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1.
The biological role of the scrapie isoform of prion protein (PrP(Sc)) as an infectious agent in numerous human and non-human disorders of the central nervous system is well established. In contrast, and despite decades of intensive research, the physiological function of the endogenous cellular form of the prion protein (PrP(C)) remains elusive. In mammals, the ubiquitous expression of PrP(C) suggests biological functions other than its pathological role in propagating the accumulation of its misfolded isotype. Other functions that have been attributed to PrP(C) include signal transduction, synaptic transmission and protection against cell death through the apoptotic pathway. More recently, immunoregulatory properties of PrP(C) have been reported. We review accumulating in vitro and in vivo evidence regarding physiological functions of PrP(C).  相似文献   
2.
Old age is associated with a deficient recovery from stroke, but the cellular mechanisms underlying such phenomena are poorly understood. To address this issue, focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague–Dawley rats. Aged rats showed a delayed and suboptimal functional recovery in the post-stroke period. Using BrdU-labeling, quantitative immunohistochemistry and 3-D reconstruction of confocal images, we found that aged rats are predisposed to rapidly develop an infarct within the first few days after ischemia. The emergence of the necrotic zone is associated with a high rate of cellular degeneration, premature accumulation of proliferating BrdU-positive cells that appear to emanate from capillaries in the infarcted area, and a large number of apoptotic cells. With double labeling techniques, we were able to identify, for the first time, over 60% of BrdU-positive cells either as reactive microglia (45%), oligodendrocyte progenitors (17%), astrocytes (23%), CD8+ lymphocytes (4%), or apoptotic cells (<1%). Paradoxically, despite a robust reactive phenotype of microglia and astrocytes in aged rats, at 1-week post-stroke, the number of proliferating microglia and astrocytes was lower in aged rats than in young rats. Our data indicate that aging is associated with rapid infarct development and a poor prognosis for full recovery from stroke that is correlated with premature cellular proliferation and increased cellular degeneration and apoptosis in the infarcted area.  相似文献   
3.
In a prospective study, the attachment style, home-leaving age, length of time in residential care, and behavioral problems among Israeli residential care children (N = 68), were studied. Data analyses showed that children removed from their homes at a later age suffered from higher levels of anxiety, depression and social problems compared to children taken from their homes at the age of 7 or less. It was also found that a prolonged stay (over 2 years) in residential care was related to higher levels of anxiety and depression. An interaction effect of a child’s attachment style and home-leaving age was found in the child’s level of aggressive behavior.  相似文献   
4.
Previous studies of dual-task performance have demonstrated that encoding and retrieval processes are differentially affected by the simultaneous performance of a secondary task. Whilst dual task demands during encoding have a detrimental effect on memory performance, dual task demands during retrieval have a detrimental effect on secondary task performance. However, dual task effects on memory during encoding appear unaffected by age, while effects at retrieval on secondary task performance are age sensitive. Most previous studies have focused on free recall or cued recall of word lists. In the current study, encoding and retrieval were examined in younger and older healthy adults performing a task typically thought to load verbal working memory, namely immediate serial ordered digit recall together with a response time (RT) task. In Experiment 1, the demands of a secondary RT task were varied as a function of response-to-stimulus interval, while in Experiment 2 the predictability of the stimulus location was manipulated. In both age groups, dual task during encoding, but not at retrieval, produced significant interference in memory performance and unlike most previous studies the impact at encoding was greater for the older group. In contrast, significantly slower RTs were demonstrated under dual task conditions during encoding and retrieval. Older adults produced significantly slower RTs than younger adults only for dual task at retrieval. Older people were more sensitive to time pressure in responding under dual task conditions, but neither group was sensitive to predictability of stimulus location. Results are consistent with the concept of a cognitive resource that supports dual task performance, and that is sensitive to the effects of age on memory encoding of items that rely heavily on the operation of verbal working memory resources. The age sensitivity to dual task only became apparent when effects at encoding and at retrieval were considered separately.  相似文献   
5.
Clinical research on facial emotions has focused primarily on differences between right and left hemiface. Social psychology, however, has suggested that differences between upper versus lower facial displays may be more important, especially during social interactions. We demonstrated previously that upper facial displays are perceived preferentially by the right hemisphere, while lower facial displays are perceived preferentially by the left hemisphere. A marginal age-related effect was observed. The current research expands our original cohort to include 26 elderly individuals over age 62. Fifty-six, strongly right-handed, healthy, adult volunteers were tested tachistoscopically by flashing randomized facial displays of emotion to the right and left visual fields. The stimuli consisted of line drawings displaying various combinations of emotions on the upper and lower face. The subjects were tested under two conditions: without attend instruction and with instructions to attend to the upper face. Based on linear regression and discriminant analyses modeling age, subject performance could be divided into two distinct groups: Young (< 62 years) and Old (> 62 years). Without attend instructions, both groups robustly identified the emotion displayed on the lower face, regardless of visual field presentation. With instructions to attend to the upper face, the Old group demonstrated a markedly decreased ability to identify upper facial displays, compared to the Young group. The most significant difference was noted in the left visual field/right hemisphere. Our results demonstrate a significant decline in the processing of upper facial emotions by the right hemisphere in older individuals, thus providing partial support for the right hemisphere hypothesis of cognitive aging. The decreased ability to perceive upper facial displays coupled with age-related deficits in processing affective prosody may well cause impaired psychosocial competency in the elderly.  相似文献   
6.
