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   69篇
  免费   1篇
教育   32篇
科学研究   3篇
各国文化   1篇
体育   7篇
信息传播   27篇
  2023年   1篇
  2022年   4篇
  2021年   1篇
  2019年   3篇
  2018年   1篇
  2017年   5篇
  2016年   2篇
  2014年   6篇
  2013年   31篇
  2012年   3篇
  2011年   1篇
  2010年   2篇
  2009年   2篇
  2007年   1篇
  2005年   2篇
  1994年   1篇
  1980年   1篇
  1977年   2篇
  1970年   1篇
排序方式: 共有70条查询结果,搜索用时 15 毫秒
61.
The library literature contains many discussions on problem-based learning as a means of engaging students in instruction and promoting information literacy. A related but relatively unexplored opportunity is available through client-based projects. Using examples from the business education literature, library literature, and the author's experience, the author attempts to connect the consulting processes of client-based projects to information literacy competencies, specifically, the ACRL Information Literacy Competency Standards for Higher Education. The correspondence in the steps reveals exceptional opportunities for librarians to simultaneously apply what they already know, stretch their own boundaries, and promote information literacy in highly-motivated students.  相似文献   
62.
63.
Lifelong learning opportunities are readily accessible through the hybridization of digital learning contexts—from formal to informal—in today's globally networked knowledge society. As such, expanded learning opportunities generate a continuum of learning contexts and experiences mediated through digital technology. Consequently, there is an urgent need to actively examine the interconnections and complex relations between what is learned in formal university scenarios and the everyday learning that happens outside of the classroom, particularly the informal learning that is afforded through expanded and emerging digital contexts. The current research problem illustrates that expanded and emerging professional development scenarios require new pedagogical designs for empowering lifelong learners to harness the affordances of the web across both formal and informal contexts and practices. This study outlines ways in which students shape their learning ecologies in virtual contexts to support formal academic learning in online higher education. The paper presents qualitative results from a larger mixed methods interpretive case study. The multicase and multisite study examines three fully online graduate programmes in Education and Digital Technology during the 2017–18 academic year, collecting data in the form of online programme documentation, student interviews and online participant observation. Purposeful and criterion sampling were used to select 13 participants across three sites in Spain, the UK and the USA. The study was underpinned by a lifelong learning ecologies theoretical perspective to analyse learning processes across a continuum of practices and contexts. Findings illustrate how students conceive of, as well as how they organize their learning ecologies through a unique configuration of activities, digital resources and networked social support, indicating that academic programmes and teachers have an essential role in empowering student learning ecologies across contexts, recognizing past trajectories and supporting the development of valued disciplinary practices and perspectives across a continuum of learning.  相似文献   
64.
Guidelines for locating alcohol research information or building alcohol collections are provided. Resource organizations, including government agencies, research institutions, and publishers are identified, and several important access tools are described. There is also a brief summary of the future directions of alcohol research and dissemination.  相似文献   
65.
From the Editor     
No abstract available for this article.  相似文献   
66.
67.
Over the past 15?years, many state governments in Mexico have initiated local programs to introduce English at the primary school level. In 2009, the Mexican Ministry of Education formalized the Programa Nacional de Inglés en Educación Básica (PNIEB) as part of the national curriculum, based on the argument that increasing the number of English speakers in Mexico is necessary for the country to be globally competitive and to follow the trend in other developing economies of augmenting English instruction in public education. This paper focuses on the implementation of PNIEB and the state programs that preceded it. The authors document the practices and challenges associated with the program based on data collected from interviews with the main stakeholders involved (students and parents, teachers, school principals, and program coordinators) and from classroom observations. The total data-set consisted of over 200 interviews and classroom observations spread over several years from 2008 to 2012. Several challenges are described, including the development of materials, the role of English in relation to other subject areas, and the training of teachers who often speak English but have uneven formal preparation. The status of the teachers, both as second-class citizens within the schools and the instability and irregularities with their contracts, was identified as the most significant challenge to the successful implementation of the programs.  相似文献   
68.
