全文获取类型
收费全文 | 228篇 |
免费 | 0篇 |
国内免费 | 19篇 |
专业分类
化学 | 33篇 |
力学 | 11篇 |
数学 | 46篇 |
物理学 | 157篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 9篇 |
2016年 | 26篇 |
2015年 | 3篇 |
2014年 | 60篇 |
2013年 | 39篇 |
2012年 | 35篇 |
2011年 | 18篇 |
2010年 | 2篇 |
2009年 | 6篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 5篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2002年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1967年 | 1篇 |
1963年 | 2篇 |
1960年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有247条查询结果,搜索用时 171 毫秒
241.
A three-level atom in a Λ configuration trapped in an optical cavity forms a basic unit in a number of proposed protocols
for quantum information processing. This system allows for efficient storage of cavity photons into long-lived atomic excitations,
and their retrieval with high fidelity, in an adiabatic transfer process through the ‘dark state’ by a slow variation of the
control laser intensity. We study the full quantum mechanics of this transfer process with a view to examine the non-adiabatic
effects arising from inevitable excitations of the system to states involving the upper level of Λ, which is radiative. We
find that the fidelity of storage is better, the stronger the control field and the slower the rate of its switching off.
On the contrary, unlike the adiabatic notion, retrieval is better with faster rates of switching on of an optimal control
field. Also, for retrieval, the behaviour with dissipation is non-monotonic. These results lend themselves to experimental
tests. Our exact computations, when applied to slow variations of the control intensity for strong atom–photon couplings,
are in very good agreement with Berry’s superadiabatic transfer results without dissipation. 相似文献
242.
Drell–Yan process at LHC, q[`(q)]? Z/g* ? l+l-q\bar {q}\to Z/\gamma ^\ast \to \ell ^+\ell ^-, is one of the benchmarks for confirmation of Standard Model at TeV energy scale. Since the theoretical prediction for the
rate is precise and the final state is clean as well as relatively easy to measure, the process can be studied at the LHC
even at relatively low luminosity. Importantly, the Drell–Yan process is an irreducible background to several searches of
beyond Standard Model physics and hence the rates at LHC energies need to be measured accurately. In the present study, the
methods for measurement of the Drell–Yan mass spectrum and the estimation of the cross-section have been developed for LHC
operation at the centre-of-mass energy of 10 TeV and an integrated luminosity of 100 pb − 1 in the context of CMS experiment. 相似文献
243.
In this paper, we report a new method to determine the effective atomic number, Z
eff, of composite materials for Compton effect in the γ-ray region 280–1115 keV based on the theoretically obtained Klein–Nishina scattering cross-sections in the angular range
50°–100° as well as a method to experimentally measure differential incoherent (Compton) scattering cross-sections in this
angular range. The method was employed to evaluate Z
eff for different inorganic compounds containing elements in the range Z = 1–56, at three scattering angles 60°, 80° and 100° at three incident gamma energies 279.1 keV, 661.6 keV and 1115.5 keV
and we have verified this method to be an appropriate method. Interestingly, the Z
eff values so obtained for the inorganic compounds were found to be equal to the total number of electrons present in the sample
as given by the atomic number of the elements constituting the sample in accordance with the chemical formula of the sample.
This was the case at all the three energies. 相似文献
244.
This paper deals with the study of behaviour of G-associated ideals and strong Krull G-associated ideals with flat base change of rings and behaviour of G-associated ideals with short exact sequences over rings graded by finitely generated abelian group G. 相似文献
245.
Calcium and barium zirconate powders based upon CaZrO3:Eu3+,A and BaZrO3:Eu3+,A (A=Li+, Na+, K+) were prepared by combustion synthesis method and heating to ~1000℃ to improve crystallinity.The structure and morphology of materials were examined by X-ray diffraction (XRD) and scanningelectron microscopy (SEM). XRD results showed that CaZrO3:Eu3+,A and BaZrO3:Eu3+,A (A=Li+, Na+, K+) perovskites possessed orthorhombic and cubic structures, respectively. The morphologies of all powderswere very similar consisting of small, coagulated, cubical particles with narrow size distributions andsmooth and regular surfaces. The characteristic luminescences of Eu3+ ions in CaZrO3:Eu3+,A (A=Li+, Na+, K+) lattices were present with strong emissions at 614 and 625 nm for 5D0→7F2 transitions with other weakeremissions observed at 575, 592, 655, and 701 nm corresponding to 5D0→7Fn transitions (where n=0, 1, 3, 4 respectively). In BaZrO3:Eu3+ both the 5D0→7F1 and 5D0→7F2 transitions at 595 and 613 nm were strong.Photoluminescence intensities of CaZrO3:Eu3+ samples were higher than those of BaZrO3:Eu3+ lattices. Thisremarkable increase of photoluminescence intensity (corresponding to 5D0→7Fn transitions) was observedin CaZrO3:Eu3+ and BaZrO3:Eu3+ if co-doped with Li+ ions. An additional broad band composed of manypeaks between 440 to 575 nm was observed in BaZrO3:Eu3+,,A samples. The intensity of this band wasgreatest in Li+ co-doped samples and lowest for K+ doped samples. 相似文献
246.
Shah R. ALI Prakash CHANDRA Mamta LATWAL Shalabh K. JAIN Vipin K. BANSAL Sudhanshu P. SINGH 《催化学报》2011,(12):1844-1849
Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H2O2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H2O2 molar ratio, and the reaction time. 相似文献
247.