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   42365篇
  免费   4688篇
  国内免费   3108篇
耳鼻咽喉   454篇
儿科学   485篇
妇产科学   584篇
基础医学   4278篇
口腔科学   723篇
临床医学   5427篇
内科学   5717篇
皮肤病学   461篇
神经病学   1777篇
特种医学   1589篇
外国民族医学   15篇
外科学   4225篇
综合类   8674篇
现状与发展   18篇
一般理论   5篇
预防医学   3777篇
眼科学   966篇
药学   4758篇
  49篇
中国医学   2771篇
肿瘤学   3408篇
  2024年   127篇
  2023年   529篇
  2022年   1356篇
  2021年   2002篇
  2020年   1544篇
  2019年   1367篇
  2018年   1414篇
  2017年   1474篇
  2016年   1287篇
  2015年   1941篇
  2014年   2405篇
  2013年   2477篇
  2012年   3304篇
  2011年   3447篇
  2010年   2560篇
  2009年   2168篇
  2008年   2417篇
  2007年   2449篇
  2006年   2257篇
  2005年   2079篇
  2004年   1828篇
  2003年   2067篇
  2002年   1762篇
  2001年   1392篇
  2000年   968篇
  1999年   775篇
  1998年   447篇
  1997年   439篇
  1996年   276篇
  1995年   275篇
  1994年   246篇
  1993年   158篇
  1992年   168篇
  1991年   155篇
  1990年   123篇
  1989年   98篇
  1988年   72篇
  1987年   58篇
  1986年   57篇
  1985年   49篇
  1984年   22篇
  1983年   25篇
  1982年   13篇
  1981年   13篇
  1979年   12篇
  1977年   10篇
  1976年   7篇
  1974年   7篇
  1973年   8篇
  1972年   6篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Because the impact of periodic limb movements in sleep (PLMS) is controversial, no consensus has been reached on the therapeutic strategy for PLMS in obstructive sleep apnea (OSA). To verify the hypothesis that PLMS is related to a negative impact on the cardiovascular system in OSA patients, this study investigated the basal autonomic regulation by heart rate variability (HRV) analysis. Sixty patients with mild‐to‐moderate OSA who underwent polysomnography (PSG) and completed sleep questionnaires were analysed retrospectively and divided into the PLMS group (n = 30) and the non‐PLMS group (n = 30). Epochs without any sleep events or continuous effects were evaluated using HRV analysis. No significant difference was observed in the demographic data, PSG parameters or sleep questionnaires between the PLMS and non‐PLMS groups, except for age. Patients in the PLMS group had significantly lower normalized high frequency (n‐HF), high frequency (HF), square root of the mean of the sum of the squares of difference between adjacent NN intervals (RMSSD) and standard deviation of all normal to normal intervals index (SDNN‐I), but had a higher normalized low frequency (n‐LF) and LF/HF ratio. There was no significant difference in the Epworth Sleepiness Scale, the Pittsburgh Sleep Quality Index, the Short‐Form 36 and the Hospital Anxiety and Depression Scale between the two groups. After adjustment for confounding variables, PLMS remained an independent predictor of n‐LF (β = 0.0901, P = 0.0081), LF/HF ratio (β = 0.5351, P = 0.0361), RMSSD (β = ?20.1620, P = 0.0455) and n‐HF (β = ?0.0886, P = 0.0134). In conclusion, PLMS is related independently to basal sympathetic predominance and has a potentially negative impact on the cardiovascular system of OSA patients.  相似文献   
992.
目的:了解双相障碍青少年的健康相关危险行为特点。方法:纳入符合疾病和有关健康问题的国际统计分类第十次修订本(ICD-10)双相障碍标准的12~18岁青少年50例(抑郁状态29人,躁狂状态19人,混合状态2人)及性别、年龄相匹配的正常对照100例,完成青少年健康相关危险行为自评问卷(AHRBI),同时由双相障碍患者父母完成青少年健康相关危险行为问卷父母版(AHRBI-P),评估双相障碍青少年在不同疾病状态下的健康相关危险行为。结果:双相障碍组青少年AHRBI总分与攻击与暴力、健康妥协、破坏纪律、无保护性、自杀自伤及吸烟饮酒等6项因子评分均高于正常对照组[如总分,55.5(38,119)vs.46(38,65);P0.05]。其中,26项行为条目双相障碍组评分均高于正常对照组(均P0.05)。双相障碍组AHRBI和AHRBI-P总分及6项因子分之间的差异无统计学意义(均P0.05)。偏相关分析显示(变量赋值抑郁发作=0,躁狂发作=1),AHRBI和AHRBI-P自杀自伤因子得分与发作状态呈负相关(r=-0.32、-0.33;均P0.05),AHRBI攻击与暴力维度下的毁坏财物行为得分与发作状态呈正相关(r=0.32,P0.05)。结论:双相障碍青少年总体健康相关危险行为多于正常对照青少年,并且,患者在6个维度均存在明显增多的健康相关危险行为。评估期间抑郁发作患者自杀风险更高,而躁狂发作患者更易出现毁坏财物行为。  相似文献   
993.
