全文获取类型
收费全文 | 666篇 |
免费 | 49篇 |
国内免费 | 22篇 |
专业分类
耳鼻咽喉 | 1篇 |
儿科学 | 62篇 |
妇产科学 | 14篇 |
基础医学 | 86篇 |
口腔科学 | 8篇 |
临床医学 | 108篇 |
内科学 | 103篇 |
皮肤病学 | 4篇 |
神经病学 | 14篇 |
特种医学 | 175篇 |
外科学 | 38篇 |
综合类 | 17篇 |
预防医学 | 54篇 |
眼科学 | 5篇 |
药学 | 30篇 |
肿瘤学 | 18篇 |
出版年
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 16篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 19篇 |
2006年 | 11篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 33篇 |
1997年 | 30篇 |
1996年 | 40篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 29篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 21篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 29篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 20篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1973年 | 6篇 |
1970年 | 3篇 |
1966年 | 2篇 |
排序方式: 共有737条查询结果,搜索用时 15 毫秒
1.
2.
3.
The observation that tumor cells of some neoplasms display major histocompatibility complex (MHC) class II molecules may be of functional significance, influencing the progression of malignancy by allowing the cancer cells to present antigen to the immune system. In the normal cervix, class II molecules are expressed by columnar but not squamous epithelium. The pattern of MHC class II expression in cervical carcinomas has been documented using immunohistochemical methods. Of 53 cervical squamous carcinomas examined for MHC class II expression, only 17% maintained a negative phenotype characteristic of the epithelium from which they were derived, while the remaining tumors exhibited either uniform (45%) or heterogeneous (38%) expression. Tumor areas which were class II positive also express class II associated invariant chain and the adhesion molecules lymphocyte function antigen 3 and intercellular adhesion molecule 1. The DR, DP, and DQ class II MHC subloci are differentially expressed, suggesting independent regulation. There is a trend for tumors with the uniform class II phenotype to predominantly express DR antigen, whereas tumors of the heterogeneous class II phenotype express with equal frequency either DR or DP antigens dominantly. There is no apparent influence of class II status on lymphocyte infiltration of the tumors. The presence of human papillomavirus 16 DNA in the cervical carcinoma specimens was analyzed by Southern blotting of restriction enzyme digested DNA and no correlation between the presence of human papilloma virus and MHC class II expression was found. 相似文献
4.
Noninvasive metabolic magnetic resonance (MR) imaging reflecting glucose metabolism in the aldose-reductase-sorbitol (ARS) pathway was performed in the rabbit head; after administration of the fluorinated glucose analogue 3-fluoro-3-deoxy-D-glucose (3FD-glucose), fluorine-19 images were generated. Images of 3FD-glucose showed significant 3FD-glucose uptake by adipose tissue, indicating its buffering effects in case of excess loads of glucose. Images of 3-fluoro-3-deoxy-D-sorbitol (3FD-sorbitol) demonstrated the spatial distribution of aldose reductase activities and significant sorbitol accumulation in the lens. Images of 3-fluoro-3-deoxy-D-fructose (3FD-fructose) showed preferential uptake of fructose by muscle tissue. The extremely low toxicity of 3FD-glucose indicates promise for its clinical application in metabolic imaging. 相似文献
5.
目的:血小板衍生生长因子在平滑肌细胞的表型转化过程中起重要作用。观察大鼠移植心脏组织中血小板衍生生长因子AmRNA表达的变化及雷帕霉素的干预效应。方法:实验于2005-10/2006-01在中南大学湘雅二医院胸心外科实验室完成。将60只SD大鼠、24只Wistar大鼠按随机数字表法分为3组:①同系移植组:供、受体各12只,均为SD大鼠。②异系移植组:供体为Wistar大鼠(n=24),受体为SD大鼠(n=24),受体大鼠随机分为雷帕霉素组(n=12)和环孢霉素组(n=12),术后分别给予雷帕霉素1.25mg/(kg·d)灌胃及环孢霉素A10mg/(kg·d)皮下注射,给药60d,给药结束后留取移植心脏待检。③另12只SD大鼠直接取心脏组织作为正常对照组。指标检测:①对移植心脏组织行VanGieson染色后采用Miassystem4.1医学图像分析管理系统分析血管狭窄程度。②应用反转录-聚合酶链反应检测血小板衍生生长因子AmRNA在移植心脏组织中的表达情况。结果:36只受体SD大鼠及12只正常SD大鼠全部进入结果分析,无脱失。①同系移植组、环孢霉素组及雷帕霉素组大鼠的冠状动脉狭窄指数均显著高于正常对照组[(13.12±0.72)%,(62.45±8.12)%,(28.91±3.24)%,(0.09±0.02)%(P<0.01)],环孢霉素组及雷帕霉素组高于同系移植组(P<0.05),环孢霉素组高于雷帕霉素组(P<0.01)。②正常对照组、同系移植组、环孢霉素组及雷帕霉素组大鼠的血小板衍生生长因子AmRNA相对含量分别为0.19±0.06,0.21±0.08,1.12±0.22及0.47±0.11,环孢霉素组、雷帕霉素组显著高于同系移植组(P<0.01),环孢霉素组高于雷帕霉素组(P<0.05)。结论:血小板衍生生长因子AmRNA的高表达与移植心脏的血管硬化有关;雷帕霉素具有预防大鼠心脏移植物血管病变的作用,其作用可能与抑制心脏组织中血小板衍生生长因子AmRNA的表达有关。 相似文献
6.
