全文获取类型
收费全文 | 3517篇 |
免费 | 412篇 |
国内免费 | 309篇 |
专业分类
化学 | 927篇 |
晶体学 | 7篇 |
力学 | 1362篇 |
综合类 | 47篇 |
数学 | 489篇 |
物理学 | 1406篇 |
出版年
2024年 | 11篇 |
2023年 | 35篇 |
2022年 | 112篇 |
2021年 | 106篇 |
2020年 | 118篇 |
2019年 | 85篇 |
2018年 | 69篇 |
2017年 | 134篇 |
2016年 | 183篇 |
2015年 | 124篇 |
2014年 | 194篇 |
2013年 | 228篇 |
2012年 | 174篇 |
2011年 | 201篇 |
2010年 | 117篇 |
2009年 | 189篇 |
2008年 | 203篇 |
2007年 | 216篇 |
2006年 | 197篇 |
2005年 | 175篇 |
2004年 | 140篇 |
2003年 | 141篇 |
2002年 | 138篇 |
2001年 | 121篇 |
2000年 | 118篇 |
1999年 | 86篇 |
1998年 | 96篇 |
1997年 | 57篇 |
1996年 | 85篇 |
1995年 | 61篇 |
1994年 | 52篇 |
1993年 | 45篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 16篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1971年 | 3篇 |
1957年 | 5篇 |
排序方式: 共有4238条查询结果,搜索用时 15 毫秒
141.
142.
143.
By means of a new force sensor based on optical beam deflection (OBD), the mechanical effects of laser-matter interaction underwater at different incident laser energy are investigated in detail. The experimental results show that a target underwater is impacted in turn by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid boundary. Furthermore, the amplitudes of the two forces increase monotonously with laser energy. According to the ablation force detected by the experiment and the theoretical relationship between laser intensity and ablation pressure, the value of liquid-jet impact against a solid boundary can be easily obtained. In addition, based on the model of a collapsing bubble, some characteristic parameters, such as the liquid-jet impact velocity, the maximum bubble radius, the bubble energy can also be obtained at different laser energy, which are valuable in the corresponding research fields. 相似文献
144.
145.
146.
The cross section of the 3s → 3p transition of sodium produced by electron impact has been calculated by performing a numerical integration of the coupled differential equations. The potential functions have been calculated exactly using the hydrogen‐like wave functions for the valence electron of the sodium with an effective charge adjusted to fit the experimental 3s → 3p line strength. The results compare very well with experimental data and with those obtained using more elaborate and sophisticated models. 相似文献
147.
A new technique for the identification of ultrasonic flaw signals using deconvolution 总被引:1,自引:0,他引:1
The identification of ultrasonic flaw signals is a difficult task in the angle beam ultrasonic testing of welded joints due to the presence of non-relevant signals from the geometric reflectors such as weld-roots and counter-bores. This paper describes a new approach to identify ultrasonic flaw signals in such a problematic situation. A similarity function is defined as the deconvolution of a target signal by a reference signal. The similarity functions for the same type of flaws/references are symmetric bandlimited impulse-like patterns with larger amplitudes while those for different types of flaws/references are asymmetrical broad patterns with relatively smaller amplitudes. Therefore, ultrasonic signals could be identified by the pattern of the similarity function. In the initial experiments, the proposed technique showed great potential for identifying ultrasonic flaw signals in the inspection of weld joints. 相似文献
148.
Real-time visualisation of deformation fields using speckle interferometry and temporal phase unwrapping 总被引:1,自引:0,他引:1
A real-time system for analysing data from speckle interferometers, and speckle shearing interferometers, has been developed. Interferograms are continuously recorded by a digital camera at a rate of 60 frames s−1 with temporal phase shifting carried out at the same rate. The images are analysed using a pipeline image processor. With a standard 4-frame phase-shifting algorithm (phase steps of π/2), wrapped phase maps are calculated and displayed at 15 frames s−1. These are unwrapped using a temporal phase unwrapping algorithm to provide a real-time colour-coded display of the relevant displacement component. Each camera pixel (or cluster of pixels) behaves in effect as an independent displacement sensor. The reference speckle interferogram is updated automatically at regular user-defined intervals, allowing arbitrarily large deformations to be measured and errors due to speckle decorrelation to be minimised. The system has been applied to the problem of detecting sub-surface delamination cracks in carbon fibre composite panels. 相似文献
149.
M. Ismail A. Farraga H. A. Abdusalam Th. El-Sherbini 《International Journal of Theoretical Physics》2004,43(1):111-125
The scattering of electrons by atomic copper has been studied using Born approximation and the concept of the generalized oscillator strength (GOS). Differential and total cross-sections for the excitation of the 3d10 4p2 P state are calculated at incident energies of 100 eV and are compared with other available experimental and theoretical data. The agreement between our calculation for the differential cross-section and the available experimental results is fairly good at the forward angles, while the agreement at large angles is poor. The calculated total cross-sections are compared with the experimental data and those predicted by several theories. It is found that our calculation for the total cross-sections are in a good agreement with the close coupling calculation of Msezane and Henry (1986a, Physical Review A
33, 1631) for incident energies greater than 20 eV. The integrated cross-section measurements of Ismail and Teubner (1995, Journal of Physics B: Atomic, Molecular and Optical Physics
28, 4164) are in good agreement with the present calculation. 相似文献
150.