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   4809篇
  免费   238篇
  国内免费   18篇
耳鼻咽喉   14篇
儿科学   53篇
妇产科学   65篇
基础医学   516篇
口腔科学   84篇
临床医学   589篇
内科学   1457篇
皮肤病学   53篇
神经病学   577篇
特种医学   90篇
外科学   421篇
综合类   13篇
预防医学   460篇
眼科学   33篇
药学   358篇
中国医学   3篇
肿瘤学   279篇
  2024年   5篇
  2023年   25篇
  2022年   85篇
  2021年   179篇
  2020年   92篇
  2019年   157篇
  2018年   198篇
  2017年   117篇
  2016年   118篇
  2015年   126篇
  2014年   217篇
  2013年   261篇
  2012年   413篇
  2011年   429篇
  2010年   262篇
  2009年   211篇
  2008年   322篇
  2007年   301篇
  2006年   311篇
  2005年   284篇
  2004年   258篇
  2003年   225篇
  2002年   201篇
  2001年   24篇
  2000年   15篇
  1999年   28篇
  1998年   38篇
  1997年   32篇
  1996年   22篇
  1995年   27篇
  1994年   18篇
  1993年   7篇
  1992年   4篇
  1991年   8篇
  1990年   8篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1981年   4篇
  1980年   1篇
  1979年   1篇
  1971年   1篇
  1964年   1篇
  1962年   2篇
  1961年   1篇
  1960年   3篇
  1933年   1篇
  1929年   1篇
排序方式: 共有5065条查询结果,搜索用时 15 毫秒
991.
BackgroundHistological diagnosis of pulmonary nodules requires surgical resection on many occasions. There are multiple localization strategies each with their own benefits and complications. The objective of this study is to compare preoperative lung nodule localization with hookwire and radiotracer injection (radioguided occult lesion localization, ROLL). To compare results, complications, and volume of the sample resected with both techniques.MethodsPatients undergoing resection of pulmonary nodules with video-assisted thoracoscopy and pre-surgical localization with hookwire or ROLL were studied. Eighty-eight pulmonary nodules were resected in 76 patients: 52 with a hook wire and 36 with a radiotracer. The localization rate, the shortest distance between the nodule and the pleura, the intrapulmonary distance of the locator, the complications, the volume of the resection piece, and the histological result were all assessed. In addition, the factors that influence the volume of the surgical piece were analyzed.ResultsAll the nodules were resected with both techniques. The intrapulmonary path of the locator is longer for the ROLL group (23.91 vs. 16.28 mm; P=0.04), with no differences in the distance from the nodule to the pleura. The rate of pneumothorax was significantly higher after the placement of a hook wire (69.2% vs. 24.2%; P<0.0001), while there were no differences in the presence of hemorrhage. The volume of the pieces resected using ROLL was more minor than with hookwire, although not statistically significant (20.19 vs. 34.26 cc; P=0.07).ConclusionsPreoperative localization with the ROLL technique is safer than the placement of hookwire. In addition, the ROLL technique shows a tendency to obtain a smaller volume of resected tissue since the marking is not affected by the intrapulmonary route used during marker placement. ROLL technique allows to locate lung nodules with fewer complications than hookwire and probably gets smaller resection samples.  相似文献   
992.
Burnishing is a plastic deformation process that reduces roughness while increasing hardness by introducing compressive residual stresses near the surface zone. These improvements will depend mainly on two fundamental variables: the applied load and the friction derived from the tool–surface interaction. Nevertheless, microstructural differences in the materials have not yet been considered within this interaction. This leads to a generalization of the process that can result in the failure of industrial components. Therefore, the aim of this work is to study the microstructural influence of the ball-burnishing process from a tribological perspective. Thus, martensitic and austenitic stainless steels were evaluated in terms of friction and surface integrity. The results show that parameterizing the process according to the tool–surface interaction is critical since improvements depend on friction as a function of the availability of plastic deformation of the crystallographic structures.  相似文献   
993.
Understanding the laminar brain structure is of great help in further developing our knowledge of the functions of the brain. However, since most layer segmentation methods are invasive, it is difficult to apply them to the human brain in vivo. To systematically explore the human brain''s laminar structure noninvasively, the K‐means clustering algorithm was used to automatically segment the left hemisphere into two layers, the superficial and deep layers, using a 7 Tesla (T) diffusion magnetic resonance imaging (dMRI)open dataset. The obtained layer thickness was then compared with the layer thickness of the BigBrain reference dataset, which segmented the neocortex into six layers based on the von Economo atlas. The results show a significant correlation not only between our automatically segmented superficial layer thickness and the thickness of layers 1–3 from the reference histological data, but also between our automatically segmented deep layer thickness and the thickness of layers 4–6 from the reference histological data. Second, we constructed the laminar connections between two pairs of unidirectional connected regions, which is consistent with prior research. Finally, we conducted the laminar analysis of the working memory, which was challenging to do in the past, and explained the conclusions of the functional analysis. Our work successfully demonstrates that it is possible to segment the human cortex noninvasively into layers using dMRI data and further explores the mechanisms of the human brain.  相似文献   
994.
Karyotypic analysis at time of diagnosis has an important value in determining initial response to treatment, remission duration and overall survival (OS) in acute myeloid leukemia (AML). Less is known about its value before allogeneic hematopoietic cell transplantation (allo‐HCT) in patients transplanted with active disease, either relapsed or primary refractory (Rel‐Ref) AML. We explored the impact of cytogenetic risk (stratification according to MRC‐UK) in 2089 patients with either Ref (n = 972) or Rel AML (n = 1117) transplanted during the period 2000‐2017. Overall, 154 patients had a favorable risk, 1283 had an intermediate risk and 652 had an adverse cytogenetic risk. Median follow‐up was 49 months. Compared to the favorable risk group, intermediate and adverse risk patients were associated with worse leukemia‐free survival and OS and also with a higher incidence of relapse. In a subgroup analysis of patients in the intermediate risk group harboring Fms‐like tyrosine kinase 3‐internal tandem duplication (FLT3‐ITD), this remained an important prognostic factor, being associated with worse outcomes. When analyzing patients according to the intensity of the conditioning regimen, no differences were observed for the main transplant outcomes. In conclusion, in patients diagnosed with AML and transplanted with active disease, karyotype remains an important prognostic factor, allowing splitting patients into different risk groups according to their cytogenetics. Similarly, FLT3‐ITD mutation also remains a negative prognostic factor in this population.  相似文献   
995.
ObjectiveThe aim of this study was to investigate the relation between health-related physical fitness and weight status in 13- to 15-year-old Latino adolescents.MethodThe final sample consisted of 73,561 adolescents aged 13–15 years (35,175 girls) from Chile (n = 48,771) and Colombia (n = 24,790). Cardiorespiratory and musculoskeletal fitness were measured using 20-m shuttle run (relative peak oxygen uptake – VO2peak) and standing broad jump test (lower body explosive strength), respectively. The International Obesity Task Force definition was used to define weight status (i.e., underweight, normal weight, overweight, and obese).ResultsThe present study found an inverted J-shape relationship between body mass index, cardiorespiratory fitness, and musculoskeletal fitness in both genders and all age groups (p < 0.01). Results also suggest that underweight adolescents, and not just overweight and obese adolescents, have lower odds of having a healthy cardiorespiratory fitness (based on new international criterion-referenced standards) profile when compared with their normal weight peers, except in girls aged 14 (p = 0.268) and 15 years (p = 0.280).ConclusionsThe present results indicate low cardiorespiratory fitness and musculoskeletal fitness levels in underweight, overweight, and obese adolescents when compared with their normal weight peers. The findings appear to suggest that exercise programs should to decrease fat mass in overweight/obese adolescents and increase muscle mass in underweight adolescents.  相似文献   
996.
997.
998.
999.
Mosquitoes are the main vectors of pathogens affecting wild animals, livestock and humans. Here, we used molecular tools to assess the local circulation of filarial parasites in mosquitoes collected during 2013 from natural, rural and urban habitats from southern Spain. We screened parasites in 22,791 female mosquitoes of the genera Aedes, Culex and Culiseta. Filarial worms were only detected in two mosquito pools. An Ae. caspius pool was positive for Setaria equina and an unidentified worm related to Onchocerca was detected in a Cx. pipiens pool. None of the mosquito pools were positive for Dirofilaria. These results underlay the role of Ae. caspius in the transmission of Setaria parasites among livestock and/or wildlife to humans in southern Spain.  相似文献   
1000.

