全文获取类型
收费全文 | 1433篇 |
免费 | 108篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
化学工业 | 424篇 |
金属工艺 | 26篇 |
机械仪表 | 59篇 |
建筑科学 | 46篇 |
矿业工程 | 6篇 |
能源动力 | 94篇 |
轻工业 | 160篇 |
水利工程 | 10篇 |
石油天然气 | 16篇 |
无线电 | 122篇 |
一般工业技术 | 216篇 |
冶金工业 | 69篇 |
原子能技术 | 11篇 |
自动化技术 | 271篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 58篇 |
2021年 | 64篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 54篇 |
2017年 | 70篇 |
2016年 | 60篇 |
2015年 | 41篇 |
2014年 | 71篇 |
2013年 | 142篇 |
2012年 | 102篇 |
2011年 | 120篇 |
2010年 | 98篇 |
2009年 | 99篇 |
2008年 | 79篇 |
2007年 | 59篇 |
2006年 | 59篇 |
2005年 | 34篇 |
2004年 | 31篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1544条查询结果,搜索用时 46 毫秒
61.
Thiago Sousa Teles Fábio Marcelo Breunig Rafaelo Balbinot William Gaida 《International journal of remote sensing》2013,34(18):4501-4518
We investigated the relationships between 11 phenological metrics, topographic shade, and anomalous temperature patterns detected using wavelet analysis in seasonal deciduous forests of south Brazil. To obtain the metrics, we applied the TIMESAT algorithm to the enhanced vegetation index (EVI) from Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra. MODIS acquires data from the study area under a large seasonal amplitude in the solar zenith angle (SZA). We evaluated the effect of topography on phenological metrics by correlating the metrics with shaded relief values. To analyse the inter-annual phenological metric variations with anomalous and regular temperature patterns, we calculated standard anomalies for each metric. Finally, we established relationships between the metrics and the minimum, maximum, and mean temperatures from growing seasons that spanned over 10 seasonal cycles between 2002 and 2012. The correlation results with shaded relief showed that the left (LD) and right derivative (RD), small integral (SInt), seasonal amplitude (SA), base level (BL), and maximum VI value (MV) were sensitive to topographic effects. The seasonal cycles with the highest temperatures in the growing season (2006/2007 and 2009/2010) exhibited a delay at the end of the cycle and a higher interval of duration and productivity, which was indicated by the positive standard anomalies for end of season (EOS), length of season (LOS), large integral (LInt), and SInt. We observed a different result for the lowest temperature cycle (2003/2004). The means for these metrics in anomalous seasons differed significantly from the metrics of other regular cycles at the 0.05 significance level using paired t-tests. Statistically significant correlations were observed between the metrics and minimum and mean temperature values of the 10 seasonal cycles. 相似文献
62.
This paper features new results on H∞ analysis and control of linear systems with Markov jump disturbances, in a scenario of partial observations of the jump process. We consider the situations in which the jump process can only be measured through a suitable detector. A distinctive feature of the approach here is that it is general enough to encompass particular scenarios such as that of perfect information, no information (mode independent) and cluster observations of the Markov jump process. The main results, comprising a new bounded real lemma and a condition for state feedback synthesis, are expressed via linear matrix inequality-based optimisation problems. The method devised for the design of H∞ controllers is applied to the control of an unmanned aerial vehicle model. 相似文献
63.
Christiana Rissing Marcelo Rains David Y. Son 《Journal of Inorganic and Organometallic Polymers and Materials》2010,20(4):616-621
Oligomers consisting of alternating phenylethynyl and monosilyl or disilanyl moieties were synthesized in 15–64% precipitated
yields by the reactions of dilithiated ethynylbenzene with dichlorodimethylsilane, dichlorodiphenylsilane, and 1,2-dichloro-1,1,2,2-tetramethyldisilane.
