全文获取类型
收费全文 | 575篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 82篇 |
金属工艺 | 14篇 |
机械仪表 | 12篇 |
建筑科学 | 18篇 |
能源动力 | 31篇 |
轻工业 | 40篇 |
水利工程 | 9篇 |
石油天然气 | 1篇 |
无线电 | 94篇 |
一般工业技术 | 116篇 |
冶金工业 | 80篇 |
原子能技术 | 2篇 |
自动化技术 | 85篇 |
出版年
2023年 | 4篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 12篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 28篇 |
2015年 | 7篇 |
2014年 | 25篇 |
2013年 | 40篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 22篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 34篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 7篇 |
1994年 | 15篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 6篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有590条查询结果,搜索用时 15 毫秒
31.
The wear and friction properties of poly (ether‐ether‐ketone) (PEEK) reinforced with 0–33 vol % (60 wt %) micron size Al2O3 composites were evaluated at a sliding speed of 1.0 m/s and nominal pressure from 0.5 to 1.25 MPa under dry sliding conditions using a pin‐on‐disk wear tester. The wear resistance of the pure PEEK is 10‐fold higher than that of mild steel under the similar test condition. It is improved to 18‐fold as compared with mild steel at 3.5 vol % Al2O3 content. The improvement in wear properties may be attributed to the thin, tenacious, and coherent transfer film formed between the steel countersurface and composite pin. However, the wear resistance of PEEK containing above 3.5 vol % Al2O3 was deteriorated, despite their higher hardness and stiffness as compared with that of composites containing lower Al2O3 content. This is attributed to the formation of thick and noncoherent transfer film, which does not prevent the wear of the composites from hard asperities of countersurface. Moreover, hard Al2O3 particles present in transfer film act as third body wear mechanism. The coefficient of friction of the composites is higher than that of pure PEEK. SEM and optical microscopy have shown that wear of pure PEEK occurs by the mechanism of adhesion mainly whereas of PEEK composites by microploughing and abrasion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
32.
The powder synchrotron X-ray diffraction pattern of a mixed sodium–silver–Y zeolite, Ag56−xNaxSi136Al56O384 x≈19, saturated with pyridine, has been analysed by the Rietveld method to reveal positions for the adsorbed molecules. Cations are distributed over three sites, SII, constrained to 100% occupancy, with 17.2(1) and 14.8(1) Ag(1) and Na(1) ions per unit cell, respectively, SI′ with 18.3(1) Ag(2) ions per cell, and SI with 1.8(1) Ag(3) ions per cell. The refinement suggests that approximately 7.5 pyridine molecules are adsorbed per supercage, located in two sites within the cavities of the zeolite. Pyridine(1) is in the 12-ring window connecting supercages. Three molecules project through each window and approach the SII cations in a supercage, with an average Ag(1)–N distance of 3.17(2) Å. An SII cation can be linked to three pyridine(1) molecules from three separate windows. These sites are full with 5.98(2) molecules per supercage. Pyridine(2) is found in the supercage, oriented with its π electron density towards the SII cations, with its centre at 2.87(2) Å from Ag(1). The average occupancy was fixed at 1.5 molecules per supercage, corresponding to 20% of the pyridine content. A local ordering scheme can be postulated, whereby alternate supercages are filled by pyridine(1) and pyridine(2) molecules, efficiently filling the channels of the zeolite. 相似文献
33.
Corrosion in the overhead condensing system of atmospheric distillation units is a common occurrence in petroleum refineries worldwide. These corrosion problems are influenced by the presence of three phases: vapours, liquid hydrocarbons and aqueous phase containing hydrochloric acid formed during distillation by decomposition of chloride salts of calcium and magnesium.Present studies highlight the corrosion control of naphtha fractions of Bombay High and Dubai crude oils in laboratory distillation device by chemical treatment using various corrosion inhibitors having different functional groups. These studies were carried out using two phase systems (aqueous-hydrocarbon) in the distillation device having facilities for monitoring the corrosion and temperatures in vapour condensing region and liquid condensate. Corrosion monitoring was carried out by potentiodynamic polarization technique and dissolved iron analysis using inductively coupled plasma atomic emission spectroscopy (ICPAES). Experimental findings indicate that Dubai naphtha fraction is more corrosive in nature when compared to Bombay High naphtha. This observation can also be explained on the basis of characterization of both crude oils and their naphtha fractions. At normally recommended dosage level as in refinery overhead systems, water soluble corrosion inhibitors are more effective than hydrocarbon soluble ones in the vapour condensing region as well as in the liquid condensate of both naphtha fractions. 相似文献
34.
