全文获取类型
收费全文 | 64992篇 |
免费 | 7496篇 |
国内免费 | 4907篇 |
专业分类
电工技术 | 5656篇 |
技术理论 | 1篇 |
综合类 | 6253篇 |
化学工业 | 8191篇 |
金属工艺 | 4345篇 |
机械仪表 | 4715篇 |
建筑科学 | 5097篇 |
矿业工程 | 2652篇 |
能源动力 | 1638篇 |
轻工业 | 7191篇 |
水利工程 | 2284篇 |
石油天然气 | 2424篇 |
武器工业 | 967篇 |
无线电 | 7169篇 |
一般工业技术 | 5603篇 |
冶金工业 | 2591篇 |
原子能技术 | 1126篇 |
自动化技术 | 9492篇 |
出版年
2024年 | 408篇 |
2023年 | 1107篇 |
2022年 | 2474篇 |
2021年 | 3314篇 |
2020年 | 2436篇 |
2019年 | 1696篇 |
2018年 | 1831篇 |
2017年 | 2107篇 |
2016年 | 1928篇 |
2015年 | 2971篇 |
2014年 | 3691篇 |
2013年 | 4195篇 |
2012年 | 5194篇 |
2011年 | 5310篇 |
2010年 | 5184篇 |
2009年 | 5020篇 |
2008年 | 5054篇 |
2007年 | 4803篇 |
2006年 | 4198篇 |
2005年 | 3492篇 |
2004年 | 2561篇 |
2003年 | 1766篇 |
2002年 | 1838篇 |
2001年 | 1562篇 |
2000年 | 1243篇 |
1999年 | 624篇 |
1998年 | 261篇 |
1997年 | 205篇 |
1996年 | 176篇 |
1995年 | 149篇 |
1994年 | 115篇 |
1993年 | 82篇 |
1992年 | 77篇 |
1991年 | 51篇 |
1990年 | 51篇 |
1989年 | 43篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1959年 | 13篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Environmentally responsive hydrogels have become attractive research subjects for many applications. In this work, a series of pH‐sensitive and color‐changing nanoparticles (nanogels) with core–shell structures were synthesized. The cores were blue latex particles synthesized by a miniemulsion technique with styrene and methacrylic acid as monomers and Neozapon Blue 807 as a dye. The shell was a pH‐sensitive polymer that was precipitation‐polymerized onto the core from 2‐(diethylamino) ethyl methacrylate with N,N′‐methylenebisacrylamide, poly(propylene glycol) diacrylate, and divinylbenzene as crosslinking agents. In the resultant latexes, the color was observed to change from deep blue to pale blue as the pH of the system was changed from a high of 10 to a low of 3. The synthesized latexes and particles (gels) were then characterized with an ultraviolet–visible spectrometer, dynamic light scattering, Fourier transform infrared, and nuclear magnetic resonance. Atomic force microscopy was also used to investigate the different morphologies of the particles after the synthesized latexes were dried at different pH values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
72.
Using nickel-2,2′-dipyridyl complex as a template, N-vinyl-2-pyrrolidone as the metal coordination functional monomer, and ethylene glycol dimethacrylate as the crosslinker, polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane as the supported membrane, metal complex imprinted polymeric membranes were prepared. The association constant of template-monomer interaction in the prepolymerization solution was estimated to be 4.38 × 104 (L/mol)2 by spectrophotometric titration analysis. The attenuated total reflection Fourier transform infrared spectroscopy and scanning electron micrograph characterization indicated that the surface of the support PVDF membrane was completely coated by the imprinted polymer layer after modification. The imprinted membranes exhibited the selective permeability for the template in certain nickel acetate solution. The molecularly imprinted membranes gave higher permeation separation factors at about pH 6, whereas increasing pressure would lower the separation ability. The effects of ion concentration, cations and counterions, ligand selectivity, pH, and trans-membrane pressure were investigated and the permeation performances of the imprinted membranes could be regarded as facilitated transport mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
73.
75.
结合青藏铁路建设物资储备基地的实际情况,探讨了铁路线统购统发材料的管理模式及业务流程,总结出在实际工作中应借鉴的经验和注意的问题。 相似文献
76.
77.
78.
Hydrothermal Synthesis of Magnesium Aluminate Platelets 总被引:1,自引:0,他引:1
Zhi-Zhan Chen Er-Wei Shi Hua-Wei Zhang Yong Zhang Xiang-Biao Li Xue-Chao Liu Bing Xiao 《Journal of the American Ceramic Society》2006,89(12):3635-3637
Magnesium aluminate (MgAl2 O4 ) platelets were first synthesized by hydrothermal treatment of γ-AlO(OH) in a magnesium nitrate aqueous solution at 400°C. The platelets are 100–200 nm in width and 25 nm in thickness. The influence of temperature, the anions of the magnesium salt, the amount of magnesium salt, and precursor pH on the formation of such structure was investigated. The experimental results indicated that the anions of the magnesium salt and precursor pH could have a significant influence on the growth of MgAl2 O4 . MgAl2 O4 formation followed the in situ transformation mechanism, which was the reason why the MgAl2 O4 crystallites had a platelet morphology. 相似文献
79.
十二烷硫基硼酸铈的合成及摩擦学行为研究 总被引:2,自引:0,他引:2
合成了油溶性化合物十二烷硫基硼酸铈(简称CeDMB),并用作润滑油添加剂。采用四球摩擦试验机和环—块试验机评价了其抗磨减摩性能。结果表明,十二烷硫基硼酸铈使HVI500基础油的抗磨性能得到明显改善,承载能力明显提高,摩擦系数明显降低。扫描电子显微镜(SEM)观察证实磨斑表面含有沉积物膜,结合X—射线光电子能谱(XPS)分析,可以推断添加剂在摩擦过程中发生摩擦化学反应,生成的Ce2O3、CeO2和B2O3沉积在摩擦副表面,形成润滑膜,从而改善其抗磨减摩性能。 相似文献
80.
Polyamide (PA6) and polycarbonate (PC) were prepared by a Brabender mixer ( PLV- 151) at 240℃ with 30 rpm for duration of 8 and 6 minutes respectively. The epoxy resin (E) addition can lead to substantial microstructural changes in the PA6/PC blends. Scanning electron microscope (SEM) was used to observe the mixtures characterized by the domains of clearly segregated homophases and voids between the two polymers. PA6/PC of polyamide 6 and polycarbonate with epoxy resin addition under the composition ratio of 20/80, 20/80/1, 40/60/1 and 40/60, were tested to verify the key role of epoxy in promoting the compatibility of PA6 with PC during blending. 相似文献