全文获取类型
收费全文 | 6626篇 |
免费 | 214篇 |
国内免费 | 55篇 |
专业分类
耳鼻咽喉 | 7篇 |
儿科学 | 29篇 |
妇产科学 | 11篇 |
基础医学 | 1340篇 |
口腔科学 | 10篇 |
临床医学 | 156篇 |
内科学 | 261篇 |
皮肤病学 | 1篇 |
神经病学 | 3120篇 |
特种医学 | 128篇 |
外科学 | 218篇 |
综合类 | 492篇 |
预防医学 | 168篇 |
药学 | 760篇 |
中国医学 | 171篇 |
肿瘤学 | 23篇 |
出版年
2023年 | 14篇 |
2022年 | 42篇 |
2021年 | 84篇 |
2020年 | 63篇 |
2019年 | 56篇 |
2018年 | 53篇 |
2017年 | 97篇 |
2016年 | 142篇 |
2015年 | 125篇 |
2014年 | 185篇 |
2013年 | 251篇 |
2012年 | 300篇 |
2011年 | 387篇 |
2010年 | 321篇 |
2009年 | 345篇 |
2008年 | 413篇 |
2007年 | 349篇 |
2006年 | 320篇 |
2005年 | 234篇 |
2004年 | 248篇 |
2003年 | 247篇 |
2002年 | 201篇 |
2001年 | 188篇 |
2000年 | 212篇 |
1999年 | 167篇 |
1998年 | 167篇 |
1997年 | 164篇 |
1996年 | 115篇 |
1995年 | 124篇 |
1994年 | 136篇 |
1993年 | 119篇 |
1992年 | 98篇 |
1991年 | 106篇 |
1990年 | 98篇 |
1989年 | 84篇 |
1988年 | 71篇 |
1987年 | 83篇 |
1986年 | 65篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 25篇 |
1982年 | 49篇 |
1981年 | 42篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 24篇 |
1975年 | 13篇 |
1974年 | 18篇 |
排序方式: 共有6895条查询结果,搜索用时 31 毫秒
91.
Enhanced inhibitory avoidance learning prevents the memory-impairing effects of post-training hippocampal inactivation 总被引:1,自引:0,他引:1
Quiroz C Martínez I Quirarte GL Morales T Díaz-Cintra S Prado-Alcalá RA 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,153(3):400-402
Rats were trained on an inhibitory avoidance task to study the effects of post-training administration of tetrodotoxin (TTX, which temporarily inactivates neural activity) on memory consolidation. During training, independent groups of rats received either a mild foot shock (0.8 mA) or a stronger (1.0 mA) foot shock. TTX was administered bilaterally into the dorsal hippocampus immediately after training, and memory of the task was measured 48 h later. We corroborated the typical amnesic effect of intrahippocampal infusions of TTX in those rats trained with the mild-intensity foot shock. More importantly, with the stronger foot shock, the same treatment was ineffective in producing amnesia. These results suggest that, after an enhanced learning experience, other brain regions are also activated, which may compensate for the amnesic effect of TTX infusions into the hippocampus.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper. 相似文献
92.
Yutaka Endo Jun -Ichi Nishimura Fukuko Kimura 《Pflügers Archiv : European journal of physiology》1994,426(3-4):183-188
The present study examined the effect of glucocorticoid manipulations on local cerebral blood flow in the hippocampus. We measured local cerebral blood flow in the hippocampus at 1-h intervals over a 1-day period in freely moving rats, by means of the H2 clearance method, before and after sham adrenalectomy, adrenalectomy or adrenalectomy with corticosterone replacement. We also measured local cerebral blood flow in the prefrontal cortex before and after adrenalectomy. Four weeks after the adrenalectomy, hippocampal blood flow at each time of day was an average of 47% greater than before the operation, showing diurnal variation as before. After the sham adrenalectomy or adrenalectomy with corticosterone replacement, hippocampal blood flow did not change significantly with respect to either its level or its diurnal variation. Local cerebral blood flow in the prefrontal cortex increased by only 19% after adrenalectomy. The present study demonstrates that adrenalectomy causes a remarkable increase in hippocampal blood flow, probably due to a lack of corticosterone. 相似文献
93.
