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   22058篇
  免费   1225篇
  国内免费   279篇
耳鼻咽喉   101篇
儿科学   159篇
妇产科学   314篇
基础医学   2155篇
口腔科学   486篇
临床医学   1670篇
内科学   1907篇
皮肤病学   313篇
神经病学   573篇
特种医学   432篇
外国民族医学   291篇
外科学   1210篇
综合类   4948篇
现状与发展   2篇
预防医学   2169篇
眼科学   123篇
药学   3282篇
中国医学   1994篇
肿瘤学   1433篇
  2023年   75篇
  2022年   146篇
  2021年   245篇
  2020年   173篇
  2019年   274篇
  2018年   334篇
  2017年   198篇
  2016年   207篇
  2015年   227篇
  2014年   4074篇
  2013年   2894篇
  2012年   2259篇
  2011年   2003篇
  2010年   3413篇
  2009年   3104篇
  2008年   1282篇
  2007年   343篇
  2006年   278篇
  2005年   234篇
  2004年   211篇
  2003年   220篇
  2002年   163篇
  2001年   126篇
  2000年   89篇
  1999年   70篇
  1998年   57篇
  1997年   46篇
  1996年   45篇
  1995年   62篇
  1994年   50篇
  1993年   45篇
  1992年   27篇
  1991年   40篇
  1990年   24篇
  1989年   22篇
  1988年   26篇
  1987年   24篇
  1986年   27篇
  1985年   50篇
  1984年   56篇
  1983年   58篇
  1982年   38篇
  1981年   34篇
  1980年   41篇
  1979年   23篇
  1978年   24篇
  1977年   16篇
  1976年   17篇
  1975年   15篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
11.
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   
12.
Objective: To construct the multi-probe ribonuclease protection assay (RPA) template set to be used for detecting expression patterns of MD-2, TLR4, CD14 mRNAs in human peripheral blood mononuclear cells. Methods : The designed cDNA fragments of the three genes were generated by polymerase chain reaction (PCR)using specific primers and directionally cloned into EcoR I and Hind III sites of expression plasmid pSP72 containing the T7/ promoter, the linearized plasmids was used as template to synthesize anti-sense RNA probes. Then we extracted total RNA from peripheral blood mononuclear cells (PBMC) and detected the dynamic expression patterns of the three genes with RPA method. Results: The proper sequence and orientation of the template set were confirmed by sequencing and the template set was successfully used to assay TLR4, MD-2 and CD14 mRNAs in human PBMC. The results showed that the three detected genes decreased transiently 1-3 hours after 100 ng/ml LPS stimulation. Conclusions: These new RPA multi-probe set provided valuable tool for the simultaneous quantitative determination of expression of TLR4, CD14 and MD-2 mRNAs in both constitutive and inducible types.  相似文献   
13.
1‐Benzyl‐4‐hydroxy[2‐14C]piperidine, a useful intermediate in labeled compound synthesis, was prepared from [14C]formaldehyde in high yield. The distribution pattern of 14C in the product is consistent with a mechanism involving reversible iminium ion formation and rapid equilibration of the iminium ion through a cationic aza‐Cope rearrangement. These steps precede the rate‐determining intramolecular cyclization step. SCH 351125 is a potent, selective CCR5 receptor antagonist with potential as a treatment for HIV infection. [14C]SCH 351125, required for metabolism studies, was prepared from 1‐benzyl‐4‐hydroxy[2‐14C]piperidine in six steps. [14C]SCH 351125 is a mixture of four atropisomers. Preparation of [14C]SCH 351125 besylate salt of the desired atropisomer pair is also described. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
14.
The natural products avemectin B 1a 1a and B 1b 1b were each site‐specifically 14C labelled at carbon 23 in a convergent synthesis for metabolism, residue, and environmental studies. The 12‐step radiosynthesis involved a stereoselective aldol condensation and later a coupling to a protected avermectin degradate 2 in a one‐pot Wittig condensation/spiroketalization to reconstitute the dioxaspirane configuration found in the natural products. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
15.
采用紫外分光光度法测定脱水穿心莲内酯琥珀酸半酯单钾盐血药浓度,并对腹腔单剂量注射给药后家兔体内药代动力学进行了研究。用计算机对血药时间数据进行了曲线拟合。结果表明:该药腹腔注射给药在家兔体内的转运符合二室开模型动力学方程。  相似文献   
16.
