全文获取类型
收费全文 | 28522篇 |
免费 | 1838篇 |
国内免费 | 854篇 |
专业分类
电工技术 | 1129篇 |
综合类 | 1372篇 |
化学工业 | 5127篇 |
金属工艺 | 1530篇 |
机械仪表 | 1266篇 |
建筑科学 | 1996篇 |
矿业工程 | 802篇 |
能源动力 | 690篇 |
轻工业 | 2108篇 |
水利工程 | 454篇 |
石油天然气 | 1517篇 |
武器工业 | 197篇 |
无线电 | 2607篇 |
一般工业技术 | 3841篇 |
冶金工业 | 3211篇 |
原子能技术 | 281篇 |
自动化技术 | 3086篇 |
出版年
2023年 | 364篇 |
2022年 | 565篇 |
2021年 | 943篇 |
2020年 | 773篇 |
2019年 | 659篇 |
2018年 | 696篇 |
2017年 | 804篇 |
2016年 | 706篇 |
2015年 | 962篇 |
2014年 | 1231篇 |
2013年 | 1609篇 |
2012年 | 1549篇 |
2011年 | 1819篇 |
2010年 | 1520篇 |
2009年 | 1504篇 |
2008年 | 1436篇 |
2007年 | 1527篇 |
2006年 | 1434篇 |
2005年 | 1229篇 |
2004年 | 836篇 |
2003年 | 767篇 |
2002年 | 742篇 |
2001年 | 594篇 |
2000年 | 596篇 |
1999年 | 656篇 |
1998年 | 496篇 |
1997年 | 460篇 |
1996年 | 414篇 |
1995年 | 427篇 |
1994年 | 375篇 |
1993年 | 288篇 |
1992年 | 255篇 |
1991年 | 167篇 |
1990年 | 166篇 |
1989年 | 166篇 |
1988年 | 168篇 |
1987年 | 140篇 |
1986年 | 135篇 |
1985年 | 152篇 |
1984年 | 145篇 |
1983年 | 129篇 |
1982年 | 140篇 |
1981年 | 130篇 |
1980年 | 89篇 |
1979年 | 123篇 |
1978年 | 120篇 |
1977年 | 103篇 |
1976年 | 87篇 |
1974年 | 90篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Haijie Li Yuting Shang Wenrui Huang Bingfeng Xue Xiaomeng Zhang Zhe Cui Peng Fu Xinchang Pang Qingxiang Zhao Minying Liu 《应用聚合物科学杂志》2021,138(39):51017
Succinic acid is an important synthetic monomer but it is difficult to use it as a precursor for synthesizing high molecular weight polyamide, due to its tendency to perform intra-cyclization reaction at high temperature. In order to solve this problem, in this paper, the direct solid-state polymerization (DSSP) method with the initial reactant, nylon salt which was composed of 1, 5-diaminopentane, succinic acid, and terephthalic acid, was applied to synthesize the bio-based copolyamide PA 5T/54. In comparison with the conventional melting polymerization method, the DSSP method can prevent the cyclization reaction of succinic acid effectively due to the lower reacting temperature as well as the restriction effect of the nylon salt. As a result, the product fabricated by DSSP method has higher molecular weight and much lighter color from red to white. Therefore, the DSSP method is advantageous for the synthesis of the polymers or copolymers composed of the succinic acid as the monomer. Furthermore, the polymerization mechanism proposed in this work can serve as a guidance for the design of the molecular structure and control of the polymerization process. 相似文献
2.
3.
4.
Yunyan Liu Ning Jiang Yao Liu Dawei Cui Chang-Feng Yu Huiqiang Liu Zhao Li 《Ceramics International》2021,47(16):22416-22423
Pulsed laser deposition (PLD) was used to prepare tungsten trioxide (WO3) films on ITO substrates with a varying laser power density of 4.0–5.5 W/cm2. XPS indicated that when the laser power density decreased, the peak positions of the W 4f and O 1s orbits shifted slightly to low energy due to the difference in oxygen vacancies. As the laser power density decreased, W6+ gradually replaced the lattice position of O2?, increasing oxygen vacancies in the lattice. The transmittance modulated values (ΔT) were over 44% at 830 nm, indicating strong absorption by the WO3 thin films in the near-infrared ray. The switching time of the WO3 thin films between bleached states and coloured states decreased as the laser power density increased due to the amorphous structure, morphology, and lower oxygen deficiency at a high power density. The high ΔT and very fast switching time of tb (1.09 s) and tc (6.01 s) demonstrated the excellent electrochromic (EC) properties of the WO3 films prepared by PLD. 相似文献
5.
