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71.
Frans Steenbrink Carel G. M. Meskers Bart van Vliet Jorrit Slaman H. E. J. Veeger Jurriaan H. De Groot 《Medical & biological engineering & computing》2009,47(5):565-572
For isometric tasks, shoulder muscle forces are assumed to scale linearly with the external arm load magnitude, i.e., muscle
force ratios are constant. Inverse dynamic modeling generally predicts such linear scaling behavior, with a critical role
for the arbitrary load sharing criteria, i.e., the “cost function”. We tested the linearity of the relation between external
load magnitude exerted on the humerus and shoulder muscle activation. Six isometric force levels ranging from 17 to 100% of
maximal arm force were exerted in 24 directions in a plane perpendicular to the longitudinal axis of the humerus. The direction
of maximum muscle activation, the experimentally observed so called Principal Action (PA), was determined for each force magnitude
in 12 healthy subjects. This experiment was also simulated with the Delft Shoulder and Elbow Model (DSEM) using two cost functions:
(1) minimizing muscle stress and (2) a compound, energy related cost function. PA, both experimental (PAexp) and simulated (PAsim), was expected not to change with arm forces magnitudes. PAexp of the mm. trapezius pars descendens, deltoideus pars medialis and teres major changed substantially as a function of external
force magnitude, indicating external load dependency of shoulder muscle activation. In DSEM simulations, using the stress
cost function, small non-linearities in the muscle force–external load dependency were observed, originating from gravitational
forces working on clavicular and scapular bone masses. More pronounced non-linearities were introduced by using the compound
energy related cost function, but no similarity was observed between PAexp and PAsim. 相似文献
72.
目的:探讨小儿脊髓拴系综合征显微手术的术中护理要点。方法:回顾2005年11月~2007年2月在显微镜下治疗脊髓拴系综合征的手术期护理记录,总结手术期间的护理要点。结果:47例患儿均在显微镜下行脊髓拴系松解术,手术全部成功,无术中并发症发生。结论:要保证手术顺利进行,必须注意以下几点:(1)术前正确的体位摆放;(2)充分的器械、物品准备;(3)保证显微器械的正常使用;(4)细致的病情观察和密切的护理配合。 相似文献
73.
目的探讨注意缺陷多动障碍与发育性运动协调障碍之间的关系。方法对我院门诊的60例注意缺陷多动障碍患儿进行评估,以发育性运动协调问卷(DCDQ)评定发育性运动协调问题。结果注意缺陷多动障碍患儿DCDQ得分低于正常儿童,差别具有显著性意义(P〈0.01)。注意缺陷多动障碍患儿中20.0%同时存在发育性运动协调障碍,33.3%为可疑发育性运动协调障碍。其中25.0%的注意缺陷型、20.0%的多动-冲动型和22.2%的混合型注意缺陷多动障碍患儿同时存在发育性运动协调障碍,三种亚型与发育性运动协调障碍的共病率间差别无显著性意义(P〉0.05)。结论注意缺陷多动障碍与发育性运动协调障碍密切相关,且注意缺陷多动障碍的三种亚型与发育性运动协调障碍均存在共病,这为注意缺陷多动障碍的治疗提供了新思路。 相似文献
74.
Influence of arm movements on saccades in humans 总被引:3,自引:0,他引:3
When reaching for an object we usually look at it before we touch it with the hand. This often unconscious eye movement prior to the arm movement allows guiding of the final part of the hand trajectory by visual feedback. We examined the temporal and spatial coordination of this control system by psychophysical measurements of eye and arm movements of naive human subjects looking or looking and pointing as fast as possible to visual targets in physical and virtual-reality setups. The reaction times of saccades to a step-displaced target were reduced, and the number of corrective saccades decreased, when the subject had to produce a corresponding simultaneous hand movement to the same target. The saccadic reaction time was increased when saccade and hand movement went in opposite directions. In a double-step task the reaction time for the second saccade was longer than for the first. Co-use of the hand leads to an additional increase of saccadic reaction time. Taken together this study shows an improvement in initial saccades if they are accompanied by hand movements to the same target. This effect might ensure that the reach target is foveated early and accurately enough to support the visual feedback control of the hand near the target. Longer reaction times for the second saccade to double-step displaced targets might reflect a saccadic refractory time intensified by simultaneous arm movements. These results are discussed in the light of recent findings from our laboratory on saccade- and reach-related neurons in the superior colliculus of macaque monkeys. 相似文献
75.
76.
Hypoglossal and reticular interneurons involved in oro-facial coordination in the rat 总被引:6,自引:0,他引:6
Popratiloff AS Streppel M Gruart A Guntinas-Lichius O Angelov DN Stennert E Delgado-García JM Neiss WF 《The Journal of comparative neurology》2001,433(3):364-379
Chewing, swallowing, breathing, and vocalization in mammals require precise coordination of tongue movements with concomitant activities of the mimetic muscles. The neuroanatomic basis for this oro-facial coordination is not yet fully understood. After the stereotaxic microinjection of retrograde and anterograde neuronal tracers (biotin-dextran, Fluoro-Ruby, Fluoro-Emerald, and Fluoro-Gold) into the facial and hypoglossal nuclei of the rat, we report here a direct bilateral projection of hypoglossal internuclear interneurons onto facial motoneurons. We also confirm the existence of a small pool of neurons in the dorsal part of the brainstem reticular formation that project ipsilaterally to both facial and hypoglossal nuclei. For precise tracer injections, both motor nuclei were located and identified by the electrical antidromic activation of their constituent motoneurons. Injections of retrograde tracers into the facial nucleus consistently labeled neurons in the hypoglossal nucleus. These neurons prevalently lay in the ipsilateral side, were small in size, and, like classic intrinsic hypoglossal local-circuit interneurons, had several thin dendrites. Reverse experiments - injections of anterograde tracers into the hypoglossal nucleus - labeled fine varicose nerve fiber terminals in the facial nucleus. These fiber terminals were concentrated in the intermediate subdivision of the facial nucleus, with a strong ipsilateral prevalence. Double injections of different tracers into the facial and the hypoglossal nuclei revealed a small, but constant, number of double-labeled neurons located predominantly ipsilateral in the caudal brainstem reticular formation. Hypoglossal internuclear interneurons projecting to the facial nucleus, as well as those neurons of the parvocellular reticular formation that project to both facial and hypoglossal nuclei, could be involved in oro-facial coordination. 相似文献
77.
