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   6865篇
  免费   814篇
  国内免费   140篇
耳鼻咽喉   73篇
儿科学   387篇
妇产科学   164篇
基础医学   1044篇
口腔科学   203篇
临床医学   683篇
内科学   1373篇
皮肤病学   92篇
神经病学   786篇
特种医学   207篇
外科学   524篇
综合类   691篇
预防医学   669篇
眼科学   104篇
药学   493篇
  6篇
中国医学   136篇
肿瘤学   184篇
  2024年   7篇
  2023年   177篇
  2022年   202篇
  2021年   447篇
  2020年   441篇
  2019年   320篇
  2018年   326篇
  2017年   341篇
  2016年   261篇
  2015年   277篇
  2014年   470篇
  2013年   490篇
  2012年   333篇
  2011年   411篇
  2010年   317篇
  2009年   289篇
  2008年   286篇
  2007年   284篇
  2006年   265篇
  2005年   240篇
  2004年   183篇
  2003年   153篇
  2002年   159篇
  2001年   114篇
  2000年   102篇
  1999年   115篇
  1998年   64篇
  1997年   52篇
  1996年   57篇
  1995年   54篇
  1994年   58篇
  1993年   54篇
  1992年   62篇
  1991年   32篇
  1990年   37篇
  1989年   33篇
  1988年   29篇
  1987年   21篇
  1986年   24篇
  1985年   44篇
  1984年   42篇
  1983年   26篇
  1982年   25篇
  1981年   20篇
  1980年   22篇
  1979年   13篇
  1978年   9篇
  1977年   7篇
  1975年   7篇
  1974年   5篇
排序方式: 共有7819条查询结果,搜索用时 15 毫秒
1.
目的 测定儿童1型糖尿病(T1DM)患者骨密度(BMD),分析探讨骨密度变化的影响因素。方法 选取于2018年1月—2021年6月于我院收治的儿童1型糖尿病患者76例,收集性别、年龄、发病年龄、身高、体重、BMI、病程等基本资料,检测空腹血糖、空腹C肽、糖化血红蛋白(HbA1c)、血碳酸氢根(HCO3-)、血清碱性磷酸酶(ALP),应用双能X线吸收测定法测定骨密度,获取Z值。结果 76例儿童1型糖尿病患者骨密度Z值为-0.93±2.14。HbA1c、病程与骨密度Z值呈负相关,差异具有统计学意义(分别B=-0.334,P<0.001;B=-0.191,P=0.017)。结论 儿童1型糖尿病患者骨密度低于健康儿童,血糖控制不良、病程长是1型糖尿病儿童骨密度减低的危险因素。  相似文献   
2.
3.
目的建立一种基于规律成簇的间隔短回文重复序列及其相关蛋白(CRISPR/Cas13a)的乙型肝炎病毒(HBV)共价闭合环状DNA(HBV cccDNA)检测方法。方法提取2017年6月至2020年10月于首都医科大学附属北京佑安医院就诊的4例乙型肝炎患者肝脏总DNA后,使用HindⅢ内切酶和质粒安全性ATP依赖DNA酶(PSAD)分别进行酶切;根据松弛环状DNA(rcDNA)和cccDNA的结构差异,设计特异性扩增HBV cccDNA的引物,对酶切后的产物进行滚环扩增(RCA)和PCR扩增;并筛选crRNA,建立基于CRISPR/Cas13a技术的HBV cccDNA检测新方法。结果利用α-1-抗胰蛋白酶(A1AT)和HBV表面抗原(HBsAg)引物对双重酶切后的产物进行扩增,验证产物中HBV基因组的存在;利用HBV cccDNA和HBV rcDNA引物对PSDA酶切后的产物扩增,验证了产物中只存在HBV cccDNA;利用RCA后的阳性样本作为模板梯度稀释,然后进行PCR扩增转录后使用CRISPR/Cas13a检测,计算出检测下限为10拷贝/μl。结论本研究建立了RCA-PCR-CRISPR-Cas13a的新型检测方法,可对HBV cccDNA进行高灵敏度和高特异性检测,为乙型肝炎患者抗病毒治疗评估、治疗终点的确定以及调整治疗方案提供了有效的监测手段。  相似文献   
4.
ObjectiveThis cohort study aimed to assess the associations between sleep duration and quality with the risk of incident chronic kidney disease (CKD) in middle-aged and older Chinese.MethodsWe used the 2011 and 2015 surveys of the China Health and Retirement Longitudinal Study (CHARLS). Nighttime sleep duration was categorized into five groups: ≤4, (4–6], (6–8], (8–10], and >10 h/night. Sleep quality was assessed by restless days in the past week (<1, 1–2, 3–4, and 5–7 days/week). Multivariate logistic regression was used to assess the association between sleep duration and quality with incident CKD.ResultsA total of 11,339 participants free of CKD at baseline were included in this study. After four years follow-up, the incidence of CKD was 7.8%. There was a “U-shaped” association between sleep duration and risk of CKD. Compared to 6–8 h of nighttime sleep duration, those who slept ≤4 h/night (RR: 1.639, 95% CI: 1.287–2.087) or >10 h/night (RR: 2.342, 95% CI: 1.007–5.451) had increased risk of developing CKD after adjustment for confounders. Participants with 5–7 restless days per week had significantly increased risk of CKD (adjusted RR: 1.686, 95% CI: 1.352–2.102), compared to those who rarely or never had a restless sleep.ConclusionsExtreme nighttime sleep duration and poor sleep quality were associated with increased risk of CKD in middle-aged and older Chinese. Obtaining an optimal nighttime sleep duration and better sleep quality might reduce the risk of CKD.  相似文献   
5.
