全文获取类型
收费全文 | 84602篇 |
免费 | 9921篇 |
国内免费 | 6952篇 |
专业分类
电工技术 | 7447篇 |
综合类 | 9029篇 |
化学工业 | 10563篇 |
金属工艺 | 5793篇 |
机械仪表 | 6310篇 |
建筑科学 | 6443篇 |
矿业工程 | 3854篇 |
能源动力 | 2293篇 |
轻工业 | 9511篇 |
水利工程 | 2647篇 |
石油天然气 | 2960篇 |
武器工业 | 1409篇 |
无线电 | 9281篇 |
一般工业技术 | 7232篇 |
冶金工业 | 3618篇 |
原子能技术 | 1279篇 |
自动化技术 | 11806篇 |
出版年
2024年 | 555篇 |
2023年 | 1496篇 |
2022年 | 3462篇 |
2021年 | 4557篇 |
2020年 | 3191篇 |
2019年 | 2139篇 |
2018年 | 2307篇 |
2017年 | 2779篇 |
2016年 | 2491篇 |
2015年 | 3883篇 |
2014年 | 4787篇 |
2013年 | 5742篇 |
2012年 | 7066篇 |
2011年 | 7286篇 |
2010年 | 6850篇 |
2009年 | 6501篇 |
2008年 | 6660篇 |
2007年 | 6471篇 |
2006年 | 5590篇 |
2005年 | 4516篇 |
2004年 | 3205篇 |
2003年 | 2189篇 |
2002年 | 2076篇 |
2001年 | 1839篇 |
2000年 | 1581篇 |
1999年 | 670篇 |
1998年 | 264篇 |
1997年 | 220篇 |
1996年 | 173篇 |
1995年 | 132篇 |
1994年 | 107篇 |
1993年 | 115篇 |
1992年 | 68篇 |
1991年 | 72篇 |
1990年 | 59篇 |
1989年 | 63篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 22篇 |
1984年 | 29篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 22篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1977年 | 7篇 |
1973年 | 6篇 |
1959年 | 12篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
83.
Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (dj) and electrospun fiber diameter (df), and scaling laws existed between them, i.e., dj-Q0.61 and df-Q0.33. The diameter reduction ratios of Do/dj (Do is the needle diameter) and dj/df were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (ηo) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the ηo effect on the electrospinning process. Our results showed that the ηo-dependence of dj and df also followed simple scaling laws: dj-ηo0.06, and df-ηo0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation. 相似文献
84.
The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L ‐lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH‐1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
85.
Han‐Lang Wu Chen‐Chi M. Ma Chun‐Chieh Lin Yie‐Chan Chiu Chih‐Yuan Chen Chin‐Lung Chiang 《应用聚合物科学杂志》2008,107(5):3236-3243
Poly(arylene ether benzonitrile) (PAEBN) was synthesized with 2,6‐dichlorobenzonitrile and biphenol. PAEBNs with various molecular weights (MWs), 1,640,000 and 185,000 g/mol, were synthesized by control of the stoichiometry of the monomers and were blended with sulfonated poly(ether ether ketone) (SPEEK). The effects of MW on the water uptake, swelling, methanol permeability, and proton conductivity of the SPEEK/PAEBN blend membranes were investigated. The molecular mobility of the SPEEK/PAEBN blends was also examined in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
86.
针对南钢历年来在高炉煤气洗涤水污泥脱水处理中遇到的压滤机的问题,指出了单隔膜压滤机的缺陷,并在充分词研和实际应用的基础上改用厢式双隔膜高效板框压滤机,取得了较好的效果。 相似文献
87.
88.
89.
90.
乙烯裂解炉内传递和反应过程综合数值模拟Ⅱ.反应管内传递和反应过程的数值模拟 总被引:4,自引:0,他引:4
采用乙烯裂解炉传递反应过程综合数学模型中的反应管数学模型,对工业裂解炉反应管进行了系统的数值模拟,得到了反应管内流场、温度场和浓度场的详细信息,揭示了反应管内流动、传热、传质和裂解反应的基本特点。模拟结果表明,沿反应管轴向油气吸热升温,裂解反应加剧,产物产率逐渐发生变化;沿反应管径向存在明显的流体流速和温度的变化,而产物产率的变化不如流体流速和温度的变化明显。通过比较湍流粘度和分子粘度的大小,认为29.975~30mm的径向区域为层流层,层流层的存在使得临近管壁的区域内流体流速和温度变化显著。 相似文献