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   2803篇
  免费   143篇
  国内免费   20篇
耳鼻咽喉   15篇
儿科学   20篇
妇产科学   19篇
基础医学   461篇
口腔科学   50篇
临床医学   273篇
内科学   476篇
皮肤病学   47篇
神经病学   187篇
特种医学   203篇
外科学   497篇
综合类   23篇
预防医学   125篇
眼科学   30篇
药学   287篇
中国医学   30篇
肿瘤学   223篇
  2024年   3篇
  2023年   25篇
  2022年   76篇
  2021年   108篇
  2020年   38篇
  2019年   78篇
  2018年   86篇
  2017年   61篇
  2016年   92篇
  2015年   137篇
  2014年   175篇
  2013年   180篇
  2012年   267篇
  2011年   242篇
  2010年   143篇
  2009年   112篇
  2008年   184篇
  2007年   142篇
  2006年   139篇
  2005年   129篇
  2004年   100篇
  2003年   83篇
  2002年   57篇
  2001年   42篇
  2000年   51篇
  1999年   40篇
  1998年   14篇
  1997年   16篇
  1996年   22篇
  1995年   6篇
  1994年   4篇
  1992年   7篇
  1991年   15篇
  1990年   9篇
  1989年   3篇
  1988年   3篇
  1987年   6篇
  1986年   5篇
  1985年   9篇
  1984年   6篇
  1983年   3篇
  1981年   3篇
  1979年   10篇
  1978年   5篇
  1977年   3篇
  1975年   3篇
  1973年   3篇
  1968年   2篇
  1967年   3篇
  1965年   2篇
排序方式: 共有2966条查询结果,搜索用时 15 毫秒
51.
Intestinal obstruction involves a partial or complete blockage of the bowel which results in the failure of intestinal contents to pass through. The mechanical causes of obstruction may include the followings: hernias, postoperative adhesions or scar tissue, impacted feces, gallstones, tumors, granulomatous processes, intussusception, volvulus, foreign bodies, and etc. Hernias are the third leading cause of intestinal obstruction by 10% approximately. However, most hernias are the cases with abdominal wall, inguinal or internal hernia. Femoral, obturator, lumbar, or sciatic hernia as the cause of obsturction is rare. Furthermore, the cases accompanying soft tissue necrosis are seldomly reported. Herein, we report a case of intestinal obstruction caused by strangulated femoral hernia accompanying soft tissue necrosis in a 78-years-old female patient.  相似文献   
52.
PURPOSE: We investigated the role of race in predicting the likelihood of using hospice and dying in a hosptial among dual-eligible (Medicare and Medicaid) nursing home residents. DESIGN AND METHODS: This follow-back cohort study examined factors associated with hospice use and in-hospital death among non-Hispanic Black and non-Hispanic White dual-eligible nursing home residents (N = 30,765) who died in Florida during one of three years: 2000, 2001, or 2002. We used logistic regression models to identify independent predictors of hospice use and in-hospital death. RESULTS: After we controlled for other factors, Black residents were significantly less likely to use hospice and more likely to die in a hospital. Principal cause of death moderated the relationship between race and hospice use: Black residents were significantly less likely to use hospice than White residents among residents without cancer as principal cause of death, but there was no difference among residents with cancer as cause of death. Further analyses for each racial group revealed that the impact of cause of death in predicting hospice use was greater among Black residents than White residents. IMPLICATIONS: Hospice care offers many benefits, including reduced risk of in-hospital death, but Black nursing home residents are less likely to use hospice and may have different perceptions of need for hospice care compared with White residents. Future research and outreach efforts should focus on developing culturally sensitive, disease-focused end-of-life education and communication interventions that target residents, families, nursing home providers, and physicians.  相似文献   
53.

