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   130篇
  免费   4篇
教育   44篇
科学研究   37篇
各国文化   1篇
体育   19篇
文化理论   16篇
信息传播   17篇
  2023年   1篇
  2022年   2篇
  2021年   5篇
  2020年   3篇
  2019年   13篇
  2018年   9篇
  2017年   9篇
  2016年   9篇
  2015年   6篇
  2014年   5篇
  2013年   17篇
  2012年   8篇
  2011年   10篇
  2010年   4篇
  2009年   6篇
  2008年   5篇
  2007年   2篇
  2006年   2篇
  2004年   1篇
  2003年   3篇
  2002年   2篇
  1999年   2篇
  1998年   1篇
  1996年   1篇
  1994年   1篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
排序方式: 共有134条查询结果,搜索用时 46 毫秒
111.
112.
Despite the critical role of regulations on competition and innovation, little is known about firm responses and related effects on performance under regulatory contingencies that are permissive or restrictive. By longitudinally investigating hybrid cars competing in the Le Mans Prototype racing (LMP1), we counter-intuitively suggest that permissive regulations increase technological uncertainty and thus decrease the firms’ likelihood of shifting their technological trajectory, while restrictive regulations lead to the opposite outcome. Further, we suggest that permissive regulations favour firms that innovate their products by sequentially upgrading core and peripheral subsystems, while restrictive regulations (in the long term) favour firms upgrading them simultaneously. Implications for theory and practice are discussed.  相似文献   
113.
More than 20 years ago, electrical impedance spectroscopy (EIS) was proposed as a potential characterization method for flow cytometry. As the setup is comparably simple and the method is label-free, EIS has attracted considerable interest from the research community as a potential alternative to standard optical methods, such as fluorescence-activated cell sorting (FACS). However, until today, FACS remains by and large the laboratory standard with highly developed capabilities and broad use in research and clinical settings. Nevertheless, can EIS still provide a complement or alternative to FACS in specific applications? In this Perspective, we will give an overview of the current state of the art of EIS in terms of technologies and capabilities. We will then describe recent advances in EIS-based flow cytometry, compare the performance to that of FACS methods, and discuss potential prospects of EIS in flow cytometry.  相似文献   
114.
This work presents the development of an array of bioreactors where finely controlled stirring is provided at the microliter scale (100–300 μl). The microliter-bioreactor array is useful for performing protocol optimization in up to 96 parallel experiments of hematopoietic stem cell (HSC) cultures. Exploring a wide range of experimental conditions at the microliter scale minimizes cost and labor. Once the cell culture protocol is optimized, it can be applied to large-scale bioreactors for stem cell production at the clinical level. The controlled stirring inside the wells of a standard 96-well plate is provided by buoyancy-driven thermoconvection. The temperature and velocity fields within the culture volume are determined with numerical simulations. The numerical results are verified with experimental velocity measurements using microparticle image velocimetry (μPIV) and are used to define feasible experimental conditions for stem cell cultures. To test the bioreactor array’s functionality, human umbilical cord blood-derived CD34+ cells were cultured for 7 days at five different stirring conditions (0.24–0.58 μm∕s) in six repeated experiments. Cells were characterized in terms of proliferation, and flow cytometry measurements of viability and CD34 expression. The microliter-bioreactor array demonstrates its ability to support HSC cultures under stirred conditions without adversely affecting the cell behavior. Because of the highly controlled operative conditions, it can be used to explore culture conditions where the mass transport of endogenous and exogenous growth factors is selectively enhanced, and cell suspension provided. While the bioreactor array was developed for culturing HSCs, its application can be extended to other cell types.  相似文献   
115.
The growing interest in the conservation of historic buildings encourages the development of water-repellent materials and methodologies to consolidate and/or protect stones. Recently, particular attention was devoted to composites of inorganic oxides nanoparticles and hybrid siloxane or silicone polymers. Here we present a study on the water repellence of a thin protective coating obtained through sol-gel process starting from Glymo and Dynasylan 40®, and loading the silicate matrix with nano-sized silica particles (Aeroxide LE1® -Degussa-Evonik). The coatings were applied to limestone, sandstone and granite samples. The silica nanoparticles have been characterized by XRD, the siloxane matrix through micro-Raman spectroscopy, while the surface morphology was examined by SEM. The efficacy of the treatments has been evaluated through static contact angle measurements and capillary water absorption. The optical appearance of the coatings was evaluated by colorimetric measurements. Nanoparticles at suitable concentration gave high values for the static contact angle (up to ∼ 150°), for all stone species even for four months exposure to atmospheric conditions. The coatings, in the water capillary absorption tests, however, behave as expected only for granite even if the long-term water direct contact reduces the hydrophobicity.  相似文献   
116.

