was also performed. The data indicate variation in cytokine patterns during the time periods after vaccination. On day 7 a type 1 pattern was observed. The LTT response was also indicative of CMI (Cell Mediated Immunity) response on the 7th and 14th days while a transient suppression on day 10 was observed. These results indicate a time dependent cytokine response with variation ultimately leading o a dominant type 1 (Ti) cytokine response.  相似文献   
67.
The 4- to 6-year outcome of orthograde retreatment was assessed for Phases I and II of the Toronto Study. In total, 523 teeth in 444 patients were retreated. With 395 teeth lost to follow-up and 25 extracted, 103 teeth (34% recall) were examined by two independent, blinded, calibrated examiners for outcome: "healed" (absence of apical periodontitis, signs, or symptoms) or "diseased" (presence of apical periodontitis, signs, or symptoms). The "healed" rate (81%) differed significantly for preoperative apical periodontitis (absent, 97%; present, 78%) and perforation (absent, 89%; present, 42%). Logistic regression revealed an increased risk of disease for preoperative perforation and adequate root filling quality, and postoperative lack of definitive restoration (odds ratios = 26.5, 6.6, and 14.0, respectively). Without perforation, inadequate intraoperative root filling length was also identified (odds ratio = 6.8). This study suggested that apical periodontitis, although a strong predictor, was secondary to preoperative perforation and root filling quality, and to postoperative restoration, in predicting the outcome of retreatment.  相似文献   
68.
The degree of III-CaSO4 to II-CaSO4 transition was estimated on wet specimens, 25 mm in diameter and 50 mm high, prepared from a gypsum-bonded investment for quick casting. After 30 min from mixing the specimens were heated in a 700 degrees C furnace until a specimen temperature of 200 degrees C to 700 degrees C was reached. The estimation was made by measuring mass changes of the specimens before and after heating. The transition reached 39% at 350 degrees C. The same estimation method, when applied to a previous study, showed no transition to this temperature in dry specimens heated slowly (5 degrees C/min). The large difference in transition found between the wet and dry specimens was attributed to the formation of alpha- and beta-hemihydrate, respectively. At 350-450 degrees C, the transition was 3% and 48%, respectively. The pronounced latter transition, generally identified by differential thermal analysis of gypsum, appears as the major investment shrinkage demonstrating its dry dehydration process.  相似文献   
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