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   28644篇
  免费   1926篇
  国内免费   532篇
耳鼻咽喉   209篇
儿科学   529篇
妇产科学   181篇
基础医学   1279篇
口腔科学   229篇
临床医学   5877篇
内科学   1867篇
皮肤病学   30篇
神经病学   2566篇
特种医学   11065篇
外科学   2313篇
综合类   2695篇
预防医学   408篇
眼科学   113篇
药学   748篇
  8篇
中国医学   138篇
肿瘤学   847篇
  2024年   22篇
  2023年   206篇
  2022年   804篇
  2021年   968篇
  2020年   821篇
  2019年   542篇
  2018年   803篇
  2017年   1025篇
  2016年   1230篇
  2015年   1066篇
  2014年   2015篇
  2013年   1639篇
  2012年   1800篇
  2011年   1991篇
  2010年   1737篇
  2009年   1726篇
  2008年   1745篇
  2007年   1635篇
  2006年   1398篇
  2005年   1307篇
  2004年   1064篇
  2003年   727篇
  2002年   436篇
  2001年   562篇
  2000年   579篇
  1999年   449篇
  1998年   443篇
  1997年   420篇
  1996年   367篇
  1995年   327篇
  1994年   235篇
  1993年   217篇
  1992年   229篇
  1991年   161篇
  1990年   119篇
  1989年   79篇
  1988年   73篇
  1987年   56篇
  1986年   35篇
  1985年   18篇
  1984年   4篇
  1983年   6篇
  1982年   3篇
  1981年   4篇
  1980年   3篇
  1978年   1篇
  1976年   1篇
  1975年   2篇
  1972年   1篇
  1970年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We describe a girl with a facial haemangioma, associated with other vascular anomalies: agenesis of the internal carotid artery, cerebral cortical dysplasia and hypoplasia of the cerebral hemisphere on the same side of the angioma. We studied the patient by conventional arteriography, T1- and T2-weighted MRI and magnetic resonance angiography.  相似文献   
62.
A woman affected by chronic progressive external ophthalmoplegia and muscle mitochondrial DNA deletion was studied by phosphorus magnetic resonance spectroscopy (31P-MRS) prior to and after 1 and 7 months of treatment with oral lipoic acid. Before treatment a decreased phosphocreatine (PCr) content was found in the occipital lobes, accompanied by normal inorganic phosphate (Pi) level and cytosolic pH. Based on these findings, we found a high cytosolic adenosine diphosphate concentration [ADP] and high relative rate of energy metabolism together with a low phosphorylation potential. Muscle MRS showed an abnormal work-energy cost transfer function and a low rate of PCr recovery during the post-exercise period. All of these findings indicated a deficit of mitochondrial function in both brain and muscle. Treatment with 600 mg lipoic acid daily for 1 month resulted in a 55% increase of brain [PCr], 72% increase of phosphorylation potential, and a decrease of calculated [ADP] and rate of energy metabolism. After 7 months of treatment MRS data and mitochondrial function had improved further. Treatment with lipoate also led to a 64% increase in the initial slope of the work-energy cost transfer function in the working calf muscle and worsened the rate of PCr resynthesis during recovery. The patient reported subjective improvement of general conditions and muscle performance after therapy. Our results indicate that treatment with lipoate caused a relevant increase in levels of energy available in brain and skeletal muscle during exercise.  相似文献   
63.
Abstract The neuroimaging findings in an infant with hypernatremic dehydration are presented. Brain parenchymal haemorrhage and extensive multiple infarcts were present in the acute stage. Follow-up CT showed bilateral, symmetrical changes presumed to indicate extrapontine myelinolysis in the thalamus and globus pallidus. MRI confirmed sparing of the pons. Only three previous cases of neuroimaging abnormalities due to hypernatraemia have been described in the radiological literature. Received: 30 December 1997 Accepted: 6 May 1998  相似文献   
64.
Cryptococcus meningoencephalitis in AIDS: parenchymal and meningeal forms   总被引:4,自引:0,他引:4  
CT and MRI in one case of Cryptococcus neoformans infection showed contrast-enhancing parenchymal lesions resembling granulomata or abscesses. After an initial phase without contrast enhancement, the full extent of the lesions was visible within 2 weeks of presentation. The enhancing masses were assumed to represent intracerebral cryptococcomas. Despite evidence of massive meningeal infection on cerebrospinal fluid (CSF) examination, no radiological signs of meningitis, invasion of the Virchow-Robin spaces or ventriculitis could be demonstrated. With antimycotic treatment the contrast enhancement disappeared and cystic, partly calcified lesions remained. Recurrence of meningeal infection without radiological correlates was apparent in this stage. In a second case of proven cryptococcus meningitis, dilation of Virchow-Robin spaces or cysts in the adjacent parenchyma were the main abnormalities on MRI. Enhancing masses were not detected. These cases may represent two different reactions of the immunocompromised hosts to infection with C. neoformans: widening of the perivascular spaces as a correlate of the more typical meningeal infection and enhancing parenchymal lesions as a sign of further invasion from the CSF spaces. Enhancement of cryptococcomas, indicating an inflammatory response in the surrounding brain, is not typical in patients with impairment of immune function. Received: 11 March 1998 Accepted: 19 June 1998  相似文献   
65.
