全文获取类型
收费全文 | 15338篇 |
免费 | 910篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 164篇 |
综合类 | 8篇 |
化学工业 | 3756篇 |
金属工艺 | 250篇 |
机械仪表 | 408篇 |
建筑科学 | 593篇 |
矿业工程 | 40篇 |
能源动力 | 529篇 |
轻工业 | 3153篇 |
水利工程 | 167篇 |
石油天然气 | 80篇 |
武器工业 | 2篇 |
无线电 | 820篇 |
一般工业技术 | 2616篇 |
冶金工业 | 1027篇 |
原子能技术 | 103篇 |
自动化技术 | 2545篇 |
出版年
2024年 | 42篇 |
2023年 | 169篇 |
2022年 | 436篇 |
2021年 | 628篇 |
2020年 | 453篇 |
2019年 | 494篇 |
2018年 | 631篇 |
2017年 | 687篇 |
2016年 | 683篇 |
2015年 | 494篇 |
2014年 | 672篇 |
2013年 | 1314篇 |
2012年 | 1014篇 |
2011年 | 1107篇 |
2010年 | 802篇 |
2009年 | 829篇 |
2008年 | 770篇 |
2007年 | 697篇 |
2006年 | 576篇 |
2005年 | 372篇 |
2004年 | 337篇 |
2003年 | 339篇 |
2002年 | 310篇 |
2001年 | 221篇 |
2000年 | 202篇 |
1999年 | 192篇 |
1998年 | 393篇 |
1997年 | 267篇 |
1996年 | 186篇 |
1995年 | 150篇 |
1994年 | 103篇 |
1993年 | 104篇 |
1992年 | 54篇 |
1991年 | 44篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 29篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 40篇 |
1983年 | 40篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 17篇 |
1976年 | 33篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
2.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献
3.
Christian P. Romero Jonathan I. Avila Edgardo Cisternas Guerau B. Cabrera Alejandro L. Cabrera Kristiaan Temst Margriet J. Van Bael 《Journal of Materials Science》2007,42(18):7667-7672
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of
4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made
by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under
ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity
at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen
TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there
are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately
8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained
for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure. 相似文献
4.
5.
Andrés Rigail-Cedeño 《Polymer》2005,46(22):9378-9384
Cure reactions of the stoichiometric mixtures of diglycidyl ether of bisphenol A (DGEBA) and two very low molecular weight aliphatic polyether diamines (PED) were studied by using fluorescence and mid- and near-IR spectroscopic techniques. As the cure proceeded, the primary amine groups in PED are converted to the secondary and the tertiary amines. Near-IR spectral analysis was used to calculate the concentration of the three amine groups as a function of cure time. The decrease in the fluorescence intensity of DGEBA at about 307 nm was observed due to more effective quenching of the tertiary amine groups in PED, in comparison to the primary and the secondary amine groups. A large decrease in fluorescence intensity at 75 and 95 °C cure was observed. The amount of all the amine species was estimated from NIR spectra to shed light on the cure kinetics of PPO (polypropylene oxide) in comparison with PEO (polyethylene oxide) epoxy, as well as to explain their fluorescence behavior.The fluorescence intensity changes were correlated to the extent of epoxy reaction obtained by mid- and near-IR spectroscopy. 相似文献
6.
A Nu?ez C De la Roza ML Rodrigo-Angulo W Bu?o F Reinoso-Suárez 《Canadian Metallurgical Quarterly》1997,754(1-2):1-11
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters. 相似文献
7.
8.
9.
Fbio Gomes Costa Elias Andrade Braga Soraia Teixeira Brando Alexandre de Freitas Espeleta Zênis Novais da Rocha Lílian Maria Tosta Simplício Emerson Andrade Sales 《Applied Catalysis A: General》2005,290(1-2):221-226
Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)2ZrCl2] with silica formed [(Cp)2ZrCl]+[SiO]− species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like” species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization. 相似文献
10.
An evaluation of the Spanish CSIC performance in Biotechnology, as compared with those of the French CNRS and the Italian
CNR, has been carried out to determine the balance between the generation of scientific knowledge and the transfer of technology.
This study shows a high scientific productivity mostly in journals with moderate impact factor, a low generation of patents
and an insufficient transfer of knowledge to the Spanish companies. Other indicators confirm the existence of competitive
human resources in biotechnological research producing scientific knowledge of interest for the development of patents and
that cooperates successfully at European level. 相似文献