In order to examine temporal changes in enhancement of transmitter release during long-term potentiation (LTP), we examined amplitude fluctuation of excitatory postsynaptic potentials (EPSPs) for longer periods than 2 h after tetanic stimulation (up to 4 h in the longest observation). The relative magnitude of excitatory postsynaptic potentiation (EPSP) fluctuation (coefficient of variation, CV) reduced throughout the observation periods in association with an increase in EPSP amplitude after tetanic stimulation. The reciprocals of squared CVs (= mean2/variance) were almost in proportion to the magnitude of LTP, and the ratio of 1/CV2 and the LTP magnitude did not change significantly for up to 4 h. These findings suggest that a prolonged enhancement of transmitter release from presynaptic terminals underlies LTP, and the relative contribution of this presynaptic enhancement does not change significantly for 2 h (maybe up to 4 h, or longer) after tetanic stimulation. 相似文献
94.
One of the most common chemicals that behaves as an endocrine disruptor is the compound 4,4′-isopronylidenediphenol, called bisphenol-A. In the previous study, we reported that exposure to bisphenol-A induced the abnormality of dopamine receptor functions in the mouse limbic area, resulting in a supersensitivity of drugs of abuse-induced pharmacological actions. The present study was undertaken to investigate whether prenatal and neonatal exposures to bisphenol-A could alter other behavioral abnormalities such as anxiogenic behavior, motor learning behavior, or memory. In the present study, adult female mice were chronically treated with bisphenol-A-admixed powder food from mating to weaning. All experiments were performed using male pups. Here we found that prenatal and neonatal exposures to bisphenol-A failed to induce anxiogenic effects and motor-learning impairment using the light-dark test, elevated plus maze test, and rota-rod test. On the other hand, we found that prenatal and neonatal exposures to bisphenol-A induced the memory impairment using the step-through passive avoidance test. Immunohistochemical study showed the dramatic reduction in choline acetyltransferase-like immunoreactivity, which is a marker of acetylcholine (ACh) production, in the hippocampus of mice prenatally and neonatally exposed to bisphenol-A. These results suggest that chronic exposures to bisphenol-A could induce the memory impairment associated with the reduction in ACh production in the hippocampus. 相似文献
95.
Soluble and membrane-bound forms of brain acetylcholinesterase in Alzheimer''s disease 总被引:1,自引:0,他引:1
Kathleen M. Schegg Leslie S. Harrington Surl Neilsen Richard M. Zweig John H. Peacock 《Neurobiology of aging》1992,13(6):697-704
In order to determine the effect of Alzheimer's disease on the relative distribution of soluble and membrane-bound molecular forms of acetylcholinesterase (AChE) in the brain, postmortem samples (delay interval less than 12 h) were obtained from parietal cortex (Brodmann area 40) and hippocampus as well as the areas containing their respective projection nuclei, i.e., substantia innominata and septal nucleus, in 9 patients with Alzheimer's disease (AD) and 4 normal controls. The monomer (G1), dimer (G2), and tetramer (G4) forms of AChE were examined. In AD compared to controls, significant changes occurred in area 40 and hippocampus but not in the areas containing projection nuclei, and included loss of mean total AChE activity, decrease in the relative percentage of membrane-bound G4, and increase in the relative percentage of soluble G1---G2. Percent of soluble G4 was unaffected in AD brain. In area 40 but not hippocampus a large increase in percent membrane-bound G1-G2 occurred. Thus, these results emphasize that the selective decrease in membrane-bound G4 accounts for the decrease in total G4 activity in AD brain. 相似文献
96.
Ole Petter Ottersen Jon H. Laake Winfried Reichelt Finn-Mogens Haug Reidun Torp 《Journal of chemical neuroanatomy》1996,12(1):1-14
More than 10 years ago, it was shown by microdialysis that the excitatory transmitter glutamate accumulates in the interstitial space of brain subjected to ischemic insult. This was one of the key observations leading to the formulation of the `glutamate hypothesis' of ischemic cell death. It is now assumed that even a transient glutamate overflow may set in motion a number of events that ultimately cause cell loss in vulnerable neuronal populations. The aim of the present review is to discuss the intracellular changes that underlie the dysregulation of extracellular glutamate during and after ischemia, with emphasis on data obtained by postembedding, electron microscopic immunogold cytochemistry. While the time resolution of this approach is necessarily limited, it can reveal, quantitatively and at a high level of spatial resolution, how the intracellular pools of glutamate and metabolically related amino acids are perturbed during and after an ischemic insult. Moreover, this can be done in animals whose extracellular amino acid levels are monitored by microdialysis, allowing a direct correlation of extra- and intracellular changes. Immunogold analyses of brains subjected to ischemia have identified dendrites and neuronal somata as likely sources of glutamate efflux, probably mediated by reversal of glutamate uptake. The vesicular glutamate pool has been found to be largely unchanged after 20 min of ischemia. Ischemia causes an increased glutamate content and an increased glutamate/glutamine ratio in glial cells, as revealed by double immunogold labelling. This argues against the idea that glial cells contribute to the extracellular overflow of glutamate in the ischemic brain. 相似文献
97.
