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   549篇
  免费   38篇
  国内免费   6篇
耳鼻咽喉   3篇
儿科学   3篇
妇产科学   32篇
基础医学   71篇
口腔科学   15篇
临床医学   128篇
内科学   111篇
皮肤病学   1篇
神经病学   60篇
特种医学   8篇
外科学   43篇
综合类   9篇
预防医学   16篇
眼科学   4篇
药学   61篇
中国医学   5篇
肿瘤学   23篇
  2023年   4篇
  2022年   4篇
  2021年   3篇
  2020年   4篇
  2019年   6篇
  2018年   8篇
  2017年   10篇
  2016年   8篇
  2015年   4篇
  2014年   12篇
  2013年   25篇
  2012年   47篇
  2011年   30篇
  2010年   30篇
  2009年   19篇
  2008年   36篇
  2007年   27篇
  2006年   35篇
  2005年   35篇
  2004年   32篇
  2003年   19篇
  2002年   24篇
  2001年   22篇
  2000年   21篇
  1999年   17篇
  1998年   6篇
  1997年   7篇
  1996年   4篇
  1995年   5篇
  1994年   8篇
  1993年   5篇
  1992年   13篇
  1991年   6篇
  1990年   11篇
  1989年   12篇
  1988年   8篇
  1987年   9篇
  1986年   7篇
  1985年   3篇
  1984年   1篇
  1982年   1篇
  1973年   2篇
  1972年   2篇
  1970年   1篇
排序方式: 共有593条查询结果,搜索用时 46 毫秒
551.
We report a patient who presented with intestinal obstruction; his small intestine showed intense segmentary lipomatosis associated with unusually situated multiple intussusceptions. Preoperatively, we diagnosed intussusception in the ileocecal region by ultrasonography and computed tomographic scan. During surgery, the ileum was dilated and contained numerous movable polypoid masses. One reducible intussusception was encountered in the ileocecal region. In addition, an ileoileal intussusception that could not be reduced was resected with an end-to-end anastomosis. At histological examination, more than 150 submucosal lipomas were found.  相似文献   
552.
Cefprozil, a new oral cephalosporin, consists of a 90:10 cis:trans isomer mixture. Sensitive, specific and reproducible high performance liquid chromatographic methods have been developed for the simultaneous quantification of the two stereoisomers of cefprozil in plasma and urine samples from human and rats. Cephalexin acted as the internal standard. Plasma protein was precipitated with acetonitrile and trichloracetic acid with subsequent extraction of acetonitrile. After vortexing and centrifuging, the aqueous phase was injected onto a reverse phase C8 column. Urine samples were acidified with sodium acetate buffer (pH 3.8) and then directly injected onto a reverse phase C18 column. The detector was set at 280 nm. These methods were applied to determine protein binding of both isomers in human and rat sera, and to perform a pharmacokinetic study in human. Results showed that both isomers bound moderately to serum proteins with no interference by the other isomer. The pharmacokinetic study in human indicated that cefprozil was well absorbed and the cis and trans isomers have similar pharmacokinetics.  相似文献   
553.
Cefprozil, a new broad-spectrum oral cephalosporin, is composed of cis and trans isomers in an approximate 90:10 ratio. The pharmacokinetics of a single oral 1000-mg dose of cefprozil were evaluated in 6 healthy subjects and 24 patients with various degrees of renal impairment. Six of these subjects were studied both while receiving hemodialysis and during an interdialytic period. Plasma, urine, and hemodialysate that were collected at predetermined times were analyzed for concentrations of the cis and trans isomers of cefprozil using reverse-phase HPLC assay with UV detection. The maximum plasma concentration of the cis isomer ranged from 12.3 micrograms/mL in subjects with normal renal function to 36.7 micrograms/mL in hemodialysis patients. Similarly the area under the plasma concentration-time curve and the elimination half-life increased from 46 micrograms.h/mL to 373 micrograms.h/mL and from 1.72 hours to 5.94 hours, respectively. Renal clearance of the cis isomer decreased from 198 mL/min in normal subjects to 19 mL/min in volunteers with creatinine clearances of less than or equal to 30 mL/min; there was a strong correlation (r2 greater than or equal to .93) between the renal clearance of the cis isomer and creatinine clearance. Urinary recovery of the cis isomer decreased from 57% in those with normal renal function to 24% in the group with a creatinine clearance of less than or equal to 30 mL/min. Hemodialysis decreased the half-life of the cis isomer to 2 hours and removed approximately 55% of it from the body during a 3-hour dialysis period (hemodialysis clearance equaled approximately 87 mL/min). The pharmacokinetics of the trans isomer were similar to those observed for the cis isomer and were affected similarly by declining renal function. A reduction in dosage is recommended in patients with a creatinine clearance of 30 mL/min or less. It may be necessary to administer a dose after hemodialysis to maintain therapeutic plasma concentrations.  相似文献   
554.