目的 观察动态轴向压应变对三维丝素蛋白支架内成骨细胞成骨相关基因表达的影响。方法 应用动态力学加载仪对实验组小鼠胚胎成骨细胞MC3T3-E1加载动态轴向压应变(5%应变幅度,1 Hz,30 min/d,共21 d),对照组细胞常规静置培养,不施加力学刺激。应用定量PCR检测细胞成骨基因碱性磷酸酶(ALP)、I型胶原(COLⅠ)、骨特异性转录因子(Runx2)、成骨相关转录因子(Osx)、骨钙蛋白(OCN) mRNA表达量。结果 成骨细胞在周期性轴向压应力刺激下,Runx2、Osx及COLⅠ表达分别增加280%、68.9%和79.6%,ALP及OCN表达也分别增加10.7%和26.9%。实验组成骨相关基因mRNA表达与对照组比较,差异具有统计学意义(P<0.05)。结论 成骨细胞复合丝素蛋白生物支架材料在周期性轴向压应力刺激下,成骨基因COLⅠ、Runx2、Osx及OCN表达明显上调,可能是生理状态下压应力刺激促进骨折愈合的重要机制之一。研究结果对于以力学信号为基础的细胞疗法修复骨缺损等疾病具有重要临床价值。  相似文献   
994.
Sturge–Weber syndrome (SWS) is a rare syndrome characterized by capillary‐venous malformations involving skin and brain. Many patients with SWS also suffer from drug‐resistant epilepsy. We retrospectively studied a series of six SWS patients with epilepsy and extensive neurosurgical resections. At time of surgery, the patients' age ranged from 11 to 35 years (with a mean of 20.2 years). All surgical specimens were well preserved, which allowed a systematic microscopical inspection utilizing the 2011 ILAE classification for focal cortical dysplasia (FCD). Neuropathology revealed dysmorphic‐like neurons with hypertrophic cell bodies reminiscent to those described for FCD type IIa in all cases. However, gross architectural abnormalities of neocortical layering typical for FCD type IIa were missing, and we propose to classify this pattern as FCD ILAE type IIIc. In addition, our patients with earliest seizure onset also showed polymicrogyria (PMG; n = 4). The ictal onset zones were identified in all patients by subdural electrodes, and these areas always showed histopathological evidence for FCD type IIIc. Four out of five patients had favorable seizure control after surgery with a mean follow‐up period of 1.7 years. We concluded from our study that FCD type IIIc and PMG are frequently associated findings in SWS. FCD type IIIc may play a major epileptogenic role in SWS and complete resection of the associated FCD should be considered a prognostic key factor to achieve seizure control.  相似文献   
995.
Probing a wide range of cellular phenotypes in neurodevelopmental disorders using patient-derived neural progenitor cells (NPCs) can be facilitated by 3D assays, as 2D systems cannot entirely recapitulate the arrangement of cells in the brain. Here, we developed a previously unidentified 3D migration and differentiation assay in layered hydrogels to examine how these processes are affected in neurodevelopmental disorders, such as Rett syndrome. Our soft 3D system mimics the brain environment and accelerates maturation of neurons from human induced pluripotent stem cell (iPSC)-derived NPCs, yielding electrophysiologically active neurons within just 3 wk. Using this platform, we revealed a genotype-specific effect of methyl-CpG-binding protein-2 (MeCP2) dysfunction on iPSC-derived neuronal migration and maturation (reduced neurite outgrowth and fewer synapses) in 3D layered hydrogels. Thus, this 3D system expands the range of neural phenotypes that can be studied in vitro to include those influenced by physical and mechanical stimuli or requiring specific arrangements of multiple cell types.Neuronal migration and maturation is a key step in brain development. Defects in this process have been implicated in many disorders, including autism (1) and schizophrenia (2). Thoroughly understanding how neural progenitor cell (NPC) migration is affected in neurodevelopmental disorders requires a means of dissecting the process using cells with genetic alterations matching those in patients. Existing in vitro assays of migration generally involve measurement of cell movement across a scratch or gap or through a membrane toward a chemoattractant in 2D culture systems. Although widely used, such assays may not accurately reveal in vivo differences, as neuronal migration is tightly regulated by physical and chemical cues in the extracellular matrix (ECM) that NPCs encounter as they migrate.In vitro 3D culture systems offer a solution to these limitations (37). Compared with 2D culture, a 3D arrangement allows neuronal cells to interact with many more cells (4); this similarity to the in vivo setting has been shown to lengthen viability, enhance survival, and allow formation of longer neurites and more dense networks in primary neurons in uniform matrices or aggregate culture (8, 9). Indeed, 3D culture systems have been used to study nerve regeneration, neuronal and glial development (1012), and amyloid-β and tau pathology (13). Thus, measuring neuronal migration through a soft 3D matrix would continue this trend toward using 3D systems to study neuronal development and pathology.We sought to develop a 3D assay to examine potential migration and neuronal maturation defects in Rett syndrome (RTT), a genetic neurodevelopmental disorder that affects 1 in 10,000 children in the United States and is caused by mutations in the X-linked methyl-CpG-binding protein-2 (MECP2) gene (14). Studies using induced pluripotent stem cells (iPSCs) from RTT patients in traditional 2D adherent culture have revealed reduced neurite outgrowth and synapse number, as well as altered calcium transients and spontaneous postsynaptic currents (1). However, 2D migration assays seemed unlikely to reveal inherent defects in this developmental process, which could be affected because MeCP2 regulates multiple developmental related genes (15). Migration of RTT iPSC-derived NPCs has not previously been studied.Using a previously unidentified 3D tissue culture system that allows creation of layered architectures, we studied differences in migration of MeCP2-mutant iPSC-derived versus control iPSC-derived NPCs. This approach revealed a defect in migration of MeCP2-mutant iPSC-derived NPCs induced by either astrocytes or neurons. Further, this 3D system accelerated maturation of neurons from human iPSC-derived NPCs, yielding electrophysiologically active neurons within just 3 wk. With mature neurons derived from RTT patients and controls, we further confirmed defective neurite outgrowth and synaptogenesis in MeCP2-mutant neurons. Thus, this 3D system enables study of morphological features accessible in 2D system as well as previously unexamined phenotypes.  相似文献   
996.
OBJECTIVE: Human cord blood (CB) is a potential source of hematopoietic stem cells (HSC) for gene therapy to treat patients with hematopoietic disorders. However, limited numbers of CB CD34(+) cells, low transduction efficiency with lentiviral vectors (LVs), and low engraftment efficiency of nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cells (SRC), a measure of HSC, are blocks to this procedure. To optimize culture and transduction conditions, we compared various lengths of time for prestimulation before transduction, transduction duration, and posttransduction cell culture. MATERIALS AND METHODS: We used a LV to transduce human CB CD34(+) cells followed by engraftment into NOD/SCID mice. We evaluated the effects of prestimulation and transduction time and optimized ex vivo cell culture duration before transplantation. RESULTS: We were able to achieve up to 40% transduction efficiency and up to 50% engraftment efficiency of SRC in CB CD34(+) cells when CB CD34(+) cells were either not prestimulated or prestimulated in 1% fetal bovine serum medium for 1 hour, followed by 5 hours transduction and 3 days culture in a cocktail of growth factors after transduction. No apparent functional changes of CB CD34(+) cells were noted under these conditions. CONCLUSION: This gene-transduction/cell-expansion protocol is the first systematic study to optimize prestimulation time, transduction time, and, very importantly, ex vivo culture time after transduction, and may be of use for LV gene transduction in a gene therapy setting.  相似文献   
997.
BACKGROUND: Patent foramen ovale (PFO) is a well-recognized risk factor for ischemic strokes. The true prevalence of PFO among stroke patients is still under debate. Transesophageal echocardiography (TEE) is the "gold standard" in diagnosing PFO but the physiology requires right-to-left atrial shunting. In this report, we evaluate the prevalence of PFO in a diverse group of ischemic stroke patients studied by TEE. METHODS: TEE of 1,663 ischemic stroke patients were reviewed for cardiac source of embolism, including PFO and atrial septal aneurysm (ASA). Agitated saline bubble injection was performed to look for right to left atrial shunting. Success of maneuvers to elevate right atrial pressure (RAP) was noted by looking at the atrial septal bulge. RESULTS: Among 1,435 ischemic stroke patients analyzed, the presence or absence of PFO could not be determined in 32.1% because bulging of the septum could not be demonstrated in patients with negative contrast study despite aggressive maneuvers to elevate RAP. Of the remaining 974 patients, 294 patients (30.2%) had a PFO. The mean age was 61.5 years in both groups, with a bimodal distribution of PFO and the highest prevalence occurring in < or =30-year-old group. Prevalence of PFO was similar in men (32.4%) and women (28.15%, P = 0.15); and in Caucasian (32.1%) and African American (27.7%; P = 0.15). ASA was present in 2.02% and hypermobile septum in 2.49% of the 1,435 patients. PFO was seen in 79.3% of the patients with ASA. CONCLUSION: Successful elevation of RAP cannot be achieved in a significant number of patients undergoing TEE and determination of PFO may be difficult. In our series, the true prevalence of PFO among ischemic stroke patients was 30.2% taking into account only those patients who showed no shunting despite bulging of the atrium septum into the left atrium (PFO absent group) during the contrast study. There was no gender or racial difference in the prevalence of PFO, but there was a bimodal distribution in prevalence with age.  相似文献   
998.
