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31.
Kinematic differences of elite and high-performance tennis players in the cross court and down the line forehand 总被引:1,自引:0,他引:1
Landlinger J Lindinger SJ Stöggl T Wagner H Müller E 《Sports biomechanics / International Society of Biomechanics in Sports》2010,9(4):280-295
This study identified and compared the full body kinematics of different skill levels in the forehand groundstroke when balls were hit cross court and down the line. Forty-three three-dimensional retroreflective marker trajectories of six elite and seven high-performance players were recorded using an eight-camera 400 Hz, Vicon motion analysis system. The six highest horizontal velocity forehands with reliable kinematics of all participants were analysed for each specific situation (a total of 156 analysed shots). Significant differences (p < 0.01) and large effect sizes were observed between elite and high-performance players in linear velocity of the shoulder (2.0 vs. 1.2 m/s), angular velocity of the pelvis (295 vs. 168 degrees/s), and angular velocity of the upper trunk (453 vs. 292 degrees/s) at impact. The elite group showed a tendency towards higher racquet velocities at impact (p < 0.05). No significant differences were found in angular displacement of the racquet, hip alignment, or shoulder alignment at the completion of the backswing; nor did angular displacement vary significantly at impact. Irrespective of the group, different shoulder, hip, and racquet angles were found at impact, depending on the situation. The results should assist coaches when striving to improve their players' forehand. 相似文献
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This article examines how education unfolded as a science in Estonia in the period 1944–1991, i.e. from the second Soviet occupation to the fall of the USSR. Historical analysis of the way prominent scholars and institutions succeeded in overcoming the adverse conditions of that period is conducted by viewing their respective contributions through two theoretical lenses: cultural trauma theory to explore the adversities they had to contend with, and resilience theory to explain how those challenges were overcome. Through these means an account is constructed of how individuals and institutions succeeded in preserving the national Estonian and inter-war European legacy of educational philosophy, in the process confronting and countering adverse socio-cultural-political conditions. 相似文献
34.
Oscillating electrowetting on dielectrics (EWOD) with coplanar electrodes is investigated in this paper as a way to provide efficient stirring within a drop with biological content. A supporting model inspired from Ko et al. [Appl. Phys. Lett. 94, 194102 (2009)] is proposed allowing to interpret oscillating EWOD-induced drop internal flow as the result of a current streaming along the drop surface deformed by capillary waves. Current streaming behaves essentially as a surface flow generator and the momentum it sustains within the (viscous) drop is even more significant as the surface to volume ratio is small. With the circular electrode pair considered in this paper, oscillating EWOD sustains toroidal vortical flows when the experiments are conducted with aqueous drops in air as ambient phase. But when oil is used as ambient phase, it is demonstrated that the presence of an electrode gap is responsible for a change in drop shape: a pinch-off at the electrode gap yields a peanut-shaped drop and a symmetry break-up of the EWOD-induced flow pattern. Viscosity of oil is also responsible for promoting an efficient damping of the capillary waves which populate the surface of the actuated drop. As a result, the capillary network switches from one standing wave to two superimposed traveling waves of different mechanical energy, provided that actuation frequency is large enough, for instance, as large as the one commonly used in electrowetting applications (f ∼ 500 Hz and beyond). Special emphasis is put on stirring of biological samples. As a typical application, it is demonstrated how beads or cell clusters can be focused under flow either at mid-height of the drop or near the wetting plane, depending on how the nature of the capillary waves is (standing or traveling), and therefore, depending on the actuation frequency (150 Hz–1 KHz). 相似文献
35.
