全文获取类型
收费全文 | 57464篇 |
免费 | 2619篇 |
国内免费 | 2062篇 |
专业分类
电工技术 | 2507篇 |
技术理论 | 1篇 |
综合类 | 3019篇 |
化学工业 | 12298篇 |
金属工艺 | 5941篇 |
机械仪表 | 2724篇 |
建筑科学 | 2130篇 |
矿业工程 | 680篇 |
能源动力 | 1492篇 |
轻工业 | 2454篇 |
水利工程 | 249篇 |
石油天然气 | 1203篇 |
武器工业 | 350篇 |
无线电 | 5862篇 |
一般工业技术 | 7683篇 |
冶金工业 | 1354篇 |
原子能技术 | 860篇 |
自动化技术 | 11338篇 |
出版年
2024年 | 131篇 |
2023年 | 604篇 |
2022年 | 1137篇 |
2021年 | 1310篇 |
2020年 | 1042篇 |
2019年 | 961篇 |
2018年 | 839篇 |
2017年 | 1144篇 |
2016年 | 1549篇 |
2015年 | 1844篇 |
2014年 | 2988篇 |
2013年 | 3012篇 |
2012年 | 3433篇 |
2011年 | 5047篇 |
2010年 | 4082篇 |
2009年 | 4332篇 |
2008年 | 3754篇 |
2007年 | 4028篇 |
2006年 | 3623篇 |
2005年 | 3102篇 |
2004年 | 2598篇 |
2003年 | 2529篇 |
2002年 | 2197篇 |
2001年 | 1299篇 |
2000年 | 1101篇 |
1999年 | 852篇 |
1998年 | 632篇 |
1997年 | 505篇 |
1996年 | 384篇 |
1995年 | 261篇 |
1994年 | 227篇 |
1993年 | 229篇 |
1992年 | 194篇 |
1991年 | 137篇 |
1990年 | 125篇 |
1989年 | 116篇 |
1988年 | 73篇 |
1987年 | 61篇 |
1986年 | 80篇 |
1985年 | 82篇 |
1984年 | 66篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 41篇 |
1980年 | 44篇 |
1978年 | 36篇 |
1977年 | 45篇 |
1976年 | 46篇 |
1975年 | 48篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
We demonstrate that alkali-halide salts, particularly potassium bromide, can reduce the photothermal emission (PTE) from single walled carbon nanotubes (SWNT). PTE is a prominent spectral feature in Raman spectroscopy when a near infrared laser is used to analyze a dark colored sample. We subsequently show that trapping salts inside SWNT and coating SWNT with the salt has a more pronounced impact on not only reducing PTE, but also enhancing the intensity of the Raman spectral features. The effect, which we have called nanotube enhanced Raman spectroscopy (NERS), has differences and similarities to the widely studied surface enhanced Raman spectroscopy (SERS). 相似文献
2.
John Bensted 《Cement and Concrete Composites》2003,25(8):873-877
Two main formation routes for thaumasite exist below 15 °C. One is the direct route from C–S–H reacting with appropriate carbonate, sulfate, Ca2+ ions and excess water. The other route is the woodfordite route from ettringite reacting with C–S–H, carbonate, Ca2+ ions and excess water, in which thaumasite arises through the intermediate formation of the solid solution woodfordite. The woodfordite route for thaumasite formation appears to be relatively quicker (although still slow) than the direct route, presumably because with the former the ettringite already has the octahedral [M(OH)6] units that can facilitate the critical change from [Al(OH)6]3− to [Si(OH)6]2− groupings. Both routes are mutually dependent on each other. The presence of magnesium salts can modify the path to thaumasite formation. High pressure might be able to stabilise [Si(OH)6]2− groupings and allow thaumasite to become formed above 15 °C. This possibility is discussed. 相似文献
3.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
4.
5.
介绍了Freescale公司嵌入式微处理器MCF5282的原理、特点,给出了该处理器在嵌入式操作系统uClinux下通过I2C硬件扩展数字输入的原理,以及I2C总线的驱动程序设计流程. 相似文献
6.
基于ISPl581的USB2.0键盘数码管控制设备的设计严格遵循USB2.0协议,体现了USB即插即用、易扩展、低干扰的特点,实现了主机和设备之间简单、快速、可靠的连接和通信。文章介绍了基于ISP1581的USB2.0键盘数码管控制设备的硬件、软件的设计方法。 相似文献
7.
介绍了数字信号处理器ADSP21XX芯片的特点以及实现FFT(快速离散付里叶变换)的方法,给出了ADSP21XX的C和汇编混合编程的特点及技巧。 相似文献
8.
J. Gegner 《Materialwissenschaft und Werkstofftechnik》2003,34(3):290-297
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed. 相似文献
9.
Incorporation of silicon species from an alloy substrate into anodic titania is shown to stabilise the structure of the film, facilitating investigation of the ionic transport processes in amorphous titania grown at high efficiency. Thus, an amorphous anodic film developed on a sputtering-deposited Ti-6 at.%Si alloy formed to 100 V in phosphoric acid electrolyte in contrast to a partially crystalline film developed on relatively pure titanium at <20 V. Silicon species, which are immobile and act as marker species in the growing film, are present in the inner 58% of the film thickness. Evidently, the film material forms simultaneously at the film/electrolyte and alloy/film interfaces by co-operative transport of cations and anions, as is usual in amorphous anodic oxides. The phosphate anions incorporated from the electrolyte migrate inward at 0.34 times the rate of O2− ions and hence are present in the outer 62% of the film thickness. 相似文献
10.
简单介绍了碳氧比测井的原理及通常的数据处理方法。分析了由常规数据处理所得曲线仍然存在的问题及可能的成因 ,并给出了可行的修正办法。讨论了另一种可行的曲线异常数据的检测、剔除方法。实践表明 :文章讨论的两点建议都是可行的 ,并且在提高测量曲线质量的同时也提高了地层含油饱和度的解释精度。 相似文献