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   48949篇
  免费   3557篇
  国内免费   2473篇
耳鼻咽喉   254篇
儿科学   1361篇
妇产科学   472篇
基础医学   11262篇
口腔科学   387篇
临床医学   3679篇
内科学   13571篇
皮肤病学   579篇
神经病学   1215篇
特种医学   621篇
外国民族医学   7篇
外科学   2107篇
综合类   6329篇
现状与发展   18篇
预防医学   7336篇
眼科学   386篇
药学   2469篇
  13篇
中国医学   852篇
肿瘤学   2061篇
  2024年   47篇
  2023年   612篇
  2022年   1861篇
  2021年   2147篇
  2020年   1693篇
  2019年   1478篇
  2018年   1493篇
  2017年   1466篇
  2016年   1731篇
  2015年   2033篇
  2014年   2822篇
  2013年   2991篇
  2012年   2756篇
  2011年   3237篇
  2010年   2684篇
  2009年   2445篇
  2008年   2397篇
  2007年   2532篇
  2006年   2274篇
  2005年   2002篇
  2004年   1775篇
  2003年   1547篇
  2002年   1241篇
  2001年   1204篇
  2000年   989篇
  1999年   880篇
  1998年   755篇
  1997年   770篇
  1996年   627篇
  1995年   631篇
  1994年   594篇
  1993年   473篇
  1992年   354篇
  1991年   302篇
  1990年   269篇
  1989年   244篇
  1988年   231篇
  1987年   167篇
  1986年   142篇
  1985年   287篇
  1984年   180篇
  1983年   134篇
  1982年   120篇
  1981年   98篇
  1980年   68篇
  1979年   58篇
  1978年   51篇
  1977年   31篇
  1976年   31篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BACKGROUND: Hepatitis C virus (HCV) viraemia is one of the factors for histological prognosis of chronic hepatitis C. METHODS: One hundred and thirty-five patients who received hepatic biopsies twice at intervals of 5 years or longer were followed up for a mean of 9.7 +/- 4.0 years were studied retrospectively. The amount of HCV viraemia present was measured as the concentration of HCV core protein by using the fluorescence enzyme immunoassay method. RESULTS: Multiple-regression analysis, using deterioration of the histological stage as a dependent variable, showed that greater age (P = 0.041), higher stage of hepatic histology at the start of follow up (P = 0.029), and higher serum concentration of core protein (P < 0.001) were independent factors affecting the deterioration of the liver's histological stage. At follow up, no significant difference in histological stage was seen between patients with serum HCV core protein > or = 100 pg/mL (n = 60) and those with serum core protein < 100 pg/mL (n = 75). The histological grade in patients with high serum core-protein levels tended to be significantly worse and the deterioration rate of the histological stage was significantly higher than in those with low HCV core protein levels (68 vs 35%, P < 0.001). The mutation rate of the HCV envelope-2/non-structural 1 (E2/NS1) nucleotide region was compared in two patients who had high serum concentrations of HCV core protein and whose histological stage had deteriorated with two patients who had low serum concentrations of the core protein and whose histological stages remained unchanged. No significant difference in E2/NS1 mutation was found. CONCLUSIONS: The amount of HCV viraemia was suggested to be a significant factor for determining histological outcome in patients with chronic hepatitis C. The mutation rate in the E2/NS1 region did not seem to be associated with the prognosis of chronic hepatitis C.  相似文献   
992.
HBV感染血清标志物、HBV DNA水平与性别的关系   总被引:9,自引:0,他引:9  
探讨HBV感染者血清标志物、HBVDNA水平和性别之间的关系.选择495例HBsAg阳性的血清标本和502例HBV DNA高于1×108copy/ml以上的血清标本,分别通过ELISA法以及实时荧光定量法进行HBV感染血清标志物HBV DNA的检测.三种组合[组合1为HBsAg( )HBeAg( )抗-HBc( ),组合2为HBsAg( )抗-HBe( )抗-HBc( ),组合3为HBsAg( )抗-HBc( )]的HBV DNA阳性率(分别为95%、18%和53%)存在极显著差异(P<0.01);女性在HBAg阴性模式中的比例与在HBeAg阳性模式中的比例差异显著(P<0.05).HBV感染血清标志物、HBV DNA水平和性别之间存在着重要的关系;对于组合3的患者要给予足够重视;女性在高HBV DNA水平而且HBeAg阴性组合中的比例非常小,这也许与女性在肝癌患者中所占比例较低存在着一定的关系.  相似文献   
993.
N-acetylcysteine improves survival in established acute liver failure following paracetamol overdose by reducing the incidence of multiorgan failure. These benefits are thought to be related to decreased tissue hypoxia by the enhancement of both oxygen delivery and oxygen extraction. Similar findings have been recorded in critically ill patients from an alternative aetiology. The cardiovascular properties of N-acetylcysteine are to increase stroke volume index, and thus cardiac output, although there is no effect on cardiac output in normal subjects. N-acetylcysteine is known to improve myocardial contraction in a hamster model of chronic myocardial ischaemia, but such effects have not previously been described in humans. We report the beneficial circulatory effect of N-acetylcysteine in a patient with marked left ventricular dysfunction secondary to acute viral myocarditis.  相似文献   
994.
995.
