全文获取类型
收费全文 | 16950篇 |
免费 | 874篇 |
国内免费 | 279篇 |
专业分类
耳鼻咽喉 | 145篇 |
儿科学 | 85篇 |
妇产科学 | 24篇 |
基础医学 | 3907篇 |
口腔科学 | 50篇 |
临床医学 | 639篇 |
内科学 | 617篇 |
皮肤病学 | 9篇 |
神经病学 | 9311篇 |
特种医学 | 294篇 |
外科学 | 541篇 |
综合类 | 730篇 |
预防医学 | 126篇 |
眼科学 | 292篇 |
药学 | 1112篇 |
1篇 | |
中国医学 | 183篇 |
肿瘤学 | 37篇 |
出版年
2023年 | 71篇 |
2022年 | 99篇 |
2021年 | 280篇 |
2020年 | 321篇 |
2019年 | 313篇 |
2018年 | 279篇 |
2017年 | 350篇 |
2016年 | 339篇 |
2015年 | 398篇 |
2014年 | 574篇 |
2013年 | 716篇 |
2012年 | 701篇 |
2011年 | 910篇 |
2010年 | 804篇 |
2009年 | 872篇 |
2008年 | 925篇 |
2007年 | 873篇 |
2006年 | 831篇 |
2005年 | 695篇 |
2004年 | 584篇 |
2003年 | 560篇 |
2002年 | 428篇 |
2001年 | 365篇 |
2000年 | 317篇 |
1999年 | 336篇 |
1998年 | 295篇 |
1997年 | 292篇 |
1996年 | 240篇 |
1995年 | 251篇 |
1994年 | 257篇 |
1993年 | 241篇 |
1992年 | 249篇 |
1991年 | 255篇 |
1990年 | 234篇 |
1989年 | 217篇 |
1988年 | 234篇 |
1987年 | 214篇 |
1986年 | 267篇 |
1985年 | 376篇 |
1984年 | 281篇 |
1983年 | 237篇 |
1982年 | 213篇 |
1981年 | 201篇 |
1980年 | 168篇 |
1979年 | 106篇 |
1978年 | 73篇 |
1977年 | 64篇 |
1976年 | 48篇 |
1974年 | 31篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
《Clinical neurophysiology》2021,132(9):2003-2011
ObjectiveA large N20 and P25 of the median nerve somatosensory evoked potential (SEP) predicts short survival in amyotrophic lateral sclerosis (ALS). We investigated whether high frequency oscillations (HFOs) over N20 are enlarged and associated with survival in ALS.MethodsA total of 145 patients with ALS and 57 healthy subjects were studied. We recorded the median nerve SEP and measured the onset-to-peak amplitude of N20 (N20o-p), and peak-to-peak amplitude between N20 and P25 (N20p-P25p). We obtained early and late HFO potentials by filtering SEP between 500 and 1 kHz, and measured the peak-to-peak amplitude. We followed up patients until endpoints (death or tracheostomy) and analyzed the relationship between SEP or HFO amplitudes and survival using a Cox analysis.ResultsPatients showed larger N20o-p, N20p-P25p, and early and late HFO amplitudes than the control values. N20p-P25p was associated with survival periods (p = 0.0004), while early and late HFO amplitudes showed no significant association with survival (p = 0.4307, and p = 0.6858, respectively).ConclusionsThe HFO amplitude in ALS is increased, but does not predict survival.SignificanceThe enlarged HFOs in ALS might be a compensatory phenomenon to the hyperexcitability of the sensory cortex pyramidal neurons. 相似文献
4.
