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   1530篇
  免费   220篇
  国内免费   16篇
  1766篇
  2024年   7篇
  2023年   27篇
  2022年   34篇
  2021年   47篇
  2020年   48篇
  2019年   56篇
  2018年   41篇
  2017年   60篇
  2016年   48篇
  2015年   52篇
  2014年   110篇
  2013年   93篇
  2012年   61篇
  2011年   68篇
  2010年   39篇
  2009年   64篇
  2008年   62篇
  2007年   70篇
  2006年   61篇
  2005年   50篇
  2004年   46篇
  2003年   30篇
  2002年   22篇
  2001年   27篇
  2000年   38篇
  1999年   40篇
  1998年   29篇
  1997年   31篇
  1996年   29篇
  1995年   37篇
  1994年   27篇
  1993年   37篇
  1992年   25篇
  1991年   17篇
  1990年   22篇
  1989年   28篇
  1988年   25篇
  1987年   14篇
  1986年   20篇
  1985年   14篇
  1984年   19篇
  1983年   12篇
  1982年   17篇
  1981年   17篇
  1980年   9篇
  1979年   6篇
  1977年   6篇
  1973年   5篇
  1972年   5篇
  1970年   6篇
排序方式: 共有1766条查询结果,搜索用时 11 毫秒
21.
Summary Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion ofCiona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods.Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP),-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth hormone (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP).Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract.No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion.At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.  相似文献   
22.
Abstract Cationic amphiphilic drugs (CADs) of varied clinical use were screened to determine their capacity to alter the pattern of labeling with 32Pj of cerebral cortex mince phospholipids. The altered phospholipid labeling patterns were qualitatively similar, the prominent features being reduced incorporation into phosphatidylcholine and increased incorporation into phosphatidic acid. Relative potencies were: (±)-propranolol > chlorpromazine = 4,4'-bis(diethylaminoethoxy) α,β -diethyldiphenylethane > desipramine > di-bucaine > pimozide > oxymetazoline = fenfluramine = haloperidol = chloroquine > amphetamine = no drug added. Propranolol was used to study the action of CADs further. Its effect was time- and dose-dependent, but in contrast with pineal gland, no label appeared in phosphatidyl-CMP (CDP-diacylglycerol), nor did dialysis of the mince to reduce diffusible substrates or exogenous addition of substrates cause appearance of liponucleotide. Thus lack of diffusible precursors is not responsible for CAD effects in vitro. Pulse-chase experiments with 32P1 and [2-3H]glycerol suggested that inhibition of phosphatidate phosphohydrolase may be partly responsible for the observed alterations in phospholipid labeling in the presence of CADs.  相似文献   
23.
In response to injury of the central nervous system, astrocytes become reactive and express high levels of the intermediate filament (IF) proteins glial fibrillary acidic protein (GFAP), vimentin, and nestin. We have shown that astrocytes in mice deficient for both GFAP and vimentin (GFAP-/-vim-/-) cannot form IFs even when nestin is expressed and are thus devoid of IFs in their reactive state. Here, we have studied the reaction to injury in the central nervous system in GFAP-/-, vimentin-/-, or GFAP-/-vim-/- mice. Glial scar formation appeared normal after spinal cord or brain lesions in GFAP-/- or vimentin-/- mice, but was impaired in GFAP-/-vim-/- mice that developed less dense scars frequently accompanied by bleeding. These results show that GFAP and vimentin are required for proper glial scar formation in the injured central nervous system and that some degree of functional overlap exists between these IF proteins.  相似文献   
24.
Photoacoustics and high frequency ultrasound stands out as powerful tools for neurobiological applications enabling high-resolution imaging on the central nervous system of small animals. However, transdermal and transcranial neuroimaging is frequently affected by low sensitivity, image aberrations and loss of space resolution, requiring scalp or even skull removal before imaging. To overcome this challenge, a new protocol is presented to gain significant insights in brain hemodynamics by photoacoustic and high-frequency ultrasounds imaging with the animal skin and skull intact. The procedure relies on the passage of ultrasound (US) waves and laser directly through the fissures that are naturally present on the animal cranium. By juxtaposing the imaging transducer device exactly in correspondence to these selected areas where the skull has a reduced thickness or is totally absent, one can acquire high quality deep images and explore internal brain regions that are usually difficult to anatomically or functionally describe without an invasive approach. By applying this experimental procedure, significant data can be collected in both sonic and optoacoustic modalities, enabling to image the parenchymal and the vascular anatomy far below the head surface. Deep brain features such as parenchymal convolutions and fissures separating the lobes were clearly visible. Moreover, the configuration of large and small blood vessels was imaged at several millimeters of depth, and precise information were collected about blood fluxes, vascular stream velocities and the hemoglobin chemical state. This repertoire of data could be crucial in several research contests, ranging from brain vascular disease studies to experimental techniques involving the systemic administration of exogenous chemicals or other objects endowed with imaging contrast enhancement properties. In conclusion, thanks to the presented protocol, the US and PA techniques become an attractive noninvasive performance-competitive means for cortical and internal brain imaging, retaining a significant potential in many neurologic fields.  相似文献   
25.
