全文获取类型
收费全文 | 3535篇 |
免费 | 190篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 52篇 |
综合类 | 3篇 |
化学工业 | 985篇 |
金属工艺 | 76篇 |
机械仪表 | 86篇 |
建筑科学 | 138篇 |
矿业工程 | 6篇 |
能源动力 | 154篇 |
轻工业 | 266篇 |
水利工程 | 28篇 |
石油天然气 | 3篇 |
无线电 | 368篇 |
一般工业技术 | 697篇 |
冶金工业 | 178篇 |
原子能技术 | 32篇 |
自动化技术 | 659篇 |
出版年
2023年 | 28篇 |
2022年 | 80篇 |
2021年 | 105篇 |
2020年 | 55篇 |
2019年 | 76篇 |
2018年 | 86篇 |
2017年 | 91篇 |
2016年 | 120篇 |
2015年 | 104篇 |
2014年 | 144篇 |
2013年 | 242篇 |
2012年 | 220篇 |
2011年 | 284篇 |
2010年 | 183篇 |
2009年 | 218篇 |
2008年 | 228篇 |
2007年 | 168篇 |
2006年 | 179篇 |
2005年 | 124篇 |
2004年 | 108篇 |
2003年 | 105篇 |
2002年 | 123篇 |
2001年 | 57篇 |
2000年 | 51篇 |
1999年 | 50篇 |
1998年 | 68篇 |
1997年 | 72篇 |
1996年 | 42篇 |
1995年 | 33篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有3731条查询结果,搜索用时 0 毫秒
11.
12.
As-produced nanotubes form a light, fragile and isotropic soot. Different efforts are made to process nanotubes into macroscopic forms of more practical use and more controlled properties. We briefly review in this paper two methods recently proposed to make films of magnetically aligned nanotubes and fibers by using an electrophoretic method. Preferential orientation of the nanotubes in the plane of the films or along the fiber axis is an important feature of the obtained materials. Then we describe in details a different, spinning like, process for making fibers out of single wall carbon nanotubes. This process consists of dispersing the nanotubes in a surfactant solution, re-condensing the nanotubes in the flow of a polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. The behaviors of the surfactant-stabilized dispersions, which are also presented, are critical for this process. The degree of nanotubes alignment in dried fibers has been characterized by X-ray scattering. It is found to be smaller than the alignment obtained in the previous materials. However, the processing is simpler and faster and potentially scalable for large-scale production. 相似文献
13.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
14.
Nowadays, the complex manufacturing processes have to be dynamically modelled and controlled to optimise the diagnosis and the maintenance policies. This article presents a methodology that will help developing Dynamic Object Oriented Bayesian Networks (DOOBNs) to formalise such complex dynamic models. The goal is to have a general reliability evaluation of a manufacturing process, from its implementation to its operating phase. The added value of this formalisation methodology consists in using the a priori knowledge of both the system's functioning and malfunctioning. Networks are built on principles of adaptability and integrate uncertainties on the relationships between causes and effects. Thus, the purpose is to evaluate, in terms of reliability, the impact of several decisions on the maintenance of the system. This methodology has been tested, in an industrial context, to model the reliability of a water (immersion) heater system. 相似文献
15.
Thermoforming (free blowing) of poly(ethylene terephthalate) preforms was successfully and quickly performed in a rotating system designed for dielectric hysteresis heating. Temperature profile modeling was carried out with the amorphous poly(ethylene terephthalate) permittivity at different temperatures. The Maxwell and heat equations were used to determine the best profile and power tuning. The determination of the theoretical boundary conditions was accomplished by the adjustment of the numerical transient external surface wall temperature with experimental infrared pyrometry results. In comparison with infrared, microwaves allowed high power density absorption inside the perform wall without a dramatic temperature gradient. Consequently, the heat blowing stage could be accelerated, and the process took at least 5 times less energy than infrared heating. Industrial applications involve the integration of the molding step and the design of the overall process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
16.
The use of phosphazene bases in combination with water was proved to be efficient in order to obtain polysiloxane polymers from cyclic monomers. Only a few minutes are necessary to obtain polymer chains with a monomer concentration of 5% at the equilibrium. For that purpose the space which is between a rheometer's plates is the most convenient device to monitor this reaction concerning a chemical and viscoelastic point of view. Therefore, here is proposed a chemo-rheology study that leads in the same time to the chemical kinetics equations and to the variation of the viscoelastic functions during the polymerization. In this way different catalysts are used and their efficiencies are compared as a function of their “basicity tank”. Whatever the experimental conditions involved are, viscosity versus polymer concentration or conversion shows a master curve for catalysts suitable to be used under extrusive conditions. Thus, only a few experiments are needed in order to develop a model which can be used to foresee the variation of the viscosity during the reaction. 相似文献
17.
