全文获取类型
收费全文 | 70973篇 |
免费 | 7592篇 |
国内免费 | 2795篇 |
专业分类
电工技术 | 1271篇 |
技术理论 | 1篇 |
综合类 | 2871篇 |
化学工业 | 26082篇 |
金属工艺 | 10147篇 |
机械仪表 | 1282篇 |
建筑科学 | 1771篇 |
矿业工程 | 948篇 |
能源动力 | 1346篇 |
轻工业 | 9704篇 |
水利工程 | 310篇 |
石油天然气 | 1084篇 |
武器工业 | 336篇 |
无线电 | 3125篇 |
一般工业技术 | 16756篇 |
冶金工业 | 3147篇 |
原子能技术 | 254篇 |
自动化技术 | 925篇 |
出版年
2024年 | 506篇 |
2023年 | 1749篇 |
2022年 | 2414篇 |
2021年 | 3209篇 |
2020年 | 3105篇 |
2019年 | 2628篇 |
2018年 | 2922篇 |
2017年 | 3287篇 |
2016年 | 3297篇 |
2015年 | 3370篇 |
2014年 | 3982篇 |
2013年 | 5242篇 |
2012年 | 4462篇 |
2011年 | 5492篇 |
2010年 | 3697篇 |
2009年 | 4039篇 |
2008年 | 3339篇 |
2007年 | 3661篇 |
2006年 | 3476篇 |
2005年 | 2734篇 |
2004年 | 2691篇 |
2003年 | 2286篇 |
2002年 | 1867篇 |
2001年 | 1292篇 |
2000年 | 1183篇 |
1999年 | 903篇 |
1998年 | 793篇 |
1997年 | 696篇 |
1996年 | 520篇 |
1995年 | 472篇 |
1994年 | 348篇 |
1993年 | 244篇 |
1992年 | 257篇 |
1991年 | 197篇 |
1990年 | 245篇 |
1989年 | 237篇 |
1988年 | 83篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 70篇 |
1984年 | 69篇 |
1983年 | 33篇 |
1982年 | 55篇 |
1981年 | 7篇 |
1980年 | 35篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 4 毫秒
991.
以成分为Nd28.5Fe余B1.0Ga0.3Nb0.3 (%)的钕铁硼合金锭作为原料,采用 HDDR 工艺制备各向异性钕铁硼磁粉。重点研究了HDDR工艺过程中钙添加量对磁粉氧含量和磁性能的影响。结果表明,在不改变原有HDDR工艺参数的基础上,添加少量金属钙即可显著降低磁粉的氧化程度,大幅提高磁粉的磁性能。钙添加量小于0.1%时,由于磁粉的氧含量仍然较高而导致内禀矫顽力Hcj和最大磁能积(BH)max低劣;钙添加量大于0.3%时,由于磁粉中残留的非磁性相过多以及颗粒团聚加重会导致磁性能指标全面下降;钙添加量为0.1 ~ 0.3%是适宜的,在钙添加量为0.2%时,磁粉的综合磁性能最佳,其Br为1.37 T、Hcj为1 296 kA/m、(BH)max为340 kJ/m3。 相似文献
992.
Microwave heating has become popular in wheat-based food processing owing to its environmental friendliness, high-efficiency and low energy consumption. Water plays an important role in microwave food processing as it is a highly dielectric material that can react with many food components while being dynamic in complex food systems and affecting the overall dielectric response. In this study, hydrated systems of wheat starch, gluten (GLU) and starch-GLU mixtures (CBF) with different moisture contents were prepared and the variation patterns of their water mobility, dielectric properties and microwave absorption properties were measured. The results of low-field nuclear magnetic resonance (LF-NMR) analysis showed that water mobility was strongly influenced by moisture content and interactions between starch or GLU and water-restricted dynamic migration. In CBF, interactions between starch and water predominated under a reduced effect of GLU. As the water content increased, the complex permittivity showed an upward tendency, and the coupling capability of the hydrated systems with microwave was best at 35% moisture content. And the dielectric response and absorption characteristics of the hydrated systems fluctuated in a non-additive manner due to the interplay between moisture and the system components. Moreover, the correlation analysis was confirmed that the relationship between dielectric response behavior and water mobility, as higher water mobility more strongly influenced the augmentation of the dielectric characteristics and dominated changes in the locations of the microwave absorption peak and reflection loss value. These findings provide a possibility to manipulate the dielectric response changes of wheat-based materials under a microwave field through regulating the water mobility, thereby laying a theoretical basis to improve the utilization of microwave for wheat-based food production. 相似文献
993.
《International Journal of Hydrogen Energy》2019,44(16):8384-8391
Al was partially substituted by Mn in Mg3AlNi2 to improve the discharge capacity and electrochemical kinetic properties of Mg3AlNi2 alloy electrode. By means of pretreatment of ultrasonic dispersion, followed by mechanical milling and combustion synthesis, a series of quaternary alloys, namely Mg3Al1-xMnxNi2 (x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized. X-ray diffraction analysis shows that partial substitution of Mn for Al can cause lattice expansion of Mg3AlNi2 and the samples all appear similar multiphase structures. The introduction of Mn enhances obviously the maximum discharge capacity of Mg3AlNi2 alloy electrode. The high rate dischargeability of the alloys can also be remarkably enhanced by substitution of Mn for Al. The exchange current density (I0) and charge transfer resistance (Rct) of the alloy electrode increase and decrease continuously with increasing the Mn substitution content, respectively, indicating the improvement of electrochemical kinetics properties. Combining with the potentiostatic discharge test, it is concluded that in the MgAlMnNi quaternary alloys, the kinetic properties are mainly controlled by charge transfer reaction on the electrode surface. 相似文献
994.