Degrees of polymerization were fairly low due to chain termination reactions involving the deprotonation of ethynyl groups
by aryllithium species. The presence of butyl chain ends was confirmed by 1H and 29Si NMR spectroscopy. 29Si NMR spectroscopy was utilized to illustrate the random pattern of connectivity along the oligomer backbones. The oligomers
exhibit fluorescent behavior in solution. 相似文献
64.
The demand for new, soft materials with bespoke physical and biological characteristics and functionality has fuelled the research into nanocomposite hydrogels. ‘Soft’ nanocomposites – nanoparticles within a hydrated, polymeric gel matrix – offer a simple, yet versatile, platform for the design of materials with specific – and tunable – properties. Indeed, the ‘soft’ properties of the matrix can be combined with the inherent functionality of the nanoparticles (drug loading, antimicrobial, light refraction etc.) or give rise to altogether new characteristics (toughness, optical properties, self‐healing etc.) evolved from the synergistic interaction of the polymer chains with the particles. In this review, we report the evolution and achievements of nanocomposite gels, with a focus on mechanisms and structure. The review is therefore structured around the properties resulting from the gel/nanoparticle association, rather than a classification based on applications or specific types of polymer or nanoparticles. How can nanoparticles tune mechanical, optical, biological properties or impart stimuli‐responsiveness to a polymer gel matrix ? and how is this behaviour linked to the underlying structure? © 2015 Society of Chemical Industry 相似文献
65.
Vivian Maria Carminato Blanco Lucas Tadeu Fuess Marcelo Zaiat 《International Journal of Hydrogen Energy》2017,42(17):12181-12196
Biohydrogen (bioH2) production via dark fermentation is an attractive approach to overcome the drawbacks of conventional hydrogen production methods and represents a preliminary alternative for the management of organic wastes. Fundamental studies are still required to enhance the performance of bioH2 production systems, with emphasis on the development of novel reactor configurations. The anaerobic structured-bed reactor (ASTBR) is a recently developed configuration with great potential for bioH2 production, although operating strategies are still required to minimize biomass washout in such systems. In this context, calcium dosing has been investigated as a strategy to enhance both biomass retention and bioH2 production rates in the ASTBR. The present study employed varying COD/calcium ratios (4423, 2079, 1357, 1012, 884, and 632) in continuous experiments under mesophilic conditions (25 °C). Calcium dosing effectively enhanced biomass retention within the ASTBR, directly increasing the availability of metabolic energy for different metabolic pathways rather than cell synthesis. An optimal COD/calcium ratio of 1360 was mathematically estimated for bioH2 production, which is consistent with the results obtained experimentally. The specific organic loading rate (SOLR) was better controlled at this ratio, indicating the establishment of balanced conditions in terms of substrate availability and biomass concentration. Conversely, bioH2 production was severely impaired at COD/calcium values below and above the optimal range, most likely due to enhancement of the homoacetogenic pathway as a result of unbalanced conditions in the SOLR. Furthermore, biomass accumulation did not strongly affect the mean residence time of the ASTBR, facilitating its robust and enhanced solid retention. 相似文献
66.
Alan P. O. da Silva Cicilia R. M. Leite Larry McMillan Carlos A. Paz de Araujo Marcelo A. C. Fernandes ANA M. G. Guerreiro 《Integrated ferroelectrics》2015,159(1):23-33
In this work we propose the implementation of boolean logic through artificial neurons with Ferroelectric Capacitor (FeCapacitor) as its basic unit on a reconfigurable hardware platform. Two neurons were implemented: the Perceptron and the Spiking Neuron model. Both neurons use the phenomenon of the hysteresis loop as an activation function and were embedded on a Field Gate Programmable Gate Array (FPGA) hardware platform. The implementations were carried out by Simulink models and hardware synthesizable blocks from DSP Builder software and the results are shown in the form of the models and the boolean functions implemented by them. 相似文献
67.
