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   2871篇
  免费   273篇
  国内免费   10篇
耳鼻咽喉   34篇
儿科学   154篇
妇产科学   49篇
基础医学   306篇
口腔科学   35篇
临床医学   250篇
内科学   644篇
皮肤病学   105篇
神经病学   293篇
特种医学   87篇
外国民族医学   1篇
外科学   527篇
综合类   85篇
一般理论   2篇
预防医学   207篇
眼科学   72篇
药学   131篇
中国医学   17篇
肿瘤学   155篇
  2023年   18篇
  2022年   28篇
  2021年   88篇
  2020年   40篇
  2019年   74篇
  2018年   89篇
  2017年   69篇
  2016年   69篇
  2015年   68篇
  2014年   115篇
  2013年   143篇
  2012年   210篇
  2011年   185篇
  2010年   94篇
  2009年   121篇
  2008年   143篇
  2007年   165篇
  2006年   134篇
  2005年   132篇
  2004年   115篇
  2003年   95篇
  2002年   81篇
  2001年   82篇
  2000年   89篇
  1999年   70篇
  1998年   40篇
  1997年   55篇
  1996年   35篇
  1995年   27篇
  1994年   38篇
  1993年   34篇
  1992年   43篇
  1991年   29篇
  1990年   46篇
  1989年   39篇
  1988年   30篇
  1987年   19篇
  1986年   20篇
  1985年   17篇
  1984年   19篇
  1983年   9篇
  1982年   7篇
  1981年   10篇
  1980年   9篇
  1979年   11篇
  1977年   9篇
  1976年   9篇
  1973年   6篇
  1952年   16篇
  1951年   23篇
排序方式: 共有3154条查询结果,搜索用时 140 毫秒
951.
952.
OBJECTIVE: To investigate changes in T-lymphocyte subsets, CD4+ and CD8+ lymphocytes, WBC, lymphocytes and eosinophil granulocytes during the acute and the convalescence phase of chickenpox infection. METHODS: During an epidemic of chickenpox, a household study was performed in a semi-urban area of Bissau, Guinea-Bissau. Varicella antibodies were determined to assess diagnostic certainty. To determine the timing of changes, haematological markers and T-cell subsets (immunocytochemical method) were analysed in the acute phase, 0-9 days after the rash, and in the convalescence phase, 35-45 days after the rash. RESULTS: In the acute phase, the CD4 percentage, CD4/CD8 ratio, and neutrophil percentage declined, whereas the CD8 percentage, WBC, CD4 and CD8 counts, and the lymphocyte percentage increased over the same period, most markedly for the CD8 count. The eosinophil percentage increased significantly with time from onset of rash. Between acute and convalescence samples there was an increase in CD4 percentage, CD4/CD8 ratio, and CD4 count, and a marked decrease in CD8 percentage and CD8 count. The changes were not significant for WBC, lymphocyte percentage, neutrophil percentage, and monocyte percentage, but eosinophil percentage was significantly increased 5-7 weeks after the onset of rash. The haematological changes were related to number of pox and intensity of exposure; a high eosinophil percentage was associated with less severe disease, i.e. less pox. CONCLUSION: We report significant changes in T-lymphocyte subsets during the acute phase of chickenpox infection, including a suppression of CD4+ T-cells and an augmentation of CD8+ T-cells. The levels were normalized 1 month later except for eosinophils, and we found no persistent CD4 suppression after chickenpox. An increased number of eosinophils in the peripheral blood was demonstrated early in the acute phase of the disease, and remained elevated in the convalescence phase.  相似文献   
953.
