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   132篇
  免费   2篇
系统科学   10篇
理论与方法论   4篇
现状及发展   62篇
研究方法   20篇
综合类   29篇
自然研究   9篇
  2019年   3篇
  2018年   4篇
  2017年   7篇
  2016年   9篇
  2015年   7篇
  2014年   7篇
  2013年   2篇
  2012年   9篇
  2011年   8篇
  2010年   4篇
  2009年   3篇
  2008年   3篇
  2007年   9篇
  2006年   10篇
  2005年   2篇
  2004年   1篇
  2003年   2篇
  2002年   6篇
  2001年   1篇
  1999年   3篇
  1989年   1篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1976年   3篇
  1975年   2篇
  1974年   1篇
  1973年   4篇
  1972年   3篇
  1971年   2篇
  1970年   2篇
  1969年   3篇
  1968年   4篇
  1967年   2篇
  1966年   1篇
  1964年   1篇
排序方式: 共有134条查询结果,搜索用时 359 毫秒
71.
This paper analyzes the impact of transparency on fiscal performance. Our sample considers the 100 largest Spanish municipalities for the years 2008, 2009, 2010, 2012, and 2014. The results show that the level of municipal transparency influences budget forecast deviations in tax revenues and current expenditures. On the one hand, less transparent municipalities overestimate their revenues, allowing them to provide more public services without an immediate increase in taxes. On the other, these local governments, which are aware of the overestimation of their revenues, may spend less than they budgeted. More transparent municipalities, meanwhile, seem to be more prudent in their revenue estimations, since they underestimate their revenues, meaning they can spend more than projected. Our results also show that the behavior of politicians is influenced by the phase of the electoral cycle in which they find themselves, with politicians overestimating expenditures in the year before election.  相似文献   
72.
In several rural areas in Colombia there is a serious lack of water quality supply. Thereby the problematic situation is understood as complex one that involves stakeholders with pluralistic interests, multiple variables and requires the development of sustainable and suitable solutions. In order to address this issue, this paper proposes an integration of engineering design framework (CDIO) with a systemic approach. Particularly the approach emphasizes on systemic elements such as autonomy, systems within systems, cooperation between stakeholders and cause effect relations; it also proposes a previous observing phase for engineering design framework. Thus the proposed systemic framework aims to generate projects that improve living conditions in rural communities and promote the production of knowledge between the stakeholders to ensure sustainability in the long term. To illustrate the proposal, this work contains a case study that discusses a project carried out by a research team—Ingenieros Sin Fronteras Colombia—in a rural district near to Colombia’s capital. The experience, which involved and benefited 16 families in the community, provided strong evidence to support the proposed framework. The paper concludes with a discussion about the replication of this proposal in other contexts.  相似文献   
73.
ABSTRACT

Manakins (Pipridae) are a group of Neotropical birds well known for their spectacular lekking displays and non-monogamous mating system. Nevertheless, the two species of Antilophia have been traditionally considered monogamous and, therefore, an exception to this rule. In this paper, we studied the home range and the mating system of a colour-ringed population of the Helmeted Manakin Antilophia galeata in southeastern Brazil. We propose that it is a non-monogamous species that ranges widely during the breeding season, presenting a lekking behaviour in the form of unspectacular but aggressive chasing courtship displays.  相似文献   
74.
Much of the focus on Poincaré’s philosophy of science has been on the notion of convention, a crucial concept that has become distinctive of his position. However, other notions have received much less attention. That is the case of verifiable hypotheses. This kind of hypotheses seems to be constituted from the generalization of several observable facts. So, in order to understand what these hypotheses are, we need to know what a fact to Poincaré is. He divides facts into brute and scientific facts. The characterization of this duality is not trivial at all, and leads us to the following questions that we will discuss in this paper: (1) which the part of construction that exists in a scientific fact and which the part of translation, that is, what remains from the brute fact in the scientific one?; and (2) when we conceive a generalized hypothesis, are we supposed to do it from scientific or from brute facts? The clarification of these questions could lead to distinguish the part of construction and the part of translation in the first steps of science, which is essential to get a better understanding of Poincaré’s conception of science.  相似文献   
75.
This paper presents an approach to the belief system based on a computational framework in three levels: first, the logic level with the definition of binary local rules, second, the arithmetic level with the definition of recursive functions and finally the behavioural level with the definition of a recursive construction pattern. Social communication is achieved when different beliefs are expressed, modified, propagated and shared through social nets. This approach is useful to mimic the belief system because the defined functions provide different ways to process the same incoming information as well as a means to propagate it. Our model also provides a means to cross different beliefs so, any incoming information can be processed many times by the same or different functions as it occurs is social nets.  相似文献   
76.
The choroid plexuses (CP) release numerous biologically active enzymes and neurotrophic factors, and contain a subpopulation of neural progenitor cells providing the capacity to proliferate and differentiate into other types of cells. These characteristics make CP epithelial cells (CPECs) excellent candidates for cell therapy aiming at restoring brain tissue in neurodegenerative illnesses, including Alzheimer’s disease (AD). In the present study, using in vitro approaches, we demonstrated that CP were able to diminish amyloid-β (Aβ) levels in cell cultures, reducing Aβ-induced neurotoxicity. For in vivo studies, CPECs were transplanted into the brain of the APP/PS1 murine model of AD that exhibits advanced Aβ accumulation and memory impairment. Brain examination after cell implantation revealed a significant reduction in brain Aβ deposits, hyperphosphorylation of tau, and astrocytic reactivity. Remarkably, the transplantation of CPECs was accompanied by a total behavioral recovery in APP/PS1 mice, improving spatial and non-spatial memory. These findings reinforce the neuroprotective potential of CPECs and the use of cell therapies as useful tools in AD.  相似文献   
77.
78.
The late survival of archaic hominin populations and their long contemporaneity with modern humans is now clear for southeast Asia. In Europe the extinction of the Neanderthals, firmly associated with Mousterian technology, has received much attention, and evidence of their survival after 35 kyr bp has recently been put in doubt. Here we present data, based on a high-resolution record of human occupation from Gorham's Cave, Gibraltar, that establish the survival of a population of Neanderthals to 28 kyr bp. These Neanderthals survived in the southernmost point of Europe, within a particular physiographic context, and are the last currently recorded anywhere. Our results show that the Neanderthals survived in isolated refuges well after the arrival of modern humans in Europe.  相似文献   
79.
80.
Resumen Se inmunizaron ratones BALB con glóbulos rojos de ratas de una línea endocriada. A estos ratones se les extrajo el ARN del bazo y se inyectó a otro grupo de animales de la misma cepa. Además, se inyectó el ARN proveniente de bazo de ratón normal a un segundo grupo de animales. Cinco días después de la inyección del ARN normal e inmune, ambos grupos, y un tercero, testigo, recibieron una inyección de glóbulos rojos de rata.  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