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   6198篇
  免费   423篇
  国内免费   51篇
耳鼻咽喉   41篇
儿科学   136篇
妇产科学   138篇
基础医学   1176篇
口腔科学   100篇
临床医学   519篇
内科学   1563篇
皮肤病学   187篇
神经病学   618篇
特种医学   87篇
外科学   575篇
综合类   26篇
一般理论   3篇
预防医学   465篇
眼科学   84篇
药学   504篇
中国医学   21篇
肿瘤学   429篇
  2024年   10篇
  2023年   107篇
  2022年   275篇
  2021年   406篇
  2020年   195篇
  2019年   269篇
  2018年   295篇
  2017年   191篇
  2016年   228篇
  2015年   230篇
  2014年   310篇
  2013年   353篇
  2012年   496篇
  2011年   526篇
  2010年   275篇
  2009年   233篇
  2008年   366篇
  2007年   361篇
  2006年   317篇
  2005年   305篇
  2004年   241篇
  2003年   218篇
  2002年   206篇
  2001年   26篇
  2000年   11篇
  1999年   34篇
  1998年   29篇
  1997年   25篇
  1996年   15篇
  1995年   16篇
  1994年   5篇
  1993年   5篇
  1992年   8篇
  1991年   10篇
  1990年   9篇
  1989年   4篇
  1988年   5篇
  1987年   8篇
  1986年   4篇
  1981年   3篇
  1980年   2篇
  1979年   2篇
  1978年   5篇
  1977年   2篇
  1975年   3篇
  1974年   2篇
  1973年   5篇
  1972年   2篇
  1970年   3篇
  1968年   2篇
排序方式: 共有6672条查询结果,搜索用时 0 毫秒
71.
H9N2 influenza viruses are isolated in Israel since 2000 and became endemic. From November 2006 to the beginning of 2012, many H9N2 viruses were identified, all belonged to the Asian G1-like lineage represented by A/qu/Hong Kong/G1/97 (H9N2). In the present study, 66 isolates were selected for their hemagglutinin gene characterization. Most H9N2 isolates were distributed between two main groups, identified as the 4th and 5th introductions. The 5th introduction, was represented by a compact cluster containing viruses isolated in 2011–2012; the 4th introduction was subdivided into two subgroups, A and B, each containing at least two clusters, which can be identified as A-1, A-2, B-1, and B2, respectively. Genetic analysis of the deduced HA proteins of viruses, belonging to the 4th and 5th introductions, revealed amino acid variations in 79 out of 542 positions. All isolates had typical low pathogenicity motifs at the hemagglutinin (HA) cleavage site. Most viruses had leucine at position 216 in a receptor binding pocket that enables the virus to bind successfully with the cellular receptors intrinsic to mammals, including humans. It was shown that the differences between the HA proteins of viruses used for vaccine production and local field isolates increased in parallel with the duration and intensity of vaccine use, illustrating the genetic diversity of the H9N2 viruses in Israel.  相似文献   
72.

It has been demonstrated that obesity is an independent risk factor for worse outcomes in patients with COVID-19. Our objectives were to investigate which classes of obesity are associated with higher in-hospital mortality and to assess the association between obesity and systemic inflammation. This was a retrospective study which included consecutive hospitalized patients with COVID-19 in a tertiary center. Three thousand five hundred thirty patients were included in this analysis (female sex: 1579, median age: 65 years). The median body mass index (BMI) was 28.8 kg/m2. In the overall cohort, a J-shaped association between BMI and in-hospital mortality was depicted. In the subgroup of men, BMI 35–39.9 kg/m2 and BMI ≥40 kg/m2 were found to have significant association with higher in-hospital mortality, while only BMI ≥40 kg/m2 was found significant in the subgroup of women. No significant association between BMI and IL-6 was noted. Obesity classes II and III in men and obesity class III in women were independently associated with higher in-hospital mortality in patients with COVID-19. The male population with severe obesity was the one that mainly drove this association. No significant association between BMI and IL-6 was noted.

