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   19110篇
  免费   1123篇
  国内免费   146篇
耳鼻咽喉   223篇
儿科学   505篇
妇产科学   665篇
基础医学   2096篇
口腔科学   530篇
临床医学   1585篇
内科学   3804篇
皮肤病学   380篇
神经病学   888篇
特种医学   726篇
外国民族医学   11篇
外科学   3358篇
综合类   341篇
现状与发展   2篇
一般理论   11篇
预防医学   1645篇
眼科学   549篇
药学   1777篇
中国医学   138篇
肿瘤学   1145篇
  2024年   17篇
  2023年   249篇
  2022年   772篇
  2021年   1120篇
  2020年   608篇
  2019年   759篇
  2018年   1022篇
  2017年   599篇
  2016年   628篇
  2015年   638篇
  2014年   898篇
  2013年   1046篇
  2012年   1521篇
  2011年   1674篇
  2010年   950篇
  2009年   683篇
  2008年   965篇
  2007年   971篇
  2006年   893篇
  2005年   860篇
  2004年   736篇
  2003年   685篇
  2002年   607篇
  2001年   144篇
  2000年   119篇
  1999年   97篇
  1998年   76篇
  1997年   73篇
  1996年   72篇
  1995年   65篇
  1994年   59篇
  1993年   50篇
  1992年   47篇
  1991年   57篇
  1990年   55篇
  1989年   49篇
  1988年   50篇
  1987年   50篇
  1986年   39篇
  1985年   41篇
  1984年   42篇
  1983年   38篇
  1982年   35篇
  1981年   24篇
  1980年   21篇
  1978年   16篇
  1977年   14篇
  1976年   17篇
  1974年   13篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
941.
AIM: To investigate the benefits of insulin like growth factor-1 (IGF-1) supplementation to serum-free institut georges lopez-1 (IGL-1) solution to protect fatty liver against cold ischemia reperfusion injury. METHODS: Steatotic livers were preserved for 24 h in IGL-1  solution supplemented with or without IGF-1 and then perfused "ex vivo " for 2 h at 37℃. We examined the effects of IGF-1 on hepatic damage and function (transaminases, percentage of sulfobromophthalein clearance in bile and vascular resistance). We also studied other factors associated with the poor tolerance of fatty livers to cold ischemia reperfusion injury such as mitochondrial damage, oxidative stress, nitric oxide, tumor necrosis factor-α (TNF-α) and mitogen-activated protein kinases.RESULTS: Steatotic livers preserved in IGL-1 solutionsupplemented with IGF-1 showed lower transaminase levels, increased bile clearance and a reduction in vascular resistance when compared to those preserved in IGL-1solution alone. These benefits are mediated by activation of AKT and constitutive endothelial nitric oxide synthase (eNOS), as well as the inhibition of inflammatory cytokines such as TNF-α. Mitochondrial damage and oxidative stress were also prevented.CONCLUSION: IGL-1  enrichment with IGF-1 increasedfatty liver graft preservation through AKT and eNOS activation, and prevented TNF-α release during normothermic reperfusion.  相似文献   
942.
BackgroundAlthough direct oral anticoagulants (DOACs) have been shown to be effective at reducing the risk of stroke in patients with atrial fibrillation/flutter (AF), they are sometimes underdosed off-label to mitigate their associated higher bleeding risk. We sought to evaluate frequency and clinical outcomes of inappropriate underdosing of DOACS in patients with AF.MethodsWe conducted a study of subjects with AF who had a clinical indication for stroke prophylaxis (with a congestive heart failure, hypertension, age ≥75 years, diabetes mellitus, stroke or transient ischemic attack, vascular disease, age 65 to 47 years, sex category [CHA2DS2-VASc] of 2 or greater) and were prescribed 1 of the 4 clinically approved DOACs (apixaban, rivaroxaban, dabigatran, or edoxaban). We compared all-cause mortality, composite of stroke and systemic embolism, composite of myocardial infarction (MI), acute coronary syndromes (ACS), and coronary revascularization, and major bleeding between patients appropriately dosed and inappropriately underdosed.ResultsA total of 8125 patients met inclusion criteria, with a mean follow up of 2.2 ± 2 years. Of those, 1724 patients (21.2%) were inappropriately dosed. After adjusting for baseline variables, there was no difference in all-cause mortality, risk of stroke or systemic embolism, International Society on Thrombosis and Haemostasis (ISTH) major bleeding, or composite of myocardial infarction, acute coronary syndromes, or coronary revascularization between patients appropriately dosed and inappropriately underdosed. In subgroup analysis, only apixaban demonstrated an increased incidence all-cause mortality (hazard ratio [HR] 1.24, 95% confidence interval [CI] 1.03-1.49) with inappropriate underdosing. There was no difference in the remaining clinical outcomes noted on subgroup analysis.ConclusionUnderdosing of DOACs did not minimize risk of bleeding, systemic embolization or all-cause mortality in patients with AF. Inappropriate underdosing with apixaban in particular was associated with increased all-cause mortality.  相似文献   
943.
