全文获取类型
收费全文 | 3933篇 |
免费 | 221篇 |
专业分类
4154篇 |
出版年
2024年 | 7篇 |
2023年 | 45篇 |
2022年 | 45篇 |
2021年 | 76篇 |
2020年 | 92篇 |
2019年 | 120篇 |
2018年 | 155篇 |
2017年 | 158篇 |
2016年 | 181篇 |
2015年 | 120篇 |
2014年 | 138篇 |
2013年 | 477篇 |
2012年 | 212篇 |
2011年 | 240篇 |
2010年 | 142篇 |
2009年 | 140篇 |
2008年 | 195篇 |
2007年 | 162篇 |
2006年 | 135篇 |
2005年 | 104篇 |
2004年 | 126篇 |
2003年 | 130篇 |
2002年 | 99篇 |
2001年 | 76篇 |
2000年 | 83篇 |
1999年 | 58篇 |
1998年 | 43篇 |
1997年 | 39篇 |
1996年 | 21篇 |
1995年 | 28篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 38篇 |
1991年 | 28篇 |
1990年 | 47篇 |
1989年 | 43篇 |
1988年 | 39篇 |
1987年 | 21篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1972年 | 12篇 |
1938年 | 6篇 |
排序方式: 共有4154条查询结果,搜索用时 0 毫秒
181.
Profile subtypes, based on the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) factor index scores, were examined in a sample of 166 patients with traumatic brain injury (TBI) by means of a two-stage clustering procedure. Three reliable subtypes were found that were differentiated primarily by level of performance across all factor index scores, although each of them demonstrated a relative weakness on the Processing Speed index. These subtypes were then validated on the basis of demographic variables, injury parameters, and additional psychometric measures that had not been included in the clustering procedures. The results indicated that performance on the WAIS-III after TBI was affected by both injury severity and level of education. It is concluded that there is no unique "signature" profile on the WAIS-III after TBI, except that a relative strength on the Processing Speed index is uncommon with this condition. 相似文献
182.
Towards a Logic of Rational Agency 总被引:4,自引:0,他引:4
183.
Electrophysiological correlates of anterior cingulate function in a go/no-go task: Effects of response conflict and trial type frequency 总被引:1,自引:0,他引:1
Nieuwenhuis S Yeung N van den Wildenberg W Ridderinkhof KR 《Cognitive, affective & behavioral neuroscience》2003,3(1):17-26
Neuroimaging and computational modeling studies have led to the suggestion that response conflict monitoring by the anterior cingulate cortex plays a key role in cognitive control. For example, response conflict is high when a response must be withheld (no-go) in contexts in which there is a prepotent tendency to make an overt (go) response. An event-related brain potential (ERP) component, the N2, is more pronounced on no-go than on go trials and was previously thought to reflect the need to inhibit the go response. However, the N2 may instead reflect the high degree of response conflict on no-go trials. If so, an N2 should also be apparent when subjects make a go response in conditions in which nogo events are more common. To test this hypothesis, we collected high-density ERP data from subjects performing a go/no-go task, in which the relative frequency of go versus no-go stimuli was varied. Consistent with our hypothesis, an N2 was apparent on both go and no-go trials and showed the properties expected of an ERP measure of conflict detection on correct trials: (1) It was enhanced for low-frequency stimuli, irrespective of whether these stimuli were associated with generating or suppressing a response, and (2) it was localized to the anterior cingulate cortex. This suggests that previous conceptions of the no-go N2 as indexing response inhibition may be in need of revision. Instead, the results are consistent with the view that the N2 in go/no-go tasks reflects conflict arising from competition between the execution and the inhibition of a single response. 相似文献
184.
Merijn?van?TilborgEmail author Jan?N.?C.?van der?Pers Peter?Roessingh Maurice?W.?Sabelis 《Behavior research methods》2003,35(3):478-482
A novel type of locomotion compensator was designed and tested for its use in orientation behavior experiments with a predatory mite. In this apparatus, displacements of the test animal in the two-dimensional plane are recorded using video equipment and a servosphere that keeps the animal in focus. Thex andy displacements are registeredusing two rotation encoders and are compensated using a pair of servo-motors, in such a way that the animal is always positioned on top of the sphere, yet moves freely. Well-fed and starved predators were tested for their responses to (1) still air, (2) a stimulus-free air flow, (3) an air flow with odors from uninfested Lima bean leaves, and (4) an air flow with odors from Lima bean leaves infested by plant-feeding mites, the prey of the predatory mites. Anemotactic responses of adultPhytoseivlus persimilis females were feeding state dependent. Well-fed predators moved downwind under Treatments 1–3 but moved neither up-nor downwind in the presence of odors from infested plants (Treatment 4). Starved predators moved upwind under all treatments. These results are in agreement with those of earlier studies in a wind tunnel, and therefore, the new type of locomotion compensator (LC-100) offers an excellent method for studying the orientation behavior of micro-arthropods. 相似文献
185.
186.
