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   81642篇
  免费   7086篇
  国内免费   3795篇
耳鼻咽喉   939篇
儿科学   985篇
妇产科学   1432篇
基础医学   11662篇
口腔科学   1940篇
临床医学   8314篇
内科学   14344篇
皮肤病学   1342篇
神经病学   5300篇
特种医学   2776篇
外国民族医学   22篇
外科学   9958篇
综合类   8916篇
现状与发展   8篇
一般理论   11篇
预防医学   5107篇
眼科学   2240篇
药学   7941篇
  19篇
中国医学   2516篇
肿瘤学   6751篇
  2024年   103篇
  2023年   658篇
  2022年   1513篇
  2021年   2087篇
  2020年   1543篇
  2019年   1664篇
  2018年   2196篇
  2017年   1936篇
  2016年   1848篇
  2015年   2319篇
  2014年   3040篇
  2013年   3195篇
  2012年   4466篇
  2011年   4557篇
  2010年   2777篇
  2009年   2459篇
  2008年   3448篇
  2007年   3513篇
  2006年   3276篇
  2005年   2943篇
  2004年   2370篇
  2003年   2291篇
  2002年   2084篇
  2001年   5254篇
  2000年   5100篇
  1999年   4476篇
  1998年   1762篇
  1997年   1355篇
  1996年   875篇
  1995年   780篇
  1994年   691篇
  1993年   588篇
  1992年   2118篇
  1991年   1850篇
  1990年   1651篇
  1989年   1607篇
  1988年   1411篇
  1987年   1272篇
  1986年   1126篇
  1985年   956篇
  1984年   612篇
  1983年   502篇
  1982年   255篇
  1981年   194篇
  1980年   153篇
  1979年   294篇
  1978年   84篇
  1974年   82篇
  1973年   104篇
  1972年   75篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
No association between a presenilin 1 polymorphism and Alzheimer disease   总被引:1,自引:0,他引:1  
BACKGROUND: Homozygosity of allele 1 of a presenilin 1 intron 8 polymorphism (PS1-1) has been associated with doubling of the risk of sporadic late-onset Alzheimer disease (LOAD), in some, but not all studies. OBJECTIVE: To genotype the PS1 intron 8 polymorphism in predominantly Hispanic families with LOAD to test for association and for linkage between this polymorphism and LOAD. DESIGN: A family-based, case-control, genetic-linkage study. SETTING: Predominantly Hispanic families were selected from probands who were part of a random sample of 2128 Medicare beneficiaries aged 65 years or older who were residing in the community of Washington Heights, which is located in the northern part of Manhattan, NY. PARTICIPANTS: Fifty-one families with 103 affected family members, 67 unaffected family members, and 7 family members with other diagnoses were genotyped for the PS1 polymorphism. All patients met National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria for either probable or possible Alzheimer disease. Age was truncated at 55 years or older. MAIN OUTCOME MEASURES: Association analyses, conditional logistic regression, and traditional linkage methods were applied to the families for the PS1 polymorphism and for the presence of the gene for apolipoprotein E (APOE). Results of the association and conditional logistic regression analyses of PS1 intron 8 polymorphism were subsequently adjusted for the effect of APOE-epsilon4, sex, age, and education of each sibling. RESULTS: No association between the PS1 intron 8 polymorphism and LOAD was observed (relative risk, 0.99; 95% confidence interval, 0.3-3.4). An association between presence of the APOE-epsilon4 allele and LOAD (relative risk 4.05; 95% confidence interval, 1.3-12.5) was observed. CONCLUSION: We could not confirm the relationship between the PS1 intron 8 polymorphism and LOAD in this collection of families.  相似文献   
992.
Anti-GQ1b antibodies are typically found in patients with the Miller Fisher syndrome, all of whom will have, by definition, acute ophthalmoplegia. The authors describe three patients with chronic ophthalmoplegia in the presence of persistently high titers of immunoglobulin G anti-GQ1b antibody detected in an ELISA, one of whom improved with immunotherapy. Anti-GQ1b antibodies may be associated with some cases of chronic ophthalmoplegia of unknown cause.  相似文献   
993.
A 38 year-old woman, without previous medical history, presented, since 1993, several paraplegic fits carrying herself progressively through to a severe paraplegia. Diagnoses successively proposed were spinal cord compressions by slipped discs, spinal cord infarct and multiple sclerosis. In November 1998, the patient presented back pain and fever. Spinal cord magnetic resonance imaging (MRI) revealed a mildly enlarged dorsal cord with signal abnormalities. The lesions were isointense on T1-weighted images, hyperintense on T2-weighted images and showed a ringlike contrast enhancement. A lumbar puncture showed a trouble cerebrospinal fluid (CSF) with leucocytes 600/mm(3) (85 p.100 polynuclear), protein 6.7 g/l, glucose 0.26 g/l, chloride 109 mmol/l. The patient was first treated with parenteral unspecific antibiotherapy. Microbiological studies of blood and CSF were negative. CSF examination with polymerase chain reaction (PCR) was positive for Mycobacterium tuberculosis. Clinical (pain and fever) symptoms and CSF abnormalities decreased after antituberculous treatment. However, paraparesis remain severe. Spinal tuberculous localizations often lead to diagnostic and therapeutic errors. Improvement of spinal cord MRI sequences and using of PCR technics in CSF would contribute to reduce these difficulties.  相似文献   
994.
