全文获取类型
收费全文 | 176810篇 |
免费 | 18120篇 |
国内免费 | 9413篇 |
专业分类
电工技术 | 14263篇 |
技术理论 | 8篇 |
综合类 | 18056篇 |
化学工业 | 17374篇 |
金属工艺 | 7232篇 |
机械仪表 | 16468篇 |
建筑科学 | 20485篇 |
矿业工程 | 6797篇 |
能源动力 | 7894篇 |
轻工业 | 14103篇 |
水利工程 | 7601篇 |
石油天然气 | 8322篇 |
武器工业 | 2021篇 |
无线电 | 10325篇 |
一般工业技术 | 17445篇 |
冶金工业 | 7030篇 |
原子能技术 | 2530篇 |
自动化技术 | 26389篇 |
出版年
2024年 | 1645篇 |
2023年 | 2528篇 |
2022年 | 4690篇 |
2021年 | 5328篇 |
2020年 | 5580篇 |
2019年 | 4695篇 |
2018年 | 4653篇 |
2017年 | 5627篇 |
2016年 | 6823篇 |
2015年 | 7054篇 |
2014年 | 11346篇 |
2013年 | 11429篇 |
2012年 | 13264篇 |
2011年 | 14334篇 |
2010年 | 10279篇 |
2009年 | 10476篇 |
2008年 | 9829篇 |
2007年 | 11791篇 |
2006年 | 10229篇 |
2005年 | 8598篇 |
2004年 | 7269篇 |
2003年 | 6198篇 |
2002年 | 5008篇 |
2001年 | 4122篇 |
2000年 | 3522篇 |
1999年 | 2935篇 |
1998年 | 2523篇 |
1997年 | 2124篇 |
1996年 | 1745篇 |
1995年 | 1438篇 |
1994年 | 1293篇 |
1993年 | 965篇 |
1992年 | 891篇 |
1991年 | 654篇 |
1990年 | 550篇 |
1989年 | 468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.
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
72.
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
73.
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
74.
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
75.
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
76.
The constrained blister test is investigated through finite element analysis to determine the applicabilities and the limitations of the new technique. Numerical results confirm that the strain energy release rate asymptotically approaches a constant value. These results also show that the test technique and the approximate solution for strain energy release rate are applicable for some practical cases. 相似文献
77.
78.
We present a simple and fast algorithm to test the thermodynamic stability and determine the necessary chemical environment for the production of a multiternary material, relative to competing phases and compounds formed from the constituent elements. If the material is found to be stable, the region of stability, in terms of the constituent elemental chemical potentials, is determined from the intersection points of hypersurfaces in an (n−1)-dimensional chemical potential space, where n is the number of atomic species in the material. The input required is the free energy of formation of the material itself, and that of all competing phases. Output consists of the result of the test of stability, the intersection points in the chemical potential space and the competing phase to which they relate, and, for two- and three-dimensional spaces, a file which may be used for visualization of the stability region. We specify the use of the program by applying it both to a ternary system and to a quaternary system. The algorithm automates essential analysis of the thermodynamic stability of a material. This analysis consists of a process which is lengthy for ternary materials, and becomes much more complicated when studying materials of four or more constituent elements, which have become of increased interest in recent years for technological applications such as energy harvesting and optoelectronics. The algorithm will therefore be of great benefit to the theoretical and computational study of such materials. 相似文献
79.
A series of phosphorus‐containing, wholly aromatic thermotropic copolyesters from acetylated 2‐(6‐oxide‐6H‐dibenz〈c,e〉〈1,2〉oxa phosphorin‐6‐yl)‐1,4‐dihydroxy phenylene, p‐acetoxybenzoic acid, terephthalic acid, and isophthalic acid were prepared by melting polycondensation. The structure and basic properties of the polymers, such as the glass‐transition temperature (Tg), melting temperature (Tm), thermal stability, crystallinity, and liquid crystallinity, were investigated with Fourier transform infrared, elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray diffraction, and hot‐stage polarizing optical microscopy. The copolyesters had relatively high Tg values ranging from 183 to 192°C. The Tm values obtained from DSC curves for samples P‐20 and P‐25 were 290 and 287°C, respectively (where the number in the sample name indicates the molar fraction of the phosphorus‐containing monomer in the reactants). The initial flow temperatures of other samples observed with hot‐stage polarizing microscopy were 271–290°C. The 5% degradation temperatures in nitrogen ranged from 431 to 462°C, and the char yields at 640°C were 41–52%. All the copolyesters, except P‐40, were thermotropic and nematic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1278–1284, 2002 相似文献
80.