全文获取类型
收费全文 | 2763篇 |
免费 | 65篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 33篇 |
综合类 | 9篇 |
化学工业 | 903篇 |
金属工艺 | 142篇 |
机械仪表 | 88篇 |
建筑科学 | 122篇 |
矿业工程 | 17篇 |
能源动力 | 248篇 |
轻工业 | 188篇 |
水利工程 | 14篇 |
石油天然气 | 34篇 |
无线电 | 156篇 |
一般工业技术 | 553篇 |
冶金工业 | 35篇 |
原子能技术 | 13篇 |
自动化技术 | 279篇 |
出版年
2024年 | 1篇 |
2023年 | 51篇 |
2022年 | 49篇 |
2021年 | 69篇 |
2020年 | 99篇 |
2019年 | 79篇 |
2018年 | 54篇 |
2017年 | 155篇 |
2016年 | 160篇 |
2015年 | 123篇 |
2014年 | 160篇 |
2013年 | 178篇 |
2012年 | 145篇 |
2011年 | 164篇 |
2010年 | 124篇 |
2009年 | 169篇 |
2008年 | 116篇 |
2007年 | 162篇 |
2006年 | 130篇 |
2005年 | 94篇 |
2004年 | 62篇 |
2003年 | 89篇 |
2002年 | 60篇 |
2001年 | 51篇 |
2000年 | 38篇 |
1999年 | 44篇 |
1998年 | 28篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 4篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 16篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有2834条查询结果,搜索用时 31 毫秒
51.
S. L. Correia A. P. N. Oliveira D. Hotza A. M. Segadães 《Journal of the American Ceramic Society》2006,89(11):3356-3365
The effect of raw materials type and content on the properties of clay–feldspar–quartz compositions was studied using the statistical design of mixture experiments. Based on wall and floor tile industrial practice, 10 mixtures of three raw materials were selected and processed. Characterization results were used to calculate statistically significant and valid regression equations, relating fired body properties with clay, feldspar, and quartz contents in the unfired mixture. Such statistical modeling is discussed against quantitative X-ray diffraction and scanning electron microscopy results. The glassy phase present was found to control the microstructure and the mechanical strength of the fired ceramic body. 相似文献
52.
Summary In 1985 China began the reform of its Science & Technology (S&T) sector inherited from the planned economy. To disclose the
impact of the drawn-out reform on the efficiency of the whole sector, we measure the scientific productivity of China's S&T
institutes. The analysis is based on R&D input and output data at the country aggregate and provincial level. We utilize Polynomial
Distributed Lag model to uncover the structure of the lag between R&D input and output. The findings reveal that the growth
rate of scientific productivity of China's S&T institutes has been negative since the 1990s. 相似文献
53.
Guanghua Liu Kexin Chen Heping Zhou Xiaoshan Ning C. Pereira J. M. F. Ferreira 《Journal of Materials Science》2006,41(6):1791-1796
Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion
synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development,
and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the
added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals
the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk
density and hardness at the same time. 相似文献
54.
This paper reports on the affect of lead content on the absorption and emission spectra of the Ho3+ ion doped lead-zinc-borate glasses in the composition (mol%) of (20 − x)PbO-20ZnO-(59 + x)B2O3-1.0Ho2O3 where x = 0, 5,10,15 of PbO content with λexc = 405 nm. The experimental absorption band energies have satisfactorily been correlated with the theoretical results with an r.m.s deviation of zero with the following correction factors obtained by a least square fit analysis: ΔE1 = 348.495936 cm− 1, ΔE2 = 1.436043 cm− 1, ΔE3 = 46.481575 cm− 1, Δξ4f = − 28.512979 cm− 1, Δα = 55.508936 cm− 1, Δβ = − 1394.339908 cm− 1 and Δγ = 1208.424336 cm− 1. By applying the Judd-Ofelt intensity parameter Ω2 has been found to be linearly decreasing with the PbO content from 5 to 10 mol% and then increasing. And also radiative (A, AT, β, τr) characteristic factors of the luminescent transitions (5I8 ← 5F3,4,5 and 5S2) of the glasses have been evaluated. Stimulated emission cross-sections (σpE) of the measured emission transitions of holmium glasses have also been computed. 相似文献
55.
《Materials Research Bulletin》2006,41(3):547-552
In this paper, (Ca + Yb)- and (Ca + Sr)-stabilized α-SiAlON powders were fabricated by combustion synthesis. The influence of Ca2+ incorporation on the phase composition and grain morphology of combustion products was discussed. The experimental results showed that with the incorporation of Ca2+ well-developed rod-like (Ca + Yb) α-SiAlON crystals could be produced. It was also found that, when only Sr2+ was used as stabilizing cation, the reaction product was (α + β)-SiAlON composite, in which β-SiAlON was the predominant phase and the relative content of α-SiAlON was low. With the incorporation of Ca2+, however, both the relative content and the lattice parameters of α-SiAlON were clearly increased. These results indicated that the incorporation of Ca2+ could assist Sr2+ into the α-SiAlON lattice structure. 相似文献
56.