BACKGROUND AND PURPOSE: Long-term daily aspirin is of benefit in the years after ischemic stroke, and 2 large randomized trials (the Chinese Acute Stroke Trial [CAST] and the International Stroke Trial [IST]), with 20 000 patients in each, have shown that starting daily aspirin promptly in patients with suspected acute ischemic stroke also reduces the immediate risk of further stroke or death in hospital and the overall risk of death or dependency. However, some uncertainty remains about the effects of early aspirin in particular categories of patient with acute stroke. METHODS: To assess the balance of benefits and risks of aspirin in particular categories of patient with acute stroke (eg, the elderly, those without a CT scan, or those with atrial fibrillation), a prospectively planned meta-analysis is presented of the data from 40 000 individual patients from both trials on events that occurred in the hospital during the scheduled treatment period (4 weeks in CAST, 2 weeks in IST), with 10 characteristics used to define 28 subgroups. This represents 99% of the worldwide evidence from randomized trials. RESULTS: There was a highly significant reduction of 7 per 1000 (SD 1) in recurrent ischemic stroke (320 [1.6%] aspirin versus 457 [2. 3%] control, 2P<0.000001) and a less clearly significant reduction of 4 (SD 2) per 1000 in death without further stroke (5.0% versus 5. 4%, 2P=0.05). Against these benefits, there was an increase of 2 (SD 1) per 1000 in hemorrhagic stroke or hemorrhagic transformation of the original infarct (1.0% versus 0.8%, 2P=0.07) and no apparent effect on further stroke of unknown cause (0.9% versus 0.9%). In total, therefore, there was a net decrease of 9 (SD 3) per 1000 in the overall risk of further stroke or death in hospital (8.2% versus 9.1%, 2P=0.001). For the reduction of one third in recurrent ischemic stroke, subgroup-specific analyses found no significant heterogeneity of the proportional benefit of aspirin (chi(2)(18)=20. 9, NS), even though the overall treatment effect (chi(2)(1)=24.8, 2P<0.000001) was sufficiently large for such subgroup analyses to be statistically informative. The absolute risk among control patients was similar in all 28 subgroups, so the absolute reduction of approximately 7 per 1000 in recurrent ischemic stroke does not differ substantially with respect to age, sex, level of consciousness, atrial fibrillation, CT findings, blood pressure, stroke subtype, or concomitant heparin use. There was no good evidence that the apparent decrease of approximately 4 per 1000 in death without further stroke was reversed in any subgroup or that in any subgroup the increase in hemorrhagic stroke was much larger than the overall average of approximately 2 per 1000. Finally, there was no significant heterogeneity between the reductions in the composite outcome of any further stroke or death (chi(2)(18)=16.5, NS). Among the 9000 patients (22%) randomized without a prior CT scan, aspirin appeared to be of net benefit with no unusual excess of hemorrhagic stroke; moreover, even among the 800 (2%) who had inadvertently been randomized after a hemorrhagic stroke, there was no evidence of net hazard (further stroke or death, 63 aspirin versus 67 control). CONCLUSIONS: Early aspirin is of benefit for a wide range of patients, and its prompt use should be routinely considered for all patients with suspected acute ischemic stroke, mainly to reduce the risk of early recurrence.  相似文献   
995.
996.
Lucas C  Leclerc X  Pruvo JP  Leys D 《Revue neurologique》2000,156(12):1096-1105
Vertebral artery dissection is a frequent cause of ischemic stroke in young adults but time course of VA dissections remains poorly documented. Angiography was considered as the gold standard for the diagnosis. Recently, non-invasive methods have been developed such as helical CT and magnetic resonance angiography. The purpose of the study was to assess the reliability of a gadolinium-enhanced fast three dimensional (3D) magnetic resonance (MR) angiographic sequence to image vertebral arteries and to assess the long-term follow-up of vertebral artery (VA) dissections. Sixteen consecutive patients with 18 angiographically documented VA dissections were followed-up by gadolinium-enhanced 3D MR angiography and cervical T1-weighted MR imaging at a median delay of 22 months. Ten patients had MR imaging scan at the acute stage as well and nine had early follow-up angiography at a median delay of 3 months. MR angiography was evaluated in a consensus manner including image quality, presence of residual stenosis, luminal irregularities and occlusion. All patients clinically improved. Ten of 11 stenotic dissections returned to normality whereas one stenotic dissection progressed to occlusion. Two pseudoaneurysms detected on the initial angiography resolved spontaneously, one appeared only on a delayed MR angiographic scan and one was detected on early MR angiograms and finally resolved on a late one. Of the seven initially occluded VAs, five reopened with a hairline residual lumen in three. Contrast MR angiography is an interesting tool to assess the late course of VA dissections. Most lesions resolved spontaneously but persisting occlusion or pseudoaneurysm may be found in long term follow-up.  相似文献   
997.
