全文获取类型
收费全文 | 14007篇 |
免费 | 1040篇 |
国内免费 | 311篇 |
专业分类
电工技术 | 72篇 |
综合类 | 145篇 |
化学工业 | 3459篇 |
金属工艺 | 1014篇 |
机械仪表 | 3773篇 |
建筑科学 | 100篇 |
矿业工程 | 30篇 |
能源动力 | 198篇 |
轻工业 | 689篇 |
水利工程 | 15篇 |
石油天然气 | 69篇 |
武器工业 | 8篇 |
无线电 | 1192篇 |
一般工业技术 | 4147篇 |
冶金工业 | 110篇 |
原子能技术 | 125篇 |
自动化技术 | 212篇 |
出版年
2024年 | 15篇 |
2023年 | 165篇 |
2022年 | 264篇 |
2021年 | 332篇 |
2020年 | 331篇 |
2019年 | 373篇 |
2018年 | 341篇 |
2017年 | 462篇 |
2016年 | 462篇 |
2015年 | 481篇 |
2014年 | 639篇 |
2013年 | 836篇 |
2012年 | 785篇 |
2011年 | 1138篇 |
2010年 | 858篇 |
2009年 | 864篇 |
2008年 | 801篇 |
2007年 | 662篇 |
2006年 | 705篇 |
2005年 | 564篇 |
2004年 | 507篇 |
2003年 | 502篇 |
2002年 | 463篇 |
2001年 | 304篇 |
2000年 | 265篇 |
1999年 | 260篇 |
1998年 | 258篇 |
1997年 | 245篇 |
1996年 | 173篇 |
1995年 | 157篇 |
1994年 | 130篇 |
1993年 | 113篇 |
1992年 | 94篇 |
1991年 | 116篇 |
1990年 | 101篇 |
1989年 | 89篇 |
1988年 | 98篇 |
1987年 | 74篇 |
1986年 | 74篇 |
1985年 | 85篇 |
1984年 | 70篇 |
1983年 | 53篇 |
1982年 | 32篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
The oxidation behavior of Ni—20Cr foils of 100- and 200-m thickness wasstudied in air between 500 and 900°C. Simultaneously, the morphology,microstructure, and composition of the oxide layers were determined byscanning and transmission electron microscopies. Depending on thetemperature, the oxide layer differed significantly. The scale formedat all temperatures was complex, with an outer NiO layer having columnargrains, and an inner layer of equiaxedNiCr2O4+NiO+Cr2O3 grains. At low temperatures (500 and 600°C),the chromium content was insufficient to form a continuousCr2O3 layer, while such a continuous layer formed at theinner interface at oxidation temperatures of 700 to 900°C. At 600°C,internal oxidation of chromium occurred in the substrate. The oxidationmechanism is described taking into account these morphologies and theoxidation kinetics. The observation of no significant differences betweenthe oxidation behavior of thin strips and thick materials is related to thelimited exposure times of the study. 相似文献
133.
Effects of intermetallic compound on the electrical and mechanical properties of friction welded Cu/Al bimetallic joints during annealing 总被引:11,自引:0,他引:11
Al/Cu metal joints applied for the electrical connector was joined by the friction welding method to limit the formation of intermetallic compound under optimum friction welding condition. To guarantee the reliability of the Al/Cu joints in service requirement, the effects of the intermetallic compound layer on the electrical and mechanical properties have been investigated under various annealing conditions. Two kinds of intermetallic compounds layer were formed in the joints interface and identified by AlCu and Al2Cu. The growth kinetic of these intermetallics during the annealing can be followed by volume diffusion process. The activation energy of Al2Cu, AlCu and total intermetallic compound (AlCu + Al2Cu) represented 107.5, 98.42 and 110.22 kJ/mol, respectively. A thicker intermetallic compound layers could seriously degrade the electrical resistivity and tensile strength. The electrical resistivity with 21 μm thickness of intermetallic compound was 45 μΩ cm and increased to be 85 μΩ cm with 107 μm of intermetallic compound. Tensile strength remarkably decreased from 85 MPa to near zero at the annealing condition of 773 K and 129.6 ks and fracture occurred through the intermetallic compound layers. 相似文献
134.
Mingru Zhang Jianqing Qian Haicheng Gu 《Journal of Materials Engineering and Performance》2007,16(5):635-639
Metallographic structures of carbide-free bainite steel wheel rim are mainly composed of supersaturated lath ferrite and retained
austenite film among bainitic ferrite laths. It is suspected that supersaturated ferrite and retained austenite are likely
to decompose under the influence of temperature change and mechanical stress. Stability of wheel rim structure is studied
by means of x-ray diffraction, dye microscopy, and micro-hardness test. When the samples are tempered in the range of 150-350 °C,
the retained austenite films are at the state of relative stability. Fifty percent of retained austenite is decomposed when
the sample is tempered at 400 °C. Microhardness increases when the sample is tempered at 150 °C. The decrease in hardness
is mild when the samples are tempered from 200 to 500 °C. The mechanical stability of retained austenite film is studied with
tensile sample under the effect of tensile stress. The retained austenite appears to be stable in low and middle degree of
deformation, and decomposition occurs at great amount of deformation. Diffraction peak of carbide is not found in all above
experiments. The steel enriched silicon prevents the carbide precipitation during the transformation. It indicates the carbide-free
bainite wheel steels have an excellent thermal and mechanical stability. 相似文献
135.
《Ceramics International》2020,46(10):15851-15857
136.
Ji-Er Huang 《Carbon》2003,41(14):2731-2736
Single-walled carbon nanotube (SWNT)/polyaniline (PANI) composite films with good uniformity and dispersion were prepared by electrochemical polymerization of aniline containing well-dissolved SWNTs. The results of atomic force microscopy (AFM) and UV-Vis adsorption spectroscopy show that aniline can be used to solubilize SWNTs via formation of donor-acceptor complexes. The electrochemical deposition of SWNT-aniline solutions have been investigated by cyclic voltammetry. The results show that SWNT-based aniline solutions exhibit a drastic increase in peak current within the potential scanning region. The doping effect of SWNTs on PANI films was investigated by electrochemistry and FTIR spectroscopy. The results indicate that the enhanced electroactivity and conductivity of the SWNT/PANI composite films may be due to the strong interaction between SWNTs and PANI, which facilitates the effective degree of electron delocalization. 相似文献
137.
Perylene-sensitized multi-walled carbon nanotubes (PV-MWNT) have been prepared by a π-stacking between nanotubes and perylene derivatives, N,N′-diphenyl glyoxaline-3,4,9,10-perylene tetracarboxylic acid diacidamide (PV). The resultant nanocomposites have been characterized by transmission electron microscope (TEM), UV-vis absorption, photoluminescence (PL) and photocurrent spectra. Long range ordering can be observed in the form of PV-MWNT via π-stacking by TEM. Red-shift in the optical spectra consisting of the UV-vis absorption and PL spectra with the attraction of PV on the surface of the MWNTs were observed. The evident quenching in PL spectra of PV-MWNT was ascribed to the absorption and transfer of recombination energy by MWNT. Photosensitivity spectra demonstrated an increasing photocurrent in the ultraviolet region and a broadening photosensitivity in the red spectral region for solar cells based on PV-MWNT. 相似文献
138.
139.
140.