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   120696篇
  免费   12205篇
  国内免费   6607篇
耳鼻咽喉   864篇
儿科学   1272篇
妇产科学   1621篇
基础医学   32050篇
口腔科学   3451篇
临床医学   7644篇
内科学   16896篇
皮肤病学   2361篇
神经病学   9050篇
特种医学   2469篇
外国民族医学   25篇
外科学   10527篇
综合类   17262篇
现状与发展   22篇
一般理论   2篇
预防医学   3826篇
眼科学   2951篇
药学   13042篇
  16篇
中国医学   3806篇
肿瘤学   10351篇
  2024年   131篇
  2023年   1586篇
  2022年   2245篇
  2021年   4159篇
  2020年   3867篇
  2019年   3737篇
  2018年   3763篇
  2017年   4107篇
  2016年   4433篇
  2015年   5059篇
  2014年   7625篇
  2013年   9245篇
  2012年   7210篇
  2011年   8390篇
  2010年   6785篇
  2009年   6529篇
  2008年   6762篇
  2007年   6662篇
  2006年   6089篇
  2005年   5361篇
  2004年   4579篇
  2003年   3736篇
  2002年   2753篇
  2001年   2382篇
  2000年   2034篇
  1999年   1777篇
  1998年   1665篇
  1997年   1558篇
  1996年   1405篇
  1995年   1469篇
  1994年   1280篇
  1993年   1112篇
  1992年   897篇
  1991年   865篇
  1990年   723篇
  1989年   724篇
  1988年   605篇
  1987年   565篇
  1986年   501篇
  1985年   809篇
  1984年   785篇
  1983年   519篇
  1982年   646篇
  1981年   531篇
  1980年   431篇
  1979年   388篇
  1978年   272篇
  1977年   209篇
  1976年   194篇
  1975年   94篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The effects of the flavonoid quercetin on cell proliferation and voltage-dependent K+ current were studied on mouse neuroblastoma×glioma hybrid cells. In the presence of 1 % fetal calf serum, quercetin inhibited both cell proliferation and K+ current with effective doses inducing half-maximum effects of 10 M and 70 M respectively. Valinomycin (1 nM) antagonized 80 % of the growth-inhibitory effects of 10 M quercetin. The results suggest that at least a part of the antiproliferative effect of quercetin is mediated by a K+ channel blockade. They further confirm a role for K+ channels in mitogenesis and cell proliferation.  相似文献   
992.
CpG-ODN免疫学功能及其应用研究   总被引:5,自引:1,他引:5  
近年来研究表明,细菌DNA与人工合成的寡核苷酸含有非甲基化的CpG基序,均能激活机体的免疫系统、诱导和增强天然免疫和获得性免疫反应,尤其显示出有效的T_(h1)型免疫佐剂效应,在某些感染性疾病、过敏性疾病和肿瘤等的防治中具有重要的应用前景。本文就近年来关于CpG-ODN的免疫学效应以及CpG-ODN在疫苗研制中的应用等问题进行综述。  相似文献   
993.
吴燕  于顺  丁爱石  范明 《神经解剖学杂志》2002,18(2):184-186,T035
为了探讨一种适合培养细胞的低本底、低成本免疫细胞化学方法 ,本研究将低浓度的 Triton X-10 0加入抗体稀释液和洗液中 ,观察了其对 ABC反应时的抗体和 ABC的使用浓度和反应效果的影响。结果证明 ,在抗体稀释液和洗液中加入 0 .1%Triton X-10 0可以增强细胞对抗体的通透性 ,在不减弱阳性信号的状况下使 -抗的使用浓度明显降低 ,使生物素化二抗和 ABC的使用浓度达到 1/ 10 0 0~ 1/ 40 0 0 ,并大大减弱染色本底。本研究结果提示 ,在这一稀释度明显低于目前试剂盒建议的使用浓度。在充分显示阳性信号的前提下 ,使抗体的使用浓度和量大幅度减少 ,从而实现了降低本底和实验成本的目的  相似文献   
994.
