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   48037篇
  免费   5306篇
  国内免费   1827篇
耳鼻咽喉   377篇
儿科学   392篇
妇产科学   469篇
基础医学   6201篇
口腔科学   1449篇
临床医学   4467篇
内科学   5041篇
皮肤病学   519篇
神经病学   3917篇
特种医学   1603篇
外国民族医学   1篇
外科学   4430篇
综合类   8127篇
现状与发展   6篇
预防医学   6774篇
眼科学   952篇
药学   5259篇
  73篇
中国医学   2889篇
肿瘤学   2224篇
  2024年   101篇
  2023年   1003篇
  2022年   1424篇
  2021年   2387篇
  2020年   2206篇
  2019年   1730篇
  2018年   1685篇
  2017年   1872篇
  2016年   1754篇
  2015年   1899篇
  2014年   3159篇
  2013年   3594篇
  2012年   2921篇
  2011年   3330篇
  2010年   2584篇
  2009年   2668篇
  2008年   2661篇
  2007年   2652篇
  2006年   2245篇
  2005年   2007篇
  2004年   1597篇
  2003年   1423篇
  2002年   1060篇
  2001年   950篇
  2000年   886篇
  1999年   723篇
  1998年   526篇
  1997年   484篇
  1996年   409篇
  1995年   407篇
  1994年   383篇
  1993年   294篇
  1992年   287篇
  1991年   218篇
  1990年   229篇
  1989年   191篇
  1988年   164篇
  1987年   160篇
  1986年   113篇
  1985年   167篇
  1984年   116篇
  1983年   78篇
  1982年   85篇
  1981年   78篇
  1980年   65篇
  1979年   53篇
  1978年   37篇
  1977年   30篇
  1976年   27篇
  1975年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
目的评估并比较基于不同机器学习算法建立的乳腺癌超声影像组学预测模型的诊断性能。 方法回顾性收集2017年1月至2019年4月就诊皖南医学院第一附属医院、有明确病理结果的乳腺肿块病例828例,以2018年8月31日为节点将其分为训练集(526例)和验证集(302例),提取肿块的超声影像组学特征并进行特征筛选,运用k最近邻(kNN)、逻辑回归(LR)、朴素贝叶斯(NB)、随机森林(RF)和支持向量机(SVM)5种机器学习算法分别建立预测模型,使用重复交叉验证方法做内部验证,计算比较各模型的敏感度、特异度、阳性预测值(PPV)和阴性预测值(NPV),并实施外部验证,绘制ROC曲线并比较ROC曲线下面积(AUC)以评价模型的鉴别诊断性能,绘制校准曲线评价模型校准度。 结果从提取的109个影像组学特征中筛选出19个特征建立了5种机器学习算法模型。在内部验证中,5种模型的敏感度、特异度、PPV、NPV比较,总体差异均有统计学意义(P均<0.001)。LR模型的特异度、PPV、NPV中位数分别为0.769、0.816、0.778,3项指标均高于其他4种模型;敏感度中位数为0.824,高于kNN、RF和SVM模型。此外,SVM模型的特异度、PPV、NPV中位数分别为0.706、0.774、0.759,虽均低于LR模型,但均高于其他3种模型。在外部验证中,LR、SVM、RF、kNN和NB的AUC依次为0.890、0.832、0.821、0.746和0.703,其中LR与SVM的AUC差异有统计学意义(P=0.012);此外,各模型在校准性能上表现并不一致,LR和SVM模型的校准曲线显示乳腺癌实际概率与预测概率之间的一致性较好。 结论以超声影像组学特征为基础,运用不同机器学习算法建立的乳腺癌超声预测模型,均表现出较高的诊断性能,其中LR模型表现最为突出;选择合适的机器学习算法有助于进一步提高预测模型的诊断性能,提供更加准确的量化预测结果。  相似文献   
12.
13.