PurposeThe purpose of this study was to compare morphologic assessment and relaxometry of patellar hyaline cartilage between conventional sequences (fast spin-echo [FSE] T2-weighted fat-saturated and T2-mapping) and synthetic T2 short-TI inversion recovery (STIR) and T2 maps at 1.5 T magnetic resonance imaging (MRI).MethodThe MRI examinations of the knee obtained at 1.5 T in 49 consecutive patients were retrospectively studied. There were 21 men and 28 women with a mean age of 45 ± 17.7 (SD) years (range: 18–88 years). Conventional and synthetic acquisitions were performed, including T2-weighted fat-saturated and T2-mapping sequences. Two radiologists independently compared patellar cartilage T2-relaxation time on conventional T2-mapping and synthetic T2-mapping images. A third radiologist evaluated the patellar cartilage morphology on conventional and synthetic T2-weighted images. The presence of artifacts was also assessed. Interobserver agreement for quantitative variables was assessed using intraclass correlation coefficient (ICC).ResultsIn vitro, conventional and synthetic T2 maps yielded similar mean T2 values 58.5 ± 2.3 (SD) ms and 58.8 ± 2.6 (SD) ms, respectively (P = 0.414) and 6% lower than the expected experimental values (P = 0.038). Synthetic images allowed for a 15% reduction in examination time compared to conventional images. On conventional sequences, patellar chondropathy was identified in 35 patients (35/49; 71%) with a mean chondropathy grade of 4.8 ± 4.8 (SD). On synthetic images, 28 patients (28/49; 57%) were diagnosed with patellar chondropathy, with a significant 14% difference (P = 0.009) and lower chondropathy scores (3.7 ± 4.9 [SD]) compared to conventional images. Motion artifacts were more frequently observed on synthetic images (18%) than on conventional ones (6%). The interobserver agreement was excellent for both conventional and synthetic T2 maps (ICC > 0.83). Mean cartilage T2 values were significantly greater on synthetic images (36.2 ± 3.8 [SD] ms; range: 29-46 ms) relative to conventional T2 maps (31.8 ± 4.1 [SD] ms; range: 26-49 ms) (P < 0.0001).ConclusionDespite a decrease in examination duration, synthetic images convey lower diagnostic performance for chondropathy, greater prevalence of motion artifacts, and an overestimation of T2 values compared to conventional MRI sequences.  相似文献   
6.
《Clinical neurophysiology》2021,132(1):157-164
ObjectiveEarly EEG contains reliable information for outcome prediction of comatose patients after cardiac arrest. We introduce dynamic functional connectivity measures and estimate additional predictive values.MethodsWe performed a prospective multicenter cohort study on continuous EEG for outcome prediction of comatose patients after cardiac arrest. We calculated Link Rates (LR) and Link Durations (LD) in the α, δ, and θ band, based on similarity of instantaneous frequencies in five-minute EEG epochs, hourly, during 3 days after cardiac arrest. We studied associations of LR and LD with good (Cerebral Performance Category (CPC) 1–2) or poor outcome (CPC 3–5) with univariate analyses. With random forest classification, we established EEG-based predictive models. We used receiver operating characteristics to estimate additional values of dynamic connectivity measures for outcome prediction.ResultsOf 683 patients, 369 (54%) had poor outcome. Patients with poor outcome had significantly lower LR and longer LD, with largest differences 12 h after cardiac arrest (LRθ 1.87 vs. 1.95 Hz and LDα 91 vs. 82 ms). Adding these measures to a model with classical EEG features increased sensitivity for reliable prediction of poor outcome from 34% to 38% at 12 h after cardiac arrest.ConclusionPoor outcome is associated with lower dynamics of connectivity after cardiac arrest.SignificanceDynamic functional connectivity analysis may improve EEG based outcome prediction.  相似文献   
7.
8.
9.
2019年12月以来,新型冠状病毒肺炎(Coronavirus Disease 2019,COVID-19)在武汉暴发并蔓延至全国,给整个社会带来巨大的挑战。部分COVID-19感染者早期发病并不十分凶险,但后期会突然加速进展,病人很快进入多脏器功能衰竭的状态,李兰娟院士等提出了"细胞因子风暴"概念。但目前并没有特效药物,认为IL-6是诱发细胞因子风暴的重要通路,本文结合相关文献的复习和分析,旨在综述IL-6受体阻断剂托珠单抗在新型冠状病毒肺炎危重患者使用的可行性。  相似文献   
10.
《Cirugía espa?ola》2020,98(5):288-291
The true short esophagus is an entity of controversy among surgeons. Studies have been published about its diagnosis and laparoscopic treatment, without existing to date, publication of the treatment with robotic approach. We present, as a case report, our experience in robotic surgery for hiatal hernia with true short esophagus treated with Collis gastroplasty and Toupet fundoplication. Robotic surgery on the true short esophagus can facilitate mediastinal dissection and allow a more accurate suture technique. Studies are needed to compare the long-term results of this surgical technique between the conventional laparoscopic approach and the robotic approach.  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