Chronic spinal subdural haematoma is a uncommon. We describe the CT and MRI appearances of chronic spinal and intracranial subdural haematomas following minor trauma. The aetiology, pathogenesis and differential diagnosis are discussed. Received: 7 January 1998 Accepted: 15 July 1998  相似文献   
66.
In this study, thirty-eight patients with a variety of upper abdominal diseases were examined with three-dimensional time-resolved MR angiography (7 sec/data set). Visualisation of arterial and venous anatomy was excellent in the majority of patients. Moreover, subtraction images could be calculated and organ perfusion could be assessed. It is concluded that this technique opens new perspectives for a comprehensive evaluation of vascular and parenchymal disease. Received: 14 April 1998; Revision received: 23 October 1998; Accepted: 9 November 1998  相似文献   
67.
Patients with non-Hodgkin’s lymphoma occasionally develop widespread invasion of peripheral nerves by tumor cells or neurolymphomatosis (NL). Clinically this usually results in asymmetrical, progressive, and painful polyneuropathy. Diagnosis rests on the identification of tumor cells in peripheral nerves. To avoid false-negative biopsy findings in patients with malignant lymphomatous infiltration of peripheral nerves it has been recommended to biopsy clinically involved nerves. We present two patients with histologically confirmed NL in whom sural the nerve biopsy finding was negative despite clinical and neurophysiological evidence of involvement of the sural nerve a. The clinical features of NL are reviewed. Some patients with neurolyphomatosis have only focal or proximal involvement of nerves, requiring the biopsy of an affected part of these nerves. Magnetic resonance imaging may be useful in identifying affected nerves. Received: 28 January 1999 Received in revised form: 7 July 1999 Accepted: 17 July 1999  相似文献   
68.
We report a case of central European tick-borne encephalitis with cervical myelitis presenting clinically as a lower motor neuron syndrome of the upper limbs with proximal asymmetrical pareses and atrophies. There were no sensory deficits nor signs of lesions of the spinal pathways or signs of encephalitis or meningitis. The affected motor fibers of the upper limbs were electrically inexcitable, but sensory findings were normal. Electromyography of the paralyzed muscles revealed pathological denervation activity without voluntary activation. The initial magnetic resonance imaging (MRI) showed a large hyperdense lesion in the anterior part of the cervical cord from C3 to T1. Despite the fact that MRI changes disappeared completely within 6 weeks the patient showed only little improvement in the paralyzed muscles after 6 months. To our knowledge, these MRI changes in patients with tick-borne encephalitis, consistent with an isolated anterior horn lesion, have never been reported previously. The course may have been aggravated by an initial antibiotic treatment with cephalosporins. Received: 4 May 1999 Received in revised form: 22 July 1999 Accepted: 26 July 1999  相似文献   
69.
Ornithine decarboxylase (ODC) transgenic and alpha-difluoromethyl ornithine (DFMO)-treated rats were exposed to transient middle cerebral occlusion (MCAO) to examine the role of intraischaemic ODC-activity on the evolution of ischaemia-reperfusion damage. Magnetic resonance imaging (MRI) data show that the damage develops slower in ODC transgenic than in DFMO-treated rats, which is not caused by a difference in perfusion. Furthermore, infarct volumes are smaller in the former animals one day later. These data support the idea of endogenous neuroprotective action of ODC.  相似文献   
70.
Summary The precision of four methods of quantifying neuroelectric signals has been improved by increasing EEG spatial sampling, using up to 124 electrodes, and by accurate anatomical registration of the EEG with Magnetic Resonance Images (MRIs). One such method, equivalent dipole modeling, is a well-known form of source localization which is useful when the generator of the scalp recorded signal approximates a simple dipolar source, as is usually the case with early and mid-latency Evoked Potentials (EPs). Two methods of enhancing spatial detail which benefit from increased spatial sampling include the Laplacian Derivation and the Finite Element Deblurring method. The latter is a new technique which estimates the EP distribution at the superficial cortical surface. The fourth method, Evoked Potential Covariance, characterizes the spatiotemporal relationships among EP segments at different recording sites. This is useful when studying functional neural networks underlying higher cognitive functions. These methods are reviewed and examples of results of their application in recent experiments are presented.Supported by competitive grants from The National Institute of Mental Health, The National Institute of Neurological Diseases and Stroke, The Air Force Office of Scientific Research, The Office of Naval Research, The National Science Foundation NASA and The National Institute on Alcohol Abuse and Alcoholism of the United States Federal Government. Thanks to all members of the EEG Systems Laboratory and SAM Technology, past and present, for their vital contributions to the work presented here.This paper is based on an invited lecture given at the Tenth Anniversary Meeting of The Japanese Society for Brain Electromagnetic Topography held in Fukuoka, Japan in September, 1992.  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