全文获取类型
收费全文 | 1215篇 |
免费 | 109篇 |
国内免费 | 94篇 |
专业分类
电工技术 | 28篇 |
综合类 | 44篇 |
化学工业 | 213篇 |
金属工艺 | 73篇 |
机械仪表 | 76篇 |
建筑科学 | 15篇 |
矿业工程 | 13篇 |
能源动力 | 57篇 |
轻工业 | 119篇 |
水利工程 | 1篇 |
石油天然气 | 19篇 |
无线电 | 347篇 |
一般工业技术 | 268篇 |
冶金工业 | 23篇 |
原子能技术 | 56篇 |
自动化技术 | 66篇 |
出版年
2024年 | 7篇 |
2023年 | 22篇 |
2022年 | 46篇 |
2021年 | 53篇 |
2020年 | 50篇 |
2019年 | 43篇 |
2018年 | 23篇 |
2017年 | 38篇 |
2016年 | 43篇 |
2015年 | 46篇 |
2014年 | 60篇 |
2013年 | 73篇 |
2012年 | 64篇 |
2011年 | 77篇 |
2010年 | 64篇 |
2009年 | 37篇 |
2008年 | 63篇 |
2007年 | 49篇 |
2006年 | 59篇 |
2005年 | 43篇 |
2004年 | 48篇 |
2003年 | 41篇 |
2002年 | 36篇 |
2001年 | 33篇 |
2000年 | 27篇 |
1999年 | 21篇 |
1998年 | 38篇 |
1997年 | 28篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 5篇 |
排序方式: 共有1418条查询结果,搜索用时 15 毫秒
1.
《Advanced Powder Technology》2020,31(12):4585-4597
Focussing on visible light active ferrites for high performance removal of noxious pollutants, we report the synthesis of Mg0.5NixZn0.5-xFe2O4 (x = 0.1, 0.2, 0.3, 0.4, & 0.5) ferrite nanoparticle for degradation of reactive blue-19 (RB-19). Lattice parameters calculated using intense X-ray diffraction (XRD) peaks and Nelson-Riley plots (N-R plot) are in well agreement with each other. The sample Mg0.5Ni0.4Zn0.1Fe2O4 (M5N4) exhibits best performance with 99.5% RB-19 degradation in 90 min under visible light. Photoluminescence (PL) results confirm that recombination of charge carriers is highly reduced in the photocatalyst. Scavenging experiments suggest that O2− radicals were the dominant species responsible for photocatalytic performance. The photocatalytic mechanism was explained in terms of dopant driven shifting of conduction bands and valence bands (calculated by Mott-Schottky plots). The thermodynamic probability of radical generation along with role of redox cycles of metal ions has been discussed in the mechanism. The dye degradation was ascertained by detection of intermediates via mass spectrometry analysis and a possible degradation route was also predicted. The findings in this work provide intriguing opportunities to modify the electronic band structure of spinel ferrites for visible and solar light photocatalytic activity for environmental detoxification. 相似文献
2.
研究了电子束、离子束作用于Al2O3表面时成分的变化,表明无论电子束或离子束都能使Al2O3发生分解,产生导电的元素Al。实验在PHI610·SAM上进行,电子束轰击下(3keV,O.5μA,入射角60°)10s就有元素Al分解出来,2min以后就达到饱和,分解析出量随时间成a(1-e-bt)的关系。离子束轰击下同样发生元素Al的分解,但当Ei>3keV时,由于剥离速率加大,溅射5min时表面Al峰反而比1min时要弱。这时表面Al含量处于分解析出与溅射剥离的动态平衡中。实验还发现了Al2O3的解析与表面成分有关(如碳的含量)。最后讨论电子束与离子束的解析机理。 相似文献
3.
张庆瑜 《真空科学与技术学报》1996,(1)
着重讨论了TiNx薄膜俄歇电子谱的定量分析方法和X射线光电子谱中线形的变化。利用已知组元强度定量分析技术和Ti的LMV俄歇电子峰,探讨TiNx薄膜中N含量的定量方法。由该方法给出的定量结果与X射线光电子谱定量结果相一致。同时,利用X射线光电子谱测定了TiN和Ti2N2p轨道的结合能。并针对Ti2p峰形随N含量的变化,给出新的解释。 相似文献
4.
V. Gaidarova 《Vacuum》2007,81(9):1082-1087
An investigation of the structure formation of as-cast Al-11 wt% Si (AlSi11) and Al-11 wt% Si-2 wt% Fe (AlSi11Fe2) rapidly solidified (RS) ribbons is performed. Ribbon samples are examined in detail using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). A nanoscale thickness layer of Si-precipitations, at both Al-grains boundary and oxide/Al-matrix interface, is found to be characteristic for “pure” AlSi11 ribbons. For Fe-doped ribbons, this layer comprises Fe-containing phase also, which appears to possess amorphous nature and is situated between the Si-grains and Al-matrix. A possible mechanism of altering the thermally activated volume diffusion of elements, due to the effect of Fe on the structure modification, is speculated based on the obtained results. 相似文献
5.
