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   6563篇
  免费   48篇
  国内免费   11篇
教育   4429篇
科学研究   729篇
各国文化   97篇
体育   562篇
综合类   13篇
文化理论   87篇
信息传播   705篇
  2022年   37篇
  2021年   92篇
  2020年   117篇
  2019年   208篇
  2018年   294篇
  2017年   250篇
  2016年   230篇
  2015年   141篇
  2014年   205篇
  2013年   1345篇
  2012年   194篇
  2011年   158篇
  2010年   135篇
  2009年   126篇
  2008年   144篇
  2007年   124篇
  2006年   133篇
  2005年   118篇
  2004年   102篇
  2003年   93篇
  2002年   78篇
  2001年   70篇
  2000年   80篇
  1999年   77篇
  1998年   83篇
  1997年   59篇
  1996年   60篇
  1995年   50篇
  1994年   52篇
  1993年   58篇
  1992年   59篇
  1991年   64篇
  1990年   72篇
  1989年   72篇
  1988年   72篇
  1987年   61篇
  1986年   63篇
  1985年   59篇
  1984年   66篇
  1983年   61篇
  1982年   59篇
  1980年   47篇
  1979年   63篇
  1978年   53篇
  1977年   48篇
  1976年   50篇
  1974年   37篇
  1973年   38篇
  1937年   41篇
  1936年   40篇
排序方式: 共有6622条查询结果,搜索用时 15 毫秒
61.
The purpose of this paper was to determine the effects of deep approaches to learning on the moral reasoning development of 1,457 first-year students across 19 institutions. Results showed a modest positive relationship between our measures of deep approaches to learning and moral reasoning at the end of the first year of college even after controlling for precollege moral reasoning. After accounting for a host of demographic and relevant student characteristics and for the natural clustering of students, we found that the integrative learning subscale, which captures students’ participation in activities designed to integrate information from varied sources and diverse perspectives, positively affected moral reasoning among first-year students. Implications for researchers and practitioners are discussed.  相似文献   
62.
63.
Iowa students and parents completed related attitude and belief questionnaires about school subjects. Grade K–3 students received simpler questionnaires than did Grade 4–6 students or parents. Among Grade 4–6 children, girls perceived higher competence in reading than did boys, but boys perceived higher competence in physical science. All children perceived physical science competence lower than reading or math competence. Parents perceived boys as more competent in science. Girls like reading more than boys did; boys and girls did not differ in liking of science. Grade 4–6 children also expected lower grades in and attached lower importance to physical science than to reading. Parents perceived science as more important for boys and expected higher performance of boys. Jobs related to math or science were seen as more male dominated. These results provided a more comprehensive picture of attitudes and beliefs about science in the elementary school than had existed and suggested that attitudinal gender differences related to physical science begin to develop by the earliest elementary school years. Policy implications are that intervention programs designed to promote gender equity should be extended to the early elementary school years and also should address parental attitudes. Additional implications for policy and research are discussed. © 1999 John Wiley & Sons, Inc. J Res Sci Teach 36: 719–747, 1999  相似文献   
64.
65.
66.
The aim of this research is to characterize the development of fatigue damage by means of stress-strain hysteresis. Experiments were conducted on 14 specimens made of cold-finished unannealed AISI 1018 steel. Results demonstrate that the mechanical hysteresis loop areas, when plotted as a function of the number of loading cycles, show significant variations and demonstrate the three principal stages concerning the progress of the fatigue failure--initial accommodation, accretion of damage and terminal failure. These three stages of fatigue are marked by the transitions at cycles N2 and N3. Experimental results show that although fatigue life Nf ranges from 2644 cycles to 108 992 cycles, the ratios of N2/Nf and N3/Nf tend to be stable: N2/Nf=I 0.7%, N3/Nf=91.3%.  相似文献   
67.
The study was conducted to find out the extent of lipid peroxidation and antioxidant status in ischemic stroke patients (ISPs) with and without diabetes. Malondialdehyde (MDA) was studied as a marker of lipid peroxidation. Glutathione (GSH), uric acid and ceruloplasmin were estimated to study the antioxidant potential of ISPs. Significantly higher levels of MDA were found in both the groups of ISPs and the increase in MDA was more in ISPs without diabetes. GSH levels were decreased significantly in both the groups of ISPs and maximum decline was found in ISPs with diabetes. Uric acid levels were significantly increased in both the groups of ISPs. Ceruloplasmin levels were increased significantly in ISPs without diabetes, whereas its levels were slightly decreased in ISPs with diabetes. A negative correlation was found between MDA and the antioxidants GSH, uric acid and ceruloplasmin in ISPs with diabetes. This study suggests that there is an association between ischemic stroke and increased oxidative stress and the antioxidant potential is impaired in both the groups of ISPs with and without diabetes.  相似文献   
68.
In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use λ (48.5 kbp) and T4GT7 (165.6 kbp) DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of 0.4 μm. Numerical simulation of the electrokinetic force distribution inside the channels is in qualitative agreement with our experimentally observed trajectories. We discuss a possible physical mechanism for the DNA polarization and dielectrophoresis inside confining channels, based on the observed dielectrophoresis responses due to different DNA sizes and various electric fields applied between the inlet and the outlet. The proposed physical mechanism indicates that further extensive investigations, both theoretically and experimentally, would be very useful to better elucidate the forces involved at DNA dielectrophoresis. When applied for size-based sorting of DNA molecules, our sorting method offers two major advantages compared to earlier attempts with insulative dielectrophoresis: Its continuous operation allows for high-throughput analysis, and it only requires electric field strengths as low as ∼10 V∕cm.  相似文献   
69.
The objective of this study was to evaluate acrosin activity in spermatozoa of infertile Nigerian men and to compare with those of the fertile men. The acrosin activity was evaluated using the Acroscreen reagent kit. The acrosin activity of the fertile men was 40.7±5.2 mIU/106 sperm (range 30.1–51.3) and those of the infertile men was 22.4±8.33 mIU/106 sperm (range 5.7–39.1). The difference in the mean was statistically significant (P<0.001). There was a subpopulation of the infertile men who had their acrosin activity within normal range of the fertile men, 32.9±1.57 mIU/106 sperm. But the difference in the mean was statistically significant (P<0.001). Acrosin activity decreased with increased morphological changes in the spermatozoa. It is concluded that acrosin activity in the infertile Nigerian men is significantly lower than that in the fertile men. Acrosin activity may also be affected by morphological changes in the spermatozoa.  相似文献   
70.
The Inductive Query By Example (IQBE) paradigm allows a system to automatically derive queries for a specific Information Retrieval System (IRS). Classic IRSs based on this paradigm [Smith, M., & Smith, M. (1997). The use of genetic programming to build Boolean queries for text retrieval through relevance feedback. Journal of Information Science, 23(6), 423–431] generate a single solution (Boolean query) in each run, that with the best fitness value, which is usually based on a weighted combination of the basic performance criteria, precision and recall.  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