全文获取类型
收费全文 | 1910篇 |
免费 | 531篇 |
国内免费 | 83篇 |
专业分类
化学 | 303篇 |
晶体学 | 10篇 |
力学 | 99篇 |
综合类 | 16篇 |
数学 | 76篇 |
物理学 | 2020篇 |
出版年
2024年 | 2篇 |
2023年 | 22篇 |
2022年 | 55篇 |
2021年 | 57篇 |
2020年 | 69篇 |
2019年 | 48篇 |
2018年 | 46篇 |
2017年 | 78篇 |
2016年 | 82篇 |
2015年 | 67篇 |
2014年 | 151篇 |
2013年 | 139篇 |
2012年 | 132篇 |
2011年 | 139篇 |
2010年 | 106篇 |
2009年 | 119篇 |
2008年 | 145篇 |
2007年 | 139篇 |
2006年 | 137篇 |
2005年 | 99篇 |
2004年 | 104篇 |
2003年 | 71篇 |
2002年 | 64篇 |
2001年 | 69篇 |
2000年 | 69篇 |
1999年 | 49篇 |
1998年 | 53篇 |
1997年 | 39篇 |
1996年 | 32篇 |
1995年 | 26篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2524条查询结果,搜索用时 359 毫秒
991.
The impact of measurement noise and tomographic methods on reconstruction quality are investigated via simulation studies under a hypothesis harsh flow field environment. Computer tomographic methods based on direct absorption spectroscopy and wavelength modulation spectroscopy are conducted under different measurement noise levels to assess the noise effect quantitatively. It turns out that the wavelength modulation spectroscopy-based tomographic method shows efficient immunity to measurement noise. However, the direct absorption spectroscopy-based tomographic method is found to be susceptible to the measurement noise, which makes the reconstruction quality decline with the increasing noise level. In addition, two kinds of tomographic methods including linear and nonlinear method are investigated under a complex multimodal temperature distribution environment with limited projection data. The reconstructed distribution for the nonlinear tomographic method reveals great fidelity to the original value with a maximum deviation of 51.9?K, while the reconstructed distribution for the linear tomographic method under parallel beam arrangement shows an obvious distortion. 相似文献
992.
A model containing two two-level atoms and a single-mode cavity is considered, and the effect of the time-dependent atom-field couplings on entanglement between the two atoms is studied. The results indicate that both for one-photon processes and for two-photon processes, the disappearance of the initial entanglement is delayed due to the linear modulation of the atom-field coupling coefficients as compared to the constant coupling model. The delayed time of the disappearance of the initial entanglement for the two-photon processes is much longer than that for the one-photon processes in the case of adiabatic variation. 相似文献
993.
994.
995.
A polarization modulation technique is presented which utilizes the manipulation of a wide band, incoherent source. An application to the measurement of sugar concentration is described. A conceptual fibre-optic sensor, based on the technique, is discussed. Particular attention is given to the design of a dielectric multilayer filter which will provide the means of dividing the spectrum into polarized and unpolarized components with the latter being used to calibrate the former. 相似文献
996.
In this paper, a new theta modulation multiplexing scheme for producing multiplexed computer-generated holograms (CGHs) is proposed. Under this scheme, normal Lohmann-type CGHs are individually modulated by gratings with different orientations and then superimposed to form a single hologram. The proposed method results in a higher storage capacity without the increase of hologram space. Theoretical analysis and experimental results are presented. 相似文献
997.
象增强高速电影摄影系统MTF及其改善 总被引:5,自引:2,他引:3
象增强高速电影摄影在提高探测能力的同时,也引起了成象质量的变化。文章讨论了引起这一变化的各种因素的调制传递函数,给出了在不同的参数下,系统总的调制传递函数数值。并且提出了改善系统MTF的途径。 相似文献
998.
H. Gerlach 《Applied Physics A: Materials Science & Processing》1973,1(5):279-283
The frequency dependence of some electrooptic tensor coefficients of KDP, LiIO3, and benzil was measured by means of a lock-in amplifier. The technique was also used above the upper frequency limit of
the lock-in amplifier. This was achieved by modulating the high frequency voltage at a fixed low frequency and inserting a
fast demodulator into the receiving circuit. The resolution in phase shift was 10−5 degree and when modulated about 10−4 degree. 相似文献
999.
CO2激光器的腔长调制及动力学参数的测定 总被引:1,自引:1,他引:0
采用含有振转能级在内的多能级理论模型,对CO_2激光器动力学参量进行调制,取得实验与理论一致的满意结果.利用理论与实验曲线拟合的方法,较精确地测出该激光器的动力学参数. 相似文献
1000.
In this paper we present a novel technique for acoustic field imaging. This technique is based on reflection of a collimated laser beam at the free surface of a liquid. The reflected beam becomes phase modulated by the acoustic wave as in acoustical holographic systems. We do not use a reference acoustical beam for holographic reconstruction but we observe this phase modulation using dark-field techniques. It gives a measurement of the acoustic field power as a function of the position. The authors have built an optical imaging system and carried out experiments with piezocomposite transducers. The technique presented in this work is able to give fast quantitative information about the performance of individual ceramic rods of the piezocomposite. 相似文献