Antonio Montalvo Afonso Fernando Ruiz Juretschke Rosario González Rodrigálvarez Olga Mateo Sierra Begoña Iza Vallejo Roberto García Leal Marc Valera Melé Vicente Casitas Hernando Jose Manuel Hernández Poveda Carlos Fernández Carballal 《Neurocirugía (Asturias, Spain)》2021,32(1):1-9
Background and objectivesThe treatment of deafferentation pain by spinal DREZotomy is a proven therapeutic option in the literature. In recent years, use of DREZotomy has been relegated to second place due to the emergence of neuromodulation therapies. The objectives of this study are to demonstrate that DREZotomy continues to be an effective and safe treatment and to analyse predictive factors for success.Patients and methodsA retrospective study was conducted of all patients treated in our department with spinal DREZotomy from 1998 to 2018. Bulbar DREZotomy procedures were excluded. A visual analogue scale (VAS) and the reduction of routine medication were used as outcome variables. Demographic, clinical and operative variables were analysed as predictive factors for success.ResultsA total of 27 patients (51.9% female) with a mean age of 53.7 years underwent DREZotomy. The main cause of pain was brachial plexus injury (BPI) (55.6%) followed by neoplasms (18.5%). The mean time of pain evolution was 8.4 years with a mean intensity of 8.7 according to the VAS, even though 63% of the patients had previously received neurostimulation therapy. Favourable outcome (≥ 50% pain reduction in the VAS) was observed in 77.8% of patients during the postoperative period and remained in 59.3% of patients after 22 months average follow-up (mean reduction of 4.9 points). This allowed for a reduction in routine analgesic treatment in 70.4% of them. DREZotomy in BPI-related pain presented a significantly higher success rate (93%) than the other pathologies (41.7%) (p = .001). No association was observed between outcome and age, gender, DREZ technique, duration of pain or previous neurostimulation therapies. There were six neurological complications, four post-operative transient neurological deficits and two permanent deficits.ConclusionDorsal root entry zone surgery is effective and safe for treating patients with deafferentation pain, especially after brachial plexus injury. It can be considered an alternative treatment after failed neurostimulation techniques for pain control. However, its indication should be considered as the first therapeutic option after medical therapy failure due to its good long-term results. 相似文献
5.
《Brain stimulation》2021,14(4):1005-1014
BackgroundPrevious studies show that activity in the posterior default mode network (pDMN), including the posterior cingulate cortex and the precuneus, is correlated with the success of long-term episodic memory retrieval. However, the role of the anterior DMN (aDMN) including the medial prefrontal cortex is still unclear. Some studies show that activating the medial prefrontal cortex improves memory retrieval while other studies show deactivation of the medial prefrontal cortex in successful retrieval of episodic memories, suggesting a possible functional dissociation between the aDMN and pDMN.ObjectiveIn the current study, we aim to causally explore this probable dissociation using high-definition transcranial direct current stimulation (HD-tDCS).MethodsWe perform a randomised double-blinded two-visit placebo-controlled study with 84 healthy young adults. During Visit 1 they learn 75 Swahili-English word-associations. Seven days later, they randomly receive either anodal, cathodal or sham HD-tDCS targeting the pDMN or aDMN while they recall what they have previously learned.ResultsWe demonstrate that anodal stimulation of the pDMN and cathodal stimulation of the aDMN, equally improve the percentage of Swahili-English word-associations recalled 7 days after learning.ConclusionsModulating the activity in the aDMN and pDMN causally affect memory retrieval performance. HD-tDCS of the aDMN and pDMN shows that anodal stimulation of the pDMN and cathodal stimulation of the aDMN increases memory retrieval performance one week after the learning phase. Given consistent evidence, it is highly likely that we are increasing the activity in the pDMN with anodal pDMN stimulation. However, it is not clear if cathodal HD-tDCS targetting aDMN works via decoupling from the pDMN or via indirectly disinhibit pDMN. 相似文献
6.
Perceiving faces and understanding emotions are key components of human social cognition. Prior research with adults and infants suggests that these social cognitive functions are supported by superior temporal cortex (STC) and medial prefrontal cortex (MPFC). We used functional near-infrared spectroscopy (fNIRS) to characterize functional responses in these cortical regions to faces in early childhood. Three-year-old children (n = 88, M(SD) = 3.15(.16) years) passively viewed faces that varied in emotional content and valence (happy, angry, fearful, neutral) and, for fearful and angry faces, intensity (100%, 40%), while undergoing fNIRS. Bilateral STC and MPFC showed greater oxygenated hemoglobin concentration values to all faces relative to objects. MPFC additionally responded preferentially to happy faces relative to neutral faces. We did not detect preferential responses to angry or fearful faces, or overall differences in response magnitude by emotional valence (100% happy vs. fearful and angry) or intensity (100% vs. 40% fearful and angry). In exploratory analyses, preferential responses to faces in MPFC were not robustly correlated with performance on tasks of early social cognition. These results link and extend adult and infant research on functional responses to faces in STC and MPFC and contribute to the characterization of the neural correlates of early social cognition. 相似文献
7.
