全文获取类型
收费全文 | 5150篇 |
免费 | 395篇 |
国内免费 | 266篇 |
专业分类
电工技术 | 56篇 |
综合类 | 152篇 |
化学工业 | 1510篇 |
金属工艺 | 319篇 |
机械仪表 | 226篇 |
建筑科学 | 18篇 |
矿业工程 | 33篇 |
能源动力 | 149篇 |
轻工业 | 385篇 |
水利工程 | 5篇 |
石油天然气 | 68篇 |
武器工业 | 8篇 |
无线电 | 1182篇 |
一般工业技术 | 1489篇 |
冶金工业 | 75篇 |
原子能技术 | 83篇 |
自动化技术 | 53篇 |
出版年
2024年 | 21篇 |
2023年 | 146篇 |
2022年 | 147篇 |
2021年 | 181篇 |
2020年 | 187篇 |
2019年 | 191篇 |
2018年 | 180篇 |
2017年 | 211篇 |
2016年 | 212篇 |
2015年 | 171篇 |
2014年 | 268篇 |
2013年 | 326篇 |
2012年 | 288篇 |
2011年 | 443篇 |
2010年 | 263篇 |
2009年 | 326篇 |
2008年 | 254篇 |
2007年 | 255篇 |
2006年 | 277篇 |
2005年 | 212篇 |
2004年 | 210篇 |
2003年 | 183篇 |
2002年 | 160篇 |
2001年 | 127篇 |
2000年 | 83篇 |
1999年 | 61篇 |
1998年 | 58篇 |
1997年 | 40篇 |
1996年 | 48篇 |
1995年 | 50篇 |
1994年 | 47篇 |
1993年 | 36篇 |
1992年 | 33篇 |
1991年 | 26篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5811条查询结果,搜索用时 15 毫秒
991.
We report an application of low-temperature Raman scattering on in-plane CuO
nanowires, in which an overview of the characteristic parameter of spin-phonon
coefficient, the interaction of incident light with the spin degrees of freedom, and
size effects will be given. The appearance of spin-phonon coefficient decrease
reflects the existence of finite size effect. 相似文献
992.
Xinhua Zhu Qiming Hang Zhenjie Tang Zhibiao Xing Ye Song Jianmin Zhu 《Integrated ferroelectrics》2013,141(1):178-183
Microstructures of BaTiO3 (BT) nanoparticles synthesized by hydrothermal process, were investigated by transmission electron microscopy (TEM) and Raman spectra. TEM images showed that BT nanoparticles synthesized at high Ba/Ti molar ratios in the precursors had large particle sizes and cubic morphology. Small faceted-particles were observed in the BT powders synthesized by using ethylene glycol (EG) as solvent, in comparison to reactive medium of pure water or water-EG mixed solution. X-ray diffraction and selected area electron diffraction revealed that the as-produced BT nanoparticles exhibited a room temperature-stabilized cubic structure, whereas Raman spectra indicated a tetragonal phase BT existing in the produced nanoparticles, which is not the dominant phase due to the weak characteristic peak of tetragonal structure at 305 cm?1. HRTEM images demonstrated that the BT nanoparticles with either cubic or rectangular shapes, were bounded by their {100} facets, and a terrace-ledge-kink surface structure was frequently observed at the edges of rough nanoparticles. Surface steps lying on the {100} planes were clearly observed. However, in the spherical nanoparticles, their surface edges were very smooth, and no surface steps were observed. 相似文献
993.
Qinghui Li Song Liu Bomin Su Hongxia Zhao Qiang Fu Junqing Dong 《Microscopy research and technique》2013,76(2):133-140
A total of nine tin‐contained ancient glass beads were characterized by a combination of scanning electron microscopy coupled with energy‐dispersive X‐ray spectrometry and Raman spectroscopy. These glass beads dated from 1st century BC to 10th century AD were excavated from the Xinjiang and Guangxi provinces of China. Two kinds of tin‐based opacifiers/colorants included crystalline cassiterite (SnO2) and lead‐tin yellow types II were first found in these soda lime glass beads. The tentative chronology of the tin‐based opacifiers/colorants used in ancient glasses from China and the West was compared. In addition, several transition metal ions colorants were also found in these beads. The detailed study of the glassy matrices, crystalline inclusions, and the microstructural heterogeneities for these glass beads has revealed some valuable information to trace the possible making technology and provenances. Microsc. Res. Tech., 2013. © 2012 Wiley Periodicals, Inc. 相似文献
994.
Abstract A method for estimating the extent of tooth caries and providing imaging information based on Raman Spectral Imaging is suggested. This non‐destructive optical method is able to characterize and differentiate between normal enamel tooth surface, and initial and advanced tooth caries. Images and corresponding spectra were acquired from various tooth sites, and it was demonstrated that normal, white opaque, brown discoloured, and pitted tooth surfaces all have different distinct spectral features which characterize the different degrees of dental caries. Spectral analysis allows for detection of early changes in the surfaces of carious teeth, and the associated mapping capability allows for morphological characterization. It was found that the emission at 960 cm?1, which corresponds to PO stretching in the hydroxyapatite bond, is the most significant and can be used for diagnosis of caries. The emissions at 1070 cm?1 and at 590 cm?1 can also be applied, but are less accurate. The results suggest that this technique may be further developed and applied for clinical diagnosis of initial and more advanced demineralization processes of the enamel tooth surfaces. 相似文献
995.
