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   130188篇
  免费   12595篇
  国内免费   5288篇
耳鼻咽喉   1551篇
儿科学   3157篇
妇产科学   1408篇
基础医学   10494篇
口腔科学   2863篇
临床医学   14634篇
内科学   19100篇
皮肤病学   2548篇
神经病学   5825篇
特种医学   4841篇
外国民族医学   2篇
外科学   13332篇
综合类   22783篇
现状与发展   13篇
一般理论   16篇
预防医学   15388篇
眼科学   2322篇
药学   11936篇
  125篇
中国医学   8930篇
肿瘤学   6803篇
  2024年   544篇
  2023年   1769篇
  2022年   3159篇
  2021年   4756篇
  2020年   3911篇
  2019年   3000篇
  2018年   4190篇
  2017年   3971篇
  2016年   3303篇
  2015年   4841篇
  2014年   5907篇
  2013年   8002篇
  2012年   10791篇
  2011年   11545篇
  2010年   9100篇
  2009年   7730篇
  2008年   9128篇
  2007年   8906篇
  2006年   7935篇
  2005年   6857篇
  2004年   5369篇
  2003年   4744篇
  2002年   4059篇
  2001年   3350篇
  2000年   3160篇
  1999年   1716篇
  1998年   696篇
  1997年   614篇
  1996年   606篇
  1995年   502篇
  1994年   371篇
  1993年   362篇
  1992年   349篇
  1991年   277篇
  1990年   247篇
  1989年   275篇
  1988年   253篇
  1987年   198篇
  1986年   193篇
  1985年   182篇
  1984年   156篇
  1983年   135篇
  1982年   105篇
  1981年   97篇
  1980年   81篇
  1979年   48篇
  1978年   52篇
  1977年   62篇
  1976年   51篇
  1975年   36篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Guidelines recommend that patients with COPD are stratified arbitrarily by baseline severity (FEV1) to decide when to initiate combination treatment with a long-acting β2-agonist and an inhaled corticosteroid. Assessment of baseline FEV1 as a continuous variable may provide a more reliable prediction of treatment effects. Patients from a 1-year, parallel-group, randomized controlled trial comparing 50 μg salmeterol (Sal), 500 μg fluticasone propionate (FP), the combination (Sal/FP) and placebo, (bid), were categorized post hoc into FEV1 <50% and FEV1 ≥50% predicted subgroups (n=949/513 respectively). Treatment effects on clinical outcomes – lung function, exacerbations, health status, diary card symptoms, and adverse events – were investigated. Treatment responses based on a pre-specified analysis explored treatment differences by severity as a continuous variable. Lung function improved with active treatment irrespective of FEV1; Sal/FP had greatest effect. This improvement appeared additive in milder disease; synergistic in severe disease. Active therapy significantly reduced exacerbation rate in patients with FEV1 <50% predicted, not in milder disease. Health status and breathlessness improved with Sal/FP irrespective of baseline FEV1; adverse events were similar across subgroups. The spirometric response to Sal/FP varied with baseline FEV1, and clinical benefits were not restricted to patients with severe disease. These data have implications for COPD management decisions, suggesting that arbitrary stratifications of baseline severity are not necessarily indicative of treatment efficacy and that the benefits of assessing baseline severity as a continuous variable should be assessed in future trials.  相似文献   
72.
Carcinoma of the papilla of Vater is classified as periampullary cancer representing 5% of all gastrointestinal tract malignancies. Early and accurate diagnosis is important for those patients with a tumor of the papilla, as the prognosis is more favorable than in other periampullary neoplasms. Endoscopically obtained biopsies from suspicious papillae can detect an early tumor, although even for skilled pathologists it is often difficult to differentiate carcinomas from noninvasive lesions on the basis of forceps biopsies. The purpose of this study was to assess the preoperative diagnostic accuracy of duodenoscopy appearance and biopsy in all cases with suspicion of tumor. Thirty patients with suspicion of carcinoma of the papilla of Vater and with final diagnosis established by pancreatoduodenectomy were included in this retrospective study. In each case, a comparison was made between endoscopic biopsy and duodenoscopic appearance. Duodenoscopic appearance sensitivity and accuracy for malignancy were 86% and 83%, respectively, whereas endoscopic biopsy sensitivity and accuracy were 65% and 67%, respectively. Although preoperative diagnosis of carcinoma of the papilla of Vater is useful for making therapeutic decisions, the diagnostic value of the endoscopic appearance was superior to endoscopic biopsy in this series. Presented at the 2003 American Hepato-Pancreato-Biliary Association Congress, Miami, Florida, February 27-March 3, 2003. Supported by FADA-CAPES/PROP 200J (M.L.D.).  相似文献   
73.
