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   2949篇
  免费   172篇
  国内免费   23篇
耳鼻咽喉   38篇
儿科学   123篇
妇产科学   48篇
基础医学   392篇
口腔科学   136篇
临床医学   229篇
内科学   691篇
皮肤病学   66篇
神经病学   117篇
特种医学   323篇
外科学   268篇
综合类   69篇
预防医学   281篇
眼科学   42篇
药学   151篇
中国医学   44篇
肿瘤学   126篇
  2023年   17篇
  2022年   54篇
  2021年   59篇
  2020年   66篇
  2019年   70篇
  2018年   82篇
  2017年   74篇
  2016年   61篇
  2015年   83篇
  2014年   118篇
  2013年   183篇
  2012年   210篇
  2011年   194篇
  2010年   140篇
  2009年   126篇
  2008年   118篇
  2007年   143篇
  2006年   120篇
  2005年   106篇
  2004年   66篇
  2003年   67篇
  2002年   62篇
  2001年   51篇
  2000年   46篇
  1999年   36篇
  1998年   90篇
  1997年   62篇
  1996年   68篇
  1995年   50篇
  1994年   53篇
  1993年   52篇
  1992年   23篇
  1991年   14篇
  1990年   16篇
  1989年   47篇
  1988年   38篇
  1987年   43篇
  1986年   29篇
  1985年   23篇
  1984年   22篇
  1983年   22篇
  1982年   18篇
  1981年   20篇
  1980年   15篇
  1979年   10篇
  1978年   11篇
  1977年   17篇
  1976年   11篇
  1975年   13篇
  1970年   5篇
排序方式: 共有3144条查询结果,搜索用时 0 毫秒
31.
BACKGROUND: This study was designed to determine if an anti-necrotic compound, glycine, and/or an anti-apoptotic agent, ZVAD-fmk, improved the viability and function of hepatocytes in a bioartificial liver. METHODS: Isolated rat hepatocytes were entrapped in collagen gel (1.0-10.0 x 10(6) cells/mL) and cultured in serum-free medium (1:10 ratio of gel:media) supplemented with glycine alone, ZVAD-fmk alone, or glycine and ZVAD-fmk. The cytoprotective effects of glycine and ZVAD-fmk on gel-entrapped rat hepatocytes (GERH) were determined after anoxic exposure (0-20 hours). Cell functionality (measured by urea production), cell viability (quantitated by vital staining with fluorescein diacetate:ethidium bromide [FDA:EB]), and the mechanism of cell death (verified by electron microscopy and DNA fragmentation studies) were determined for each condition. RESULTS: The viability of GERH declined gradually and then stabilized 12 hours after hepatocyte isolation. The rate of urea production by GERH was directly proportional to the number of viable hepatocytes. Apoptotic death predominated at low cell density, and necrotic cell death became significant at high cell density. Hepatocyte necrosis became more significant after exposure to longer periods of anoxia (4, 8, 12, and 20 hours). ZVAD-fmk provided dose-dependent cytoprotection to GERH with an optimum benefit at a concentration of 60 mumol/L. After anoxic exposure or under high cell density culture, glycine demonstrated a maximum benefit of inhibiting necrosis at a concentration of 3 mmol/L. The beneficial effects of glycine and ZVAD-fmk were additive. CONCLUSIONS: The metabolic activity of a hepatocyte bioartificial liver may benefit from the use of cytoprotective agents such as ZVAD-fmk and glycine.  相似文献   
32.
OBJECTIVES: To determine the spectrum of N and G genotypes of respiratory syncytial virus (RSV) causing respiratory tract infection and whether particular genotypes are associated with severity of infection. PATIENTS AND METHODS: Nasopharyngeal aspirates (NPAs) were obtained from 114 infants with acute respiratory tract infection due to RSV over two seasons. Viral mRNA was extracted from NPAs or cultured virus, reverse transcribed, and the cDNA amplified by the polymerase chain reaction using primers directed to parts of the N and G gene respectively. Amplicons were separately digested with four different restriction endonucleases for each gene. The fragments were separated by agarose gel, electrophoresis, and the electrophoretic patterns used to assign the various genotypes. Disease severity was assessed as very mild (upper respiratory tract signs only), mild (coryza and signs of lower respiratory tract infection), moderate (requiring nasogastric or intravenous fluids), and severe (requiring oxygen or ventilation). RESULTS: Five of the six known N genotypes were detected, but NP4 and NP2 were found most frequently. There was no association between N genotype and disease severity. Six G (SHL) genotypes were detected. Significantly (p = 0.04) more of the infants infected with the SHL2 genotype had severe or moderate disease. CONCLUSIONS: During the seasonal peaks of RSV respiratory tract infection at least 10 different RSV genotypes cocirculated. While there is no association between N genotypes and disease severity, infection with the SHL2 G genotype appears to result in moderate to severe disease.  相似文献   
33.
