全文获取类型
收费全文 | 288740篇 |
免费 | 6427篇 |
国内免费 | 1651篇 |
专业分类
电工技术 | 5702篇 |
综合类 | 762篇 |
化学工业 | 42558篇 |
金属工艺 | 11971篇 |
机械仪表 | 8219篇 |
建筑科学 | 7812篇 |
矿业工程 | 685篇 |
能源动力 | 7384篇 |
轻工业 | 29568篇 |
水利工程 | 2356篇 |
石油天然气 | 1733篇 |
武器工业 | 82篇 |
无线电 | 34624篇 |
一般工业技术 | 52758篇 |
冶金工业 | 60601篇 |
原子能技术 | 4180篇 |
自动化技术 | 25823篇 |
出版年
2021年 | 2923篇 |
2020年 | 2155篇 |
2019年 | 2427篇 |
2018年 | 4087篇 |
2017年 | 3978篇 |
2016年 | 4276篇 |
2015年 | 3356篇 |
2014年 | 5033篇 |
2013年 | 13970篇 |
2012年 | 8351篇 |
2011年 | 10596篇 |
2010年 | 8479篇 |
2009年 | 8926篇 |
2008年 | 9738篇 |
2007年 | 9587篇 |
2006年 | 8504篇 |
2005年 | 7717篇 |
2004年 | 7340篇 |
2003年 | 7230篇 |
2002年 | 7156篇 |
2001年 | 6971篇 |
2000年 | 6388篇 |
1999年 | 7134篇 |
1998年 | 19903篇 |
1997年 | 13647篇 |
1996年 | 10295篇 |
1995年 | 7486篇 |
1994年 | 6606篇 |
1993年 | 6407篇 |
1992年 | 4307篇 |
1991年 | 4183篇 |
1990年 | 3766篇 |
1989年 | 3670篇 |
1988年 | 3546篇 |
1987年 | 2978篇 |
1986年 | 2977篇 |
1985年 | 3569篇 |
1984年 | 3163篇 |
1983年 | 2809篇 |
1982年 | 2642篇 |
1981年 | 2667篇 |
1980年 | 2516篇 |
1979年 | 2314篇 |
1978年 | 2271篇 |
1977年 | 2952篇 |
1976年 | 4524篇 |
1975年 | 1917篇 |
1974年 | 1796篇 |
1973年 | 1806篇 |
1972年 | 1481篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
62.
Giorgio Benedek Joseph R. Manson Salvador Miret-Artés 《Advanced materials (Deerfield Beach, Fla.)》2020,32(25):2002072
Atom scattering is becoming recognized as a sensitive probe of the electron–phonon interaction parameter λ at metal and metal-overlayer surfaces. Here, the theory is developed, linking λ to the thermal attenuation of atom scattering spectra (in particular, the Debye–Waller factor), to conducting materials of different dimensions, from quasi-1D systems such as W(110):H(1 × 1) and Bi(114), to quasi-2D layered chalcogenides, and high-dimensional surfaces such as quasicrystalline 2ML-Ba(0001)/Cu(001) and d-AlNiCo(00001). Values of λ obtained using He atoms compare favorably with known values for the bulk materials. The corresponding analysis indicates in addition, the number of layers contributing to the electron–phonon interaction, which is measured in an atom surface collision. 相似文献
63.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
64.
There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments. 相似文献
65.
66.
67.
68.
Dr. Jiayao Y. Wang Dr. Jiaqi Q. Li Prof. Dr. Yumei M. Xiao Prof. Dr. Bin Fu Prof. Dr. Zhaohai H. Qin 《ChemMedChem》2020,15(5):404-410
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant. 相似文献
69.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
70.