全文获取类型
收费全文 | 22521篇 |
免费 | 112篇 |
国内免费 | 20篇 |
专业分类
教育 | 16313篇 |
科学研究 | 2386篇 |
各国文化 | 105篇 |
体育 | 1426篇 |
综合类 | 6篇 |
文化理论 | 496篇 |
信息传播 | 1921篇 |
出版年
2021年 | 83篇 |
2020年 | 136篇 |
2019年 | 207篇 |
2018年 | 2467篇 |
2017年 | 2396篇 |
2016年 | 1852篇 |
2015年 | 305篇 |
2014年 | 357篇 |
2013年 | 2158篇 |
2012年 | 462篇 |
2011年 | 984篇 |
2010年 | 1066篇 |
2009年 | 613篇 |
2008年 | 864篇 |
2007年 | 1396篇 |
2006年 | 248篇 |
2005年 | 570篇 |
2004年 | 628篇 |
2003年 | 563篇 |
2002年 | 302篇 |
2001年 | 186篇 |
2000年 | 193篇 |
1999年 | 176篇 |
1998年 | 88篇 |
1997年 | 107篇 |
1996年 | 125篇 |
1995年 | 90篇 |
1994年 | 109篇 |
1993年 | 110篇 |
1992年 | 174篇 |
1991年 | 172篇 |
1990年 | 151篇 |
1989年 | 145篇 |
1988年 | 129篇 |
1987年 | 130篇 |
1986年 | 157篇 |
1985年 | 148篇 |
1984年 | 118篇 |
1983年 | 141篇 |
1982年 | 128篇 |
1981年 | 114篇 |
1980年 | 105篇 |
1979年 | 177篇 |
1978年 | 117篇 |
1977年 | 117篇 |
1976年 | 111篇 |
1975年 | 88篇 |
1974年 | 98篇 |
1972年 | 72篇 |
1971年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M. P. Narayanan Vaidyanathan Kannan K. P. Vinayan D. M. Vasudevan 《Indian journal of clinical biochemistry : IJCB》2011,26(4):347-353
Organic acid disorders are inherited metabolic disorders in which organic acids accumulate in tissues and biological fluids
of affected individuals. Classical organic acidurias include methylmalonic aciduria, propionic aciduria, isovaleric aciduria
and maple syrup urine disease (MSUD). They are considered the most frequent metabolic disorders among severely ill children.
Patients frequently present with acute symptoms early in life. 420 cases clinically suspected to have organic aciduria, with
upper age limit of 12 years for a 2-year period (January 2007–December 2008) were enrolled into this study. Metabolic acidosis
and neurological symptoms were the most common signs. Screening tests and thin layer chromatography were done for detection
of organic acidurias. Identification and quantitation of organic acids in urine and quantification of amino acids in blood
were done by high performance liquid chromatography. Out of 420 patients, 45 patients (10.7%) were found to have organic acidurias.
15 cases of methylmalonic aciduria, 16 cases of propionic aciduria, 13 cases of MSUD, and one case of isovaleric aciduria
were diagnosed. Results demonstrate the importance of testing for organic acidurias. Since organic aciduria may cause irreversible
brain damage if not treated, we recommend selective screening amongst severely ill children despite implied extra costs. 相似文献
992.
Rikers Remy M.J.P. Van Gerven Pascal W.M. Schmidt Henk G. 《Instructional Science》2004,32(1-2):173-182
This special issue is dedicated to recentdevelopments within cognitive load theory (CLT)and identifies some instructional implicationsof the interaction between informationstructures and cognitive architecture. Thepresent article discusses the different studiesin this special issue. An important conclusionis that recent CLT research recognizes thelearners' level of expertise as an importantfactor mediating the relation between cognitivearchitecture, information structures, andlearning outcomes. In this context, we discussthe role of expertise in CLT research and therole of CLT in expertise research. Based onthis discussion, the use of CLT as a tool todevelop expertise is identified as a verypromising approach. 相似文献
993.