Experience with a new operation for patients with aortic valve disease and aneurysm or dissection of the ascending aorta is described. Twenty-four patients aged 66-87 years were operated on using a subcoronary implantation technique with a stentless aortic valve bioprosthesis and an extension using a vascular tube prosthesis. No major adverse cardiac events were observed in the postoperative period. This operation offers a safe alternative to the technically more demanding procedures of composite bioprosthetic ascending aortic replacement or full root replacement.  相似文献   
944.
Although mature dendritic cells (DCs) are potent initiators of adaptive immune response, immature steady-state DCs contribute to immune tolerance. In this study, we show that ex vivo splenic DCs are capable of inducing conversion of naïve CD4+ T cells to adaptive Foxp3+CD4+ regulatory T cells (aTreg) in the presence of TGF-β. In particular, when compared with splenic CD8α DCs, the CD8α+ DC subset were superior in inducing higher frequencies of conversion. This was not attributable to the difference in basal level of costimulation, because deficiency of CD40 or CD80/86 signaling did not diminish the differential induction of Foxp3. Conversion was regulated by DC maturation status. Further insights into the molecular mechanisms of conversion were gained by analyzing the contribution of several costimulatory and coinhibitory receptors. Costimulatory signals through GITR suppressed conversion, whereas coinhibitory signaling via programmed death 1 ligand (PD-L1) but not PD-L2 was required for conversion. Ex vivo PD-L1−/− DCs failed to support Foxp3 induction in the presence of TGF-β. In vivo blocking PD-L1 signaling abolished conversion in a tumor-induced aTreg conversion model. Collectively, this study highlights the cellular and molecular parameters that might be exploited to control the de novo generation of aTregs and peripheral tolerance.  相似文献   
945.
A 62-year-old white male presented with recurrent pulmonary embolism (PE) despite having an inferior vena cava (IVC) filter. Investigations ruled out upper limb deep vein thrombosis (DVT) and IVC thrombus, the common causes for a PE in the presence of IVC filter. The culprit was double IVC with a persisting left supracardinal vein that allowed an alternate route for the leg DVT to cause PE. IVC anomalies have a propensity to cause lower limb DVT. Although rarely suspected recent studies have revealed that IVC anomalies are not rare if anticipated and evaluated. Chest CT scans in cases of suspected idiopathic PE should extend up to the renal veins as this will identify common IVC anomalies. Therapy to prevent recurrent DVT can be instituted. A good quality venacavagram should always precede any IVC filter placement as this will identify almost all IVC anomalies and appropriate steps can prevent a recurrent PE.  相似文献   
946.
OBJECTIVES: To evaluate in naive patients with chronic hepatitis C 1- the efficacy and safety of one month interferon alpha (IFN-alpha) induction regimen; 2- the potential virological benefit of a secondary adjunction of ribavirin among HCV RNA negative patients after 20 weeks of IFN therapy, with or without an initial 4-week IFN induction. MATERIAL AND METHODS: 151 naive HCV-RNA positive patients presenting with biopsy- proven chronic hepatitis C and elevated ALT were randomised in a 2: 1 ratio in two arms: IFN-alpha 3 MU thrice a week (tiw) for 24 weeks (non-induced patients); IFN-alpha 6 MU daily for two weeks, then 3 MU daily for two weeks then 3 MU tiw for 20 weeks (induced patients). At week 24, HCV-RNA negative patients were randomised to receive in addition or not ribavirin 1-1.2 g daily for 24 additional weeks. Induction efficacy was assessed on the early viral response (EVR) defined as undetectable HCV RNA at week 4 then week 20. Ribavirin efficacy was assessed on the proportion of maintained complete response until the end of follow-up, 24 weeks after discontinuation of treatment. Data were analysed on an intent-to-treat basis. RESULTS: Efficacy of IFN-alpha induction: 104 patients were randomised to the non-induction group, 47 to the induction group. Gender, age, genotype distribution and HCV viral load at baseline did not differ significantly between the two groups. There was one treatment discontinuation because of adverse events in induced patients versus four in non-induced patients (P > 0.05). The 4 week EVR was significantly greater in induced patients in patients with HCV genotype 1, 4 or 5 (47% vs 12%, P=0.0002) only. There was no impact of induction in patients with HCV genotype 2 or 3. Efficacy of ribavirin: at week 24, 28 and 26 HCV-RNA negative patients were randomised to addition of ribavirin or not, respectively. Patients randomised to secondary additive ribavirin were more often HCV-RNA negative at the end of follow-up than patients treated with IFN-alpha alone: 18/28 (64%) vs 10/26 (39%); P=0.06. Among patients randomised to bitherapy, the relapse rate was significantly lower in patients with genotype 2 or 3 (0/12 vs 6/13, P=0.01) and not in those with genotype 1, 4 or 5 (5/11 vs 3/6, P=0.99). CONCLUSION: A 4 week IFN-alpha induction significantly increases the EVR rate in patients with HCV genotype 1, 4 or 5. Late secondary adjunction of ribavirin to IFN-alpha for 6 months in HCV-RNA negative patients after 6 months of IFN-alpha significantly decreases the relapse rate in patients with HCV genotype 2 or 3, but not in patients with genotypes 1, 4 or 5.  相似文献   
947.
