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   20853篇
  免费   935篇
  国内免费   92篇
耳鼻咽喉   287篇
儿科学   315篇
妇产科学   196篇
基础医学   2316篇
口腔科学   425篇
临床医学   1331篇
内科学   5309篇
皮肤病学   370篇
神经病学   2093篇
特种医学   708篇
外科学   3357篇
综合类   105篇
预防医学   841篇
眼科学   494篇
药学   1457篇
中国医学   43篇
肿瘤学   2233篇
  2023年   92篇
  2022年   186篇
  2021年   323篇
  2020年   177篇
  2019年   220篇
  2018年   298篇
  2017年   244篇
  2016年   293篇
  2015年   329篇
  2014年   430篇
  2013年   585篇
  2012年   872篇
  2011年   1056篇
  2010年   545篇
  2009年   511篇
  2008年   954篇
  2007年   1074篇
  2006年   1122篇
  2005年   1150篇
  2004年   1074篇
  2003年   1069篇
  2002年   1117篇
  2001年   751篇
  2000年   821篇
  1999年   671篇
  1998年   337篇
  1997年   270篇
  1996年   250篇
  1995年   181篇
  1994年   149篇
  1993年   148篇
  1992年   416篇
  1991年   400篇
  1990年   358篇
  1989年   391篇
  1988年   362篇
  1987年   314篇
  1986年   277篇
  1985年   284篇
  1984年   211篇
  1983年   173篇
  1982年   84篇
  1980年   81篇
  1979年   138篇
  1978年   102篇
  1977年   81篇
  1974年   90篇
  1973年   85篇
  1972年   82篇
  1971年   80篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Lewis Y (Ley) antigen, a difucosylated tetrasaccharide found on type 2 blood group oligosaccharides of glycolipids and glycoproteins, is thought to be a phenotypic marker predictive of cell differentiation. The distribution of this antigen in human anagen hair follicles was examined by immunohistochemical staining using a monoclonal antibody (AH-6) to Ley. In the bulbar and suprabulbar portion of anagen hair follicles, Ley antigen was detected in the three layers of the inner root sheath. Subsequently, the positive staining became translocated to the innermost layer of the outer root sheath in the middle part of the hair follicles. In the upper portion of the hair follicles, Ley antigen was found in the outer cells of the outer root sheath. These findings suggested that the expression of Ley antigen in the anagen hair follicles was correlated with the processes of keratinization or terminal differentiation.  相似文献   
42.
Design of a Centrifugal Blood Pump with Magnetic Suspension   总被引:1,自引:0,他引:1  
Abstract: A new concept blood pump, whose impeller is suspended by permanent magnets and a mechanical pivot without seals or ball bearings, is presented in this paper. The primary aim of the blood pump is an application to implantable artificial hearts. The prototype model is of a centrifugal type with a four-vaned semiopen impeller 50 mm in diameter. Since this mechanism has no seals or ball bearings, flow stagnation or heat generation that might cause blood cell denaturation is expected to be small. The results of performance testing for the prototype model 2 were satisfactory regarding pump head and efficiency. The radial-suspension magnets and the magnetic coupling were stable. As a result, the present mechanism has been verified to be a candidate applicable to implantable artificial hearts.  相似文献   
43.
44.