Gui-Jia Gao Mei-Qi Zeng En-Liang Zhang Rong-Chang Zeng Lan-Yue Cui Dao-kui Xu Feng-Qin Wang M.Bobby Kannan 《材料科学技术学报》2021,83(24):161-178
The microstructure and chemical compositions of the solid solution-treated Mg-3Nd-1Li-0.2Zn alloy were characterized using optical microscope,scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The corrosion behaviour of the alloy was investigated via electrochemical polarization,electrochemical impedance spectroscopy(EIS),hydrogen evolution test and scanning Kelvin probe(SKP).The results showed that the microstructure of the as-extruded Mg-3Nd-1Li-0.2Zn alloy contained α-Mg matrix and nanometric second phase Mg41 Nd5.The grain size of the alloy increased significantly with the increase in the heat-treatment duration,whereas the volume fraction of the second phase decreased after the solid solution treatment.The surface film was composed of oxides(Nd2O3,MgO,Li2O and ZnO)and carbonates(MgCO3 and Li2CO3),in addition to Nd.The as-extruded alloy exhibited the best corrosion resistance after an initial soaking of 10 min,whereas the alloy with 4h-solution-treatment possessed the lowest corrosion rate after a longer immersion(1 h).This can be attributed to the formation of Nd-containing oxide film on the alloys and a dense corrosion product layer.The dealloying corrosion of the second phase was related to the anodic Mg41Nd5 with a more negative Volta potential relative to α-Mg phase.The preferential corrosion of Mg41Nd5 is proven by in-situ observation and SEM.The solid solution treatment of Mg-3Nd-1Li-0.2Zn alloy led to a shift in corrosion type from pitting corrosion to uniform corrosion under long-term exposure. 相似文献
6.
采用有限元模拟和实验研究了挤压钛合金弯曲管件。通过实验验证了工件的形状和尺寸精度,并通过有限元模拟分析了工艺参数对挤出过程中变形体的平均压应力分布情况和挤出弯管件的曲率半径的影响规律。结果表明:有限元模拟中,弯管件的曲率半径误差为6.03%,弯管直径误差为3.82%;在靠近定径带处,平均压应力呈非均匀分布;在焊合腔内,靠近细分流孔区域的平均压应力小于靠近粗分流孔区域的平均压应力,平均压应力的大小顺序在通过粗、细分流孔前后相反;在模具结构固定不变时,弯管件的曲率半径随挤压速度的减小而增大,不随挤压温度的变化而变化。 相似文献
7.
8.
Nowadays, oil pollution has become more serious, which causes great threats both to the ecological environment and human life. In this study, a novel type of multifunctional deacetylated cellulose acetate/polyurethane (d-MCA:MTPU) composite nanofiber membranes for oil/water separation are successfully fabricated by electrospinning, which show super-amphiphilicity in air, super-hydrophilicity in oil, and oleophobicity in water. All the d-MCA:MTPU composite nanofiber membranes with different mass ratios can be used as water-removing, oil-removing, and emulsion separation substance only by gravity driving force. The highest separation flux for water and oil reaches up to 37 000 and 74 000 L m−2 h−1, respectively, and all the separation efficiencies are more than 99%. They have outstanding comprehensive mechanics performance, which can be controlled by simply adjusting the mass ratios. They show excellent antifouling and self-cleaning ability, endowing powerful cyclic stability and reusability. Those results show that d-MCA:MTPU composite nanofiber membranes have great application prospects in oil/water separation. 相似文献
9.
10.
Eitan Oksenberg Calvin Fai Ivan G. Scheblykin Ernesto Joselevich Eva L. Unger Thomas Unold Charles Hages Aboma Merdasa 《Advanced functional materials》2021,31(22):2010704
Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr3 nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr3 nanowires, an ambipolar carrier mobility of μ = 35 cm2 V−1 s−1 is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL. 相似文献