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   9749篇
  免费   825篇
  国内免费   176篇
耳鼻咽喉   340篇
儿科学   167篇
妇产科学   48篇
基础医学   1405篇
口腔科学   291篇
临床医学   1266篇
内科学   899篇
皮肤病学   125篇
神经病学   983篇
特种医学   535篇
外科学   800篇
综合类   1330篇
预防医学   1003篇
眼科学   340篇
药学   765篇
  4篇
中国医学   272篇
肿瘤学   177篇
  2023年   130篇
  2022年   160篇
  2021年   329篇
  2020年   338篇
  2019年   320篇
  2018年   315篇
  2017年   355篇
  2016年   309篇
  2015年   314篇
  2014年   642篇
  2013年   698篇
  2012年   521篇
  2011年   634篇
  2010年   522篇
  2009年   461篇
  2008年   458篇
  2007年   454篇
  2006年   457篇
  2005年   411篇
  2004年   316篇
  2003年   315篇
  2002年   238篇
  2001年   221篇
  2000年   182篇
  1999年   162篇
  1998年   117篇
  1997年   118篇
  1996年   109篇
  1995年   118篇
  1994年   111篇
  1993年   67篇
  1992年   85篇
  1991年   68篇
  1990年   59篇
  1989年   59篇
  1988年   58篇
  1987年   61篇
  1986年   42篇
  1985年   75篇
  1984年   70篇
  1983年   56篇
  1982年   44篇
  1981年   37篇
  1980年   38篇
  1979年   18篇
  1978年   21篇
  1977年   16篇
  1976年   17篇
  1975年   7篇
  1974年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
目的:相关关系是叙词表中一种重要的概念关系。对具有相关关系的概念间属性进行研究,对叙词表相关关系的构建和更新维护有重要意义。方法:假设具有“捕食”关系的概念数量变化符合生态学中Lotka-Volterra捕食者-猎物模型,以农业领域中一个主题概念为起点,获取相关关系概念网络,在对各组相关关系进行判断之后,在中国知网(CNKI)中获取各个概念2000-2021年历年文献量,使用SPSS软件对数据进行统计分析。结果:80%具有“捕食”关系的概念符合Lotka-Volterra捕食者-猎物模型。结论:可通过概念间词频的关系来为叙词表的编制和维护工作提供参考建议。  相似文献   
2.
目的探析脑梗死患者应用重复经颅磁刺激与中频电疗对其上肢运动功能康复的影响。方法选取2021年3月~2021年8月期间收治的46例脑梗死患者进行分组研究,随机分为对照组(n=23)与观察组(n=23)。对照组给予常规药物与肢体功能康复治疗,观察组基于对照组治疗方案给予重复经颅磁刺激与中频电疗,对比两组临床疗效,运动功能量表(Fugl-Meyer)评分及不良反应发生率。结果观察组临床总有效率为95.65%,对照组为73.91%,观察组显著高于对照组(P<0.05)。观察组治疗后Fugl-Meyer评分显著高于对照组(P<0.05)。观察组不良反应发生率为8.70%,对照组为4.34%,差异无统计学意义(P>0.05)。结论脑梗死患者应用重复经颅磁刺激与中频电疗后,可进一步提高临床疗效,改善神经功能及运功功能,且不会增加不良反应。  相似文献   
3.
BackgroundDietary supplement use is common, particularly among cancer survivors and those at increased risk for cancer.ObjectiveThe objectives of this study were to assess 1-year test–retest reproducibility of dietary supplement use reported via food frequency questionnaire (FFQ-1 vs FFQ-2) and relative validity in comparison to repeated 24-hour dietary recalls (FFQ-2 vs DRs).DesignThis ancillary study was conducted within a large prospective cohort, the American Cancer Society’s Cancer Prevention Study-3.Participants/settingBetween 2015 and 2016, 684 participants in the United States (64% women; 62% non-Hispanic White, 23% non-Hispanic Black, and 15% Hispanic) completed two FFQs and up to six unannounced telephone interviewer-administered DRs over 1 year as part of the Cancer Prevention Study-3 Diet Assessment Substudy.Primary outcome measuresFFQs queried current multivitamin-mineral supplement (≥10 components) use, frequency and dose (range) for seven supplements taken individually or as part of a complex (individual/complex) including calcium, vitamins D, C, and E, folic acid, fish oil, and glucosamine. DRs allowed exact reporting of supplement frequency and dose.Statistical analysesWeighted κ statistics were used to evaluate reproducibility between FFQ-1 and FFQ-2 and Spearman correlation coefficients assessed agreement between supplemental nutrient amounts assessed by FFQ-2 and the average of DRs.ResultsJust more than half of the participants reported taking multivitamin-mineral supplements on the baseline FFQ. Kappa statistics for the comparison of categorical responses between FFQ-1 and FFQ-2 were 0.67 for multivitamin-mineral supplements. Kappas for individual/complex supplements ranged from 0.47 for folic acid to 0.74 for vitamin D, with a mean of 0.64. Results were similar between men and women. Spearman correlation coefficients comparing FFQ-2 with the average of DRs (validity) for nutrient intakes from all sources ranged from 0.65 (fish oil for women) to 0.77 (vitamin D for men and calcium for women); results were similar among men and women.ConclusionsThese findings suggest the FFQ used in Cancer Prevention Study-3 has good reproducibility over 1 year and yields estimates comparable to a more detailed assessment for commonly consumed dietary supplements.  相似文献   
4.