This study attempts to answer two questions. First, can a single cultural event impact the stock prices of a wide range of companies and sectors? Second, was the positive stock market response in the information technology (IT) sector as well as performing arts sector significant? To answer these questions, we examine whether a hit pop single, “Gangnam Style” by Park Jae-Sang in 2012, affected related sectors of the Korean stock market and whether market reactions went beyond the stock price of the singer’s agency to affect those of other firms. We use an event study approach. The results show two notable empirical findings. First, although the findings indicating abnormal returns and cumulative abnormal returns appear mixed, the overall results imply that the unprecedented worldwide hit single by the South Korean singer positively affected the Recreation & Culture and Digital Content sectors. In other words, the market interpreted the event as good news, with shareholders expecting positive effects on the related sectors. Second, a positive stock market response was observed in the IT sector as well. 相似文献
994.
This article describes a study of how Chinese preservice teachers unpacked a learning goal pertaining to adding fractions and understanding the concepts underlying the operation. Based on work in the USA by Morris, Hiebert, and Spizter (Journal for Research in Mathematics Education, 40(5), 491–529, 2009), 50 Chinese preservice teachers completed a task, anticipating an ideal student response, in the context of four representations: (1) fraction pieces, (2) graph paper, (3) common denominator algorithm, and (4) pennies. Like the US-based study, this study shows that Chinese preservice teachers’ ability to unpack a learning goal was highly influenced by how the problem was represented. The pennies and graph paper problems provided more supportive contexts for unpacking the learning goal; the algorithm problem provided the least supportive context. The main difference between the preservice teachers from these two countries was the US preservice teachers chose the pennies and graph paper problems as having the most potential for revealing students’ understanding of the learning goal; while the Chinese preservice teachers chose the algorithm problem despite the problem’s unsupportive context. Chinese preservice teachers’ preference suggests that they privileged algorithmic/symbolic representations over pictorial/concrete representations. Based on our results, we argue that it is time for cross-cultural comparative research to refocus on the common barriers, challenges, and benefits as related to mathematics teacher preparation and professional development. A cooperative instead of competitive orientation will lead to richer and deeper dialogues among mathematics educators. 相似文献
995.
Philip J. Nickel 《Ethics and Information Technology》2011,13(4):355-363
In this paper, I examine the ethics of e-trust and e-trustworthiness in the context of health care, looking at direct computer-patient interfaces (DCPIs), information systems that provide medical
information, diagnosis, advice, consenting and/or treatment directly to patients without clinicians as intermediaries. Designers,
manufacturers and deployers of such systems have an ethical obligation to provide evidence of their trustworthiness to users.
My argument for this claim is based on evidentialism about trust and trustworthiness: the idea that trust should be based on sound evidence of trustworthiness. Evidence of trustworthiness
is a broader notion than one might suppose, including not just information about the risks and performance of the system,
but also interactional and context-based information. I suggest some sources of evidence in this broader sense that make it
plausible that designers, manufacturers and deployers of DCPIs can provide evidence to users that is cognitively simple, easy
to communicate, yet rationally connected with actual trustworthiness. 相似文献
996.
