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   4277篇
  免费   229篇
  国内免费   13篇
耳鼻咽喉   87篇
儿科学   119篇
妇产科学   144篇
基础医学   582篇
口腔科学   225篇
临床医学   363篇
内科学   712篇
皮肤病学   78篇
神经病学   403篇
特种医学   176篇
外科学   594篇
综合类   11篇
一般理论   1篇
预防医学   323篇
眼科学   123篇
药学   250篇
中国医学   4篇
肿瘤学   324篇
  2023年   36篇
  2022年   56篇
  2021年   108篇
  2020年   78篇
  2019年   94篇
  2018年   114篇
  2017年   63篇
  2016年   125篇
  2015年   107篇
  2014年   143篇
  2013年   210篇
  2012年   279篇
  2011年   269篇
  2010年   158篇
  2009年   149篇
  2008年   300篇
  2007年   276篇
  2006年   304篇
  2005年   250篇
  2004年   230篇
  2003年   232篇
  2002年   212篇
  2001年   39篇
  2000年   28篇
  1999年   44篇
  1998年   60篇
  1997年   35篇
  1996年   30篇
  1995年   36篇
  1994年   34篇
  1993年   39篇
  1992年   25篇
  1991年   21篇
  1990年   19篇
  1989年   28篇
  1988年   22篇
  1987年   21篇
  1986年   22篇
  1985年   22篇
  1984年   24篇
  1983年   23篇
  1982年   20篇
  1981年   17篇
  1980年   13篇
  1979年   24篇
  1978年   17篇
  1977年   8篇
  1976年   13篇
  1974年   11篇
  1972年   8篇
排序方式: 共有4519条查询结果,搜索用时 15 毫秒
41.

Purpose

With increasing resistance of microorganisms to antibiotics, photodynamic inactivation (PDI) may also be a potential therapeutic option in infectious keratitis. As part of the inflammatory response in infectious keratitis, keratocytes produce various interleukins. The purpose of this study was to evaluate the potential anti-inflammatory effect of PDI, analyzing interleukin-1 alpha (IL-1α), interleukine-1 beta (IL-1β), interleukin-6 (IL-6), and interleukin-8 (IL-8) secretion of human keratocytes following PDI, in vitro.

Methods

Primary human keratocytes were isolated by digestion in collagenase A (1.0 mg/ml) from human corneal buttons, and cultured in DMEM/Ham’s F12 medium supplemented with 10 % FCS. Keratocyte cell cultures underwent illumination using red (670 nm) light for 13 min following exposure to 100 nM concentration of the photosensitizer chlorin e6 (Ce6) in the culture medium. Five and 24 hours after PDI, secretion of IL-1α, IL-1β, IL-6, and IL-8 was measured by enzyme-linked immunoabsorbent assay (ELISA).

Results

The secretion of IL-1α was under the measurement limit in treated and untreated cell cultures 5 and 24 h after PDI. Compared to untreated controls, IL-6 and IL-8 secretion of keratocytes decreased (p?<?0.05 and 0.0001) significantly 5 hours after PDI, whereas IL-1β secretion remained unchanged. Twenty-four hours after PDI, secretion of IL-1β, IL-6, and IL-8 did not differ significantly from untreated controls.