Objective To compare the effects of 2 vascular carriers, arteriovenous loop and arteri-ovenous bundle, on inducing angiogenesis in coral scaffold of vascularized tissue-engineered bone in animal models.Methods Thirty-six adult male New Zealand rabbits were randomized into 2 even groups.In group A, an arteriovenous loop (AVL) was formed by microsurgical anastomosis at the proximal ends between the femoral poptiteal artery and vein, and placed in the circular side groove of the coral block (6 mm × 8 mm × 10 mm) .In group B, flow-through vessels bundles of both femoral artery and vein were placed in the side grooves of the coral block.All the implants in 2 groups were wrapped by a micro-porous expand-ed-polytetrafluoroethylene (ePTFE) membrane, and fixed subcutaneously by suturing.Evaluation methods included gross morphological observations, histological examinations, India ink perfusion and vascular casting after 2, 4, 6 weeks.The density of blood vessels was analyzed by the statistical software SPSS 10.0.Results All the corals were encased by newly formed fibrovascular tissues in 2 groups.Ink-stained vessels distributed the surfaces and side grooves, and invaded the interspaces of corals.The degree of vascularization increased over the course of experiment.Blood vessel density demonstrated a significant continuous increase between 2 and 6 weeks after implantation in group A.The mean value of blood vessel density in group A (2 weeks 276.60±4.67, 4 weeks 517.20±10.66, 6 weeks 707.00 ±11.87) was significantly higher than in group B (2 weeks 153.60 ±7.16, 4 weeks 269.40±6.80, 6 weeks 279.20±6.53) (P <0.01).Vascular casting showed that in group A, significant blood vessels sprouted from all areas of the loop, espe-cially at the entrance of the arteriovenous pediele where the small tubes were densely interconnected.In group B, however, no blood vessels sprouted from the arteriovenous bundles and only some small vessels grew from the entrance and exit.Conclusions A vascularized coral model can be constructed by inserting an ar-teriovenous loop or an arteriovenous bundle, useful in vascular bone tissue engineering.The former, however, have stronger abilities to induce angiogenesis than the latter.  相似文献   
74.
75.
Six cases were examined to review the important anaesthetic implications of Larsen's syndrome. Potential problems arising in these patients are highlighted and emphasis placed on cervical spine and airway/respiratory management.  相似文献   
76.
目的:制备脑干缺血动物模型并观察大鼠脑干缺血后早期组织学病理的超微结构。方法:应用两点电凝基底动脉的方法制作鼠脑干缺血动物模型。结果:病理学观察发现脑干缺血2小时即可出现超早期病理变化,并随时间的延长缺血性损害逐渐加重。结论:两点电凝基底动脉后可以造成稳定的脑干缺血,对急性脑干缺血的病理学研究有一定的价值。  相似文献   
77.
