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   3609091篇
  免费   261758篇
  国内免费   9453篇
耳鼻咽喉   48812篇
儿科学   119912篇
妇产科学   99373篇
基础医学   508158篇
口腔科学   102092篇
临床医学   330915篇
内科学   704339篇
皮肤病学   85342篇
神经病学   292563篇
特种医学   137175篇
外国民族医学   941篇
外科学   540069篇
综合类   77770篇
现状与发展   8篇
一般理论   1392篇
预防医学   276598篇
眼科学   83752篇
药学   263937篇
  12篇
中国医学   7988篇
肿瘤学   199154篇
  2019年   28665篇
  2018年   40851篇
  2017年   31138篇
  2016年   35437篇
  2015年   40150篇
  2014年   55566篇
  2013年   83037篇
  2012年   111927篇
  2011年   118468篇
  2010年   70945篇
  2009年   67347篇
  2008年   110317篇
  2007年   117425篇
  2006年   119047篇
  2005年   114195篇
  2004年   109883篇
  2003年   105682篇
  2002年   102076篇
  2001年   175748篇
  2000年   179883篇
  1999年   151291篇
  1998年   42997篇
  1997年   37869篇
  1996年   37994篇
  1995年   36842篇
  1994年   33682篇
  1993年   31563篇
  1992年   117091篇
  1991年   112937篇
  1990年   109312篇
  1989年   105605篇
  1988年   96567篇
  1987年   94588篇
  1986年   88802篇
  1985年   84782篇
  1984年   63206篇
  1983年   53635篇
  1982年   31459篇
  1981年   28041篇
  1979年   55910篇
  1978年   39252篇
  1977年   33407篇
  1976年   31142篇
  1975年   32958篇
  1974年   39314篇
  1973年   37578篇
  1972年   35095篇
  1971年   32575篇
  1970年   30102篇
  1969年   28769篇
排序方式: 共有10000条查询结果,搜索用时 116 毫秒
991.
2000年11月,作者得知从Aarhus大学医院皮肤科患者分离到的金黄色葡萄球菌对苯唑西林出现界线耐药(BORSA)。本文旨在描述其表型和基因型,并评估可能的传播途径以干预和阻止进一步蔓延。菌株由脉冲场凝胶电泳鉴定。几个感染控制方案的缺口显示患者间可直接或间接传播。皮肤屏障缺陷、皮肤病患者金黄色葡萄球菌的高携带率和院内双氯西林的高消耗率可促使传播。改善普通感染控制措施和重新评价院内抗生素政策后,该菌的暴发感染消失。  相似文献   
992.
The onset of the sporadic Creutzfeldt-Jakob disease is usually characterized by dementia or neurological symptoms. We are reporting the case of a 31 year-old man with a sporadic Creutzfeldt-Jakob disease characterized by a schizophrenia-like onset. The schizophrenic symptoms developed for sixteen months before the neurological symptoms appeared. The psychiatric onset of the present case was linked with the early age of onset and the long duration of the disease and could have been influenced by polymorphism of the codon 129 of the prion protein gene (PRNP) and a type of pathological prion protein (PrPres).  相似文献   
993.
We report a case of a six years age girl who presented to our out patients department with the history and findings suggestive of recurrent respiratory tract infections. She was also noticed to have; non homogeneous hyper- pigmented patches on the face since three months of age, sparse hair on the scalp and eyebrows, conical peg like teeth and delayed dentition, prominent and low set ears, perpetually flexed third toe bilaterally. Axillary skin biopsy showed adenexal structures and eccrine glands in subcutaneous fat which were reduced in number. The diagnosis made was: Anhydrotic/ Hypohidrotic type of ectodermal dysplasia. Key words: Ectodermal Dysplasia, Anhidreotic, Hypohidrotic.  相似文献   
994.
Bifid mandibular canal.   总被引:1,自引:0,他引:1  
PURPOSE: To determine the incidence and characteristics of bifid mandibular canals. METHODS: A retrospective study was performed using panoramic radiographs of 2012 patients subjected to dental treatment in the Dental Clinic of the Valencia University Dental School (Valencia, Spain) between 1996 and 1999. The goal was to investigate the presence of double mandibular canals. RESULTS: The extraoral panoramic radiographs revealed a total of 7 images suggestive of bifid canals. Mandibular computed tomography revealed the existence of this anatomic variant in 2 of 3 patients. An analysis was performed on the incidence of this type of image in extraoral panoramic radiography, its possible interpretations, and the clinical implications of bifid mandibular canals. CONCLUSIONS: In this study, 0.35% of canals were bifid. All cases were in women.  相似文献   
995.
