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   28266篇
  免费   2955篇
  国内免费   2051篇
耳鼻咽喉   168篇
儿科学   214篇
妇产科学   260篇
基础医学   3304篇
口腔科学   421篇
临床医学   3929篇
内科学   3909篇
皮肤病学   258篇
神经病学   1492篇
特种医学   1277篇
外国民族医学   18篇
外科学   3004篇
综合类   5188篇
现状与发展   14篇
一般理论   4篇
预防医学   1927篇
眼科学   686篇
药学   2992篇
  41篇
中国医学   1847篇
肿瘤学   2319篇
  2024年   99篇
  2023年   471篇
  2022年   1245篇
  2021年   1752篇
  2020年   1328篇
  2019年   1149篇
  2018年   1120篇
  2017年   1012篇
  2016年   948篇
  2015年   1362篇
  2014年   1756篇
  2013年   1558篇
  2012年   2220篇
  2011年   2344篇
  2010年   1470篇
  2009年   1161篇
  2008年   1389篇
  2007年   1378篇
  2006年   1356篇
  2005年   1280篇
  2004年   839篇
  2003年   886篇
  2002年   811篇
  2001年   642篇
  2000年   625篇
  1999年   634篇
  1998年   394篇
  1997年   392篇
  1996年   270篇
  1995年   272篇
  1994年   238篇
  1993年   155篇
  1992年   151篇
  1991年   145篇
  1990年   84篇
  1989年   75篇
  1988年   83篇
  1987年   59篇
  1986年   32篇
  1985年   23篇
  1984年   22篇
  1983年   12篇
  1982年   4篇
  1981年   9篇
  1980年   2篇
  1979年   7篇
  1978年   3篇
  1972年   2篇
  1970年   1篇
  1968年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
自1991年11月到1992年2月,用酶联免疫吸附试验对延边地区87例各种肝病患者.65例HBsAg携带者及5例单项ALT增高者血清共157份进行了抗-HCV检测.33例呈阳性,总阳性率为21.0%,其中单项ALT增高者高达80.O%.其次.急性肝炎为35.2%.慢性迁延性肝炎为18.2%.HBsAg携带者为6.2%,肝硬化为0%.  相似文献   
92.
Background. Heparin bonding of the cardiopulmonary bypass (CPB) circuit may be associated with a reduced inflammatory response and improved clinical outcome. The relative contribution of a heparin-bonded oxygenator (ie, >80% of circuit surface area) to these effects was assessed in a group of pediatric patients.

Methods. Twenty-one pediatric patients undergoing CPB operations were assigned randomly to receive either a heparin-bonded oxygenator (group H, n = 11) or a nonbonded oxygenator (group C, n = 10) in otherwise nonbonded circuits. The two groups were similar in pathology, age, weight, CPB time, and cross-clamp time. Plasma levels of the cytokines tumor necrosis factor-, interleukin-6, and interleukin-8, as well as terminal complement complex, neutrophils, and elastase, were analyzed before, during, and after CPB.

Results. Significant levels of tumor necrosis factor- were not detected in either group. Plasma levels of all other markers increased during and after CPB compared with baseline. Plasma levels of interleukin-6 peaked in both groups 2 hours after the administration of protamine but remained significantly higher in group C 24 hours after operation. Plasma concentrations of interleukin-8 peaked at similar levels in both groups 30 minutes after protamine administration and returned to baseline thereafter. Levels of terminal complement complex and elastase peaked in both groups 30 minutes after protamine administration. Plasma levels of terminal complement complex were significantly higher at the end of CPB and after protamine administration in group C. Elastase levels were significantly higher 2 and 24 hours after CPB in group C. The ventilation time of patients in group H was significantly lower than that of patients in group C: 10 (range, 3 to 24) versus 22 (range, 7 to 24) hours, respectively (p < 0.01).

Conclusions. The present study confirms the proinflammatory nature of pediatric operations and demonstrates a lessened systemic inflammatory response with the use of heparin-bonded oxygenators. This is achieved without bonding of the entire circuit, which could have significant cost-benefit implications by negating the need for custom-built heparin-bonded circuitry.  相似文献   

93.
OBJECTIVE: This study was conducted to investigate the effect of MgO additive to Al2O3 on the flexural strength, fracture toughness of glass infiltrated alumina for CAD/CAM application. METHODS: Alumina blanks with additive of 0.5 wt% MgO were prepared via isostatic pressing and sintering at 1400 degrees C for 2h, and then alumina-glass composites were fabricated by infiltrating the molten glass into the partially sintered alumina compact. Flexural strength and fracture toughness were determined using three point bending methods and a single edge notched beam method. The mechanism of crack propagation was observed under a field emission scanning electron microscope. RESULTS: The three-point flexural strength and fracture toughness of partially sintered alumina and alumina-glass composite were 210 MPa, 1.86 MPam(1/2), and 432.2 MPa, 5.12 MPam(1/2), respectively, and they were free of shrinkage during the processing of glass infiltration. The field emission SEM micrograph indicated that indentation caused a non-planar crack propagation including crack deflection and crack bowing. SIGNIFICANCE: MgO was used as an additive to alumina to improve the strength and fracture toughness of partially sintered alumina and alumina-glass composite. The high strength and toughness are related to toughening by the distribution of alumina with uniform particle sizes, crack bowing, crack deflection and the beneficial wetting properties of the particle surface.  相似文献   
94.