Retinoic acid receptor responder 1 (RARRES1) is a retinoid regulated gene. Its expression is frequently down-regulated through DNA hypermethylation in several types of malignant tissues. This study investigated the clinical significance of RARRES1 protein and its association with RARRES3 protein expression in 161 (26 adenoma, 13 distal normal mucosa and 122 primary colorectal adenocarcinoma) paraffin-embedded colorectal tissues by immunohistochemistry. RARRES1 protein was detected at the highest levels in terminally differentiated cells of normal mucosal tissues and all 26 adenoma tissues. Among 122 colorectal adenocarcinomas, the poorly differentiated adenocarcinomas and Dukes' stage D tumours showed a significant decrease in RARRES1 expression (P < 0.001 and P < 0.01, respectively). RARRES1 expression was significantly (P < 0.001) correlated with RARRES3 expression, which was positively associated with tumour differentiation (P < 0.001). Difference in expression of RARRES1 among 119 patients had no apparent effect on patient survival. Our results suggest the role of RARRES1 in colorectal epithelial differentiation, and the down-regulation of RARRES1 is related to stage D progression.  相似文献   
555.
OBJECTIVES: The aim of the present study was to determine whether the liberal use of second-trimester maternal serum screening in Taiwan started in 1994 had a measurable impact on birth prevalence of infants with Down syndrome (DS) in the past decade. METHODS: We based our study on the databases of 'National Birth Defect Registration and Notification System', 'Amniocentesis in Pregnant Women', and 'Demographic Fact Book' in Taiwan. Collected data included total registered birth number, the registered number of stillbirths, the registered numbers of live births and of DS stillbirths affected with DS, amniocentesis rates each year in pregnant women aged 35 or more, and the age distribution of pregnant women in Taiwan. The live birth rate of and total birth rate of fetuses affected with DS, and the rates of live birth and stillbirth to total birth with DS, were analyzed year by year, in order to understand the change of birth rate of infants affected with DS between 1993 and 2001. Those with isolated cleft palate (ICP) were also analyzed as internal control variable. Confidence interval of live birth rate of infants with DS under Poisson distribution was calculated. Chi-square test for trend in binomial proportions was performed to see if there is an increasing (or decreasing) trend in the proportion of incidence of fetuses affected with DS. The difference was statistically significant if a p value was <0.05. RESULTS: A total of 1 331 616 deliveries were collected during the study period, including 840 cases of DS confirmed by karyotyping study. A marked decrease in the live birth rates of case with DS occurred in 1994-95, from 0.63 per 1000 births to 0.23 per 1000 births. There was a crossover from more live births with DS to more stillbirths with DS during 1994 to 1996 after the implementation of second-trimester maternal serum screening for DS in 1994. In 1993, 76.9% of births diagnosed with DS were born alive, compared to 32.5% in 2001 (p < 0.001). CONCLUSIONS: The policy of prenatal diagnosis program including amniocentesis for pregnant women aged 35 or more and the liberal application of maternal serum screening for DS in younger women was responsible for the marked decrease in the live births affected with DS in Taiwan from 1993 to 2001.  相似文献   
556.
Wang CC  Shyu BC 《Brain research》2004,995(2):226-235
The aim of the present study was to investigate afferent projections from the medial thalamic nuclei (MT) to the frontal cortical areas using a single small iontophoretic injection of biotinylated dextran amine (BDA) and analysis of the anterogradely labeled fibers and varicosities. Projections from the mediodorsal (MD) nuclei were found primarily and extensively in the anterior cingulate cortex (ACC), whereas those from the centrolateral (CL) thalamic nucleus were found in the frontal motor cortex. The density of terminals in the ACC was high in layers II and III and sparse in layer I. The majority of projected fibers from the CL were found at a high density in layer V, with a moderate density in the superficial layers. The differential projection patterns were topographically organized in the medial prefrontal cortex and sensory motor cortex. These findings support the results of our previous electrophysiological studies suggesting that neurons in the medial thalamic nuclei relay nociceptive information to the limbic or sensory motor cortical areas. The present results agree with the current notion that the medial thalamo-frontal cortical network circuitry plays an important role in processing the emotional aspect of nociception.  相似文献   
557.
The relative contribution of the gut and the liver to the first-pass metabolism of BMS-181101 (3-[3-[4-(5-methoxy-4-pyrimidinyl)-1-piperazinyl]propyl]-5-fluoro-1H-indole dihydrochloride), a potential antidepressant agent, has been evaluated in rats. Nine male Sprague–Dawley rats were divided into three groups of three and each rat received a single 20 mg kg?1 dose of [14C]BMS-181101 via a 30 min constant-rate intravenous infusion, a 30-min constant-rate intraportal infusion or oral gavage. Serial blood samples were collected for 8 h after dosing and plasma was analysed for unchanged BMS-181101 and total radioactivity. Extraction ratios for BMS-181101 by the gut and liver were calculated on the basis of ratios of the area under the plasma BMS-181101 concentration–time curve. The gut had a high intrinsic capacity for metabolizing BMS-181101-extraction ratios were 93% and 10% for the gut and liver, respectively. After oral administration BMS-181101 is sequentially exposed to the gut then the liver. As a result, the contribution of the gut to the overall first-pass effect (ca. 93%) was significantly greater than that of the liver  相似文献   
558.