如何准确、合理地衡量中枢神经系统调控下的肌间耦合关系,是一个富有挑战性的研究课题。在时变copula函数的基础上,通过与熵理论相结合,提出一种时变copula互信息估计方法,并将其应用于10名被试腕屈、腕展运动过程中,肱二头肌(BB)和肱三头肌(TB)记录的表面肌电(sEMG)信号在theta、alpha、beta等特征频段的耦合分析,同时对照静态copula函数验证其有效性,所用数据源自Ninapro DB4。实验结果表明,较之静态copula函数,时变copula函数对肌间相依结构的拟合优度更高,由时变copula互信息描述的肌间耦合强度存在显著的频段差异(P<0.05),具体表现为频段越高肌间耦合强度越低(腕屈:0.075 7~0.214 7 bit;腕展:0.078 0~0.237 3 bit),而静态copula互信息严重地低估肌间耦合强度。时变copula互信息为肌间耦合分析提供一种先进的理论指导方法,具有广阔的应用前景。  相似文献   
5.
BackgroundPuerto Rican adults residing in the US mainland experience a high prevalence of metabolic syndrome (MetS). A diet containing healthy protein-rich sources may help control risk factors for MetS.ObjectiveThis study aimed to evaluate 2-year longitudinal associations between intake of various protein-rich foods and changes in the six MetS components.DesignThis is a secondary analysis of a longitudinal cohort study using data from the baseline (2004–2007) and 2-year follow-up visits (2006–2011) in the Boston Puerto Rican Health Study.Participants/settingParticipants were self-identified Puerto Ricans, aged 45 to 75 years, residing in Boston, Massachusetts, or the surrounding area (n = 1,126).Main outcome measuresMetS components were fasting glucose, high-density lipoprotein (HDL) cholesterol, triglycerides, systolic and diastolic blood pressures, and waist circumference.Statistical analysisBaseline intake of foods reported in a semiquantitative food frequency questionnaire were expressed as servings/day, and protein-rich foods were categorized as unprocessed white meat, unprocessed red meat, processed meat, milk and yogurt, cheese, fish and seafood, beans, nuts, and eggs. Associations between each continuous protein food group and continuous 2-year change in MetS components were assessed using linear mixed models adjusted for socioeconomic and behavioral factors, and other dietary sources.ResultsThe top contributors to total protein intake were unprocessed red meat (13.3%) and unprocessed poultry (13.0%), and the lowest were eggs (2.92%) and nuts (0.91%). Higher intake of processed meats was associated with an increase in waist circumference over 2 years (β = 1.28; standard error [SE] = 0.63), whereas higher intake of fish and seafood was associated with a decrease in waist circumference (β = ?3.47; SE = 1.39). Intake of unprocessed poultry was associated with a decrease in triglycerides (β = ?24.5; SE = 9.13). No other significant associations were observed between protein sources and 2-year changes in MetS components.ConclusionsConsuming less processed meat and more fish and seafood and unprocessed poultry was associated with decreases in waist circumference and triglycerides among US mainland Puerto Ricans. Other dietary protein sources were not related to cardiometabolic health.  相似文献   
6.
目的:研究血液与刀豆凝集素相互作用形成血凝过程中血细胞的阻抗特性。方法:选用家兔血细胞与刀豆凝集素构成实验组,以精密阻抗分析仪为基础搭建阻抗监测平台,持续采集各实验组反应过程的复阻抗幅模量、相位角、频率、实部值、虚部值等阻抗特征参数进行整理分析。结果:在50%比容的家兔血细胞悬浮液中,分别加入10、20和30 mg/mL浓度的刀豆凝集素后,家兔血细胞的特征频率从19.80 MHz提高到(27.31±2.19) MHz;在特征频率下,随反应时间的增加,复阻抗幅模量的增量均值和相位角的增量均值分别为(-18.27±1.29) Ω、3.86°±0.38°,与不含刀豆凝集素的空白对照组呈相反趋势。结论:刀豆凝集素可使家兔血细胞的特征频率升高,复阻抗幅模量降低,相位角增大,凝集速度加快。  相似文献   
7.