Laursen PB Knez WL Shing CM Langill RH Rhodes EC Jenkins DG 《Journal of sports sciences》2005,23(10):1111-1120
The aim of the present study was to examine the relationship between the performance heart rate during an ultra-endurance triathlon and the heart rate corresponding to several demarcation points measured during laboratory-based progressive cycle ergometry and treadmill running. Less than one month before an ultra-endurance triathlon, 21 well-trained ultra-endurance triathletes (mean +/- s: age 35 +/- 6 years, height 1.77 +/- 0.05 m, mass 74.0 +/- 6.9 kg, = 4.75 +/- 0.42 l x min(-1)) performed progressive exercise tests of cycle ergometry and treadmill running for the determination of peak oxygen uptake (VO2peak), heart rate corresponding to the first and second ventilatory thresholds, as well as the heart rate deflection point. Portable telemetry units recorded heart rate at 60 s increments throughout the ultra-endurance triathlon. Heart rate during the cycle and run phases of the ultra-endurance triathlon (148 +/- 9 and 143 +/- 13 beats x min(-1) respectively) were significantly (P < 0.05) less than the second ventilatory thresholds (160 +/- 13 and 165 +/- 14 beats x min(-1) respectively) and heart rate deflection points (170 +/- 13 and 179 +/- 9 beats x min(-1) respectively). However, mean heart rate during the cycle and run phases of the ultra-endurance triathlon were significantly related to (r = 0.76 and 0.66; P < 0.01), and not significantly different from, the first ventilatory thresholds (146 +/- 12 and 148 +/- 15 beats x min(-1) respectively). Furthermore, the difference between heart rate during the cycle phase of the ultra-endurance triathlon and heart rate at the first ventilatory threshold was related to marathon run time (r = 0.61; P < 0.01) and overall ultra-endurance triathlon time (r = 0.45; P < 0.05). The results suggest that triathletes perform the cycle and run phases of the ultra-endurance triathlon at an exercise intensity near their first ventilatory threshold. 相似文献
997.
998.
Vandana Rai 《Indian journal of clinical biochemistry : IJCB》2016,31(4):402-413
The C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene was implicated to be associated with thrombophilia due to its role in catalyzing the formation of 5-methylenetetrahydrofolate, a co-substrate for the conversion of homocysteine to methionine. Several case–control studies were investigated MTHFR C677T polymorphism as risk for recurrent pregnancy loss (RPL). These studies rendered contradictory results, some indicating that the polymorphism is associated with the risk of RPL whereas others concluded there is no association. To shed light on these inconclusive findings, a meta-analysis of all available studies published from Asian population relating the C677T polymorphism to the risk of RPL was conducted. The following electronic databases were searched without language restrictions: PubMed, Google Scholars, Elsevier and Springer Link up to December, 2015. Meta-analysis was performed using MetaAnalyst and Mix version 1.7. Meta-analysis results suggested that MTHFR C677T polymorphism contributed to the increased RPL risk in Asian population using all five genetic models (for T vs. C: OR 1.35, 95 % CI 1.09–1.68, p = 0.009; for TT + CT vs. CC: OR 1.44, 95 % CI 1.14–1.82, p = 0.006; for CT vs. CC: OR 1.39, 95 % CI 1.07–1.8, p = 0.01; for TT vs. CC: OR 1.79, 95 % CI 1.23.2.6, p = 0.007; for TT vs. CT + CC: OR 1.61, 95 % CI 1.02–2.56, p = 0.04). In conclusion, this meta-analysis demonstrates a strong association between the MTHFR C677T variant and RPL in Asian population and raising the importance of the use of folate in its treatment and prevention. 相似文献
999.
Valdivia WD 《Minerva》2011,49(1):25-46
Evaluation studies of the Bayh-Dole Act are generally concerned with the pace of innovation or the transgressions to the independence
of research. While these concerns are important, I propose here to expand the range of public values considered in assessing
Bayh-Dole and formulating future reforms. To this end, I first examine the changes in the terms of the Bayh-Dole debate and
the drift in its design. Neoliberal ideas have had a definitive influence on U.S. innovation policy for the last thirty years,
including legislation to strengthen patent protection. Moreover, the neoliberal policy agenda is articulated and justified
in the interest of “competitiveness.” Rhetorically, this agenda equates competitiveness with economic growth and this with
the public interest. Against that backdrop, I use Public Value Failure criteria to show that values such as political equality,
transparency, and fairness in the distribution of the benefits of innovation, are worth considering to counter the “policy
drift” of Bayh-Dole. 相似文献
1000.