全文获取类型
收费全文 | 175136篇 |
免费 | 16258篇 |
国内免费 | 9390篇 |
专业分类
电工技术 | 13840篇 |
技术理论 | 8篇 |
综合类 | 17875篇 |
化学工业 | 17318篇 |
金属工艺 | 7164篇 |
机械仪表 | 15781篇 |
建筑科学 | 20312篇 |
矿业工程 | 6731篇 |
能源动力 | 7796篇 |
轻工业 | 13447篇 |
水利工程 | 7491篇 |
石油天然气 | 8286篇 |
武器工业 | 2002篇 |
无线电 | 10003篇 |
一般工业技术 | 17051篇 |
冶金工业 | 7019篇 |
原子能技术 | 2524篇 |
自动化技术 | 26136篇 |
出版年
2024年 | 721篇 |
2023年 | 2141篇 |
2022年 | 4361篇 |
2021年 | 5110篇 |
2020年 | 5380篇 |
2019年 | 4507篇 |
2018年 | 4427篇 |
2017年 | 5417篇 |
2016年 | 6554篇 |
2015年 | 6890篇 |
2014年 | 11238篇 |
2013年 | 11282篇 |
2012年 | 13012篇 |
2011年 | 14339篇 |
2010年 | 10282篇 |
2009年 | 10477篇 |
2008年 | 9830篇 |
2007年 | 11801篇 |
2006年 | 10240篇 |
2005年 | 8599篇 |
2004年 | 7274篇 |
2003年 | 6211篇 |
2002年 | 5010篇 |
2001年 | 4118篇 |
2000年 | 3522篇 |
1999年 | 2937篇 |
1998年 | 2528篇 |
1997年 | 2126篇 |
1996年 | 1745篇 |
1995年 | 1439篇 |
1994年 | 1294篇 |
1993年 | 966篇 |
1992年 | 891篇 |
1991年 | 654篇 |
1990年 | 551篇 |
1989年 | 470篇 |
1988年 | 395篇 |
1987年 | 268篇 |
1986年 | 233篇 |
1985年 | 214篇 |
1984年 | 252篇 |
1983年 | 239篇 |
1982年 | 196篇 |
1981年 | 95篇 |
1980年 | 94篇 |
1979年 | 65篇 |
1978年 | 53篇 |
1977年 | 46篇 |
1976年 | 43篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
指出混凝土小型空心砌块是一种节能型的新型墙体材料。本文从经济角度对该种材料和粘土砖材料进行了实例分析、比较,得出了这种新型材料值得推广使用的结论。 相似文献
75.
A. Domingue K. Piyakis E. Sacher M. Di Renzo S. D nomm e T. H. Ellis 《The Journal of Adhesion》1993,40(2):151-162
The irreversibly bound interfacial layer deposited by the γ-aminopropysilanetriol adhesion promoter onto a crystalline silicon substrate, which remains even after profuse washing, was found by XPS to have resulted from the fragmentation and rearrangement of the original γ-aminopropylsilanetriol molecule. A mechanism is proposed, involving the homolytic scission of the terminal N-C bond. One of the subsequent reactions is believed to involve hydrogen loss by abstraction and the formation of a terminal vinyl group, which bonds to the substrate. Support for this mechanism is found in IR spectroscopy of this layer. 相似文献
76.
Using a Debye function analysis, the presence of icosahedral and face centered cuboctahedral gold in a 1 1 ratio has been found in freshly prepared Au/Mg(OH)2 catalyst. The results support earlier studies which suggest the icosahedral form to be more stable at small nanometer sizes. Interactions between the gold and the Mg(OH)2 support appear to be weak, with the gold rapidly coagulating over a period of three months. Re-analysis of the aged sample shows the gold to be mainly in the form of truncated decahedra. 相似文献
77.
Bituminous coal samples from 84 distinct sources were analysed by conventional British Standards (BS) methods for phosphorus, sulphur, chlorine, ash and the ash-forming elements (calcium, silicon, aluminium, iron, sodium, magnesium, potassium, titanium and manganese). In most cases four determinations were made per element per source. Samples were crushed to ?212 μm (72 BS mesh) and pressed into aluminium cups at 20 t in?2 (309 MPa) without binder or backing. Two pellets from each sample were analysed by wave-length dispersive X-ray fluorescence techniques, using a spectrometer equipped with a rhodium rube; the X-ray count took 60 s. The X-ray results were calibrated against the conventional results using multiple regression. The accuracy obtained was comparable with routine ‘wet chemical’ techniques. The X-ray technique is suitable for the routine determination of large numbers of samples. 相似文献
78.
双波长分光光度法测定自来水中Fe2+和Fe3+的含量 总被引:5,自引:0,他引:5
采用双波长分光光度法测定 Fe2 和 Fe3 的方法 ,结果表明 ,在 λ1 =4 0 0 nm,λ2 =5 4 2 nm处 ,显色时间在 6 0 min~ 80 min,p H =4~ 5时能联合测定水中 Fe2 和 Fe3 ,其结果具有较高的精密度和准确度。 相似文献
79.
Zinc Coated Steel/Epoxy Adhesive Systems: Investigation of the Interfacial Zone by FTIR Spectroscopy
The present study takes advantage of the ability of Fourier Transform Infrared Spectroscopy (FTIR) for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) is used in order to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels.
Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180°C, as evidenced by the frequency shift of the absorption band (at about 2200 cm-1) characteristic for nitrile groups. As real systems consist of thick layers of a fully formulated adhesive cured onto a metallic substrate, the direct investigation of such a buried interphase is no longer possible by FTIR and by most of the known spectroscopies. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 μm in diameter, advocate for the presence of an ultrathin layer of modified polymer still covering the substrate. 相似文献
Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180°C, as evidenced by the frequency shift of the absorption band (at about 2200 cm-1) characteristic for nitrile groups. As real systems consist of thick layers of a fully formulated adhesive cured onto a metallic substrate, the direct investigation of such a buried interphase is no longer possible by FTIR and by most of the known spectroscopies. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 μm in diameter, advocate for the presence of an ultrathin layer of modified polymer still covering the substrate. 相似文献
80.
抗蚜威原药和制剂的气相色谱分析 总被引:2,自引:0,他引:2
本文报道了抗蚜威的气相色谱分析方法,其标准偏差为0.019,变异系数为0.244%,回收率为99 ̄101%,适于抗蚜威原药和制剂的分析。 相似文献