全文获取类型
收费全文 | 5455篇 |
免费 | 337篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 71篇 |
综合类 | 5篇 |
化学工业 | 1501篇 |
金属工艺 | 83篇 |
机械仪表 | 129篇 |
建筑科学 | 237篇 |
矿业工程 | 9篇 |
能源动力 | 203篇 |
轻工业 | 773篇 |
水利工程 | 27篇 |
石油天然气 | 19篇 |
无线电 | 340篇 |
一般工业技术 | 886篇 |
冶金工业 | 398篇 |
原子能技术 | 50篇 |
自动化技术 | 1070篇 |
出版年
2024年 | 10篇 |
2023年 | 47篇 |
2022年 | 199篇 |
2021年 | 255篇 |
2020年 | 135篇 |
2019年 | 149篇 |
2018年 | 194篇 |
2017年 | 179篇 |
2016年 | 226篇 |
2015年 | 159篇 |
2014年 | 215篇 |
2013年 | 379篇 |
2012年 | 340篇 |
2011年 | 417篇 |
2010年 | 284篇 |
2009年 | 309篇 |
2008年 | 294篇 |
2007年 | 246篇 |
2006年 | 241篇 |
2005年 | 180篇 |
2004年 | 144篇 |
2003年 | 129篇 |
2002年 | 113篇 |
2001年 | 95篇 |
2000年 | 83篇 |
1999年 | 79篇 |
1998年 | 143篇 |
1997年 | 95篇 |
1996年 | 80篇 |
1995年 | 64篇 |
1994年 | 43篇 |
1993年 | 49篇 |
1992年 | 11篇 |
1991年 | 25篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 4篇 |
排序方式: 共有5801条查询结果,搜索用时 15 毫秒
41.
The catalytic hydrogenation of acrylonitrile‐butadiene copolymer (nitrile rubber, NBR) using Pd(OAc)2 or RuCl2(PPh3)3 catalysts has been investigated in order to produce a totally saturated nitrile rubber. The hydrogenation of NBR is effective with both catalysts and achieved total conversion under the appropriate reaction conditions. In the case of palladium the effects of reaction parameters such as reaction temperature, pressure, time, catalyst concentration, and NBR concentration have been investigated. Even though both ruthenium‐ and palladium‐based catalysts are effective in the production of HNBR, the former requires harsh reaction conditions and has the drawback of gel formation under high conversion, motivating the migration to RuCl2 (PPh3)3 as an alternative catalyst. The degree of hydrogenation was determined by IR and NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
42.
43.
The influence has been studied of the partial pressure of hydrogen (0–30 kPa) upon the coking rate of a Cr2O3/Al2O3 commercial catalyst during 1-butene dehydrogenation. Coke deposition has been analysed using a monolayer-multilayer reversible coke growth model (MMRC model). This model provides good fits to the experimental data, within the range of partial pressure of H2 studied, and allows us to estimate the main kinetic parameters involved in the coking-deactivation process. The results obtained reveal a dual effect of hydrogen: competition against 1-butene for the active sites and the removal of coke precursors from the catalyst surface. Bom effects diminish the coking rate as the H2 partial pressure is increased. 相似文献
44.
Aranzazu García M Victoria Ruiz-Méndez Concepción Romero Manuel Brenes 《Journal of the American Oil Chemists' Society》2006,83(2):159-164
By definition, virgin olive oil is consumed unrefined, although a great proportion of the olive oil produced has to be refined
to render it edible. Phenolic compounds are among the substances eliminated during the refining process; in the present work
these were characterized by HPLC, and their evolution during the different refining steps was studied. The complete refining
process removed most polyphenols from oils, but the behavior of individual compounds at each step also was observed. o-Diphenols
(hydroxytyrosol, catechol, and hydroxytyrosol acetate) and flavonoids (luteolin and apigenin) were eliminated first during
the alkaline treatment. Tyrosol and 4-ethylphenol remained in the oil until the deodorization step. A large amount of phenolic
compounds was discovered in the refining by-products such as soapstocks and deodorization distillates. In the latter streams,
the concentrations of tyrosol and 4-ethylphenol reached up to 149 and 3720 mg/kg by-product, respectively. This high level
of 4-ethylphenol and its well-known strong off-odor can interfere during further processing of the deodorization distillates,
and this must be taken into account when deciding what is to become of them. Similarly, the results of this work open the
possibility of recovering phenolic compounds from the “second centrifugation olive oils” by adding a new washing step prior
to the refining process. By including this new step, the most polar polyphenols, hydroxytyrosol and tyrosol, will diffuse
from oil to water and a concentration of up to 1400 mg/L of hydroxytyrosol may be achieved. 相似文献
45.
The impact that some membrane preparation steps had on ultrafiltration (UF) membrane characteristics and performance was studied. Polyethersulfone (PES) was employed as base polymer, while N‐methyl pyrrolidone (NMP) was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a nonsolvent pore‐forming additive. The manufacturing variables studied were solvent evaporation time and membrane surface modification, using a fluorine‐based copolymer referred to as surface‐modifying macromolecule (SMM). The flat sheet membranes, prepared via phase inversion, were characterized using solute transport data, X‐ray photoelectron spectroscopy (XPS), and contact angle measurements. Membrane performance was evaluated via filtration test protocol that included a 6‐day filtration of concentrated river water. The flux reduction with time was modeled using single and dual mechanisms of fouling. The pore blockage/cake filtration model described better the behavior of the permeation rate along the experiments. Increasing the solvent evaporation time decreased the size of the pores and the permeation rate. However, it did not significantly affect the removal of the organic compounds naturally present in the river water used as feed. XPS and contact angle measurements proved that the short evaporation periods did not allow enough SMM migration to the surface to provoke a significant effect on the membrane performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006 相似文献
46.