Objective

The reliability of child witness testimony in sexual abuse cases is often controversial, and few tools are available. Criteria-Based Content Analysis (CBCA) is a widely used instrument for evaluating psychological credibility in cases of suspected child sexual abuse. Only few studies have evaluated CBCA scores in children suspected of being sexually abused. We designed this study to investigate the reliability of CBCA in discriminating allegations of child sexual abuse during court hearings, by comparing CBCA results with the court's final, unappealable sentence. We then investigated whether CBCA scores correlated with age, and whether some criteria were better than others in distinguishing cases of confirmed and unconfirmed abuse.

Methods

From a pool of 487 child sexual abuse cases, confirmed and unconfirmed cases were selected using various criteria including child IQ ≥ 70, agreement between the final trial outcome and the opinion of 3 experts, presence of at least 1 independent validating informative component in cases of confirmed abuse, and absence of suggestive questions during the child's testimonies. This screening yielded a study sample of 60 confirmed and 49 unconfirmed cases. The 14 item version of CBCA was applied to child witness testimony by 2 expert raters.

Results

Of the 14 criteria tested, 12 achieved satisfactory inter-rater agreement (Maxwell's Random Error). Analyses of covariance, with case group (confirmed vs. unconfirmed) and gender as independent variables and age as a covariate, showed no main effect of gender. Analyses of the interaction showed that the simple effects of abuse were significant in both sex. Nine CBCA criteria were satisfied more often among confirmed than unconfirmed cases; seven criteria increased with age.

Conclusion

CBCA scores distinguish between confirmed and unconfirmed cases. The criteria that distinguish best between the 2 groups are Quantity of Details, Interactions, and Subjective Experience. CBCA scores correlate positively with age, and independently from abuse; all the criteria test except 2 (Unusual Details and Misunderstood Details) increase with age. The agreement rate could be increased by merging criteria Unusual and Superfluous details that achieve a low inter-rater agreement when investigated separately.

Practice implication

Given its ability to distinguish between confirmed and unconfirmed cases of suspected child abuse, the CBCA could be a useful tool for expert opinion. Because our strict selection criteria make it difficult to generalize our results, further studies should investigate whether the CBCA is equally useful in the cases we excluded from our study (for example mental retardation).  相似文献   
117.
118.
119.
This paper analyses the market transformation in heritage tourism destinations when excessive tourism demand determines the emergence of a class of excursionists among visitors. Building on the approach of Keane (1997) and Shapiro (1983), some important dimensions of sustainable tourism development are highlighted. The lesser capacity of excursionists to learn the true quality of the tourist goods provides an opportunity for producers to cut back on quality. To serve high quality goods and keep up the reputation of the destination, producers need to gain a mark-up on price that might not be sustained in a competitive market. Hence the decline in ``high-paying' demand segments, increasingly substituted by visitors with lesser quality expectations, has significant consequences on the use and preservation of the heritage. The proposed formulation allows the identification of appropriate policy instruments to reverse this process.  相似文献   
120.
Handwriting is a complex activity that involves continuous interaction between lowerlevel perceptual-motor and higher-level cognitive processes. All handwriting models describe involvement of executive functions (EF) in handwriting development. Particular EF domains associated with handwriting include maintenance of information in working memory, inhibition of prepotent responses, and shifting and sustaining of attention. Generativity, an EF domain that has not been extensively studied, may play a role in the acquisition and automation of handwriting. We hypothesized that neuropsychological performances and handwriting fluency would be mutually associated, and that visuospatial generativity could have a specific role in handwriting speed. We enrolled 96 children who completed a comprehensive neuropsychological battery. The study found that handwriting speed was associated with visuospatial fluency, which involves behavioural execution and initiation. In learning and performing handwriting, there is an inherent non-exclusive role of fine motor skills.  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