Conclusions

In the short term, PDI does not have an impact on IL-1α and IL-1β secretion of keratocytes, in vitro. Photodynamic inactivation inhibits IL-6 and IL-8 secretion of keratocytes transiently (5 h), which normalizes 24 h following treatment. Through the short-term impact of chlorine e6-PDI on IL-6 and IL-8 secretion, PDI may inhibit the inflammatory cascade in at least keratocyte cultures.  相似文献   
42.
Primary central nervous system lymphoma (PCNSL) is an aggressive brain disease where lymphocytes invade along perivascular spaces of arteries and veins. The invasion markedly changes (peri)vascular structures but its effect on physiological brain pulsations has not been previously studied. Using physiological magnetic resonance encephalography (MREGBOLD) scanning, this study aims to quantify the extent to which (peri)vascular PCNSL involvement alters the stability of physiological brain pulsations mediated by cerebral vasculature. Clinical implications and relevance were explored. In this study, 21 PCNSL patients (median 67y; 38% females) and 30 healthy age‐matched controls (median 63y; 73% females) were scanned for MREGBOLD signal during 2018–2021. Motion effects were removed. Voxel‐by‐voxel Coefficient of Variation (CV) maps of MREGBOLD signal was calculated to examine the stability of physiological brain pulsations. Group‐level differences in CV were examined using nonparametric covariate‐adjusted tests. Subject‐level CV alterations were examined against control population Z‐score maps wherein clusters of increased CV values were detected. Spatial distributions of clusters and findings from routine clinical neuroimaging were compared [contrast‐enhanced, diffusion‐weighted, fluid‐attenuated inversion recovery (FLAIR) data]. Whole‐brain mean CV was linked to short‐term mortality with 100% sensitivity and 100% specificity, as all deceased patients revealed higher values (n = 5, median 0.055) than surviving patients (n = 16, median 0.028) (p < .0001). After adjusting for medication, head motion, and age, patients revealed higher CV values (group median 0.035) than healthy controls (group median 0.024) around arterial territories (p ≤ .001). Abnormal clusters (median 1.10 × 105mm3) extended spatially beyond FLAIR lesions (median 0.62 × 105mm3) with differences in volumes (p = .0055).  相似文献   
43.
OBJECTIVE: To evaluate neurodevelopmental status of children treated with intrauterine red blood cell and platelet transfusion for fetal hydrops caused by parvovirus B19. METHODS: Maternal and neonatal records of all intrauterine transfusions for congenital parvovirus B19 infection in our center between 1997 and 2005 were reviewed. Congenital B19 virus infection was confirmed by the presence of parvovirus B19-specific immunoglobulin M or parvovirus B19 DNA in fetal blood samples. All children underwent a general pediatric and neurological examination. Primary outcome measure was neurodevelopmental status (developmental index by Bayley Scales of Infant Development or Snijders-Oomen test). Secondary outcome measure was general health status of surviving children. RESULTS: A total of 25 intrauterine transfusions were performed in 24 hydropic fetuses. Median fetal hemoglobin concentration, platelet count, and blood pH before intrauterine transfusions were 4.5 g/dL (range 2.4-11.4 g/dL), 79x10(9)/L (range 37-238x10(9)/L) and 7.36 (range 7.31-7.51), respectively. Sixteen survivors aged 6 months to 8 years were included in the follow-up study. Eleven children (68%) were normal, and 5 children (32%) demonstrated a delayed psychomotor development with an suboptimal neurological examination (mild delay n=3, severe delay n=2). Neurodevelopmental status did not correlate with pre-intrauterine transfusion hemoglobin, platelet, or blood pH values. Growth and general health status were normal in all. Two children had minor congenital defects. CONCLUSION: Neurodevelopmental status was abnormal in 5 of 16 survivors and was not related to the severity of fetal anemia and acidemia. We hypothesize that fetal parvovirus B19 infection may induce central nervous system damage. LEVEL OF EVIDENCE: III.  相似文献   
44.

Objective

To verify whether a multidomain intervention lowers the risk of developing new chronic diseases in older adults.

Methods

Multicenter, double-blind randomized controlled trial started in October 2009, with 2-year follow-up. A total of 1260 people aged 60 to 77?years were enrolled in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER). Participants were randomly assigned in a 1:1 ratio to a 2-year multidomain intervention (n?=?631) (nutritional guidance, exercise, cognitive training, and management of metabolic and vascular risk factors) or a control group (n?=?629) (general health advice). Data on most common chronic diseases were collected by a physician at baseline and 2?years later.

Results

At 2-year follow-up, the average number of new chronic diseases was 0.47 [standard deviation (SD) 0.7] in the intervention group and 0.58 (SD 0.8) in the control group (P?<?.01). The incidence rate per 100 person-years for developing 1+?new disease(s) was 17.4 [95% confidence interval (CI)?=?15.1-20.1] in the intervention group and 20.5 (95% CI?=?18.0-23.4) in the control group; for developing 2+?new diseases, 4.9 (95% CI?=?3.7-6.4) and 6.1 (95% CI?=?4.8-7.8); and for 3+?new diseases, 0.7 (95% CI?=?0.4-1.5) and 1.8 (95% CI?=?1.1-2.8), respectively. After adjustment for age, sex, education, current smoking, alcohol intake, and the number of chronic diseases at baseline, the intervention group had a hazard ratio ranging from 0.80 (0.66-0.98) for developing 1+?new chronic disease(s) to 0.38 (0.16-0.88) for developing 3+?new chronic diseases compared to the control group.