BackgroundIn order to avoid excessive treatment of thyroid nodules in the clinic, it is necessary to find a simple and practical analysis method to comprehensively and accurately reflect benign or malignant thyroid nodules. This study aimed to construct and validate a comprehensive and reliable network-based predictive model using a variety of imaging and laboratory criteria for thyroid nodules to stratify the risk of malignancy prior to surgery.MethodsWe retrospectively analyzed data from patients who underwent surgical treatment for thyroid nodules at the Thyroid and Breast Diagnosis and Treatment Center of Weifang Hospital of Traditional Chinese Medicine between January 2018 and December 2020. Binary logical regression analysis was performed to predict whether nodules were malignant or benign. The developmental dataset included 457 patients (January 2018–December 2020). The validation set included separate data points (n = 225, January 2018–December 2020).ResultsIn this study, criteria that showed significant predictive value for malignant nodules included TI-RADS: 4b (p = 0.065); Bethesda IV, Bethesda V, Bethesda VI (P < 0.0001); BRAFV600E mutation (P < 0.0001); Calcitonin>5 pg/ml (p = 0.0037); and FNA-Tg>30 ng/ml (p = 0.0003). A 10-grade risk scoring system was developed. The risk of malignancy risk ranged from 2.06% to 100% and was positively associated with increasing risk grade. The areas under the receiver-operating characteristic curve of the development and validation sets were 0.972 and 0.946, respectively.ConclusionA simple, comprehensive and reliable web-based predictive model was designed using a variety of imaging and laboratory criteria to stratify thyroid nodules by probability of malignancy.  相似文献   
14.
BackgroundThe social ecological approach suggests that the spatial context among other factors influence physical activity behavior. Ample research documents physical environmental effects on physical activity. Yet, to date inconsistent associations remain, which might be explained by conceptual and methodological challenges in measuring the spatial dimensions of health behavior. We review methods applied to measure the spatial contexts in the social ecological physical activity literature.MethodsOnline databases and selected reviews were used to identify papers published between 1990 and 2020. A total of 2167 records were retrieved, from which 412 studies that used physical activity as a primary outcome variable, included measures of the physical environment and applied the main principles of the social ecological approach, were included.ResultsSubjective approaches were the dominant method to capture the spatial context of physical activities. These approaches were applied in 67% (n=279) of the studies. From the objective approaches an administrative unit was most prevalent and was applied in 29% (n=118) of the studies. The most comprehensive objective spatial methods that capture the true environmental exposure, were used only in 2% (n=10) of the studies.ConclusionsCurrent social ecological physical activity research applies simple conceptualizations and methods of the spatial context. While conceptual and methodological concerns have been repeatedly expressed, no substantive progress has been made in the use of spatial approaches. To further our understanding on place effects on health, future studies should carefully consider the choice of spatial approaches, and their effect on study results.  相似文献   
15.
目的 梳理总结中医药人工智能领域近40年的研究情况,分析该领域研究主题演化过程,发现热点主题和研究前沿。方法 本研究检索了CNKI和WOS中中医药人工智能领域的文献,根据生命周期理论划分不同时间片,将文献摘要作为研究对象,采用LDA主题模型挖掘文本主题,分析主题的演化过程,识别热点主题。结果 纳入中英文文献2750篇,根据生命周期理论划分中医药人工智能领域发展阶段,分别建立全局和各阶段的LDA模型,挖掘出全局热点主题有中医专家系统、中医辅助诊断系统、中医药数据挖掘等,发现主题演化路径并进行可视化展示。结论 中医药与人工智能主要的结合点在中医智能系统、中医药知识组织和中医智能诊疗机器人这3方面,这3个方向的研究均离不开神经网络技术的支持,同时也结合了关联规则发现、复杂网络研究等方法。  相似文献   
16.
目的 研究蒙药安神补心六味丸对大鼠心肌缺血损伤的保护作用和氧化应激机制。方法 将60只大鼠随机分为空白组、模型组、阳性对照组(丹参滴丸)及蒙药安神补心六味丸低、中、高剂量组,使用腹腔注射异丙肾上腺素方法制备大鼠急性心肌缺血模型,记录并观察大鼠心电图活动变化,然后进行腹主动脉取血,分离血清,测定乳酸脱氢酶(Lactic dehydrogenase,LDH)、肌酸激酶(Creatine kinase,CK)、磷酸肌酸激酶(Creatine kinase isoenzyme,CK-MB)、谷草转氨酶(Aspartate aminotransferase,AST)、超氧化物歧化酶(Superoxide dismutase,SOD)、丙二醛(Malondialdehyde,MDA)和谷胱甘肽过氧化物酶(Glutathione peroxidase,GSH-PX)含量变化。取心肌组织固定,对大鼠心肌组织进行HE染色,通过对心肌酶学和和心肌组织形态学两个方面来考察蒙药安神补心六味丸对大鼠心肌缺血模型的保护作用。结果 与空白组比较,模型组大鼠血清中LDH活性极显著升高(P<0.01),CK、CK-MB、AST、MDA活性均显著升高(P<0.05),SOD活性显著降低(P<0.05),GSH-PX活性高度显著降低(P<0.001),且差异均具有统计学意义;与模型组比较,蒙药安神补心六味丸组高剂量组大鼠血清中LDH、CK、CK-MB、MDA活性显著降低(P<0.05),SOD活性显著升高(P<0.05),GSH-PX活性极显著升高(P<0.01),且差异均具有统计学意义。从HE染色分析,蒙药安神补心六味丸能够改善因缺血而造成的心肌组织损伤。结论 蒙药安神补心六味丸能有效改善心肌组织病理状态,减轻大鼠心肌缺血损伤,以达到保护心肌作用,机制可能与氧化应激机制相关。  相似文献   
17.
