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   15054篇
  免费   225篇
  国内免费   22篇
教育   10291篇
科学研究   1792篇
各国文化   122篇
体育   1379篇
综合类   21篇
文化理论   189篇
信息传播   1507篇
  2022年   120篇
  2021年   174篇
  2020年   245篇
  2019年   337篇
  2018年   484篇
  2017年   499篇
  2016年   469篇
  2015年   299篇
  2014年   426篇
  2013年   2360篇
  2012年   399篇
  2011年   379篇
  2010年   374篇
  2009年   319篇
  2008年   336篇
  2007年   346篇
  2006年   338篇
  2005年   287篇
  2004年   304篇
  2003年   261篇
  2002年   288篇
  2001年   358篇
  2000年   362篇
  1999年   277篇
  1998年   163篇
  1997年   198篇
  1996年   186篇
  1995年   126篇
  1994年   139篇
  1993年   125篇
  1992年   208篇
  1991年   190篇
  1990年   225篇
  1989年   216篇
  1988年   190篇
  1987年   198篇
  1986年   181篇
  1985年   211篇
  1984年   161篇
  1983年   136篇
  1982年   129篇
  1981年   115篇
  1980年   117篇
  1979年   184篇
  1978年   135篇
  1977年   117篇
  1975年   103篇
  1974年   100篇
  1973年   95篇
  1971年   91篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
941.
Aim of present study was to compare the adenosine deaminase (ADA) activity in various types of arthritis conditions with synovial effusion. No. significant difference was observed in ADA activity in serum of control and study groups but results have shown a definite pattern of ADA activity in synovial fluid in various arthritic conditions. The highest value of ADA activity was observed in synovial fluid of patients with tubercular arthritis followed by rheumatoid, septic, osteo and post traumatic arthritis. Thus measurement of ADA activity in synovial fluid can be used as a parameter of differential diagnosis of arthritis specially tubercular in initial stages.  相似文献   
942.
The structure of a retrospective information retrieval system that uses equifrequent word or text fragments is described, and its advantages over word oriented systems are mentioned briefly. Word fragments are proposed as retrieval elements, and a discussion is given of the changes required in order to process a query. Some necessary modifications in the treatment of logical operators are described, and two conditions are postulated as necessary for the successful operation of the system. Aspects of query processing are illustrated by experimental results obtained from single and two-term queries applied to a portion of the MARC tapes.  相似文献   
943.
Nomographs for determining the filter order of classical filters based on selectivity requirements are presented. The selectivities for a variety of standard classical filters are summarized in equation form and the general selectivity nomograph is constructed. The selectivity equations are then converted into nomograph form by applying the relationship between the transfer function and the response slope. Design examples are presented to demonstrate the usefulness of the selectivity nomographs. These nomographs can be used to gauge filter performance and combined with optimization techniques can yield superior classical filter designs.  相似文献   
944.
A study is made of the orthogonal polynomials on certain curves in the complex plane. Necessary and sufficient conditions for a set of polynomials to be orthogonal on the curves are obtained in terms of symmetric matrices. The relations of the symmetric matrices to Toeplitz matrices and innerwise matrices are shown.  相似文献   
945.
The purpose of this study was to examine which emergent literacy skills contribute to preschool children's emergent writing (name-writing, letter-writing, and spelling) skills. Emergent reading and writing tasks were administered to 296 preschool children aged 4-5 years. Print knowledge and letter-writing skills made positive contributions to name writing; whereas alphabet knowledge, print knowledge, and name writing made positive contributions to letter writing. Both name-writing and letter-writing skills made significant contributions to the prediction of spelling after controlling for age, parental education, print knowledge, phonological awareness, and letter-name and letter-sound knowledge; however, only letter-writing abilities made a significant unique contribution to the prediction of spelling when both letter-writing and name-writing skills were considered together. Name writing reflects knowledge of some letters rather than a broader knowledge of letters that may be needed to support early spelling. Children's letter-writing skills may be a better indicator of children's emergent literacy and developing spelling skills than are their name-writing skills at the end of the preschool year. Spelling is a developmentally complex skill beginning in preschool and includes letter writing and blending skills, print knowledge, and letter-name and letter-sound knowledge.  相似文献   
946.
947.
The purpose of this study was to explore patterns of within-group variability in the emergent literacy skills of preschoolers who are at risk for academic difficulties. We used the person-centered approach of cluster analysis to identify profiles of emergent literacy skills, taking into account both oral language and code-related skills. Participants were 492 preschoolers (aged 42-60 months) enrolled in needs-based programs. In the fall of the academic year, children were administered eight measures of emergent literacy: four oral language measures (i.e., expressive and receptive grammar, expressive and receptive vocabulary) and four code-related measures (i.e., print concepts, alphabet knowledge, name writing, and rhyme). Controlling for age, hierarchical-agglomerative and K-means cluster analysis procedures were employed. Five psychometrically sound profiles emerged: highest emergent literacy (prevalence = 14%); three profiles with average oral language and differential code-related abilities (16%, 24%; 23%); and lowest oral language with broad code-related weaknesses (23%). Profiles were then compared on midyear teacher ratings of emergent literacy as well as end-of-kindergarten literacy performance; results provided convergent evidence of predictive validity. This study highlights the considerable heterogeneity of emergent literacy abilities within an “at-risk” group. The resulting profiles have theoretical and practical relevance when examining both concurrent relationships between oral language and code-related skills as well as longitudinal relationships between early patterns of performance and later reading achievement.  相似文献   
948.
The purpose of this study was to concurrently examine the development of written language across different writing tasks and to investigate how writing features develop in preschool children. Emergent written language knowledge of 372 preschoolers was assessed using numerous writing tasks. The findings from this study indicate that children demonstrate knowledge about writing before beginning school and receiving formal instruction. There was clear evidence to support the claim that universal writing features develop before language-specific features. Children as young as 3 years possess knowledge regarding universal and language-specific writing features. Preschoolers appear to progress along a continuum from scribbling to conventional spelling. Although this progression is sequential, children’s writing proficiency is task dependent. Implications of these findings on writing development are discussed.  相似文献   
949.
950.
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