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   427362篇
  免费   40083篇
  国内免费   26754篇
耳鼻咽喉   3429篇
儿科学   5499篇
妇产科学   5198篇
基础医学   48977篇
口腔科学   7486篇
临床医学   57736篇
内科学   60595篇
皮肤病学   4952篇
神经病学   21979篇
特种医学   15362篇
外国民族医学   230篇
外科学   40412篇
综合类   73971篇
现状与发展   87篇
一般理论   36篇
预防医学   30576篇
眼科学   12060篇
药学   45100篇
  509篇
中国医学   25759篇
肿瘤学   34246篇
  2024年   4730篇
  2023年   7439篇
  2022年   15265篇
  2021年   19230篇
  2020年   15570篇
  2019年   12442篇
  2018年   13159篇
  2017年   12499篇
  2016年   11626篇
  2015年   17683篇
  2014年   22060篇
  2013年   20416篇
  2012年   30202篇
  2011年   33633篇
  2010年   22570篇
  2009年   18560篇
  2008年   22937篇
  2007年   22777篇
  2006年   21721篇
  2005年   20552篇
  2004年   13918篇
  2003年   13437篇
  2002年   11171篇
  2001年   12614篇
  2000年   12297篇
  1999年   11822篇
  1998年   6459篇
  1997年   5954篇
  1996年   4530篇
  1995年   4179篇
  1994年   3555篇
  1993年   2418篇
  1992年   4177篇
  1991年   3647篇
  1990年   3173篇
  1989年   2870篇
  1988年   2439篇
  1987年   2239篇
  1986年   1871篇
  1985年   1499篇
  1984年   901篇
  1983年   694篇
  1982年   370篇
  1981年   332篇
  1980年   249篇
  1979年   403篇
  1978年   150篇
  1977年   114篇
  1974年   117篇
  1973年   132篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Twins with Duchenne muscular dystrophy (DMD) have been widely studied. We report the first rare case of monozygotic triplets with DMD who shared consistent phenotypes, including delayed motor and language milestones, muscle wasting and weakness, joint contracture, and lumbar lordosis. Muscle magnetic resonance imaging and biopsy revealed the similar muscle injury characteristics and dystrophin absence. Short tandem repeat analysis confirmed monozygosity. A de novo mutation (exon 49–52 deletion) was found in the triplets but not in their mother. Treatment included prednisone, idebenone, and rehabilitation management. At the 2-year follow-up, motor function had deteriorated, and muscle fatty infiltration was more extensive and severe. Our case offers a unique opportunity for genetic and therapeutic research. Furthermore, it highlights the critical role of genetic factors in DMD phenotypes and provides a potential choice for treatment observations.  相似文献   
12.
13.

Background

Vitiligo is an autoimmune disease with varying pathological features. Activation of the CCL20-CCR6 axis plays an important role in chronic inflammatory diseases. However, whether CCL20-CCR6 and Th1/17 cells are indicative of active vitiligo is unclear.

Objective

To investigate the potential role of CCL20 and the involvement of Th1/17 and Tc1/17 cells in the mechanism in vitiligo.

Methods

One hundred patients with vitiligo, and 20 healthy controls were included. The serum and blister fluid IL-17, IFN-γ, CCL20, and CXCL10 were studied using enzyme-linked immunosorbent assays. The numbers of Th1/17 cells and Tc1/17 cells in circulation were quantified using flow cytometry. CCR6 mRNA in peripheral blood mononuclear cells (PBMCs) was analyzed by real-time polymerase chain reaction and the protein level was confirmed by western blotting. CCR6 and CCL20 expression in lesions was analyzed by immunohistochemistry.

Results

The serum CCL20 level was significantly elevated in patients with vitiligo. The level of serum CCL20 was higher in active than in the stable stage, which correlated positively with the Vitiligo European Task Force spreading score and the Vitiligo Area Scoring Index score. Patients with active vitiligo had elevated numbers of circulating Th1/17 cells and Tc1/17 cells, and upregulated expression of CCR6 in PBMCs and lesions. After effective treatment, the level of CCL20 in sera and blister fluid was significantly decreased, as were the numbers of circulating Th1/17 cells and Tc1/17 cells.

