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   82228篇
  免费   5956篇
  国内免费   3739篇
耳鼻咽喉   349篇
儿科学   1480篇
妇产科学   846篇
基础医学   13044篇
口腔科学   1671篇
临床医学   6910篇
内科学   14436篇
皮肤病学   1027篇
神经病学   7728篇
特种医学   1309篇
外国民族医学   15篇
外科学   4817篇
综合类   13981篇
现状与发展   22篇
预防医学   4815篇
眼科学   966篇
药学   10539篇
  9篇
中国医学   2593篇
肿瘤学   5366篇
  2024年   146篇
  2023年   833篇
  2022年   2152篇
  2021年   2979篇
  2020年   2387篇
  2019年   2048篇
  2018年   2018篇
  2017年   2337篇
  2016年   2670篇
  2015年   3020篇
  2014年   5076篇
  2013年   5680篇
  2012年   5388篇
  2011年   6019篇
  2010年   4764篇
  2009年   4626篇
  2008年   4751篇
  2007年   4609篇
  2006年   4138篇
  2005年   3893篇
  2004年   3183篇
  2003年   2717篇
  2002年   2081篇
  2001年   1783篇
  2000年   1543篇
  1999年   1321篇
  1998年   1226篇
  1997年   1073篇
  1996年   918篇
  1995年   733篇
  1994年   702篇
  1993年   590篇
  1992年   507篇
  1991年   477篇
  1990年   397篇
  1989年   310篇
  1988年   295篇
  1987年   287篇
  1986年   259篇
  1985年   362篇
  1984年   317篇
  1983年   211篇
  1982年   244篇
  1981年   191篇
  1980年   164篇
  1979年   109篇
  1978年   91篇
  1977年   77篇
  1976年   67篇
  1975年   53篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
A protein C deficient woman, with a past history of recurrent thrombosis and purpura fulminans, was successfully treated with protein C concentrate in the peripartum period. © 1992 Wiley-Liss, Inc.  相似文献   
192.
We identified and characterized a neurodifferentiation compound from the marine brown alga Sargassum fulvellum collected from the Japanese coastline. Several instrumental analyses revealed the compound to be pheophytin a. Pheophytin a did not itself promote neurite outgrowth of PC12 cells. However, when PC12 cells were treated with a low concentration of pheophytin a (3.9 microg/ml) in the presence of a low level of nerve growth factor (10 ng/ml), the compound produced neurite outgrowth similar to that produced by a high level of nerve growth factor (50 ng/ml). Pheophytin a also enhanced signal transduction in the mitogen-activated protein kinase signaling pathway, which is also induced by nerve growth factor. The effect of pheophytin a on neurite outgrowth of PC12 cells was completely blocked by U0126, a representative mitogen-activated protein kinase kinase inhibitor. These results suggest that pheophytin a enhances the neurodifferentiation of PC12 cells in the presence of a low level of nerve growth factor and that this effect is mediated by activation of a mitogen-activated protein kinase signaling pathway.  相似文献   
193.
目的观察褪黑素(MT)对ANP大鼠肺组织趋化因子巨噬细胞炎性蛋白-2(MIP-2)表达的影响,探讨MIP-2在ANP相关肺损伤发病机制中的作用。方法35只SD大鼠随机分为假手术组(SO组),ANP 3h、6h、12h组和MT 3h、6h、12h组,每组5只。采用4%牛磺胆酸钠胰胆管逆行注射制备ANP动物模型,MT组在ANP诱导前30min腹腔注射MT 20mg/kg体重。检测血淀粉酶,观察肺组织病理学改变,采用实时定量RT-PCR法和免疫组化检测肺组织中MIP-2 mRNA和蛋白的表达。结果与SO组相比,ANP 3h、6h和12h组肺组织MIP-2 mRNA表达分别增加48%,137%和230%。ANP组MIP-2蛋白表达量分别为3.40±0.84,5.80±0.55和6.40±0.45。MT干预组肺组织损伤得到改善,MIP-2 mRNA表达分别为ANP相应时间点的87%,77%和84%,MIP-2蛋白表达分别为2.20±0.84.4.20±0.45和5.20±0.50,与ANP相应时间点比较,相差显著(P<0.05)。结论MIP-2在ANP相关肺损伤发病中起一定作用,MT可能通过下调MIP-2的表达以减轻ANP相关肺损伤的程度。  相似文献   
194.