In 24 patients with vascular dementia of Binswanger's type (VDBT) and 14 age-matched neurologically normal volunteers, we investigated the relationship between clinical features, white matter lesions (leucoaraiosis) and cerebral atrophy on computed tomography (CT) scan, and regional cerebral blood flow. All subjects underwent the Mini-Mental State Examination of Taiwan, version 1 (MMSE-T1), for assessing the severity of cognitive impairment. The patients were subdivided into two groups, one with mild to moderate (group I, MMSE-T1 scores: 11–24,n=ll), and the other with severe dementia (group II, MMSE-T1 scores: below 10,n=13). White matter degeneration was evaluated with densitometric methods. Loss of brain parenchyma was estimated with seven linear measurements (Evan's ratio, third ventricle ratio, width of temporal horn tip, anterior-posterior length of temporal horn, anterior-posterior length of Sylvian fissure and width of frontal interhemispheric fissure) by CT scans. Regional cerebral blood flow was determined with technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomography (SPET). In neuroimaging studies, subcortical leuco-araiosis was localized at the frontal region in group I patients and scattered diffusely in group II patients.99mTc-HMPAO SPET analysis revealed reduction of regional cerebral blood flow in the frontal lobe in group I patients and widespread reduction of regional cerebral blood flow in group II patients. A correlation between frontal leuco-araiosis and perfusion defect of the frontal pole was demonstrated in group I patients, showing findings typical of subcortical dementia. There was no difference in frontal atrophic measurements between group I patients and controls. Ratios of volumes of lost brain parenchyma and leuco-araiosis were significantly higher in group II patients than in the age-matched controls, corresponding to a diffuse cerebral perfusion defect. These results suggest that patients with VDBT have early frontal lobe involvement with posterior progression. Patients with mild VDBT are more likely to show reduction of frontal cerebral blood flow and leuco-araiosis, while those with severe VDBT are more likely to have diffuse leuco-araiosis, cerebral hypoperfusion and brain atrophy.  相似文献   
559.
OBJECTIVES: Myostatin, a negative regulator of muscle growth, is increased in hypertrophied and infarcted heart. However, the mechanism of regulation is not known. Mechanical stress is an important regulatory factor for cardiomyocyte growth. The aim of the study was to investigate the effect of cyclic stretch on the expression of myostatin gene in cardiomyocytes. METHODS: Neonatal Wistar rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation at 60 cycles/min. An in vivo model of aorta-caval shunt in adult rats was used to investigate the myostatin expression. RESULTS: Cyclic stretch significantly increased myostatin protein and mRNA expression after 6 to 18 h of stretch. Addition of the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580, insulin-like growth factor-1 (IGF-1) monoclonal antibody, and p38 siRNA 30 min before stretch inhibited the induction of myostatin protein. Cyclic stretch increased, while SB203580, IGF-1, and IGF-1 receptor antibody abolished, the phosphorylated p38 protein. Gel shift assays showed significant increase of DNA-protein binding activity of myocyte enhancer factor 2 (MEF2) after stretch, and transfection with p38 siRNA abolished the DNA-protein binding activity induced by cyclic stretch. Cyclic stretch significantly increased the IGF-1 secretion from myocytes. Both conditioned media from stretched myocytes and exogenous administration of IGF-1 recombinant protein to the non-stretched myocytes increased myostatin protein expression similar to that seen after cyclic stretch. An in vivo model of aorta-caval shunt in adult rats also demonstrated the increased myostatin expression in the myocardium. CONCLUSIONS: Cyclic mechanical stretch enhances myostatin expression in cultured rat neonatal cardiomyocytes. The stretch-induced myostatin is mediated by IGF-1 at least in part through a p38 MAP kinase and MEF2 pathway.  相似文献   
560.
BACKGROUND AND OBJECTIVES: In situ polymerase chain reaction (ISPCR) promises to considerably enhance our ability to detect a few copies of target nucleic acid sequences in fixed tissues and cells. The aim of this study was to investigate cervical carcinoma to determine the human papillomavirus (HPV) types on paraffin-embedded tissue sections by ISPCR and standard in situ hybridization. The results will correlate the morphological characteristics of lesions with viral typing results. METHODS: This study examined prevalence of HPV 16 and 18 DNA in biopsies from 85 cervical cancer patients by ISPCR, employing HPV 16, 18 consensus primers. There are 45 patients with squamous cell carcinomas, 13 with adenocarcinoma, 2 with adenosquamous carcinomas, 3 with small cell carcinomas, and 22 carcinoma in situ. The relation between the types of HPV detected, tumor type, and clinical stage were analyzed. RESULTS: Fifty-two of 85 biopsies were HPV 16- or 18-positive, HPV 16 being the most prevalent type. Squamous cell carcinoma had a high prevalence of HPV 16 and adenocarcinoma had a high prevalence of HPV 18. HPV 18 was the predominant type among high clinical stage (III-IV) cases while HPV 16 and mixed HPV 16 with HPV18 were significantly correlated with low clinical stage (0-I-II). CONCLUSION: Our results indicate that certain malignant cervical tumor phenotypes and stages correlate with specific HPV type, and that ISPCR is a sensitive and fast method to detect HPV in these patients.  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