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   1797篇
  免费   96篇
  国内免费   28篇
耳鼻咽喉   74篇
儿科学   72篇
妇产科学   74篇
基础医学   108篇
口腔科学   71篇
临床医学   154篇
内科学   489篇
皮肤病学   17篇
神经病学   91篇
特种医学   55篇
外科学   440篇
综合类   31篇
预防医学   44篇
眼科学   84篇
药学   49篇
中国医学   1篇
肿瘤学   67篇
  2024年   1篇
  2023年   10篇
  2022年   18篇
  2021年   31篇
  2020年   23篇
  2019年   35篇
  2018年   51篇
  2017年   36篇
  2016年   70篇
  2015年   119篇
  2014年   108篇
  2013年   122篇
  2012年   147篇
  2011年   155篇
  2010年   89篇
  2009年   69篇
  2008年   146篇
  2007年   156篇
  2006年   137篇
  2005年   139篇
  2004年   120篇
  2003年   69篇
  2002年   45篇
  2001年   5篇
  2000年   3篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1989年   1篇
  1987年   1篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
排序方式: 共有1921条查询结果,搜索用时 0 毫秒
61.
Background: The level and activity of indoleamine 2,3-dioxygenase (IDO) and the concentrations of L-tryptophan and its metabolite L-kynurenine were determined in association with various renal diseases. However, there have been no data regarding these parameters in patients on peritoneal dialysis compared to those undergoing hemodialysis or kidney transplantation.

Methods: This study investigated the level and activity of IDO and determined oxidative balance by calculating the total oxidant status (TOS), total antioxidant status (TAS), and oxidative stress index (OSI). We enrolled 60 kidney disease patients, including 20 on peritoneal dialysis (PD group), 19 on hemodialysis (HD group), and 21 with kidney transplantation (KT group), as well as 21 control group.

Results: IDO levels were increased in the PD, HD, and KT groups compared to the control group. The concentration of kynurenine was significantly increased in the PD group compared to the other groups (p?p?p?Conclusion: The results showed that IDO levels were increased in peritoneal dialysis and hemodialysis patients and in renal transplant recipients, while oxidative stress was found to be related to IDO activity and was most increased in the patients on peritoneal dialysis.  相似文献   
62.
63.
64.
65.
66.
OBJECTIVE: To increase retention of overdentures in cleft palate patients by means of heightened telescopic copings with a newly designed attachment. In this study, a "precision attachment" is described to develop the stability and retention of telescopic overdentures. CASE: A cleft palate patient was treated with a newly designed overdenture. Intraoral examination revealed poor tooth structure and retention. Therefore, a new semiprecision attachment was designed in order to increase retention and stabilization. CONCLUSION: The patient's tolerance was increased with the new overdenture.  相似文献   
67.
68.
A review of the literature indicated that sirtuin-1 expression, a regulator of nitric oxide bioavailability in erectile dysfunction (ED) after melatonin therapy, has not yet been investigated. The objective of this study was to evaluate the protective effects of melatonin for erectile function with sirtuin-1 protein expression in type 1 diabetic rat models. Fifty male Sprague Dawley rats were placed into five groups. Except for those in the control group (C), each animal received a single dose (60 mg/kg) of streptozotocin to induce diabetes. The animals were placed into the diabetes (D) group, insulin (I) group (6 U/kg/day), melatonin (Mel) group (10 mg kg−1 day−1) and combined treatment (I + Mel) group. Ten weeks later, the serum testosterone levels, intracavernosal pressure (ICP), mean arterial pressure (MAP), malondialdehyde (MDA), cyclic guanosine monophosphate (c-GMP), 8-hydroxydeoxyguanosine (8-OHdG), nitric oxide synthase (NOS), caspase-3 activity, sirtuin-1 and endothelial nitric oxide synthase (eNOS) protein expression and histological findings were assessed. The mean ICP/MAP ratio for the D group was lower than the mean ratios for the other groups. The treatment groups, particularly the I + Mel group, exhibited lower 8-OHdG and MDA levels and caspase-3 activity than the D group. The sirtuin-1 and eNOS expression and cavernosal tissue (CT) histology seemed to have been preserved by the melatonin and/or insulin therapy. These results were indicative of a profound protective effect of melatonin by the activation of sirtuin-1 protein expression against hyperglycemia-induced oxidative CT injury.  相似文献   
69.