《Clinical neurophysiology》2021,132(2):315-322
ObjectivePrevious studies have demonstrated voluntary movement alterations as well as motor cortex excitability and plasticity changes in patients with mild cognitive impairment (MCI). To investigate the pathophysiology of movement abnormalities in MCI, we tested possible relationships between movement abnormalities and primary motor cortex alterations in patients.MethodsFourteen amnestic MCI (aMCI) patients and 16 healthy controls were studied. Cognitive assessment was performed using clinical scales. Finger tapping was recorded by a motion analysis system. Transcranial magnetic stimulation was used to test the input/output curve of motor evoked potentials, intracortical inhibition, and short-latency afferent inhibition. Primary motor cortex plasticity was probed by theta burst stimulation. We investigated correlations between movement abnormalities, clinical scores, and cortical neurophysiological parameters.ResultsMCI patients showed less rhythmic movement but no other movement abnormalities. Cortical excitability measures were normal in patients, whereas plasticity was reduced. Movement rhythm abnormalities correlated with frontal dysfunction scores.ConclusionOur study in MCI patients demonstrated abnormal voluntary movement and plasticity changes, with no correlation between the two. Altered rhythm correlated with frontal dysfunction.SignificanceOur results contribute to the understanding of pathophysiological mechanisms of motor impairment in MCI. 相似文献
8.
A man and a woman were rescued from a room that had exploded. Many empty cassette gas cylinders were found in the room. The man and woman were hospitalized immediately for the treatment of burns. The woman died 6 days later, and the man died 31 days later without regaining consciousness. Carbonization and hardening of the frontal facial skin and parts of the left and right fingers were observed on the man's body. In both cases, systemic burns had led to progressive systemic edema and markedly suppressed circulation. Analytical samples for butanes obtained from their bodies at autopsy were stored at −20 °C for 14 and 25 days, respectively, before analysis. Normal butane and isobutane were quantified in the brain and subcutaneous adipose tissue of the woman. Only the isobutane was quantified in the adipose tissue of the man. The evidence suggests that the man lit a cigarette while breathing gas and the entire room exploded. Our results also suggest that butane can be detected in the adipose tissue of autopsy cases long after inhalation even under the present storage conditions, and isobutane may remain in adipose tissue longer than n-butane. 相似文献
9.
Alan W. Freeman 《The Journal of neuroscience》2021,41(1):89
Motion perception is a vital part of our sensory repertoire in that it contributes to navigation, awareness of moving objects, and communication. Motion sense in carnivores and primates originates with primary visual cortical neurons selective for motion direction. More than 60 years after the discovery of these neurons, there is still no consensus on the mechanism underlying direction selectivity. This paper describes a model of the cat''s visual system in which direction selectivity results from the well-documented orientation selectivity of inhibitory neurons: inhomogeneities in the orientation preference map for inhibitory neurons leads to spatially asymmetric inhibition, and thus to direction selectivity. Stimulation of the model with a drifting grating shows that direction selectivity results from the relative timing of excitatory and inhibitory inputs to a neuron. Using a stationary contrast-reversing grating reveals that the inhibitory input is spatially displaced in the preferred direction relative to the excitatory input, and that this asymmetry leads to the timing difference. More generally, the model yields physiologically realistic estimates of the direction selectivity index, and it reproduces the critical finding with contrast-reversing gratings that response phase advances with grating spatial phase. It is concluded that a model based on intracortical inhibition can account well for the known properties of direction selectivity in carnivores and primates.SIGNIFICANCE STATEMENT Motion perception is vital for navigation, communication, and the awareness of moving objects. Motion sense depends on cortical neurons that are selective for motion direction, and this paper describes a model for the physiological mechanism underlying cortical direction selectivity. The essence of the model is that intracortical inhibition of a direction-selective cell is spatially inhomogeneous and therefore depends on whether a stimulus generates inhibition before or after reaching the cell''s receptive field: the response is weaker in the former than in the latter case. If the model is correct, it will contribute to the understanding of motion processing in carnivores and primates. 相似文献
10.
Cadmium is a toxic metal that can damage the brain and other organs. This study aimed to explore the protective effects of Potentilla anserine L. polysaccharide (PAP) against CdCl2-induced neurotoxicity in N2a and SH-SY5Y cells and in the cerebral cortex of BALB/c mice. In addition, we aimed to identify the potential mechanisms underlying these protective effects. Relative to CdCl2 treatment alone, pretreatment with PAP prevented the reduction in cell viability evoked by CdCl2, decreased rates of apoptosis, promoted calcium homeostasis, decreased ROS accumulation, increased mitochondrial membrane potential, inhibited cytochrome C and AIF release, and prevented the cleavage of caspase-3 and PARP. In addition, PAP significantly decreased the CdCl2-induced phosphorylation of CaMKII, Akt, and mTOR. In conclusion, PAP represents a potential therapeutic agent for the treatment of Cd-induced neurotoxicity, functioning in part via attenuating the activation of the mitochondrial apoptosis pathway and the Ca2+-CaMKII-dependent Akt/mTOR pathway. 相似文献