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   13591篇
  免费   175篇
  国内免费   124篇
教育   9061篇
科学研究   1406篇
各国文化   117篇
体育   2099篇
综合类   19篇
文化理论   142篇
信息传播   1046篇
  2022年   113篇
  2021年   162篇
  2020年   291篇
  2019年   418篇
  2018年   562篇
  2017年   564篇
  2016年   488篇
  2015年   343篇
  2014年   371篇
  2013年   2327篇
  2012年   355篇
  2011年   311篇
  2010年   268篇
  2009年   285篇
  2008年   262篇
  2007年   243篇
  2006年   266篇
  2005年   218篇
  2004年   420篇
  2003年   401篇
  2002年   369篇
  2001年   434篇
  2000年   261篇
  1999年   183篇
  1998年   131篇
  1997年   115篇
  1996年   124篇
  1995年   131篇
  1994年   127篇
  1993年   93篇
  1992年   159篇
  1991年   132篇
  1990年   150篇
  1989年   170篇
  1988年   128篇
  1987年   140篇
  1986年   127篇
  1985年   140篇
  1984年   127篇
  1983年   128篇
  1982年   103篇
  1981年   87篇
  1980年   93篇
  1979年   141篇
  1978年   94篇
  1977年   76篇
  1976年   97篇
  1975年   72篇
  1974年   79篇
  1973年   71篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The purpose of these studies was to examine the relationship between perceptions of exercise-related changes (i.e., perceived mastery and physical change) and certainty with regard to the self-as-exerciser. It was hypothesized that seeing "change" would be associated with more favorable levels of exercise self-certainty and behavior relative to "no change." Online surveys were repeatedly administered across 4 months (Study 1) and 4 weeks (Study 2) to 196 university students (M(age) = 20.17), and 250 community dwellers (M(age) = 38.44), respectively. Data were analyzed via latent variable modeling procedures. Consistent with hypotheses, latent classes (i.e., subgroups) reflecting interindividual differences in levels and trajectories of perceived change were associated with distinct patterns of self-certainty and exercise behavior. The findings suggest that adults who experience mastery of skills and physiological changes also have greater self-certainty and exercise more regularly than those who do not see progress or feel as certain of their exercise identity.  相似文献   
962.
We assessed how golfers cope with the commonly observed systematic overshoot errors in the perception of the direction between the ball and the hole. Experiments 1 and 2, in which participants were required to rotate a pointer such that it pointed to the center of the hole, showed that errors in perceived direction (in degrees of deviation from the perfect aiming line) are destroyed when the head is constrained to move within a plane perpendicular to the green. Experiment 3 compared the errors in perceived direction and putting errors of novice and skilled players. Unlike the perceived direction, putting accuracy (in degrees of deviation from the perfect aiming line) was not affected by head position. Novices did show a rightward putting error, while skilled players did not. We argue that the skill-related differences in putting accuracy reflect a process of recalibration. Implications for aiming in golf are discussed.  相似文献   
963.
Many motile bacteria are propelled by the rotation of flagellar filaments. This rotation is driven by a membrane protein known as the stator-complex, which drives the rotor of the bacterial flagellar motor. Torque generation is powered in most cases by proton transit through membrane protein complexes known as stators, with the next most common ionic power source being sodium. Sodium-powered stators can be studied through the use of synthetic chimeric stators that combine parts of sodium- and proton-powered stator proteins. The most well studied example is the use of the sodium-powered PomA-PotB chimeric stator unit in the naturally proton-powered Escherichia coli. Here we designed a fluidics system at low cost for rapid prototyping to separate motile and non-motile populations of bacteria while varying the ionic composition of the media and thus the sodium-motive force available to drive this chimeric flagellar motor. We measured separation efficiencies at varying ionic concentrations and confirmed using fluorescence that our device delivered eightfold enrichment of the motile proportion of a mixed population. Furthermore, our results showed that we could select bacteria from reservoirs where sodium was not initially present. Overall, this technique can be used to implement the selection of highly motile fractions from mixed liquid cultures, with applications in directed evolution to investigate the adaptation of motility in bacterial ecosystems.  相似文献   
964.