中国人群缺血性脑卒中相关基因的多态性分析   总被引:1,自引:0,他引:1  
目的 探讨中国人缺血性脑卒中与凝血因子、细胞粘附分子、血小板膜糖蛋白、血浆凝血酶原激活物抑制剂1以及肿瘤坏死因子基因多态性的关系。方法 利用PCR技术和分子杂交技术对1122例缺血性脑卒中患者进行10个基因17个多态性位点的检测和分析,并与1123例非卒中对照进行比较。结果 缺血性脑卒中患者肿瘤坏死因子βthr26asn多态性分布与对照组相比具有显著差异。其他基因多态性的基因型频率和等位基因频率与对照组相比无明显差异。结论 肿瘤坏死因子βthr26asn多态性分布与中国人缺血性脑卒中的发生具有关联性,提示TNFβ thr26asn多态性可能是中国人群缺血性脑卒中发生的一个遗传学危险因素。  相似文献   
999.
PURPOSE: To report the need for multiple surgical interventions to treat recurrent aortic aneurysms in a patient with Cogan syndrome. CASE REPORT: A 17-year-old Chinese man with clinical Marfanoid features had a left common carotid artery pseudoaneurysm electively repaired with an autologous saphenous vein graft. Four months later, he presented with acute chest pain. Computed tomography (CT) revealed a 1-cm pseudoaneurysm at the mid descending aorta; a 24 x 100-mm Talent stent-graft was implanted to exclude the pseudoaneurysm. He was also found to have increasing left-sided hearing loss. A month later, the patient was re-admitted with vertigo and keratitis, which were treated appropriately. Nine months following stent-graft insertion, he was admitted with acute hemoptysis. Urgent CT showed a rupture at the proximal end of the stent-graft, with hemorrhage into the lung parenchyma. In an emergent procedure, the stent-graft was removed, and the descending thoracic aorta was repaired. Intraoperatively, a large pseudoaneurysm was found arising from the proximal part of the stented aorta, which appeared thickened. His postoperative recovery was uneventful. Nine months after the thoracotomy, a routine CT revealed an aneurysm at the distal descending thoracic aorta. On re-thoracotomy, a de novo saccular aneurysm was found 2.5 cm from the distal anastomosis. The affected segment was replaced with a Dacron graft. The distal aorta appeared thickened and edematous; histology confirmed aortitis. The patient was subsequently diagnosed with Cogan syndrome and given corticosteroids and methotrexate. There is no evidence of recurrence at nearly 2 years after the last intervention. CONCLUSION: This case highlights the pitfalls of stent-graft repair in a patient with presumed connective tissue disease.  相似文献   
1000.
目的:采用荷瘤动物模型经化疗联合被动免疫治疗,初步探讨化疗免疫"窗口期"对卵巢癌免疫应答的影响及其可能的免疫学机制。方法:以荷瘤大鼠为研究对象,根据紫杉醇联合卡铂对荷瘤鼠免疫功能改变的不同时期给予CTL(cytotoxic T-lymphocyte)主动免疫治疗。观察荷瘤体积及机体免疫微环境改变。结果:荷瘤鼠紫杉醇和卡铂化疗后不同时期给予CTL转输治疗,其中化疗后第6天即淋巴细胞数最少期,给予免疫治疗,肿瘤生长最缓慢;CT扫描结果示,化疗后6天+免疫治疗组的瘤体积最小,且与其余治疗组有统计学意义。荷瘤鼠免疫功能示,化疗后6天+免疫治疗组中淋巴细胞抗原特异性增殖及CD8+T细胞最明显,而Treg(T-Lymphocytes,Regulatory)细胞明显降低。结论:紫杉醇和卡铂联合CTL治疗肿瘤具有协同作用,其中化疗后6天(即淋巴细胞降到最低期)是CTL免疫治疗的最佳时间点。化疗造成的肿瘤个体免疫功能的低下或是免疫系统空间的释放(所谓的免疫"窗口期")为诱导特异性的抗肿瘤免疫应答提供了可能,免疫状态的检测是保证肿瘤患者化疗联合免疫治疗方案治疗有效性的重要前提之一。  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