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   52614篇
  免费   2917篇
  国内免费   686篇
耳鼻咽喉   651篇
儿科学   416篇
妇产科学   119篇
基础医学   1846篇
口腔科学   2195篇
临床医学   8419篇
内科学   5588篇
皮肤病学   111篇
神经病学   1201篇
特种医学   16227篇
外国民族医学   21篇
外科学   4403篇
综合类   7401篇
现状与发展   2篇
预防医学   1787篇
眼科学   890篇
药学   2106篇
  120篇
中国医学   331篇
肿瘤学   2383篇
  2025年   186篇
  2024年   662篇
  2023年   1069篇
  2022年   1795篇
  2021年   2280篇
  2020年   2083篇
  2019年   1701篇
  2018年   1613篇
  2017年   1635篇
  2016年   1877篇
  2015年   1756篇
  2014年   3231篇
  2013年   2625篇
  2012年   3118篇
  2011年   3320篇
  2010年   2979篇
  2009年   2938篇
  2008年   2810篇
  2007年   2859篇
  2006年   2646篇
  2005年   2198篇
  2004年   1813篇
  2003年   1501篇
  2002年   1280篇
  2001年   1114篇
  2000年   919篇
  1999年   640篇
  1998年   529篇
  1997年   448篇
  1996年   364篇
  1995年   354篇
  1994年   330篇
  1993年   225篇
  1992年   157篇
  1991年   145篇
  1990年   121篇
  1989年   111篇
  1988年   133篇
  1987年   95篇
  1986年   69篇
  1985年   89篇
  1984年   121篇
  1983年   50篇
  1982年   54篇
  1981年   43篇
  1980年   35篇
  1979年   23篇
  1978年   20篇
  1977年   17篇
  1976年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.

Background

The optimal noninvasive test (NIT) for patients with diabetes and stable symptoms of coronary artery disease (CAD) is unknown.

Objectives

The purpose of this study was to assess whether a diagnostic strategy based on coronary computed tomographic angiography (CTA) is superior to functional stress testing in reducing adverse cardiovascular (CV) outcomes (CV death or myocardial infarction [MI]) among symptomatic patients with diabetes.

Methods

PROMISE (Prospective Multicenter Imaging Study for Evaluation of Chest Pain) was a randomized trial evaluating an initial strategy of CTA versus functional testing in stable outpatients with symptoms suggestive of CAD. The study compared CV outcomes in patients with diabetes (n = 1,908 [21%]) and without diabetes (n = 7,058 [79%]) based on their randomization to CTA or functional testing.

Results

Patients with diabetes (vs. without) were similar in age (median 61 years vs. 60 years) and sex (female 54% vs. 52%) but had a greater burden of CV comorbidities. Patients with diabetes who underwent CTA had a lower risk of CV death/MI compared with functional stress testing (CTA: 1.1% [10 of 936] vs. stress testing: 2.6% [25 of 972]; adjusted hazard ratio: 0.38; 95% confidence interval: 0.18 to 0.79; p = 0.01). There was no significant difference in nondiabetic patients (CTA: 1.4% [50 of 3,564] vs. stress testing: 1.3% [45 of 3,494]; adjusted hazard ratio: 1.03; 95% confidence interval: 0.69 to 1.54; p = 0.887; interaction term for diabetes p value = 0.02).