Cecilia Cugini Ottavio A. Rombol Antonino Giarrusso Lido Porri Giovanni Ricci 《Macromolecular chemistry and physics.》2005,206(16):1684-1690
Summary: Homopolymerization of 4‐methyl‐1,3‐pentadiene (MP) and copolymerization of 4‐methyl‐1,3‐pentadiene with alkenes (ethylene, 1‐pentene, 4‐methyl‐1‐pentene) were performed to investigate the effect of the so‐called backbiting coordination on the chemoselectivity of 1,3‐diene polymerization. Three homogeneous catalyst systems were used: CpTiCl3‐MAO, Cp2TiCl2‐MAO and Cp2TiCl‐MAO. Backbiting coordination is possible with the first catalyst, but not with the other two. The three catalysts gave similar results, which indicates that backbiting has no effect on the polymerization chemoselectivity, contrary to what has been reported in recent literature. An interpretation is presented for the formation of 1,4 units in MP/alkene copolymers. This interpretation is based on the fact that allyl groups have predominantly a syn configuration in MP homopolymerization, whereas allyl groups of anti configuration are formed in MP/alkene copolymerization. The role of backbiting in diene polymerization is discussed.
78.
d'Avella A Bizzi E 《Proceedings of the National Academy of Sciences of the United States of America》2005,102(8):3076-3081
Selecting the appropriate muscle pattern to achieve a given goal is an extremely complex task because of the dimensionality of the search space and because of the nonlinear and dynamical nature of the transformation between muscle activity and movement. To investigate whether the central nervous system uses a modular architecture to achieve motor coordination we characterized the motor output over a large set of movements. We recorded electromyographic activity from 13 muscles of the hind limb of intact and freely moving frogs during jumping, swimming, and walking in naturalistic conditions. We used multidimensional factorization techniques to extract invariant amplitude and timing relationships among the muscle activations. A decomposition of the instantaneous muscle activations as combinations of nonnegative vectors, synchronous muscle synergies, revealed a spatial organization in the muscle patterns. A decomposition of the same activations as a combination of temporal sequences of nonnegative vectors, time-varying muscle synergies, further uncovered specific characteristics in the muscle activation waveforms. A mixture of synergies shared across behaviors and synergies for specific behaviors captured the invariances across the entire dataset. These results support the hypothesis that the motor controller has a modular organization. 相似文献
79.
Renner CI Woldag H Atanasova R Hummelsheim H 《Journal of the neurological sciences》2005,239(1):25-30
BACKGROUND AND PURPOSE: The relearning of daily activities after stroke also involves performance of bimanual tasks. This raises the possibility that concurrent activation of the healthy hemisphere interferes with reorganization processes in the affected hemisphere due to inhibitory pathways between homologous motor cortex representations. This study investigated the effect of voluntary, simultaneous activation of both hands upon the non-dominant (healthy subjects) or affected (stroke patients) hemisphere. METHODS: Eleven healthy subjects and 16 stroke patients were investigated using transcranial stimulation (TMS). TMS was applied over the non-dominant/affected hemisphere during performance of an isometric pinch grip at different force levels (10% or 50% of maximal voluntary contraction) with the contralateral hand. The ipsilateral hand had to perform the pinch grip at various force levels (10%, 50%, or 100% of maximal voluntary contraction) simultaneously. Peak-to-peak amplitudes of motor evoked potentials (MEPs) were compared to assess differences in motor cortex excitability. RESULTS: Unilateral activity of either hand alone exerted a facilitatory effect upon the non-dominant or affected hemisphere. In healthy subjects, the activation of the ipsilateral hand simultaneously with the contralateral hand did not produce any significant change of the MEP amplitudes compared to unilateral activation of the contralateral hand. In patients, however, the additional activation of the ipsilateral hand caused an additional increase of the peak-to-peak amplitudes. CONCLUSION: In healthy subjects voluntary activation of the ipsilateral hand does not change the excitability of the motor cortex of the non-dominant hemisphere, when the contralateral hand is simultaneously activated. The facilitation of the contralateral hand seems to gate further facilitation by the ipsilateral hand. However, in stroke patients simultaneous activation of both hands causes an additional facilitation compared to activation of the affected hand alone. 相似文献
80.
We interact daily with moving objects. How accurate are our predictions about objects' motions? What sources of information do we use? These questions have received wide attention from a variety of different viewpoints. On one end of the spectrum are the ecological approaches assuming that all the information about the visual environment is present in the optic array, with no need to postulate conscious or unconscious representations. On the other end of the spectrum are the constructivist approaches assuming that a more or less accurate representation of the external world is built in the brain using explicit or implicit knowledge or memory besides sensory inputs. Representations can be related to naive physics or to context cue-heuristics or to the construction of internal copies of environmental invariants. We address the issue of prediction of objects' fall at different levels. Cognitive understanding and perceptual judgment of simple Newtonian dynamics can be surprisingly inaccurate. By contrast, motor interactions with falling objects are often very accurate. We argue that the pragmatic action-oriented behaviour and the perception-oriented behaviour may use different modes of operation and different levels of representation. 相似文献