全文获取类型
收费全文 | 132篇 |
免费 | 2篇 |
专业分类
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 |
出版年
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 15 毫秒
91.
Janneth Arias María Catalina Ramírez Diana María Duarte María Paula Flórez Juan Pablo Sanabria 《Systemic Practice and Action Research》2016,29(4):379-403
Currently, both public and private organizations, as well as the academic milieu are developing social projects in order to strengthen and improve the quality of life. This is the case of Engineers Without Borders Colombia (ISFCOL for its Spanish acronym), an organization formed by engineering teachers and students from Los Andes University and the Minuto de Dios University Corporation that develops engineering projects within communities in order to solve environmental and social problems. However, based in the group’s experience, a problem has been identified regarding the absence of a methodology that promotes the active and effective participation of all the parties involved, which can prevent the accomplishment of otherwise technically viable, socially responsible, and sustainable projects. Looking to address this issue, this paper presents a methodological proposal for promoting the active participation of all the parties involved in engineering projects that have a social impact. The proposal is structured following the stages of the oCDIO context (Observe, Conceive, Design, Implement and Operate), and is successfully applied during the development of an ISFCOL project in which the participation of all the parties involved becomes a key element for the effective accomplishment of the engineering proposal and for the generation of socially responsible impacts. Namely, the project “Fortalecimiento Negocios Verdes Comunitarios Provincia del Guavio” (Community Green Businesses Strengthening in the Guavio Province) whose main goal was to strengthen the innovation and the entrepreneurship in the Guavio region communities, consolidating thus an active participation network of 400 members made up by small entrepreneurs and students from rural communities close to the city of Bogota and from higher education institutions. 相似文献
92.
93.
Silvia Lisa Massimiliano Meli Gema Cabello Ruth Gabizon Giorgio Colombo María Gasset 《Cellular and molecular life sciences : CMLS》2010,67(16):2825-2838
The conversion of the cellular prion protein (PrPC) into its disease-associated form (PrPSc) involves a major conformational change and the accumulation of sulfoxidized methionines. Computational and synthetic approaches
have shown that this change in the polarity of M206 and M213 impacts the C-terminal domain native α-fold allowing the flexibility
required for the structural conversion. To test the effect in the full-length molecule with site-specificity, we have generated
M-to-S mutations. Molecular dynamics simulations show that the replacement indeed perturbs the native state. When this mutation
is placed at the conserved methionines of HaPrP(23–231), only substitutions at the Helix-3 impair the α-fold, stabilizing
a non-native state with perturbed secondary structure, loss of native tertiary contacts, increased surface hydrophobicity,
reduced thermal stability and an enhanced tendency to aggregate into protofibrillar polymers. Our work supports that M206
and M213 function as α-fold gatekeepers and suggests that their redox state regulate misfolding routes. 相似文献
94.
95.
96.
97.
A large-cavity zeolite with wide pore windows and potential as an oil refining catalyst 总被引:3,自引:0,他引:3
Crude oil is an important feedstock for the petrochemical industry and the dominant energy source driving the world economy, but known oil reserves will cover demand for no more than 50 years at the current rate of consumption. This situation calls for more efficient strategies for converting crude oil into fuel and petrochemical products. At present, more than 40% of oil conversion is achieved using catalysts based on faujasite; this zeolite requires extensive post-synthesis treatment to produce an ultrastable form, and has a large cavity accessible through four 0.74-nm-wide windows and thus limits the access of oil molecules to the catalytically active sites. The use of zeolites with better accessibility to their active sites should result in improved catalyst efficiency. To date, two zeolites with effective pore diameters exceeding that of faujasite have been reported, but their one-dimensional pore topology excludes use in oil refining. Similarly, zeolites with large pores and a three-dimensional pore topology have been reported, but in all these materials the pore openings are smaller than in faujasite. Here we report the synthesis of ITQ-21, a zeolite with a three-dimensional pore network containing 1.18-nm-wide cavities, each of which is accessible through six circular and 0.74-nm-wide windows. As expected for a zeolite with this structure, ITQ-21 exhibits high catalytic activity and selectivity for valuable products in preliminary oil refining tests. 相似文献
98.
The 'progress zone' model provides a framework for understanding progressive development of the vertebrate limb. This model holds that undifferentiated cells in a zone of fixed size at the distal tip of the limb bud (the progress zone) undergo a progressive change in positional information such that their specification is altered from more proximal to more distal fates. This positional change is thought to be driven by an internal clock that is kept active as long as the cells remain in the progress zone. However, owing to cell division, the most proximal of these cells are continually pushed outside the confines of the zone. As they exit, clock function ceases and cells become fixed with the positional value last attained while within the zone. In contrast to this model, our data suggest that the various limb segments are 'specified' early in limb development as distinct domains, with subsequent development involving expansion of these progenitor populations before differentiation. We also find, however, that the distal limb mesenchyme becomes progressively 'determined', that is, irreversibly fixed, to a progressively limited range of potential proximodistal fates. 相似文献
99.
100.
C. Valenti María I. Vacas D. P. Cardinali 《Cellular and molecular life sciences : CMLS》1979,35(1):120-122
Summary Tubulin levels of the medial basal hypothalamus (MBH) were greater in male than in female rats. Orchidectomy brought about a decrease of MBH tubulin concentration, whereas testosterone injection augmented it in the MBH and adenohypophysis. Estradiol administration augmented MBH tubulin and protein concentration.This study was supported in part by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina (CONICET) (grant No. 6638), and the Programa Latinoamericano de Investigación en Reproducción Humana (PLAMIRH 2.3.1.75 R). 相似文献