Conclusions

Findings from this randomized controlled trial suggest that a multidomain intervention could reduce the risk of developing new chronic diseases in older people.  相似文献   
45.
46.
Patients with mild cognitive impairment (MCI) represent a risk population for progressing to dementia of the Alzheimer type (DAT). However, clinical criteria do not ensure reliable individual prognosis in these patients. The objective of this longitudinal, prospective study was to examine the value of (18)F-FDG PET of cerebral glucose metabolism and of genetic susceptibility, as defined by an APOEepsilon4-positive genotype, with regard to the early diagnosis of DAT in patients with MCI. METHODS: In 30 patients with the diagnosis of MCI (16 female, 14 male; age, 70 +/- 8 y), baseline and follow-up examinations (mean observation period, 16 mo) were performed. In all patients, the APOE genotype was assessed and cerebral glucose metabolism was evaluated at baseline using cranial (18)F-FDG PET. Individual PET data were screened for findings suggestive of Alzheimer's disease (AD), with the help of an automated computer program. After stereotactical normalization of the PET images, this program performs an observer-independent statistical comparison with an age-matched reference database (n = 22). RESULTS: In 43% of all MCI subjects, a PET scan suggestive of AD pathology according to our predefined criteria was observed at baseline (PET+); 57% of all MCI patients were carriers of the APOE epsilon4 allele (e4+). In 40% of all patients, progression of symptoms within the observation period justified the clinical diagnosis of probable DAT at the time of follow-up reevaluation. Statistical evaluation revealed the best results for PET with regard to early diagnosis of DAT in MCI patients (sensitivity, 92%; specificity, 89%). Classification according to the APOE genotype was significantly less successful (sensitivity, 75%; specificity, 56%). However, a combination of both diagnostic tests allowed early diagnosis with either very high specificity (PET+ AND e4+: sensitivity, 67%; specificity, 100%) or very high sensitivity (PET+ OR e4+: sensitivity, 100%; specificity, 44%). CONCLUSION: (18)F-FDG PET of cerebral glucose metabolism is a valuable diagnostic tool for the prediction of clinical outcome in individual MCI patients. Results are superior to the exclusive assessment of the APOE genotype. A combination of both functional imaging and genotyping may allow an early high-risk or low-risk stratification of patients with either very high sensitivity or very high specificity. This may be valuable, for example, for patient selection in scientific studies.  相似文献   
47.
High levels of cytokines are risk factors for type 2 diabetes. Therefore, we investigated whether the promoter polymorphisms of the tumor necrosis factor-alpha (TNF-alpha; G-308A) and interleukin 6 (IL-6; C-174G) genes predict the conversion from impaired glucose tolerance (IGT) to type 2 diabetes in the Finnish Diabetes Prevention Study. Altogether, 490 overweight subjects with IGT whose DNA was available were randomly divided into one of the two treatment assignments: the control group and the intensive, individualized diet and exercise intervention group. The -308A allele of the TNF-alpha gene was associated with an approximate twofold higher risk for type 2 diabetes compared with the G-308G genotype (odds ratio 1.80, 95% CI 1.05-3.09; P = 0.034). Subjects with both the A allele of the TNF-alpha gene and the C-174C genotype of the IL-6 gene had a 2.2-fold (CI 1.02-4.85, P = 0.045) higher risk of developing type 2 diabetes than subjects without the risk genotypes. We conclude that the -308A allele of the promoter polymorphism (G-308A) of the TNF-alpha gene is a predictor for the conversion from IGT to type 2 diabetes. Furthermore, this polymorphism seems to have a gene-gene interaction with the C-174C genotype of the IL-6 gene.  相似文献   
48.
49.
The General Health Questionnaire (GHQ-12) is a popular measure of psychological distress. Despite its widespread use, an ongoing controversy pertains to its internal structure. Although the GHQ-12 was originally constructed to capture a unitary construct, empirical studies identified different factor structures. Therefore, this study examined the dimensionality of the GHQ-12 in two independent meta-analyses. The first meta-analysis used summary data published in 38 primary studies (total N?=?76,473). Meta-analytic exploratory factor analyses identified two factors formed by negatively and positively worded items. The second meta-analysis included individual responses of 410,640 participants from 84 independent samples. Meta-analytic confirmatory factor analyses corroborated the two-dimensional structure of the GHQ-12. However, bifactor modelling showed that most of the variance was explained by a general factor. Therefore, subscale scores reflected rather limited unique variance. Overall, the two meta-analyses demonstrated that the GHQ-12 is essentially unidimensional. It is not recommended to use and interpret subscale scores because they primarily reflect general mental health rather than distinct constructs.  相似文献   
50.
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