Anton J. Slagers Inge van den Akker-Scheek Jan H. B. Geertzen Johannes Zwerver Inge H. F. Reininga 《Journal of sports sciences》2013,31(21):2499-2505
ABSTRACTThe ACL-Return to Sport after Injury (ACL-RSI) and Injury-Psychological Readiness to Return to Sport (I-PRRS) scales were developed to assess psychological factors associated with return to sports. Validity and reliability have been determined. The aim of this study was to investigate the responsiveness of the Dutch ACL-RSI and I-PRRS. Seventy patients with ACL reconstruction completed both scales twice 2 months apart, plus a Global Rating of Change (GRC) questionnaire. Distribution and logistic regression-based methods were used to study responsiveness. The Standardized Response Mean (SRM) for the ACL-RSI was 0.3 and for the I-PRRS 0.1, indicating low responsiveness. The minimally important change (MIC) for ACL-RSI was 2.6 and for the I-PRRS 0.9. Since the standard error of measurement (SEM) and smallest detectable change (SDC) were larger than MIC in individual patients, it does not seem possible to distinguish minimally important changes from measurement error in individual patients with either scale. At the group level responsiveness seemed sufficient; hence, both scales can be used to investigate the effectiveness of an intervention at the group level. Both scales can also be used in cross-sectional research and in clinical practice as screening instruments to identify patients at risk of not returning to sports. 相似文献
36.
The results of an intervention program forstudents with difficulties learning mathematicsare reported. Two kinds of math intervention,guided versus structured instruction, werecompared to regular math instruction. A totalof 75 students from regular and specialeducation, aged seven to thirteen,participated. Ability and automaticitymultiplication tests were administered beforeand after the four-month training period. Theresults show that the students in both of theexperimental conditions improved more than thestudents in the control condition. Someadditional differences were found between thetwo experimental interventions. Guidedinstruction appeared to be more effective forlow performing students than structuredinstruction and especially for those studentsin regular education. Special educationstudents appear to benefit most from structuredinstruction for the automaticity ofmultiplication problems. A three monthfollow-up test showed the acquired knowledge tobe well-established in both groups. 相似文献
37.
Johannes Westberg 《History of education》2019,48(1):19-40
Drawing inspiration from the new social history of livelihood, this article examines how rural nineteenth-century teachers made a living by engaging in livelihood diversification. By using a wide variety of source materials from nineteenth-century Sweden, this article shows that, far from specialising exclusively in teaching, teachers were often engaged in multiple occupations as late as the year 1900, and that teachers’ work ranged from activities that were encouraged to those that were frowned upon or even illegal. As a result, this article sheds new light on teaching as an occupation in the nineteenth century and contributes to the discussion of the social and economic positions of teachers. By investigating how teachers earned their livelihoods, this article also addresses the role of teachers’ multiple occupations in the expansion of mass schooling during the nineteenth century. 相似文献
38.
This study investigated the possibility of enhancing the level of preschoolers’ number sense by introducing two intervention programmes, Let’s think! and Young children with special educational needs count, too! .Forty‐five preschoolers, mean age 66.4 months, were randomly assigned to the experimental and control groups. The experimental group received instruction twice a week, for half an hour, and for a period of nine months. Pretest–postest comparison revealed that the experimental group showed enhanced number‐sense performance immediately after the instruction ended, but the between‐group difference faded after six months. There were no statistically significant differences between the groups in general mathematical thinking abilities (transfer tasks) after the intervention. 相似文献
39.
Constructivism is a popular concept in contemporary teacher education programs. However, a genuine concern arises with the concept's application because many teachers and teacher educators claim that knowledge is constructed, without appreciating the epistemological and pedagogical implications such a claim entails. This article employs Phillips' (1995) analytic framework that divides the pedagogical applications of constructivism into three distinct categories: the good, the bad, and the ugly. Reviewing the constructivist epistemologies of Dewey and Vygotsky also enables the exploration of how constructivism might inform both our understanding of the impediments students confront when learning new knowledge and our understanding of general constructivist pedagogical practices. The primary objective in this article is to provide teacher educators and teachers with a richer understanding of constructivism—its limitations and its strengths—while offering concrete pedagogical strategies for its classroom application. 相似文献
40.
Social media are increasingly being used for educational purposes. The first part of this article briefly reviews literature that reports on educational applications of social media tools. The second part discusses theories that may provide a basis for analyzing the processes that are relevant for individual learning and collective knowledge construction. We argue that a systems-theoretical constructivist approach is appropriate to examine the processes of educational social media use, namely, self-organization, the internalization of information, the externalization of knowledge, and the interplay of externalization and internalization providing the basis of a co-evolution of cognitive and social systems. In the third part we present research findings that illustrate and support this systems-theoretical framework. Concluding, we discuss the implications for educational design and for future research on learning and collective knowledge construction with social media. 相似文献