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   9160篇
  免费   555篇
  国内免费   42篇
耳鼻咽喉   88篇
儿科学   209篇
妇产科学   250篇
基础医学   1283篇
口腔科学   197篇
临床医学   949篇
内科学   2163篇
皮肤病学   89篇
神经病学   805篇
特种医学   293篇
外科学   1100篇
综合类   112篇
一般理论   13篇
预防医学   717篇
眼科学   181篇
药学   702篇
中国医学   5篇
肿瘤学   601篇
  2023年   54篇
  2022年   82篇
  2021年   169篇
  2020年   136篇
  2019年   156篇
  2018年   178篇
  2017年   137篇
  2016年   118篇
  2015年   212篇
  2014年   263篇
  2013年   424篇
  2012年   660篇
  2011年   674篇
  2010年   349篇
  2009年   310篇
  2008年   576篇
  2007年   648篇
  2006年   636篇
  2005年   605篇
  2004年   586篇
  2003年   527篇
  2002年   567篇
  2001年   97篇
  2000年   90篇
  1999年   120篇
  1998年   111篇
  1997年   101篇
  1996年   91篇
  1995年   92篇
  1994年   69篇
  1993年   67篇
  1992年   73篇
  1991年   75篇
  1990年   64篇
  1989年   47篇
  1988年   45篇
  1987年   37篇
  1986年   43篇
  1985年   37篇
  1984年   39篇
  1983年   28篇
  1982年   57篇
  1981年   29篇
  1980年   26篇
  1979年   28篇
  1978年   25篇
  1977年   31篇
  1976年   15篇
  1975年   25篇
  1973年   21篇
排序方式: 共有9757条查询结果,搜索用时 15 毫秒
101.
Abeta is the major component of amyloid plaques characterizing Alzheimer's disease (AD). Abeta accumulation can be affected by numerous factors including increased rates of production and/or impaired clearance. Insulin-degrading enzyme (IDE) has been implicated as a candidate enzyme responsible for the degradation and clearance of Abeta in the brain. We have previously shown that AD patients exhibit abnormalities in insulin metabolism that are associated with apoliprotein E (APOE) status. The possible association of IDE with AD, as well as the link between APOE status and insulin metabolism, led us to examine the expression of IDE in AD. We report that hippocampal IDE protein is reduced by approximately 50% in epsilon4+ AD patients compared to epsilon4- patients and controls. The allele-specific decrease of IDE in epsilon4+ AD patients is not associated with neuronal loss since neuron-specific enolase levels were comparable between the AD groups, regardless of APOE status. Hippocampal IDE mRNA levels were also reduced in AD patients with the epsilon4 allele compared to AD and normal subjects without the epsilon4 allele. These findings show that reduced IDE expression is associated with a significant risk factor for AD and suggest that IDE may interact with APOE status to affect Abeta metabolism.  相似文献   
102.
103.
104.
We would like to thank John Ellis for expert photographic assistance, Mervin Jones and Linda Lovell for expert animal husbandry, and Dr. Dorothy Easty for establishing the cell line LICR-LON-HN-5, without which this study would not have been possible.

We report a light microscopic and ultrastructural analysis of the comparative degrees of differentiation seen in keratinocytes derived from the tongue and epidermis with those of a well-differentiated human squamous carcinoma cell line (LICR-LON-HN5). When growing on plastic substrates, all cultures had a similar morphology, with multilayering and the production of cornified envelopes. When cultured on collagen gels the structure was more organized, with keratohyalin granules and keratin whorl formation in both the normal and the malignant cultures. Normal keratinocytes injected into athymic mice produced epidermal cysts, while cells from the cell line produced well-differentiated squamous cell carcinomas, which were partially solid and partially cystic. The tumor was well organized, with identifiable basal cells, spin-ous cells, keratohyalin granules, and a prominent basal lamina at the stromal/epithelial interface. This model is to be developed for comparative studies between normal and malignant cells, with particular reference to basement membrane production and to investigations of the relative importance of extrinsic and intrinsic factors in the control of squamous differentiation.  相似文献   
105.
We report the early results of a series of 86 femoropopliteal bypass operations in which a 5 mm diameter thin wall polytetrafluoroethylene (Gore-Tex) prosthesis was used. Sixty-five bypasses were implanted in men and 21 in women. Thirty bypasses were done in conjunction with an aortic bifurcation graft and 18 patients had a bilateral procedure. The indication for operation was severe claudication in 74 cases and critical ischaemia in 12 cases. The angiographic run-off was good (three patent vessels) in 22 limbs and poor (one or two patent vessels) in 64 limbs. The cumulative patency rate for the whole group was 62% after 18 months. Angiographic run-off and the indication for operation were both found to influence cumulative patency rate significantly (p=0.035 and p=0.055, respectively). We also compared the results obtained when run-off was poor with equivalent data from our own previously published series in which a standard 6 mm diameter Gore-Tex prosthesis was used. This shows a difference in patency rate, for example 57% against 37% after 18 months, in favour of the smaller bore thin wall graft.  相似文献   
106.