G. Wang X. Tuo L. Kou W. Zhao X. Zhu 《Materialwissenschaft und Werkstofftechnik》2020,51(12):1686-1699
Salt spray corrosion test was carried out on 6061 aluminum alloy, and quasi-static tensile test at room temperature was carried out on the sample with universal testing machine. The effect of salt spray corrosion on the mechanical properties of 6061 aluminum alloy was studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemistry. The corrosion rate of 6061 aluminum alloy was quantitatively characterized by different corrosion parameters. It was found that local corrosion of 6061 aluminum alloy occurred in salt spray environment, mainly pitting corrosion and intergranular corrosion. With the increase of corrosion time, the polarization resistance of 6061 aluminum alloy decreases, and the corrosion rate significantly increases. The average corrosion rate and the maximum corrosion rate of 6061 aluminum alloy were characterized by corrosion weight loss and corrosion pit depth. And they can be transformed into each other. The mechanical properties of 6061 aluminum alloy were mainly affected by the depth of corrosion pit. With the increase of corrosion time, the tensile strength and fracture strain decreased, resulting in poor plasticity of the sample. At the same time, the change of elongation of 6061 aluminum alloy can be accurately predicted by the depth of corrosion pit. 相似文献
995.
996.
Bo Wu Huiying Du Ping Hu Zhanyu Gao Ruikai Liu Chonghua Pei 《Journal of Energetic Materials》2021,39(1):10-22
ABSTRACT In recent years, the exploration of a practical strategy for novel energetic molecules with high energy and low sensitivity is very desirable but highly challenging. Novel ionic energetic molecules have attracted much attention in this area due to their prominent advantages including low sensitivities, high thermal stability, and excellent energy performances. Herein, five different ionic energetic molecules based on new monovalent and divalent 4-oxyl-3,5-dinitropyrazolate moieties with enhanced oxygen balance have been synthesized, characterized and evaluated as potential high-energy materials. Thermal stability, sensitivities and energy output test were measured and studied in detail. The heats of formation and energetic parameters were calculated by using Gaussian 09 suite of programs and EXPLO 5 code. The results suggest that all as-prepared new molecules exhibit good thermal stability with high decomposition temperature (3, 231°C; 5, 160°C; 6, 185°C; 7, 180°C; 8, 213°C), and relative low sensitivity (IS > 20 J, FS = 324 N). Inheriting the significant oxygen content of monovalent and divalent 4-oxyl-3,5-dinitropyrazolate moieties, they also possess good energy properties (v D = 8238 ~ 9208 m s?1, P = 26.8 ~ 36.7 GPa, V o = 481.8 ~ 959.4 L kg?1), which make them competitive high-energy materials. 相似文献
997.
998.
Maria Cazacu Carmen Racles Mihaela Alexandru Aurelia Ioanid Angelica Vlad 《Polymer International》2009,58(6):697-702
BACKGROUND: It is well known that, due to their extremely low polarity, polysiloxanes are incompatible with almost any organic system. This incompatibility leads to phase separation in mixed siloxane–organic systems. RESULTS: Three siloxane–organic copolymers, poly[(5,5′‐methylene‐bis‐salicylaldehyde)‐imine‐(1,3‐bis(propylene)tetramethyldisiloxane)] (Paz1), poly[(2,5‐dihydroxy‐1,4‐benzoquinone)‐imine‐(1,3‐bis(propylene)tetramethyldisiloxane)] (Paz2) and poly[1,3‐bis(propylene)tetramethyldisiloxane diamide] (Pam), were prepared by the reaction of 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane with appropriate organic partners (5,5′‐methylene‐bis‐salicylaldehyde, 2,5‐dihydroxy‐1,4‐benzoquinone and oxalyl chloride, respectively). The morphologies dictated by the incompatibility between siloxane and polar organic moieties were investigated using differential scanning calorimetry and scanning electron microscopy. The surface activity of the copolymers and water vapour sorption capacity were also measured. CONCLUSION: Even though the polar sequences are very short ones, the highly flexible siloxane‐containing sequence permits the self‐assembly of these into more or less polar domains. Such an organization influences the properties of the resulting materials, an important place being occupied by the surface properties. Copyright © 2009 Society of Chemical Industry 相似文献
999.
Bi2−xLaxAlNbO7 (0 ≤ x ≤ 0.5) photocatalysts were synthesized by the solid-state reaction method and characterized by powder X-ray diffraction (XRD), infrared (IR) spectra and ultraviolet-visible (UV-vis) spectrophotometer. The band gaps of the photocatalysts were estimated from absorption edge of diffuse reflectance spectra, which were increased by the doping of lanthanum. It was found from the electronic band structure study that orbitals of La 5d, Bi 6p and Nb 4d formed a conduction band at a more positive level than Bi 6p and Nb 4d orbitals, which results in increasing the band gap. Photocatalytic activity for water splitting of Bi1.8La0.2AlNbO7 was about 2 times higher than that of nondoped Bi2AlNbO7. The increased photocatalytic activity of La-doped Bi2AlNbO7 was discussed in relation to the band structure and the strong absorption of OH groups at the surface of the catalyst. 相似文献
1000.