全文获取类型
收费全文 | 14391篇 |
免费 | 2067篇 |
国内免费 | 1101篇 |
专业分类
电工技术 | 595篇 |
技术理论 | 1篇 |
综合类 | 600篇 |
化学工业 | 3660篇 |
金属工艺 | 307篇 |
机械仪表 | 1573篇 |
建筑科学 | 201篇 |
矿业工程 | 130篇 |
能源动力 | 208篇 |
轻工业 | 1141篇 |
水利工程 | 48篇 |
石油天然气 | 1046篇 |
武器工业 | 158篇 |
无线电 | 3615篇 |
一般工业技术 | 2231篇 |
冶金工业 | 135篇 |
原子能技术 | 543篇 |
自动化技术 | 1367篇 |
出版年
2024年 | 69篇 |
2023年 | 349篇 |
2022年 | 555篇 |
2021年 | 648篇 |
2020年 | 646篇 |
2019年 | 587篇 |
2018年 | 608篇 |
2017年 | 666篇 |
2016年 | 737篇 |
2015年 | 741篇 |
2014年 | 886篇 |
2013年 | 986篇 |
2012年 | 1015篇 |
2011年 | 1045篇 |
2010年 | 769篇 |
2009年 | 793篇 |
2008年 | 776篇 |
2007年 | 787篇 |
2006年 | 711篇 |
2005年 | 525篇 |
2004年 | 554篇 |
2003年 | 486篇 |
2002年 | 397篇 |
2001年 | 282篇 |
2000年 | 302篇 |
1999年 | 286篇 |
1998年 | 228篇 |
1997年 | 189篇 |
1996年 | 195篇 |
1995年 | 126篇 |
1994年 | 139篇 |
1993年 | 111篇 |
1992年 | 95篇 |
1991年 | 69篇 |
1990年 | 57篇 |
1989年 | 40篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
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
44.
介绍采用射线方法检测功率管芯片与基座之间的焊接质量。试验证明,选用合适的透照参数可使X射线照相和X射线实时成像对焊接部位的检测均得到较高的对比灵敏度,但X射线照相法成本低廉,一次可透照多个工件,效率高,为该功率管焊接质量的理想检测方法。 相似文献
45.
Masahito Matsubayashi Takashi Hibiki Kaichiro Mishima Koji Yoshii Koji Okamoto 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2003,510(3):325-333
A fluorescent converter for fast neutron radiography (FNR) comprising a scintillator and hydrogen-rich resin has been developed and applied to electronic imaging. The rate of the reaction between fast neutrons and the converter is increased by thickening the converter, but its opaqueness attenuates emitted light photons before they reach its surface. To improve the luminosity of a fluorescent converter for FNR, a novel type of converter was designed in which wavelength-shifting fibers were adopted to transport radiated light to the observation end face. The performance of the converter was compared with that of a polypropylene-based fluorescent converter in an experiment conducted at the fast-neutron-source reactor YAYOI in the University of Tokyo. 相似文献
46.
基于模型正演的叠前深度偏移 总被引:2,自引:1,他引:1
川西龙门山前缘构造非常复杂,逆掩推覆构造带构造形变强烈,构造幅度大,地层倾角陡,断块发育,波场复杂,速度横向变化大,常规叠后时间偏移处理成像效果较差。文章将地震资料模型正演技术应用到叠前深度偏移,探讨了一种有助于川西龙门山前缘逆掩推覆构造地震资料精确成像技术。先利用已有地震资料解释成果,根据地质任务建立二维地质模型,在此基础上进行射线追踪、模拟出单炮地震记录和自激自收剖面,从而对观测系统的最大炮检距、道间距等参数进行论证的一些实用方法,这些方法对地震资料采集具有很好的指导作用;然后根据这些结果,再比较准确地进行叠前深度偏移的初始速度模型建立,从而达到了复杂地表下复杂构造精确成像的目的。 相似文献
47.
We propose an asymmetric integral imaging method to adjust the resolution and depth of a three‐dimensional image. Our method is obtained by use of two lenticular sheets with different pitches fabricated under the same F/#. The asymmetric integral imaging is the generalized version of integral imaging, including both conventional integral imaging and one‐dimensional integral imaging. We present experimental results to test and verify the performance of our method computationally. 相似文献
48.
In this paper, the microstructure of a 1 wt.% Cu/γ-Al2O3 catalyst that was reduced in a 4% hydrogen/argon atmosphere at temperatures of 523, 773 and 1073 K, is studied by Z-contrast imaging and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Results show that the copper species are well dispersed when the catalyst is reduced below 523 K. At 773 K, separated Cu(I) and Cu(0) species are found existing as ring-like and bulk-like particles. This appears to indicate that the copper has not been reduced to its metallic form due to the interaction between the copper oxide and the support. Large spherical particles having core-shell structures with Cu(I) in the shells and Cu(0) in the cores are generated when the catalyst is reduced at 1073 K. The formation of partially oxidized copper species upon reduction at 1073 K is attributed to the metallic copper interaction with the alumina support. This study also demonstrates that high-spatial resolution Z-contrast imaging and EELS performed simultaneously can provide unique information on the morphology and chemistry of metal species in supported metal catalysts. 相似文献
49.
用红外、质谱、核磁共振等手段确证了江阴农药厂合成的苯菌灵的化学结构,并进行了该化合物核磁共振谱线的归属。 相似文献
50.
Grard J Martin Doubou Danho Claude Vallet 《Journal of the science of food and agriculture》1991,56(4):419-434
More than 500 carbohydrate samples have been characterised by hydrogen, carbon and oxygen isotopic parameters measured on ethanol and water resulting from controlled fermentation. Different chemical states of the carbohydrate pool have been considered: polysaccharides from cereals, tubers and leguminosae (maize, sorghum, rice, wheat, barley, potato, bean), glucose, fructose and sucrose from fruits (pineapple, citrus, apple, soft fruits), sucrose from sugar plants (beet, cane). The overall carbon-13 content of ethanol and the deuterium and oxygen-18 contents of water before fermentation were determined by mass spectrometry of isotope ratios whereas the investigation of site-specific natural isotope fractionation by deuterium NMR has provided access to the deuterium contents in the methyl (I) and methylene (II) sites of ethanol. The results have been analysed in the multidimensional space of these isotopic variables. Hierarchical clustering, principal component and discriminant analyses have been performed. Among fruits, for example, the pineapple group exhibits a 100% discrimination with respect to the apple and citrus groups which are themselves well distinguished. A still higher discrimination is reached between the three groups, citrus, cane and beet, and the addition of 10% exogenous cane or beet sucrose to citrus juice is unambiguously detected. 相似文献