H Koyama  K Nishimura  T Mio  A Ikeda  N Sugiura    T Izumi 《Thorax》1994,49(6):540-544
BACKGROUND--Diffuse panbronchiolitis (DPB) is characterised clinically by chronic airflow limitation and respiratory tract infection, and pathologically by chronic bronchiolar inflammation. To elucidate the functional differences between chronic obstructive pulmonary disease (COPD) and DPB the bronchial responsiveness to methacholine was compared in 64 patients with COPD and 32 patients with DPB, and the bronchodilator response was compared in 72 patients with COPD and 49 with DPB. METHODS--Bronchial responsiveness to methacholine was determined by the dosimeter method and expressed as PD20FEV1, and bronchodilator response was measured as the change in percentage predicted response with 5 mg nebulised salbutamol. RESULTS--Baseline FEV1 was similar in the two groups of patients. Patients with COPD were more responsive to methacholine than were those with DPB (geometric mean PD20FEV1 8.87 v 48.0 cumulative units). Reversibility of air flow obstruction, expressed as the difference between the percentage predicted postbronchodilator FEV1 and prebronchodilator FEV1, was significantly larger in patients with COPD than in those with DPB (7.87 (6.52)% v 4.16 (4.43)%). CONCLUSIONS--The observation that patients with DPB differ substantially in bronchial responsiveness from those with COPD is thought to reflect the difference in the mechanisms of these two diseases--that is, airway disease in DPB and more parenchymal disease in the group of patients with COPD. The nature of bronchiolar inflammation in COPD and DPB is also different, possibly explaining the difference in bronchial responsiveness. More fixed airflow limitation as a result of structural bronchiolar lesions in DPB will explain the smaller reversibility of airflow obstruction.  相似文献   
45.
46.
We report on a family with ataxia type 6 (SCA6) showing peculiar oculomotor symptoms. The proband presented with periodic alternating nystagmus (PAN), and her 2 brothers had rebound nystagmus and gaze-evoked nystagmus. They carried the identical mutation (the number of expanded CAG repeat, 24) in the CACNA1A gene. The intrafamilial variability of oculomotor symptoms may be ascribed to factors other than CAG repeat expansion size in SCA6.  相似文献   
47.
Objective: Reoperative coronary bypass grafting is at high risk. Particularly in redo cases where the patent graft is running near the midline of the sternum, the graft may be exposed to injury by a median sternotomy and subsequent dissection. Whereas, off-pump bypass grafting from the left axillary artery or descending thoracic artery by a left thoracotomy approach is safe for preventing graft damage.Methods: From March 1998 to February 2002, we performed off-pump coronary artery bypass grafting by a left thoracotomy approach in 9 patients. The left axillary artery was used as the inflow vessel in 4 cases, and the descending thoracic, aorta in 5.Results: The radial artery was anastomosed proximally to the axillary artery in 4 cases and the descending thoracic aorta in one case. The saphenous vein graft was anastomosed, proximally to the descending thoracic aorta in 4 cases. Transdiaphragmatic minimally invasive bypass grafting for the right coronary artery was simultaneously performed in 3 cases. Postoperative cardiac events were ventricular arrhythmia in 6 cases and supraventricular arrhythmia in 3 cases. There was no damage to the patent grafts. Postoperative coronary angiography performed, in 8 cases revealed all the grafts to be patent without stenosis. Cardiac symptoms were not found after the operation in any of the cases.Conclusions: These procedures can prevent the injury to patent grafts caused by a median sternotomy, and will be one of the useful strategies for reoperative off-pump coronary artery bypass grafting.  相似文献   
48.
49.
50.
Different responses of retinal ganglion cells to iontophoretically applied NMDA receptor antagonists and non-NMDA receptor antagonists were studied in anaesthetized cats. Cells with normal range of spontaneous firing and those with abnormally high spontaneous firing levels showed a different response to these drugs. Both visually driven and spontaneous firing of cells with 'normal' spontaneous firing level were blocked by non-NMDA receptor antagonists, but not by NMDA receptor antagonists which often raised spontaneous firing. In contrast, the responses of cells with abnormally high spontaneous firing level were blocked effectively by NMDA antagonists including MK-801, an NMDA channel blocker, as well as by non-NMDA receptor antagonists. The results suggest that under normal physiological conditions, NMDA receptors which are not involved in synaptic transmission may play a role in reducing the resting discharge level of the retinal ganglion cells. NMDA receptors, however, appear to open ion channels in response to glutamate input when ganglion cells become abnormally depolarized.  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