The alpha-synuclein (alpha SN) protein is thought to play a central role in the pathogenesis of neurodegenerative diseases where it aggregates to form intracellular inclusions. We have used Western blotting to examine the expression levels and solubility of alpha SN in brain homogenates from dementia with Lewy bodies (DLB), Parkinson's disease (PD), Alzheimer's disease (AD), and normal controls using samples from the parahippocampus/transentorhinal cortex. Compared to controls, DLB brains accumulate significantly greater amounts of sodium dodecyl sulfate (SDS)-soluble and SDS-insoluble alpha SN but levels of TBS-soluble alpha SN did not change. Levels of synaptophysin, a marker of synaptic integrity, were significantly lower in DLB cases than in normal aged controls regardless of whether concurrent changes of AD were present. This limbic synaptic dysfunction may contribute to cognitive impairment in DLB. Whether aggregated alpha SN is a cause or effect of the disease process in DLB and PD remains to be determined, but the presence of aggregated alpha SN is consistent with a pathogenesis similar to that associated with aggregates of Abeta amyloid in AD.  相似文献   
998.
Researchers from Japan, China and Singapore have initiated a collaborative project, with the aim of comparing adolescent quality of life (QOL) internationally. This study presents the primary results of the investigation conducted in Beijing, China, and Kobe, Japan. The 70-item Quality of Life Questionnaire for Adolescents (QOLQA) was developed and evaluated in Japan and China. In total, 1114 Japanese and 613 Chinese junior high school students, aged 12-15 years, completed the questionnaire. Chinese students scored significantly higher than the Japanese students in overall QOL scores and in most domains. For both groups, subjects had highest score in the independence domain and lowest in psychological domain. In terms of overall QOL score, Chinese male students ranked first, followed by Chinese girls, Japanese boys, and Japanese girls. In the Japanese group, a continuing decrease of QOL scores with age was observed without exception, but no such tendency was present in their Chinese counterparts. No parallel relationship was observed between the higher level of economic development and better quality of life. The results also suggest that mental health promotion should be a priority in improving overall quality of life of adolescents both in Japan and China.  相似文献   
999.
The effects of combined transcatheter arterial chemoembolization (TACE) and radiotherapy in patients with large hepatocellular carcinoma (HCC) were analysed retrospectively. A total of 107 patients with large unresectable HCC was treated with TACE followed by external beam irradiation. The largest dimension of the tumours ranged from 5 cm to 18 cm. Acute effects, survival rates, toxicity and prognostic factors were analysed. Follow-up ranged from 4 months to 98 months (median 24 months). An objective response, i.e. reduction of tumour area greater than 50%, was achieved in 48.6% of cases. In 64.9% of the cases with increased alpha-feto protein (AFP) values, AFP level underwent a reduction of more than 25%. The cumulative survival rates at 1, 3 and 5 years were 59.4%, 28.4% and 15.8%, respectively (median survival 18 months). The combination therapy was generally well tolerated. Only two patients died from liver failure or variceal bleeding associated with therapy. The Cox proportional hazards model showed that the number of tumours and the irradiation dose were independent prognostic factors. The results indicate that combined TACE with radiotherapy is a promising therapeutic approach for large unresectable HCC. Prospective controlled trials to ascertain the real potential benefit of this approach are required.  相似文献   
1000.
Towards understanding the pathogenesis of HIV dementia, we molecularly cloned and sequenced human immundeficiency virus type 1 (HIV-1) gp160 genes from uncultured post-mortem tissues collected from a patient with HIV dementia. Sequences from bone marrow, lymph node, lung, and four regions of brain - the deep white matter, head of caudate, choroid plexus and meninges - were compared. Also included were gp160 sequences recovered from blood monocytes collected 5 months prior to death. Phylogenetic analyses showed that the sequences from deep white matter were more closely related to those from bone marrow, than to those from the other tissues, and moreover, were most closely related to sequences from the blood monocytes. These findings suggest trafficking of bone marrow-derived monocytes into the deep white matter during this late stage of infection. Another cluster included sequences from choroid plexus, meninges and lymph node, and interestingly, identical patterns of four or nine stop codons were shared among these tissues. These mutations appear to be the consequence of G-->A hypermutation, and could reflect independent events, or the movement of virions or infected cells, from the choroid plexus into the cerebrospinal fluid and ultimately, into the lymph node. We propose that a critical step towards the development of HIV dementia is an increase in monocyte trafficking into the brain, and that this process is either initiated and/or accelerated during late-stage infection, which could explain why dementia occurs primarily during this time.  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