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   1645篇
  免费   110篇
  国内免费   19篇
耳鼻咽喉   14篇
儿科学   85篇
妇产科学   14篇
基础医学   132篇
口腔科学   32篇
临床医学   148篇
内科学   542篇
皮肤病学   46篇
神经病学   70篇
特种医学   253篇
外科学   91篇
综合类   63篇
预防医学   83篇
眼科学   29篇
药学   91篇
中国医学   9篇
肿瘤学   72篇
  2023年   7篇
  2022年   9篇
  2021年   11篇
  2020年   8篇
  2019年   21篇
  2018年   17篇
  2017年   13篇
  2016年   12篇
  2015年   24篇
  2014年   50篇
  2013年   90篇
  2012年   42篇
  2011年   42篇
  2010年   44篇
  2009年   68篇
  2008年   63篇
  2007年   80篇
  2006年   49篇
  2005年   49篇
  2004年   52篇
  2003年   46篇
  2002年   48篇
  2001年   24篇
  2000年   36篇
  1999年   35篇
  1998年   93篇
  1997年   56篇
  1996年   70篇
  1995年   48篇
  1994年   52篇
  1993年   50篇
  1992年   24篇
  1991年   24篇
  1990年   22篇
  1989年   51篇
  1988年   46篇
  1987年   40篇
  1986年   30篇
  1985年   26篇
  1984年   23篇
  1983年   21篇
  1982年   15篇
  1981年   23篇
  1980年   14篇
  1979年   12篇
  1978年   15篇
  1977年   19篇
  1976年   11篇
  1975年   12篇
  1969年   6篇
排序方式: 共有1774条查询结果,搜索用时 15 毫秒
991.
BACKGROUND: The clinically significant antigens of the Duffy (Fy [FY]) blood group system are expressed on the red cell form of the FY glycoprotein, a promiscuous chemokine receptor and also a receptor for malarial parasites. After the cloning of cDNA coding for FY glycoprotein, the molecular basis of the three major alleles (Fya/Fyb/Fy) has been established. Because of the mistyping of the silent Fy allele as Fyb, the error rate of current genotyping methods is high in black populations. STUDY DESIGN AND METHODS: Two hundred blood donors (European whites and African Blacks) and some amniotic DNA samples were investigated by a new allele-specific primer polymerase chain reaction technique. Sense primers corresponding to normal and GATA-1-mutated FY gene promoter region sequences were combined with antisense primers discriminating the Fya/Fyb polymorphism. RESULTS: Complete correlation between FY phenotypes and genotypes was obtained in all samples studied, although, in two whites and one black, serology showed weak Fyb expression while polymerase chain reaction indicated a Fyb allele. Gene frequencies were calculated. CONCLUSION: This simple and rapid polymerase chain reaction method was shown to detect the three common alleles at the FY locus in two representative ethnic populations. Its future use as an independent technique in red cell FY investigations and for fetal genotyping in hemolytic disease of the newborn is predicted.  相似文献   
992.
Monitoring of platelet counts 1 hour after transfusion has become standard practice in most centers. In this study, platelet counts obtained 10 and 60 minutes after 48 platelet transfusions were compared. There was a close, linear relationship (r = 0.98) between these values over a wide range of posttransfusion counts, indicating rapid equilibration of transfused platelets. Ten-minute posttransfusion samples are easier to obtain and are convenient for both patients and medical staff.  相似文献   
993.