69.
70.
We present a simple microchip device consisting of an overlaid pattern of micromagnets and microwells capable of capturing magnetically labeled cells into well-defined compartments (with accuracies >95%). Its flexible design permits the programmable deposition of single cells for their direct enumeration and pairs of cells for the detailed analysis of cell-cell interactions. This cell arraying device requires no external power and can be operated solely with permanent magnets. Large scale image analysis of cells captured in this array can yield valuable information (e.g., regarding various immune parameters such as the CD4:CD8 ratio) in a miniaturized and portable platform.The emergent need for point-of-care devices has spurred development of simplified platforms to organize cells across well-defined templates.1 These devices employ passive microwells, immunospecific adhesive islands, and electric, optical, and acoustic traps to manipulate cells.2–6 In contrast, magnetic templating can control the spatial organization of cells through its ability to readily program ferromagnetic memory states.7 While it has been applied to control the deposition of magnetic beads,8–13 it has not been used to direct the deposition of heterogeneous cell pairs, which may help provide critical insight into the function of single cells.14,15 As such, we developed a simple magnetographic device capable of arraying single cells and pairs of cells with high fidelity. We show this magnetic templating tool can use immunospecific magnetic labels for both the isolation of cells from blood and their organization into spatially defined wells.We used standard photolithographic techniques to fabricate the microchips (see supplementary material16). Briefly, an array of 10 × 30 μm cobalt micromagnets were patterned by a photolithographic liftoff process and overlaid with a pattern of dumbbell-shaped microwells formed in SU-8 photoresist (Fig. 1(a)). The micromagnets were designed to produce a predominantly vertical field in the microwells by aligning the ends of the micromagnet at the center of each well of the dumbbell. These features were deposited across an area of ≈400 mm2 (>50 000 well pairs per microchip) (Fig. 1(b)). Depending on the programmed magnetization state with respect to the external field, magnetic beads or cells were attracted to one pole and repelled by the other pole of each micromagnet, leading to a biased deposition (Fig. 1(c)).12Open in a separate windowFIG. 1.Magnetographic array for single cell analysis. (a) SEM image of the dumbbell-shaped well pairs for capturing magnetically labelled cells. (b) Photograph of the finished device. (c) An array of well pairs displaying a pitch of 60 × 120 μm before (top) and 10 min after the deposition of magnetic beads (bottom).To demonstrate the capability of the array to capture cells into a format amenable for rapid image processing, we organized CD3+ lymphocytes using only hand-held permanent magnets. We isolated CD3+ lymphocytes from blood via positive selection using anti-CD3 magnetic nanoparticles (EasySep™, STEMCELL Technologies) with purities confirmed by flow cytometry (97.8%; see supplementary material16). We then stained 1 × 106 CD3+ cells with anti-CD8 Alexa-488 and anti-CD4 Alexa-647 (5 μl of each antibody in 100 μl for 20 min; BD Bioscience) to determine the CD4:CD8 ratio, a prognostic ratio for assessing the immune system.17,18Variably spaced neodymium magnets (0.5 in. × 0.5 in. × 1 in.; K&J Magnetics, Inc.) were fixed on either side of the microchip to generate a tunable magnetic field (0–400 G; Fig. 2(a)). Using this setup, fluorescently labeled cells were deposited, and the populations of CD4+ and CD8+ cells were indiscriminately arrayed, imaged, and enumerated using ImageJ. The resulting CD4:CD8 ratio of 1.84 ± 0.18 (Fig. 2(b)) was confirmed by flow cytometry with a high correlation (5.4% difference; Fig. 2(c)), indicating the magnetographic microarray can pattern cells for the rapid and accurate assessment of critical phenotypical parameters without complex equipment (e.g., function generators or flow cytometers).Open in a separate windowFIG. 