Background

Perceived social support has been found to be associated with depression, subjective well-being and psychological health in cross-sectional studies in people with physical disabilities. No longitudinal studies have been conducted to examine these associations over time using a comprehensive measure of social support.

Objective/hypothesis

We hypothesized that: (1) the amount of perceived social support would be similar across individuals with different diagnoses often associated with disability (i.e., multiple sclerosis [MS], spinal cord injury [SCI], muscular dystrophy [MD]) but (2) lower among men, relative to women, and (3) changes over time in perceived social support would be negatively associated with changes in depressive symptoms across diagnostic groups.

Methods

A survey-based six-year longitudinal study. Depressive symptoms were measured with the PROMIS Depression scale. General (Total Scale), Friend, Family and Significant Other social support were measured with the Multi-dimensional Scale of Perceived Social Support (MSPSS).

Results

The findings indicated no significant differences in any of the perceived social support scales as a function of diagnosis or sex. However, over the course of six years, those reporting increases in social support reported decreases in depressive symptoms, while those reporting decreases in social support reported increases in depressive symptoms.

Conclusions

Changes in perceived social support are inversely related with the changes in depressive symptoms in adults with MS, SCI, and MD. Social support would be a reasonable treatment target in interventions seeking to improve psychological wellbeing in individuals with conditions that are often associated with disabilities.  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