全文获取类型
收费全文 | 5054篇 |
免费 | 62篇 |
国内免费 | 1篇 |
专业分类
教育 | 3647篇 |
科学研究 | 387篇 |
各国文化 | 75篇 |
体育 | 432篇 |
综合类 | 3篇 |
文化理论 | 63篇 |
信息传播 | 510篇 |
出版年
2022年 | 33篇 |
2021年 | 60篇 |
2020年 | 107篇 |
2019年 | 146篇 |
2018年 | 175篇 |
2017年 | 183篇 |
2016年 | 162篇 |
2015年 | 100篇 |
2014年 | 150篇 |
2013年 | 1125篇 |
2012年 | 128篇 |
2011年 | 130篇 |
2010年 | 116篇 |
2009年 | 104篇 |
2008年 | 120篇 |
2007年 | 112篇 |
2006年 | 123篇 |
2005年 | 114篇 |
2004年 | 108篇 |
2003年 | 97篇 |
2002年 | 82篇 |
2001年 | 70篇 |
2000年 | 76篇 |
1999年 | 68篇 |
1998年 | 67篇 |
1997年 | 54篇 |
1996年 | 50篇 |
1995年 | 44篇 |
1994年 | 46篇 |
1993年 | 55篇 |
1992年 | 39篇 |
1991年 | 48篇 |
1990年 | 55篇 |
1989年 | 55篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 48篇 |
1982年 | 36篇 |
1981年 | 24篇 |
1980年 | 29篇 |
1979年 | 49篇 |
1978年 | 40篇 |
1977年 | 35篇 |
1976年 | 40篇 |
1974年 | 28篇 |
1973年 | 27篇 |
1969年 | 21篇 |
排序方式: 共有5117条查询结果,搜索用时 15 毫秒
101.
A Methylome‐Wide Association Study of Trajectories of Oppositional Defiant Behaviors and Biological Overlap With Attention Deficit Hyperactivity Disorder
下载免费PDF全文
![点击此处可从《Child development》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Edward D. Barker Esther Walton Charlotte A.M. Cecil Richard Rowe Sara R. Jaffee Barbara Maughan Thomas G. O'Connor Argyris Stringaris Alan J. Meehan Wendy McArdle Caroline L. Relton Tom R. Gaunt 《Child development》2018,89(5):1839-1855
In 671 mother–child (49% male) pairs from an epidemiological birth cohort, we investigated (a) prospective associations between DNA methylation (at birth) and trajectories (ages 7–13) of oppositional defiant disorder (ODD), and the ODD subdimensions of irritable and headstrong; (b) common biological pathways, indexed by DNA methylation, between ODD trajectories and attention deficit hyperactivity disorder (ADHD); (c) genetic influence on DNA methylation; and (d) prenatal risk exposure associations. Methylome‐wide significant associations were identified for the ODD and headstrong, but not for irritable. Overlap analysis indicated biological correlates between ODD, headstrong, and ADHD. DNA methylation in ODD and headstrong was (to a degree) genetically influenced. DNA methylation associated with prenatal risk exposures of maternal anxiety (headstrong) and cigarette smoking (ODD and headstrong). 相似文献
102.
Mergers and acquisitions: Their effect on the innovative performance of companies in high-tech industries 总被引:6,自引:0,他引:6
This study examines the post-M&A innovative performance of acquiring firms in four major high-tech sectors. Non-technological M&As appear to have a negative impact on the acquiring firm's post-M&A innovative performance. With respect to technological M&As, a large relative size of the acquired knowledge base reduces the innovative performance of the acquiring firm. The absolute size of the acquired knowledge base only has a positive effect during the first couple of years after which the effect turns around and we see a negative effect on the innovative performance of the acquiring firm. The relatedness between the acquired and acquiring firms’ knowledge bases has a curvilinear impact on the acquiring firm's innovative performance. This indicates that companies should target M&A ‘partners’ that are neither too unrelated nor too similar in terms of their knowledge base. 相似文献
103.
104.
Suneesh Kumar Pachathundikandi Earaly Thomas Varghese 《Indian journal of clinical biochemistry : IJCB》2006,21(2):114-117
Blood zinc protoporphyrin (ZPP), serum total protein (TP), and total cholesterol (TC) levels in automobile workshop workers
in relation to lead toxicity were analysed. In the present study, automobile workshop workers (healthy male workers at an
age between 28 and 35 from four major automobile workshops in Kottayam, Kerala State, India) and the control (male healthy
adults at an age between 28 and 35 residing at Aymanam, a distant village at Kottayam District, Kerala having reduced or no
chance of lead exposure) displayed significant difference in blood lead (BPb) and blood ZZP (BZPP) level. The mean value of
BPb in automobile workshop workers was 15.76±0.33 μg/dl, while in the control it was 8.20±0.15 μg/dl. In automobile workshop
workers, the mean value of BZPP was 34.2±0.62 μg/dl. The control group exhibited a mean of 11.5±0.22 μg/dl. Automobile workshop
workers exhibited significant increase in BZPP was corresponding to the increase in BPb level. The total protein levels estimated
in automobile workshop workers showed significant decrease compared to control individuals, but was within the reference range
of healthy individuals. The mean value of TP level in automobile workshop workers and control was 6.9±0.13 g/dl and 7.71±0.18
g/dl, respectively. There was no significant difference in blood haemoglobin (BHb) level among the automobile workshop workers
and control. The serum TC level in automobile workshop workers showed significant decrease compared to the control individuals,
but was with in the reference range of healthy individuals. The mean level of serum TC in automobile workshop workers was
162.00±3.44 mg/dl and the same in control was 172.86±4.32 mg/dl. The present study affirms occupational lead toxicity in automobile
workshop workers and its effect on serum protein and cholesterol levels. 相似文献
105.