A novel gene therapy approach for treating damaged cartilage is proposed that involves placing endotoxin-free cDNA containing the gene for bone morphogenetic protein-2 (BMP-2) in type I collagen sponges and then transferring the naked plasmid DNA construct to the injury site. A full-thickness cartilaginous defect in rabbits implanted with plasmid containing a marker gene (beta-galactosidase) showed expressed protein as detected by immunostaining. At 1 week postimplantation, mesenchymal cells subjacent to the defect had incorporated the implanted naked plasmid DNA and, once transfected, served as local bioreactors, transiently producing the gene product. Plasmids containing the gene for BMP-2 implanted in collagen sponges in cartilage lesions stimulated hyalinelike articular cartilage repair at 12 weeks postimplantation, nearly equivalent in quality to that induced by collagen sponges with recombinant BMP-2 protein. Our approach circumvents the risks of inflammation and immunogenic response associated with the use of viral vectors. Naked plasmid DNA as a vehicle for transferring therapeutic genes has been shown to be effective in a therapeutic model within rabbit articular cartilage and appears to be safe and cost effective.  相似文献   
195.
禁食对蛋鸡肝脏腺苷-磷酸激活的蛋白激酶活性的影响   总被引:4,自引:0,他引:4  
腺苷 -磷酸 (AMP)激活的蛋白激酶 (AMP- acti-vated protein kinase,AMPK)是丝氨酸激酶家族的一员 ,由 AMP和其上游激酶 AMPK激酶所活化 ,对细胞内 AMP/ATP的变化非常敏感 [1] ,被称为真核细胞的“代谢感受器”[2 ]。研究发现在跑步 [3 ,4 ]、电刺激肌肉 [5,6]或禁食应激后 [7] ,大鼠肝脏和肌肉中的AMPK活性升高数倍 ,乙酰辅酶 A羧化酶 (ACC)活性显著下降甚至丧失 ,丙二酸单酰辅酶 A产量降低甚至为零 ,脂肪酸合成受抑。同时 ,AMPK活化后 ,脂肪酸的氧化率显著提高 ,CO2 和酮体生成量明显增加[4 ,8] 。这些均表明 ,AMPK活化…  相似文献   
196.
目的探讨温度、抗凝剂(EDTA-K2)对血嗜酸性粒细胞阳离子蛋白(ECP)水平的影响。方法采用固相双位点酶放大化学发光法,分别对22例健康体检者在两种不同温度(25℃和37℃)的血清标本,以及在相同温度(37℃)下,加抗凝剂和不加抗凝剂的血标本进行ECP水平测定。结果25℃组和37℃组血清ECP水平分别为8.92±6.45μg/L(x±s)和19.87±12.16μg/L(x±s),两组有显著性差异(P<0.01);37℃温度下加抗凝剂和不加抗凝剂血标本的ECP水平分别为5.26±2.60μg/L(x±s)和19.87±12.16μg/L(x±s),两组也有显著性差异(P<0.001)。结论温度和抗凝剂(EDTA-K2)对血标本的ECP水平测定有不同程度的影响。  相似文献   
197.
