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   5782篇
  免费   357篇
  国内免费   152篇
耳鼻咽喉   52篇
儿科学   26篇
妇产科学   11篇
基础医学   1061篇
口腔科学   20篇
临床医学   189篇
内科学   515篇
皮肤病学   1篇
神经病学   3473篇
特种医学   24篇
外科学   123篇
综合类   161篇
预防医学   40篇
眼科学   106篇
药学   366篇
  1篇
中国医学   65篇
肿瘤学   57篇
  2024年   16篇
  2023年   46篇
  2022年   135篇
  2021年   242篇
  2020年   146篇
  2019年   102篇
  2018年   128篇
  2017年   140篇
  2016年   141篇
  2015年   164篇
  2014年   251篇
  2013年   291篇
  2012年   242篇
  2011年   320篇
  2010年   263篇
  2009年   299篇
  2008年   374篇
  2007年   288篇
  2006年   271篇
  2005年   246篇
  2004年   228篇
  2003年   191篇
  2002年   157篇
  2001年   122篇
  2000年   91篇
  1999年   87篇
  1998年   102篇
  1997年   120篇
  1996年   111篇
  1995年   73篇
  1994年   81篇
  1993年   87篇
  1992年   69篇
  1991年   68篇
  1990年   64篇
  1989年   45篇
  1988年   56篇
  1987年   49篇
  1986年   56篇
  1985年   70篇
  1984年   45篇
  1983年   32篇
  1982年   35篇
  1981年   37篇
  1980年   32篇
  1979年   8篇
  1978年   12篇
  1977年   14篇
  1976年   11篇
  1973年   8篇
排序方式: 共有6291条查询结果,搜索用时 12 毫秒
991.
Galanin is a widely-distributed neuropeptide that acts as an endogenous anticonvulsant. We have recently generated a galanin receptor type 1 knockout mouse (Galr1(-/-)) that develops spontaneous seizures. Our aim here was to characterize the seizures by making electroencephalogram (EEG) recordings from this animal, and also to elucidate the cellular basis of its epileptic phenotype by studying the neurophysiology of CA1 pyramidal neurons in acute hippocampal slices. EEGs showed that major seizures had a partial onset with secondary generalization, and that paroxysms of spike-and-slow waves occurred and were associated with hypoactivity. The interictal EEG was also abnormal, with a marked excess of spike-and-slow waves. Slice experiments showed that resting potential, input resistance, intrinsic excitability, paired-pulse facilitation of excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs), stimulus--response plots for EPSCs, and several properties of spontaneous miniature EPSCs and IPSCs were all unchanged in the mutant mouse compared with wildtype. However, the frequency of miniature IPSCs was significantly reduced in the mutants. These results suggest that impaired synaptic inhibition in the hippocampus may contribute to the local onset of seizures in the Galr1(-/-) mouse.  相似文献   
992.
Research concerned with the effects of early brain damage upon the ontogeny of feeding and drinking behaviors is described. The neural areas discussed are the olfactory bulbs, frontal cortex, lateral hypothalamic area, substantia nigra-nigrostriatal bundle, reticular formation, and central gustatory structures. The effects of early (infancy) and late (adulthood) brain damage upon consummatory behaviors are described, and critical ages are defined. For each neural area, the critical age is the age during development when damage to a specified neural area produces consummatory behavior alteration which is equivalent to consummatory behavior alteration produced when the neural area is destroyed in adults. Critical ages were found to differ for different neural areas, e.g., 7–8 days of age for lateral hypothalamic area, 60 days of age for frontal cortex. These critical ages may serve to signal the ontogenetic onset of function of neural substrates of consummatory behaviors and/or neural plasticity preserves function when damage occurs prior to the critical age.  相似文献   
993.
Glutamate decarboxylase (GAD)activity, a marker for GABAergic structures, was studied in the cat red nucleus. GAD is more concentrated in the rostral than in the caudal third of the structure.GAD levels were measured after chronic unilateral lesions of the cerebellum. Destruction of the dentate area and of the nucleus interpositus induced increases of GAD in the contralateral but not in the ipsilateral red nucleus. Similar changes also occurred in the denervated nucleus ventralis lateralis (VL) and nucleus ventralis anterior (VA) of the thalamus.Results show that loss of the excitatory cerebellar input could lead to changes in inhibitory GABAergic nerve terminals. This increase may be induced transsynaptically within existing neurons or, more likely, additional GAD-containing nerve terminals may be formed by axonal sprouting.  相似文献   
994.
