全文获取类型
收费全文 | 1780篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
教育 | 1333篇 |
科学研究 | 63篇 |
各国文化 | 28篇 |
体育 | 192篇 |
综合类 | 1篇 |
文化理论 | 18篇 |
信息传播 | 180篇 |
出版年
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 31篇 |
2019年 | 44篇 |
2018年 | 63篇 |
2017年 | 70篇 |
2016年 | 69篇 |
2015年 | 46篇 |
2014年 | 48篇 |
2013年 | 405篇 |
2012年 | 48篇 |
2011年 | 48篇 |
2010年 | 48篇 |
2009年 | 42篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 33篇 |
2005年 | 42篇 |
2004年 | 23篇 |
2003年 | 33篇 |
2002年 | 35篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 23篇 |
1993年 | 25篇 |
1992年 | 11篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1983年 | 20篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 9篇 |
1976年 | 17篇 |
1974年 | 17篇 |
1973年 | 10篇 |
1971年 | 9篇 |
1969年 | 10篇 |
1967年 | 11篇 |
排序方式: 共有1815条查询结果,搜索用时 296 毫秒
141.
The evolution of graduate education in electrical engineering began in the early 1890' s and progressed at a rapid pace in the 1920' s, particularly in metropolitan areas conscious of community needs. In these areas, evening programs held the spotlight because of the ever-demanding need to provide graduate engineers with advanced knowledge. Such cooperation between community interests and colleges has resulted in a wide variety of patterns of part-time study on campus and, more recently, off campus. The later development is viewed with criticism in several educational circles although off-campus programs are filling tremendous requirements arising from industrial concentrations not within easy reach of a university or college. The evolution seems to indicate that off campus programs are not a passing fancy and that such requirements are very likely to be best satisfied in the long run by the establishment of graduate centers with a faculty in residence. As an example, the Polytechnic Graduate Center on Long Island is described. (The Center, actually located in Farmingdale, N. Y., began its operation on September 25, 1961, with a graduate student body of nearly 700 in day and evening programs involving advanced courses in Aerospace Engineering, Electrical Engineering, Electrophysics, Mathematics, Mechanical Engineering, Physics, and Industrial Management. Close to 150 part-time day students are attending on a released-time basis, in addition to 45 full-time students in residence.) 相似文献
142.
143.
144.
In this paper, a detailed numerical and experimental investigation into the optimisation of hydrodynamic micro-trapping arrays for high-throughput capture of single polystyrene (PS) microparticles and three different types of live cells at trapping times of 30 min or less is described. Four different trap geometries (triangular, square, conical, and elliptical) were investigated within three different device generations, in which device architecture, channel geometry, inter-trap spacing, trap size, and trap density were varied. Numerical simulation confirmed that (1) the calculated device dimensions permitted partitioned flow between the main channel and the trap channel, and further, preferential flow through the trap channel in the absence of any obstruction; (2) different trap shapes, all having the same dimensional parameters in terms of depth, trapping channel lengths and widths, main channel lengths and widths, produce contrasting streamline plots and that the interaction of the fluid with the different geometries can produce areas of stagnated flow or distorted field lines; and (3) that once trapped, any motion of the trapped particle or cell or a shift in its configuration within the trap can result in significant increases in pressures on the cell surface and variations in the shear stress distribution across the cell’s surface. Numerical outcomes were then validated experimentally in terms of the impact of these variations in device design elements on the percent occupancy of the trapping array (with one or more particles or cells) within these targeted short timeframes. Limitations on obtaining high trap occupancies in the devices were shown to be primarily a result of particle aggregation, channel clogging and the trap aperture size. These limitations could be overcome somewhat by optimisation of these device design elements and other operational variables, such as the average carrier fluid velocity. For example, for the 20 μm polystyrene microparticles, the number of filled traps increased from 32% to 42% during 5–10 min experiments in devices with smaller apertures. Similarly, a 40%–60% reduction in trapping channel size resulted in an increase in the amount of filled traps, from 0% to almost 90% in 10 min, for the human bone marrow derived mesenchymal stem cells, and 15%–85% in 15 min for the human embryonic stem cells. Last, a reduction of the average carrier fluid velocity by 50% resulted in an increase from 80% to 92% occupancy of single algae cells in traps. Interestingly, changes in the physical properties of the species being trapped also had a substantial impact, as regardless of the trap shape, higher percent occupancies were observed with cells compared to single PS microparticles in the same device, even though they are of approximately the same size. This investigation showed that in microfluidic single cell capture arrays, the trap shape that maximizes cell viability is not necessarily the most efficient for high-speed single cell capture. However, high-speed trapping configurations for delicate mammalian cells are possible but must be optimised for each cell type and designed principally in accordance with the trap size to cell size ratio. 相似文献
145.