Thomas B. Åstebro 《Research Policy》2005,34(9):1404-1418
Research on technological opportunity has typically focused on the impact of broad industry characteristics on R&D intensity of firms. This study complements such approaches by examining the impact of a multidimensional vector that measures technological opportunity on independent inventors’ decisions to patent and commercialize inventions. Using data from 559 inventions and controlling for demand, appropriability, and competitive conditions, we found two of four tested dimensions of technological opportunity - technical performance and technical uncertainty - to be significant and important determinants of the likelihood of commercialization. Technical feasibility appears important in affecting patenting but unimportant in affecting commercialization. Technical significance carries a negative, although insignificant, sign conditioning commercialization. 相似文献
106.
Thomas E. Gaston Francesca Ounsworth Tessa Senders Sarah Ritchie Emma Jones 《Learned Publishing》2020,33(2):154-162
Previous research has found that researchers rank journal reputation and impact factor (IF) amongst the key selection criteria when choosing where to submit. We explored the actual effect upon submission numbers of several possible factors. We retrieved 10 years of submission data from over a thousand journals, as well as data on IF, retractions, and other factors. We performed statistical analysis and identified correlations. We also undertook case study research on the 55 most significant submission decreases. We found a statistically significant correlation between changes in IF, ISI percentage ranking, and changes in submissions numbers in subsequent years. We also found a statistically significant effect on submission numbers in the year following the publication of a retraction. Our case studies identified other factors, including negative feedback on the peer review process. Our findings regarding IF confirm previous indications about the significance of IF on submissions. We explain the correlation with retractions through the concept of ‘peer review reputation’. These results indicate that editors and publishers need to focus on a journal's peer review practices, as well as a journal's IF, if they are to maintain and grow submissions. 相似文献
107.
Vaughan Van Hecke A Mundy PC Acra CF Block JJ Delgado CE Parlade MV Meyer JA Neal AR Pomares YB 《Child development》2007,78(1):53-69
Infant joint attention has been observed to be related to social-emotional outcomes in at-risk children. To address whether this relation is also evident in typically developing children, 52 children were tested at 12, 15, 24, and 30 months to examine associations between infant joint attention and social outcomes. Twelve-month initiating and responding to joint attention were related to 30-month social competence and externalizing behavior, even when accounting for 15-month temperament ratings, 24-month cognition and language, and demographic variables. These results suggest that, in addition to associations with language and cognition, infant joint attention reflects robust aspects of development that are related to individual differences in the emergence of social and behavioral competence in childhood. 相似文献
108.
This study examined developmental trends in object and spatial working memory (WM) using heart rate (HR) to provide an index of covert cognitive processes. Participants in 4 age groups (6-7, 9-10, 11-12, 18-26, n=20 each) performed object and spatial WM tasks, in which each trial was followed by feedback. Spatial WM task performance reached adult levels before object WM task performance. The differential developmental trends for object and spatial WM found in this study are taken to suggest that these WM components are separable. Negative performance feedback elicited HR slowing that was more pronounced for adults than for children. The development of performance monitoring as indexed by covert HR slowing following performance feedback contributes to WM performance. 相似文献
109.
Cognition-related brain responses to meaningful and meaningless figures were registered in 5-year-old kindergarten children who either had been subtyped as being at-risk of developing an L- or P-type dyslexia (LAL versus LAP) or who were not at-risk. While identifying, naming, or categorizing pictures, event-related potentials (ERP) were registered. Three cognition-related components were found: the N460, the P780, and the Slow Wave (SW). LAP-children produced weak N460 activity across tasks, whereas LAL children, and to a lesser degree, non-risk children produced robust task-dependent activity. This finding may indicate that LAP-children lack semantic input while processing the figures. P780 latencies to frequently occurring figures were found hemisphere-dependent: LAP-children showed longer latencies in the right than in the left hemisphere, whereas the distribution was reversed in the LAL and non-risk children. It was also found that the right hemisphere is generally responsible for a lion's share of the processing of figures and therefore it seems that the right hemisphere of LAP-children invests ample time in doing so. Whereas LAP-children showed largest SW amplitude differences between frequent and infrequent stimuli at posterior locations, LAL children did so at frontal locations. Assuming that the SW represents working-memory processes, it may be that working-memory in LAP-children deals with figure-relevant visual-spatial information and with figure-derived concepts in LAL children. Overall, the findings suggest that LAL and LAP represent two different groups of kindergartners at risk of dyslexia and that these differences, to some degree, fit with the presumed etiology of L- and P-type dyslexia. 相似文献
110.
Matthew Krehl Edward Thomas Benjamin Jay Whitburn 《British Journal of Sociology of Education》2019,40(2):159-173
This article examines the constraints of modern temporality which are antithetical to the careful consideration that working with diverse learners requires for the development of inclusive, democratic education. We take up the conceptual construct of time to explore how it mediates systemic practices that impact policy positions of inclusion in initial teacher education and schooling. Our analysis demonstrates that temporality shapes the possibilities of inclusive practice within which a dominant agenda of compliance frames classroom complexities – both in schooling and higher education environments – into fragmented and preconceived responses to challenging situations. Education systems position educators in risk discourses concentrated on compliance and performance, in part through an emphasis that is placed on the diagnosis of learner differences and subsequent compartmentalised responses. Through schisms in modern time, we demonstrate the ways in which inclusion, like other educational demands, may be supported through a diffraction in time rather than subjugated to it. 相似文献