全文获取类型
收费全文 | 278015篇 |
免费 | 4839篇 |
国内免费 | 831篇 |
专业分类
电工技术 | 5458篇 |
综合类 | 387篇 |
化学工业 | 41757篇 |
金属工艺 | 10773篇 |
机械仪表 | 8923篇 |
建筑科学 | 7091篇 |
矿业工程 | 1197篇 |
能源动力 | 6724篇 |
轻工业 | 25400篇 |
水利工程 | 2681篇 |
石油天然气 | 3934篇 |
武器工业 | 72篇 |
无线电 | 35832篇 |
一般工业技术 | 54791篇 |
冶金工业 | 47055篇 |
原子能技术 | 5577篇 |
自动化技术 | 26033篇 |
出版年
2021年 | 2450篇 |
2020年 | 1878篇 |
2019年 | 2352篇 |
2018年 | 4092篇 |
2017年 | 4175篇 |
2016年 | 4448篇 |
2015年 | 2929篇 |
2014年 | 4802篇 |
2013年 | 12765篇 |
2012年 | 7443篇 |
2011年 | 9965篇 |
2010年 | 7908篇 |
2009年 | 8696篇 |
2008年 | 9613篇 |
2007年 | 9515篇 |
2006年 | 8475篇 |
2005年 | 7685篇 |
2004年 | 7328篇 |
2003年 | 7164篇 |
2002年 | 6826篇 |
2001年 | 6820篇 |
2000年 | 6492篇 |
1999年 | 6519篇 |
1998年 | 14460篇 |
1997年 | 10497篇 |
1996年 | 8301篇 |
1995年 | 6615篇 |
1994年 | 5874篇 |
1993年 | 5720篇 |
1992年 | 4693篇 |
1991年 | 4334篇 |
1990年 | 4155篇 |
1989年 | 3885篇 |
1988年 | 3715篇 |
1987年 | 3268篇 |
1986年 | 3145篇 |
1985年 | 3765篇 |
1984年 | 3560篇 |
1983年 | 3152篇 |
1982年 | 2964篇 |
1981年 | 3094篇 |
1980年 | 2872篇 |
1979年 | 2738篇 |
1978年 | 2593篇 |
1977年 | 3029篇 |
1976年 | 3632篇 |
1975年 | 2401篇 |
1974年 | 2389篇 |
1973年 | 2392篇 |
1972年 | 1886篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
T. Galvin N.C. Hyatt W.M. Rainforth I.M. Reaney D. Shepherd 《Journal of the European Ceramic Society》2018,38(14):4585-4589
The molten salt method was used to synthesise the MAX phase compounds Ti2AlC and Ti3AlC2 from elemental powders. Between 900–1000?°C, Ti2AlC was formed alongside ancillary phases TiC and TiAl, which decreased in abundance with increasing synthesis temperature. Changing the stoichiometry and increasing the synthesis temperature to 1300?°C resulted in formation of Ti3AlC2 alongside Ti2AlC and TiC. The type of salt flux used had little effect on the product formation. The reaction pathway for Ti2AlC was determined to be the initial formation of TiC1-x templating on the graphite and titanium aluminides. 相似文献
132.
Hierarchical micro-nanostructured albite-based glass-ceramic for high dielectric strength insulators
V. Fuertes M.J. Cabrera J. Seores D. Muñoz J.F. Fernández E. Enríquez 《Journal of the European Ceramic Society》2018,38(7):2759-2766
A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94%?Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1?MHz, low dielectric losses, (~10?3 at 1?MHz, and a large dielectric strength, ~60?kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications. 相似文献
133.
Shchelkunov E. B. Vinogradov S. V. Shchelkunova M. E. Pronin A. I. Buravitsyn D. A. 《Russian Engineering Research》2020,40(5):367-371
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the... 相似文献
134.
Application of high‐temperature Fenton oxidation for the treatment of sulfonation plant wastewater
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
135.
136.
137.
This study addresses the thermo‐diffusion and the diffusion‐thermo phenomena in a semi‐infinite absorbent channel whose walls are contracting/expanding, with heat source/sink effects. The governing partial differential equations with suitable boundary conditions are transformed to a system of dimensionless ordinary differential equations. An analytic solution of the problem has been found using a technique called homotopy analysis method (HAM). HAM gives consistently valid answers to the problem over an extensive variety of parameters and also provides better accuracy. To validate the analytical results, a comparison has been presented with a numerical solution calculated by using the parallel shooting method. The effects of dimensionless parameters, that is, deformation parameter, Reynolds number, Soret and Dufour numbers, and heat source/sink parameter on the expressions of velocity, temperature, and concentration profiles are analyzed graphically to understand the physics of the deformable channel. It has been noted that the velocity across the channel is higher for the expanding channel, as compared to that for the contracting channel. Also the Soret and Dufour number increases the temperature of the fluid, and decreases the concentration. The temperature profile has an increasing behavior in the case of heat source, and a decreasing behavior in the case of heat sink. 相似文献
138.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
139.
D. A. Kudryashov A. S. Gudovskikh A. M. Mozharov A. D. Bol’shakov I. S. Mukhin Zh. I. Alferov 《Technical Physics Letters》2015,41(12):1120-1123
Design and operation modes of double-junction monolithic lattice-matched solar cells based on the ZnSiP2/Si system of materials have been calculated. The effect of the photoactive region thickness and minority carrier lifetime in ZnSiP2 layers on the efficiency of conversion of the incident solar light energy into electrical power was determined. It is shown that solar cells based on ZnSiP2/Si heterostructures can provide efficiencies of 28.8% at AM1.5D, 100 mW/cm2, and 33.3% at AM1.5D, 200 W/cm2. 相似文献
140.
Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献