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   21050篇
  免费   2006篇
  国内免费   1425篇
耳鼻咽喉   124篇
儿科学   213篇
妇产科学   194篇
基础医学   2631篇
口腔科学   370篇
临床医学   2912篇
内科学   2964篇
皮肤病学   218篇
神经病学   1106篇
特种医学   722篇
外国民族医学   13篇
外科学   2036篇
综合类   3951篇
现状与发展   5篇
预防医学   1086篇
眼科学   556篇
药学   2285篇
  20篇
中国医学   1314篇
肿瘤学   1761篇
  2024年   15篇
  2023年   375篇
  2022年   549篇
  2021年   1032篇
  2020年   900篇
  2019年   718篇
  2018年   814篇
  2017年   687篇
  2016年   700篇
  2015年   1062篇
  2014年   1280篇
  2013年   1108篇
  2012年   1653篇
  2011年   1798篇
  2010年   1054篇
  2009年   840篇
  2008年   1107篇
  2007年   1066篇
  2006年   1107篇
  2005年   1065篇
  2004年   699篇
  2003年   633篇
  2002年   545篇
  2001年   481篇
  2000年   502篇
  1999年   510篇
  1998年   301篇
  1997年   299篇
  1996年   207篇
  1995年   205篇
  1994年   218篇
  1993年   116篇
  1992年   128篇
  1991年   125篇
  1990年   124篇
  1989年   89篇
  1988年   86篇
  1987年   73篇
  1986年   61篇
  1985年   57篇
  1984年   21篇
  1983年   12篇
  1982年   15篇
  1981年   14篇
  1980年   3篇
  1979年   15篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1974年   3篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
目的研究超声低频探头和低频探头联合高频探头检查在新生儿颅脑疾病诊断中的准确率和敏感性。 方法选取河源市妇幼保健院自2017年1月至2018年12月收治的有颅脑疾病高危因素(早产、低体质量、多胎妊娠、出生过程有缺氧窒息及产时感染)的新生儿90例作为研究对象。采用随机数字表法将所有新生儿平均分为2组,研究组(45例)给予低频探头联合高频探头进行探查,对照组(45例)仅给予低频探头进行探查。结合CT检查结果和临床治疗,比较2种检测方法的准确率和敏感性。 结果研究组检测新生儿缺氧缺血性脑病、脑室内出血和室管膜下出血诊断准确率分别为87.5%、100%、100%,高于相应对照组(15.38%、12.5%、0%),差异有统计学意义(P<0.05);研究组和对照组检测脑实质内出血和脑积水的诊断准确率分别为87.5%、100%以及42.85%、66.67%,差异无统计学意义(P>0.05)。研究组检测新生儿颅脑疾病的效率为82.22%,高于对照组(22.22%),差异具有统计学意义(P<0.05)。 结论使用超声低频探头联合高频探头的方法提高了缺氧缺血性脑病、脑室内出血、室管膜下出血等新生儿颅脑疾病诊断的准确率,在诊断新生儿脑实质内出血和脑积水的准确率没有差异,且对颅脑疾病诊断的敏感性较高,因此具有较为重要的临床意义。  相似文献   
32.
目的探讨胃癌术后病人肠道菌群的变化及其对病人术后围手术期恢复的影响。方法选择2018年6月至2019年6月南昌大学第二附属医院胃肠外科收治的行胃癌根治术的100例病人,对每位病人术前与术后的粪便进行菌群检测(双歧杆菌、嗜酸乳杆菌、大肠杆菌、链球菌),并根据病人术后有益菌相对丰度分为丰度高组和丰度低组,同时检测病人术后生化指标(白细胞计数、中性粒细胞百分比、C反应蛋白、淋巴细胞计数、淋巴细胞百分比、总蛋白、白蛋白和前白蛋白)。结果通过高通量测序检测胃癌病人手术前后菌群变化,发现胃癌术后病人双歧杆菌、嗜酸乳杆菌明显减少,大肠杆菌、链球菌明显增多,差异有统计学意义(P<0.05)。100例病人中双歧杆菌和嗜酸乳杆菌相对丰富的病人肠道功能恢复较早,炎症指标相对较低,免疫指数有所提高,同时提高总蛋白及白蛋白营养指标,差异有统计学意义(P<0.05)。结论胃癌术后病人肠道菌群发生改变,体内有益菌双歧杆菌、嗜乳酸杆菌减少,大肠杆菌、链球菌明显增加。同时体内有益菌减少会影响病人术后恢复,增加病人炎症反应,降低机体免疫能力,影响病人营养状态。  相似文献   
33.
Objective To compare the expression level of exosomal miR-503 in peritoneal dialysis effluent (PDE) from patients of different peritoneal transport characteristics, predict the target genes of miR-503 and provide bioinformatic data for researches of peritoneal transport characteristics. Methods Twenty-four stable peritoneal dialysis (PD) patients were selected and divided into high transport group (H group, n=12) and low transport group (L group, n=12) according to the results of peritoneal equilibration tests (PET). The 500 ml PDE that was left on the patient's abdomen overnight was collected and concentrated using ultrafiltration cell. Exosomes in PDE were resuspended in phosphate buffered saline (PBS) after ultracentrifugation and the characteristics of PDE exosomes were identified by transmission electron microscope (TEM), nanoparticle tracking analysis (NTA), Western blotting and fluorescent staining. MicroRNAs were extracted from PDE exosomes. The expression levels of PDE exosomal miR-503 in the two groups were detected by quantitative real-time PCR. Then the relations between the relative quantity of PDE exosomal miR-503 and PET values or 24 h ultrafiltration volume (UF) were analyzed. Targetscan and miRDB databases were used to predict the target genes of miR-503. Gene ontology (GO) functional enrichment and Kyoto encyclopedia of genes and genomes (KEGG) signaling pathway analysis were relied on DAVID (https://david.ncifcrf.gov/). Results The exosomes in PDE showed a round and cup-shaped morphology under TEM, and the diameters were approximately 100 nm measured by NTA. The specific biomarkers of exosomes, CD63, CD81 and heat shock protein -70 (HSP-70) were all detected by Western blotting. The internalization and uptake of the exosomes was observed after fluorescent staining. The relative expression level of PDE exosomal miR-503 in H group was found to be significantly higher than that in L group (P=0.002), and the relative quantity of PDE exosomal miR-503 was significantly positively correlated with PET values (r=0.547, P=0.006), but not 24 h UF (r=-0.297, P=0.159). There were 156 target genes of miR-503 in total that could be predicted by two different databases at the same time. GO analysis of these 156 target genes was mainly focused on kinase binding, regulation of protein modification and catabolic process as well as regulation of epithelial cell proliferation. KEGG enriched many tumor associated or classical signaling pathways, including transforming growth factor-β (TGF-β) signaling pathway and vascular endothelial growth factor (VEGF) signaling pathway. The prediction showed that vascular endothelial growth factor A (VEGFA) was a direct target gene of miR-503 and it was also related to many proteins involved in fibrosis mechanism. Conclusions The expression level of PDE exosomal miR-503 is significantly higher in H group, and positively correlates with PET values, which may regulate the angiogenesis of peritoneal vessels by targeting VEGFA.  相似文献   
34.
近年来,免疫治疗研究在肺癌上取得突破性进展,能显著改善肺癌患者的总生存期,且耐受性良好。然而临床研究入组人群具有高度选择性,并不能完全代表真实世界人群。真实世界免疫治疗的疗效及安全性是否与临床研究的一致,何时应用,选择单药还是联合治疗,老年、PS≥2分、自身免疫疾病、使用激素、脑转移等特殊人群的应用,以及疗效标志物的选择,疗效评估标准,不良反应的管理等问题都值得进一步思考。本文通过真实世界数据与临床研究的比较,对真实世界免疫治疗存在问题进行初步分析。  相似文献   
35.
医院信息系统是医院业务不可或缺的部分,加强计算机网络安全治理与防护对医院信息化具有重要意义。从分析当前国内医院网络安全现状出发,总结医院网络安全存在的隐患和面临的挑战,提出纵深防御体系,网络架构演进和人员安全风险意识以及能力培养等方面的治理策略。  相似文献   
36.
37.
BACKGROUND AND PURPOSE:The coronavirus disease 2019 (COVID-19) pandemic has led to decreases in neuroimaging volume. Our aim was to quantify the change in acute or subacute ischemic strokes detected on CT or MR imaging during the pandemic using natural language processing of radiology reports.MATERIALS AND METHODS:We retrospectively analyzed 32,555 radiology reports from brain CTs and MRIs from a comprehensive stroke center, performed from March 1 to April 30 each year from 2017 to 2020, involving 20,414 unique patients. To detect acute or subacute ischemic stroke in free-text reports, we trained a random forest natural language processing classifier using 1987 randomly sampled radiology reports with manual annotation. Natural language processing classifier generalizability was evaluated using 1974 imaging reports from an external dataset.RESULTS:The natural language processing classifier achieved a 5-fold cross-validation classification accuracy of 0.97 and an F1 score of 0.74, with a slight underestimation (−5%) of actual numbers of acute or subacute ischemic strokes in cross-validation. Importantly, cross-validation performance stratified by year was similar. Applying the classifier to the complete study cohort, we found an estimated 24% decrease in patients with acute or subacute ischemic strokes reported on CT or MR imaging from March to April 2020 compared with the average from those months in 2017–2019. Among patients with stroke-related order indications, the estimated proportion who underwent neuroimaging with acute or subacute ischemic stroke detection significantly increased from 16% during 2017–2019 to 21% in 2020 (P = .01). The natural language processing classifier performed worse on external data.CONCLUSIONS:Acute or subacute ischemic stroke cases detected by neuroimaging decreased during the COVID-19 pandemic, though a higher proportion of studies ordered for stroke were positive for acute or subacute ischemic strokes. Natural language processing approaches can help automatically track acute or subacute ischemic stroke numbers for epidemiologic studies, though local classifier training is important due to radiologist reporting style differences.