  相似文献   
73.
74.
75.
BackgroundFamilial hypercholesterolemia (FH) is an inherited disorder mainly caused by mutations in the LDL receptor (LDL-R) and characterized by elevation of low-density lipoprotein cholesterol (LDL-C) levels and premature cardiovascular disease.ObjectiveIn this study, we evaluated the clinical phenotype of the p.Asp47Asn, described as an uncertain pathogenic variant, and its effect on the structure of LDL-R and ligand interactions with apolipoproteins.Methods27 children and adolescents with suspected FH diagnosis were recruited from a pediatric endocrinology outpatient clinic. Blood samples were collected after 12 h fasting for lipid profile analysis. DNA sequencing was performed for six FH-related genes by Ion Torrent PGM platform and copy number variation by MLPA. For index cases, a familial cascade screening was done restricted to the same mutation found in the index case. In silico analysis were developed to evaluate the binding capacity of LDL-R to apolipoproteins B100 and E.ResultsLipid profile in children and adolescents demonstrated higher LDL-C levels in p.Asp47Asn carriers compared to the wild type genotype. In silico analysis predicted a reduction in the binding capacity of the ligand-binding modules LA1-2 of p.Asp47Asn LDL-R for ApoB100 and ApoE, which was not produced by local structural changes or folding defects but as a consequence of a decreased apparent affinity for both apolipoproteins.ConclusionThe clinical phenotype and the structural effects of p.Asp47Asn LDL-R mutation suggest that this variant associates to FH.  相似文献   
76.
77.
Ciliopathies are genetically heterogeneous disorders characterized by variable expressivity and overlaps between different disease entities. This is exemplified by the short rib‐polydactyly syndromes, Jeune, Sensenbrenner, and Mainzer‐Saldino chondrodysplasia syndromes. These three syndromes are frequently caused by mutations in intraflagellar transport (IFT) genes affecting the primary cilia, which play a crucial role in skeletal and chondral development. Here, we identified mutations in IFT140, an IFT complex A gene, in five Jeune asphyxiating thoracic dystrophy (JATD) and two Mainzer‐Saldino syndrome (MSS) families, by screening a cohort of 66 JATD/MSS patients using whole exome sequencing and targeted resequencing of a customized ciliopathy gene panel. We also found an enrichment of rare IFT140 alleles in JATD compared with nonciliopathy diseases, implying putative modifier effects for certain alleles. IFT140 patients presented with mild chest narrowing, but all had end‐stage renal failure under 13 years of age and retinal dystrophy when examined for ocular dysfunction. This is consistent with the severe cystic phenotype of Ift140 conditional knockout mice, and the higher level of Ift140 expression in kidney and retina compared with the skeleton at E15.5 in the mouse. IFT140 is therefore a major cause of cono‐renal syndromes (JATD and MSS). The present study strengthens the rationale for IFT140 screening in skeletal ciliopathy spectrum patients that have kidney disease and/or retinal dystrophy.  相似文献   
78.
79.

PURPOSE

Anthracosis often results in mediastinal nodal enlargement. The aim of this comparative study was to evaluate if it is possible to differentiate endobronchial ultrasound-guided trans-bronchial needle aspiration (EBUS-TBNA) proven anthracotic lymph nodes from malignant lymph node enlargement by means of multislice computed tomography (MSCT).

METHODS

We compared the MSCT findings of 89 enlarged lymph nodes due to anthracosis with 54 malignant lymph nodes (non-small cell lung cancer 75.9%, small cell lung cancer 18.5%, and non-Hodgkin lymphoma 5.6%). The lymph nodes were assessed for density (calcification, fat, and necrosis), shape (oval, round), contrast enhancement, and contour (sharp, ill-defined).

RESULTS

Malignant lymph nodes showed significantly greater axis diameters (P < 0.001). Both anthracotic and malignant nodes were most often oval (86.5% of all malignant nodes vs. 81.5% of all anthracotic nodes, P = 0.420) and showed confluence in a remarkable percentage (28.1% vs. 42.6%, P = 0.075). Anthracotic nodes showed calcifications more often (18% vs. 0%, P < 0.001). Malignant lymph nodes showed a significantly greater short and long axis diameter (P < 0.001), and they had a higher frequency of ill-defined contours (27.8% vs. 2.2%, P < 0.001) and contrast enhancement (27.8% vs. 5.6%, P < 0.001). Nodal necrosis, which appeared in one third of the malignant nodes, was not observed in anthracosis (35.2% vs. 0%, P < 0.001). Confluence of enlarged lymph nodes was seen in malignant lymph nodes (42.6%), as well as in lymph node enlargement due to anthracosis (28.1%, P = 0.075).

CONCLUSION

Our results show that there are significant differences in MSCT findings of malignant enlarged lymph nodes and benign lymph node enlargement due to anthracosis.Anthracosis is characterized by alterations not only of the lung parenchyma and bronchioles but also of the lymphatic system, resulting in chronic lymphadenopathy and nodal enlargement (1). Since finding of enlarged mediastinal lymph nodes on computed tomography (CT) may raise the suspicion of metastasis in patients with a known primary neoplasm (2, 3), and lymph node anthracosis may appear as false positive on positron emission tomography (PET) (46), it can confuse clinicians in staging of lung cancer patients.The aim of this comparative study of endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) and chest CT was to evaluate whether it is possible to differentiate enlarged anthracotic lymph nodes from malignant lymph node enlargement by means of CT. To the best of our knowledge, this study seems to be the first to deal with the differential diagnosis of enlarged anthracotic and malignant lymph nodes in this setting.  相似文献   
80.
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