全文获取类型
收费全文 | 5092篇 |
免费 | 395篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 67篇 |
综合类 | 3篇 |
化学工业 | 1342篇 |
金属工艺 | 59篇 |
机械仪表 | 149篇 |
建筑科学 | 208篇 |
矿业工程 | 9篇 |
能源动力 | 228篇 |
轻工业 | 860篇 |
水利工程 | 67篇 |
石油天然气 | 24篇 |
无线电 | 358篇 |
一般工业技术 | 837篇 |
冶金工业 | 193篇 |
原子能技术 | 27篇 |
自动化技术 | 1064篇 |
出版年
2024年 | 12篇 |
2023年 | 43篇 |
2022年 | 57篇 |
2021年 | 245篇 |
2020年 | 161篇 |
2019年 | 187篇 |
2018年 | 225篇 |
2017年 | 195篇 |
2016年 | 248篇 |
2015年 | 187篇 |
2014年 | 255篇 |
2013年 | 456篇 |
2012年 | 364篇 |
2011年 | 434篇 |
2010年 | 284篇 |
2009年 | 321篇 |
2008年 | 292篇 |
2007年 | 250篇 |
2006年 | 202篇 |
2005年 | 164篇 |
2004年 | 144篇 |
2003年 | 110篇 |
2002年 | 112篇 |
2001年 | 51篇 |
2000年 | 44篇 |
1999年 | 38篇 |
1998年 | 60篇 |
1997年 | 37篇 |
1996年 | 37篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 27篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有5495条查询结果,搜索用时 35 毫秒
71.
This paper presents the analysis of temperature effect on the copper electrocrystallization process from the stainless steel/Cu(II)-Cu(I)-NH4Cl-NH3-H2O system. Electrochemical techniques and scanning electron microscopy with energy dispersion spectroscopy were employed. An increment in temperature had a favorable effect in increasing the kinetic and nucleation parameters, favoring the copper reduction on the stainless steel substrate. From the chronoamperometric study, it was possible to find the transfer coefficient (α), which does not have a significant variation with temperature, and the exchange current density (i0) for different temperatures, where a 50.63 kJ/mol value was estimated for the activation energy. The potentiostatic study suggested the presence of two processes involved: an electron transfer reaction and a 3D nucleation—growth process, under combined charge transfer and diffusion limitations. In addition, an important current contribution could be accounted for on the basis of the existence of a capacitive component in the system. This capacitive behavior was associated to the oxide layer (Cr2O3)-chloride interactions on the stainless steel surface. Current transients analyses at different potentials, based on the models of: Milchev (low overpotential), Scharifker-Mostany (SM) and Heermann-Tarallo (HT) (high overpotential) allowed to obtain the values of nucleation parameters, such as: the nucleation rate constant (A), the active nucleation sites number (N0), the stationary nucleation rate (Ist = A × N0) and the nuclei saturation number (Ns). Finally, the deposits obtained were analyzed by SEM, showing an acceptable correlation between the nucleation parameters and morphology of the deposits obtained. An increment in temperature favored the growth of the cluster before the coalescence occurred. 相似文献
72.
Luis M. Rodríguez-Lorenzo Krlis A. Gross 《Journal of the American Ceramic Society》2004,87(5):814-818
Modification of hydroxyapatite surfaces can improve the properties of biomedical devices. The objective of this work was to encapsulate hydroxyapatite particles with a fluorapatite layer. A suspension of hydroxyapatite microspheres was prepared in a solution at different pH and treated with ammonium fluoride. pH, calcium, and fluoride were monitored in real time and particles subjected to fluoride analysis. After addition of fluoride, it was found that more material is released from the particle surface at low pH conditions, but leads to a high fluoride uptake from solution. Low solution fluoride levels produce a fluorapatite layer, but higher fluoride levels produce calcium fluoride. 相似文献
73.
