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   41911篇
  免费   69篇
  国内免费   116篇
系统科学   389篇
丛书文集   1020篇
教育与普及   107篇
理论与方法论   236篇
现状及发展   18766篇
研究方法   1598篇
综合类   19495篇
自然研究   485篇
  2013年   213篇
  2012年   527篇
  2011年   1081篇
  2010年   240篇
  2008年   703篇
  2007年   753篇
  2006年   748篇
  2005年   766篇
  2004年   687篇
  2003年   778篇
  2002年   715篇
  2001年   1285篇
  2000年   1214篇
  1999年   762篇
  1992年   739篇
  1991年   606篇
  1990年   645篇
  1989年   643篇
  1988年   643篇
  1987年   637篇
  1986年   650篇
  1985年   792篇
  1984年   622篇
  1983年   539篇
  1982年   470篇
  1981年   496篇
  1980年   598篇
  1979年   1302篇
  1978年   1116篇
  1977年   1114篇
  1976年   825篇
  1975年   872篇
  1974年   1300篇
  1973年   1052篇
  1972年   1072篇
  1971年   1326篇
  1970年   1764篇
  1969年   1384篇
  1968年   1269篇
  1967年   1328篇
  1966年   1127篇
  1965年   827篇
  1964年   220篇
  1959年   503篇
  1958年   731篇
  1957年   577篇
  1956年   486篇
  1955年   442篇
  1954年   483篇
  1948年   265篇
排序方式: 共有10000条查询结果,搜索用时 237 毫秒
31.
To examine the cognitive dissonance in Chinese luxury consumption,the paper contains a review of the research and development in the field of cognitive dissonance and the distinctive motivations applicable in Chinese luxury consumption.On the basis of the review,the link between cognitive dissonance and intention to repurchase luxury goods is discussed.This research aims to investigate the impact of Chinese culture on the reflections of cognitive dissonance as well as their repurchase intentions.The study was based on quantitative research,in which the motivations and the levels of cognitive dissonance were explored in the luxury consumption domain.In the study,the effects of Chinese culture(i.e.,Mianzi,group orientation,and buying out of emotions) on luxury consumption and cognitive dissonance were also examined in order to develop a more precise research framework.This study shed light on the different levels of cognitive dissonance relative to the different dimensions of Chinese culture.  相似文献   
32.
33.
Four methods of model selection—equally weighted forecasts, Bayesian model‐averaged forecasts, and two models produced by the machine‐learning algorithm boosting—are applied to the problem of predicting business cycle turning points with a set of common macroeconomic variables. The methods address a fundamental problem faced by forecasters: the most useful model is simple but makes use of all relevant indicators. The results indicate that successful models of recession condition on different economic indicators at different forecast horizons. Predictors that describe real economic activity provide the clearest signal of recession at very short horizons. In contrast, signals from housing and financial markets produce the best forecasts at longer forecast horizons. A real‐time forecast experiment explores the predictability of the 2001 and 2007 recessions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
34.
35.
36.
37.

Age-related macular degeneration (AMD) is a chronic and progressive degenerative disease of the retina, which culminates in blindness and affects mainly the elderly population. AMD pathogenesis and pathophysiology are incredibly complex due to the structural and cellular complexity of the retina, and the variety of risk factors and molecular mechanisms that contribute to disease onset and progression. AMD is driven by a combination of genetic predisposition, natural ageing changes and lifestyle factors, such as smoking or nutritional intake. The mechanism by which these risk factors interact and converge towards AMD are not fully understood and therefore drug discovery is challenging, where no therapeutic attempt has been fully effective thus far. Genetic and molecular studies have identified the complement system as an important player in AMD. Indeed, many of the genetic risk variants cluster in genes of the alternative pathway of the complement system and complement activation products are elevated in AMD patients. Nevertheless, attempts in treating AMD via complement regulators have not yet been successful, suggesting a level of complexity that could not be predicted only from a genetic point of view. In this review, we will explore the role of complement system in AMD development and in the main molecular and cellular features of AMD, including complement activation itself, inflammation, ECM stability, energy metabolism and oxidative stress.

  相似文献   
38.
39.
40.
ABSTRACT

The island of New Guinea has been identified as biologically megadiverse but many taxa are still poorly known. This is especially the case for many of the island’s snakes, which by their very nature can be difficult to collect and study. Here we examine the phylogenetic and phylogeographic structure of a poorly studied snake genus, Stegonotus, focusing on the species of New Guinea; until now, Stegonotus has never been examined using modern phylogenetic methods. Using molecular data from 49 individuals representing eight of the ten described species, and including all New Guinea taxa, we estimate a multilocus phylogeny and examine population structure to help identify undescribed taxa. We use morphological data from the corresponding museum vouchered specimens (where available) and also examine additional specimens for taxa not included in the molecular data set to determine morphological differences among putative taxa. We find molecular evidence for four new species of Stegonotus, both morphologically obvious and cryptic, and describe them herein. The recognition of these four species indicates that Stegonotus diversity has been previously underestimated and also suggests that there are likely additional undescribed taxa within the genus. These four taxa increase the number of described species by 40% and further confirm New Guinea as the centre of diversity for the genus.

www.zoobank.org/urn:lsid:zoobank.org:pub:9E21390E-3FD4-40EB-9442-31BC92A76B4F  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