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   200546篇
  免费   15243篇
  国内免费   4530篇
耳鼻咽喉   1702篇
儿科学   2615篇
妇产科学   3074篇
基础医学   24206篇
口腔科学   3541篇
临床医学   16889篇
内科学   23529篇
皮肤病学   2197篇
神经病学   12487篇
特种医学   16623篇
外国民族医学   1篇
外科学   15971篇
综合类   26814篇
现状与发展   21篇
一般理论   8篇
预防医学   15061篇
眼科学   3256篇
药学   26031篇
  57篇
中国医学   12725篇
肿瘤学   13511篇
  2024年   253篇
  2023年   2256篇
  2022年   3537篇
  2021年   7952篇
  2020年   6512篇
  2019年   6224篇
  2018年   6489篇
  2017年   7236篇
  2016年   7514篇
  2015年   7001篇
  2014年   8648篇
  2013年   12202篇
  2012年   10639篇
  2011年   12690篇
  2010年   8424篇
  2009年   8637篇
  2008年   10101篇
  2007年   10880篇
  2006年   10256篇
  2005年   9394篇
  2004年   8000篇
  2003年   7133篇
  2002年   5656篇
  2001年   5096篇
  2000年   4177篇
  1999年   3525篇
  1998年   2795篇
  1997年   2832篇
  1996年   2516篇
  1995年   2219篇
  1994年   2132篇
  1993年   1765篇
  1992年   1617篇
  1991年   1505篇
  1990年   1302篇
  1989年   1072篇
  1988年   1033篇
  1987年   931篇
  1986年   859篇
  1985年   1243篇
  1984年   998篇
  1983年   752篇
  1982年   775篇
  1981年   642篇
  1980年   620篇
  1979年   496篇
  1978年   319篇
  1977年   270篇
  1976年   262篇
  1975年   189篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
The colour reaction of 4-hydroxyiminomethyl-1-methylpyridinium chloride (PAM-4Cl) and palladium(II) chloride has been investigated. The optimum reaction conditions, spectral characteristics, conditional stability constant and composition of the yellow water-soluble complex have been established. A new spectrophotometric method is proposed for the microdetermination of PAM-4Cl.  相似文献   
992.
脾虚和肾虚雌性大鼠生育能力的实验观察   总被引:18,自引:2,他引:16  
为系统观察脾虚和肾虚雌性SD大鼠的生育能力,将大鼠随机分为:脾虚组、脾虚复健组、肾虚组、肾虚复健组、正常组。脾虚组和肾虚组分别按常规方法用利血平和羟基脲制成脾虚模型和肾虚模型。虚证动物模型出现与人类相似的症状:动情周期紊乱,甚至消失;生殖器官萎缩;血清卵泡刺激素(FSH)、雌二醇(E2)水平下降;子宫腺体数目减少,卵巢次级和成熟卵泡数减少,生育能力下降。而肾虚大鼠上述变化更显著。用四群子喂饲脾虚模  相似文献   
993.
Abstract  We previously demonstrated that cytomegalovirus (CMV) infection enhanced perivascular inflammation in rat aortic allografts. In this study, we investigated the relationship between the CMV infection load and the magnitude of perivasculitis (chronic rejection) in aortic transplants. Rats received or-thotopic abdominal aortic grafts, different degrees of total body irradiation (TBI) for immunosuppres-sion and CMV inoculation. The spleens of the rats receiving 5 Gy of TBI contained more infectious virus and viral antigens than those of rats receiving 3 Gy of TBI or no TBI. Although the number of inflammatory cells infiltrating the perivascular area was decreased after TBI, CMV infection resulted in increased perivasculitis in rats that received 5 Gy of TBI as compared to non-infected animals. This virus-induced effect was characterized predominantly by an increased T-cell infiltration, including CD4 and CD8 T-cells. It is concluded that an enhanced systemic CMV infection during severe immunosuppressive therapy can accelerate the development of chronic rejection, which seems to be mediated mainly by T-cells.  相似文献   
994.
Zinc(II) phthalocyanine is the active component of the liposomal formulation CGP 55847 which showed a high activity in photodynamic therapy in a variety of animal tumours. The photophysical properties of zinc(II) phthalocyanine have been studied in detail and compared to those of Photofrin, the only sensitizing agent approved so far for phase III/IV clinical trials. Since the efficacy of photodynamic therapy intrinsically depends on the spectroscopic features of the sensitizer, quantum chemical methods have proven to be an efficient means for optimizing chemical structures. As will be shown, a simple modification of the time-honoured INDO model of Pople allows a prediction of the singlet and triplet state properties of molecules of the size of zinc(II) phthalocyanine with an rms error of ≤ 1000 cm−1.  相似文献   
995.