目的探讨cAMP/PKA-pCREB信号通路是否在康复训练促进的缺血性脑卒中大鼠运动功能的恢复方面发挥作用。方法采用Longa改良线栓法制备大鼠大脑中动脉缺血再灌注模型(middle cerebral artery ischemia-reperfusion model,MCAO),造模成功的大鼠随机分为自然恢复组(n=24)、自然恢复+Rp-cAMP组(n=24)、康复训练组(n=18)和康复训练+Rp-cAMP组(n=18)。同时设立假手术组(n=12)。于侧脑室注射RpcAMP后立即进行MCAO模型的制备。训练组大鼠于术后48 h开始每天给予平衡木、转棒及滚筒训练。采用平衡木试验评定大鼠的运动功能。酶联免疫法(ELISA)检测缺血灶周围的脑组织内PKA表达,蛋白免疫印迹法(Western blot)检测pCREB蛋白表达,同时采用免疫组化法对pCREB进行定位检测。结果 (1)运动功能评分结果揭示,自然恢复+Rp-cAMP组大鼠的运动功能低于自然恢复组,提示Rp-cAMP可抑制脑缺血大鼠运动神经功能的恢复;康复训练组大鼠的运动功能明显高于自然恢复组,也高于康复训练+Rp-cAMP组,提示Rp-cAMP明显减弱康复训练促进脑缺血大鼠运动神经功能的恢复;(2)于术后2 d、7 d、14 d、21 d检测缺血灶周围的脑组织PKA、pCREB的蛋白表达结果显示:康复训练组明显高于自然恢复组,同时高于康复训练+Rp-cAMP组,提示康复训练促进脑缺血大鼠的PKA、pCREB蛋白的表达,且Rp-cAMP明显抑制了康复训练促进脑缺血大鼠的PKA、pCREB蛋白的表达。结论 cAMP/PKA-pCREB信号通路可能介导康复训练促进的脑缺血大鼠运动功能的恢复。  相似文献   
26.
Adenosine is a neuromodulator, and it has been suggested that cerebral acetate metabolism induces adenosine formation. In the present study the effects that acetate has on cerebral intermediary metabolism, compared with those of glucose, were studied using the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Fasted rats received an intravenous injection of CCPA, DPCPX, or vehicle. Fifteen minutes later either [1,2-13C]acetate or [1-13C]glucose was given intraperitoneally; after another 30 min the rats were decapitated. Cortical extracts were analyzed with 13C NMR spectroscopy and HPLC analysis. DPCPX affected neuronal and astrocytic metabolism. De novo synthesis of GABA from neuronal and astrocytic precursors was significantly reduced. De novo syntheses of glutamate and aspartate were at control levels, but their degradation was significantly elevated. In glutamine the anaplerotic activity and the amount of label in the position representing the second turn in the tricarboxylic acid cycle were significantly increased, suggesting elevated metabolic activity in astrocytes. CCPA did not influence GABA, aspartate, or glutamine synthesis. In glutamate the contribution from the astrocytic anaplerotic pathway was significantly decreased. In the present study the findings in the [1,2-13C]acetate and [1-13C]glucose control, CCPA, and DPCPX groups were complementary, and no adenosine A1 agonist effects arising from cerebral acetate metabolism were detected.  相似文献   
27.
高血压脑出血是当今社会一种发病率及死亡率都非常高的神经科疾病,对于它的治疗,则是神经内外科的重点难点。目前治疗高血压脑出血的方法分为内科保守治疗和外科手术治疗两种,作者阅读了大量国内外临床相关文献,综述了高血压脑出血相关内外科治疗的方法,以及具体应用,望能为其相关研究提供有益的思路。  相似文献   
28.
29.