BACKGROUND: Inflammation and malnutrition are common in chronic kidney disease (CKD) patients, and plasma concentrations of free amino acids (AAs) in these patients are often abnormal. Malnutrition contributes to alterations in AA concentrations. OBJECTIVE: The objective was to study the effects of inflammation on plasma AA concentrations. DESIGN: Concentrations of plasma AAs, serum albumin, and several inflammatory markers were analyzed in 200 fasting, nondiabetic CKD patients who were close to the start of renal replacement therapy. The nutritional status of these patients was assessed by a subjective global assessment. RESULTS: The patients with inflammation [C-reactive protein (CRP) concentrations >10 mg/L] or malnutrition had lower AA concentrations than did the patients with no inflammation or malnutrition. The presence of both inflammation and malnutrition was associated with more marked reductions in AA concentrations than was malnutrition alone. Significant inverse correlations were observed between the plasma concentrations of most of the essential and nonessential AAs and inflammatory markers, whereas serum albumin concentrations were positively correlated with several AA concentrations. A stepwise multivariate regression analysis showed that serum CRP concentrations were independently associated with low concentrations of the sums of both nonessential AAs and all AAs. An analysis of all-cause mortality with a Kaplan-Meier test showed that the patients with higher AA concentrations had significantly better survival than did the patients with lower AA concentrations. CONCLUSIONS: Plasma AA concentrations are low in CKD patients with inflammation and are inversely correlated with concentrations of inflammatory markers. Although inflammation and malnutrition are closely related, CRP concentrations were independently associated with low concentrations of the sums of both nonessential AAs and all AAs, which suggests an independent role of inflammation as a cause of low plasma AA concentrations in CKD patients.  相似文献   
954.
955.
956.
A 12-year-old boy reported in outpatient department with history of shortness of breath and dyspnoea on moderate exertion. Physical examination was significant for bounding pulses and for a continuous murmur III/VI, best heard at the left upper sternal border. Echocardiography confirmed a large patent arterial duct with shortening fraction of 33%. He underwent successful transcatheter closure of the patent arterial, using Amplatzer duct occluder 12/10. Few hours later echocardiography revealed an unexpected, yet important depression of left ventricular systolic function with shortening fraction decreasing to 24% and then two weeks later decreasing further to 20%. At a follow-up after four months, he had improved clinically but left ventricular dysfunction still persisted with shortening fraction of 24%.  相似文献   
957.
AIM: To determine the resistance of microorganisms associated with refractory endodontic infections to sodium hypochlorite used as a root canal irrigant. METHODOLOGY: Two strains each of Actinomyces naeslundii, Candida albicans and Enterococcus faecalis were tested as late logarithmic phase inocula, against sodium hypochlorite adjusted to 0.5, 1.0, 2.5 and 5.25% w/v. Contact times used were 0, 10, 20, 30, 60 and 120 s. In the case of E. faecalis, additional experiments used contact times of 1.0, 2.0, 5.0, 10.0 and 30.0 min. Anti-microbial action was halted by sodium thiosulphate addition. Survivors were measured primarily using viable counts on drop plates. Additionally, pour plates were used to count low colony-forming units (cfu) and dilutions to 10(-6) were used to count high cfu. RESULTS: All concentrations of NaOCl lowered cfu below the limit of detection after 10 s in the case of A. naeslundii and C. albicans. However, E. faecalis proved to be more resistant to NaOCl. Using 0.5% NaOCl for 30 min reduced cfu to zero for both strains tested. This compares with 10 min for 1.0%, 5 min for 2.5% and 2 min for 5.25% (P < 0.001). Regression analysis for the dependent variable log(e)(count + 1) with log(e)(time + 1) and concentration as explanatory variables gave rise to a significant interaction between time and concentration (P < 0.001). CONCLUSION: The published association of E. faecalis with refractory endodontic infection may result, at least partially, from high resistance of this species to NaOCl. This does not appear to be the case with A. naeslundii or C. albicans.  相似文献   
958.
