全文获取类型
收费全文 | 4800篇 |
免费 | 181篇 |
国内免费 | 23篇 |
专业分类
化学 | 3233篇 |
晶体学 | 40篇 |
力学 | 107篇 |
数学 | 528篇 |
物理学 | 1096篇 |
出版年
2023年 | 29篇 |
2022年 | 107篇 |
2021年 | 117篇 |
2020年 | 87篇 |
2019年 | 96篇 |
2018年 | 76篇 |
2017年 | 69篇 |
2016年 | 149篇 |
2015年 | 147篇 |
2014年 | 161篇 |
2013年 | 285篇 |
2012年 | 279篇 |
2011年 | 321篇 |
2010年 | 205篇 |
2009年 | 194篇 |
2008年 | 290篇 |
2007年 | 252篇 |
2006年 | 204篇 |
2005年 | 189篇 |
2004年 | 174篇 |
2003年 | 118篇 |
2002年 | 154篇 |
2001年 | 88篇 |
2000年 | 111篇 |
1999年 | 68篇 |
1998年 | 71篇 |
1997年 | 61篇 |
1996年 | 57篇 |
1995年 | 67篇 |
1994年 | 65篇 |
1993年 | 60篇 |
1992年 | 61篇 |
1991年 | 64篇 |
1990年 | 48篇 |
1989年 | 31篇 |
1988年 | 46篇 |
1987年 | 27篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 43篇 |
1983年 | 30篇 |
1982年 | 44篇 |
1981年 | 31篇 |
1980年 | 25篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 15篇 |
排序方式: 共有5004条查询结果,搜索用时 0 毫秒
1.
2.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
3.
Humberto Bustos Rodriguez Dagoberto Oyola Lozano Yebrayl A. Rojas Martínez Germán A. Pérez Alcázar Stefan Flege Adam G. Balogh Louis J. Cabri Michael Tubrett 《Hyperfine Interactions》2007,175(1-3):195-206
X-ray diffraction (XRD), Mössbauer spectrometry (MS), secondary ions mass spectroscopy (SIMS) and laser-ablation microprobe–inductively coupled plasma–mass spectrometry (LAM–ICP–MS) were used to study mineral samples of Colombian auriferous ores collected from the “El Diamante” mine, located in the municipality of Guachavez-Nariño, in Colombia. The samples were prepared as polished thin sections and polished sections. From XRD data, quartz, sphalerite and pyrite were detected and their respective cell parameters were estimated. From MS analyses, pyrite, arsenopyrite and chalcopyrite were identified; their respective hyperfine parameters and respective texture were deduced. Multiple regions of approximately 200 × 200 μm in each sample were analyzed with SIMS; the occurrence of “invisible gold” associated mainly with pyrite and secondarily with arsenopyrite could thus be assigned. It was also found that pyrite is of the arsenious type. Spots from 30 to 40 μm in diameter were analyzed with LAM–ICP–MS for pyrite, arsenopyrite and sphalerite; Au is “homogeneously” distributed inside the structure of the arsenious pyrite and the arsenopyrite (not as inclusions); the chemical composition indicates similarities of this “invisible gold”, forming a solid solution with arsenious pyrite and arsenopyrite. One hundred nineteen and 62 ppm of ‘invisible gold’ was quantified in 21 spots analyzed on pyrite and in 14 spots on arsenopyrite, respectively. 相似文献
4.
5.
Azuelos G. Benslama K. Costanzo D. Couture G. Garcia J.E. Hinchliffe I. Kanaya N. Lechowski M. Mehdiyev R. Polesello G. Ros E. Rousseau D. 《The European Physical Journal C - Particles and Fields》2004,39(2):13-24
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the... 相似文献
6.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003 相似文献
7.
Humberto César Chaves Fernandes Arthur Rodrigo Barros da Rocha 《International Journal of Infrared and Millimeter Waves》2003,24(7):1171-1176
The use of photonic materials has been used in the theory of optical waves. The PBG (Photonic Band Gap) theory and material, was developed recently for optical frequencies and can be easily applied to millimeter waves, microwaves and planar antenna frequencies. The presence of photonic materials as substrate in antennas has some good characteristics such as, supression of light spontaneous emission and suppression of surface waves, allowing the application in planar antenna array. In this work an elaborate analysis using the full wave Transverse Transmission Line - TTL method, that provides efficient and concise results is applied to the planar antennas array with PBG substrate. 相似文献
8.
9.
M. Alves Da Silva M. Helena Gil A. P. Piedade J. S. Redinha A. M. Oliveira Brett J. M. Caridade Costa 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):269-274
The immobilization of catalase on grafted membranes of poly(ethylene)-g-co-acrylic acid and poly(tetrafluoroethylene)-g-co-acrylic acid and their application in hydrogen peroxide electrochemical sensors is described. The introduction of carboxylic acid groups onto a hydrophobic support provides a good environment for subsequent enzyme immobilization. This single membrane, hydrogen peroxide sensor showed significant improvement with respect to the double membrane versions. The response is very rapid, the linear range being from 10 μM up to 6 mM, with a detection limit of 4.7 μM, and a lifetime of more than 4 months. 相似文献
10.
Eggenhffner R. Masini R. Bellingeri E. Cimberle M. R. Ferdeghini C. Costa G. A. Kaiser E. Signorelli E. 《Il Nuovo Cimento D》1994,16(10):1659-1664
Il Nuovo Cimento D - The formation of Hg-based HTSC materials was investigated through the development of non-conventional techniques. The former was based on a singlestep synthesis at temperatures... 相似文献