Summary The renin-angiotensin system relevantly contributes to the maintenance of systemic vascular tone and there is experimental evidence that large amounts of angiotensin-converting enzyme (ACE) are present in peripheral vascular tissues, including resistance vessels. To determine and quantify peripheral vascular conversion of angiotensin-I (ANG-I) to angiotensin-II (ANG-II) across the human leg, the response of regional blood flow to local regional intra-arterial infusion of ANG-I and changes in associated ANG-I1 balance were evaluated during ANG-I infusion and following additional ACE inhibition. Ten sodium-loaded healthy men were enrolled in the study. Following cannulation of both femoral arteries and the right femoral vein, leg blood flow was determined (indocyanine-green dye-dilution method) at baseline conditions and during constant intra-arterial infusion of haemodynamically ineffective doses of ANG-I as well as following concomitant intra-arterial administration of low doses of the non-sulfhydril ACE inhibitor cilazapril. From the transfemoral arterio-venous differences in ANG-II plasma concentrations and the corresponding regional blood (plasma) flow, the ANG-II balance across the leg was calculated. Systemic blood pressure did not change throughout the trial, indicating that no major systemic effects were present during ANG-I infusion or concomitant ACE inhibition. Moreover, arterial ANG-II plasma concentrations were not significantly changed by ANG-I infusion. Leg blood flow decreased to below baseline values following ANG-I infusion, increasing again then in a dose-dependent manner during concomitant cilazapril administration. The calculated baseline ANG-II balance across the leg revealed a net extraction in 6 out of 10 subjects and a net ANG-II formation in 4. Following ANG-I, a shift towards net ANG-II formation or decrease in extraction was seen in 8 subjects, while 2 had no change in ANG-II balance.During concomitant ACE inhibition, ANG-II balance was again shifted towards net extraction or reduced formation. Our results confirm that, in man, considerable regional arterio-venous differences in ANG-II plasma concentrations are present, resulting in either net transfemoral extraction or net formation of the peptide. It is suggested that systemic vascular conversion of circulating ANG-I might contribute to the maintenance of peripheral vasuclar tone in man. Send offprint requests to S. Gasic at the above address  相似文献   
996.
BACKGROUND: Although 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), a product of 15-lipoxygenase (15-LO), may be involved in mild to moderate asthma, little is known about its potential roles in severe asthma. OBJECTIVES: This study was performed to evaluate 15(S)-HETE levels in bronchoalveolar lavage fluid (BALF) from severe asthmatics with and without airway eosinophils and from the control groups. In addition, 15-LO protein expression was examined in endobronchial biopsy, while its expression and activation were evaluated in BAL cells. RESULTS: While 15(S)-HETE levels in BALF were significantly higher in all severe asthmatics than normal subjects, severe asthmatics with airway eosinophils had the highest levels compared with mild, moderate asthmatics and normal subjects. 15(S)-HETE levels were associated with tissue eosinophil numbers, sub-basement membrane thickness and BALF tissue inhibitor of metalloproteinase-1 levels, and were accompanied by increased 15-LO expression in bronchial epithelium. In addition, activation of 15-LO was suggested by the increased proportion of 15-LO in the cytoplasmic membrane of alveolar macrophages from severe asthmatics. CONCLUSION: The data suggest that severe asthmatics with persistent airway eosinophils manifest high levels of 15(S)-HETE in BALF, which may be associated with airway fibrosis. It is likely that 15-LO expression and activation by airway cells explain the increased 15(S)-HETE levels.  相似文献   
997.
2,6—二叔丁基对甲酚对大鼠尿生化指标的影响   总被引:2,自引:0,他引:2  
以20,60和180mg/kg体重剂量给大鼠喂食2,6-二叔丁基对甲酚(BHT),检测尿中AST、ALP、LDH和GGT等指标变化。结果表明:随染毒时间延长,各尿酶含量逐渐出现显著性增高,病理学检查发现高剂量组有1例间质性肾炎,提示BHT对肾功能可能产生有害作用。  相似文献   
998.
男性不育症患者中YRRM2基因缺陷的研究   总被引:2,自引:1,他引:1  
YRRM基因是控制精子生成与成熟的一个重要因素,一旦该基因缺陷,将会造成无精或少精。本研究对340例无精与少精患者的外周血标本进行了PCR基因扩增筛查,结果发现7例为该基因缺陷,占2%。证明YRRM2的缺陷也是造成中国人群男性不育的一个原因,从而可作为指导医生采用适当治疗方法的一个可靠指标。在实验过程中,采用直接加热白细胞提取基因组DNA,并以此作为模板对YRRM2基因进行扩增,既节省时间和经费,又保持良好的扩增效果,使之可用于临床医院作为常规检查。  相似文献   
999.
为探讨醇脱氢酶(ADH)基因和醛脱氢酶(ALDH)基因多态性与酒依赖患病的相互关系,用耳血干血痕聚合酶链反应、等位基因特异性寡核苷酸探针方法,检测乙醇代谢酶ADH和ALDH基因型在我国蒙、汉民族酒依赖与非酒依赖者中分布频率。结果显示在酒依赖组(汉族52例,蒙族31例)与正常对照组(汉族48例,蒙族35例)之间:汉族的ALDH2基因型频率与等位基因频率的分布差异有非常显著性(P<0.01),而蒙族则表示为ADH2基因型频率与等位基因频率的分布差异有非常显著性(P<0.01)。这提示汉族酒依赖的发病与ALDH2基因有关,蒙族则与ADH2基因有关。  相似文献   
1000.
膈疝的CT诊断价值(附15例分析)   总被引:3,自引:0,他引:3  
目的:探讨膈疝的CT诊断及其临床手术指导价值。方法:通过以横膈部位为中心行胸腹部螺旋CT扫描,获得理想的CT扫描图像,通过15例膈疝患者的扫描图像,结合临床综合分析。结果:膈上有疝囊15例,囊内有液平面13例,有小肠及结肠肠型的1例,有脂肪组织1例,胸腔内有积液2例。结论:CT检查对膈疝的诊断应当作为首选的检查方法,其不仅能对膈疝做出正确的诊断,而且,对临床手术指导具有重要的临床治疗意义。  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