Jose Saldana Julián Fernández-Navajas José Ruiz-Mas Eduardo Viruete-Navarro Luis Casadesus 《Multimedia Tools and Applications》2014,71(3):1823-1856
First Person Shooters are a genre of online games in which users demand a high interactivity, because the actions and the movements are very fast. They usually generate high rates of small packets which have to be delivered to the server within a deadline. When the traffic of a number of players shares the same link, these flows can be aggregated in order to save bandwidth. Certain multiplexing techniques are able to merge a number of packets, in a similar way to voice trunking, creating a bundle which is transmitted using a tunnel. In addition, the headers of the original packets can be compressed by means of standard algorithms. The characteristics of the buffers of the routers which deliver these bundled packets may have a strong influence on the network impairments (mainly delay, jitter and packet loss) which determine the quality of the game. A subjective quality estimator has been used in order to study the mutual influence of the buffer and multiplexing techniques. Taking into account that there exist buffers which size is measured in terms of bytes, and others measured in packets, both kinds of buffers have been tested, using different sizes. Traces from real game parties have been merged in order to obtain the traffic of 20 simultaneous players sharing the same Internet access. The delay and jitter produced by the buffer of the access router have been obtained using simulations. In general, the quality is expected to be reduced as the background traffic grows, but the results show an anomalous region in which the quality rises with the background traffic amount. Small buffers present better subjective quality results than bigger ones. When the total traffic amount gets above the available bandwidth, the buffers measured in bytes add to the packets a fixed delay, which grows with buffer size. They present a jitter peak when the offered traffic is roughly the link capacity. On the other hand, buffers which size is measured in packets add a smaller delay, but they increase packet loss for gaming traffic. The obtained results illustrate the need of knowing the characteristics of the buffer in order to make the correct decision about traffic multiplexing. As a conclusion, it would be interesting for game developers to identify the behaviour of the router buffer so as to adapt the traffic to it. 相似文献
74.
The lower halides of zinc, namely, ZnCl2 , ZnBr2 , and ZnI2 , may act as network formers in glasses that also contain modifying alkali halides such as KCI, KBr, KI, NaI, or CsI. Compositions which contain only Br− or I− anions are of particular interest because of their extended infrared transmission, which includes the ∼10-μm region, in addition to full visible transparency. A series of modified zinc halide glasses were prepared and characterized by differential scanning calorimetry, middle and far Fourier transform infrared spectroscopy, and polarized Raman spectroscopy. T g values were characteristically low, around 40°C. Bulk glass infrared transmission up to 15 to 20 μm was recorded. The most probable glass structures are discussed and compared to oxide glass models. An attenuation of 0.001 dB/km has been projected as a possible intrinsic minimum for optical fibers operating near ∼6 μm. 相似文献
75.
The present paper summarizes a comprehensive Second-Law analysis of the SYNTHANE process of coal gasification(1), based on the available-energy concept as applied to design conditions and data. The analysis yields an overall process efficiency of 46%. For every 100 MJ of useful energy supplied with coal, 51 MJ are consumed during the various unit operations while effluents carry 3 MJ. Unit 30, Steam and Power Production, consumes nearly 20 MJ; Unit 15, Gasification, used up nearly 16 MJ; Units 12 and 14, Coal Preparation and Feeding, about 5 MJ; Units 16 and 17, Raw Gas Quenching and Shift Conversion, 4 MJ; Unit 32, Oxygen Plant, approximately 2 MJ; other miscellaneous units contribute a combined available-energy destruction of 4 MJ. The Second-Law analysis unveils the inefficiencies present in the process and their sources, thus pinpointing the opportunities for improvement in the SYNTHANE process. 相似文献
76.
Luis Carlos Ferreira Jr.Marcos A.S. Costa Pedro Ivo C. GuimarãesLuiz Claudio de Santa Maria 《Polymer》2002,43(14):3857-3862
Styrene polymerization was carried out with Ni(acac)2/MAO and Ni(acac)2/SiO2/MAO. The influence of reaction parameters (Al/Ni mole ratio, catalyst concentration, temperature and time polymerization) on styrene polymerization was evaluated. It was observed that both catalytic systems were affected by reaction parameters and that the heterogeneous catalyst presented higher activity than the homogeneous one. Polystyrenes with different molecular weight, stereoregularity and polydispersity were obtained. These results suggest that different active catalyst species could have been present. In addition, two types of methylaluminoxane (MAO) with different molecular weights were also evaluated as cocatalyst. As a result, the catalyst activity and stereospecificity were strongly affected by the MAO type. 相似文献
77.