Conclusion

CCL20 might be a vital biomarker of active vitiligo, and circulating Th1/17 and Tc1/17 cells are involved in the pathogenesis of vitiligo.  相似文献   
14.
Objective: The main pathological change of Parkinson’s disease (PD) is progressive degeneration and necrosis of dopaminergic neurons in the midbrain, forming a Lewy body in many of the remaining neurons. Studies have found that in transgenic Drosophila, mutations in the PTEN-inducible kinase 1 (PINK1) gene may cause indirect flight muscle defects in Drosophila, and mitochondrial structural dysfunction as well.

Methods: In this study, Wnt4 gene overexpression and knockdown were performed in PINK1 mutant PD transgenic Drosophila, and the protective effect of Wnt4 gene on PD transgenic Drosophila and its possible mechanism were explored. The Wnt4 gene was screened in the previous experiment; And by using the PD transgenic Drosophila model of the MHC-Gal4/UAS system, the PINK1 gene could be specifically activated in the Drosophila muscle tissue.

Results: In PINK1 mutation transgenic fruit flies, the Wnt4 gene to study its implication on PD transgenic fruit flies’ wing normality and flight ability. We found that overexpression of Wnt4 gene significantly reduced abnormality rate of PD transgenic Drosophila and improved its flight ability, and then, increased ATP concentration, enhanced mitochondrial membrane potential and normalized mitochondrial morphology were found. All of these findings suggested Wnt4 gene may have a protective effect on PD transgenic fruit flies. Furthermore, in Wnt4 gene overexpression PD transgenic Drosophila, down-regulation autophagy and apoptosis-related proteins Ref(2)P, Pro-Caspase3, and up-regulation of Beclin1, Atg8a, Bcl2 protein were confirmed by Western Blotting.

Conclusion: The results imply that the restoring of mitochondrial function though Wnt4 gene overexpression in the PINK1 mutant transgenic Drosophila may be related to autophagy and/or apoptosis.  相似文献   

15.
16.

Objective

To assess the impact of focality and location of positive surgical margins (PSM) on long-term outcomes after radical prostatectomy (RP) for prostate cancer (PCa), including biochemical recurrence (BCR), metastasis and overall mortality.

Patients and Methods

From a total of 2796 cases of RP between 1993 and 2007 in our single hospital, 476 cases with PSMs were identified and included in this study. PSM location was categorized into apex, peripheral, and bladder neck. Survival was estimated using the Kaplan-Meier method. Cox proportional hazard regression models were used to analyze the impact of PSM focality and location status on oncologic survival.

Results

Of these 476 cases with PSMs, 335 (70.4%) cases were with single focal (sF) PSMs and 141 (29.6%) cases were with multifocal (mF) PSMs. Furthermore, 406 (85.3%) cases were found to have single location (sL) PSMs, and 70 (14.7%) cases were with multilocation (mL) PSMs. The median follow-up was 12.9 years. mF-PSMs and mL-PSMs showed significant impact on increased BCR risk on univariate analysis, and mL-PSMs remained significant on multivariate analysis (P = .048). Furthermore, the combination of multifocality and multilocation showed added prognostic value on predicting BCR-free survival, but not on metastasis-free survival or overall survival.

Conclusion

The presence of mF-PSMs and mL-PSMs, and especially the combination of both, demonstrated significant impact on BCR prognosis. Patients with apex sLsF-PSMs were less likely to have BCR when compared with all those with non-apex sLsF-PSMs. These results should be considered when evaluating patients for adjuvant therapy.  相似文献   
17.
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   
18.
19.
In the previous research, we found that anticancer agent LS-1-2F could cause the vacuolation of tumor cells. Herein we investigated the effect of compound LS-1-2F on the endocytosis of macromolecules, including fluorescence quantum dots, human serum albumin, single-stranded RNA, and monoclonal antibody, into tumor cells. We found that LS-1-2F could accelerate the endocytosis of these large molecules by laser confocal microscope and flow cytometry. The effect of LS-1-2F on the improvement of the internalization efficiency of Herceptin biosimilar was particularly significant. Promoting endocytosis will help increase the efficiency of liquid-phase drug uptake in drug-resistant cancer cells and could potentially facilitate the use of drugs in nanoparticle delivery vehicles.  相似文献   
20.
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