Enhancement of the basic properties of the X zeolite with FAU framework has been carried out during synthesis, without further treatment such as ion-exchange or impregnation. Control of the washing stage enables retention of the optimum amount of alkaline hydroxides, which increases the basic catalytic activity of X zeolite in the alkylation of toluene. This alkaline hydroxides neither affect the FAU framework nor the silicon/aluminium molar ratio of the X zeolite. The optimum (Na + K)/Al molar ratio of the improved catalyst was 1.06 corresponding to a washing volume of 200 mL. This X zeolite presented better catalytic activity than a cesium-zeolite prepared by ion-exchange. The presence of hydroxysodalite impurity in the X zeolite increased the amount of impregnated alkaline hydroxides but not the catalytic activity. The present study shows that it is possible to increase the basic properties of the X zeolite directly in the synthesis process. 相似文献
47.
Vincenzo Tufano Roberto Andreozzi Vincenzo Caprio Maria Giovanna D'Amore Amedeo Insola 《臭氧:科学与工程》1994,16(3):181-195
A method for the assessment of the optimal operating conditions for a mechanically stirred gas–liquid reactor is presented. The method exploits both fluid dynamic and chemical information. First, the behavior of the specific stirring power as a function of the stirrer speed allows singling out the dispersion region, in which the most efficient gas–liquid mass transfer is achieved. Inside this region, the analysis of experimental data obtained when considering a chemical system reacting at moderate Hatta numbers (i.e., Ha < about 2) allows determination of the rate constants and the fluid dynamic parameters (i.e., the mass transfer coefficient in the absence of chemical reaction and the characteristic diffusion time). 相似文献
48.
Emilio Soto Candela Mario Ortega Pérez Clemente Marín Romero David C. Pérez López Gustavo Salvador Herranz Manuel Contero Mariano Alcañiz Raya 《Multimedia Tools and Applications》2014,70(3):1837-1868
In this paper, a computer vision based interactive multi-touch tabletop system called HumanTop is introduced. HumanTop implements a stereo camera vision subsystem which allows not only an accurate fingertip tracking algorithm but also a precise touch-over-the-working surface detection method. Based on a pair of visible spectra cameras, a novel synchronization circuit makes the camera caption and the image projection independent from each other, providing the minimum basis for the development of computer vision analysis based on visible spectrum cameras without any interference coming from the projector. The assembly of both cameras and the synchronization circuit is not only capable of performing an ad-hoc version of a depth camera, but it also introduces the recognition and tracking of textured planar objects, even when contents are projected over them. On the other hand HumanTop supports the tracking of sheets of paper and ID-code markers. This set of features makes the HumanTop a comprehensive, intuitive and versatile augmented tabletop that provides multitouch interaction with projective augmented reality on any flat surface. As an example to exploit all the capabilities of HumanTop, an educational application has been developed using an augmented book as a launcher to different didactic contents. A pilot study in which 28 fifth graders participated is presented. Results about efficiency, usability/satisfaction and motivation are provided. These results suggest that HumanTop is an interesting platform for the development of educational contents. 相似文献
49.
The adsorption equilibrium data of pentachlorophenol (PCP) onto activated carbon fiber (ACF) in felt form were obtained in a batch adsorber at T = 25 °C and pH 12 and the Langmuir isotherm fitted reasonably well with the experimental data. The rate of adsorption of PCP on ACF was investigated in this work and the experimental concentration decay data were obtained in a differential column batch adsorber. The overall rate of adsorption of PCP was interpreted by a diffusional model that takes into account the external mass transport and intrafiber diffusion. The experimental concentration decay can be described quite well with the diffusional model if the overall rate of adsorption is mainly controlled by intrafiber diffusion and the external mass transport is not important to the overall rate of adsorption. Moreover, intrafiber diffusion was significantly affected by restricted diffusion since the molecular diameter of the PCP was closed to 55% of the average pore diameter. The effect of restricted diffusion was estimated using correlations reported in the literature. The molecules of PCP adsorbed on the surface of the pore also hindered the diffusion of PCP molecules inside the pores. 相似文献
50.
This paper analyzes the deactivation effects of NiMo/Al2O3 catalyst during the operation in an Ebullated bed reactor for Heavy residue hydrocracking. The spent catalysts were characterized by chemical analysis, 13C NMR, ESM, DRX, and by using thermal programmed oxidation and diffusion studies in a shallow bed micro-reactor. The deactivations were performed in a 5 l continuously stirred tank reactor, while the spent catalysts were tested in a 0.05 l micro-reactor. The study focused on determining the properties of the external layer of the catalyst and on evaluating the internal coke and metal deposition. The results indicated that initial deactivation is mainly due to coke depositions, while its impact on mass transfer reaction control depends on temperature. In long-term deactivation, the metal deposition plays a more important role in blocking the internal micro- and meso-structures and in building up the external layer of the pellets. 相似文献