Billette J; Janse MJ; van Capelle FJ; Anderson RH; Touboul P; Durrer D 《The American journal of physiology》1976,231(4):1129-1139
7.
Breast cancer detection: one versus two views 总被引:2,自引:0,他引:2
Mammographic examinations of 169 patients with 172 biopsy-proved carcinomas, and of 194 healthy subjects, were interpreted independently and retrospectively by three experienced mammographers, initially as single-view oblique examinations and 6 months later as two-view oblique-cephalocaudal examinations. For the single-view examinations of the cancer patients, 67% of the cancers were correctly recommended for biopsy, additional views were requested for 23%, and a "negative" interpretation was made for 10%. For the single-view examinations of healthy subjects, biopsy was recommended for 7% and additional views were recommended for 32%. For the two-view examinations of women with cancer, 80% of the cancers were correctly recommended for biopsy, additional views were requested for 4%, and a "negative" interpretation was made for 16%. For two-view examinations of healthy subjects, biopsy was recommended for 7% and additional views were requested for only 5%. The authors conclude that single-view screening should not be performed, because it would lead to an excessive number of "call-back" examinations of healthy patients, producing additional cost and anxiety that would outweigh any theoretical benefit. 相似文献
8.
Striated intramural gallbladder lucencies on US studies: predictors of acute cholecystitis 总被引:1,自引:0,他引:1
Ultrasound scans of 51 consecutive patients with gallbladder wall thickening were reviewed, and specific sonographic features were correlated with surgical and clinical follow-up. Two patterns of thickening were identified as specific indicators of the presence or absence of acute cholecystitis. "Striated" wall thickening, consisting of several alternating, irregular, discontinuous, lucent and echogenic bands, was seen in eight of 13 patients (62%) with acute cholecystitis. This pattern was not encountered in any of the patients who did not have acute cholecystitis. Conversely, "three-layer" thickening, consisting of a single circumferential lucent zone between two relatively uniform echogenic layers, was seen in only one of 13 patients (8%) with acute cholecystitis but in 11 of 38 patients (29%) with other diagnoses. Other abnormalities, including the presence of intramural echogenic foci and wall irregularities, were more frequently seen in patients with acute cholecystitis but were not as helpful. Use of these features may suggest or help exclude a diagnosis of acute cholecystitis in those patients in whom the cause of gallbladder wall thickening is otherwise not apparent. 相似文献
9.
Ralph F Jozefowicz Bruce M Koeppen Susan Case Robert Galbraith David Swanson Robert H Glew 《Academic medicine》2002,77(2):156-161
PURPOSE: Most medical schools test their students throughout the curriculum using in-house examinations written by the faculty who teach the courses. The authors assessed the quality of in-house examinations used in three U.S. medical schools. METHOD: In 1998, nine basic science examinations from the three schools were gathered and each question was subjected to quality assessment by three expert biomedical test developers, each of whom has had extensive experience in reviewing and evaluating questions for the United States Medical Licensing Examination (USMLE) Steps 1 and 2. Questions were rated on a five-point scale: 1 = tested recall only and was technically flawed to 5 = used a clinical or laboratory vignette, required reasoning to answer, and was free of technical flaws. Each rater made independent assessments, and the mean score for each question was calculated. Mean quality scores for National Board of Medical Examiners (NBME) who were trained question writers were compared with the mean scores for question writers without NBME training. The raters' quality assessments were made without knowledge of the test writers' training background or the study's hypothesis. RESULTS: A total of 555 questions were analyzed. The mean score for all questions was 2.39 +/- 1.21. The 92 questions written by NBME-trained question writers had a mean score of 4.24 +/- 0.85, and the 463 questions written by faculty without formal NBME training had a mean score of 2.03 +/- 0.90 (p <.01). CONCLUSIONS: The in-house examinations were of relatively low quality. The quality of examination questions can be significantly improved by providing question writers with formal training. 相似文献
10.
BACKGROUND: The lack of an early, sensitive marker for intestinal ischemia has led to delay in diagnosis and worsended outcome for patients with acute onset of this condition. Our preliminary studies revealed that guinea pig cytosolic beta-glucosidase (CBG) is expressed predominantly in the small intestine, with lower levels in the liver and pancreas and undetectable levels in other organs. Cytosolic beta-glucosidase was investigated as a serum marker of small intestinal ischemia in a guinea pig model. METHODS: Guinea pigs underwent anesthesia, sham laparotomy, 30 minutes of mesenteric ischemia followed by 6 hours of reperfusion 6 hours of sustained mesenteric ischemia, or closed-loop small bowel obstruction. Serum samples were assayed for CBG activity. At the conclusion of the ischemia/reperfusion experiments, small bowel samples were assayed for residual enzyme activity, and paraffin sections were graded for the severity of histologic injury. RESULTS: Serum CBG activity rose rapidly after intestinal ischemia with and without reperfusion. Peak enzyme activities were elevated 23-fold for reperfused animals (P < .001) by 4 hours. For nonreperfused animals, peak serum CBG activities reached 29-fold above baseline and were significantly higher than the CBG activities of reperfused animals at 4 hours (P < .01) and at 6 hours (P < .05). Mucosal injury ranged from undetectable to moderate and corresponded in severity with both peak serum enzyme activity and decreased residual activity in the small bowel. In animals subjected to closed-loop obstruction, there was a mean increase of serum CBG of 9.2-fold from 4 to 6 hours after establishment of obstruction (P < .05). CONCLUSIONS: In the guinea pig model, CBG is a sensitive marker of ischemic injury caused by arterial occlusion or closed-loop obstruction of the small bowel. 相似文献