摘要 目的:分析颈性眩晕中医证型与经颅超声脑动脉血流检测结果的相关性。方法:选取2021年5月-2023年5月收治颈性眩晕患者作为研究对象,根据不同中医证型分为痰湿中阻组、肝阳上亢组、肝肾阴虚组和气血亏虚组,每组各纳入20例;并另选取健康体检患者30例作为对照组,均给予多普勒超声检查。分析不同中医证型者与对照组者多普勒超声检查特征与脑动脉血流变化[左右椎动脉、基底动脉及大脑中动脉收缩期峰值血流速度(VS)、平均血流速度(Vm)、舒张期峰值血流速度(Vd)及搏动指数(PI)]。结果:痰湿中阻组、肝肾阴虚组和气血亏虚组左右椎动脉、基底动脉及大脑中动脉VS均低于对照组(P<0.05);肝阳上亢组左右椎动脉、基底动脉及大脑中动脉VS均高于对照组(P<0.05);不同中医证型组间VS比较,肝阳上亢组>痰湿中阻组>肝肾阴虚组>气血亏虚组;痰湿中阻组左右椎动脉、基底动脉均高于对照组(P<0.05),大脑中动脉Vm均低于对照组(P<0.05);肝阳上亢组左右椎动脉、基底动脉及大脑中动脉Vm均高于对照组(P<0.05);肝肾阴虚组左右椎动脉、基底动脉及大脑中动脉Vm均低于对照组(P<0.05);气血亏虚组大脑中动脉Vm均低于对照组(P<0.05),左右椎动脉、基底动脉Vm和对照组无显著性差异(P>0.05);不同中医证型组间Vm比较,肝阳上亢组>痰湿中阻组>气血亏虚组>肝肾阴虚组;痰湿中阻组左右椎动脉、基底动脉Vd均低于对照组(P<0.05),大脑中动脉Vd均高于对照组(P<0.05);肝阳上亢组左右椎动脉、基底动脉及大脑中动脉Vd均低于对照组(P<0.05);肝肾阴虚组左右椎动脉及大脑中动脉Vd均低于对照组(P<0.05),基底动脉Vd和对照组无差异(P>0.05);气血亏虚组左右椎动脉Vd均低于对照组(P<0.05),基底动脉Vd和对照组无差异(P>0.05),大脑中动脉Vd均高于对照组(P<0.05);不同中医证型组间Vd比较,气血亏虚组>痰湿中阻组>肝肾阴虚组>肝阳上亢组;痰湿中阻组和气血亏虚组左右椎动脉、基底动脉及大脑中动脉PI均低于对照组(P<0.05);肝阳上亢组和肝肾阴虚组左右椎动脉、基底动脉及大脑中动脉PI均高于对照组(P<0.05);不同中医证型组间PI比较,肝阳上亢组>肝肾阴虚组>痰湿中阻组>气血亏虚组。结论:不同中医证型的眩晕患者会出现不同程度脑动脉血流动力学异常,且不同组间存在差异,通过经颅多普勒超声检查,可以对眩晕中医证型提供参考价值。  相似文献   
30.
摘要 目的:研究银杏内酯注射液联合胞磷胆碱钠片对脑梗死恢复期患者脑血流动力学、氧化应激和血清单核细胞趋化蛋白-1(MCP-1)、脂蛋白相关磷脂酶A2(Lp-PLA2)的影响。方法:按照随机数字表法,将安徽中医药大学第一附属医院146例脑梗死恢复期患者分为对照组(n=73,采用常规治疗和胞磷胆碱钠片治疗)和研究组(n=73,对照组基础上结合银杏内酯注射液)。对比两组临床疗效、Barthel指数(BI)评分、美国国立卫生研究院卒中量表(NIHSS)评分、脑血流动力学指标、血清氧化应激指标、MCP-1、Lp-PLA2和用药安全性。结果:与对照组的82.19%临床总有效率对比,研究组的97.26%更高(P<0.05)。治疗后,研究组BI评分、平均血流速度(Vm)、血清超氧化物歧化酶(SOD)、过氧化氢酶(CAT)较对照组更高,NIHSS评分、搏动指数(PI)、阻力指数(RI)、血清活性氧(ROS)、血清MCP-1、Lp-PLA2较对照组更低(P<0.05)。两组不良反应发生率组间对比未见差异(P>0.05)。结论:银杏内酯注射液联合胞磷胆碱钠片可减轻脑梗死恢复期患者的神经功能损伤,改善患者的脑血流动力学,减轻氧化应激,调节血清MCP-1、Lp-PLA2水平,且用药安全性良好。  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