2.CD8 analysis of CD3+ lymphocytes. (a) Photograph of the magnetographic device activated by permanent magnets (covered with green tape). The CD4:CD8 ratio determined by the (b) magnetographic microarray and (c) and (d) flow cytometry was 1.84 and 1.74, respectively.More complex operations, such as the programmed deposition of cell pairs, can be achieved by leveraging the switchable, bistable magnetization of the micromagnets for the detailed studies of cell-cell interactions (Figs. 3(a)–3(d)).12 For these studies, a 200 G horizontal field generated from an electromagnetic coil was used to magnetize the micromagnets.19 We then captured different concentrations of magnetic beads as surrogates for cells (8.4 μm polystyrene, Spherotech, Inc.) and found that higher bead concentrations did not affect the capture accuracy (>95%; see supplementary material16).Open in a separate windowFIG. 3.Programmed pairing of magnetic beads and CD3+ lymphocytes. (a) Schematic of the magnetographic cell pair isolations. (b) Polarized micromagnets isolate cells of one type to one side in a vertical magnetic field and then cells of a second type to the other side when the field is reversed. (c) Fluorescent image of magnetically trapped green stained (top) and red stained (bottom) cell pairs. (d) SEM image of magnetically labeled cells in the microwells. (e) Capture accuracy of magnetic bead pairs. (Each color (and shape) represents the field strength of the reversed field.) (f) Change in the capture accuracy (loss) of initially captured beads after reversing the magnetic field. The capture accuracy of (g) magnetically labeled cell pairs and (h) the second magnetically labeled cell (for (e)–(h): n = 5; time starts from the deposition of the second set of cells or beads).The opposite side of each micromagnet was then populated with the second (yellow fluorescent) bead by reversing the direction of the applied magnetic field. We tested several field strengths (i.e., 10, 25, 40, or 55 G) to optimize the conditions for isolating the desired bead in the opposite well without ejecting the first bead. If the field strength was too large, the previously deposited beads could be ejected from their wells due to the repulsive magnetic force overcoming gravity.12 As shown in Figure 3(e), increasing the field strength from 10 to 25 G significantly increased the capture accuracy at 60 min from the deposition of the second bead (p < 0.01), but increases from 25 to 55 G did not affect the capture accuracy (p > 0.10). As shown in Figure 3(f), higher field strengths (i.e., 40 and 55 G) resulted in lower capture accuracies compared to lower field strengths (i.e., 10 and 25 G) (p < 0.01), which was primarily due to ejection of the initially captured beads when the micromagnets reversed their polarity.We then arranged pairs of membrane dyed (calcein AM, Invitrogen; PKH26, Sigma) magnetically labeled CD3+ lymphocytes. First, red stained cells (150 μl of 2 × 104 cells/ml) were deposited on the microchip in the presence of 250 G vertical magnetic field. After 20 min, the field was reversed (i.e., to 40, 55, and 70 G) and green stained cells (150 μl of 2 × 104 cells/ml) were deposited on the microchip with images taken in 10 min intervals. Fluorescence images were overlaid (Fig. 3(c)) and the capture accuracy of cell pairs was determined (ImageJ).As seen in Figure 3(g), the capture accuracy of pairs of CD3+ lymphocytes was lower than that of magnetic beads (Fig. 3(e)). However, as shown in Figure 3(h), the second set of cells (green fluorescent) exhibited an average capture accuracy of 91.8% ± 1.9%. This indicates that the lower capture accuracy of cell pairs was either due to the ejection of initially captured (red fluorescent) cells or the migration of initially captured cells through the connecting channel, resulting from their relatively high deformability compared to magnetic beads.In summary, we developed a simple device capable of organizing magnetic particles, cells, and pairs of cells into well-defined compartments. A major advantage of this system is the use of specific magnetic labels to both isolate cells and program their deposition. While the design of this device does not enable dynamic control of the spacing between captured cell pairs as does some dielectrophoresis-based devices,20 it can easily capture cells with high fidelity using only permanent magnets and has clinical relevance in the assessment of immune parameters. These demonstrations potentiate a relatively simple and robust device where highly organized spatial arrangement of cells facilitates rapid and accurate analyses towards a functional and low-cost point-of-care device.  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