Harri?tte?RieseEmail author Paul?F.?C.?Groot Mireille?van den?Berg Nina?H.?M.?Kupper Ellis?H.?B.?Magnee Ellen?J.?Rohaan Tanja?G.?M.?Vrijkotte Gonneke?Willemsen Eco?J.?C.?de?Geus 《Behavior research methods》2003,35(3):467-477
Impedance cardiography has been used increasingly to measure human physiological responses to emotional and mentally engaging stimuli. The validity of large-scale ensemble averaging of ambulatory impedance cardiograms was evaluated for preejection period (PEP), interbeat interval, and dZ/dt(min) amplitude. We tested whether the average of “classical” 60-sec ensemble averages across periods with fixed activity, posture, physical load, social situation, and location could be accurately estimated from a single large-scale ensemble average spanning these entire periods. Impedance and electrocardiograms were recorded for about 24-h from 21 subjects. Recordings were scored by seven raters, using both methods for each subject. Good agreement (average intraclass correlation coefficient was .91) between both ensemble averaging methods was found for all three cardiac function measures. The results indicate that for unambiguous ambulatory impedance cardiograms, large-scale ensemble averaging is valid, which makes measuring prolonged changes in cardiac sympathetic activity by measuring ambulatory PEP feasible even in large epidemiological samples. 相似文献
187.
In 2 experiments, the effects of mental stress on limb stiffness were investigated. The relative contribution to arm stiffness of individual muscle activity, co-contraction, muscle reflexes, and postural adjustments were examined. In each experiment, participants (N = 24, Experiment 1; N = 16, Experiment 2) held their supinated hand under a tray that they were required to return to horizontal after it had been suddenly released. Electromyographic activity in the biceps and triceps muscles was recorded, as were elbow and wrist angles and tray displacement. In Experiment 1, mental arithmetic stress was shown to lead to decreased tray displacement (i.e., increased resistance) compared with displacements under the control, unstressed condition, as well as to increased elbow flexion before tray release. In Experiment 2, the increased resistance to perturbation caused by mental stress was found to be independent of initial elbow angle, but to vary as a function of the amount of upward force exerted before tray release. The authors conclude that stress-induced increases in limb stiffness result from changes in the initial position of the elbow, specified by its angle, together with the initial force exerted by participants to counteract the mechanical perturbations. 相似文献
188.
TenVergert EM Vermeulen KM Geertsma A van Enckevort PJ de Boer WJ van der Bij W Koëter GH 《Psychological reports》2001,89(3):707-717
Whether lung transplantation improves Health-related Quality of Life in patients with emphysema and other end-stage lung diseases before and after lung transplantation was examined. Between 1992 and 1999, 23 patients with emphysema and 19 patients with other indications completed self-administered questionnaires before lung transplantation, and at 4, 7, 13, and 25 mo. after transplantation. The questionnaire included the Nottingham Health Profile, the State-Trait Anxiety Inventory, the Self-rating Depression Scale, the Index of Well-being, the self-report Karnofsky Index, and four respiratory-specific questions. Neither before nor after transplantation were significant differences found on most dimensions of Health-related Quality of Life between patients with emphysema and other indications. Before transplantation, both groups report major restrictions on the dimensions Energy and Mobility of the Nottingham Health Profile, low experienced well-being, depressive symptoms, and high dyspnea. About 4 mo. after transplantation, most Health-related Quality of Life measures improved significantly in both groups. These improvements were maintained in the following 21 mo. 相似文献
189.
Chronic, severe hypertension does not impair spatial learning and memory in Sprague-Dawley rats 总被引:1,自引:0,他引:1 下载免费PDF全文
This study tested the hypothesis that long-term hypertension impairs spatial learning and memory in rats. In 6-wk-old Sprague-Dawley rats, chronic hypertension was induced by placing one of three sizes of stainless steel clips around the descending aorta (above the renal artery), resulting in a 20–80-mm Hg increase of arterial pressure in all arteries above the clip, that is, the upper trunk and head. Ten months later, the rats were tested for 5 d in a repeated-acquisition water maze task, and on the fifth day, they were tested in a probe trial; that is, there was no escape platform present. At the end of the testing period, the nonsurgical and sham control groups had similar final escape latencies (16±4 sec and 23±9 sec, respectively) that were not significantly different from those of the three hypertensive groups. Rats with mild hypertension (140–160 mm Hg) had a final escape latency of 25±6 sec, whereas severely hypertensive rats (170–199 mm Hg) had a final escape latency of 21±7 sec and extremely hypertensive rats (>200 Hg) had a final escape latency of 19±5 sec. All five groups also displayed a similar preference for the correct quadrant in the probe trial. Together, these data suggest that sustained, severe hypertension for over 10 mo is not sufficient to impair spatial learning and memory deficits in otherwise normal rats. 相似文献
190.
Regulation of distinct attractive and aversive mechanisms mediating benzaldehyde chemotaxis in Caenorhabditis elegans 总被引:1,自引:0,他引:1 下载免费PDF全文
Nuttley WM Harbinder S van der Kooy D 《Learning & memory (Cold Spring Harbor, N.Y.)》2001,8(3):170-181
Olfactory-mediated chemotaxis in nematodes provides a relatively simple system to study biological mechanisms of information processing. Analysis of the kinetics of chemotaxis in response to 100% benzaldehyde revealed an initial attractive response that is followed by a strong aversion to the odorant. We show that this behavior is mediated by two genetically separable attraction- and aversion-mediating response pathways. The attraction initially dominates behavior but with prolonged exposure habituation leads to a behavioral change, such that the odorant becomes repulsive. This olfactory habituation is susceptible to dishabituation, thereby re-establishing the attractive response to the odorant. Re-examination of the putative olfactory adaptation mutant adp-1(ky20) revealed that the phenotype observed in this line is due to a supersensitivity to a dishabituating stimulus, rather than a defect in the adaptation to odorants per se. A modified benzaldehyde chemotaxis assay was developed and used for the isolation of a mutant with a specific defect in habituation kinetics, expressed as a persistence of the attractive response. 相似文献