目的评价血清铁参数与高血胆固醇症(HCL)病人心肌灌注、室壁运动异常及血管造影显示的冠状动脉疾病(CAD)程度的相互关系.方法选择38名具有高血胆固醇症(LDL-C>3.38mmol/L)从未治疗过的男性病人(平均年龄59±6岁)作为HCL组和32名年龄匹配而胆固醇水平正常(NCL)的男性为NCL组,进行冠状动脉造影并在10d内行SPECT检查,应用99mTc-甲氧基异丙基异氰(MIBI)进行静息/负荷门控断层心肌灌注显像、室壁运动功能图像分析;同时测定血清铁参数、血脂及常规血液学参数.结果在HCL组发现血清铁蛋白(SF)与心肌灌注系数(r=0.70,P<0.01),可逆系数(r=0.66,P<0.01)和室壁运动系数(r=0.53,P<0.05)之间呈显著性相关;而总铁结合力与灌注系数之间呈一弱(负)相关(r=-0.52,P<0.05).在NCL组铁参数与灌注系数及室壁运动系数之间无显著性相关.多元回归分析证实血清铁蛋白水平是决定HCL病人中心肌灌注的独立因素(β=0.55,P>0.05).铁参数与两组通过冠状动脉造影(CAG)进行评分所定义的CAD程度无关.结论体内铁贮水平升高与HCL病人心肌灌注和功能异常的严重性和程度有着密切的关系,但与CAD的造影显示的病变范围无关.血清铁蛋白水平增高,可增加铁介导的氧化应力和LDL过氧化作用,导致HCL相关的血管内皮功能紊乱并进一步损伤心肌灌注和室壁运动功能.  相似文献   
78.
BACKGROUND AND PURPOSE: In intensity modulated radiotherapy (IMRT), the complexity and the number of treatment fields have expanded. This may imply that the delivery time for each fraction becomes prolonged. In a number of IMRT techniques used in the clinic, the delivery time per fraction is usually 10-15 min, sometimes more than 15 min. In studies on human skin, prolonged delivery time is shown to cause significant reduction of radiation effects compared with acute irradiation. In this paper the effect of changes in fraction delivery time was studied by in vitro irradiation of mammalian cells. MATERIAL AND METHODS: Chinese hamster fibroblasts (V79-379-A) were used for simulating clinical situations. Most experiments were performed with 2Gy/fraction with 4-h intervals in 40-60 replicates. Each fraction was divided into different subfractions, simulating the delivery of a complicated treatment. The effect of changing the delivery time for each fraction was studied. Parameters for the cell survival curve and repair kinetics were determined experimentally. The same methods were also used for large fraction sizes (8Gy). The validity of the most widely used models in the literature, all derived from linear-quadratic formalism, were tested against the experimental results. RESULTS: The effect of prolonging the fraction time for 2-Gy fractions was underestimated by the biological models. The experiments showed that 10-min prolonged delivery time gave a ratio between surviving fractions at 2Gy (S-ratio) of 1.054 with a 95% confidence interval (CI) 1.030-1.080, while the models predicted 1.007 and 1.009. Extending the fraction time to 20 min gave an S-ratio of 1.063 with CI of 1.045-1.080, while the models predicted 1.012 and 1.014. For 8-Gy fractions, there was a good agreement between predications and experimental results. The ratio between surviving fractions at 8Gy is 1.370 with CI of 1.300-1.440, while the models predicated 1.37 and 1.35. CONCLUSIONS: The effect of prolonging fraction time at conventional dose/fraction is underestimated by biological models. Prolonging the fraction time will spare tissues with a fast DNA repair. There is a risk for sparing tumours. This should be considered when IMRT technique is implemented in the clinic.  相似文献   
79.
远端蒂筋膜皮瓣内浅静脉干定时放血的临床应用   总被引:3,自引:1,他引:2  
[目的]探讨预防远端蒂筋膜皮瓣静脉危象和提高皮瓣成活质量的方法. [方法]通过于26例大面积下肢皮神经营养血管远端蒂筋膜皮瓣内浅静脉干远心端蒂部结扎,近心端留置静脉留置针外引流,每天6 h定量放血,连续5d,密切观察皮瓣血供及肿胀情况. [结果]26例皮瓣全部成活,无1例出现静脉危象,无明显肿胀期.随访1~2年,皮瓣质地柔软,无明显色素沉着,均恢复保护性感觉. [结论]此方法能预防远端蒂筋膜皮瓣的静脉危象,提高皮瓣的成活质量.  相似文献   
80.
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