对国内涉及便携式拉曼光谱仪的专利申请进行分析,介绍重点申请人及重点专利技术。也对国外主要厂商的相关专利申请进行分析,介绍热点技术及专利布局。 相似文献
996.
997.
A.M. Funde Nabeel Ali Bakr D.K. Kamble R.R. Hawaldar D.P. Amalnerkar S.R. Jadkar 《Solar Energy Materials & Solar Cells》2008,92(10):1217-1223
Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited from pure silane (SiH4) and hydrogen (H2) gas mixture by conventional plasma enhanced chemical vapour deposition (PE-CVD) method at low temperature (200 °C) using high rf power. The structural, optical and electrical properties of these films are carefully and systematically investigated as a function of hydrogen dilution of silane (R). Characterization of these films with low angle X-ray diffraction and Raman spectroscopy revealed that the crystallite size in the films tends to decrease and at same time the volume fraction of crystallites increases with increase in R. The Fourier transform infrared (FTIR) spectroscopic analysis showed at low values of R, the hydrogen is predominantly incorporated in the nc-Si:H films in the mono-hydrogen (SiH) bonding configuration. However, with increasing R the hydrogen bonding in nc-Si:H films shifts from mono-hydrogen (SiH) to di-hydrogen (SiH2) and (SiH2)n complexes. The hydrogen content in the nc-Si:H films decreases with increase in R and was found less than 10 at% over the entire studied range of R. On the other hand, the Tauc's optical band gap remains as high as 2 eV or much higher. The quantum size effect may responsible for higher band gap in nc-Si:H films. A correlation between electrical and structural properties has been found. For optimized deposition conditions, nc-Si:H films with crystallite size 7.67 nm having good degree of crystallinity (84% ) and high band gap (2.25 eV) were obtained with a low hydrogen content (6.5 at%). However, for these optimized conditions, the deposition rate was quite small (1.6 Å/s). 相似文献
998.
K. Polychronopoulou M.A. Baker J. Neidhardt A.E. Reiter A. Leyland C. Mitterer 《Surface & coatings technology》2009,204(3):246-255
The composition, nanostructure, tribological and corrosion behaviour of reactive arc evaporated CrBxNy coatings have been studied and compared to CrN. The CrBxNy coatings were deposited on a commercial Oerlikon Balzers RCS coating system employing 80:20 Cr:B targets. To vary the composition, the nitrogen fraction was adjusted (N2 fraction = N2/(Ar + N2)) and a moderate bias voltage of − 20 V was applied during coating growth. The coating composition and nanostructure was determined using time-of-flight elastic recoil detection analysis (TOF-ERDA), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Ball-on-disc dry sliding wear tests were conducted using an alumina ball counterface both at room temperature and at 500 °C with the relative humidity controlled at 20%. Potentiodynamic corrosion tests were undertaken in 3.5% NaCl aqueous solution. The wear tracks were examined using optical profilometry and scanning electron microscopy (SEM); the surface composition inside and outside of the wear tracks were investigated using Raman spectroscopy and XPS. All coatings exhibit nanocomposite structures and phase compositions which are in fair agreement with those expected from the equilibrium phase diagram. The lowest wear rate at room temperature and 500 °C was found for CrB0.14N1.14, which was shown to exhibit the highest hardness and possesses a nanocomposite nc-CrN/a-BN structure. CrB0.12N0.84 coatings showed the lowest passive current density in potentiodynamic corrosion tests. 相似文献
999.
M. Urgen V. Ezirmik E. Senel Z. Kahraman K. Kazmanli 《Surface & coatings technology》2009,203(16):2272-2277
CrN, Cr-O-N and Cr-O coatings with different oxygen contents were produced with reactive cathodic arc physical vapor deposition on high speed steel substrates. The temperature dependent friction and wear behaviours of these coatings were investigated within the temperature range of 25-100 °C. The results of the study showed that it is possible to produce CrN coatings with temperature independent, low coefficient of friction (CoF) and wear behavior by introducing oxygen into them. The amount of oxygen in the coating played a critical role on the tribological behavior. Only, in the coatings produced with oxygen content higher than 46%, a temperature independent wear behavior was observed. The structure and chemistry of the coatings and wear tracks were investigated with XRD and micro Raman spectroscopy. The coatings, with an oxygen content higher than 46%, consisted of Cr2O3 and other compounds that are giving broad Raman shifts between 675-834 cm− 1. With the presence of compounds giving Raman shifts at 675-834 cm− 1, in the film and/or in the wear track, it became possible to achieve films with temperature independent, low CoF and wear behavior. 相似文献
1000.
A facile method to prepare silver–polypyrrole composite (Ag–PPy) by a modified silver mirror reaction is reported. PPy films pretreated by Al(NO3)3 solution were immersed into the silver ammonia with glucose. Silver ammonia ions were reduced to two-dimensional staggered silver nanosheets which immobilized on the surface of polypyrrole. The silver nanosheets with different morphologies and sizes can serve as active-substrates for surface-enhanced Raman spectroscopy (SERS). Using 4-mercaptopyridine (4-Mpy) as probe molecules, the as-prepared composites exhibited excellent surface-enhanced Raman scattering. 相似文献