《Materials Research Bulletin》2006,41(7):1259-1265
ZnO bulk porous nanosolids were prepared by a novel solvothermal hot press (STHP) method with different pore-forming agents using ZnO nanoparticles. The samples were characterized with SEM, XRD, FTIR, a mercury intrusion porosimeter and N2 adsorption–desorption method. Experimental results showed that pore size of the nanosolids was between 20–32 and 20–100 nm when de-ionized water and CTAB solution were used as pore-forming agents, respectively. There was no obvious morphological change in the samples when all pore-forming agents were removed from the autoclave. 相似文献
57.
《Materials Science and Engineering: B》2006,126(2-3):148-150
Ferromagnetism persisting above 375 K and anisotropic ferromagnetic resonance (FMR) spectra have been detected for the first time in Si co-implanted with Mn and As and annealed under appropriate conditions. For comparison, semi-insulating GaAs samples have been implanted with the same ions and subsequently annealed. They also exhibit ferromagnetism with a Curie temperature well in excess of 375 K. High-resolution transmission electron microscopy (HR TEM) performed on the samples with the best magnetic characteristics has shown the presence of nanoclusters due to the segregation of the implanted species in both Si and GaAs. The angular dependence of the FMR spectra reveals the existence of magnetic entities with the hard magnetization axes aligned along the four equivalent 〈1 1 1〉 crystal axes. The spectra are very similar in Si and GaAs, indicating that hexagonal MnAs clusters might be formed in Si. 相似文献
58.
R.C. Picu G. Vincze F. Ozturk J.J. Gracio F. Barlat A.M. Maniatty 《Materials Science and Engineering: A》2005,390(1-2):334-343
The mechanical behavior of the commercial aluminum alloy AA5182-O is investigated at temperatures ranging from −120 to 150 °C and strain rates from 10−6 to 10−1 s−1. The strain rate sensitivity parameter is determined as a function of temperature and plastic strain, and the strain rate and temperature range in which dynamic strain aging leads to negative strain rate sensitivity is mapped. The effect of dynamic strain aging on ductility and strain hardening is investigated. The sensitivity of the measured quantities to the experimental method employed and their dependence on grain shape are discussed. The experimental data are compared with the predictions of a model constructed based on a recently proposed mechanism for dynamic strain ageing. The mechanism is based on the effect solute clustering at forest dislocations has on the strength of dislocation junctions. The model is shown to reproduce qualitatively the experimental trends. 相似文献
59.
Balamurugan A Benhayoune H Kannan S Laquerriere P Michel J Balossier G Ferreira JM 《Microscopy research and technique》2008,71(9):684-688
The present study deals with the short-term physicochemical reactions at the interface between bioactive glass particles [55SiO(2)-20CaO-9P(2)O(5)-12Na(2)O-4MgO. mol%] and biological fluid (Dulbecco Modified Eagle's Medium (DMEM)). The physicochemical reactions within the interface are characterized by scanning transmission electron microscopy (TEM) (STEM) associated with Energy-dispersive X-ray spectroscopy (EDXS). Microanalysis of diffusible ions such as sodium, potassium, or oxygen requires a special care. In the present investigation the cryo-technique was adopted as a suitable tool for the specimen preparation and characterization. Cryosectioning is essential for preserving the native distribution of ions so that meaningful information about the local concentrations can be obtained by elemental microanalysis. The bioglass particles immersed in biological fluid for 24 h revealed five reaction stages: (i) dealkalization of the surface by cationic exchange (Na(+), Ca(2+) with H(+) or H(3)O(+)); (ii) loss of soluble silica in the form of Si(OH)(4) to the solution resulting from the breakdown of Si--O--Si bonds (iii); repolymerization of Si(OH)(4) leading to condensation of SiO(2)); (iv) migration of Ca(2+) and PO(4) (3-) to the surface through the SiO(2)-rich layer to form CaO-P(2)O(5) film; (v) crystallization of the amorphous CaO-P(2)O(5) by incorporating OH-- or CO(3) (2-) anions with the formation of three different surface layers on the bioactive glass periphery. The thickness of each layer is approximately 300 nm and from the inner part to the periphery they consist of Si--OH, which permits the diffusion of Ca(2+) and PO(4) (3-) ions and the formation of the middle Ca--P layer, and finally the outer layer composed of Na--O, which acts as an ion exchange layer between Na(+) ions and H(+) or H(3)O(+) from the solution. 相似文献
60.
《Wear》2007,262(5-6):649-654
This paper fabricated tungsten carbide (WC) particles reinforced iron matrix surface composites on gray cast iron substrate using vacuum evaporative pattern casting (V-EPC) infiltration process, investigated dry three-body abrasive wear resistance of the composites containing different volume fractions of WC particles, comparing with a high chromium cast iron. The fabricated composites contained WC particles of 5, 10, 19, 27, 36, and 52 vol.%, respectively. The results in abrasive wear tests showed that, with the increase in the volume fraction of WC particles, the wear resistance of the composites first increased until reached the maximum when the volume fraction of WC was 27%, then decreased, and was 1.5–5.2 times higher than that of the high chromium cast iron. The changes of the wear resistance of the composites with the volume fraction of WC particles and the mode of material removal in dry three-body abrasive wear condition were analyzed. 相似文献