全文获取类型
收费全文 | 317篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 182篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 67篇 |
物理学 | 70篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 18篇 |
2011年 | 31篇 |
2010年 | 12篇 |
2009年 | 7篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1956年 | 5篇 |
1948年 | 3篇 |
1947年 | 5篇 |
1946年 | 4篇 |
1944年 | 2篇 |
排序方式: 共有328条查询结果,搜索用时 15 毫秒
21.
An analysis considering small departures from radiative equilibrium within a gas, for which radiative heating is approximately formulated in terms of a radiative response time, is compared with an exact solution. It is shown that the approximate formulation does not properly describe local departures from radiative equilibrium, although it is useful in a spatially averaged context. 相似文献
22.
23.
Anodic dissolution of copper in glycine solution at various hydrogen peroxide concentrations was investigated. The dissolution
rate increases, reaches a maximum, and then decreases with hydrogen peroxide concentration. Anodic polarization studies and
electrochemical impedance spectroscopy (EIS) studies were carried out to determine the mechanistic pathway of anodic dissolution
of copper in glycine system at three different hydrogen peroxide concentrations: one at low hydrogen peroxide concentration
in the active dissolution region, another in the maximum dissolution region, and the third at the high hydrogen peroxide concentration
in the post-peak-dissolution region. The EIS data in complex plane plots show presence of two capacitance loops and one negative
capacitance loop. The impedance plot patterns strongly depend on the hydrogen peroxide concentration in solution. Reaction
mechanism analysis technique was employed to model the EIS data. A three-step mechanism with two intermediate adsorbates and
a parallel dissolution by catalytic mechanism simulates EIS patterns which match the experimental trends. The intermediates
are likely to be cupric and cuprous oxides. The essential features of impedance spectra at various overpotentials at three
different hydrogen peroxide concentrations are captured by the proposed mechanism. The results also show that the film present
on the copper surface in glycine and hydrogen peroxide solutions does not passivate the surface. 相似文献
24.
We study the effect of finite chemical potential for the QGP constituents in the Ramanathan et al. statistical model [Phys. Rev.
C70, 027903, (2004)]. While the earlier computations using this model with vanishing chemical potentials indicated a weakly first
order phase transition for the system in the vicinity of 170 MeV [Pramana
68 757 (2007)], the introduction of finite values for the chemical potentials of the constituents makes the transition a smooth
roll over of the phases, while allowing fireball formation with radius of a few ‘fermi’ to take place. This seems to be in
conformity with the latest consensus on the nature of the QGP-Hadron phase transition. 相似文献
25.
Ramanathan A Wright KC Muniz SR Zelan M Hill WT Lobb CJ Helmerson K Phillips WD Campbell GK 《Physical review letters》2011,106(13):130401
We have created a long-lived (≈40 s) persistent current in a toroidal Bose-Einstein condensate held in an all-optical trap. A repulsive optical barrier across one side of the torus creates a tunable weak link in the condensate circuit, which can affect the current around the loop. Superflow stops abruptly at a barrier strength such that the local flow velocity at the barrier exceeds a critical velocity. The measured critical velocity is consistent with dissipation due to the creation of vortex-antivortex pairs. This system is the first realization of an elementary closed-loop atom circuit. 相似文献
26.
We identify conditions under which correlations resulting from quantum measurements performed on macroscopic systems (systems composed of a number of particles of the order of the Avogadro number) can be described by local realism. We argue that the emergence of local realism at the macroscopic level is caused by an interplay between the monogamous nature of quantum correlations and the fact that macroscopic measurements do not reveal properties of individual particles. 相似文献
27.
We give a heuristic proof of a conjecture of Hardy and Littlewood concerning the density of prime pairs to which twin primes and Sophie Germain primes are special cases. The method uses the Ramanujan-Fourier series for a modified von Mangoldt function and the Wiener-Khintchine theorem for arithmetical functions. The failing of the heuristic proof is due to the lack of justification of interchange of certain limits. Experimental evidence using computer calculations is provided for the plausibility of the result. We have also shown that our argument can be extended to the m-tuple conjecture of Hardy and Littlewood. 相似文献
28.
Katkar Santosh Shriram Lande Machhindra Karbhari Arbad Balasaheb Ramrao Gaikwad Suresh Tukaram 《中国化学》2011,29(1):199-202
4H‐Benzo[b]pyrans was synthesized under reflux condition in ethanol via condensation of benzaldehyde, malononitrile and dimedone with ZnO‐beta zeolite as an inexpensive and effective catalyst. The key features of the reported protocols are good to excellent yields, short reaction time and recovery and reusability of catalytic material. 相似文献
29.
Kamsali Murali Mohan Achari Chinnasamy Ramaraj Ramanathan 《Tetrahedron: Asymmetry》2017,28(6):830-836
A conformationally rigid chiral molecule LB-I with Lewis basic site has been designed and synthesized in racemic form from ferrocene via Lewis acid mediated diastereoselective cyclization of hydroxy lactam. Both isomers were successfully obtained in enantiomerically pure form through classical resolution using dibenzoyl-d-tartaric acid as the chiral resolving agent in acetone. The nature of the diastereomeric salt formed in the resolution process was investigated by single crystal X-ray crystallographic studies. The absolute configuration of (+)-LB-I was unambiguously assigned as (S,Rp) by single crystal analysis of the salt I obtained from precipitate fraction containing (+)-LB-I and dibenzoyl-d-tartaric acid. 相似文献
30.
The effect of electric field assisted annealing on the microstructure, composition and ionic conductivity properties in CeO2/YSZ oxide heterostructures have been investigated using molecular dynamics simulations. Amorphization–recrystallization steps were performed with and without external electric field of strength 10?MV/cm along three different orientations: in-plane (YZ), normal (X) and 45° resultant (XY) with respect to the oxide heterointerfaces. The microstructural and compositional differences at the interfaces and in the interior of the oxide heterolayers were evaluated and were found to show a clear correlation with the orientations of the applied field. In particular, the XY configuration displayed a compressive lattice strain of ~9% along with a reduced oxygen vacancy concentration when compared to the others. Ionic density profiles suggest pronounced segregation (~60% higher compared to the average value in the interior) of yttrium ions closer to the YSZ/CeO2 interface for the XY configuration. Other configurations exhibit minimal to no such variations. These microstructural differences are found to affect the number of mobile charge carriers and the activation barriers associated with ionic migration through the oxide lattice and consequently, influence the ionic conductivity. 相似文献