Conclusions

In diabetic patients presenting with stable chest pain, a CTA strategy resulted in fewer adverse CV outcomes than a functional testing strategy. CTA may be considered as the initial diagnostic strategy in this subgroup. (PROspective Multicenter Imaging Study for Evaluation of Chest Pain [PROMISE]; NCT01174550)  相似文献   
2.
新生儿呕吐性疾病的消化道造影研究   总被引:2,自引:0,他引:2  
目的:研究新生儿呕吐性疾病的造影技术,探讨其影像特征。方法:对比剂引入方式采用吸吮法和插胃管抽液后再注入对比剂两种方法;选用对比剂有6 0 %~80 % (W/V)的硫酸钡混悬液30~4 0ml或30 %泛影葡胺30ml;采用不同体位多轴位观察摄片,并对5 4例造影表现进行分析。结果:5 4例新生儿消化道造影均满足诊断要求,其中先天性幽门狭窄11例(19 6 % ) ,胃食管反流34例(6 3 0 % ) ,环形胰腺9例(16 .7% )。经手术治疗2 0例均与术前X线诊断相一致。结论:传统的上消化道造影是诊断新生儿呕吐病因的有效方法,熟练掌握造影技术和特有的造影征像能够及时地明确诊断。  相似文献   
3.
Depressive symptoms are common in patients with neurodegenerative disorders. Imaging studies suggest that a disruption of frontal-subcortical pathways may underlie depression associated with basal ganglia disease. This pilot study tested the hypothesis that frontal dysfunction contributes to depression associated with multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). Depressed patients with MSA (n = 11), PSP (n = 9), and age-matched controls (n = 25) underwent measures of cerebral glucose metabolism applying positron emission tomography with (18)F-fluorodeoxyglucose. Regional metabolism in the patient groups was compared to the normal subjects using the voxel-based statistical parametric mapping. Depressive symptom severity (Hamilton Depression Rating) and degree of locomotor disability (Hoehn & Yahr) were assessed in the patient groups. The association between prefrontal metabolism and the occurrence of depressive symptoms and the degree of locomotor disability was investigated. When compared to controls, MSA patients revealed significant metabolic decreases in bilateral frontal, parietal, and cerebellar cortex and in the left putamen. In PSP patients, significant hypometabolism was demonstrated in bilateral frontal cortex, right thalamus, and midbrain. Depression severity but not the patients' functional condition was significantly associated with dorsolateral prefrontal glucose metabolism in both patient groups. The findings of this pilot study support the hypothesis that depressive symptoms in MSA and PSP are associated with prefrontal dysfunction.  相似文献   
4.
The light microscopic and polarization appearances of calcium pyrophosphate dihydrate crystal deposits in tissues are reviewed. In routine sections haematoxylinophilic crystalline deposits with a feathery or brush-like pattern are typical of calcium pyrophosphate dihydrate. Short rhomboidal crystals showing positive birefringence are seen on polarization; X-ray microanalytical and infrared spectroscopic data support the specificity of these appearances. The appearances of the crystal deposits in decalcified specimens are also described. We include six cases of calcium pyrophosphate dihydrate deposition within periarticular bone; to the best of our knowledge this has not previously been described.  相似文献   
5.
To compare the diagnostic yield of magnetic resonance imaging (MRI) with computed tomography (CT) in posterior circulation infarction, we used proton MRI with a 0.3 Tesla magnet and a 3rd generation CT scanner in 25 patients. Age-matched controls were compared in a blinded fashion. Seventeen patients (68%) showed relevant pathology on MRI not seen on CT, 11 with normal CT and six with more extensive lesions, chiefly in the brain stem. Evidence of abnormal vertebrobasilar blood flow was seen in 8/25 (32%) of patients, suggested by vascular high intensity signals on MRI. Two tissue and one flow abnormality were seen in the control group. MRI provides additional information concerning infarct site, extent and pathogenesis in posterior circulation infarction.  相似文献   
6.
Reports of parkinsonism in phenylketonuria are exceedingly rare. We report on a patient who had received a delayed diagnosis of phenylketonuria as an infant and subsequently developed levodopa-responsive parkinsonism at the age of 33. Single-photon emission computed tomography (SPECT) using (123)I-FP-CIT ([(123))I]-2 beta-carbomethoxy-3beta-(-4-iodophenyl)-N-(3-fluoropropyl)-nortropane) used to measure dopamine transporter levels on two occasions, 7 and 9 years after the onset of neurological symptoms, were normal. Iodine-123-iodo-lisuride SPECT (IBZM) imaging, however, showed reduced caudate over putamen binding. This combination of imaging findings indicates a possible upregulation of postsynaptic D2 receptors in the context of intact presynaptic dopamine nerve terminal density.  相似文献   
7.
Summary Using xenon-enhanced computed tomography for the study of cerebral blood flow, simultaneous measurements of end-tidal and arterial blood xenon concentrations using the blood collection method were performed to investigate the validity of substituting the end-tidal for the arterial blood xenon concentration. Simultaneous measurement by both methods was performed 68 times in 27 patients. There was no statistical correlation between the arterial blood accumulation rate constant obtained by arterial blood and end-tidal samples, nor between the arterial blood saturation value obtained by the two methods, even when correction was made for age. In brain tissue, all parameters calculated using the end-tidal concentration were lower than those using arterial blood. We therefore suggest that cerebral blood flow values calculated using end-tidal xenon concentration are useful only for qualitative cerebral blood flow mapping, and not applicable to absolute values of cerebral blood flow.  相似文献   
8.
Since the clinical significance of CT abnormalities found in bipolar patients remains obscure, we studied 26 DSM-III bipolar patients who had specific CT abnormalities (third ventricle enlargement, and hyperdensity of the caudate, thalamus, anterior frontal white matter, and right temporal lobe) on numerous parameters such as EEG, the Halstead-Reitan Neuropsychological Battery, premorbid personality adjustment, family history of affective disorder, positive and negative symptoms, employment history, and response to lithium carbonate treatment. None of these measures could differentiate between the CT abnormal and CT normal subgroups. The implications of these findings are discussed.  相似文献   
9.
目的 评价第三代CT定量诊断胆囊结石的准确率及敏感性.方法 120例胆囊结石的病人在使用第三代CT检查后7天内施行胆囊切除手术,术后剖开胆囊,进行结石计数和最大结石的最大径线测量.结果 120例胆囊结石患者,其中87例有确切结石计数和测量结果(72.5%);33例CT检查未发现胆囊结石(27.5%).CT图像中显示的胆囊结石的数目:均数±标准差=3±15个;范围为2~82个与手术发现的数目:均数±标准差=68±316个;范围为2~1326个,两者比较具有显著性差异(P<0.001).CT图像发现的胆囊内最大结石的最大径线值:均数±标准差=1.08±1.06cm,范围为0~2.4cm;与手术测量值均数±标准=1.68±0.14cm范围为0.67~3.1cm,两者比较有显著性差异(P<0.001).结论 用第三代CT进行胆囊结石的定量诊断不够准确,敏感性也有不足.  相似文献   
10.
Of 46 consecutive patients who underwent percutaneous transluminalcoronary angioplasty (PTCA) from April 1980 to August 1982 andwho had a satisfactory angiographic result six months later,one died of cancer and 41 had a detailed evaluation with exercisesingle-photon emission computed tomography (SPECT, 40 patients)or repeat coronary angiography (one patient), 48–78 monthsafter the procedure. During follow-up, two patients had recurrentangina due to progression of coronary artery disease requiringa second PTCA procedure of another coronary artery; one of themlater had a limited myocardial infarction in an area suppliedby the vessel initially dilated. At follow-up, only one patienthad definite angina. All but one patient had a negative exercisetest. Myocardial perfusion during exercise in the PTCA-relatedarea, assessed by SPECT, was normal in 90% of the patients andshowed a limited defect due to reversible ischaemia in the remainingfour (10%). It is concluded that patients with a less than 50%stenosis six months after PTCA show sustained improvement intheir functional status and myocardial perfusion, four to sixyears after the procedure suggesting continued patency of thecoronary artery.  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