全文获取类型
收费全文 | 29221篇 |
免费 | 2865篇 |
国内免费 | 1530篇 |
专业分类
电工技术 | 1143篇 |
综合类 | 2171篇 |
化学工业 | 10267篇 |
金属工艺 | 1604篇 |
机械仪表 | 1076篇 |
建筑科学 | 1222篇 |
矿业工程 | 943篇 |
能源动力 | 629篇 |
轻工业 | 3874篇 |
水利工程 | 556篇 |
石油天然气 | 1427篇 |
武器工业 | 206篇 |
无线电 | 1133篇 |
一般工业技术 | 3331篇 |
冶金工业 | 1195篇 |
原子能技术 | 211篇 |
自动化技术 | 2628篇 |
出版年
2024年 | 193篇 |
2023年 | 480篇 |
2022年 | 926篇 |
2021年 | 998篇 |
2020年 | 966篇 |
2019年 | 796篇 |
2018年 | 852篇 |
2017年 | 963篇 |
2016年 | 1002篇 |
2015年 | 1018篇 |
2014年 | 1536篇 |
2013年 | 1733篇 |
2012年 | 2166篇 |
2011年 | 2258篇 |
2010年 | 1715篇 |
2009年 | 1735篇 |
2008年 | 1458篇 |
2007年 | 1997篇 |
2006年 | 1774篇 |
2005年 | 1552篇 |
2004年 | 1335篇 |
2003年 | 1082篇 |
2002年 | 883篇 |
2001年 | 807篇 |
2000年 | 627篇 |
1999年 | 565篇 |
1998年 | 453篇 |
1997年 | 373篇 |
1996年 | 257篇 |
1995年 | 218篇 |
1994年 | 176篇 |
1993年 | 147篇 |
1992年 | 123篇 |
1991年 | 105篇 |
1990年 | 69篇 |
1989年 | 43篇 |
1988年 | 40篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1955年 | 2篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility. 相似文献
92.
超高分子量聚乙烯衬板在煤仓中的应用 总被引:2,自引:0,他引:2
介绍了井底煤仓溜煤斜面采用超高分子量聚乙烯衬板安装及应用情况 ,对井底煤仓棚煤原因及解决办法进行了探讨 相似文献
93.
热带城市垃圾典型组分的热解特性研究 总被引:7,自引:0,他引:7
对热带城市垃圾的几种典型组分进行了热解实验,得到了它们的失重曲线,通过对失重曲线进行分析,得到了这几种典型组分的热解规律,并通过建立热解动力学模型,求出了其中两种组分的活化能E和频率因子A。 相似文献
94.
95.
96.
已二醇二丙烯酸酯对真丝的接枝改性研究 总被引:2,自引:0,他引:2
研究了用二醇二丙烯酸酯为接枝单体、过硫酸铵(APS)为引发剂对真丝的接枝共聚反应,分析了接枝率的影响素,并测试了改性真丝的主要应用性能。结果表明:乳液和乙醇/水为溶剂的2种体系都能在真丝上获得较高接枝率。对于乙醇/水体系v(乙醇):v(H2O)=1:1,接枝单体20~30g/L,2%甲酸4ml,引发剂APS 0.5g/L,65~70℃接枝60min的接枝率高。改性后真丝的断裂强度、延伸度、吸湿性能都可获得改善,对酸、碱的溶解性提高,但染色性能提高不明显,对泛黄性改善一般。 相似文献
97.
偶联剂处理硅灰石填充不饱和聚酯树脂的研究 总被引:2,自引:0,他引:2
对针状硅灰石 (L∶D≥ 10∶32 5目 )提纯后 ,采用偶联剂进行表面处理 ,将硅灰石按不同比例填充于不饱和聚酯树脂体系中 ,研究了材料的性能。结果表明 ,改性后的硅灰石可显著改善不饱和聚酯的性能。 相似文献
98.
Free‐radical solution copolymerization of itaconic acid and acrylonitrile was carried out in DMSO using azodiisobutyronitrile as an initiator, changing the feed rate of itaconic acid. The resulting polymerization solution was spun to form polyacrylonitrile (PAN) precursors of carbon fibers. The precursors were treated with a CoSO4 aqueous solution on‐line. The structure and properties of untreated and treated PAN precursors and the resultant carbon fibers were characterized by SEM and TEM, a stabilization process, etc. It is suggested that CoSO4 acts as a catalyst in the formation of a ladder structure and reduces the temperature of cyclization, and the carbon fibers developed from treated PAN fibers showed improvement in the tensile strength and the Young's modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 153–158, 2002 相似文献
99.
The equations for predicting the number-average molecular weight are derived on the basis of the three stage polymerization model (TSPM) in this paper. By applying the equations, a plotting approach is proposed to determine the apparent initiator efficiency defined as f[(αtd+1)/2] and the constant of chain transfer to monomer, where f is the initiator efficiency and αtd denotes the fraction of the termination rate constants by disproportionation. Using the approach to plot the experimental data in the literature, it is found that the chain transfer to monomer can be neglected for both methylmethacrylate (MMA) and styrene (St) polymerizations, but it can exert a significant effect on ethylmethacrylate (EMA) polymerization. In addition, the apparent initiator efficiency is found to be independent of reaction temperature and initiator concentration at each stage. The values of f[(αtd+1)/2] at gel effect stage are slightly reduced as compared with that at low conversion stage for MMA and EMA polymerizations. However, it decreases significantly at gel effect stage for St polymerization. Using the equations derived and the apparent initiator efficiencies obtained from TSPM plots, the number-average molecular weights at different conversions can be predicted. Comparisons show that the agreement between predictions and experimental data is satisfactory. 相似文献
100.
Two series of polypropylenes with different molecular weight distribution and tacticity characteristics were injection molded into flexural test specimens by varying cylinder temperature and the effects of the molecular weight distribution and tacticity on the structure and properties of the moldings were studied. Measured propertied were flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and structures studied were crystallinity, the thickness of skin layer, a*‐axis‐oriented component fraction and crystalline orientation functions. The relations between the structures and properties were also studied. It was found that the molecular weight distribution and tacticity characteristics affect the properties mainly through the molecular orientation and crystallinity, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2142–2156, 2002 相似文献