M. R. Islam R. V. Chelakaea J. G. Neff K. G. Fertitta P. A. Grudowski A. L. Holmes F. J. Ciuba R. D. Dupuis J. E. Fouquet 《Journal of Electronic Materials》1995,24(6):787-792
AlGaAs double heterostructures are grown by low-pressure metalorganic chemical vapor deposition to evaluate the level of oxygen
contamination in different trimethylaluminum sources. Effects of arsine purifiers, misoriented substrates, atmospheric exposure
of the growth chamber, and possible phosphorus contamination are also studied. Extensive characterization is performed on
these films by a variety of methods, including high-resolution x-ray diffraction, photoluminescence (PL), time-resolved photoluminescence,
and secondary-ion mass spectrometry. The PL intensities for structures grown with the low-alkoxide grade are reproducibly
much greater than those grown with the regular-grade TMA1. The use of AsH3 purification improves the PL intensity. 相似文献
6.
Seong Hyuk Lee Junghee Lee Kwan-Gu Kang Joon Sik Lee 《Journal of Mechanical Science and Technology》2006,20(8):1292-1301
This article investigates numerically the carrier-phonon interactions in thin gallium arsenide (GaAs) film structures irradiated
by subpicosecond laser pulses to figure out the role of several recombination processes on the energy transport during laser
pulses and to examine the effects of laser fluences and pulses on non-equilibrium energy transfer characteristics in thin
film structures. The self-consistent hydrodynamic equations derived from the Boltzmann transport equations are established
for carriers and two different types of phonons, i.e., acoustic phonons and longitudinal optical (LO) phonons. From the results,
it is found that the two-peak structure of carrier temperatures depends mainly on the pulse durations, laser fluences, and
nonradiative recombination processes, two different phonons are in nonequilibrium state within such lagging times, and this
lagging effect can be neglected for longer pulses. Finally, at the initial stage of laser irradiation, SRH recombination rates
increases sufficiently because the abrupt increase in carrier number density no longer permits Auger recombination to be activated.
For thin GaAs film structures, it is thus seen that Auger recombination is negligible even at high temperature during laser
irradiation. 相似文献
7.
Yeast mutants with increased bacterial transposon Tn5 excision 总被引:7,自引:0,他引:7
D A Gordenin Y Y Proscyavichus A L Malkova M V Trofimova A Peterzen 《Yeast (Chichester, England)》1991,7(1):37-50
Five complementing recessive mutations that exhibit increased bacterial transposon Tn5 precise excision in yeast Saccharomyces cerevisiae were obtained by ethylmethanesulfonate treatment. One of these mutations (tex1) was submitted to extensive genetic analysis. tex1 is a recessive temperature-sensitive mutation resulting in a 20-100-fold increase in Tn5 excision. It also has increased frequencies of ochre mutation reversion, of forward mutation to canavanine resistance, and loss of chromosome III or its right arm. The possible mechanism of tex1 effects is discussed. 相似文献
8.
9.
The decomposition of NO and of N2O over a CuZSM-5 zeolite and a Fe-mordenite, respectively, has been studied using tracer techniques. The results demonstrate the high mobility of the lattice oxygen ions in self-diffusion. They afford a possible explanation for the problem of how two extralattice oxygens located at positions remote from each other may combine to form the O2 molecules which are spontaneously desorbed in these redox reactions. They show that a portion of the lattice oxygen mixes into the O2 released on decomposition. The data also show that N18O and N2
18O undergo exchange with the catalyst oxygen under reaction conditions.On leave from Central Research Institute for Chemistry, Hungarian Academy of Sciences, H-1525 Budapest, Hungary. 相似文献
10.
Fe-30Ni alloy specimens were oxidized for 10–240 min at 433–473 K in pure oxygen at a pressure of 1.33×104 Pa. The thickness of oxide films was measured by a multiple-angle-of-incidence ellipsometer. The kinetics of film growth were found to obey a parabolic rate law. The depth-profiling of oxidized surfaces, performed with simultaneous use of Auger electron spectroscopy (AES) and argon-ion sputter-etching technique, reveals that iron component is selectively oxidized and an iron-depeletion zone is formed in the underlying alloy. The thickness of the iron depletion zone increases with increasing oxidation time or oxidation temperature. During surface oxidation of the alloy, the transport rate of iron component in the film is almost equal to the interdiffusion rate in the underlying alloy, indicating the establishment of a steady state. The values of the interdiffusion coefficient,
, of the underlying alloy estimated from the depth-composition profiles are more than 10 orders of magnitude as large as the values extrapolated from the lattice diffusion data of the corresponding alloy obtained at high temperature. The enormously large values of
may be explained in terms of the vacancy (monovacancy or divacancy)-enhanced lattice diffusion mechanism. 相似文献