全文获取类型
收费全文 | 59548篇 |
免费 | 4515篇 |
国内免费 | 2826篇 |
专业分类
电工技术 | 883篇 |
技术理论 | 1篇 |
综合类 | 3819篇 |
化学工业 | 29724篇 |
金属工艺 | 2757篇 |
机械仪表 | 1060篇 |
建筑科学 | 878篇 |
矿业工程 | 626篇 |
能源动力 | 3836篇 |
轻工业 | 3943篇 |
水利工程 | 164篇 |
石油天然气 | 3311篇 |
武器工业 | 614篇 |
无线电 | 2665篇 |
一般工业技术 | 7686篇 |
冶金工业 | 1765篇 |
原子能技术 | 741篇 |
自动化技术 | 2416篇 |
出版年
2024年 | 173篇 |
2023年 | 1191篇 |
2022年 | 1587篇 |
2021年 | 1884篇 |
2020年 | 1848篇 |
2019年 | 1724篇 |
2018年 | 1639篇 |
2017年 | 1811篇 |
2016年 | 1889篇 |
2015年 | 1800篇 |
2014年 | 2852篇 |
2013年 | 3152篇 |
2012年 | 3562篇 |
2011年 | 4210篇 |
2010年 | 3166篇 |
2009年 | 3446篇 |
2008年 | 3009篇 |
2007年 | 3860篇 |
2006年 | 3469篇 |
2005年 | 3112篇 |
2004年 | 2633篇 |
2003年 | 2418篇 |
2002年 | 2154篇 |
2001年 | 1840篇 |
2000年 | 1596篇 |
1999年 | 1335篇 |
1998年 | 1064篇 |
1997年 | 814篇 |
1996年 | 717篇 |
1995年 | 582篇 |
1994年 | 551篇 |
1993年 | 418篇 |
1992年 | 312篇 |
1991年 | 225篇 |
1990年 | 196篇 |
1989年 | 120篇 |
1988年 | 98篇 |
1987年 | 80篇 |
1986年 | 40篇 |
1985年 | 45篇 |
1984年 | 52篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1964年 | 9篇 |
1955年 | 8篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
K Madhusudan Reddy Sunkara V Manorama R.D.K Misra 《Materials Research Bulletin》2004,39(10):1491-1498
A comparative study of gas sensing behavior of nanocrystalline nickel ferrite synthesized by micro-emulsion and hydrothermal method to liquefied petroleum gas (LPG) is presented. Nanocrystalline nickel ferrite synthesized by hydrothermal method indicated higher electrical conductivity and gas sensitivity at low operating temperature compared to nanocrystalline nickel ferrite synthesized by reverse micelle technique. This difference in the gas sensing behavior can be attributed to the presence of more oxygen vacancies (i.e. non-stoichiometry) in the hydrothermally synthesized nickel ferrite. Incorporation of palladium had a catalytic effect and the operating temperature was significantly reduced in both the samples. The higher operating temperature of the reverse micelle nickel ferrite material makes the sensor response speed faster (∼10 s) compared to the hydrothermally synthesized material (∼1 min). 相似文献
23.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
24.
O. Khamman 《Materials Letters》2007,61(3):639-643
The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb2O6) powders. The formation of the NiNb2O6 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb2O5 precursors and the Ni4Nb2O9 phase tend to form together with the columbite NiNb2O6 phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb2O6 in an orthorhombic phase. 相似文献
25.
G. N. Churilov R. B. Weisman N. V. Bulina N. G. Vnukova A. P. Puzir L. A. Solovyov S. M. Bachilo D. A. Tsyboulski G. A. Glushenko 《Fullerenes, Nanotubes and Carbon Nanostructures》2003,11(4):371-382
The addition of metallic Ir and Pt to a fullerene-forming, atmospheric-pressure plasma reactor was found to influence the generation of carbonaceous products. It was observed that the added metals were efficiently dispersed into the plasma and that their presence increased the yield of fullerenes. The addition of Ir led to a noticeable shift in the fullerene distribution towards C60, whereas the addition of Pt increased the proportion of C60 oxides and decreased the proportion of higher fullerenes. Addition of Ir also caused a reduction of the soot particle size and the formation of a considerable quantity of carbon nanotubes. 相似文献
26.
R. Wongmaneerung W. Chaisan O. Khamman R. Yimnirun S. Ananta 《Ceramics International》2008,34(4):813-817
The potential of the vibro-milling technique as a simple method to obtain usable quantities of single-phase electroceramic powders with nanosized particles was examined. A detailed study considering the role of both milling time and firing condition on phase formation and particle size of the final product was performed. The calcination temperature for the formation of the desired phase was lower when longer milling times have been applied. More importantly, by employing an appropriate choice of the milling time and calcination condition, high purity electroceramic nanopowders have been successfully prepared with a simple solid-state reaction method. 相似文献
27.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
28.
The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in A1-TiO2-B2O3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al2O3 is the lowest among all the combustion products, followed by TiB2 and Al3Ti. It is noted that when the B2O3/TiO2 mole ratio is below 1, the reaction products are composed of particle-like α-Al2O3, TiB2 and rod-like Al3Ti. The α-Al2O3 crystallites, resulting from the reaction between A1 and TiO2 or B2O3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al3Ti phase distributes uniformly in the matrix. When the BEO3/TiO2 mole ratio is around 1, the Al3Ti phase almost disappears in the composites, and the distribution of α-Al2O3 particulates is improved evidently. 相似文献
29.
Calculations and detailed first principle and thermodynamic analyses have been performed to understand the formation mechanism of K2Ti6O13 nanowires (NWs) by a hydrothermal reaction between bulk Na2Ti3O7 crystals and a KOH solution. It is found that direct ion exchange between K+ and Na+ plus H+ interactions with [TiO6] octahedra in Na2Ti3O7 promote the formation of an intermediate H2K2Ti6O14 phase. The large lattice mismatch between this intermediate phase and the bulk Na2Ti3O7 structure, and the large energy reduction associated with the formation of this intermediate phase, drive the splitting of the bulk crystal into H2K2Ti6O14 NWs. However, these NWs are not stable because of large [TiO6] octahedra distortion and are subject to a dehydration process, which results in uniform K2Ti6O13 NWs with narrowly distributed diameters of around 10 nm. 相似文献
30.