In the phase III MM‐003 trial, pomalidomide plus low‐dose dexamethasone (POM+LoDEX) improved overall survival (OS) versus high‐dose dexamethasone (HiDEX) in 455 patients with relapsed and refractory multiple myeloma (RRMM) after treatment with bortezomib and lenalidomide. Here, a two‐stage Weibull method was used to adjust for the crossover of patients in the HiDEX arm to pomalidomide‐based therapy. The adjusted difference in median OS between patients in the POM+LoDEX and HiDEX arms was 7·0 months (12·7 vs. 5·7 months, respectively). These findings provide important evidence for understanding the clinical efficacy of pomalidomide on OS benefits seen in RRMM patients.  相似文献   
948.
The variation in cystic echinococcosis (CE) prevalence and mean intensity was studied in relation to site, season and host age and sex. A total of 12,911 slaughtered animals, 140 camels, 2668 cattle, 6525 sheep and 3578 goats were inspected for hydatid cysts in Al Baha region, Saudi Arabia, in three study areas during four seasons from June 2008 to May 2009. The prevalence of infection was 32.85%, 8.28%, 12.61% and 6.56% in camels, cattle, sheep and goats respectively. The prevalence of the parasite varied significantly in relation to site, season and host age classes and sex in most host species. Spring showed the highest prevalence in camels, cattle and sheep. A significant association was found among host age classes and likelihood of infection in all examined hosts and the oldest age class was significantly more likely to be infected. The main effects in parasite intensity were host sex and age in most examined host species. A positive correlation was found between intensity of CE and host age class in all animal species examined. The most commonly infected organs were liver and lungs which constituted 48.75% and 32.83% respectively, of the total infected organs. There was a significant difference among host species in fertile cysts (P < 0.0001). The higher percentages of fertile cysts were in sheep (47.67%) and goats (23.99%) indicating that sheep and goats are the most important intermediate hosts for Echinococcus granulosus. Examined hydatid cysts of the liver had a higher fertility rate (38.79%) than those of the lungs (25.13%). Cysts size ranged from 1 to 8 cm in diameter. The mean cyst diameter was found in the lungs higher than that in the liver in all hosts. The range in the number of cysts was 1-33 in infected animals. The mean number of cysts was higher in lungs than that in liver in all examined animals. The viability rate of protoscoleces of liver fertile cysts (62.20%) was significantly higher than that of lung cysts (52.73%). In conclusion, these findings of infection, mean abundance and fertility rates of CE in slaughtered animals, prompt plans for further epidemiological studies and control programmes.  相似文献   
949.
Acute necrotizing esophagitis is rare. The exact etiology is unknown in most cases. The esophagus appears black, necrotic and ulcerated on the upper endoscopy, thus the term "black esophagus" is used. Histologically, there is necrosis of the esophageal mucosa and submucosa. Here, we present a patient with cholangiocarcinoma who had upper gastrointestinal bleeding and was found to have acute necrotizing esophagitis on the upper endoscopy.  相似文献   
950.
The viscacha (Lagostomus maximus maximus) is a rodent with photoperiod‐dependent seasonal reproduction. The aim of this work was to study the morphological variations of the prostate during periods of maximal (summer, long photoperiod) and minimal (winter, short photoperiod) reproductive activity. Prostates of adult male viscachas were studied by light and electron microscopy, immunohistochemistry for androgen receptor, and morphometric analysis. The prostate consisted of two regions: peripheral and central. The peripheral zone exhibited large adenomeres with a small number of folds and lined with a pseudostratified epithelium. The central zone had small adenomeres with pseudostratified epithelium and the mucosa showed numerous folds. The morphology of both zones showed variations during periods of maximal and minimal reproductive activity. The prostate weight, prostate‐somatic index, luminal diameter of adenomeres, epithelial height and major nuclear diameter decreased during the period of minimal reproductive activity. Principal cells showed variations in their shape, size and ultrastructural characteristics during the period of minimal reproductive activity in comparison with the active period. The androgen receptor expression in epithelial and fibromuscular stromal cells was different between the studied periods. Our results suggest a reduced secretory activity of viscacha prostate during the period of minimal reproductive activity. Thus, the morphological variations observed in both the central and peripheral zones of the viscacha prostate agree with the results previously obtained in the gonads of this rodent of photoperiod‐dependent reproduction. Additionally, the variations observed in the androgen receptors suggest a direct effect of the circulating testosterone on the gland. Anat Rec, 298:1919–1931, 2015. © 2015 Wiley Periodicals, Inc.  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