Background

Intracranial aneurysm (IA) is a disease of the vascular wall resulting in abnormal enlargement of the vessel lumen. It is a common pathology with a prevalence of 2%‐3% in the adult population. IAs are mostly small, quiescent and asymptomatic; yet, upon rupture, severe brain damage or even death is frequently encountered. In addition to clinical factors, hemodynamic forces, mainly wall shear stress (WSS), have been associated with the initiation of IAs and possibly with their risk of rupture. However, the mechanism by which WSS contributes to aneurysm growth and rupture is not completely understood.

Design

PubMed and Ovid MEDLINE databases were searched. In addition, key review articles were screened for relevant original publications.

Results

Current knowledge about the relation between WSS and IA has been obtained from both computational fluid dynamic studies in patients and experimental models of IA formation and growth. It is increasingly recognized that a high wall shear stress (gradient) participates to IA formation and that both low and high WSS can drive IA growth. Primary cilia (PC) play an important role as mechanosensors as patients with polycystic kidney disease, which is characterized by the absence or dysfunction of PC, have increased risk to develop IAs as well as increased risk of rupture.

Conclusion

Wall shear stress is a key player in IA initiation and progression. It is involved in vascular wall remodelling and inflammation, processes underlying aneurysm pathophysiology.  相似文献   
54.
The aim of this study was to assess the frequency and clinical characteristics of arrhythmogenic right ventricular cardiomyopathy (ARVC) in young victims of sudden cardiac death (SCD). From January 1999 to December 2000, postmortem studies were conducted in 38 cases of SCD (age < or =35 (27+/-7) years old, 26 male) from the Taegu-Kyungpook region of southeastern Korea. Cases of sudden infant death syndrome were excluded. The causes of SCD were ARVC in 42%, acute myocardial infarction in 11%, myocarditis in 11%, pulmonary embolism in 8%, hypertrophic cardiomyopathy in 5%, aortic rupture in 3%, aortic stenosis in 3%, and unknown in 18%. The mean age of the 16 ARVC victims was 27+/-5 years and 10 were male. None were competitive athletes, or had been suspected of having cardiovascular disease before death. SCD was not related to vigorous physical or competitive activity and occurred during sleep in 7 cases, during work in 4, during bathing in 2, while driving, praying and eating in 1 case each. ARVC is an important cause of SCD in young people in this area of Korea.  相似文献   
55.
ObjectiveTo evaluate the reliability of CT measurements of muscle quantity and quality using variable CT parameters.Materials and MethodsA phantom, simulating the L2–4 vertebral levels, was used for this study. CT images were repeatedly acquired with modulation of tube voltage, tube current, slice thickness, and the image reconstruction algorithm. Reference standard muscle compartments were obtained from the reference maps of the phantom. Cross-sectional area based on the Hounsfield unit (HU) thresholds of muscle and its components, and the mean density of the reference standard muscle compartment, were used to measure the muscle quantity and quality using different CT protocols. Signal-to-noise ratios (SNRs) were calculated in the images acquired with different settings.ResultsThe skeletal muscle area (threshold, −29 to 150 HU) was constant, regardless of the protocol, occupying at least 91.7% of the reference standard muscle compartment. Conversely, normal attenuation muscle area (30–150 HU) was not constant in the different protocols, varying between 59.7% and 81.7% of the reference standard muscle compartment. The mean density was lower than the target density stated by the manufacturer (45 HU) in all cases (range, 39.0–44.9 HU). The SNR decreased with low tube voltage, low tube current, and in sections with thin slices, whereas it increased when the iterative reconstruction algorithm was used.ConclusionMeasurement of muscle quantity using HU threshold was reliable, regardless of the CT protocol used. Conversely, the measurement of muscle quality using the mean density and narrow HU thresholds were inconsistent and inaccurate across different CT protocols. Therefore, further studies are warranted in future to determine the optimal CT protocols for reliable measurements of muscle quality.  相似文献   
56.
BackgroundThe association of age with coronary plaque dynamics is not well characterized by coronary computed tomography angiography (CCTA).MethodsFrom a multinational registry of patients who underwent serial CCTA, 1153 subjects (61 ± 5 years old, 61.1% male) were analyzed. Annualized volume changes of total, fibrous, fibrofatty, necrotic core, and dense calcification plaque components of the whole heart were compared by age quartile groups. Clinical events, a composite of all-cause death, acute coronary syndrome, and any revascularization after 30 days of the initial CCTA, were also analyzed. Random forest analysis was used to define the relative importance of age on plaque progression.ResultsWith a 3.3-years’ median interval between the two CCTA, the median annual volume changes of total plaque in each age quartile group was 7.8, 10.5, 10.8, and 12.1 mm3/year and for dense calcification, 2.5, 4.6, 5.4, and 7.1 mm3/year, both of which demonstrated a tendency to increase by age (p-for-trend = 0.001 and < 0.001, respectively). However, this tendency was not observed in any other plaque components. The annual volume changes of total plaque and dense calcification were also significantly different in the propensity score-matched lowest age quartile group versus the other age groups as was the composite clinical event (log-rank p = 0.003). In random forest analysis, age had comparable importance in the total plaque volume progression as other traditional factors.ConclusionsThe rate of whole-heart plaque progression and dense calcification increases depending on age. Age is a significant factor in plaque growth, the importance of which is comparable to other traditional risk factors.Clinical trial registrationURL: http://www.clinicaltrials.gov. Unique identifiers: NCT02803411.  相似文献   
57.