BACKGROUND: Compounds generated during the routine storage of platelet concentrates may have deleterious effects on the transfusion recipient. STUDY DESIGN and METHODS: Daily plasma samples from platelet concentrates, both apheresis platelets and those separated from whole blood, were obtained serially during routine storage. These plasma samples were assayed for their ability to prime the NADPH oxidase in isolated human neutrophils. Quantitative and qualitative analysis of the priming agents was completed by lipid extraction, high-pressure liquid chromatography separation, and gas chromatography/mass spectroscopy. RESULTS: Compounds were generated in both apheresis and whole-blood platelets that significantly primed the NADPH oxidase after 24 and 48 hours of storage, respectively. The priming activity was maximal by component outdate: 2.6-fold that of the buffer-treated control neutrophils (apheresis) and 3.9-fold that of the buffer-treated control neutrophils (whole blood). These agents were generated by cellular constituents, as stored plasma did not demonstrate such priming activity. Inhibition of this priming activity by WEB 2170, a specific platelet-activating factor receptor antagonist, suggested that the observed priming involved the platelet-activating factor receptor. A portion of the priming activity from platelet concentrates was organically extractable: 69 percent of that from apheresis platelets and 46 percent of that from whole-blood platelets. Further purification of the lipid's priming activity by normal-phase high-pressure liquid chromatography demonstrated a single peak of priming activity at the retention time of lysophosphatidylcholines. Because 46 percent of the priming activity from whole-blood platelets was chloroform insoluble and because it has been reported that interleukin 8 is generated during routine storage of whole-blood platelets, the effects of interleukin 8 on the NADPH oxidase were examined. Recombinant monocyte interleukin 8 rapidly primed the oxidase but was not inhibited by WEB 2170. CONCLUSION: Lipids were generated during the routine storage of platelet concentrates that prime the NADPH oxidase, and they may play a role in the severe complications of transfusion therapy. Other non- lipid compounds, such as interleukin 8, that are generated in whole- blood platelets may also contribute to the observed priming activity of plasma.  相似文献   
994.
Organ transplant recipients (OTRs) have a 100‐fold increased risk of cutaneous squamous cell carcinoma (cSCC). We prospectively evaluated the association between β genus human papillomaviruses (βPV) and keratinocyte carcinoma in OTRs. Two OTR cohorts without cSCC were assembled: cohort 1 was transplanted in 2003‐2006 (n = 274) and cohort 2 was transplanted in 1986‐2002 (n = 352). Participants were followed until death or cessation of follow‐up in 2016. βPV infection was assessed in eyebrow hair by using polymerase chain reaction–based methods. βPV IgG seroresponses were determined with multiplex serology. A competing risk model with delayed entry was used to estimate cumulative incidence of histologically proven cSCC and the effect of βPV by using a multivariable Cox regression model. Results are reported as adjusted hazard ratios (HRs). OTRs with 5 or more different βPV types in eyebrow hair had 1.7 times the risk of cSCC vs OTRs with 0 to 4 different types (HR 1.7, 95% confidence interval 1.1‐2.6). A similar risk was seen with high βPV loads (HR 1.8, 95% confidence interval 1.2‐2.8). No significant associations were seen between serum antibodies and cSCC or between βPV and basal cell carcinoma. The diversity and load of βPV types in eyebrow hair are associated with cSCC risk in OTRs, providing evidence that βPV is associated with cSCC carcinogenesis and may present a target for future preventive strategies.  相似文献   
995.
SUMMARY This study was conducted to assess the long-term safety of fluticasone propionate 50 μg twice daily (100 μg/day) or 100 μg twice daily (200 μg/day) administered via a dry powder inhaler in children aged 4–17 years with moderately severe asthma. A total of 257 patients received open treatment for 12 months. Of these, 110 had not received treatment with fluticasone propionate in any prior study. The remaining 147 patients had completed one of two previous short-term inhaled fluticasone propionate studies. In all, 132 patients (51%) reported 273 adverse events, the pattern of which was as expected in an atopic population with asthma; only 26 (10%) of these reports were considered either certainly, probably or possibly related to study treatment. The events most commonly reported either as a single or multiple diagnosis were: asthma and related events (25%), upper respiratory tract infection (13%), and rhinitis (6%). For most patients who reported a worsening of asthma, additional therapy was all that was required to control symptoms, and they continued in the study. There was a low incidence (2%) of pharmacologically predictable adverse events. Eight patients (3%) withdrew from the study because of an adverse event, five of which events (one each of hypertension, hoarseness and asthma and two of oral candidiasis) were recorded as being possibly or probably drug-related. Sixteen adverse events reported by 15 patients (6%) were classified as serious but none was considered to be related to the study drug. Of these reports 10 (9 patients; 4%) were exacerbations of asthma requiring hospital admission; the other six adverse events were unrelated to asthma. Fluticasone propionate was thus well tolerated during long-term treatment in children, and asthma control was maintained over the 12 months.  相似文献   
996.
997.