目的: 探讨 LPS作用下p38蛋白激酶激活的动力学特点及其在细胞内超微结构中的定位。方法: 应用激酶活性测定、胶体金标记的免疫电镜技术观察LPS刺激前后p38蛋白激酶的动力学特点及在单核细胞株Raw264.7中的分布特征。结果: 动力学检测结果显示,LPS作用后15 min,p38磷酸化活性明显升高,30 min达到高峰,2 h达基线水平;p38在LPS浓度为100 μg/L时达最大激活效应。超微定位结果显示,未受刺激的及EGF刺激的细胞,p38在胞浆和胞核中金颗粒呈弥散性分布,金颗粒弥散在细胞的各个部分,如细胞质中线粒体、内质网、溶酶体;单核细胞株受到LPS刺激后,细胞核区的金颗粒明显增多,而胞浆区域的金颗粒显著减少。结论: 单核细胞株Raw264.7受LPS刺激后,其p38蛋白激酶由胞浆移位到胞核。  相似文献   
995.
Classic Menkes disease is a rare X‐linked recessive disorder of copper metabolism caused by pathogenic variants in the copper transporter gene, ATP7A. Untreated affected individuals suffer failure to thrive and neurodevelopmental delays that begin at 6–8 weeks of age and progress inexorably to death, often within 3 years. Subcutaneous injections of Copper Histidinate (US Food and Drug Administration IND #34,166, Orphan product designation #12‐3663) are associated with improved survival and neurological outcomes, especially when commenced within a month of birth. We previously identified internal jugular vein phlebectasia (IJP) in four Menkes disease subjects. This feature and other connective tissue abnormalities appear to be consequences of deficient activity of lysyl oxidase, a copper‐dependent enzyme. Here, we report results from a prospective study of IJP based on 178 neck ultrasounds in 66 Menkes subjects obtained between November 2007 and March 2018. Nine patients met the criterion for IJP (one or more cross‐sectional area measurements exceeding 2.2 cm2) and five subjects had clinically apparent neck masses that enlarged over time. Our prospective results suggest that IJP occurs in approximately 14% (9/66) of Menkes disease patients and appears to be clinically benign with no specific medical or surgical actionability. We surveyed the medical literature for prior reports of IJP in pediatric subjects and identified 85 individuals and reviewed the distribution of this abnormality by gender, sidedness, and underlying etiology. Taken together, Menkes disease accounts for 16% (15/94) of all reported IJP individuals. Neck masses from IJP represent underappreciated abnormalities in Menkes disease.  相似文献   
996.
目的: 观察卡维地洛对氧自由基(OFR)培养的人脐静脉内皮细胞(HUVECs)二甲精氨酸-二甲赖氨酸水解酶 (DDAH)活性及表达的影响,以探讨卡维地洛对不对称二甲精氨酸(ADMA)代谢机制的影响。 方法: 采用改良的Jaffe法培养原代人脐静脉内皮细胞(HUVECs),取生长良好的3-6代HUVECs用于实验,分为①空白对照组:加DMEM培养液;②OFR组:加入OFR(0.01 mmol/L,0.1 mmol/L);③OFR+卡维地洛组: 同时加入0.1 mmol/L OFR及卡维地洛(10 μmol/L)共孵24 h后, 检测上清液中一氧化氮(NO)、内皮素(ET)、ADMA含量、L-胍氨酸(L-cit)浓度及一氧化氮合酶(NOS)活性。用Western blotting法测定细胞裂解液中二甲基精氨酸-二甲基赖氨酸水解酶 (DDAH)的蛋白表达。 结果: OFR条件培养下,内皮细胞的代谢产物ADMA、ET的量均高于空白对照组,而NO的量及NOS的活性少于空白对照组;反映DDAH酶活性的L-cit浓度显著降低,且有浓度依赖性,而DDAH的表达无明显变化。卡维地洛干预组的ADMA、ET的量均低于OFR组,NOS活性及NO、L-cit浓度明显高于OFR组。 结论: OFR培养下,内皮损伤ADMA的增加与DDAH的活性减弱有关,而与DDAH的表达无关。卡维地洛通过增加DDAH活性促进ADMA代谢,使NOS活性增加,抑制OFR对内皮功能的损伤。  相似文献   
997.
目的观察抑制人脐静脉内皮细胞系ECV304细胞内内皮高表达脂多糖相关因子1(endothe-lial-overexpressed lipopolysaccharide-associated factor 1,EOLA1)基因表达后细胞生长的变化。方法构建EGFP-EOLA1融合蛋白表达载体pEGFP-N2/EOLA1,转染ECV304细胞,G418压力筛选获得稳定表达株;设计靶点特异性的寡核苷酸,连接到经BamHⅠ和HindⅢ酶切线性化的pSlincer3.1/H1质粒上。转染重组质粒到稳定表达EGFP-EOLA1融合蛋白的ECV304细胞,检测靶基因的抑制情况,观察EOLA1表达被抑制后细胞生长的改变。结果抑制EOLA1表达后ECV304细胞生长明显减慢。结论EOLA1基因在细胞内参与了细胞生长的调控。  相似文献   
998.