There is much concern regarding the impact of the coronavirus disease 2019 (COVID-19) pandemic on the quality of stroke care, including issues with hospital capacity, clinical resource re-allocation, and the safety of patients and clinicians.1,2 Previous reports have shown that there have been substantial decreases in stroke neuroimaging volume during the pandemic.3,4 In addition, acute ischemic infarcts have been found on neuroimaging studies in many hospitalized patients with COVID-19, though the causal relationship is unclear.5,6 Studies like these and other epidemiologic analyses usually rely on the creation of manually curated databases, in which identification of cases can be time-consuming and difficult to update in real-time. One way to facilitate such research is to use natural language processing (NLP), which has shown utility for automated analysis of radiology report data.7 NLP algorithms have been developed previously for the classification of neuroradiology reports for the presence of ischemic stroke findings and acute ischemic stroke subtypes.8,9 Thus, NLP has the potential to facilitate COVID-19 research.In this study, we developed an NLP machine learning model that classifies radiology reports for the presence or absence of acute or subacute ischemic stroke (ASIS), as opposed to chronic stroke. We used this model to quantify the change in ASIS detected on all CT or MR imaging studies performed at a large comprehensive stroke center during the COVID-19 pandemic in the United States. We also evaluated NLP model generalizability and different training strategies using a sample of radiology reports from a second stroke center.  相似文献   
38.