目的:观察人牙胚组织中成釉蛋白的表达特点。方法:实验于2002-02/04在解放军第四军医大学口腔内科实验室完成。取孕5个月流产男性胎儿(产妇知情同意),截取上、下颌骨,常规方法制备人牙胚组织石蜡切片。用兔抗人AMBN多克隆抗体,对人牙胚组织石蜡切片和正常狗牙周组织石蜡切片进行免疫组织化学染色。标记人成釉蛋白cDNA探针,对人牙胚组织石蜡切片进行原位杂交。结果:①免疫组织化学染色发现成釉蛋白由内釉上皮细胞在分化为成熟成釉细胞前开始表达,分泌期成釉细胞高度表达并持续整个釉质形成期,新形成的牙釉质染色阳性;成牙本质细胞在分泌牙本质基质之前开始表达成釉蛋白,在牙本质形成过程中成牙本质细胞持续表达成釉蛋白,呈弱阳性,前期牙本质中呈弱阳性染色;上皮根鞘细胞染色阳性。狗牙周组织染色发现牙骨质表层细胞呈强阳性染色,新形成的牙骨质中可见阳性染色颗粒,呈网状分布。②对人牙胚组织石蜡切片的原位杂交显示,成釉蛋白在成釉细胞、成牙本质细胞、上皮根鞘细胞中有表达,表达部位与免疫组织化学结果一致。结论:内釉上皮首先表达成釉蛋白,之后前成牙本质细胞达成釉蛋白。成釉细胞、成牙本质细胞、上皮根鞘细胞表达成釉蛋白。  相似文献   
95.
Introduction There is now increasing evidence that proximal tubular cells (PTCs) contribute to renal interstitial fibrosis by alteration of matrix turnover and by the generation of pro‐fibrotic cytokines such as TGF‐β1. Recent studies suggest that, through a process of transdifferentiation, the PTCs are one source of the interstitial myofibroblasts that directly drive the fibrotic process. The aim of this work was to examine the role and mechanism by which TGF‐β1 may regulate PTC phenotype and function. Methods Experiments were performed using both primary‐cultures of PTC and the human PTC cell line HK2. All experiments were performed on growth‐arrested cells in the absence of serum. Results TGF‐β1 altered cell phenotype, assessed by light microscopy, with cells appearing elongated and spindle‐shaped. This was associated with loss of cell–cell contact and rearrangement of the actin cytoskeleton, increased formation of stress fibres and focal adhesions. Disruption of the actin cytoskeleton with cytochalasin‐D prevented phenotypic alterations following addition of TGF‐β1. Transient transfection with Smad‐2/‐4 or Smad‐3/‐4 expression vectors did not alter cell phenotype. Previously, we have demonstrated β‐catenin translocation to PTC nuclei and its association with Smad proteins following addition of TGF‐β1, suggesting the possibility that TGF‐β1 may modulate Wnt signalling. Wnt‐responsive Xtwn‐reporter construct was, however, silent in response to TGF‐β1. Similarly, a second Wnt‐/LEF‐1‐regulated element Toplflash, which does not contain Smad‐binding sites, was insensitive to TGF‐β1 signalling. In contrast, phenotypic changes in response to TGF‐β1 were abrogated by inhibitors of the RhoA downstream target ROCK, which also prevented loss of cell–cell contact and adherens junction disassembly. Removal of TGF‐β1 and addition of 1% FCS, however, reverted cell phenotype to a typical cobblestone epitheliod appearance, suggesting that TGF‐β1 did not result in terminal PTC transdifferentiation. Cells grown on tissue culture dishes coated with either type‐I or type‐III collagen also acquired an elongated fibroblastic phenotype; this effect was exaggerated by the addition of TGF‐β1. In contrast to the cells stimulated with TGF‐β1 alone, following stimulation by both TGF‐β1 and exposure to interstitial collagens, cell phenotype was stable in that it was not reversed upon removal of TGF‐β1 and addition of FCS. Addition of TGF‐β1 to cells grown on type‐IV collagen had no greater effect than TGF‐β1 alone. Addition of TGF‐β1 alone had little effect on the expression of α‐SMA. In contrast, cells grown on either type‐I or type‐III collagen, following addition of TGF‐β1, demonstrated marked increased expression of α‐SMA, which appeared to be incorporated into the cell cytoskeleton. Similarly, the combination of interstitial collagen (either type‐I or type‐III) and TGF‐β1 had synergistic effect on the relocation and down‐regulation of the epithelial markers E‐cadherin and cytokeratin. Finally, the results demonstrated synergistic effects of coating with interstitial collagen (either type‐I or type‐III), on cell ‘fibroblastic’ cell function as assessed by cell migration and by the synthesis of type‐III and type‐IV collagen. Conclusion The results of these in vitro experiments suggest that terminal transdifferentiation of proximal tubular epithelial cells is the result of a combination of the effects of the pro‐fibrotic cytokine TGF‐β1 and exposure of the cells to components of the interstitial extra‐cellular matrix to which the cells are not exposed in the absence of damage to the tubular basement membrane.  相似文献   
96.
