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We studied the mobility of DNA molecules driven by an electric field through a nanofluidic device containing a periodic array of deep and shallow regions termed entropic traps. The mobility of a group of DNA molecules was measured by fluorescent video microscopy. Since the depth of a shallow region is smaller than the DNA equilibrium size, DNA molecules are trapped for a characteristic time and must compress themselves to traverse the boundary between deep and shallow regions. Consistent with previous experimental results, we observed a nonlinear relationship between the mobility and electric field strength, and that longer DNA molecules have larger mobility. In repeated measurements under seemingly identical conditions, we measured fluctuations in the mobility significantly larger than expected from statistical variation. The variation was more pronounced for lower electric field strengths where the trapping time is considerable relative to the drift time. To determine the origin of these fluctuations, we investigated the dependence of the mobility on several variables: DNA concentration, ionic strength of the solvent, fluorescent dye staining ratio, electroosmotic flow, and electric field strength. The mobility fluctuations were moderately enhanced in conditions of reduced ionic strength and electroosmotic flow.  相似文献   
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The aim of this study was to examine stressors, coping, and coping effectiveness as a function of gender, type of sport, and skill. The sample consisted of 749 undergraduate athletes (455 males, 294 females) aged 18-38 years (mean= 19.8 years). Skill was classified as international/national, county, university, and club standard. Participants completed a stressor and coping concept map (Novak & Gowin, 1984). The results revealed gender, type of sport, and skill differences in relation to stressor frequencies, coping strategy deployment, and coping effectiveness. In contrast to previous research, females used a variety of problem-focused (e.g. planning, communication, technique-orientated coping) strategies more frequently than males. Team sport athletes reported a variety of sport-specific stressors relating to the demands of playing in a team environment. The group of national/international athletes reported using more planning, blocking, and visualization, and also reported that their coping was more effective than that of less-skilled athletes.  相似文献   
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This study examined the validity and reliability of decisional balance scales for exercise (i.e., pros and cons) in a large longitudinal population-based randomized sample of Canadian adults ages 18 to 65 years (N = 703). Assessments were taken over 3 time points with 6-month intervals between testing. Content, factorial, concurrent, and construct validity along with internal consistency and test-retest reliability were established for the decisional balance scales. The developed measures have utility for researchers and practitioners who test and apply the exercise decisional balance constructs of the Transtheoretical Model.  相似文献   
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The purpose of the present paper is to demonstrate how many more subjects are required to achieve equal power when testing certain hypotheses concerning proportions if the randomized response technique is employed for estimating a population proportion instead of the conventional technique.  相似文献   
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Chemical bonding is one of the key and basic concepts in chemistry. The learning of many of the concepts taught in chemistry, in both secondary schools as well as in the colleges, is dependent upon understanding fundamental ideas related to chemical bonding. Nevertheless, the concept is perceived by teachers, as well as by learners, as difficult, with teaching commonly leading to students developing misconceptions. Many of these misconceptions result from over‐simplified models used in text books, by the use of traditional pedagogy that presents a rather limited and sometimes incorrect picture of the issues related to chemical bonding and by assessments of students' achievement that influence the way the topic is taught. In addition, there are discrepancies between scientists regarding key definitions in the topic and the most appropriate models to teach it. In particular, teaching models that are intended to have transitional epistemological value in introducing abstract ideas are often instead understood by students as accounts of ontological reality. In this review paper we provide science educators, curricula developers and pre‐service and in‐service professional development providers an up‐to‐date picture regarding research and developments in teaching about chemical bonding. We review the external and internal variables that might lead to misconceptions and the problematic issue of using limited teaching/learning models. Finally, we review the approaches to teaching the concept that might overcome some of these misconceptions.  相似文献   
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Societies’ relative use of private and public services is an abiding and significant issue of scholarly and policy interest. For higher education, however, there has hitherto been no comprehensive dataset and, accordingly, no extensive, reliable analysis of the private-public distribution. As this article provides both the dataset and the analysis, it allows us to discover both the size and geographical shape of global private higher education. Having grown greatly for decades, the private sector now holds a third (32.9%) of the world’s total higher education enrollment. We find striking patterns of concentration and dispersion. The several largest country systems account for much of the private enrollment but, simultaneously, private sectors now exist in all but a few systems; a stunning 97.6% of the world’s present enrollment is in systems with dual-sector provision. Societies no longer rely exclusively on public provision. We discover too that private enrollment concentrates mostly in developing regions, though it is noteworthy in developed regions as well. Asia and Latin America are the twin giants but in all regions, at least 10% of students are in the private sector.  相似文献   
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In this digital ITEMS module, Dr. Roy Levy describes Bayesian approaches to psychometric modeling. He discusses how Bayesian inference is a mechanism for reasoning in a probability-modeling framework and is well-suited to core problems in educational measurement: reasoning from student performances on an assessment to make inferences about their capabilities more broadly conceived, as well as fitting models to characterize the psychometric properties of tasks. The approach is first developed in the context of estimating a mean and variance of a normal distribution before turning to the context of unidimensional item response theory (IRT) models for dichotomously scored data. Dr. Levy illustrates the process of fitting Bayesian models using the JAGS software facilitated through the R statistical environment. The module is designed to be relevant for students, researchers, and data scientists in various disciplines such as education, psychology, sociology, political science, business, health, and other social sciences. It contains audio-narrated slides, diagnostic quiz questions, and data-based activities with video solutions as well as curated resources and a glossary.  相似文献   
40.
The purpose of this quasi-experimental study was to determine the effects of a field-based, inquiry-focused course on pre-service teachers?? geoscience content knowledge, attitude toward science, confidence in teaching science, and inquiry understanding and skills. The field-based course was designed to provide students with opportunities to observe, compare, and investigate geological structures in their natural environment and to gain an understanding of inquiry via hands-on learning activities designed to immerse students in authentic scientific investigation. ANCOVA and MANCOVA analyses examining differences in outcome measures between students in the field experience (n?=?25) and education students enrolled in the traditional, classroom-based course (n?=?37) showed that students in the field course generally had significantly higher scores. Results provide evidence of the value of the field and inquiry-based approach in helping pre-service teachers develop the needed skills and knowledge to create effective inquiry-based science lessons.  相似文献   
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