Summary Levels of soluble IL-2 receptors, IL-6, soluble CD23, soluble CD14 and ECP (eosinophilic cationic protein) were measured as markers of T-cell, B-cell, monocyte and eosinophilic leucocyte activation in 26 patients with atopic dermatitis (AD) on admission to (A) and at discharge from (D) the Department of Dermatology in Zurich. The serum levels of sIL-2R, IL-6, sCD23, sCD14 and ECP were significantly elevated in AD patients in comparison with the normal values of healthy donors. A significant decrease in sIL-2R (p=0.0093) and in sCD14 (p=0.0134) levels was demonstrated between A and D, correlating with the improvement in the skin intensity score (SIS). In addition, a significant correlation of the sCD14 levels and the SIS at A was demonstrated (p=0.0415). These results also incriminate monocytes in the pathogenesis of AD, indicating that, besides sIL-2R and ECP, SCD14 could also be a possible marker for the disease activity.  相似文献   
17.
作者曾经体外实验证明,均聚寡脱氧胞嘧啶核苷酸片段(dC14)有抗病毒活性,现继续研究其在体内的作用。不给dC14的对照组小鼠,接种腹水瘤细胞后:100%发病和死亡,潜伏期为6d,存活期11d;给每只小鼠dC14 1.3~3.2 mg,发病率和死亡率降低至20%,疾病潜伏期和存活期推迟。在未经dC14处理的种瘤细胞和淋巴组织与经处理的淋巴组织中,多聚酶链反应(PCR)法都检测到病毒核酸,而正常小鼠中则无此种病毒核酸顺序。研究结果提示,dC14对小鼠SRS腹水瘤的发病和生长有抑制作用。此种抑制作用可能是通过抑制病毒基因的表达来实现的。  相似文献   
18.
The threshold beta-ray energy for Cerenkov photon production can be reduced to about 0.07 MeV by using a transparent ceramic with a high refractive index. This makes it possible to measure the low-energy beta-emitters 14C and 45Ca by Cerenkov counting with efficiencies of 1.5% and 2.3%, respectively.  相似文献   
19.
Two middle-aged patients presented with rapidly progressive dementia and ataxia, nonspecific electroencephalography findings, and negative cerebrospinal fluid (CSF) protein 14-3-3. Both patients underwent brain magnetic resonance imaging (MRI) scans that demonstrated abnormalities on diffusion-weighted imaging (DWI) sequences, and both were later confirmed to have Creutzfeldt-Jakob disease. (CJD) by tissue examination. Because a recent position paper from the American Academy of Neurology characterized CSF protein 14-3-3 as a gold standard for clinically diagnosing CJD, the authors reviewed studies of CJD in which DWI-MRI imaging and CSF protein 14-3-3 studies were both performed. Among 19 reported cases of CJD with DWI-MRI lesions, CSF protein 14-3-3 was negative in 6 cases and positive in 2 others. The authors' findings suggest that multifocal cortical and subcortical hyperintensities confined to gray matter regions in DWI-MRI may be a more useful noninvasive diagnostic marker for CJD than CSF protein 14-3-3. These observations provide a compelling rationale for a prospective comparative study.  相似文献   
20.
质疑Frank—Starling心脏定律   总被引:4,自引:4,他引:0  
何川  何培芳 《西部医学》2009,21(10):1639-1646
心脏收缩释放的能量(作功)是心肌纤维长度(心室舒张末期容积,EDV)的函数,即Frank—Star一1ing(FS)心脏作功定律,被誉为心脏生理学中的“经典”理论。对此,笔者从各种不同角度进行了探讨:首先分析了Frank伸展离体心肌和Starling及其同事使用心肺制备做的实验与动物生理实际的差异,以及人们在实验中观测到的增加心肌前负荷引起收缩力增强的现象(FS现象),认为:①在正常生理条件下的动物体内,来自心脏以外的、如同心肺制备中那样人工控制心室充盈压力升高、引起EDV增加的那种血液的重力动力是不存在的。②另一方面,人为地增加前负荷,那是改变了心肌收缩时的外环境条件。③由此而激发出的FS现象,是心脏适应其外环境条件变化所作出的反应。④此种心肌收缩力增强的反应,需通过心肌细胞内部与收缩过程发生有关的心肌兴奋一收缩和化学一力学偶联等一系列生化机制(不恒定因素)方能得以实现。⑤根据他们实验中观测到的FS现象,在逻辑上不能得出前负荷这一心肌收缩时的外环境条件变化调控其作功的推论。换言之,所有的在实验中被激发出来的FS现象,都不足以成为支持FS心脏定律的证据。然后,引用国内外公认的计算心脏每搏射血作功(w)的生物物理学公式“w=P×(EDV—ESV)”,证明了w和EDV之间没有函数关系。根据心脏作功的医用物理学和生物数学的基本原理,笔者认为Frank—Starling心脏定律表达的不是心脏作功的规律。  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