BACKGROUND: Increased production of nitric oxide (NO) and oxidative stress following bone marrow transplantation may play a role in the pathogenesis of idiopathic pneumonia syndrome (IPS). We hypothesize that patients who received high-dose chemotherapy followed by autologous peripheral hematopoietic stem-cell transplantation (APHSCT) have increased exhaled NO. METHOD: We measured exhaled lower respiratory tract NO concentration with a chemiluminescent NO analyzer during a slow vital capacity maneuver against a positive pressure of 16 cm H(2)O at an expiratory flow rate of 50 mL/s in 20 female patients who received high-dose chemotherapy (cyclophosphamide, carmustine, and cisplatin) followed by APHSCT for the treatment of stage III or IV breast carcinoma. Pulmonary function tests were performed, and exhaled NO measurements and clinical and laboratory data were obtained before transplantation and at every 6-week visit after transplantation for 24 weeks. RESULTS: All study patients had evidence of IPS with dyspnea and reduction in diffusion capacity of the lung for carbon monoxide (DLCO). Lower respiratory tract exhaled NO was significantly higher after APHSCT and during the 6 months of follow-up. Mean (+/- SD) exhaled NO increased from (mean +/- SD) 12.54 +/- 1.32 parts per billion (ppb) before APHSCT to 21.26 +/- 1.94 ppb at 6 weeks (p = 0.099), 21.26 +/- 1.94 ppb (p = 0.006) at 12 weeks, 24.62 +/- 2.55 ppb (p = 0.012) at 18 weeks, and 25.28 +/- 3.31 ppb (p = 0.013) at 24 weeks (all p values were compared to baseline). There was a strong negative correlation between DLCO and exhaled NO (regression coefficient - 0.60, p = 0.01). CONCLUSION: Lower respiratory tract concentration of exhaled NO is significantly increased following APHSCT and correlates with reduction in DLCO. Increase in lower respiratory tract concentration of NO is a potential marker of IPS.  相似文献   
959.
Qureshi AI 《Lancet》2004,363(9411):804-813
Cerebrovascular diseases are an important cause of morbidity and mortality worldwide. Endovascular treatment has emerged as a minimally invasive approach to treat cerebrovascular diseases and possibly intracranial neoplasms. Practice patterns for selection of patients for endovascular treatment are continuously being modified on the basis of new information derived from clinical studies. In this review, I discuss the various endovascular treatments for diseases such as ischaemic stroke, carotid and intracranial stenosis, intracranial aneurysms, arteriovenous malformations, malignant gliomas, and meningiomas.  相似文献   
960.
BACKGROUND: Myocardial perfusion single-photon emission computed tomography (SPECT) permits assessment of stress perfusion and resting left ventricular (LV) function. Quantitative analysis of perfusion patterns among patients with LV dysfunction offers an opportunity for developing criteria to differentiate ischemic from nonischemic cardiomyopathy. HYPOTHESIS: Quantitative assessment of SPECT may allow differentiation between ischemic and nonischemic cardiomyopathy. METHODS: We evaluated 144 patients with LV ejection fraction < or =40%, divided into 63 patients with nonischemic and 81 with ischemic cardiomyopathy. Mean relative myocardial counts were obtained for regions drawn over defect and normal zones on rest and stress polar perfusion maps. RESULTS: Multivariate logistic regression analysis of significant univariate SPECT predictors of ischemic cardiomyopathy revealed that the stress defect severity ratio (SDSR) was the best predictor of ischemic cardiomyopathy (p < 0.0001). By receiver operator characteristic (ROC) curve analysis, an SDSR of < or =45% optimized prediction of ischemic cardiomyopathy (sensitivity 81%, specificity 96%). An SDSR of < or =45% occurred in 65 of 81 (80%) patients with ischemic cardiomyopathy, but in only 3 of the 63 (4%) patients with nonischemic cardiomyopathy (p < 0.0001). Applying the < or =45% SDSR threshold to a prospective group of 89 patients yielded a somewhat lower sensitivity (60%), but retained high specificity (91%) for identifying ischemic cardiomyopathy (p = NS vs. retrospective group). CONCLUSIONS: Presence of a severe and extensive stress perfusion defect is a hallmark of ischemic cardiomyopathy. By contrast, a mild stress perfusion defect (SDSR of >45%) is commonly present among patients with ischemic and nonischemic cardiomyopathy. An SDSR of < or =45% is a reproducible specific marker for identifying the presence of ischemic cardiomyopathy.  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