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   2707篇
  免费   203篇
  国内免费   13篇
耳鼻咽喉   21篇
儿科学   91篇
妇产科学   43篇
基础医学   499篇
口腔科学   36篇
临床医学   369篇
内科学   542篇
皮肤病学   39篇
神经病学   272篇
特种医学   58篇
外科学   295篇
综合类   10篇
预防医学   261篇
眼科学   47篇
药学   169篇
中国医学   2篇
肿瘤学   169篇
  2023年   26篇
  2022年   16篇
  2021年   65篇
  2020年   62篇
  2019年   77篇
  2018年   80篇
  2017年   53篇
  2016年   80篇
  2015年   74篇
  2014年   85篇
  2013年   152篇
  2012年   213篇
  2011年   236篇
  2010年   107篇
  2009年   118篇
  2008年   166篇
  2007年   180篇
  2006年   162篇
  2005年   148篇
  2004年   152篇
  2003年   155篇
  2002年   152篇
  2001年   13篇
  2000年   15篇
  1999年   19篇
  1998年   29篇
  1997年   20篇
  1996年   11篇
  1995年   24篇
  1994年   11篇
  1993年   8篇
  1992年   8篇
  1989年   5篇
  1988年   9篇
  1987年   6篇
  1985年   6篇
  1984年   5篇
  1983年   6篇
  1982年   11篇
  1981年   7篇
  1980年   6篇
  1978年   10篇
  1975年   10篇
  1974年   7篇
  1938年   5篇
  1937年   7篇
  1935年   5篇
  1931年   7篇
  1928年   7篇
  1925年   4篇
排序方式: 共有2923条查询结果,搜索用时 19 毫秒
1.
2.
Objectives: The current study aims to investigate the association between subjective social status (SSS) and prospective cognitive functioning of older adults and their spouses, and to explore the potential mediating roles of health habits and physical activities in this association.

Method: Using the longitudinal data of 512 pairs of community-dwelling older couples aged 65–91 years (M = 72.2 ± 4.6), we tested the effects of SSS in cognitive functioning using an Actor-Partner Interdependence Model. SSS was measured by a self-anchoring social ladder, and cognitive functioning was measured by the Mini-Mental State Examination at baseline and 4-year follow-up. Socioeconomic status (i.e. education) was tested as a moderator, and physical activity (measured by the Physical Activity Scale for the Elderly) as well as health habits (i.e. tobacco and alcohol consumption) were included as potential mediators.

Results: A partner effect of SSS was found only in the low-education group, in which the wife's higher level of SSS in the community was associated with the husband's better cognitive functioning in the follow-up. A small proportion of this effect was found to be partially mediated by participation in housework, such that the wife's higher SSS was associated with the husband's increased housework activity, which was related to higher prospective cognitive functioning.

Conclusion: By examining the dyadic effects of SSS with a longitudinal design, our findings extended the understanding on how subjective social status influenced older couples’ cognitive health, and provided evidence-based insights for future studies on cognitive health in later life.  相似文献   

3.
This study aimed to evaluate changes in sleep during the COVID‐19 outbreak, and used data‐driven approaches to identify distinct profiles of changes in sleep‐related behaviours. Demographic, behavioural and psychological factors associated with sleep changes were also investigated. An online population survey assessing sleep and mental health was distributed between 3 April and 24 June 2020. Retrospective questions were used to estimate temporal changes from before to during the outbreak. In 5,525 Canadian respondents (67.1% females, 16–95 years old: Mean ± SD = 55.6 ± 16.3 years), wake‐up times were significantly delayed relative to pre‐outbreak estimates (p < .001,  = 0.04). Occurrences of clinically meaningful sleep difficulties significantly increased from 36.0% before the outbreak to 50.5% during the outbreak (all p < .001, g ≥ 0.27). Three subgroups with distinct profiles of changes in sleep behaviours were identified: “Reduced Time in Bed”, “Delayed Sleep” and “Extended Time in Bed”. The “Reduced Time in Bed” and “Delayed Sleep” subgroups had more adverse sleep outcomes and psychological changes during the outbreak. The emergence of new sleep difficulties was independently associated with female sex, chronic illnesses, being employed, family responsibilities, earlier wake‐up times, higher stress levels, as well as heavier alcohol use and television exposure. The heterogeneity of sleep changes in response to the pandemic highlights the need for tailored interventions to address sleep problems.  相似文献   
4.
5.
Increased expression of GLI1, the main Hedgehog signalling pathway effector, is related to unfavourable prognosis and progressive disease of certain breast cancer subtypes. We used conditional transgenic mice induced to overexpress GLI1 in the mammary epithelium either alone or in combination with deletion of one Trp53 allele to address the role of elevated GLI1 expression in breast tumour initiation and progression. Induced GLI1 expression facilitates mammary gland tumour formation and this was further increased upon heterozygous deletion of Trp53. The GLI1-induced primary tumours were of different murine molecular subtypes, including Normal-likeEx, Class8Ex, Claudin-LowEx and Erbb2-likeEx. The gene expression profiles of some of the tumours correlated well with the PAM50 subtypes for human breast cancer. Whole-exome sequencing revealed somatic mutation profiles with only little overlap between the primary tumours. Orthotopically serially transplanted GLI1-induced tumours maintained the main morphological characteristics of the primary tumours for ≥10 generations. Independent of Trp53 status and molecular subtype, the serially transplanted GLI1-induced tumours were able to grow both in the absence of transgenic GLI1 expression and in the presence of the GLI1 inhibitor GANT61. These data suggest that elevated GLI1 expression has a determinant role in tumour initiation; however, additional genetic events are required for tumour progression.  相似文献   
6.
Neuroplasticity has classically been understood to arise through changes in synaptic strength or synaptic connectivity. A newly discovered form of neuroplasticity, neurotransmitter switching, involves changes in neurotransmitter identity. Chronic exposure to different photoperiods alters the number of dopamine (tyrosine hydroxylase, TH+) and somatostatin (SST+) neurons in the paraventricular nucleus (PaVN) of the hypothalamus of adult rats and results in discrete behavioral changes. Here, we investigate whether photoperiod-induced neurotransmitter switching persists during aging and whether epigenetic mechanisms of histone acetylation and DNA methylation may contribute to this neurotransmitter plasticity. We show that this plasticity in rats is robust at 1 and at 3 months but reduced in TH+ neurons at 12 months and completely abolished in both TH+ and SST+ neurons by 18 months. De novo expression of DNMT3a catalyzing DNA methylation and anti-AcetylH3 assessing histone 3 acetylation were observed following short-day photoperiod exposure in both TH+ and SST+ neurons at 1 and 3 months while an overall increase in DNMT3a in SST+ neurons paralleled neuroplasticity reduction at 12 and 18 months. Histone acetylation increased in TH+ neurons and decreased in SST+ neurons following short-day exposure at 3 months while the total number of anti-AcetylH3+ PaVN neurons remained constant. Reciprocal histone acetylation in TH+ and SST+ neurons indicates the importance of studying epigenetic regulation at the circuit level for identified cell phenotypes. The findings may be useful for developing approaches for noninvasive treatment of disorders characterized by neurotransmitter dysfunction.  相似文献   
7.
8.
9.
10.
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   
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