Induction of labour is a common obstetrical procedure and is undertaken when the benefits of delivery are considered to outweigh the risks of continuation of pregnancy. However, more than one-fifth of induction cases fail to result in vaginal births and lead to unplanned caesarean deliveries, which compromise the birth experience and have negative clinical and resource implications. The need for accurate prediction of successful labour induction is increasingly recognised and many researchers have attempted to evaluate the potential predictability of different factors including maternal characteristics, Bishop score, various biochemical markers and ultrasound markers and derive predictive models to address this issue.  相似文献   
18.
目的分析超长住院患者分布及影响因素,探讨减少超长住院日的措施。方法从江苏省某三甲医院病案管理系统中调取2020年1月1日-2020年12月31日134016例出院患者的住院病案首页资料,对住院时间≥30天的1401例超长住院患者的分布特征进行统计描述,采用Logistic回归模型分析超长住院日的影响因素。结果2020年全院平均住院日为7.13天,其中超长住院患者平均住院日为41.85天。超长住院患者以60岁以上年龄组最多(39.61%);出院科室主要分布在血液科(42.18%)、普通外科(11.85%)、骨科(7.49%)等;疾病类别主要为肿瘤(47.32%)、影响健康状态和与保健机构接触的因素(10.56%)、循环系统疾病(7.07%)等;多因素Logistic回归结果显示,男性(OR=1.188)、离院方式为非医嘱离院或其他(OR=2.046)和死亡病例(OR=3.362)是超长住院的危险因素。结论控制超长住院日对平均住院日影响显著,医院应加强重点人群、重点科室和重点病种管理提高诊疗管理水平,缩短平均住院日。  相似文献   
19.
20.
《Vaccine》2022,40(33):4889-4896
BackgroundDuring the COVID-19 pandemic, the number of hepatitis B virus (HBV) vaccinations among men who have sex with men (MSM) has been considerably lower than before the pandemic. Moreover, less frequent HBV testing and a reduction in numbers of sex partners have been reported. We assessed the impact of these COVID-19-related changes on HBV transmission among MSM in the Netherlands.MethodsWe estimated the changes in sexual activity, HBV testing, and HBV vaccination among MSM during the pandemic from Dutch data. We used a deterministic compartmental model and investigated scenarios with small or large declines in sexual activity, testing, and vaccination for the current phase of the pandemic (without available data). We examined the increase in HBV vaccinations needed to prevent further increase in HBV incidence.ResultsWith a decrease in numbers of sex partners of 15–25% during the first lockdown and 5% during the second lockdown, we found a decline of 6.6% in HBV incidence in 2020, despite a >70% reduction in HBV testing and vaccination during the first lockdown. With numbers of sex partners rebounding close to pre-pandemic level in 2021, and a reduction of 15% in testing and 30% in vaccination in 2021, we found an increase of 1.4% in incidence in 2021 and 3.1% in 2026. With these changes, an increase of ≥60% in HBV vaccinations in 2022 would be needed to bring the HBV incidence in 2023 back to the level that it would have had if the COVID-19-related changes had not occurred.ConclusionsDespite reductions in sexual activity during the COVID-19 pandemic, the decrease in HBV vaccinations may result in a small increase in HBV incidence after 2021, which may persist for years. It is important to restore the vaccination level and limit further increase in HBV transmission among MSM.  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