Purpose

The aim of this study was to find an optimal range of activated clotting time (ACT) during off-pump coronary artery bypass surgery (OPCAB) yielding ischemic protection without the risk of hemorrhagic complications in patients with recent exposure to dual antiplatelet therapy.

Materials and Methods

Three hundred and five patients who received aspirin and clopidogrel within 7 days of isolated multi-vessel OPCAB were retrospectively studied. Combined hemorrhagic and ischemic outcome was defined as the occurrence of 1 of the following: significant perioperative bleeding (>30% of estimated blood volume), transfusion of packed red blood cell (pRBC) ≥2 U, or myocardial infarction (MI). This was compared in relation to the tertile distribution of the time-weighted average ACT-212-291 sec (first tertile), 292-334 sec (second tertile), 335-485 sec (third tertile).

Results

The amount of perioperative blood loss was 937±313 mL, 1014±340 mL, and 1076±383 mL, respectively (p=0.022). Significantly more patients in the third tertile developed MI (4%, 4%, and 12%, respectively, p=0.034). The incidence of significant perioperative blood loss and transfusion of pRBC ≥2 U were lower in the first tertile than those of other tertiles without statistical significance. In the multivariate analysis, the first tertile was associated with a 52% risk reduction of combined hemorrhagic and ischemic outcomes (95% confidence interval: 0.25-0.92, p=0.027).

Conclusion

A lower degree of anticoagulation with a reduced initial heparin loading dose should be carefully considered for patients undergoing OPCAB who have recently been exposed to clopidogrel.  相似文献   
58.

Purpose

To investigate the ultrasonographic (US) features of anaplastic thyroid cancer (ATC) and the diagnostic performance of US-guided fine needle aspiration biopsy (FNAB) therein.

Materials and Methods

Eighteen cases of ATC diagnosed between January 2001 and May 2011 were included. FNAB was performed in all cases. Initial FNAB results were divided into three groups: 1) the cytological ATC group, cytological diagnosis of ATC; 2) the underestimated group, cytological diagnoses of malignancy other than ATC; and 3) the false negative group, cytological diagnoses of atypical, benign and non-diagnostic lesions. We retrospectively reviewed US findings and compared treatment modalities between each group.