Separation and sorting of biological entities (viruses, bacteria, and cells) is a critical step in any microfluidic lab-on-a-chip device. Acoustofluidics platforms have demonstrated their ability to use physical characteristics of cells to perform label-free separation. Bandpass-type sorting methods of medium-sized entities from a mixture have been presented using acoustic techniques; however, they require multiple transducers, lack support for various target populations, can be sensitive to flow variations, or have not been verified for continuous flow sorting of biological cells. To our knowledge, this paper presents the first acoustic bandpass method that overcomes all these limitations and presents an inherently reconfigurable technique with a single transducer pair for stable continuous flow sorting of blood cells. The sorting method is first demonstrated for polystyrene particles of sizes 6, 10, and 14.5 μm in diameter with measured purity and efficiency coefficients above 75 ± 6% and 85 ± 9%, respectively. The sorting strategy was further validated in the separation of red blood cells from white blood cells and 1 μm polystyrene particles with 78 ± 8% efficiency and 74 ± 6% purity, respectively, at a flow rate of at least 1 μl/min, enabling to process finger prick blood samples within minutes.  相似文献   
965.
Modern patent systems are slow, inefficient, expensive, and may result in outcomes that actively harm technological progress. This paper proposes a substantive re-think of these systems and lays a foundation upon which practical solutions can be built. Many solutions proposed in the past, such as prior-art bounties, outsourced examination, and dynamic fee setting, have gone unheeded due to the cost of administering them and the rigidity of the patent system. We explore how distributed ledger technologies (DLTs) enable these major changes by altering the way stakeholders are able to interact with the patent records system. We find that transitioning to a DLT-based patent records system can enable many previously suggested improvements to current patent systems in a flexible, scalable, and transparent manner. The case for such a transition is strengthened when jointly considering the complex but common roots of problems facing modern patent systems, rather than a balkanised set of technical solutions to address each issue independently. Noting that a DLT-based system is not a panacea, we also provide comment on the political, legal, and organisational challenges that must be overcome for such changes to be implemented at scale.  相似文献   
966.
Can public libraries become hubs for citizen science? In line with the principles of citizen science, this question was answered collaboratively with librarians from the Barcelona Network of Public Libraries who performed two hands-on activities. One activity was a training course taken by 30 librarians from 24 different libraries which enabled them to envisage citizen science implementation at each library. The other activity consisted of co-creating a citizen social science project and involved 40 library users, seven librarians from three different cities, and professional scientists. The analysis considers the perspectives of both librarians and users, through participant observation, surveys, and a focus group to identify strengths and challenges. The overall results suggest that public libraries can offer leadership in the promotion of citizen science and contribute to the mission of public libraries to act as local community hubs. The main challenges identified were related to the complexity of collaboration, uncertainty regarding research co-creation, and participant retention strategies.  相似文献   
967.
In this paper, we explore how local governments are using Instagram as a communication tool to engage with their citizens, using data from the municipalities of Andalusia (Spain). We seek to identify the determinants of local government use of Instagram, the determinants of activity in this channel and the determinants of citizen reactions in order to understand the influence of media types (picture, video or album) used in municipality posts, and to understand content type (what the post is about). Instaloader, an open source intelligence (OSINT) tool for Instagram, was applied. It made it possible to automatically extract all posts of the analysed municipalities (14,742 posts). These were later automatically analysed using R, an open source software. It was determined that of the 29 Andalusian local governments with the highest populations, only those that maintain an account on Instagram, totalling 17 municipalities (58.62%), would be part of the final analysis. Our findings demonstrate that when local governments have a high level of debt, they do not maintain and actively use Instagram accounts. We also found that quality of posts’ content is more important than quantity of followers, since there is no significant relationship between citizen reactions and the number of inhabitants of a municipality or the number of followers (audience), while there is a significant negative relationship between the number of posts (activity) and reactions. Our results also highlight that the level of reactions can be stimulated by certain media and content types.  相似文献   
968.
Educational technology research and development - The objective has been to know the impact of the flipped classroom methodology on the academic performance of students during their training...  相似文献   
969.
970.
Educational technology research and development - In recent years, many psycho-educational technologies were studied to address the school-related difficulties encountered by students with autism...  相似文献   
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