首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9423篇
  免费   107篇
  国内免费   6篇
教育   6302篇
科学研究   1104篇
各国文化   324篇
体育   731篇
综合类   5篇
文化理论   62篇
信息传播   1008篇
  2021年   88篇
  2020年   120篇
  2019年   172篇
  2018年   219篇
  2017年   239篇
  2016年   218篇
  2015年   145篇
  2014年   191篇
  2013年   1621篇
  2012年   204篇
  2011年   196篇
  2010年   175篇
  2009年   187篇
  2008年   232篇
  2007年   220篇
  2006年   190篇
  2005年   169篇
  2004年   186篇
  2003年   140篇
  2002年   117篇
  2001年   159篇
  2000年   186篇
  1999年   162篇
  1998年   90篇
  1997年   88篇
  1996年   76篇
  1994年   68篇
  1993年   83篇
  1992年   138篇
  1991年   149篇
  1990年   148篇
  1989年   158篇
  1988年   121篇
  1987年   117篇
  1986年   118篇
  1985年   157篇
  1984年   128篇
  1983年   119篇
  1982年   100篇
  1981年   81篇
  1980年   91篇
  1979年   144篇
  1978年   89篇
  1977年   90篇
  1976年   79篇
  1975年   76篇
  1974年   89篇
  1973年   82篇
  1971年   74篇
  1968年   74篇
排序方式: 共有9536条查询结果,搜索用时 0 毫秒
901.
During the past several years, Baylor College of Medicine has made a substantial commitment to the use of information technology in support of its corporate and academic programs. The concept of an Integrated Academic Information Management System (IAIMS) has proved central in our planning, and the IAIMS activities that we have undertaken with funding from the National Library of Medicine have proved to be important extensions of our technology development. Here we describe our Virtual Notebook system, a conceptual and technologic framework for task coordination and information management in biomedical work groups. When fully developed and deployed, the Virtual Notebook will improve the functioning of basic and clinical research groups in the college, and it currently serves as a model for the longer-term development of our entire information management environment.  相似文献   
902.
A simple microfluidic 3D hydrodynamic flow focusing device has been developed and demonstrated quantitative determinations of quantum dot 525 with antibody (QD525-antibody) and hemagglutinin epitope tagged MAX (HA-MAX) protein concentrations. This device had a step depth cross junction structure at a hydrodynamic flow focusing point at which the analyte stream was flowed into a main detection channel and pinched not only horizontally but also vertically by two sheath streams. As a result, a triangular cross-sectional flow profile of the analyte stream was formed and the laser was focused on the top of the triangular shaped analyte stream. Since the detection volume was smaller than the radius of laser spot, a photon burst histogram showed Gaussian distribution, which was necessary for the quantitative analysis of protein concentration. By using this approach, a linear concentration curve of QD525-antibody down to 10 pM was demonstrated. In addition, the concentration of HA-MAX protein in HEK293 cell lysate was determined as 0.283 ± 0.015 nM. This approach requires for only 1 min determining protein concentration. As the best of our knowledge, this is the first time to determinate protein concentration by using single molecule detection techniques.  相似文献   
903.
The aim of this case study was to determine whether a sailor's deliberate choice of a conservative strategy to manage sleep deprivation would allow him to cross the Pacific Ocean and to minimize his state of anxiety and perceived fatigue. The participant, who had more than 10 years' sailing experience in severe conditions, was tested on a small catamaran without any living quarters during a solo Pacific Ocean crossing. Estimations of sleep hours, state anxiety, and perceived fatigue were self-reported by the sailor on a daily basis using a specific questionnaire. The most important finding is that the sailor's deliberate sleep strategy, 5.4 h sleep per day (24% less than on-shore), was enough to keep his anxiety and perceived fatigue within acceptable limits and enabled him to achieve his goal, which was the first crossing of the Pacific Ocean on a catamaran of less than 6 m. In conclusion, our results suggest that the sailor observed in the present case study was able to minimize anxiety and perceived fatigue with adequate sleep to optimize his performance, security, and to achieve his goal.  相似文献   
904.
The aims of this study were to establish whether anthropometry, muscle strength and endurance accounted for differences between junior and senior elite rowing ergometer performance, and to determine annual development rates for juniors associated with training. Twenty-six junior (8 females, age 18.0 ± 0.3 years and 18 males, age 17.9 ± 0.2 years) and 30 senior (12 females, 23.7 ± 3.0 years and 18 males, 24.0 ± 3.9 years) heavyweight rowers, were assessed anthropometrically, performed a 2000-m ergometer time-trial, and completed various muscular strength and endurance tests. There were no anthropometrical differences between males; however after controlling for body-fat and standing-height, senior females were of greater body-mass (70.5 ± 4.6 kg and 77.2 ± 5.9 kg, P = 0.01) and sitting-height (89.8 ± 2.2 cm and 92.2 ± 6.1 cm, P = 0.04) than juniors. Moderate to very large standardised differences in all strength and endurance tests were observed between juniors and seniors (effect size (ES) range 0.9-1.9). Greater development rates (5.0% to 6.0%) and adjusted 2000-m performance was associated with upper-body strength (males) and endurance (females). In conclusion, after identification of desirable anthropometry, the 2000-m ergometer potential of juniors may be accounted for by upper-body strength and endurance.  相似文献   
905.
The behavioural modifications that accompany Ramadan intermittent fasting (RIF) are usually associated with some alterations in the metabolic, physiological, and psychological responses of athletes that may affect sport performance. Muslim athletes who are required to train and/or compete during the month-long, diurnal fast must adopt coping strategies that allow them to maintain physical fitness and motivation if they are to perform at the highest level. This updated review aims to present the current state of knowledge of the effects of RIF on training and performance, focusing on key-factors that contribute to the effects of Ramadan on exercise performance: energy restriction, sleep deprivation, circadian rhythm perturbation, dehydration, and alterations in the training load. The available literature contain few studies that have examined the effects of RIF on physical performance in athletes and, to date, the results are inconclusive, so the effects of RIF on competition outcomes are not at present wholly understood. The diverse findings probably indicate individual differences in the adaptability and self-generated coping strategies of athletes during fasting and training. However, the results of the small number of well-controlled studies that have examined the effects of Ramadan on athletic performance suggest that few aspects of physical fitness are negatively affected, and where decrements are observed these are usually modest. Subjective feelings of fatigue and other mood indicators are often cited as implying additional stress on the athlete throughout Ramadan, but most studies show that these factors may not result in decreases in performance and that perceived exercise intensity is unlikely to increase to any significant degree. Current evidence from good, well-controlled research supports the conclusion that athletes who maintain their total energy and macronutrient intake, training load, body composition, and sleep length and quality are unlikely to suffer any substantial decrements in performance during Ramadan. Further research is required to determine the effect of RIF on the most challenging events or exercise protocols and on elite athletes competing in extreme environments.  相似文献   
906.
Abstract High physical fitness in childhood and adolescence is positively associated with favourable health-related outcomes. Our aim was to examine the relationship between relatives' (father, mother, brother, sister, and best friend) physical activity engagement and encouragement on adolescents' physical fitness. Adolescents were part of the HELENA study, a multi-centre study conducted in 10 cities from nine European countries in 2006-2008. Participants were 3288 adolescents (48% boys, 52% girls) aged 12.5-17.5 years with valid data on at least one of the three fitness variables studied: muscular strength (standing long jump), speed/agility (4×10 m shuttle run), and cardiorespiratory fitness (20 m shuttle run). The adolescents reported their relatives' physical activity engagement and encouragement. Analysis of covariance showed that relatives' physical activity engagement (father, mother, brother, and best friend) was positively related to cardiorespiratory fitness (P?相似文献   
907.
908.

