全文获取类型
收费全文 | 6389篇 |
免费 | 1248篇 |
国内免费 | 917篇 |
专业分类
化学 | 4794篇 |
晶体学 | 94篇 |
力学 | 372篇 |
综合类 | 66篇 |
数学 | 496篇 |
物理学 | 2732篇 |
出版年
2024年 | 15篇 |
2023年 | 130篇 |
2022年 | 215篇 |
2021年 | 280篇 |
2020年 | 339篇 |
2019年 | 310篇 |
2018年 | 274篇 |
2017年 | 287篇 |
2016年 | 372篇 |
2015年 | 395篇 |
2014年 | 441篇 |
2013年 | 542篇 |
2012年 | 617篇 |
2011年 | 619篇 |
2010年 | 428篇 |
2009年 | 402篇 |
2008年 | 519篇 |
2007年 | 354篇 |
2006年 | 336篇 |
2005年 | 280篇 |
2004年 | 231篇 |
2003年 | 179篇 |
2002年 | 195篇 |
2001年 | 142篇 |
2000年 | 142篇 |
1999年 | 94篇 |
1998年 | 54篇 |
1997年 | 61篇 |
1996年 | 40篇 |
1995年 | 44篇 |
1994年 | 37篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 18篇 |
1990年 | 26篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1957年 | 1篇 |
1911年 | 4篇 |
排序方式: 共有8554条查询结果,搜索用时 15 毫秒
61.
62.
AN EFFECTIVE APPROACH FOR TWO-DIMENSIONAL POLARONS IN AN ASYMMETRIC QUANTUM DOT 总被引:1,自引:0,他引:1 下载免费PDF全文
Within the framework of Feynman-Haken path integral theory, we calculate the ground-state energy of two-dimensional polarons in asymmetric quantum dots for arbitrary electron-phonon coupling constants. From a general three-dimensional Hamiltonian, some interesting problems, such as polarons in quasi-one-dimensional quantum wires and quasi-zero-dimensional asymmetric or symmetric quantum dots can be easily discussed only by taking different limit in the whole coupling regime. After the numerical calculation, we find that the relative polaronic correction increases monotonically with the decrease of effective dot size, and it becomes more pronounced with increasing dimension and asymmetry. Moreover, despite the insensitivity of relative polaronic enhancement to the variation of coupling constant at weak coupling, the correction is related to the coupling constant as the latter becomes larger. 相似文献
63.
The universal magneto-optic (MO) coupled-mode equations for magnetostatic waves (MSWs) and guided optical waves (GOWs) under arbitrarily tilted bias magnetic fields are presented for the first time and, as an example, applied to the noncollinear Stokes interaction between the incident TE0-mode light and magnetostatic backward volume wave (MSBVW) excited by single-element microstrip line transducer in yttrium–iron–garnet (YIG) film. Our calculation indicates that, for the case of magnetization parallel to the MSBVW propagation direction, the diffraction efficiency (DE) is equal to the mode-conversion efficiency of the diffracted lights (MCDE) and the calculated curve of relative DE for the MSBVW-based MO Bragg cell in pure YIG waveguide is in good agreement with the experimental data. In contrast, the diffraction performance can be greatly improved by optimizing the bias magnetic field and the DE gain can be increased by 6.3 dB in the tangentially magnetized film. The angular dependences of the DE and the corresponding Bragg angle upon the magnetization direction are also discussed in the paper. 相似文献
64.
We prepared two vinyl copolymers P1 and P2 containing pendant distyrylbenzene and aromatic 1,3,4‐oxadiazole derivatives, respectively, from their precursor poly(styrene‐ran‐4‐vinylbenzyl chloride) (Mw = 11,400, PDI = 1.18), which had been prepared by the controlled radical polymerization (RAFT). Two main chain polymers containing similar isolated distyrylbenzene ( P3) and aromatic 1,3,4‐oxadiazole ( P4 ) chromophores were also synthesized for comparative study. The resulted copolymers ( P1 – P4 ) are soluble in common organic solvents and are basically amorphous materials with 5% weight‐loss temperature higher than 360 °C. The PL spectral results reveal that the architecture of P1 prevents the formation of inter‐ or intramolecular interaction. The HOMO and LUMO levels of P2 , estimated from cyclic voltammetric data, are ?5.96 and ?3.81 eV, respectively, which are much lower than those of P1 (?5.12 and ?3.11 eV). The emission of blend from P1 and P2 are contributed mainly from distyrylbenzene fluorophore (~450 nm) owing to efficient energy transfer. Moreover, the blend exhibits three kinds of redox behavior depending on their weight ratios. The luminance and current efficiency of the EL device lpar;ITO/PEDOT/ MEH ‐ PPV + P2 /Al) are 503 cd/m2 and 0.11 cd/A, which can be improved to 1285 cd/m2 and 0.44 cd/A, respectively, as the weight ratio of P2 increases from 0 to 20%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5362–5377, 2006 相似文献
65.
Hong Oh Kim Rae Young Kim Jae Kun Lim Zuowei Shen 《Journal of Approximation Theory》2007,147(2):196-204
We start with a characterization of a pair of frames to be orthogonal in a shift-invariant space and then give a simple construction of a pair of orthogonal shift-invariant frames. This is applied to obtain a construction of a pair of Gabor orthogonal frames as an example. This is also developed further to obtain constructions of a pair of orthogonal wavelet frames. 相似文献
66.
67.
X. H. Jiao P. Guillon L. Bermudes 《International Journal of Infrared and Millimeter Waves》1989,10(4):519-528
This paper proposes a new type of high permittivity whispering gallery mode cylindrical dielectric resonators with a geometry which is very suitable for use in microstrip type integrated circuits. These oversized resonators, together with high Q factors and ease of fabrication, are potentially interesting for millimeter wave integrated filters and oscillators. In this paper, we report an experimental investigation of such resonators carried out in Ka band (26.5–40 GHz). Measured results including resonant frequencies and loaded quality factors will be presented. Application to millimeter wave filters will also be demonstrated. 相似文献
68.
ZnCuCoAlNO3型四元水滑石及其多氧阴离子柱撑物的合成与催化氧化性能 总被引:4,自引:0,他引:4
Anionic clay, ZnCuCoAlNO3 and its polyoxometalate intercalates were synthesized, and were characterized by XRD, IR, 31PMAS NMR, DTA and elemental analysis. The pillared products are found to be effective catalysts for oxidation of cyclohexene with molecular oxygen under mild reaction conditions 相似文献
69.
海螵蛸入药部分和废弃部分8种无机元素分析 总被引:3,自引:0,他引:3
为合理开发利用海螵蛸 ,用原子吸收分光光度法测定了海螵蛸中入药部分和废弃部分中8种人体必需无机元素含量。结果表明 ,入药部分和废弃部分中钙含量丰富 ,分别达到 742 1 3× 1 0 - 3和 65 9 76× 1 0 - 3。入药部分铜、铁含量较废弃部分高 ,分别为 9 41× 1 0 - 6 、 91 86× 1 0 - 6 和2 3 5× 1 0 - 6 、 2 5 7× 1 0 - 6 。废弃部分含锌丰富 ,为 3 5 3 62× 1 0 - 6 ,数倍于入药部分 64 65× 1 0 - 6 。可见海螵蛸入药部分和废弃部分均具有良好的开发前景 相似文献
70.