雄激素对家兔动脉粥样硬化的影响   总被引:6,自引:1,他引:6       下载免费PDF全文
目的:探讨雄激素在兔动脉硬化模型中是否 具有抗动脉硬化的作用。方法: 37只哈尔滨大耳白兔,饲以高脂饮食, 作如下分组:去势组:切除双侧睾丸;睾酮Ⅰ组:切除双侧睾丸并给予外源性雄激素0.25 mg·kg-1·d-1;睾酮Ⅱ组:切除双侧睾丸并给予外源性雄激素2.5 mg· kg -1·d-1;睾酮Ⅲ组:切除双侧睾丸并给予外源性雄激素12.5 mg·kg-1 ·d-1;假手术组。3个月后检测血中睾酮含量、血脂(包括TG、LDL-C、HDL-C)浓度、 PAI活性、一氧化氮(NO)、内皮素(ET)、血管紧张素Ⅱ(AngⅡ)含量。结果:去势组血清睾酮含量明显低于其它组; TG、LDL-C同其它组相比无显著差异,而HDL-C明 显降低; NO2-/NO3-含量低于其它组,而PAI活性、ET、AngⅡ却高于其它组。结论: 在高脂饮食诱发的兔动脉硬化模型中,雄激素可以发挥一定抗动脉硬化 的作用。  相似文献   
999.
Experiments on (CBA x C57BL)F1 mice showed that injection of hydrocortisone into the animals in a dose of 1 mg per mouse 24 h after immunization with sheep's erythrocytes, and against the background of repeated injections of EDTA, leads to a reduction in the relative number of plaque-forming cells by more than two-thirds in the spleen of the mice compared with the effect of the two agents separately, and by more than five-sixths compared with the control. It is suggested that this may be the result of the more intensive incorporation of hydrocortisone associated with the prolonged hypocalcemic action of the complexone, EDTA.Laboratory of Regulation of Immunopoiesis, Institute of Clinical and Experimental Medicine, Siberian Branch, Academy of Medical Sciences of the USSR, Novosibirsk. (Presented by Academician of the Academy of Medical Sciences of the USSR V. P. Kaznacheev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 3, pp. 320–322, March, 1978.  相似文献   
1000.
Summary This paper is the first of a series in which the processing of information in the cerebellum has been studied by investigating the effects that known inputs from limb nerves produce on the unitary spike potentials in the cerebellar cortex. These spikes have been recorded extracellularly at all depths along microelectrode tracks in the 5th, 4th and 3rd lobules of the anterior lobe in the lateral vermis or in the pars intermedia. These units have a background frequency of discharge, often very irregular, and computer averaging techniques have been employed in order to derive reliable information on the time course and intensity of the excitatory and/or inhibitory actions produced by the input against this background.Most of the spike responses recorded from the granular layer fall into two classes, one characteristic of impulses in mossy fibers, and the other of impulse discharges from granule cells. Both in the spontaneous background and in the response to afferent volleys in limb nerves the mossy fibers exhibit a performance in close accord with that described for the discharges up the spino-cerebellar tracts. The short latency of 6–9 msec for hindlimb stimuli and the high frequency burst response of 2–4 impulses are characteristic. The mossy fibers displayed a wide variety of responses to the wide range of testing inputs, there being various combinations of excitatory and inhibitory responses and also delayed excitatory actions, all of which must be assumed to be reflections of synaptic influences on the cells of origin of the mossy fibers in the spinal cord.Granule cells have a longer latency by several milliseconds, 9–20 msec for the hindlimb, and a slower frequency in their burst response which tended to be longer and more irregular. The small unitary spike potentials are more difficult to isolate. Also with repetitive stimulation granule cells are more readily depressed than are mossy fibers.Usually a granule cell exhibits a wider range of response to the various cutaneous and muscular afferents of a limb. Both mossy fibers and granule cells may display reciprocal responses to volleys from muscle nerves to antagonistic muscles. This attempt to define properties of the mossy fiber and granule cell spike potentials should help in their identification in future investigations.Post-Doctoral Fellow NINDS (1F2NB40,544101 NSRB).Post-Doctoral Fellow UHF Grant No. FTF-3-UB-70.  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