Aims

To investigate the 29-year (1985–2014) trends in body dimensions and physical fitness test performances among 12-year-old Chinese children living in urban and rural areas.

Methods

The data were from the findings of seven cross-sectional surveys from the Chinese National Survey on Students’ Constitution and Health. In the seven surveys, there were 34,238; 11,664; 17,485; 18,057; 19,254; 17,962; and 17,906 children, respectively. Anthropometric measurements and physical fitness performances of 12-year-old Chinese children living in rural and urban areas were analyzed. Polynomial models were used to analyze trends in test performances. Analysis of variance was used to assess the urban–rural differentials.

Results

The height and weight of both urban and rural children substantially increased from 1985 to 2014. Urban children were taller and heavier than rural children. A slight narrowing of the urban–rural differential in height was observed. The disparity in weight increased from 1985 to 2000 and decreased thereafter. Urban children performed better in most of the physical fitness tests examined, such as standing long jump, 50-m run, and sit-ups. The urban–rural disparity decreased from 1985 to 2014 in 50-m run, standing long jump, and sit-up score; the largest difference in 10?×?50 m run and pull-up score was observed in 2000 and 2005, respectively.

Conclusions

There was a general decline in physical fitness in both urban and rural children after 2000. Urgent, targeted actions need to be taken by public health policy officials and parents to maintain or improve the physical fitness of children.  相似文献   
39.
姜黄为我国传统中药,味辛、苦,性温,具有破血行气、通经止痛之功效,其用药历史悠久,最早收载于《新修本草》。对姜黄化学成分及主要药理活性进行总结,并基于传统性效及现代研究两方面对姜黄质量标志物进行预测分析。建议对姜黄的芳姜黄酮、α-姜黄酮、β-姜黄酮、姜黄素、去甲氧基姜黄素、双去甲氧基姜黄素及黄酮类等成分进行定性、定量分析,进一步开展其所含的萜类和甾醇类等成分化学物质组的深入研究,为明确姜黄的质量标志物和姜黄质量评价研究提供科学依据。  相似文献   
40.
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