Nitrate-rich food can increase nitric oxide production and improve vascular and brain functions. This study examines the feasibility of a randomised controlled trial (RCT) testing the effects of prolonged consumption of different doses of dietary nitrate (NO3) in the form of beetroot juice (BJ) in overweight and obese older participants. A single-blind, four-arm parallel pilot RCT was conducted in 62 overweight and obese (30.4 ± 4 kg/m2) older participants (mean ± standard deviation (SD), 66 ± 4 years). Participants were randomized to: (1) high-NO3 (HN: 2 × 70 mL BJ/day) (2) medium-NO3 (MN: 70 mL BJ/day), (3) low-NO3 (LN: 70 mL BJ on alternate days) or (4) Placebo (PL: 70 mL of NO3-depleted BJ on alternate days), for 13 weeks. Compliance was checked by a daily log of consumed BJ, NO3 intake, and by measuring NO3 and NO2 concentrations in plasma, saliva, and urine samples. Fifty participants completed the study. Self-reported compliance to the interventions was >90%. There were significant positive linear relationships between NO3 dose and the increase in plasma and urinary NO3 concentration (R2 = 0.71, p < 0.001 and R2 = 0.46 p < 0.001, respectively), but relationships between NO3 dose and changes in salivary NO3 and NO2 were non-linear (R2 = 0.35, p = 0.002 and R2 = 0.23, p = 0.007, respectively). The results confirm the feasibility of prolonged BJ supplementation in older overweight and obese adults.  相似文献   
107.
Increasing sugar-sweetened beverages (SSB) consumption and associated health impacts warrant health-policy action. We assessed associations of socioeconomic and lifestyle variables with adolescents’ consumption of regular soda (RSD), sport (SD), and energy (ED) drinks. Cross-sectional study of 3930 Spanish adolescents (2089 girls, 1841 boys) aged 13–18 years). We compared frequency of consuming each SSB type (European Food Safety Authority questionnaire) with sociodemographic and lifestyle variables (standardized questions). RSD, SD, and ED were consumed at least weekly by 72.7%, 32.3%, and 12.3% of participants, respectively, and more frequently (p < 0.001) by boys, compared to girls. Multivariate ordinal logistic regression showed inverse association between RSD, SD, and ED consumption and parental occupation-based socioeconomic status (p < 0.01). Daily smoking was associated (p < 0.001) with higher ED (OR 3.64, 95% CI 2.39–5.55) and RSD (OR 2.15, 95% CI 1.56–2.97) consumptions. SD intake was associated inversely with smoking (OR 0.60, 95% CI 0.40–0.89, p = 0.012) and directly with physical activity (OR 2.93, 95% CI 2.18–3.95, p < 0.001). School performance was lower among ED (OR 2.14, 95% CI, 1.37–3.35, p = 0.001) and RSD (OR 1.81, 95% CI 1.24–2.64, p = 0.002) consumers, compared to SD. Maleness and low socioeconomic status predicted SSB consumption. Smoking and low school performance were associated with higher ED and RSD intakes.  相似文献   
108.
The European Journal of Health Economics - Economic cost estimates have the potential to provide a valuable alternative perspective on the COVID-19 burden. We estimate the premature mortality...  相似文献   
109.
BackgroundFew studies evaluate racial disparities in costs and clinical outcomes for patients undergoing distal pancreatectomy (DP).MethodsWe queried the Healthcare Cost and Utilization Project State Inpatient Databases to identify patients undergoing DP. Multivariable regression (MVR) was used to evaluate the association between race and postoperative outcomes.Results2,493 patients underwent DP; 265 (10%) were black, and 221 (8%) were of Hispanic ethnicity. On MVR, black and Hispanic patients were less likely than whites to undergo surgery in high volume centers (OR 0.53, 95% CI [0.40, 0.71]; OR 0.45, 95% CI [0.32, 0.62]). Black patients had a greater risk of postoperative complication (OR 1.40, 95% CI [1.07, 1.83]), 90-day readmission (OR 1.53, 95% CI [1.15, 2.02]), prolonged length of stay (OR 1.74, 95% CI [1.25–2.44]), and of being a high cost outliers (OR 1.40, 95% CI [1.02, 1.91]) compared to white patients.ConclusionBlack patients have increased risk of having a postoperative complication, prolonged hospitalization, and of being a high-cost outlier than non-Hispanic whites.  相似文献   
110.
Purpose: Injuries are one of the leading causes of death and lead to a high social and financial burden. Injury patterns can vary significantly among different age groups and body regions. This study aimed to evaluate the relationship between mechanism of injury, patient comorbidities and severity of injuries. Methods: The study included trauma patients from July 2016 to June 2018, who were admitted to Sina Hospital, Tehran, Iran. The inclusion criteria were all injured patients who had at least one of the following: hospital length of stay more than 24 h, death in hospital, and transfer from the intensive care unit of another hospital. Data collection was performed using the National Trauma Registry of Iran minimum dataset. Results: The most common injury mechanism was road traffic injuries (49.0%), followed by falls (25.5%). The mean age of those who fell was significantly higher in comparison with other mechanisms (p < 0.001). Severe extremity injuries occurred more often in the fall group than in the vehicle collision group (69.0% vs. 43.5%, p < 0.001). Moreover, cases of severe multiple trauma were higher amongst vehicle collisions than injuries caused by falls (27.8% vs. 12.9%, p = 0.003). Conclusion: Comparing falls with motor vehicle collisions, patients who fell were older and sustained more extremity injuries. Patients injured by motor vehicle collision were more likely to have sustained multiple trauma than those presenting with falls. Recognition of the relationship between mechanisms and consequences of injuries may lead to more effective interventions.  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