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   530篇
  免费   30篇
  国内免费   1篇
电工技术   10篇
化学工业   152篇
金属工艺   2篇
机械仪表   10篇
建筑科学   19篇
能源动力   11篇
轻工业   78篇
石油天然气   1篇
无线电   29篇
一般工业技术   111篇
冶金工业   19篇
原子能技术   5篇
自动化技术   114篇
  2024年   1篇
  2023年   3篇
  2022年   21篇
  2021年   21篇
  2020年   12篇
  2019年   10篇
  2018年   18篇
  2017年   11篇
  2016年   25篇
  2015年   18篇
  2014年   20篇
  2013年   33篇
  2012年   40篇
  2011年   39篇
  2010年   34篇
  2009年   29篇
  2008年   28篇
  2007年   39篇
  2006年   16篇
  2005年   14篇
  2004年   17篇
  2003年   15篇
  2002年   8篇
  2001年   5篇
  2000年   4篇
  1999年   11篇
  1998年   3篇
  1997年   3篇
  1996年   6篇
  1995年   4篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   5篇
  1984年   4篇
  1983年   4篇
  1982年   3篇
  1981年   4篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1975年   1篇
  1974年   1篇
  1966年   1篇
排序方式: 共有561条查询结果,搜索用时 0 毫秒
101.
Irisin, the circulating peptide originating from fibronectin type III domain-containing protein 5 (FNDC5), is mainly expressed by muscle fibers under peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) control during exercise. In addition to several beneficial effects on health, physical activity positively affects nervous system functioning, particularly the hippocampus, resulting in amelioration of cognition impairments. Recently, FNDC5/irisin detection in hippocampal neurons and the presence of irisin in the cerebrospinal fluid opened a new intriguing chapter in irisin history. Interestingly, in the hippocampus of mice, exercise increases FNDC5 levels and upregulates brain-derived neurotrophic factor (BDNF) expression. BDNF, displaying neuroprotection and anti-inflammatory effects, is mainly produced by microglia and astrocytes. In this review, we discuss how these glial cells can morphologically and functionally switch during neuroinflammation by modulating the expression of a plethora of neuroprotective or neurotoxic factors. We also focus on studies investigating the irisin role in neurodegenerative diseases (ND). The emerging involvement of irisin as a mediator of the multiple positive effects of exercise on the brain needs further studies to better deepen this issue and the potential use in therapeutic approaches for neuroinflammation and ND.  相似文献   
102.
103.
World Wide Web - The integration of Cloud computing and Internet of Things led to rapid growth in the edge computing field. This would not be achievable without combining the data centers’...  相似文献   
104.
A tunnel diode non-linear transmission line has been investigated for second and third harmonic generation purposes. Design criteria are given and performance predictions have been obtained simulating the single diode behavior by means of a polynomial expression. An optimization of the non-linear transmission line as a harmonic generator has been obtained as a function of the number of diodes, their separation distances and the bias voltage.  相似文献   
105.
The interpretation of results of a chemical reaction carried out in a trickle bed reactor is not immediate when the key reactants are volatile; in fact some authors state that the overall conversion rate increases at very low liquid flow rates, i.e. when the catalyst is unevenly wetted. In these conditions, the reactants may penetrate inside the catalyst pellets directly through the “dry” zones; therefore the mass transfer resistance is diminished and the conversion rate can be increased. To investigate this phenomenon tests on the catalytic oxidation of ethyl alcohol dissolved in water were performed at different operating conditions in a trickle bed reactor. An interpretation of the results was tried by using two different models based on partially wetted particles. This approach considers both the cases in which “dry” zones are active or not for mass transfer and mass transfer rates are affected or not by the chemical reaction.  相似文献   
106.
In this paper we find new first integrals of motion for a large class of nonlinear conservative gyroscopic mechanical systems. By means of the known first integrals, utilizing the classical Chetayev (1961) method, we construct a positive-definite first integral which ensures the stability of the equilibrium.  相似文献   
107.
The increase of the water table level presently occurring in the city of Milan led to some leakage of groundwater in underground facilities and subway tunnels. These structures, in fact, were completed about three decades ago when the water table was deeply located. To locally lower the ground water, and to eliminate or limit its flow towards the submerged openings, a series of pumping wells was placed in their vicinity. This provision, however, could lead to possible erosion of the fine fraction of the granular soil and to consequent settlements of nearby buildings. To investigate this phenomenon a finite-element approach has been developed for the analysis of the erosion and transport of the fine particles of granular soils subjected to a seepage flow. First, the continuity equation governing the problem and its finite-element formulation are discussed. Then, on the basis of the results of erosion tests presented in the literature, a law is derived that accounts for the nonlinear relationship between the total amount of eroded material, for time tending to infinity, and the velocity of seepage. Finally, this law is applied to the solution of one- and two-dimensional test examples, and some conclusions are drawn on the limits of the developed numerical model and on its possible improvement.  相似文献   
108.
109.
The Journal of Supercomputing - Ordinary differential equations (ODEs) are a widespread formalism for the mathematical modeling of natural and engineering systems, whose analysis is generally...  相似文献   
110.

Software architecture involves a series of decisions based on many factors in a wide range of software development. Architects face recurring issues in different software architecture design, and to reduce huge cost and risks, software architecture decisions can rely on a set of idiomatic patterns commonly named architectural styles or patterns. Architectural pattern determines the vocabulary of components and connectors that are used in instances of the pattern together with a set of constraints to combine the two. Little contemporary data exists to document actual practices used by software professionals when selecting and incorporating architectural patterns for their projects in industry. Therefore, a comprehensive survey of software professionals was conducted to attempt to discover these practices. This exploratory survey and its quantitative results offer opportunities for further interpretation and comparison. Data from this survey are presented in this paper and include characteristics of projects, practices, organizations, and practitioners related to the usage of architectural patterns. Some of the notable findings include that architectural patterns are widely used in software projects with the Model–View–Controller being the most common. Despite reported difficulties in incorporating architectural patterns, the majority of the software professionals revealed that patterns were the most essential for completing the projects. The most difficult pattern to implement and the most expensive to adopt was the peer-to-peer, while the easiest was the client–server.

  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