全文获取类型
收费全文 | 10117篇 |
免费 | 2285篇 |
国内免费 | 1101篇 |
专业分类
化学 | 4937篇 |
晶体学 | 30篇 |
力学 | 78篇 |
综合类 | 33篇 |
数学 | 64篇 |
物理学 | 4599篇 |
无线电 | 3762篇 |
出版年
2024年 | 63篇 |
2023年 | 187篇 |
2022年 | 459篇 |
2021年 | 579篇 |
2020年 | 637篇 |
2019年 | 524篇 |
2018年 | 471篇 |
2017年 | 572篇 |
2016年 | 654篇 |
2015年 | 667篇 |
2014年 | 971篇 |
2013年 | 880篇 |
2012年 | 840篇 |
2011年 | 785篇 |
2010年 | 600篇 |
2009年 | 637篇 |
2008年 | 606篇 |
2007年 | 620篇 |
2006年 | 437篇 |
2005年 | 386篇 |
2004年 | 289篇 |
2003年 | 245篇 |
2002年 | 201篇 |
2001年 | 161篇 |
2000年 | 174篇 |
1999年 | 141篇 |
1998年 | 111篇 |
1997年 | 102篇 |
1996年 | 109篇 |
1995年 | 73篇 |
1994年 | 64篇 |
1993年 | 54篇 |
1992年 | 50篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The micro mechanism of anti-Stokes fluorescent cooling was investigated on molecular or ionic scale. A new conception of single
molecule-photon cryocooler (SMPC) was given, and the smallest cryocooler in the world was predicted. We described SMPC and
its running principle in detail. The quantum transition processes of SMPC and the largest cooling coefficient that SMPC can
get in an optical transition were given. Also we studied the random property of SMPC in cooling processes. The thermodynamic
behavior of single Yb3+ ion as a photon cryocooler was imitated. 相似文献
942.
The fluorescent spectrum and the excitation spectrum were used to present the cluster molecular structure feature in ethanol-water solutions.Through analyzing the fluorescent characteristics of an excimer,it is proposed that the excimers are formed between the ethanol-water cluster molecules in the excited state and in the ground state.The fluorescent lifetime and the fluorescent intensity decay process give information about the photo-physical and photo-chemical processes of the formation and the dissociation of an excimer.The theoretical calculation and physical analysis coincide with the experimental results.The preliminary conclusion about the structure feature of ethanol-water cluster molecule is that it has a planar one like a sandwich. 相似文献
943.
Maria F. Ebel Horst Ebel Guido Barnegg-Golwig Michael Mantler Robert Svagera 《Mikrochimica acta》1990,101(1-6):63-69
The paper gives an outline of the basic principle of our imaging technique for XPS. The advantage of the concept is its excellent applicability to quantitative pixel information. This idea is verified by two examples which are representative for routine problems in XPS. These are quantitative surface analysis and determination of overlayer thicknesses. A lateral resolution of at least 0.2 mm is achieved and thus a pixel size of 0.2 mm × 0.2 mm can be quantified automatically by means of numerical algorithms without need of reference samples.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday 相似文献
944.
945.
946.
John Walton 《Surface and interface analysis : SIA》2007,39(4):337-342
Localised corrosion on a microchannel plate has been studied using X‐ray photoelectron spectromicroscopy. Curve fitting to the spectra at each pixel in the image data set reveals the presence of sodium and carbonate species at the corrosion sites, which optical microscopy suggests originated as droplets. It is proposed that aerosol contamination of the alkali enriched microchannel plate during removal of particulate material using a stream of compressed gas was responsible for the initiation of corrosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
947.
948.
Yiming Zhao Jing Yan Yanxin Wang Qianzhen Jing Tingliang Liu 《Entropy (Basel, Switzerland)》2021,23(4)
A porcelain insulator is an important part to ensure that the insulation requirements of power equipment can be met. Under the influence of their structure, porcelain insulators are prone to mechanical damage and cracks, which will reduce their insulation performance. After a long-term operation, crack expansion will eventually lead to breakdown and safety hazards. Therefore, it is of great significance to detect insulator cracks to ensure the safe and reliable operation of a power grid. However, most traditional methods of insulator crack detection involve offline detection or contact measurement, which is not conducive to the online monitoring of equipment. Hyperspectral imaging technology is a noncontact detection technology containing three-dimensional (3D) spatial spectral information, whereby the data provide more information and the measuring method has a higher safety than electric detection methods. Therefore, a model of positioning and state classification of porcelain insulators based on hyperspectral technology is proposed. In this model, image data were used to extract edges to locate cracks, and spectral information was used to classify the surface states of porcelain insulators with EfficientNet. Lastly, crack extraction was realized, and the recognition accuracy of cracks and normal states was 96.9%. Through an analysis of the results, it is proven that the crack detection method of a porcelain insulator based on hyperspectral technology is an effective non-contact online monitoring approach, which has broad application prospects in the era of the Internet of Things with the rapid development of electric power. 相似文献
949.
《中国物理 B》2021,30(9):96106-096106
The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material, which could be benefited from pulsed neutron source. Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source. The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15% by the time-of-flight neutron Bragg-edge imaging on this system. The results show its great potential applications in materials science and engineering. 相似文献
950.
Gaining an in-depth understanding of the characteristics and dynamics of ultrasound (US)--generated bubbles is crucial to effectively remediate membrane fouling. The goal of present study is to conduct in-situ visualization of US-generated microbubbles in water to examine the influence of US frequency on the dynamics of microbubbles. This study utilized synchrotron in-line phase contrast imaging (In-line PCI) available at the biomedical imaging and therapy (BMIT) beamlines at the Canadian Light Source (CLS) to enhance the contrast of liquid/air interfaces at different US frequencies of 20, 28 and 40 KHz at 60 Watts. A high-speed camera was used to capture 2,000 frames per second of the bubble cavitation generated in water under the ultrasound influence. Key parameters at the polychromatic beamlines were optimized to maximize the phase contrast of gas/liquid of the microbubbles with a minimum size of 5.5 µm. ImageJ software was used to analyze the bubble characteristics and their behavior under the US exposure including the microbubble number, size, and fraction of the total area occupied by the bubbles at each US frequency. Furthermore, the bubble characteristics over the US exposure time and at different distances from the transducer were studied. The qualitative and quantitative data analyses showed that the microbubble number or size did not change over time; however, it was observed that most bubbles were created at the middle of the frames and close to the US field. The number of bubbles created under the US exposure increased with the frequency from 20 kHz to 40 kHz (about 4.6 times). However, larger bubbles were generated at 20 kHz such that the average bubble radius at 20 kHz was about 6.8 times of that at 40 kHz. Microbubble movement/traveling through water was monitored, and it was observed that the bubble velocity increased as the frequency was increased from 20 kHz to 40 kHz. The small bubbles moved faster, and the majority of them traveled upward towards the US transducer location. The growth pattern (a correlation between the mean growth ratio and the exposure time) of bubbles at 20 kHz and 60 W was obtained by tracking the oscillation of 22 representative microbubbles over the 700 ms of imaging. The mean growth ratio model was also obtained. 相似文献