996.
BACKGROUND: Few data are currently available investigating neurosteroids (NS) in Alzheimer's disease (AD). The NS allopregnanolone may be decreased in serum and plasma in patients with AD, but it is unclear if allopregnanolone is also reduced in brain. Because a number of NS exhibit neuroprotective effects and impact cognitive performance in rodent models, these molecules may be relevant to the pathophysiology of neurodegenerative disorders. We therefore investigated prefrontal cortex (PFC) NS levels in AD. METHODS: Neurosteroid levels (allopregnanolone, pregnenolone, dehydroepiandrosterone [DHEA]) were determined in postmortem PFC in 14 male subjects with AD and 15 cognitively intact male control subjects by gas chromatography/mass spectrometry preceded by high-performance liquid chromatography purification. RESULTS: Subjects with AD exhibit significant reductions in allopregnanolone compared with cognitively intact control subjects (median levels = 2.50 ng/g vs. 5.59 ng/g, respectively; p = .02). Allopregnanolone levels are inversely correlated with neuropathological disease stage (Braak), r = -.49, p = .007. Median DHEA levels are elevated in subjects with AD (p = .01). CONCLUSIONS: Subjects with AD demonstrate significant reductions in PFC allopregnanolone levels, a finding that may be relevant to neuropathological disease stage severity. Neurosteroids may have utility as candidate biomarkers in AD.  相似文献   
997.
998.
BACKGROUND: Stringent transcranial Doppler (TCD) criteria for diagnosing occlusion are needed for more reliable TCD performance at bedside in the acute stroke setting. SUBJECTS AND METHODS: At three academic stroke centers, we performed TCD examination for patients with symptoms of cerebral ischemia who underwent digital subtraction angiography (DSA). We used a standard insonation protocol with power M-mode Doppler (PMD) TCD (TCD 100 M, Spencer Technologies Inc., Seattle, WA). We collected mean flow velocity (MFV), pulsatility indices (PI), and power M-mode resistance signature (absent, high, or low) in symptomatic middle (MCA), anterior (ACA), posterior (PCA), and in affected (a), ipsilateral (i), and contralateral (c-lat) cerebral arteries. Ratios of aMCA/c-lat MCA, aMCA/iACA, and aMCA/iPCA MFV were subsequently calculated. PMD-TCD flow findings were evaluated with a receiver-operating characteristic (ROC) analysis for angiographically proven MCA occlusion. RESULTS: We studied 120 patients with acute cerebral ischemia with PMD-TCD examinations prior to or immediately after DSA. Lower aMCA velocities pointed to higher probability of occlusion (P= .055). The aMCA/iPCA MFV ratio was superior to the aMCA/iACA ratio and strongly predictive of occlusion at a threshold ratio of 0.5 (RR 2.31 CI(95) 2.13-2.51). High resistance or absent M-mode flow signatures in the proximal MCA were present in 87% of M1 and M2 MCA occlusions (probability 87%). In the presence of a low-resistance PMD signature, obtaining the aMCA/iPCA MFV ratio <0.5 increases probability of occlusion to 87%. Normal MFV ratios and low-resistance M-mode signatures are highly predictive of a negative angiogram for MCA occlusion. CONCLUSION: In acute cerebral ischemia, reliable criteria for proximal MCA occlusion have been developed based on combination of MFV ratios and M-mode flow resistance signatures. Validation of these criteria will require multicenter studies.  相似文献   
999.
The switching of magnetic field gradient coils in magnetic resonance imaging (MRI) inevitably induces transient eddy currents in conducting system components, such as the cryostat vessel. These secondary currents degrade the spatial and temporal performance of the gradient coils, and compensation methods are commonly employed to correct for these distortions. This theoretical study shows that by incorporating the eddy currents into the coil optimization process, it is possible to modify a gradient coil design so that the fields created by the coil and the eddy currents combine together to generate a spatially homogeneous gradient that follows the input pulse. Shielded and unshielded longitudinal gradient coils are used to exemplify this novel approach. To assist in the evaluation of transient eddy currents induced within a realistic cryostat vessel, a low-frequency finite-difference time-domain (FDTD) method using the total-field scattered-field (TFSF) scheme was performed. The simulations demonstrate the effectiveness of the proposed method for optimizing longitudinal gradient fields while taking into account the spatial and temporal behavior of the eddy currents.  相似文献   
1000.
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