Purpose

QT dispersion (QTd) was shown to be an independent predictor of mortality in hemodialysis (HD) patients. It may be hypothesized that coronary artery calcification is related to QTd in HD patients because widespread calcification may also involve the cardiac conducting system in these patients. In this study, we aimed to investigate the relationships of corrected QTd (QTcd) with coronary artery calcification score (CACS), carotid plaque score (CPS) and possible influence of these parameters on survival of HD patients.

Methods

Seventy-two HD patients (33 male, 39 female) were enrolled into the study. Mean age of the patients was 44 ± 12 years. Mean follow-up duration was 77 ± 24 months. CACS was determined by computed tomography. QTcd values were calculated as the difference of maximum and minimum QT intervals. Left ventricular mass index (LVMI) and CPS were measured by echocardiography.

Results

QTcd was significantly correlated with CACS (r = 0.233, p = 0.049), CPS (r = 0.354, p = 0.003) and LVMI (p = 0.011, r = 0.299). CPS was found to be significantly higher in the group with high QTcd (>60 ms) [2 (1–4) versus 0 (0–1), p = 0.02]. CACS was significantly correlated with age (r = 0.44, p < 0.001), LVMI (r = 0.52, p < 0.001) and CPS (r = 0.32, p = 0.003). In Kaplan–Meier analysis, survival of patients with high QTcd was significantly lower than the patients with low QTcd. In Cox regression analysis for predicting mortality, age, serum albumin and QTcd were found to be the independent predictors of mortality.

Conclusions

QTcd independently predicted mortality, and it was significantly associated with coronary artery calcification, left ventricular hypertrophy and atherosclerosis in HD patients.  相似文献   
70.
For both the B2O3-Bi2O3-CaO and B2O3-Bi2O3-SrO glass systems, γ-ray and neutron attenuation qualities were evaluated. Utilizing the Phy-X/PSD program, within the 0.015–15 MeV energy range, linear attenuation coefficients (µ) and mass attenuation coefficients (μ/ρ) were calculated, and the attained μ/ρ quantities match well with respective simulation results computed by MCNPX, Geant4, and Penelope codes. Instead of B2O3/CaO or B2O3/SrO, the Bi2O3 addition causes improved γ-ray shielding competence, i.e., rise in effective atomic number (Zeff) and a fall in half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP). Exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) were derived using a geometric progression (G–P) fitting approach at 1–40 mfp penetration depths (PDs), within the 0.015–15 MeV range. Computed radiation protection efficiency (RPE) values confirm their excellent capacity for lower energy photons shielding. Comparably greater density (7.59 g/cm3), larger μ, μ/ρ, Zeff, equivalent atomic number (Zeq), and RPE, with the lowest HVL, TVL, MFP, EBFs, and EABFs derived for 30B2O3-60Bi2O3-10SrO (mol%) glass suggest it as an excellent γ-ray attenuator. Additionally, 30B2O3-60Bi2O3-10SrO (mol%) glass holds a commensurably bigger macroscopic removal cross-section for fast neutrons (ΣR) (=0.1199 cm−1), obtained by applying Phy-X/PSD for fast neutrons shielding, owing to the presence of larger wt% of ‘Bi’ (80.6813 wt%) and moderate ‘B’ (2.0869 wt%) elements in it. 70B2O3-5Bi2O3-25CaO (mol%) sample (B: 17.5887 wt%, Bi: 24.2855 wt%, Ca: 11.6436 wt%, and O: 46.4821 wt%) shows high potentiality for thermal or slow neutrons and intermediate energy neutrons capture or absorption due to comprised high wt% of ‘B’ element in it.  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