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   10494篇
  免费   793篇
  国内免费   411篇
耳鼻咽喉   221篇
儿科学   142篇
妇产科学   46篇
基础医学   2277篇
口腔科学   148篇
临床医学   823篇
内科学   628篇
皮肤病学   89篇
神经病学   2027篇
特种医学   993篇
外科学   340篇
综合类   926篇
预防医学   682篇
眼科学   232篇
药学   595篇
  2篇
中国医学   1363篇
肿瘤学   164篇
  2024年   30篇
  2023年   172篇
  2022年   213篇
  2021年   407篇
  2020年   335篇
  2019年   310篇
  2018年   298篇
  2017年   361篇
  2016年   357篇
  2015年   380篇
  2014年   576篇
  2013年   891篇
  2012年   561篇
  2011年   713篇
  2010年   518篇
  2009年   520篇
  2008年   560篇
  2007年   494篇
  2006年   459篇
  2005年   415篇
  2004年   363篇
  2003年   308篇
  2002年   283篇
  2001年   236篇
  2000年   198篇
  1999年   172篇
  1998年   145篇
  1997年   140篇
  1996年   122篇
  1995年   161篇
  1994年   142篇
  1993年   139篇
  1992年   94篇
  1991年   107篇
  1990年   62篇
  1989年   78篇
  1988年   58篇
  1987年   48篇
  1986年   34篇
  1985年   47篇
  1984年   34篇
  1983年   29篇
  1982年   23篇
  1981年   18篇
  1980年   20篇
  1979年   13篇
  1977年   12篇
  1976年   10篇
  1974年   8篇
  1973年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
BackgroundOlder adults benefit most from engaging in higher-intensity physical activity, which is often determined using step rate thresholds. Fixed step rate thresholds that correspond to moderate (MPA) and vigorous-intensity physical activity (VPA) have been developed for heuristic activity promotion. The activPAL monitor uses step rate thresholds to determine activity intensity. Stepping thresholds may also vary based on body mass index (BMI) or aerobic fitness level in older adults. Despite the various thresholds used in the literature, it is unclear whether they produce similar outcomes.Research QuestionHow does time spent in physical activity intensities compare between different step rate thresholds in older adults?MethodsThirty-eight participants (24♀; 67 ± 4 years; BMI: 26.6 ± 4.4 kg/m2) wore an activPAL monitor 24-hr/day for up to 7-d (total: 205-d). Aerobic fitness (V̇O2max: 23 ± 8 ml/kg/min) was determined via indirect calorimetry during a maximal, graded cycling test. Time spent in each intensity category (light-physical-activity [LPA], MPA, VPA) was determined using the fixed (MPA/VPA) 100/130, 110/130, and activPAL step rate thresholds (74/212), as well as BMI-adjusted absolute (108.5 ± 2.5/134.0 ± 4.8) and BMI-adjusted relative (40%/60% V̇O2max; 111.4 ± 14.7/132.0 ± 19.0) cut-offs. Times spent in each intensity category were compared between methods.ResultsThe activPAL and 100/130 thresholds yielded less LPA and more MPA than all other methods. The activPAL had no time spent in VPA at all. The BMI-adjusted absolute and relative thresholds produced statistically equivalent time in LPA and MPA (via equivalence testing), but not VPA. No two methods yielded similar time spent in LPA, MPA, or VPA.SignificanceThe choice of step rate threshold has a major impact on physical activity intensity outcomes in older adults. Inherently, strategies that adjust for older adults’ body size and/or aerobic fitness level provide a more individualized data processing strategy than fixed thresholds that assume the same threshold for all older adults  相似文献   
2.
3.
4.
Arterial spin labeling (ASL) imaging is a powerful magnetic resonance imaging technique that allows to quantitatively measure blood perfusion non-invasively, which has great potential for assessing tissue viability in various clinical settings. However, the clinical applications of ASL are currently limited by its low signal-to-noise ratio (SNR), limited spatial resolution, and long imaging time. In this work, we propose an unsupervised deep learning-based image denoising and reconstruction framework to improve the SNR and accelerate the imaging speed of high resolution ASL imaging. The unique feature of the proposed framework is that it does not require any prior training pairs but only the subject's own anatomical prior, such as T1-weighted images, as network input. The neural network was trained from scratch in the denoising or reconstruction process, with noisy images or sparely sampled k-space data as training labels. Performance of the proposed method was evaluated using in vivo experiment data obtained from 3 healthy subjects on a 3T MR scanner, using ASL images acquired with 44-min acquisition time as the ground truth. Both qualitative and quantitative analyses demonstrate the superior performance of the proposed txtc framework over the reference methods. In summary, our proposed unsupervised deep learning-based denoising and reconstruction framework can improve the image quality and accelerate the imaging speed of ASL imaging.  相似文献   
5.
