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   8963篇
  免费   108篇
  国内免费   8篇
教育   6129篇
科学研究   1149篇
各国文化   60篇
体育   642篇
综合类   3篇
文化理论   62篇
信息传播   1034篇
  2022年   54篇
  2021年   108篇
  2020年   146篇
  2019年   190篇
  2018年   315篇
  2017年   281篇
  2016年   279篇
  2015年   172篇
  2014年   279篇
  2013年   1487篇
  2012年   217篇
  2011年   253篇
  2010年   216篇
  2009年   193篇
  2008年   234篇
  2007年   196篇
  2006年   180篇
  2005年   162篇
  2004年   180篇
  2003年   146篇
  2002年   138篇
  2001年   200篇
  2000年   204篇
  1999年   183篇
  1998年   97篇
  1997年   130篇
  1996年   113篇
  1995年   76篇
  1994年   100篇
  1993年   69篇
  1992年   168篇
  1991年   129篇
  1990年   123篇
  1989年   155篇
  1988年   133篇
  1987年   104篇
  1986年   110篇
  1985年   113篇
  1984年   81篇
  1983年   95篇
  1982年   61篇
  1981年   73篇
  1980年   63篇
  1979年   110篇
  1978年   72篇
  1977年   66篇
  1976年   56篇
  1975年   53篇
  1974年   62篇
  1973年   61篇
排序方式: 共有9079条查询结果,搜索用时 15 毫秒
211.

Introduction

Extremely high glucose concentrations have been shown to interfere with creatinine assays especially with Jaffe method in peritoneal dialysate. Because diabetes is the fastest growing chronic disease in the world, laboratories study with varying glucose concentrations. We investigated whether different levels of glucose spiked in serum interfere with 21 routine chemistry and thyroid assays at glucose concentrations between 17-51 mmol/L.

Materials and methods

Baseline (group I) serum pool with glucose concentration of 5.55 (5.44-5.61) mmol/L was prepared from patient sera. Spiking with 20% dextrose solution, sample groups were obtained with glucose concentrations: 17.09, 34.52, and 50.95 mmol/L (group II, III, IV, respectively). Total of 21 biochemistry analytes and thyroid tests were studied on Abbott c8000 and i2000sr with commercial reagents. Bias from baseline value was checked statistically and clinically.

Results

Creatinine increased significantly by 8.74%, 31.66%, 55.31% at groups II, III, IV, respectively with P values of < 0.001. At the median glucose concentration of 50.95 mmol/L, calcium, albumin, chloride and FT4 biased significantly clinically (-0.85%, 1.63%, 0.65%, 7.4% with P values 0.138, 0.214, 0.004, < 0.001, respectively). Remaining assays were free of interference.

Conclusion

Among the numerous biochemical parameters studied, only a few parameters are affected by dramatically increased glucose concentration. The creatinine measurements obtained in human sera with the Jaffe alkaline method at high glucose concentrations should be interpreted with caution. Other tests that were affected with extremely high glucose concentrations were calcium, albumin, chloride and FT4, hence results should be taken into consideration in patients with poor diabetic control.Key words: assay interference, glucose interference, preanalytical phase, creatinine, Jaffe kinetic assay, thyroid function tests  相似文献   
212.
213.
企业供应链的发展促使企业合作研发寻求新的模式。分析了上下游大型企业进行合作研发的诱因及其模式选择问题,结合宝钢一上海大众激光拼焊案例,重点讨论了建立股权制合作研发对上下游企业的影响和供应链创新的意义。  相似文献   
214.
215.
Students rarely ask questions related to course content in large-format introductory classes. The use of a Web-based forum devoted to student-generated questions was explored in a second-semester introductory biology course. Approximately 80% of the enrolled students asked at least one question about course content during each of three semesters during which this approach was implemented. About 95% of the students who posted questions reported reading the instructor's response to their questions. Although doing so did not contribute to their grade in the course, approximately 75% of the students reported reading questions posted by other students in the class. Approximately 60% of the students reported that the Web-based question-asking activity contributed to their learning of biology.  相似文献   
216.
Marital conflict and conduct problems in Children of Twins   总被引:3,自引:0,他引:3  
The Children-of-Twins design was used to test whether associations between marital conflict frequency and conduct problems can be replicated within the children of discordant twin pairs. A sample of 2,051 children (age 14-39 years) of 1,045 twins was used to estimate the genetic and environmental influences on marital conflict and determine whether genetic or environmental selection processes underlie the observed association between marital conflict and conduct problems. Results indicate that genetic and nonshared environmental factors influence the risk of marital conflict. Furthermore, genetic influences mediated the association between marital conflict frequency and conduct problems. These results highlight the need for quasiexperimental designs in investigations of intergenerational associations.  相似文献   
217.
Kohlberg's (1966) hypothesis that the attainment of gender constancy motivates children to attend to gender norms was reevaluated by examining these links in relation to age. Ninety-four 3- to 7-year-old children were interviewed to assess whether and how constancy mediates age-related changes in gender-related beliefs. As expected, results indicated a general pattern of an increase in stereotype knowledge, the importance and positive evaluation of one's own gender category, and rigidity of beliefs between the ages of 3 and 5. Moreover, the stability phase, rather than full constancy, mediated some of these relations. After age 5, rigidity generally decreased with age, with relations primarily mediated by consistency.  相似文献   
218.
Quality assurance in engineering education is a multifaceted problem further augmented by the stakeholders of engineering education. Students, parents and employers are rightfully questioning the quality of the curriculum, the instructional delivery, the learning environment, accessibility to learning technologies and equipment, employability as well as the possibilities of lifelong learning and the improvement of knowledge (Karapetrovic 2002 Karapetrovic, S. 2002. Why and how to develop a meaningful quality assurance system in engineering schools. Int. J. Engg. Educ, 18(3): 285294. [Web of Science ®] [Google Scholar]). The purpose of the study is, therefore, to identify the parameters that influence the quality of an engineering education system and develop an integrated model of hierarchical structuring and a concept map for pre-identified concept elements through a process of iterative-interactive consensus-driven methodology, as advocated by second-generation system design paradigm for evolving knowledge scenario of concepts related to quality engineering education.  相似文献   
219.
This study employed an exploratory sequential mixed-methods design to examine the intersection of race and gender among Black American adolescents, aged 11–19. The quantitative component (n = 344) used survey data to examine gender differences in peer-perpetrated and adult-perpetrated racial discrimination experiences, and no gender differences were evident. Qualitative data (n = 42) probed how males and females interpret discrimination experiences given the intersection of race and gender. Although the majority of participants believed that Black males and females have similar experiences, some believed that Black males face more racial discrimination. However, analyses revealed social disadvantages for Black females given that they report inappropriate comments and unwelcome hair touching and limited opportunities for interracial dating compared with Black males.  相似文献   
220.
This study examined to what extent adolescents’ and their friends’ risk behaviors (i.e., delinquency and alcohol use) hinder or promote their academic achievement (grade point average [GPA]), and vice versa. Longitudinal data were used (= 1,219 seventh- to ninth-grade adolescents; Mage = 13.69). Results showed that risk behaviors negatively affected adolescents’ GPA, whereas GPA protected against engaging in risk behaviors. Moreover, adolescents tended to select friends who have similar behaviors and friends’ behaviors became more similar over time (same-behavior selection and influence). Furthermore, although same-behavior effects seemed to dominate, evidence was found for some cross-behavior selection effects and a tendency in seventh grade for cross-behavior influence effects. Concluding, it is important to investigate the interplay between different behaviors with longitudinal social network analysis.  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