Reda Karoum Antonio de Lucas-Consuegra Fernando Dorado Jose Luis Valverde Alain Billard Philippe Vernoux 《Journal of Applied Electrochemistry》2008,38(8):1083-1088
The electrochemical promotion of catalysis (EPOC) of propene combustion was investigated using Pt sputtered thin film on an
O2− conductor, 8 mol% Y2O3-stabilized-ZrO2 (YSZ). In order to separate the influence of the thermal migration of the O2− oxide ions from the electrolyte to the catalyst surface and the impact of an electrical polarization on the catalytic activity,
several light-off experiments (cool down and heat up procedures) were successively performed under different polarizations,
i.e. OCV, +2 and −2 V. These experiments have clearly shown that the presence of O2− (thermally or electrochemically induced) inhibits the catalytic activity of the platinum for the propene deep oxidation.
These results demonstrate the importance to define a normalized rate enhancement ratio, ρ
n
, from a reference value of the catalytic rate corresponding to a Pt surface state free of O2− ions. 相似文献
18.
Catalysis, the turntable for a clean future 总被引:1,自引:0,他引:1
Upgrading the bottom of the barrel for clean fuel production, developing new engines with optimized catalytic posttreatments, implementing clean catalytic combustion technologies, improving the overall CO2 balance via catalytic processes and, lastly, developing new water purification techniques represent major upheavals in catalysis linked to refining and environmental protection. This paper, thus, will focus on the determining contribution of catalysis to the most recent achievements in these domains. A technico-economic approach will follow, underlining their main incentives and drawbacks within the framework of future environmental constraints. 相似文献
19.
Cécile NouvelIsabelle Ydens Philippe DegéePhilippe Dubois Edith DellacherieJean-Luc Six 《Polymer》2002,43(6):1735-1743
The silylation reaction of dextran with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in DMSO was studied as the first step of the synthesis of new amphiphilic polyester-grafted dextrans. According to the experimental conditions, i.e. dextran molar weight, medium temperature and reaction time, HMDS/OH ratio, addition of a catalyst and co-solvent, partially or totally silylated dextrans were recovered. The highest silylation yields were obtained with the lowest molecular weight dextrans. The increase in temperature medium and/or reaction time, the presence of catalyst or co-solvent favored the protection yield. Whatever the dextran used, complete silylation of the polysaccharide chain could be achieved by adequate selection of the experimental conditions. The thermal properties of resulting silylated polysaccharides were investigated by temperature modulated DSC. It was observed that Tg values of partially silylated dextran were maintained between 120 and 140 °C, independently of the dextran molecular weight. Interestingly, DMSO proved to behave as an efficient plasticizer of (partially) silylated dextrans. The partially silylated dextrans were efficiently used as multifunctional macroinitiators for the controlled ring-opening polymerization (ROP) of lactone. The ROP was then promoted from the remaining hydroxyl groups in the presence of tin or aluminium activator. After polymerization and ultimate deprotection of the silylated dextran backbone, amphiphilic polyester-grafted dextrans were readily recovered. 相似文献
20.
In this paper we present a new radiosity algorithm, based on the notion of a well distributed ray set (WDRS). A WDRS is a set of rays, connecting mutually visible points and patches, that forms an approximate representation of the radiosity operator and the radiosity distribution. We propose an algorithm that constructs an optimal WDRS for a given accuracy and mesh. The construction is based on discrete importance sampling as in previously proposed stochastic radiosity algorithms, and on quasi Monte Carlo sampling. Quasi Monte Carlo sampling leads to faster convergence rates and the fact that the sampling is deterministic makes it possible to represent the well distributed ray set very efficiently in computer memory. Like previously proposed stochastic radiosity algorithms, the new algorithm is well suited for computing the radiance distribution in very complex diffuse scenes, when it is not feasible to explicitly compute and store form factors as in classical radiosity algorithms. Experiments show that the new algorithm is often more efficient than previously proposed Monte Carlo radiosity algorithms by half an order of magnitude and more. 相似文献