生姜炮制成干姜前后挥发油透皮吸收促进作用的比较研究   总被引:1,自引:0,他引:1  
苏曼  陈军  高洁  董洁  顾薇 《中草药》2019,50(24):5988-5994
目的 比较生姜炮制成干姜前后挥发油透皮吸收促进作用及成分的变化。方法 将生姜炮制成干姜前后提取挥发油,皮肤电阻动力学实验和体外布洛芬透皮实验比较二者的促渗能力,ATR-FTIR红外分析挥发油透皮促渗主要机制,皮肤细胞毒性实验比较了生姜和干姜挥发油的细胞毒性,GC-MS分析成分变化。结果 干姜挥发油的透皮吸收促进作用显著优于生姜挥发油,其透皮促渗机制主要为对皮肤角质层脂质的萃取,而生姜和干姜挥发油的皮肤细胞毒性均显著低于化学促渗剂氮酮,炮制后干姜挥发油的倍半萜类成分比例高于生姜挥发油,透皮后干姜挥发油组皮内的倍半萜类成分比例也高于生姜挥发油组。结论 炮制后的干姜挥发油的透皮吸收作用优于生姜挥发油,验证了中药挥发油透皮吸收促进剂存在"热者易效"的规律。  相似文献   
6.
BackgroundThis investigation addresses the question of whether there exists a significant discrepancy in the cognitive abilities of children with cerebral palsy (CP) who, despite the presence of age appropriate communication and language, have reading and spelling delays.AimsWe wanted to discover whether there was a relationship between the phonological and visual perceptual abilities of children with CP and their progress in reading and spelling.Methods and proceduresFifteen children with CP (aged between 6:9 years and 11:6 years) were assessed on reading and spelling; communication and language; non-verbal reasoning; phonological processing; and visual perception.Outcomes and resultsTen of the children had very weak reading and spelling skills. Five children had (mostly) age appropriate scores of reading and spelling. No differences were found between these two groups in non-verbal reasoning or communication and language. However, phonological abilities, visual sequential memory and perception of visuospatial relationships were found to be related to reading and spelling.Conclusions and implicationsThe findings suggest that children with CP are at risk for reading and spelling delays when they have poor phonological processing, visual sequential memory and perception of visuospatial relationships. The implications of the findings for classroom practice are discussed.  相似文献   
7.
8.
中药配方颗粒品种统一标准的有关问题探讨   总被引:1,自引:0,他引:1  
徐玉玲  雷燕莉  曾立  李彩虹  王晨  刘涛 《中草药》2020,51(20):5389-5394
通过参考《中国药典》2015年版和相关文献,结合国家药典委员会2016年发布的《中药配方颗粒质量控制与标准制定技术要求(征求意见稿)》,综合考虑中药配方颗粒的实际生产情况,对《关于中药配方颗粒品种试点统一标准的公示》中质量标准特异性、定量检测指标的选择和指标性成分转移率等方面进行讨论,根据讨论结果为中药配方颗粒质量标准的完善和提高提出了相关建议,为推进配方颗粒产业健康发展提供参考。  相似文献   
9.
李明雨  孙娥  徐凤娟  徐金娣  贾晓斌 《中草药》2020,51(11):2900-2907
目的基于UPLC-Q/TOF-MS技术建立淫羊藿炮制前后指纹图谱,对其全成分进行分析并找出标志性化学成分,以明确淫羊藿炮制前后黄酮组分的变化规律。方法采用UPLC-Q/TOF-MS技术,在正离子模式下采集淫羊藿生品及炮制品样品数据,并在此基础上根据正交-偏最小二乘判别分析(OPLS-DA)整体探究9个不同产地、批次的淫羊藿炮制前后化学成分的差异。结果从淫羊藿生品及炮制品中寻找并鉴定出9个标志性化学成分,即8-乙烯-山柰酚、淫羊藿素、淫羊藿次苷I、淫羊藿素-3-O-葡萄糖苷、异戊醇基箭藿苷B、1,3-异戊二烯基朝藿定C、1,3-异戊二烯基-箭藿苷B-7-O-葡萄糖醛酸、3-O-(4-乙酰氧基)鼠李糖-2-O-(间二乙酰氧基)葡萄糖-淫羊藿苷及其同分异构体。结论淫羊藿炮制后黄酮组分结构发生变化,次级糖苷增加,多级糖苷减少,淫羊藿黄酮组分总体向低糖苷组分转化,进一步阐明了淫羊藿加热炮制后黄酮组分的变化规律。  相似文献   
10.
目的:评价维吾尔医“各立衣克买提”泥法炮制技术和在这种炮制方法前提下改进的新“库西提”法炮制技术对巴豆中脂肪油的含量测定的影响。方法:利用两种炮制方法炮制生巴豆,按《中国药典》2015年版一部巴豆项下的脂肪油含量测定方法进行测定。结果:采用这两种方法炮制的巴豆根据炮制时间不同脂肪油含量依次递减。结论:采用新“库西提”法炮制技术炮制的巴豆的脂肪油含量明显降低。  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