We used event-related functional magnetic resonance imaging (fMRI) to measure prefrontal cortex (PFC) activity while younger and older adults performed an item-recognition task in which the memory-set size varied between 1 and 8 letters. Each trial was composed of a 4-sec encoding period in which subjects viewed random letter strings, a 12-sec retention period and a 2-sec retrieval period in which subjects decided whether a single probe letter was or was not part of the memory set. For both groups, reaction-time (RT) increased and accuracy decreased with increasing memory set-size. Analyses of individual subjects' performance and cortical activity indicated that speed and accuracy accounted for variance in different task periods in dorsal and ventral PFC. Age-related differences in accuracy-activation relations were observed in dorsal PFC during encoding and ventral PFC during maintenance. Age-related differences in RT-activation relations were observed in dorsal PFC during retrieval. These results and additional fMRI data we have collected during performance of a speeded processing task, directly support a model of cognitive slowing in which processing rate is related to neural efficiency.  相似文献   
7.
While it is generally agreed that outcome following cerebral insult during childhood differs from that seen following similar pathology in adulthood, the specific relationship between timing of cerebral lesion and outcome, and the mechanism associated with observed neurobehavioral changes, remains controversial. Data from children with focal lesions suggests a non-linear relationship between age at injury and language function (e.g., Bates et al., 1999). With respect to executive function, animal models also demonstrate a non-linear relationship, and suggest that outcome is tightly linked to underlying neuronal changes (e.g., Kolb et al., 2000). Whether these models easily translate to humans, where brain morphology, cognitive function and environmental influences are more complex, is not clear. To date, focal lesion research in children has been restricted to individual case studies or, to samples of children with lesions to regions subsuming language function, or those who have undergone hemispherectomy for the treatment of intractable epilepsy. This study aimed to build on current knowledge, investigating executive function in 38 children with focal lesions involving prefrontal cortex. Aetiology and timing of lesions was diverse. Results are consistent with animal research suggesting a non-linear relationship between age at injury and outcome, with "critical periods" during development when the frontal lobes are particularly vulnerable to insult, and others when outcome is more optimal. Our findings indicate that children with prenatal lesions are at greatest risk of neurobehavioral deficits. Children with lesions sustained in middle childhood demonstrate least severe impairments across executive domains, possibly due to a period of peak synaptogenesis and dendritic arborization during this developmental stage, in keeping with animal models and research investigating frontal lobe development.  相似文献   
8.
The current study examined the hypothesis that patients with Alzheimer's disease (AD) have a selective deficit in the coordination mechanism of the central executive, which is reflected in their inability to coordinate the performance of two tasks concurrently. One criticism of the previous studies in the literature is that they employ tasks that do not necessarily draw upon the separate peripheral mechanisms within working memory but combine a memory load with a perceptuomotor load. Therefore, the aim of the study was to examine the effects of AD and healthy adult ageing on a verbal memory plus visuospatial memory dual task paradigm. We investigated the performance of 15 AD patients and 20 healthy younger and 20 healthy older individuals on three different dual task combinations (i) digit recall and visual pattern recall; ii) digit recall and tracking; and iii) digit recall and articulatory suppression. The results demonstrate a significant dual task impairment in AD patients when two memory tasks are performed simultaneously compared to healthy younger and older adults. In contrast, there was not a significant age-related disruption in performance in healthy individuals compared to single task conditions. As the demands of each task were adjusted for individual ability levels, this provides further support for there being a specific AD dual task decrement in the mechanism responsible for coordinating dual task performance, which is separate from the resources needed to perform the tasks independently.  相似文献   
9.
Two decades of research examining repetition priming in aging and Alzheimer's disease (AD) has yielded a large body of contradictory findings due to differences between studies in participant and task characteristics. Recent research that has employed methodological advances indicates that this form of implicit memory is preserved in healthy aging. When a priming deficit does occur in studies of aging, it is likely a very early signal of neurological disease. Future directions for research in this area include linking priming ability to known risk factors for development of AD, integrating priming measures into clinical neuropsychological assessment batteries, and implementing programs of cognitive retraining that enhance memory using stimulus repetition techniques.  相似文献   
10.
PURPOSE: The aim of this study was to examine the impact of clinical variables, particularly age at onset of epilepsy, on intellectual function in a group of children with temporal lobe epilepsy (TLE). METHODS: We reviewed the preoperative neuropsychological test results of 79 children with unilateral TLE who subsequently underwent surgical resection. The impact of age at onset and duration of epilepsy, pathology type, and side of resection on full-scale intelligence quotient (IQ) scores was examined. RESULTS: Intellectual dysfunction (defined as IQ < 79) was present in 57% of children, and age at onset of epilepsy was the best predictor of intellectual function. Children with epilepsy onset in the first year of life had a particularly high incidence of intellectual impairment (82.4%). CONCLUSION: These data suggest a critical period during the first year of life for the subsequent development of intellectual abilities and highlight the importance of early treatment in this population.  相似文献   
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