全文获取类型
收费全文 | 5898篇 |
免费 | 282篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 53篇 |
综合类 | 33篇 |
化学工业 | 1128篇 |
金属工艺 | 108篇 |
机械仪表 | 134篇 |
建筑科学 | 262篇 |
矿业工程 | 37篇 |
能源动力 | 107篇 |
轻工业 | 594篇 |
水利工程 | 41篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 392篇 |
一般工业技术 | 971篇 |
冶金工业 | 1599篇 |
原子能技术 | 27篇 |
自动化技术 | 719篇 |
出版年
2023年 | 35篇 |
2022年 | 49篇 |
2021年 | 111篇 |
2020年 | 89篇 |
2019年 | 71篇 |
2018年 | 179篇 |
2017年 | 170篇 |
2016年 | 174篇 |
2015年 | 150篇 |
2014年 | 150篇 |
2013年 | 373篇 |
2012年 | 320篇 |
2011年 | 312篇 |
2010年 | 236篇 |
2009年 | 202篇 |
2008年 | 271篇 |
2007年 | 212篇 |
2006年 | 197篇 |
2005年 | 171篇 |
2004年 | 140篇 |
2003年 | 164篇 |
2002年 | 138篇 |
2001年 | 104篇 |
2000年 | 105篇 |
1999年 | 100篇 |
1998年 | 525篇 |
1997年 | 298篇 |
1996年 | 194篇 |
1995年 | 120篇 |
1994年 | 99篇 |
1993年 | 107篇 |
1992年 | 27篇 |
1991年 | 44篇 |
1990年 | 27篇 |
1989年 | 35篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 39篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 38篇 |
1981年 | 36篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 48篇 |
1976年 | 46篇 |
1975年 | 19篇 |
1973年 | 16篇 |
排序方式: 共有6211条查询结果,搜索用时 15 毫秒
71.
Tristan Allard Benjamin Nguyen Philippe Pucheral 《Distributed and Parallel Databases》2014,32(2):191-244
The goal of Privacy-Preserving Data Publishing (PPDP) is to generate a sanitized (i.e. harmless) view of sensitive personal data (e.g. a health survey), to be released to some agencies or simply the public. However, traditional PPDP practices all make the assumption that the process is run on a trusted central server. In this article, we argue that the trust assumption on the central server is far too strong. We propose Met ??P, a generic fully distributed protocol, to execute various forms of PPDP algorithms on an asymmetric architecture composed of low power secure devices and a powerful but untrusted infrastructure. We show that this protocol is both correct and secure against honest-but-curious or malicious adversaries. Finally, we provide an experimental validation showing that this protocol can support PPDP processes scaling up to nation-wide surveys. 相似文献
72.
The intact preen wax esters of the red knot Calidris canutus were studied with gas chromatography/mass spectrometry (GC/MS) and GC/MS/MS. In this latter technique, transitions from the
molecular ion to fragment ions representing the fatty acid moiety of the wax esters were measured, providing additional resolution
to the analysis of wax esters. The C21−C32 wax esters are composed of complex mixtures of hundreds of individual isomers. The odd carbon-numbered wax esters are predominantly
composed of even carbon-numbered n-alcohols (C14, C16, and C18) esterified predominantly with odd carbon-numbered 2-methyl fatty acids (C7, C9, C11, and C13), resulting in relatively simple distributions. The even carbon-numbered wax esters show a far more complex distribution
due to a number of factors: (i) Their n-alcohol moieties are not dominated by even carbon-numbered n-alcohol moieties are not dominated by even carbon-numbered n-alcohols esterified with odd carbon-numbered 2-methyl fatty acids, but odd and even carbon-numbered n-alcohols participate in approximately equal amounts; (ii) odd carbon-numbered methyl-branched alcohols participate abundantly
in these wax ester clusters; and (iii) with increasing molecular weight, various isomers of the 2,6-, 2,8-, and 2,10-dimethyl
branched fatty acids also participate in the even carbon-numbered wax esters. The data demonstrate that there is a clear biosynthetic
control on the wax ester composition although the reasons for the complex chemistry of the waxes are not yet understood. 相似文献
73.
Alain A Vertès Masayuki Inui Hideaki Yukawa 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2007,82(8):693-697
The challenges of implementing biorefineries on a global scale include socioeconomic, financial, and technological constraints. In particular, the development of biorefineries is tightly linked to the continued availability of fermentation raw materials. These constraints can be relaxed by the use of diverse raw materials, while advances that confer higher flexibility would enable biotechnological plant managers to swiftly react to volatile markets. In conventional processes, Saccharomyces cerevisiae grows on a relatively limited range of substrates, and produces only a single product—ethanol. Given the observed maturity of the S. cerevisiae fermentation technology, alternatives to baker's yeast may be needed to tip the economic balance in favour of biotechnological ethanol. These alternative fermentation technologies may allow a greater diversity of substrates to be used to produce an individually tailored mix of ethanol and other chemicals. Copyright © 2007 Society of Chemical Industry 相似文献
74.