FAME Production and Fatty Acid Profiles from Moist Chlorella sp. and Nannochloropsis oculata Biomass
下载免费PDF全文
![点击此处可从《Journal of the American Oil Chemists](/ch/ext_images/free.gif)
Rui C. M. Alves Sobrinho Laércio Vauchinski Renata Rodrigues de Moura Ednei G. Primel Paulo C. V. Abreu Marcelo G. Montes D’Oca 《Journal of the American Oil Chemists' Society》2015,92(3):423-430
In the present study, we investigated the production of fatty acid methyl esters (FAME) from moist Chlorella sp. and Nannochloropsis oculata biomass using a hydrolysis–esterification process. Additionally, we evaluated for the first time the fatty acid profile before and after this process. Hydrolysis of the lipid fraction was performed on a moist biomass in the presence of differing amounts of an acid catalyst in both 50 and 100 % w/w water relative to the biomass. The esterification of the crude extracts of the free fatty acids (FFA) was then investigated. The experiments show that in the presence of 50 % w/w water relative to the biomass, the hydrolysis–esterification process results in higher FFA and FAME yields. The analysis of the fatty ester profiles did not reveal any degradation of the FFA from the microalgae biomass under the hydrolysis–esterification conditions. The results were compared with both extraction–transesterification and direct transesterification processes using dry biomass. The extraction–transesterification and hydrolysis–esterification processes resulted in similar FAME yields and similar profiles of the fatty esters from dry and moist biomass materials, respectively. 相似文献
68.
Soraya Mendes de Souza Lineu Jose Pedroso Paulo Marcelo Vieira Ribeiro 《土木工程与建筑:英文版》2013,(9):1111-1117
Problems of fluid structure interactions are governed by a set of fundamental parameters. This work aims at showing through simple examples the changes in natural vibration frequencies and mode shapes for wall-cavity systems when the structural rigidity is modified. Numerical results are constructed using ANSYS software with triangular finite elements for both the fluid (2D acoustic elements) and the solid (plane stress) domains. These former results are compared to proposed analytical expressions, showing an alternative benchmark tool for the analyst. Very rigid wall structures imply in frequencies and mode shapes almost identical to those achieved for an acoustic cavity with Neumann boundary condition at the interface. In this case, the wall behaves as rigid and fluid-structure system mode shapes are similar to those achieved for the uncoupled reservoir case. 相似文献
69.
Marcelo De Cusatis 《The Journal of Architecture》2013,18(4):433-436
The following observations are intended only to outline some concerns about, and to offer observations on, the teaching of design disciplines in the University of Buenos Aires and to rehearse the current educational challenges relating to achieving the standards expected of a professional graduate competent to improve our environmental demands. 相似文献
70.
Giulia Sierri Roberta Dal Magro Barbara Vergani Biagio Eugenio Leone Beatrice Formicola Lorenzo Taiarol Stefano Fagioli Marcelo Kravicz Lucio Tremolizzo Laura Calabresi Francesca Re 《International journal of molecular sciences》2022,23(1)
The cerebral synthesis of cholesterol is mainly handled by astrocytes, which are also responsible for apoproteins’ synthesis and lipoproteins’ assembly required for the cholesterol transport in the brain parenchyma. In Alzheimer disease (AD), these processes are impaired, likely because of the astrogliosis, a process characterized by morphological and functional changes in astrocytes. Several ATP-binding cassette transporters expressed by brain cells are involved in the formation of nascent discoidal lipoproteins, but the effect of beta-amyloid (Aβ) assemblies on this process is not fully understood. In this study, we investigated how of Aβ1-42-induced astrogliosis affects the metabolism of cholesterol in vitro. We detected an impairment in the cholesterol efflux of reactive astrocytes attributable to reduced levels of ABCA1 transporters that could explain the decreased lipoproteins’ levels detected in AD patients. To approach this issue, we designed biomimetic HDLs and evaluated their performance as cholesterol acceptors. The results demonstrated the ability of apoA-I nanodiscs to cross the blood–brain barrier in vitro and to promote the cholesterol efflux from astrocytes, making them suitable as a potential supportive treatment for AD to compensate the depletion of cerebral HDLs. 相似文献