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   15958篇
  免费   194篇
  国内免费   119篇
教育   10963篇
科学研究   2099篇
各国文化   114篇
体育   1390篇
综合类   11篇
文化理论   121篇
信息传播   1573篇
  2021年   116篇
  2020年   222篇
  2019年   319篇
  2018年   439篇
  2017年   389篇
  2016年   407篇
  2015年   251篇
  2014年   333篇
  2013年   2736篇
  2012年   308篇
  2011年   349篇
  2010年   255篇
  2009年   251篇
  2008年   265篇
  2007年   306篇
  2006年   291篇
  2005年   279篇
  2004年   267篇
  2003年   256篇
  2002年   247篇
  2001年   266篇
  2000年   281篇
  1999年   286篇
  1998年   149篇
  1997年   153篇
  1996年   188篇
  1995年   175篇
  1994年   135篇
  1993年   147篇
  1992年   219篇
  1991年   226篇
  1990年   236篇
  1989年   263篇
  1988年   210篇
  1987年   227篇
  1986年   223篇
  1985年   254篇
  1984年   227篇
  1983年   214篇
  1982年   178篇
  1981年   174篇
  1980年   160篇
  1979年   246篇
  1978年   193篇
  1977年   187篇
  1976年   150篇
  1975年   134篇
  1974年   151篇
  1973年   132篇
  1971年   119篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Measuring overall service quality (OSQ) is gaining prominence in higher education due to the increased competition among engineering education institutions (EEIs) and growing awareness about value for money among the public. Determination of OSQ on certain institutional aspects is done by various agencies throughout the world. Each system uses a different set of weighted indicators to measure the overall service quality of institutions. Five service quality factors, namely professionalism, integrated education, facilities, responsiveness and empathy are considered in the study. Trapezoidal fuzzy numbers are used to determine the aggregate weights of the factors to handle the vagueness present in the linguistic values of the stakeholders’ subjective opinions. Final weights of the factors are assessed by taking the distances of each factor between Fuzzy Positive Ideal Rating and Fuzzy Negative Ideal Rating. An illustrative study is presented to determine the OSQ of EEIs. The results help to focus on the factors which need immediate attention to enhance the quality of EEIs.  相似文献   
72.
To elucidate a higher rate of premature cardiovascular disease (CVD) in Asian Indian descendants (Roma) in Slovakia, we investigated frequency distribution, correlates and relationship of lipoprotein(a) [Lp(a)] to family CVD risk factors in Roma children and their Caucasian neighbors. The study sample consisted of 607 healthy children aged 7–18 years (55% Roma, 48% male) as part of the biracial (Roma–Caucasian) Slovak Lipid Community Study. Overall, frequency distribution data of Lp(a) were highly skewed to low concentrations, with markedly higher Lp(a) levels in Roma than in Caucasian children (median and range, mg/dL: 14.5; 0–159.2 vs 6.2; 0–112.3, P < 0.001), regardless of age and gender. Lp(a) was positively correlated with apo B (0.159, P = 0.004) in Roma, and LDL cholesterol (0.170, P = 0.005) in Caucasian children. In addition, daily income of the family was negatively related with Lp(a) in Roma (−0.134, P = 0.036) while positively in Caucasians (0.136, P = 0.047). For both race groups, no significant association was found between Lp(a) and age, body mass index, mean arterial pressure, smoking, and physical activity. Also, no significant relationships were examined between serum Lp(a) levels >30 mg/dL in children and family CVD risk factors, except for diabetes mellitus in parents of Caucasian origin (OR 4.46; 95%CI: 1.23–16.20). In a multivariate analysis, daily income, LDL cholesterol or apo B explained ~7% of the variance of Lp(a). This study suggests a significantly higher serum Lp(a) levels in Roma than in Caucasian children and a small effect, in general, of relevant CVD risk factors on the variation of Lp(a) levels in childhood.  相似文献   
73.
Benson KR 《Endeavour》2000,24(2):59-62
The modern discipline of biology was formed in the 20th century from roots deep in the natural-history tradition, which dates from Aristotle. Not surprisingly, therefore, ecology can also be traced to natural history, especially its 19th-century tradition emphasizing the adaptive nature of organisms to their environment. During the 20th century, ecology has developed and matured from pioneering work on successional stages to mathematically rich work on ecosystem energetics. By the end of the century, ecology has made a return to its natural-history heritage, emphasizing the importance of the integrity of ecosystems in considering human interactions with the environment.  相似文献   
74.
75.
Dynamic problems of axially moving materials as exemplified by strings in textile industry and band saws, belts and chains in mechanical machinery have recently received some attention (1–15). In the present study, the parametric resonance of an axially accelerated beam is investigated. The beam which has encastré ends is subjected to a periodic root force as shown in Fig. 1. The object of the investigation is to identify regions of instability of this system for various combinations of the excitation frequency and amplitude of the axial oscillations.  相似文献   
76.
77.
78.
79.
80.
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