Linda Desbois Adrien Padirac Shohei Kaneda Anthony J. Genot Yannick Rondelez Didier Hober Dominique Collard Teruo Fujii 《Biomicrofluidics》2012,6(4)
Water-in-oil microdroplets offer microreactors for compartmentalized biochemical reactions with high throughput. Recently, the combination with a sol-gel switch ability, using agarose-in-oil microdroplets, has increased the range of possible applications, allowing for example the capture of amplicons in the gel phase for the preservation of monoclonality during a PCR reaction. Here, we report a new method for generating such agarose-in-oil microdroplets on a microfluidic device, with minimized inlet dead volume, on-chip cooling, and in situ monitoring of biochemical reactions within the gelified microbeads. We used a flow-focusing microchannel network and successfully generated agarose microdroplets at room temperature using the “push-pull” method. This method consists in pushing the oil continuous phase only, while suction is applied to the device outlet. The agarose phase present at the inlet is thus aspirated in the device, and segmented in microdroplets. The cooling system consists of two copper wires embedded in the microfluidic device. The transition from agarose microdroplets to microbeads provides additional stability and facilitated manipulation. We demonstrate the potential of this method by performing on-chip a temperature-triggered DNA isothermal amplification in agarose microbeads. Our device thus provides a new way to generate microbeads with high throughput and no dead volume for biochemical applications. 相似文献
146.
M Martín-Matillas FB Ortega JR Ruiz D Martínez-Gómez G Vicente-Rodríguez A Marcos L Béghin A Kafatos M González-Gross M Zaccaria D Molnár S De Henauw M Sjöström LA Moreno MJ Castillo On Behalf Of The Helena Study 《Journal of sports sciences》2012,30(13):1329-1335
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?0.05); and mother's and sisters' physical activity engagement were positively associated with higher muscular strength in adolescents (P?0.05). Furthermore, father's physical activity encouragement was positively linked to physical fitness (all fitness components) in adolescents (P?0.05). Interventions aimed at improving physical fitness in young people might be more successful when family members, particularly mothers and fathers, are encouraged to engage in physical activity and support adolescents' physical activity. 相似文献
147.
Information literacy, often described as a person's ability to effectively find and evaluate answers to questions using a variety of information resources, is of particular importance to health care workers. This paper presents the results of an information literacy survey presented to occupational therapy (OT) students at Thomas Jefferson University during a series of required class activities. Also described are the authors' activities with the faculty and courses at Jefferson. The survey was made available to first-, second-, third-, and fourth-year occupational therapy students along with nursing students and pharmacy students. The survey is designed to identify research habits, skills, and preferences. Results confirm some commonly held perceptions about searching skills of young adults and an interesting dichotomy in students' learning habits. The paper concludes with a discussion of recommendations to OT faculty and librarians on how to improve information literacy education. The survey can be obtained by contacting the authors. 相似文献
148.
Anthony F.J. van Raan Thed N. van Leeuwen Martijn S. Visser Nees Jan van Eck Ludo Waltman 《Journal of Informetrics》2010,4(3):431-435
We reply to the criticism of Opthof and Leydesdorff on the way in which our institute applies journal and field normalizations to citation counts. We point out why we believe most of the criticism is unjustified, but we also indicate where we think Opthof and Leydesdorff raise a valid point. 相似文献
149.
150.
S. Anthony Thompson 《International Journal of Inclusive Education》2013,17(10):985-1000
The purpose of this paper to present two approaches intended to support the social lives of those typically on the borders of school life. Circles of friends (CoFs) was designed to assist students labelled with disabilities, while Gay-straight alliances (GSAs) addresses needs of supporting students who identify as lesbian, gay, bisexual, transgender, two-spirited (gay/lesbian/bisexual First Nations people), queer and/or those questioning their sexual identity (LGBTTQQ). In laying out these approaches side by side, I argue that CoFs constitute a dis/abling pedagogy breed acquiescence, further pathologise students and create essentialised identification for all students. GSAs, in contrast, are constitutive of a queer pedagogy and promote active, agentive, healthy more complex identities. In short, CoFs are critiqued through GSAs and implications for inclusive schooling are explored. 相似文献