全文获取类型
收费全文 | 2012篇 |
免费 | 84篇 |
国内免费 | 18篇 |
专业分类
化学 | 1357篇 |
晶体学 | 4篇 |
力学 | 69篇 |
数学 | 428篇 |
物理学 | 256篇 |
出版年
2022年 | 15篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 34篇 |
2018年 | 27篇 |
2017年 | 20篇 |
2016年 | 46篇 |
2015年 | 55篇 |
2014年 | 44篇 |
2013年 | 137篇 |
2012年 | 120篇 |
2011年 | 116篇 |
2010年 | 89篇 |
2009年 | 70篇 |
2008年 | 118篇 |
2007年 | 119篇 |
2006年 | 105篇 |
2005年 | 98篇 |
2004年 | 113篇 |
2003年 | 92篇 |
2002年 | 93篇 |
2001年 | 37篇 |
2000年 | 33篇 |
1999年 | 23篇 |
1998年 | 26篇 |
1997年 | 21篇 |
1996年 | 42篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 13篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1973年 | 17篇 |
排序方式: 共有2114条查询结果,搜索用时 15 毫秒
121.
High diffusion barrier and piezoelectric nanocomposites based on polyvinylidene fluoride‐trifluoroethylene copolymer and hydrophobized clay 下载免费PDF全文
Sara Dalle Vacche Fabiane Oliveira Olha Sereda Antonia Neels Alex Dommann Dragan Damjanovic Yves Leterrier 《Journal of Polymer Science.Polymer Physics》2017,55(24):1828-1836
Nanocomposites based on polyvinylidene fluoride–trifluoroethylene copolymer and up to 4 vol % of hydrophobized clay nanoparticles are investigated. The structure, piezoelectric properties, and oxygen permeability of solvent cast films are analyzed before and after annealing above the Curie temperature of the polymer. Exfoliation of the clay takes place at concentrations up to 1 vol %, beyond which it rapidly drops and is absent at a concentration of 4 vol %. The presence of clay does not change the crystallinity of the polymer, but leads to a threefold decrease of the oxygen permeability at a concentration of 0.5 vol %. Annealing at 130 °C increases the crystallinity, the proportion of β phase up to 94%, and the piezoelectric coefficient by 20–40% at clay fractions below 1 vol %. Annealing also leads to a remarkable 3‐ to 10‐fold decrease of O2 permeability and to intriguing changes of the activation energy for O2 transport, which decreases from 56 kJ/mol for the as‐cast polymer to below 10 kJ/mol for the polymer and exfoliated composite. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1828–1836 相似文献
122.
123.
124.
Shyjumon Ibrahimkutty Daniel Issenmann Stefan Schleef Anke‐Susanne Müller Yves‐Laurent Mathis Biliana Gasharova Erhart Huttel Ralph Steininger Jörg Göttlicher Tilo Baumbach Albrecht Bartels Christof Janke Anton Plech 《Journal of synchrotron radiation》2011,18(4):539-545
A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented. 相似文献
125.
126.
Emőke-Ágnes Horvát Ferenc Járai-Szabó Yves Brechet Zoltán Néda 《Central European Journal of Physics》2012,10(4):926-935
Fracture patterns resulting from point-like impact acting perpendicularly on the plane of a commercial sodalime glass plate is modelled by a spring-block system. The characteristic patterns consist of crack lines that are spreading radially from the impact point and concentric arcs intersecting these radial lines. Experimental results suggest that the number of radial crack lines is scaling linearly with the energy dissipated during the crack formation process. The elaborated spring-block model reproduces with success the observed fracture patterns and scaling law. 相似文献
127.
The A0 Lamb mode in copy paper is generated and detected by using laser ultrasonics. The frequency dependence of the group velocity of the A0 mode is found from the wavelet transform of the measured signal. A best fit of the dispersion curve against predictions based on orthotropic plate theory yields an estimate of the bending stiffness of the sample. The sample is enclosed in an environmental chamber so that the effects of temperature and humidity can be controlled. Results indicate that the bending stiffness decreases with increasing temperature at an approximate rate of 4 x 10(-6) N m/degrees C, and that it decreases with increasing percent moisture content (PMC) at an approximate rate of 2 x 10(-5) (N m)/PMC. 相似文献
128.
129.
An unprecedented surface oxidation of polystyrene substrates by wet chemistry under basic conditions
Hambardzumyan A Biltresse S Dufrêne Y Marchand-Brynaert J 《Journal of colloid and interface science》2002,252(2):443-449
The surface of polystyrene substrates has been modified by wet chemistry consisting of a treatment with sodium hydroxide in a water-methanol solution at 50 degrees C for 15 h, under air atmosphere. The resulting samples were analyzed by XPS and AFM. The surface functional groups (hydroxyl and carboxyl functions) were assayed by radiolabeling. All the results are consistent with a surface oxidation process. 相似文献
130.
Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions
Garcia P Popot MA Fournier F Bonnaire Y Tabet JC 《Journal of mass spectrometry : JMS》2002,37(9):940-953
A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control. 相似文献