Luis Carlos da Silva Ramos Joao Shogiro Tango Angelo Savi Nilson Roberto Leal 《Journal of the American Oil Chemists' Society》1984,61(12):1841-1843
Thirty-six castorbean varieties were surveyed for oil and fatty acid composition, in order to determine variability of these
seed compounds. A large variability of seed oil percentage was observed, ranging from 39.6 to 59.5%. Concerning the fatty
acids, little variability was observed for ricinoleic acid, which was the most abundant in the oil, ranging from 83.65 to
90.00%. The other fatty acids appeared in small concentrations and showed a small range: 0.87 to 2.35, 0.68 to 1.84, 2.96
to 5.64, 3.19 to 5.98, and 0.34 to 0.91%, for palmitic, stearic, oleic, linoleic, and linolenic acid, respectively. Non-significant
correlations were observed between fatty acids and seed oil percentage. However, significant correlations were observed among
fatty acid concentrations: positive and negative ones. These significant correlations could be associated with the biosynthetic
pathways of the fatty acids, which are not fully elucidated. They suggest, however, that selection for a particular fatty
acid will tend to increase those positively correlated, and decrease those negative ones. Selection and plant breeding techniques
could then be applied to modify the oil content of the castorbean seeds, considering the variability observed. For the fatty
acid composition, however, the variability was not large enough to make substantial changes in their concentrations by selection
procedures. More varieties should be surveyed to find out if such variability is available. 相似文献
78.
Carlos Rivas-Costa Luis Anido-Rifón Miguel A. Gómez-Carballa Sonia Valladares-Rodríguez Roberto Soto-Barreiros 《International journal of human-computer interaction》2014,30(6):480-494
This article discusses a modular, accessible platform that provides a computing environment for people with disabilities accessible through adapted control devices and the television set at users’ homes. Relying on a standard television set as the presentation device allows dependent individuals, especially people with disabilities, to introduce new technological advances in communication and information management in their everyday lives. As a proof-of-concept, the solution presented offers a collection of educational and training services related to teleworking and the search of employment targeted to people with disabilities. A smart job advisor included among these services, which was designed to help our target users to locate job offers that best suit the abilities and disabilities of a particular individual, is also discussed to illustrate how semantic technologies can be applied to increase the perceived accessibility and inclusion by reducing the dependence from other persons. The platform developed, the introduction of semantic technologies, and the way adapted interfacing and presentation devices were integrated may also serve as inspiration to provide services to people with disabilities. 相似文献
79.
Pedro Luis Mateo Navarro Gregorio Martínez Pérez Diego Sevilla Ruiz 《International journal of human-computer interaction》2014,30(12):946-964
This article describes a novel approach to model the quality of experience (QoE) of users in mobile environments. The context-aware and ratings interaction model (CARIM) addresses the open questions of how to quantify user experiences from the analysis of interaction in mobile scenarios, and how to compare different QoE records to each other. A set of parameters are used to dynamically describe the interaction between the user and the system, the context in which it is performed and the perceived quality of users. CARIM structures these parameters into a uniform representation, supporting the dynamic analysis of interaction to determine QoE of users and enabling the comparison between different interaction records. Its run-time nature allows applications to make context- and QoE-based decisions in real time to adapt themselves, and thus provide a better experience to users. As a result, CARIM provides unified criteria for the inference and analysis of QoE in mobile scenarios. Its design and implementation can be integrated (and easily extended if needed) into many different development environments. An experiment with real users comparing two different interaction designs and validating user behavior hypotheses proved the effectiveness of applying CARIM for the assessment of QoE in mobile applications. 相似文献
80.
Chamorro G Salazar M Araújo KG dos Santos CP Ceballos G Castillo LF 《Archivos latinoamericanos de nutrición》2002,52(3):232-240
Spirulina (Arthrospira), a filamentous, unicellular alga, is a cyanobacterium grown in certain countries as food for human and animal consumption. It is also used to derive additives in pharmaceuticals and foods. This alga is a rich source of proteins, vitamins, amino acids, minerals, and other nutrients. Its main use, therefore, is as a food supplement. Over the last few years, however, it has been found to have many additional pharmacological properties. Thus, it has been experimentally proven, in vivo and in vitro that it is effective to treat certain allergies, anemia, cancer, hepatotoxicity, viral and cardiovascular diseases, hyperglycemia, hyperlipidemia, immunodeficiency, and inflammatory processes, among others. Several of these activities are attributed to Spirulina itself or to some of its components including fatty acids omega-3 or omega-6, beta-carotene, alpha-tocopherol, phycocyanin, phenol compounds, and a recently isolated complex, Ca-Spirulan (Ca-SP). This paper aims to update and critically review the results published over the last few years with regards to these properties. The conclusion is that even if this cyanobacterium has been one of the most extensively studied from the chemical, pharmacological and toxicological points of view, it is still necessary to expand the research in order to have more consistent data for its possible use in human beings. 相似文献