全文获取类型
收费全文 | 8206篇 |
免费 | 1200篇 |
国内免费 | 424篇 |
专业分类
电工技术 | 83篇 |
综合类 | 428篇 |
化学工业 | 3667篇 |
金属工艺 | 390篇 |
机械仪表 | 349篇 |
建筑科学 | 157篇 |
矿业工程 | 99篇 |
能源动力 | 200篇 |
轻工业 | 1042篇 |
水利工程 | 10篇 |
石油天然气 | 612篇 |
武器工业 | 90篇 |
无线电 | 539篇 |
一般工业技术 | 1355篇 |
冶金工业 | 185篇 |
原子能技术 | 88篇 |
自动化技术 | 536篇 |
出版年
2024年 | 33篇 |
2023年 | 140篇 |
2022年 | 212篇 |
2021年 | 244篇 |
2020年 | 282篇 |
2019年 | 280篇 |
2018年 | 234篇 |
2017年 | 301篇 |
2016年 | 504篇 |
2015年 | 539篇 |
2014年 | 600篇 |
2013年 | 679篇 |
2012年 | 568篇 |
2011年 | 672篇 |
2010年 | 424篇 |
2009年 | 490篇 |
2008年 | 369篇 |
2007年 | 521篇 |
2006年 | 419篇 |
2005年 | 388篇 |
2004年 | 300篇 |
2003年 | 251篇 |
2002年 | 214篇 |
2001年 | 181篇 |
2000年 | 169篇 |
1999年 | 114篇 |
1998年 | 110篇 |
1997年 | 98篇 |
1996年 | 93篇 |
1995年 | 74篇 |
1994年 | 59篇 |
1993年 | 38篇 |
1992年 | 50篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有9830条查询结果,搜索用时 15 毫秒
41.
本文用不热形变栅状直丝化学气相沉积(CVD)法生长金刚石膜,在Si及WC-Co硬质合金衬底上金刚石膜晶面显露规律随衬底温度和甲烷浓度而异,经适当表面处理及选择合适的工艺条件,当生长初期衬底上就呈现出良好晶形的沉积膜,衬底与膜之间的粘结力能得到提高。Raman谱分析表明此膜仅具有特征金刚石1332cm ̄(-1)峰,通过SEM观察揭示出盒刚石膜可在表面、侧面及棱上生长,并与衬底有良好的联结。 相似文献
42.
A new surface characterization technique: RIMAPS (Rotated Image with Maximum Average Power Spectrum)
This work introduces a new imaging technique, Rotated Image with Maximum Average Power Spectrum (RIMAPS), for use in determining orientation and characteristics of surface topography. It consists of computing the maximum value of the averaged power spectrum, given by one step of the two‐dimensional Fourier transform, for each angle of rotation of a digitized image. The basic measurement science of this technique is described and different cases are studied. The characterization of simple geometrical figures explains the meaning of peaks and their angular positions given by RIMAPS analysis. A known surface pattern made on a sample of pure copper, mechanically ground, is used to study reproducibility, dependence on image quality and topography scale relative to pixel size and magnification. Samples of pure zinc, mechanically ground and chemically etched, were used to show the main features of RIMAPS analysis when characterizing a more complicated pattern on a real surface. All the studies performed under different conditions for observation and acquisition of images give strong evidence of the stability and robustness of RIMAPS as a technique for the characterization of topography. 相似文献
43.
Sandra Aparecida de Assis Pedro Fernandes Bruno Sommer Ferreira Joaquim MS Cabral Olga Maria Mascarenhas Faria Oliveira 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(3):277-280
A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry 相似文献
44.
Instrumental characterization of clay by XRF,XRD and FTIR 总被引:2,自引:0,他引:2
Instrumental characterizations of the clay were performed by different techniques such as XRF, XRD and FTIR. XRF shows the
chemical compositions of the clay where Al-oxide and silica oxide are present in major quantity whereas XRD confirms the presence
of these minerals in clay. FTIR studies show the presence of quartz, alumina, haematite and different mineral matters. 相似文献
45.
Didier SBILLEAU 《核技术(英文版)》2003,14(1)
We present here a general overview of electron spectroscopies from a practical point of view. The most frequently used ones are described and the type of structural information they can provide on materials is explained in relation to the physical processes on which they are based. Furthermore, we explore critically and in detail various tools that have been developed to allow a systematic solving of structures by these spectroscopies. 相似文献
46.
本文利用回归分析导出材料耗用的回归方程 ,并对方程进行拟合优度检测和显著性检验 ,以及对材料耗用情况进行综合评价。 相似文献
47.
Bending tests of crystalline nanotubes composed of fullerene C60 molecules are performed inside a high-resolution transmission electron microscope. We fixed one side of a C60 nanotube with a body-centered tetragonal structure with typical inner and outer diameters, i.e., 180 nm and 510 nm, respectively, and then applied concentrated forces on the other side using piezomanipulation of a silicon nanotip. The bending process was observed in situ by transmission electron microscopy with simultaneous measurements of the forces by an optical deflection method. It was found that the Young’s modulus of the nanotube was estimated to be 62–107 GPa, which was 1.1–3.3 times larger than that of C60 nanowhiskers. The result concerning the increase in the Young’s modulus of the C60 nanotube provided an experimental evidence for the structural model composed of an inner core and a surface shell for C60 nanowhiskers. 相似文献
48.
49.
How to study drying shrinkage microcracking in cement-based materials using optical and scanning electron microscopy? 总被引:3,自引:0,他引:3
Three different ‘destructive’ microscopy methods were tested on their ability to show drying shrinkage microcracks on a specimen cross-section. The first two were methods in which the microcracks were impregnated with a fluorescent epoxy and examined with fluorescence microscopy. In one method, the impregnation was applied before making the cross-section and in the other after making the cross-section. In the third method, the sample was kept wet constantly and examined in an environmental scanning electron microscope (ESEM). It was concluded that the method in which the dried specimen was impregnated before making the cross-section was the most reliable method to record drying shrinkage microcracks. With this method, it was possible to impregnate the complete drying shrinkage microcrack pattern in the studied cement-based materials from the surface, and there was no risk of recording microcracks introduced by sample preparation. 相似文献
50.
Zeolite beta with a low SiO2/Al2O3 ratio was synthesized by a novel two-step process.The synthesized sample was characterized with XRD,SEM,FTIR,and N2 adsorption-desorption and solid-state MAS NMR.The results showed that aluminium species were inserted into the framework of zeolite beta.The BET surface area,volume,and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio.Our process was proved an efficient route to synthesize zeolite beta with a low SiO2/Al2O3 ratio. 相似文献