全文获取类型
收费全文 | 205篇 |
免费 | 1篇 |
专业分类
化学 | 78篇 |
晶体学 | 1篇 |
数学 | 14篇 |
物理学 | 113篇 |
出版年
2023年 | 1篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 14篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1961年 | 1篇 |
排序方式: 共有206条查询结果,搜索用时 93 毫秒
31.
32.
The formulated ABCD matrix formalism is employed to prescribe analytical expression of coupling efficiency of a laser diode to single-mode circular core dispersion-shifted as well as dispersion-flattened fiber via hyperbolic microlens on the tip of the fiber. We assume that field distribution in case of both the source and the fiber is one parameter Gaussian type. For maximum excitation efficiency, it is required that the lens transmitted spot size of the source should match with the spot size of the fiber. Further, as regards the spot size of the fiber, we use Petermann II spot size in order to take care of non Gaussian nature of field of such fibers and to make the estimations more realistic thereby. The investigations are carried out for two different wavelengths 1.3 and 1.5 μm. Our simple method predicts the concerned coupling optics excellently and the necessary evaluations require little computations. This simple but accurate technique is expected to benefit the system designers who work in the field of optical technology. 相似文献
33.
Sukhendu Jana Sayan Das Debasish De Utpal Gangopadhyay Prajit Ghosh Anup Mondal 《Applied Physics A: Materials Science & Processing》2014,114(3):965-972
The annealing effect on structural and optical properties of the Diamond-like Nanocomposite (DLN) thin film deposited on glass substrate by Plasma Assisted Chemical Vapor Deposition (PACVD) method has been investigated. The films were annealed at temperature ranging from 300 to 600 °C, with 100 °C interval for 9 minutes by rapid thermal process (RTP) under vacuum. The structural changes of the annealed films have been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning Electron Microscope (SEM), and optical parameters have been determined using transmittance and reflectance spectra in UV-UIS-NIR range. The result shows that the refractive index increases gradually from 1.79 to 2.84 with annealing temperature due to out-diffusion of H by breaking Si–H and C–H bond leads to Si–C bond, i.e. more cross linking structure. In higher temperature range, graphitization also enhanced the refractive index. However, the optical band gap at up to 400 °C initially increases from 3.05 to 3.20 eV and then decreases due to graphitization. The film has a great potential to be used as anti-reflection coating (ARC) on silicon-based solar cell. 相似文献
34.
Wang WN An WJ Ramalingam B Mukherjee S Niedzwiedzki DM Gangopadhyay S Biswas P 《Journal of the American Chemical Society》2012,134(27):11276-11281
A facile development of highly efficient Pt-TiO(2) nanostructured films via versatile gas-phase deposition methods is described. The films have a unique one-dimensional (1D) structure of TiO(2) single crystals coated with ultrafine Pt nanoparticles (NPs, 0.5-2 nm) and exhibit extremely high CO(2) photoreduction efficiency with selective formation of methane (the maximum CH(4) yield of 1361 μmol/g-cat/h). The fast electron-transfer rate in TiO(2) single crystals and the efficient electron-hole separation by the Pt NPs were the main reasons attributable for the enhancement, where the size of the Pt NPs and the unique 1D structure of TiO(2) single crystals played an important role. 相似文献
35.
Miodrag J. Mihaljevi? Sugata Gangopadhyay Goutam Paul Hideki Imai 《Periodica Mathematica Hungarica》2012,65(2):205-227
This paper considers security implications of k-normal Boolean functions when they are employed in certain stream ciphers. A generic algorithm is proposed for cryptanalysis of the considered class of stream ciphers based on a security weakness of k-normal Boolean functions. The proposed algorithm yields a framework for mounting cryptanalysis against particular stream ciphers within the considered class. Also, the proposed algorithm for cryptanalysis implies certain design guidelines for avoiding certain weak stream cipher constructions. A particular objective of this paper is security evaluation of stream cipher Grain-128 employing the developed generic algorithm. Contrary to the best known attacks against Grain-128 which provide complexity of a secret key recovery lower than exhaustive search only over a subset of secret keys which is just a fraction (up to 5%) of all possible secret keys, the cryptanalysis proposed in this paper provides significantly lower complexity than exhaustive search for any secret key. The proposed approach for cryptanalysis primarily depends on the order of normality of the employed Boolean function in Grain-128. Accordingly, in addition to the security evaluation insights of Grain-128, the results of this paper are also an evidence of the cryptographic significance of the normality criteria of Boolean functions. 相似文献
36.
In this paper an alternative approach for measurement of στ product for 4
F
3/2→4
I
11/2 transition of Nd3+ doped YVO4 crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator
and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable.
The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is
measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO4 crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple
method for direct measurement of στ product of laser crystals. 相似文献
37.
Tunable mid-infra-red radiation by singly resonant optical parametric oscillation based on KTA crystal pumped by multi-axial
Gaussian shape beam from Q-switched Nd:YAG laser has been demonstrated. Threshold energy of oscillation at different idler
wavelengths for different cavity length has been demonstrated. Single pass conversion efficiency of incident pump energy to
infra-red wavelength has also been measured. 相似文献
38.
We have studied the effect of environment induced pure decoherence on the generalized Jaynes-Cummings model (JCM). This generalized
JCM is introduced to take into account both atom-field interaction and a class of spin-orbit interactions in the same framework.
For generalized JCM with atom-field interaction, it is shown that along with the suppression of the oscillatory behaviour
of the atomic and field variables, in the steady state, atomic energy is transferred to the field or vice versa through the
dressed state coherence depending on the initial condition of the atom-field system and the model under consideration. It
is also shown that initial Poissonian field acquires a sub-Poissonian character in the steady state and thus all the nonclassical
properties are not erased by the decoherence in JCM. An interesting effect of this decoherence mechanism is that it affects
the population and coherence properties of the individual subsystem in a different way. As an example of generalized JCM with
spin-orbit interaction, the dynamics of spin of the hydrogen atom in a magnetic field is studied to show the effect of decoherence. 相似文献
39.
Employing Gaussian field distributions for both the source and the fiber, we report a simple theoretical prediction of the coupling efficiency of a laser diode to a single-mode elliptic core fiber via hemispherical lens on the fiber tip. The analysis is based on ABCD matrix for hemispherical lens under paraxial approximation. Our formalism takes care of the allowable aperture of the hemispherical lens. The present analysis prescribes analytical expressions for the coupling efficiency and the concerned calculations are executable by pocket calculator. 相似文献