Anatomical connections between the dorsal hippocampus and subiculum were examined in the rabbit, using horseradish peroxidase (HRP) and autoradiographic methods. A previously undescribed pathway was found to project from the dorsal prosubicular-subicular region to dorsal hippocampal cell fields CA1 and CA2. Autoradiographic findings showed that subicular afferents travel via two routes. One pathway projected through the alveus and stratum oriens, with results suggesting collateral input to the basal dendritic pyramidal cell region. The other projection coursed through the stratum lacunosum-moleculare with apparent termination onto CA1 and CA2 apical dendrites. Regions of subiculum providing afferents to hippocampus were compared with subicular areas receiving efferent terminations from hippocampal CA1 and CA3 cell zones. Distribution of hippocampal-subicular terminations were regionally distinct from subicular retrograde cell fields in rostral areas of the subicular complex, extended over a much wider area of subiculum than was seen for retrograde-labeled cells, and was cytoarchitectonically organized. In total, findings indicated that a reciprocal anatomical relationship exists between dorsal hippocampus and subiculum in the rabbit.  相似文献   
995.
Long descending fibers of the medial forebrain bundle terminate on path neurons in the lateral hypothalamic and preoptic regions. The axons of the path neurons bifurcate to project rostrally and caudally giving off many short collaterals to adjacent path neurons. Thus, the path neuron system of the medial forebrain bundle forms a series of reverberatory loops in the lateral hypothalamus. findings obtained by combining conditioning test stimulation and instrumental self-stimulation techniques in the rat indicate that (a) such neurons, which, like path neurons, give short excitatory collaterals to each other, are excited by lateral hypothalamic rewarding electrical pulses. Weak stimulation of the lateral hypothalamic self-stimulation loci results in poststimulatory excitability changes time course of which resembles the shape of excitatory postsynaptic potentials. The 0.5–0.6 msec long latencies correspond to the sum of the synaptic transmission time plus a few tenths of a msec required for the conduction of excitation in the collaterals between adjacent path neurons and for the electrotonic conduction of depolarization in the postsynaptic (i.e. synaptically activated) path neurons (Experiments 1 and 2). (b) Excitability curves obtained with more intense stimulation reflect definite signs of repeated synaptic activation (Experiment 1) and reverberation (Experiment 3). Rebound aftereffects recorded immediately after the end of rewarding intracranial stimulus trains also suggest that, during stimulation, reverberatory circuits are activated. However, a negative feedback inhibition which is also reflected by the excitability curves (Experiment 3) suppresses the reverberatory activity until the end of the rewarding stimulus train and a release occurs afterwards. The observations are interpreted as indicating that the excitation of the path neuron system of medial forebrain bundle is responsible for the lateral hypothalamic self-stimulation. With regard to the various psychological theories of reinforcement (the expectancy model and motor facilitation hypothesis of Milner, Miller's go mechanism, the postinhibitory rebound theory of Grastyán, drive-reduction and drive-induction theories) a possibility is also discussed that the path neuron system is capable to serve as an unitary anatomical substrate for reward.  相似文献   
996.
Summary The barrelfield is the cortical map of the ensemble of vibrissal follicles on the mouse whiskerpad.Earlier, we had shown that the skin of the embryonic whiskerpad, when put in culture before having received its innervation, is capable of producing vibrissal follicles arranged in a pattern similar to that formed in vivo; we had also demonstrated that the destruction of vibrissal follicles, and of the terminals that innervate them, leads to important modifications in the architecture of the barrelfield.Here we report on the architecture of barrelfields made to differ from normal as a consequence of radical modifications produced in the corresponding whiskerpad during gestation and at birth: transplantation of additional whiskerpads; rotations (of 90° and 180°) of one whiskerpad; removal and reimplantation of one whiskerpad; removal of one whiskerpad; and division of the infraorbital nerve.The results of these experiments, in which only the morphological correlates of a sensory cortical map have been studied, strengthen the hypothesis that the role played by the sensory periphery in the establishment of such an entity is, indeed, an important one.  相似文献   
997.