MUC1粘蛋白在进展期胃癌中的表达及临床意义   总被引:2,自引:0,他引:2  
目的检测MUC1粘蛋白在进展期胃癌中的表达,探讨其对胃癌预后的意义.方法采用免疫组化SP法,应用抗MUC1粘蛋白核心蛋白抗体(DF3抗体)检测60例胃癌根治标本及对照组20例胃正常黏膜组织标本MUC1粘蛋白表达.采用χ2检验及Kaplan-Meier生存曲线进行统计分析.结果 MUC1粘蛋白阳性表达率55%(33/60).有淋巴结转移胃癌组MUC1粘蛋白阳性表达率为71.0%(22/31),无淋巴结转移组MUC1粘蛋白阳性表达率为37.9%(11/29),组间差别显著(P<0.05).按PTNM分期,Ⅰ期胃癌的MUC1粘蛋白阳性表达率为20%,Ⅱ期表达率68.8%,Ⅲ期表达率53.3%,Ⅳ期表达率78.6%,Ⅰ期与Ⅱ、Ⅲ、Ⅳ期间存在显著统计学差异(P<0.05).经Kaplan-Meier法生存曲线统计表明,MUC1阳性表达组5年生存状况较MUC1阴性组差(Log-Rank检验,P=0.037).结论在进展期胃癌中MUC1粘蛋白表达与淋巴结转移相关,随着胃癌的进展MUC1表达呈上升趋势;MUC1粘蛋白表达提示预后不良.  相似文献   
97.
呼吸机相关肺炎的发生原因及护理对策探讨   总被引:1,自引:0,他引:1  
目的 为进一步探讨发生呼吸机相关肺炎的因素和护理措施。方法 对 70例使用机械通气辅助治疗的重症监护病房 (ICU)病人 ,取深部痰液进行细菌培养与分离及药敏试验 ,并采用综合护理措施。结果  70例患者除 4例因原发病病情恶化死亡外 ,无一例因呼吸机相关肺炎而导致病情恶化 ,延误治疗 ,且缩短了住院时间。结论 正确的气道管理 ,合理应用抗生素 ,良好的饮食护理等辅助治疗 ,能够降低呼吸机相关因素肺炎的发病率  相似文献   
98.
[目的]探讨切除侵犯中颅窝的咽旁颞下区巨大肿瘤安全而彻底的手术进路.利用颞部切口可充分暴露中颅窝底和颞下窝以及颌下进路显露咽旁区解剖的特点,联合进路切除2例咽旁颞下区巨大肿瘤.2例侵犯中颅窝底的咽旁颞下区肿瘤顺利切除,患者术中组织损伤、出血量相对较少,术后无严重并发症.[结论]颞部-颌下联合进路适合于侵犯中颅窝底的咽旁颞下区肿瘤的手术切除.  相似文献   
99.
Inactivated whole avian influenza virus (AIV) vaccine provides protection against homologous haemagglutinin (HA) subtype virus, but poor protection against a heterologous HA virus. Moreover, it induces chickens to produce antibodies to cross-reactive antigens, especially nucleoprotein, which is limits AIV serological surveillance. In this study, a recombinant fowlpox virus co-expressing HA (H5 subtype) and NA (N1 subtype) genes of AIV was evaluated for its ability to protect chickens against intramuscular challenge with a lethal dose of highly pathogenic (HP) AIV. Susceptible chickens were also vaccinated by wing-web puncture with the parent fowlpox vaccine virus. Following challenge 4 weeks later with HPAIV, all chickens vaccinated with recombinant virus were protected, while the chickens vaccinated with either the unaltered parent fowlpox vaccine virus or unvaccinated controls experienced 100% mortality following challenge. This protection was accompanied by the high levels of specific antibody to the respective components of the recombinant vaccine. The above results showed that rFPV-HA-NA could be a potential vaccine to replace current inactivated vaccines for preventing AI.  相似文献   
100.
经直肠超声引导前列腺穿刺活检203例临床分析   总被引:8,自引:1,他引:7  
目的评估经直肠超声引导的前列腺六针穿刺活检在前列腺癌及前列腺其他疾病的诊断和鉴别诊断的价值。方法对指肛检查阳性,血清PSA〉4pg/L及经直肠超声检查前列腺声像图异常怀疑有占位性病变的203人进行经直肠超声引导的前列腺穿刺活检。结果穿刺活检的203例病理结果:良性前列腺增生(BPH)104例占51.24%,前列腺癌(PCa)95例占46.80%,前列腺结核及前列腺平滑肌肉瘤各2例,分别占0.98%。结论经直肠超声引导的前列腺穿刺活检其操作简单,病人痛苦小,并发症少,较安全。在前列腺癌及其他前列腺疾病的诊断与鉴别诊断中有重要的临床价值。  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