全文获取类型
收费全文 | 588篇 |
免费 | 11篇 |
专业分类
化学 | 331篇 |
晶体学 | 3篇 |
力学 | 52篇 |
数学 | 71篇 |
物理学 | 142篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2017年 | 17篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 49篇 |
2012年 | 35篇 |
2011年 | 46篇 |
2010年 | 36篇 |
2009年 | 14篇 |
2008年 | 28篇 |
2007年 | 31篇 |
2006年 | 28篇 |
2005年 | 14篇 |
2004年 | 23篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1968年 | 4篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1939年 | 2篇 |
排序方式: 共有599条查询结果,搜索用时 15 毫秒
591.
Narendra Chauhan Ankush Mittal Dietmar Wagner M. V. Kartikeyan M. K. Thumm 《International Journal of Infrared and Millimeter Waves》2008,29(8):792-798
In this paper the design and optimization of a nonlinear diameter taper, connecting the output section of a gyrotron cavity
to the uniform output waveguide section, is presented. The design of a nonlinear taper of a 42 GHz, 200 kW CW gyrotron operating
in the TE0,3 cavity mode with axial output collection has been taken as a case study. The taper synthesis has been carried out considering
a raised cosine type of nonlinear taper and the analysis is done using a dedicated scattering matrix code. In addition, an
improved particle swarm optimization - an evolutionary optimization - algorithm is used for the design optimization of this
nonlinear taper. The optimum design of the taper shows the effectiveness of the presented method. 相似文献
592.
A.D.D. Dwivedi A. Mittal A. Agrawal P. Chakrabarti 《Infrared Physics & Technology》2010,53(4):236-245
In this paper we report an analytical modeling of N+-InP/n0-In0.53Ga0.47As/p+-In0.53Ga0.47As p-i-n photodetector for optical fiber communication. The results obtained on the basis of our model have been compared and contrasted with the simulated results using ATLAS? and experimental results reported by others. The photodetector has been studied in respect of energy band diagram, electric field profile, doping profile, dark current, resistance area-product, quantum efficiency, spectral response, responsivity and detectivity by analytical method using closed form equations and also been simulated by using device simulation software ATLAS? from SILVACO® international. The photodetector exhibits a high quantum efficiency ~90%, responsivity ~1.152–1.2 A/W in the same order as reported experimentally by others, specific detectivity ~5 × 109 cm Hz1/2 W?1at wavelength 1.55–1.65 μm, dark current of the order of 10?11 A at reverse bias of 1.5 V and 10?13–10?12 A near zero bias. These values are comparable to those obtained for practical p-i-n detectors. The estimated noise equivalent power (NEP) is of the order of 2.5 × 10?14 W. 相似文献
593.
Rajpal S Kashyap Aliabbas A Husain Shweta H Morey Milind S Panchbhai Poonam S Deshpande Hemant J Purohit Girdhar M Taori Hatim F Daginawala 《Journal of immune based therapies and vaccines》2010,8(1):3
Background
Tuberculosis (TB) is one of the most prevalent cause of death due to a single pathogen. Bacillus Calmette Guérin (BCG) is the only vaccine available for clinical use that protects against miliary TB; however, this vaccine has shown variable levels of efficacy against pulmonary TB. In India, a single dose of BCG vaccine is given and there are few countries where repeated doses of BCG are given. The incidence of TB in India is very high inspite of primary vaccination in neonatal period and therefore requires consideration for repeated immunization. 相似文献594.
The power index formula has been used to obtain the band head spin(I_0) of all the superdeformed(SD) bands in Hg isotopes. A least squares fitting approach is used. The root mean square deviations between the determined and the observed transition energies are calculated by extracting the model parameters using the power index formula. Whenever definite spins are available, the determined and the observed transition energies are in accordance with each other. The computed values of dynamic moment of inertia J~((2)) obtained by using the power index formula and its deviation with the rotational frequency is also studied. Excellent agreement is shown between the calculated and the experimental results for J~((2)) versus the rotational frequency. Hence, the power index formula works very well for all the SD bands in Hg isotopes expect for ~(195)Hg(2, 3, 4). 相似文献
595.
596.
A systematic variation of shape variables \(\beta \) and \(\gamma \) with N and \(N_\mathrm {p}N_\mathrm {n}\) is studied in the framework of an asymmetric rotor model of Davydov and Filippov for the \(Z=\) 50–82, \(N=\) 82–126 major shell space. The role of the \(Z=64\) subshell in producing smooth systematics has been discussed. The quadrupole moments are extracted after considering both axially symmetric and axially asymmetric nuclei. The correlation of \(\beta \) with \(\gamma \) together with the measured quadrupole moments indicates that \(\gamma \)-rigidity is better observed in nuclei with modest deformation. 相似文献
597.
Archiv der Mathematik - The convergence analysis of the Landweber iteration for solving inverse problems in Banach spaces via Hölder stability estimates is well studied by de Hoop et al.... 相似文献
598.
Generalizations of fractional integral inequalities were introduced by many authors. The aim of our investigation is to establish some new fractional integral inequalities using Marichev–Saigo–Maeda (MSM) fractional integral operator for convex function. Further, we obtain some more fractional integral inequalities of Grüss type using MSM operator. 相似文献
599.
Bio-compatible ionic liquids (Bio-ILs) represent a class of solvents with peculiar properties and exhibit huge potential for their applications in different fields of chemistry. Ever since they were discovered, researchers have used bio-ILs in diverse fields such as biomass dissolution, CO2 sequestration, and biodegradation of pesticides. This review highlights the ongoing research studies focused on elucidating the microscopic structure of bio-ILs based on cholinium cation ([Ch]+) and amino acid ([AA]−) anions using the state-of-the-art and classical molecular dynamics (MD) simulations. The microscopic structure associated with these green ILs guides their suitability for specific applications. ILs of this class differ in the side chain of the amino acid anions, and varying the side chain significantly affects the structure of these ILs and thus helps in tuning the efficiency of biomass dissolution. This review demonstrates the central role of the side chain on the morphology of choline amino acid ([Ch][AA]) bio-ILs. The seemingly matured field of bio-ILs and their employment in various applications still holds significant potential, and the insights on their microscopic structure would steer the field of target specific application of these green ILs. 相似文献