Purpose

The purpose of the present review was to use existing, published data to provide an estimate of the amount of change in six-minute walk test distance (Δ6MWT) that represents a clinically meaningful change in individuals with chronic heart failure (CHF).

Methods

The present review included two separate literature searches of the CINAHL and Medline databases for articles that: (1) reported the intraclass correlation coefficient (ICC) of the 6MWT in individuals with CHF, and (2) used the 6MWT along with either aerobic capacity or health-related quality of life (HRQL) as study endpoints in randomized controlled trials (RCTs) of exercise-based intervention for individuals with CHF. The ICCs were used to calculate the minimum detectable difference (MDD) at the 95% confidence interval for each included study. The Δ6MWT associated with aerobic capacity and HRQL within-group effect sizes for the intervention and control groups in each included RCT was analyzed using receiver operating characteristic (ROC) curves.

Results

Thirteen articles reported the ICC for the 6MWT. The mean (standard deviation) MDD calculated based on these data was 43.1(16.8) m. Eighteen RCTs measured the 6MWT and either aerobic capacity and/or HRQL. A Δ6MWT of 40–45 m was associated with at least moderate aerobic capacity and HRQL effect sizes in the intervention groups. The Δ6MWT thresholds that discriminated between intervention and control groups using ROC curves revealed the following sensitivity/specificity for the respective thresholds: 19 m, 94.4/83.3%, 32 m, 83.3/94.4%, and 48 m 44.4/100% (AUC = .935, p = .009, CI95% .855, 1.015).

Conclusions

A Δ6MWT of approximately 45 m appears to exceed measurement error and be associated with significant changes in either aerobic capacity and/or HRQL.Key Words: heart failure, six-minute walk test, clinically meaningful change, minimum detectable difference  相似文献   
909.
Quantifying countermovement jump (CMJ) and landing knee flexion angle is important for performance and injury risk assessment. The purpose of the study was to compare electrogoniometer (El-Gon)- and video-derived CMJ and landing knee flexion angle. Twenty-two adults performed three CMJs while knee flexion angle was simultaneously assessed using an El-Gon and video. The average systematic offset (RMSE) of the El-Gon-derived knee flexion angle throughout the entire movement was 7.03°?±?2.69°. Excellent reliability was demonstrated by the El-Gon (ICCavg?=?0.92). Countermovement knee flexion angle, maximum landing knee flexion angle and flexion angle at maximum vertical ground reaction force were 12.0°, 10.9°, and 5.7° higher, respectively, when assessed using El-Gon (p?<?0.001), compared to video. Errors between instruments are likely due to El-Gon crosstalk, misalignment and/or axis determination. The El-Gon is a cost-effective and time-efficient alternative to video analysis for the assessment of knee flexion angle if the error is accounted for and the sensor is precisely attached.  相似文献   
910.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号