BACKGROUND: VS and V are common red cell antigens in persons of African origin. The molecular background of these Rh system antigens is poorly understood. STUDY DESIGN AND METHODS: Red cells from 100 black South Africans and 43 black persons from Amsterdam, the Netherlands, were typed serologically for various Rh system antigens. Allele-specific polymerase chain reaction and sequencing of polymerase chain reaction products were used to analyze C733G (Leu245Val) and G1006T (Gly336Cys) polymorphisms in exons 5 and 7 of RHCE and the presence of a D-CE hybrid exon 3. RESULTS: The respective frequencies of all VS+ and of VS+ V-(r's) phenotypes were 43 percent and 9 percent in the South Africans and 49 percent and 12 percent in the Dutch donors. All VS+ donors had G733 (Val245), but six with G733 were VS- (4 V+w, 2 V-). The four VS- V+w donors with G733 appeared to have a CE-D hybrid exon 5. T1006 (Cys336) was present in 12 percent and 16 percent of donors from the two populations. With only a few exceptions, T1006, a D-CE hybrid exon 3, and a C410T (Ala137Val) substitution were associated with a VS+ V-phenotype ((C)ces or r's haplotype). Two VS+ V-individuals, with the probable genotype, (C)ces/(C)ces), were homozygous for G733 and for T1006. CONCLUSIONS: It is likely that anti-VS and anti-V recognize the conformational changes created by Val245, but that anti-V is sensitive to additional conformational changes created by Cys336.  相似文献   
998.
目的探讨彩色及频谱多普勒技术在诊断下肢动脉闭塞性疾病的价值。方法对52例87条临床拟诊断下肢动脉闭塞性疾病的血管进行彩色多普勒超声检查,并与CT血管成像对照。结果彩色多普勒血流显像可以直观地显示动脉管壁情况、管腔回声及血流充盈情况,频谱多普勒可以显示血流动力学改变。诊断的准确率分别为动脉硬化和(或)闭塞症100%、动脉栓塞92%、血栓闭塞性脉管炎84%。结论彩色多普勒超声诊断下肢动脉闭塞性疾病是一种敏感、准确、方便的诊断方法。  相似文献   
999.
目的 观察不同呼气末正压(PEEP)水平对机械通气患者中心静脉压(CVP)和髂总静脉压(CIVP)及两者相关关系的影响.方法 将2007年2-8月收住重症加强治疗病房(ICU),无心肺疾患、循环稳定、无腹胀、无凝血功能异常,需机械通气的20例成年患者列为观察对象,采用自身对照,随机加用0、5和10 cm HzO(1 am H2O=0.098 kPa)PEEP,评估在此条件下,CVP、CIVP和两者压力阶差变化及其与机械通气压力变化间的相关关系.结果 CVP及CIVP随PEEP增加而增高,差异有统计学意义(P0.05);CVP及CIVP与机械通气各压力值变化呈正相关,但CVP及CIVP仅与平均气道压(Pmean)及PEEP有统计学意义(CVP与PEEP r=0.751,CIVP与PEEP r=0.685,CVP与Pmean r=0.634,CIVP与Pmena r=0.603,P均相似文献   
1000.
Mullen  CA; Anderson  KD; Blaese  RM 《Blood》1993,82(10):2961-2966
This study describes the effects of two major treatment options, splenectomy and/or bone marrow transplantation, on the natural history of the Wiskott-Aldrich (WAS) syndrome. The records of 62 patients with the WAS evaluated at the National Institutes of Health Clinical Center from 1966 to 1992 were reviewed. Nineteen patients were treated with bone marrow transplantation (BMT) and the results were largely dependent on the source of the graft. Twelve of 12 patients receiving HLA-matched sibling marrow achieved satisfactory immunologic and hematologic reconstitution. By contrast, only 2 of 7 patients receiving haploidentical, parental, or matched unrelated marrow survived more than 1 year after BMT. Thirty-nine patients who lacked suitable bone marrow donors early in their course underwent splenectomy for management of their thrombocytopenia; most received prophylactic antibiotics to minimize the risk of sepsis. Nearly all these patients achieved normal platelet counts and the rate of serious bleeding was reduced nearly sevenfold. Median survival in the untransplanted splenectomy group was 25 years, compared with less than 5 years in unsplenectomized patients. We conclude that HLA-matched sibling donor BMT is the treatment of choice for patients with WAS and that splenectomy and daily prophylactic antibiotics provide a significant survival advantage to those boys without a matched sibling donor. Splenectomy should probably be used in preference to unmatched BMT until results with alternative donor BMT significantly improve or gene therapy becomes available.  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