We describe two unusual cases in sheep of subclinical mastitis caused by Streptococcus parasanguinis. This bacterium has been associated with the development of experimental endocarditis; its presence at relatively high concentrations in apparently healthy sheep milk may pose a health risk in persons with predisposing heart lesions. 相似文献
35.
Generally, inventory control policies for deteriorating items are very sensitive to different marketing policies especially in chemical, food and pharmaceutical industries. Realizing the importance of such inventory policies in practice, an integrated production-inventory-marketing model is developed for determining the economic production quantity (EPQ) and economic order quantity (EOQ) for raw materials in a multi-stage production system. This model considers the effect of different marketing policies such as the price per unit product and the advertisement frequency on the demand of a perishable item. A search method is employed to determine the values of EPQ and EOQ which would result in the maximum total net profit. 相似文献
36.
37.
Parametric interactions of X-band Gunn diodes between the frequencies 10 and 20 GHz are studies with the help of a coaxial resonator. A diode is placed at various positions along the central conductor so that different load impedances are applied. Very strong variations in microwave amplitude behaviour of the two frequencies were observed, which indicate pronounced interactive effects. These are studied by measuring the negative-conductance as a function of r.f. diode voltage. So far, only a decrease in fundamental-frequency conductance function has been observed due to the presence of harmonic power. 相似文献
38.
S.?K.?MittalEmail author Samarjit?Goyal 《Clean Technologies and Environmental Policy》2004,6(4):263-267
Concentration levels of suspended particulate matter (SPM), organic tarry matter (BSPM), ignitable matter (LOI) and lead in the ambient air of an urban area are measured by using a high volume sampler. SPM levels in different zones of the city are reported. Organic tarry matter measured as benzene soluble particulate matter (BSPM) constitutes about 4–9% of the SPM. BSPM in the ambient air varies in a range of 10–40 g m–3. Ignitable matter measured as loss on ignition (LOI) forms about 24–40% of the SPM. Absolute values of LOI vary between 50 and 150 g m–3. Concentrations of BSPM, LOI and Pb are correlated to automobile exhaust as the probable source.The studies indicate that BSPM and LOI are integral parts of the SPM but their concentrations are independent of the SPM levels. 相似文献
39.
N. Goyal Abdolali Zolanvari S. K. Tripathi 《Journal of Materials Science: Materials in Electronics》2001,12(9):523-526
The paper reports the effect of dissolution of silver into the chalcogenide As2S3. The conductivity of As2S3 decreases with doping at lower temperatures. The a.c. conductivity is proportional to s for undoped as well as doped samples. The value of the frequency exponent s increases with doping. On the other hand, the dielectric constant of As2S3 also increases with doping and the effect is quite prominent at higher temperatures. A new structural model together with the correlated barrier hopping model has been used to explain these results. © 2001 Kluwer Academic Publishers 相似文献
40.
S. K. Deshpande V. K. Shrikhande M. S. Jogad P. S. Goyal G. P. Kothiyal 《Bulletin of Materials Science》2007,30(5):497-502
The electrical conductivity of lithium zinc silicate (LZS) glasses with composition, (SiO2)0.527 (Na2O)0.054(B2O3)0.05(P2O5)0.029(ZnO)0.34−x
(Li2O)
x
(x = 0.05, 0.08, 0.11, 0.18, 0.21, 0.24 and 0.27), was studied as a function of frequency in the range 100 Hz–15 MHz, over a
temperature range from 546–637 K. The a.c. conductivity is found to obey Jonscher’s relation. The d.c. conductivity (σ
d.c.) and the hopping frequency (ω
h), inferred from the a.c. conductivity data, exhibit Arrhenius-type behaviour with temperature. The electrical modulus spectra
show a single peak, indicating a single electrical relaxation time, τ, which also exhibits Arrhenius-type behaviour. Values of activation energy derived from σ
d.c., ω
h and τ are almost equal within the experimental error. It is seen that σ
d.c. and ω
h increase systematically with Li2O content up to 21 mol% and then decrease for higher Li2O content, indicating a mixed alkali effect caused by mobile Li+ and Na+ ions. The scaling behaviour of the modulus suggests that the relaxation process is independent of temperature but depends
upon Li+ concentration. 相似文献