Intraepithelial carcinoma of the anus in homosexual men   总被引:8,自引:8,他引:8  
Anal warts (condylomata acuminata) from seven homosexual men revealed intraepithelial carcinoma (carcinomain situ) within the condylomatous tissue or in adjacent anal mucosa. All lesions displayed morphologic evidence of papillomavirus infection and two of the seven revealed histologic changes characteristic of herpes simplex infection. This association of viral infection with malignant transformation indicates that persistent or recurrent anal warts should be excised and thoroughly examined by histologic techniques. Since four of the seven patients had histories suspicious for or diagnostic of the acquired immunodeficiency syndrome (AIDS), we further suggest that homosexual men with persistent or recurrent perianal lesons be evaluated for the presence of the syndrome.  相似文献   
996.
云南赤芍抗乙型肝炎病毒的体外实验研究   总被引:1,自引:0,他引:1  
目的:初步研究云南赤芍的抗乙型肝炎病毒(HBV)作用。方法:通过云南赤芍作用于体外培养的2.2.15细胞,观察其对2.2.15细胞两抗原分泌的影响.初步评价其抗HBV作用。结果:云南赤芍作用于2.2.15细胞12d后,药物对2.2.15细胞的半数毒性浓度为3.85g/L,对HBsAg、HBeAg的半数抑制浓度分别为<0.156g/L、0.54g/L,治疗指数分别为>24.68、7.13。结论:云南赤芍在体外细胞培养中对两抗原的分泌有较好的抑制作用。  相似文献   
997.
Hepatitis C virus (HCV) genotypes, multiple genotypes infection and HCV seroprevalence were investigated among 98 thalassemia patients and 76 haemophiliacs in Markazi province, Iran. HCV antibody was detected in 5 (5.1%) of the first group and 33 (43.4%) of the latter. Risk factors associated with anti-HCV antibody were also determined. Anti-HCV positivity in thalassemiacs were related to the number of blood transfusion units, splenectomy and duration of thalassemia. Analysis of risk factors in haemophiliacs revealed that seropositivity was significantly associated with duration of transfusion (P =0.009) and severity of disease (P = 0.000). The prevalence of HCV antibody in thalassemia subjects dropped from 8.1% to 0% after implementation of anti-HCV screening (1996). It was found that higher prevalence of HCV antibody in haemophiliacs (43.4%) compared with thalassemia patients (5.1%) correlated with clotting factor concentrates. Of the 34 seropositive haemophilia patients, HCV RNA was detected in 23 (67.7%). HCV genotype distribution was one in 50%, three in 18.2%, two in 4.54% and mixed in 27.3% (1 + 2 in 9.1%, 1 + 3 in 4.54%, 1 + 4 in 9.2% and 2 + 3a in 4.54%) cases. Among the five anti-HCV-positive thalassemiacs, two (40%) were positive for HCV RNA and one sample was found to be subtype 3a. This study confirms that multitransfused patients in Markazi province had similar genotype distribution as those previously reported form some other regions of Iran. Considering the possibilities of HCV mixed genotype among patients with haemophilia and thalassemia, accuracy and precision should be highly concerned in the detection of genotypes and their subsequent treatment.  相似文献   
998.
Assessment of prognosis from hepatitis requires liver histology. When the fibrosis stage is known, and if the fibrosis progression rate can be established, time to development of cirrhosis can be calculated. The fibrosis progression rate can be calculated from a single biopsy when duration of infection prior to biopsy is known. Sequential biopsies can also be examined. In this work, we studied histological activity and fibrosis stage in liver biopsies of 157 hepatitis C virus (HCV)-infected patients, including 92 for whom the approximate duration of infection was known. The mean fibrosis progression rate was 0.09 units per year, and was not influenced by mode of infection or viral genotype. Forty-six patients who had very mild histological changes in the initial biopsy underwent repeat biopsy 2 years later (with no intervening anti-viral treatment). Comparison of paired biopsies confirmed a tendency to histological progression and increasing hepatic fibrosis (mean, 0.15 fibrosis units per year). A normal baseline alanine aminotransferase (ALT) value was associated with slow fibrosis progression before baseline biopsy and between biopsies. These data do not differ from published cross-sectional and longitudinal studies, and suggest that histological progression will be observed during follow-up of most patients, including those with mild histological changes at time of initial assessment.  相似文献   
999.
METHODSThens3genewasobtainedfromplasmidpBns3bypolymerasechainreactionandinsertedintothecloningvectorpGEMT.Then,thens3wassubc...  相似文献   
1000.
A woman who was positive for anti-hepatitis B surface antigen (anti-HBs) and anti-hepatitis B core antigen (anti-HBc) received an orthotopic liver transplantation from an anti-HBc-seropositive donor in November 1985. Reappearance of hepatitis B surface antigen (HBsAg) was noted 5 months after the transplantation, but it was not associated with significant liver inflammation. Ten years after the transplantation, results of serum hepatitis B virus (HBV) DNA study, by nested polymerase chain reaction, were negative. However, HBV DNA was detected in the transplanted liver tissues and peripheral blood mononuclear cells. Different strains were identified in these two organs. An adw strain was found in the transplanted liver, whereas an adr strain with long segment deletions in the core gene was found in the peripheral blood mononuclear cells. Covalently closed circular HBV DNA was not detected in any of the tissues examined. Occult HBV infection in the donor as well as the recipient is common in HBV endemic areas. The recipient in this case had reappearance of hepatitis B surface antigen (HBsAg) in the serum after transplantation. Nevertheless, 10 years later, two different strains of HBV were identified in different organs, without cross infection. The present case demonstrates that HBsAg reappearance was not associated with reactivation of the virus and liver inflammation. This type of HBsAg reappearance did not appear to produce a significant hazard to the transplanted liver. Received: December 16, 1999 / Accepted: May 26, 2000  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