目的 探讨巴曲酶治疗全频下降型突发性耳聋的疗效与巴曲酶敏感性及凝血功能指标的相关性。方法 回顾性分析2019年1月—2021年2月全频下降型突发性耳聋患者48例,根据患者纤维蛋白原(FIB)的变化分为敏感组及非敏感组,检测患者凝血功能包括活化部分凝血活酶时间(APTT)、凝血酶原时间(PT)、凝血酶时间(TT)、FIB的变化及治疗前后纯音听阈变化。结果 ①48例患者总有效率为75.0%,其中平坦型总有效率为72.4%,全聋型总有效率为78.9%,敏感组有效率为85.7%,非敏感组有效率为60.0%,敏感组有效率高于非敏感组,差异具有统计学意义(P<0.05);②敏感组患者治疗后与治疗前相比FIB、APTT下降,TT、PT升高,差异具有统计学意义(P<0.05),非敏感组患者治疗后较治疗前FIB降低,TT升高,差异具有统计学意义(P<0.05)。治疗后,敏感组FIB低于非敏感组,TT、PT高于非敏感组,差异具有统计学意义(P<0.05)。结论 巴曲酶敏感性与临床治疗效果具有相关性,主要与FIB、PT、TT密切相关,与APTT相关性不大,但机体可能通过APTT内源性凝血功能,降低出血风险。巴曲酶可增强抗凝血功能,促进内耳微循环,使抗凝、纤溶和凝血在一定范围内保持平衡,安全性良好。  相似文献   
8.
BackgroundUltra-processed foods (UPFs) are associated with poor diet quality and chronic diseases. UPFs fall into 1 of the following 4 groups classified according to the extent and purpose of processing: group 1 is unprocessed or minimally processed foods (MPFs); group 2 is processed culinary ingredients; group 3 is processed foods; and group 4 is UPFs.ObjectiveThe aim of this study was to evaluate the relative validity of a semi-quantitative food frequency questionnaire (SFFQ) compared with two 24-hour dietary recalls (24DRs) `to estimate dietary intake per NOVA food group in Mexican children and adolescents.DesignThis study is a secondary analysis of dietary data from a subsample of children and adolescents who participated in the 2012 Mexican National Health and Nutrition Survey.Participants/settingThe study participants were 217 children (aged 5 through 11 years) and 165 adolescents (aged 12 through 19 years) with complete information for the SFFQ and two 24DRs.Main outcome measuresDaily averages of energy intake and percent of energy intake for each NOVA category were calculated using the SFFQ and two 24DRs.Statistical analysisTo assess relative validity, the SFFQ was compared with two 24DRs to estimate dietary intake per NOVA food group. Mean differences, Spearman correlations, intraclass correlations coefficients (ICCs), and Bland–Altman plots for continuous variables and weighted κ for ordinal variables were calculated.ResultsFor percentage of energy intake, ICCs in children and adolescents were moderate for MPFs (ICC = 0.47 and ICC = 0.56, respectively) and UPFs (ICC = 0.53 and ICC = 0.57, respectively). Bland–Altman plots indicated reasonably consistent agreement for UPFs and MPFs groups in children and adolescents. Classification by quintiles was acceptable in all groups.ConclusionsData from this study indicated reasonable relative validity of the SFFQ to rank the percentage of energy intake from MPFs and UPFs in Mexican children and adolescents.  相似文献   
9.
10.
《Radiography》2022,28(3):811-816
IntroductionScaphoid radiography has poor sensitivity for acute fracture detection and often requires repeat delayed imaging. Although magnetic resonance (MR) imaging is considered the gold standard, computed tomography (CT) is often used as an alternative due to ease of access. Cone-Beam CT (CBCT) offers equivalent diagnostic efficacy to Multi Slice CT (MSCT) at reduced dose. We aimed to establish the difference in scattered dose between modalities for scaphoid imaging.MethodsAnatomical regional entrance surface dose measurements were taken at 3 regions on an anthropomorphic torso phantom positioned as a patient to a wrist phantom undergoing scaphoid imaging for three modalities (CBCT, MSCT, four-view projection radiography). Exposure factors were based on audit of clinical exposures. Each dose measurement was repeated three times per anatomical region, modality, exposure setting and projection.ResultsUnder unpaired T-test CBCT gave significantly lower mean dose at the neck (1.64 vs 18 mGy), chest (2.78 vs 8.01) and abdomen (1.288 vs 2.93) than MSCT (p < .0001). However CBCT had significantly higher mean dose than four-view radiography at the neck, chest and abdomen (0.031, 0.035, and 0.021 mGy) (p < .0001).ConclusionCBCT of the wrist carries a significantly higher scattered radiation dose to the neck, chest and abdomen than four view scaphoid radiography, but significantly lower scattered dose than MSCT of the wrist of equivalent diagnostic value.Implications for practiceThe use of CBCT for scaphoid injury carries significantly lower scattered dose to radio-sensitive structures investigated here than equivalent MSCT, and may be of greater use as an early cross-sectional investigation for suspected scaphoid fracture.  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