34.
IL Ackerman  CA Karn  SC Denne  GJ Ensing  CA Leitch 《Pediatrics》1998,102(5):1172-1177
OBJECTIVE: The purpose of this study was to determine the effect of left-to-right shunting on the resting energy expenditure (REE), total energy expenditure (TEE), and energy intake in a group of 3- to 5-month-old infants with moderate to large unrepaired ventricular septal defects (VSDs) compared with age-matched, healthy infants. METHODS: Eight infants with VSDs and 10 healthy controls between 3 to 5 months of age participated in the study. Indirect calorimetry was used to measure REE and the doubly-labeled water method was used to measure TEE and energy intake. An echocardiogram and anthropometric measurements were performed on all study participants. Daily urine samples were collected at home for 7 days. Samples were analyzed by isotope ratio mass spectrometry. Data were compared using analysis of variance. RESULTS: No significant differences were found in REE (VSD, 42.2 +/- 8.7 kcal/kg/d; control, 43.9 +/- 14.1 kcal/kg/d) or energy intake (VSD, 90.8 +/- 19.9 kcal/kg/d; control, 87.1 +/- 11.7 kcal/kg/d) between the groups. The percent total body water was significantly higher in the VSD infants and the percent fat mass was significantly lower. TEE was 40% higher in the VSD group (VSD, 87.6 +/- 10.8 kcal/kg/d; control, 61.9 +/- 10.3 kcal/kg/d). The difference between TEE and REE, reflecting the energy of activity, was 2.5 times greater in the VSD group. CONCLUSIONS: REE and energy intake are virtually identical between the two groups. Despite this, infants with VSDs have substantially higher TEE than age-matched healthy infants. The large difference between TEE and REE in VSD infants suggests a substantially elevated energy cost of physical activity in these infants. These results demonstrate that, although infants with VSDs may match the energy intake of healthy infants, they are unable to meet their increased energy demands, resulting in growth retardation.  相似文献   
35.
36.
The authors report a case of a virilizing adrenal tumor that developed in a 2-year-old child with Beckwith-Wiedemann syndrome (BWS). He had a fetal diagnosis of omphalocele and a history of neonatal adrenal cysts. The importance of prenatal diagnosis of BWS and postnatal follow-up of tumors is discussed. The differential diagnosis of adrenal pathologies occurring in BWS also is reviewed.  相似文献   
37.
真菌性角膜角膜溃疡发病率逐年上升,目前主要采用抗真菌药物治疗、手术治疗、抗真菌药物联合手术治疗以及中西结合治疗,尚无特效的治疗方法。本文就治疗该病的最新进展进行了综述。  相似文献   
38.
39.
目的探讨腹部急性出血选择性血管造影诊断及介入治疗价值。方法回顾性分析80例行选择性动脉血管造影及血管内介入治疗的腹部及盆腔急性出血患者的临床资料。结果80例均采用Seldinger技术,经股动脉插管后作选择性血管造影,用碘化油、明胶海绵或弹簧圈栓塞治疗,80例中完全止血68例、再出血9例、无效3例。结论介入方法不仅可确定出血部位,而且可达到止血目的,效果确切。  相似文献   
40.
BackgroundHypertension is a major risk factor for cardiovascular morbidity and mortality in post-menopausal women. Although menopausal hormone therapy (MHT) is a very effective treatment for vasomotor symptoms during this period, the influence of this therapy on blood pressure is not yet clear.ObjectiveTo evaluate the relationship between the use of MHT and hypertension in participants of the ELSA-Brasil.MethodsA cross-sectional study using the baseline ELSA-Brasil data in a cohort of 2,138 women who had experienced natural menopause. This study analyzed hypertension, defined as arterial pressure ≥140/90 mmHg or previous antihypertensive use, and use of MHT, with participants being classified into never, past, and current users. Associations were assessed using an adjusted logistic regression model, with statistical significance set at p<0.05.ResultsOverall, 1,492 women (69.8%) had never used MHT, 457 (21.4%) had used it in the past, and 189 (8.8%) were current users. The use of MHT was more common in women who had a body mass index (BMI) <25 kg/m2and triglyceride levels <150 mg/dl, and who were physically less inactive, non-smokers, and non-diabetics. Current MHT users were less likely to have hypertension (OR=0.59; 95% CI: 0.41-0.85) compared to those who had never used MHT. In most cases, MHT was started at or before 59 years of age, within 10 years of becoming menopausal, and its use lasted for up to five years.ConclusionCurrent MHT use was not related to hypertension, particularly in healthy women and in those under 60 years of age.  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