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91.
The aims of this study were to investigate the energy build-up and dissipation mechanisms associated with using an arm swing in submaximal and maximal vertical jumping and to establish the energy benefit of this arm swing. Twenty adult males were asked to perform a series of submaximal and maximal vertical jumps while using an arm swing. Force, motion and electromyographic data were recorded during each performance and used to compute a range of kinematic and kinetic variables, including ankle, knee, hip, shoulder and elbow joint powers and work done. It was found that the energy benefit of using an arm swing appears to be closely related to the maximum kinetic energy of the arms during their downswing, and increases as jump height increases. As jump height increases, energy in the arms is built up by a greater range of motion at the shoulder and greater effort of the shoulder and elbow muscles but, as jump height approaches maximum, these sources are supplemented by energy supplied by the trunk due to its earlier extension in the movement. The kinetic energy developed by the arms is used to increase their potential energy at take-off but also to store and return energy from the lower limbs and to "pull" on the rest of the body. These latter two mechanisms become more important as jump height increases with the pull being the more important of the two. We conclude that an arm swing contributes to jump performance in submaximal as well as maximal jumping but the energy generation and dissipation sources change as performance approaches maximum. 相似文献
92.
The aim of this study was to examine the relationship between indicators of risk of disordered eating, body image and varied menstrual cycle lengths. Altogether, 151 female athletes were invited from 16 sports and 70 female non-athletic controls were recruited from a university lecture class. The participants completed several surveys, including demographics, menstrual cycle history, physical activity, Eating Disorder Inventory (EDI) and the Three Factor Eating Questionnaire (TFEQ). Selected EDI subscales were summed to reflect eating disorder risk and body image. Menstrual cyclicity was based on self-reported cycle length for the last 6 months (normal cycles = 26-32 days, irregular cycles < or =26 or >32 days). Athletes overall had more irregular cycles (29.1%) than the non-athletes (15.7%) (P < 0.05). There were significant differences in scores for eating disorder risk, body dissatisfaction, drive for thinness, cognitive restraint (TFEQ) and disinhibition (TFEQ), only when athletes were divided based on menstrual cyclicity (i.e. irregularly cycling athletes had higher scores than athletes with normal menstrual cycle lengths). No differences in these scores were found between non-athletes with normal or irregular menstrual cycle lengths. In conclusion, irregularly short or long menstrual cycle length is associated with subtle indications of higher risk of disordered eating in female athletes. 相似文献
93.
Achievement goal theory and the expectancy-value model of achievement choice were used to examine fourth-grade students' motivational changes in an elementary physical education running program. In fall and spring of the school year, participants (N = 113; 66 boys, 47 girls) completed questionnaires assessing achievement goals, expectancy beliefs, subjective task values, and intention for future running participation. They also completed a timed 1-mile (1.6 km) run. The number of laps they ran/walked during the school year was used to assess students' persistence/effort. Results indicated the students improved their run but became less motivated about running while participating in a year-long running program. Children's beliefs about how good they were in the running program (i.e., expectancy beliefs) and their perceptions of how interesting and fun it was (i.e., interest) emerged as the strongest positive predictors of their motivation for running over time. These findings provide strong empirical evidence that expectancy beliefs and interest are essential to children's motivation in elementary physical education. 相似文献
94.
第二课教師在問課之後,便轉到農民戰争第二階段的史實。太平天國的上層統治階級蜕化了。在残殺楊秀清之後,隨着便出现一個由高級官僚組成的新封建階級。軍事将領和負責管理地産的官吏们奪取了土地後,自己變成地主。‘人民大衆失去對自己領袖的信心,——中國的歷史家寫道——因而閃避他们’(参閥r、c、卡拉——莫爾查教授著的‘太平軍’。莫斯科,一九五○版,第一。八頁)。r、E、葉非莫夫在插寫一八五六年政變後太平天國的情形的時候,指出了‘人民的、反封建性質的運動和脫離人民的太平軍的領導政策之間的差別,越來越大了’(‘中國近代史概要’一九五一年第二版,第六一頁)。 相似文献
95.
一年多以前,在伟大的俄罗斯的伏尔加河的沿岸,在古比雪夫城和斯大林格勒城附近,世界上最巨大的水力发电站的建设工作,大规模的展开起来了。在伏尔加河的中游和下游地方将要用泥士和钢骨水泥的堤防把河分隔开来,由于这种堤防,就有巨大的蓄水池——古比雪夫“海”和斯大林格勒“海”形成起来,从那里伏尔加河的河水灌溉着伏尔加河左岸和里海沿岸的干燥和半沙漠地带。此外,蓄水池的河水贮藏,也保证了水力发电站的机器整年不断地工作。 相似文献
96.
97.
伟大的俄国公民与科学家克里孟脱·阿尔喀基也维奇季米里雅捷夫在革命前他所写的名著“植物与干旱的斗争”中说:“如果他(人)将自已耗费于相互斗争(隐蔽的或公开的)的力量,一致地集中于不流血的征服自然的斗争中,如果即使是他浪费于发明杀人武器的 相似文献
98.
<正>最佳功率负荷(Optimum power load,OPL)是指在运动中产生最大输出功率时所对应的外部负荷。该概念源于力-速曲线关系,在递增负重测试中,通过专门的仪器(如线性传感器等)测量杠铃的轨迹速度,再结合负荷推导出OPL。已有多项研究证明OPL与运动表现、专项特征之间的关联性,以及其对竞技水平产生营养的影响,并讨论其在测试和训练方面潜在的应用价值。 相似文献
99.
100.
Fisher M Paolone V Rosene J Drury D Van Dyke A Moroney D 《Research quarterly for exercise and sport》1999,70(4):361-368
Five women and 5 men were studied to examine the effects of submaximal exercise on thermoregulatory and hemodynamic variables during recovery in two environments: (a) control (C), 22 degrees C, 33% rh; and (b) hot humid (H), 32 degrees C. The participants exercised on a cycle ergometer at 60% of peak oxygen consumption for 35 min prior to 90 min of seated recovery. Sessions were identical, except for environment. Variables evaluated (p < .05) were: core temperature (TR), mean skin temperature (Ts), sweat rate (SR), heart rate (HR), stroke index (SI), cardiac index (CI), forearm blood flow (FBF), systolic blood pressure (SBP), and diastolic blood pressure (DBP). Men and women exhibited similar patterns of TR, Ts, and SR in both environments. Ts and SR (collapsed means for gender) were higher in the H than in the C. DBP was higher in men than in women throughout recovery in both environments. With combined means for gender, HR was higher in the H than in the C. CI, SI, FBF, and SBP were similar in both environments and returned to baseline within 15 min into recovery. These data suggest that heat dissipation during extended recovery was accomplished with similar contributions of cutaneous vasodilation and sweating in M and F. Furthermore, the moderate exercise level did not influence hemodynamics beyond 15 min of recovery in either environment. 相似文献