【目的】探讨不稳定性心绞痛 (UA)病变程度及其预后与血浆肌钙蛋白I (cTnI)及C反应蛋白(CRP)水平的关系。【方法】测定 5 8例经选择性冠状动脉造影证实为冠心病的患者血浆cTnI及CRP浓度 ,并与对照组 (健康者 5 0例 )相比较 ,分析cTnI及CRP的临床意义。【结果】①血浆cTnI及CRP浓度在对照组、稳定性心绞痛组 (SA)、UA组分别为 :(0 4 2± 0 0 6 ) μg/L ,(2 2 93± 10 8) μg/L ;(0 5 9± 0 13) μg/L ,(5 2 16± 32 8) μg/L ;(1 92± 0 5 8) μg/L ,(13811± 86 1) μg/L ;SA组及UA组明显高于对照组 (分别为P <0 0 5 ,P<0 0 1)。②观察 4w ,在UA组心脏事件发生率为 35 5 % ,明显高于SA组 (P <0 0 5 )。③cTnI与CRP具有一定相关性 (r =0 5 1,P <0 0 5 )。【结论】血浆cTnI及CRP水平在临床评价UA病情程度及预后方面具有一定的指导意义  相似文献   
198.
BACKGROUND: Synapsin III plays a role in neuronal plasticity and maps to chromosome 22q12-13, a region suggested to be linked to schizophrenia. To determine if synapsin III plays a role in this disease, we searched for polymorphisms in this gene in patients with schizophrenia and controls. METHODS: The synapsin III gene was initially sequenced from 10 individuals with schizophrenia to identify polymorphisms. Association analysis was then performed using 118 individuals with schizophrenia and 330 population controls. Synapsin III expression was studied by immunoblot analyses, and phosphorylation sites were mapped by sequencing trypsin-digested synapsin III fragments phosphorylated with phosphorus-32. RESULTS: A rare, missense polymorphism, S470N, was identified in the synapsin III gene and appeared more frequently in individuals with schizophrenia than in controls (p =.0048). The site affected by the polymorphism, Ser470, was determined to be a substrate for mitogen-activated protein kinase, a downstream effector of neurotrophin action. Phosphorylation at Ser470 was increased during neonatal development and in response to neurotrophin-3 in cultured hippocampal neurons. CONCLUSIONS: Our observations suggest an association of a rare polymorphism in synapsin III with schizophrenia, but further studies will be required to clarify its role in this disease.  相似文献   
199.
Progressive myoclonic ataxia, also referred to as Ramsay Hunt syndrome, is characterized by a combination of myoclonus and cerebellar ataxia, infrequently accompanied by tonic-clonic seizures. Its differential diagnosis overlaps with progressive myoclonic epilepsy, a syndrome with myoclonus, tonic-clonic seizures, progressive ataxia and dementia. In patients with progressive myoclonic epilepsy, specific diseases can frequently be recognized, but the diagnostic yield in progressive myoclonic ataxia is much lower. We describe a patient who presented with multifocal myoclonus in his thirties and who later developed cerebellar ataxia and focal dystonia. His father was similarly affected. Genetic studies revealed a mutation in the protein kinase C gamma (PRKCG) gene, known to cause spinocerebellar ataxia type 14 (SCA-14). This case illustrates that both myoclonus and dystonia are part of the clinical spectrum in SCA-14 and that myoclonus can even be the presenting symptom. We suggest that SCA-14 should be considered in the differential diagnosis of progressive myoclonic ataxia.  相似文献   
200.
目的探讨多发伤患者外周血降钙素原(procalcitonin,PCT)与C反应蛋白(C reac- tive protein,CRP)的动态变化及其临床意义。方法将96例多发伤患者按照ISS、输血量的多少、有无MODS、感染、脓毒血症及预后情况进行分类,分别检测不同类别患者外周血PCT、CRP浓度。结果与对照组相比,多发伤患者PCT和CRP均明显升高,其峰值分别出现在伤后2 d (PCT),5,7 d(CRP)。发生MODS、感染及脓毒血症时,PCT和CRP均明显升高。此外,PCT还与患者ISS评分、预后和输血量具有相关性。结论联合检测PCT、CRP有助于多发伤患者伤情的诊治及预后判断,其中PCT较CRP更具有敏感性。  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