Gilles Barnathan Joseph Mirallès Emile M. Gaydou Nicole Boury-Esnault Jean-Michel Kornprobst 《Lipids》1992,27(10):779-784
The fatty acid composition of phospholipids from the Senegalese spongeCinachyrella alloclada was examined. Two new fatty acids not hitherto found in nature, namely 10,13-octadecadienoic acid and 16-tricosenoic acid,
were identified. 8-Hexadecenoic, 13-nonadecenoic and 5,9,13-trimethyltretradecanoic fatty acids were also found for the first
time in sponges. The latter compound (1.4% of the total fatty acid mixture), an isoprenoid fatty acid, accompanies the major
fatty acid 4,8,12-trimethyltridecanoic acid (19.7%). The monomethyl branched fatty acids (22%) identified include 23-methylpentacosanoic
acid (anteiso-26∶0), not previously observed in sponged. The major long-chain fatty acids encountered were the known 17-tetracosenoic
19-heptacosadienoic and 5,9,23-tricontatrienoic acid. Some sixty fatty acids were identified as methyl esters andN-acyl pyrrolidides by gas chromatography and gas chromatography/mass spectrometry. 相似文献
75.
Ccile Donze Pavel Korovchenko Pierre Gallezot Michle Besson 《Applied catalysis. B, Environmental》2007,70(1-4):621-629
The synthesis of substituted benzaldehydes, benzoic acids, heterocyclic aromatic aldehydes and acids has been studied via the oxidation of the aromatic alcohols with air under mild pressure (<20 bar) at 100 °C, in the presence of a 1.95 wt.% Pt/C catalyst. The solvent was found to play the most important role in determining the selectivity of the oxidation products. Changing the solvent enabled tuning the reaction either to the aldehyde (pure dioxane), or the carboxylic acid (dioxane/aqueous solution without or with addition of sodium hydroxide). This oxidation method allowed to effectively oxidize many substituted benzylalcohols with various electron-releasing or -attracting groups (NO2, Me, OMe, Cl, Br, OH, phenyl, …) and heterocyclic alcohols including nitrogen and sulphur atoms (2-thiophenemethanol, 2- and 4-pyridine methanol compounds). 相似文献
76.
The ever-increasing amount of solid waste generated by wastewater treatment plants highlights emerging economic and environmental issues. In order to develop new processes producing less sludge, the use of ozone combined with anaerobic digestion was investigated for waste activated sludge treatment. This paper was aimed at evaluating the impact of ozone pretreatment on anaerobic digestion and particularly the enhancement of biogas production. Sludge solubilization was estimated in terms of modification of chemical oxygen demand, solids and nitrogen. Batch anaerobic digestion highlighted the enhancement of ozonated sludge biodegradability. Ozonation led to an increase in biogas production. The ozone dose of 0.15 g O3/g total solids resulted in a considerable increase in the soluble COD ratio from 4% to 37%. This ozone dose achieved the highest increase in biogas production: 2.4 times greater than without chemical pretreatment. 相似文献
77.
Tatjana Rades Chanho Pak Michèle Polisset-Thfoin Ryong Ryoo Jacques Fraissard 《Catalysis Letters》1994,29(1-2):91-103
NaY-supported bimetallic Pt-Pd catalysts have been studied by TEM, TPR and EXAFS. Small, randomly mixed particles are formed in the zeolite cages. When the Pt content is increased, a Pt core structure appears and the dispersion increases. Particle diameters are about 1–2 nm for bimetallic samples. 相似文献
78.
Alper Sarıoğlan Ömer Tunç Savaşçı Ayşe Erdem-Şenatalar Vu Thu Ha Gilbert Sapaly Younès Ben Taârit 《Catalysis Letters》2007,118(1-2):123-128
MFI type inorganic carrier was used in two different cationic forms, hydrogen and calcium respectively. MFI-supported molybdenum
and rhenium catalysts were prepared. The activities of the catalysts were compared for the aromatization reaction of methane.
Higher activity values were attained with the catalysts supported on HZSM-5. Aromatics were also observed with the catalysts
supported on CaZSM-5, despite their deficiency in acid sites. Highly dispersed rhenium is expected to be formed with the use
of the inorganic carrier in calcium form. On the other hand, lower reaction rates were observed with rhenium supported on
CaZSM-5, in spite of the improved dispersion of the active rhenium species on this catalyst. This was interpreted in terms
of the critical role of the acid sites in the conversion of methane to aromatics, compared to the improved dispersion of the
active metal. 相似文献
79.
Information diffusion in large-scale networks has been studied to identify the users influence. The influence has been targeted as a key feature either to reach large populations or influencing public opinion. Through the use of micro-blogs, such as Twitter, global influencers have been identified and ranked based on message propagation (retweets). In this paper, a new application is presented, which allows to find first and classify then the local influence on Twitter: who have influenced you and who have been influenced by you. Until now, social structures of tweets’ original authors that have been either retweeted or marked as favourites are unobservable. Throughout this application, these structures can be discovered and they reveal the existence of communities formed by users of similar profile (that are connected among them) interrelated with other similar profile users’ communities. 相似文献
80.
The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO2 catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO2) are discussed. 相似文献