Results

Among the 18 patients, there were nine in the initially cytological ATC group, four in the underestimated group and five in the false negative group. The most common US features of ATC were a solid (64.7%) and irregular shaped (88.2%) mass with lymph node involvement (76.4%). However, except for lymph node involvement (p=0.003), US findings for each group were not statistically different. The initial cytological diagnostic accuracy of ATC was 50% (9/18). Surgery was performed less in the ATC group (11%) and the false negative group (20%) than the underestimated group (75%).

Conclusion

The US features of ATC were not especially different from other types of aggressive thyroid cancer. A correct diagnosis of ATC by initial US-FNAB was made in 50% of the patients, which is significant in that therapeutic surgery can be undertaken in lower numbers if correctly diagnosed.  相似文献   
59.
Epstein–Barr virus-positive peripheral T cell lymphoma, not otherwise specified (EBV+ PTCL-NOS), in which virtually all neoplastic T cells harbor EBV, is a very rare disease with poor prognosis. To analyze the clinicopathologic characteristics and gene expression profile, we retrospectively collected six cases of EBV+ PTCL-NOS with no known primary immunodeficiency. The patients were 5 men and 1 woman, their age ranging from 48 years to 88 years (median 61.5 years). Lymphadenopathy was the most common presentation. Four patients had underlying disease, including HBV carrier, HCV infection, diabetes mellitus, and prostate cancer. All patients showed fatal clinical course in spite of chemotherapy. Histopathologically, monotonous infiltration of atypical lymphocytes of small to medium size was shown in four patients and medium to large tumor cells in two patients. Five patients showed CD4−/CD8+/bF-1+ phenotype with TIA-1 expression. In gene expression analysis using mRNA microarray, genes differentially expressed in EBV+ PTCL-NOS compared to normal reactive lymph nodes included 1515 genes (Mann–Whitney U-test p < 0.05, folder change ≥4 times). Enriched functional annotation terms by DAVID were mostly related to immune response, defense response, cell-to-cell signaling, and membrane signaling. Especially, the genes involved in B cell differentiation or activation were mostly down-regulated, and T cell activation was mostly suppressed by down-regulation of activation genes and up-regulation of regulatory genes. Genes associated with cytotoxic activity were mostly up-regulated. Based on its peculiar clinical, histopathologic, and gene expression findings in EBV+ PTCL-NOS, we suggest EBV+ PTCL-NOS as a distinct disease entity from PTCL-NOS. In this study, the finding that most significantly enriched the functional term was immune response, suggesting a specific relation between EBV infection and alteration of immune response in the patients with EBV+ PTCL-NOS.  相似文献   
60.
We aimed to determine the pathogenesis of gastric mixed adenoneuroendocrine carcinoma (MANEC) and pure neuroendocrine carcinoma (NEC), which is largely unknown. Targeted DNA sequencing was performed on 34 tumor samples from 21 patients – 13 adenocarcinoma (ADC)/NEC components from MANECs and eight pure NECs – and 21 matched non‐neoplastic gastric tissues. Mutational profiles of MANECs/NECs were compared with those of other tumors using public databases. The majority (64.1%; 59/92) of mutations in MANEC were shared by both ADC and NEC components. TP53 was the most commonly mutated gene in MANEC (69.2%, 9/13) and pure NEC (87.5%, 8/9). All TP53 mutations in MANEC were pathogenic mutations and were shared by both ADC and NEC components. A subset of TP53WT MANECs had a microsatellite‐unstable phenotype or amplifications in various oncogenes including ERBB2 and NMYC, and the only TP53WT pure NEC harbored MYC amplification. Compared to NEC in other organs, NECs arising from the stomach had unique features including less frequent RB1 mutations. Differentially altered genes of MANEC ADC components were significantly associated with receptor tyrosine kinase signaling pathways, while differentially altered genes of MANEC NEC components were significantly associated with the NOTCH signaling pathway. Our data provide evidence suggesting a possible clonal origin of ADC and NEC components of MANEC, and we found that gastric MANECs and pure NECs are distinct entities with unique mutational profiles and underlying protein networks. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.  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