Quantal postsynaptic currents were recorded by a macro-patch-clamp electrode from synaptic spots on the opener muscle of the walking leg of large crayfish at 0° to 4°C. Through the same electrode, current pulses were applied which de- or hyperpolarized the nerve terminal. The depolarizing test pulse of fixed amplitude and duration elicited EPSCs with an average quantum contentm 1. If the test pulse was preceded or followed immediately by a modulatory hyperpolarizing pulse, the quantum contentm 1p of the EPSC was reduced by factorsm 1/m 1p up to 10. This modulation of release increased with amplitude and duration of hyperpolarization, reaching a saturation level for durations >3 ms. If an interval was interposed between modulatory hyperpolarization and test pulse, the reduction of release decayed with increasing interval with a time constant of about 2 ms. The releasem 2 due to a second test pulse following the first one with 10 ms interval was facilitated,m 2/m 1>1. If release by the first test pulse was modulated by associated hyperpolarizing pre- or postpulses, facilitation of the second test EPSC was not reduced in comparison to facilitation without modulation. The time course of phasic release (distribution of delays of quanta after test pulse) was not appreciably affected by hyperpolarizing pre-pulses, but such post-pulses shortened the delay of the maximum of release.The effects of modulatory pre- and post-pulses could be described by an extension of the model given in H. Parnas et al. (1986). Release sites,S, are assumed to have two inactive states,T 1 andT. In the reactionT 1TS the rate constants are potential dependent, depolarization promoting the stateS and hyperpolarization the stateT 1. At rest,S is very low andT andT 1 both have high values. These reactions are essentially independent of [Ca]i. The kinetics of the system were stimulated for an assumed set of parameters. The simulated responses showed all essential features of the experimentally observed modulation.This study was supported by a grant of the Deutsche Forschungsgemeinschaft  相似文献   
998.
The effect of visual training30 on the synapses in the visual cortex of rabbits was quantitatively investigated. The number, the size and the fine structural organization of synaptic grids were analyzed in 0.5 μm E-PTA sections. The size of the pre- and postsynaptic terminals, the length of the apposition zones, the number of synaptic vesicles per terminal, the dimensions of the synaptic cleft and postsynaptic density and the frequency of mitochondria and spine apparatuses were studied in conventional OsO4 sections.As compared to control animals, the synaptic population of visually trained rabbits exhibits 3 important changes:
1. (1) the number of complex grids has significantly increased; (perforated synapses according to refs. 6 and 24),
2. (2) the size of the synaptic grids has decreased. As is deduced from careful electron microscopic observations, this decrease in size is the result of a focalization of large grids.
3. (3) a significant increase in thickness of the postsynaptic density and a decrease in synaptic cleft is observed. The changes are most pronounced in deep layers (L IV and V) and are almost absent in superficial layers (L I).
On account of recent insights into the mechanism of synaptic transmission and of the intrinsic relation between the fine structural components of the synaptic junction and the process of transmitter release, the observed changes are interpreted as an expression of enhanced synaptic efficacy. It is further postulated that modification of synaptic efficacy must be considered as an important factor in the adaptation of the nervous system to changing environmental conditions and for the consolidation of memory traces.  相似文献   
999.
Role of cholinergic synapses in vestibular compensation   总被引:1,自引:0,他引:1  
  相似文献   
1000.
Summary A cerebral biopsy was performed in a 39-year-old male patient with subacute paraparesis who later developed severe dementia and moderate cerebellar involvement. The histological examination showed a marker neuronal loss, severe neurofibrillary degeneration, and a great number of senile plaques. No PAS-positive plaques or amyloid angiopathy could be demonstrated. Golgi's sections showed (a) meshwork of fine dendrites located distally to the soma, (b) thick, coarse dendrites full of synaptic spines in neurons otherwise lacking these structures, and (c) thick dendrites with distal varicosities and filopodium-like processes resembling growth cones. These changes have been interpreted as acquired abnormal receptor sites and represent unique facts of a group of diseases not clearly defined, including atypical Alzheimer's disease and some cases of familiar Alzheimer's disease.  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