Apoptosis is an important process in the development and function of the central nervous system (CNS). To study the role of DNA fragmentation factor 45 (DFF45/ICAD) in CNS function, we previously generated DFF45 knockout mice. We found that whereas they exhibit apparently normal CNS development, DFF45 knockout mice exhibit an increased number of granule cells in the dentate gyrus and enhanced spatial learning and memory compared to wild-type mice in a Morris water maze test. In this study, we examined the performance of the DFF45 knockout mice in a novel object recognition task to measure short-term nonspatial memory that is believed to depend on the hippocampal formation. Both wild-type and DFF45 knockout mice exhibited novel object recognition 1 h posttraining. However, whereas wild-type mice no longer did so, DFF45 knockout mice were still able to differentiate the novel versus the familiar object 3 h posttraining. The longer memory retention in DFF45 knockout mice did not last up to 24 h as neither wild-type nor DFF45 knockout mice demonstrated novel object recognition 24 h posttraining. These results suggest that a lack of DFF45 facilitates hippocampus-dependent nonspatial memory, as well as hippocampus-dependent spatial memory. 相似文献
98.
C. Köhler A. Persson T. Melander E. Theodorsson G. Sedvall T. Hökfelt 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1989,75(2):375-380
Summary Using X-ray film autoradiography the distribution of 125I-galanin binding sites was studied in the forebrain of monkey and man. In the monkey a high density was found in all areas of the neocortex, especially layer 4, and in certain subfields in the hippocampal region. Also in the human brain high activity was seen in neocortex, mainly layer 6 and in hippocampal areas, as well as in amygdala, piriform cortex and hypothalamus. These results suggest that the 29-amino acid peptide galanin may be involved in the regulation of higher cortical functions in primates. 相似文献
99.
Calhoun ME Kurth D Phinney AL Long JM Hengemihle J Mouton PR Ingram DK Jucker M 《Neurobiology of aging》1998,19(6):1881-606
A loss of hippocampal neurons and synapses had been considered a hallmark of normal aging and, furthermore, to be a substrate of age-related learning and memory deficits. Recent stereological studies in humans have shown that only a relatively minor neuron loss occurs with aging and that this loss is restricted to specific brain regions, including hippocampal subregions. Here, we investigate these age-related changes in C57BL/6J mice, one of the most commonly used laboratory mouse strains. Twenty-five mice (groups at 2, 14, and 28–31 months of age) were assessed for Morris water-maze performance, and modern stereological techniques were used to estimate total neuron and synaptophysin-positive bouton number in hippocampal subregions at the light microscopic level. Results revealed that performance in the water maze was largely maintained with aging. No age-related decline was observed in number of dentate gyrus granule cells or CA1 pyramidal cells. In addition, no age-related change in number of synaptophysin-positive boutons was observed in the molecular layer of the dentate gyrus or CA1 region of hippocampus. We observed a significant correlation between dentate gyrus synaptophysin-positive bouton number and water-maze performance. These results demonstrate that C57BL/6J mice do not exhibit major age-related deficits in spatial learning or hippocampal structure, providing a baseline for further study of mouse brain aging. 相似文献
100.
目的:了解低压缺氧预处理是否能够诱导小鼠海马神经元产生延迟预适应,增强神经元耐缺氧能力。 方法: 将近交系Babl/c小鼠放入减压舱,模拟海拔7 000 m高度减压2.5 h/d,连续3 d。第3次减压毕36 h后,观察严重低压缺氧(12 000 m 4 h)、严重缺血(双侧颈总动脉阻塞18 min)、缺血合并低压缺氧 (结扎右侧颈总动脉后,低压缺氧8 000 m 4 h)对低压缺氧预处理及正常对照小鼠海马神经元的损伤情况。 结果: 7 000 m 2.5 h低压缺氧预处理对小鼠海马神经元无显著损伤,能够诱导其产生延迟预适应,显著增强海马神经元耐受严重低压缺氧、严重缺血、缺血合并低压缺氧损伤的能力。 结论: 本研究所采用的低压缺氧预处理方法能够诱导海马神经元产生延迟预适应,增强其抗缺血缺氧能力。 相似文献