全文获取类型
收费全文 | 22618篇 |
免费 | 835篇 |
国内免费 | 104篇 |
专业分类
化学 | 12536篇 |
晶体学 | 358篇 |
力学 | 689篇 |
综合类 | 1篇 |
数学 | 1781篇 |
物理学 | 4944篇 |
无线电 | 3248篇 |
出版年
2024年 | 98篇 |
2023年 | 271篇 |
2022年 | 657篇 |
2021年 | 715篇 |
2020年 | 762篇 |
2019年 | 774篇 |
2018年 | 712篇 |
2017年 | 632篇 |
2016年 | 937篇 |
2015年 | 612篇 |
2014年 | 996篇 |
2013年 | 1801篇 |
2012年 | 1415篇 |
2011年 | 1490篇 |
2010年 | 997篇 |
2009年 | 825篇 |
2008年 | 996篇 |
2007年 | 1018篇 |
2006年 | 817篇 |
2005年 | 740篇 |
2004年 | 570篇 |
2003年 | 476篇 |
2002年 | 399篇 |
2001年 | 263篇 |
2000年 | 230篇 |
1999年 | 191篇 |
1998年 | 157篇 |
1997年 | 177篇 |
1996年 | 192篇 |
1995年 | 154篇 |
1994年 | 166篇 |
1993年 | 199篇 |
1992年 | 195篇 |
1991年 | 148篇 |
1990年 | 163篇 |
1989年 | 143篇 |
1988年 | 130篇 |
1987年 | 116篇 |
1986年 | 94篇 |
1985年 | 194篇 |
1984年 | 194篇 |
1983年 | 138篇 |
1982年 | 126篇 |
1981年 | 131篇 |
1980年 | 134篇 |
1979年 | 136篇 |
1978年 | 133篇 |
1977年 | 121篇 |
1976年 | 107篇 |
1973年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Towards a microchannel‐based X‐ray detector with two‐dimensional spatial and time resolution and high dynamic range 下载免费PDF全文
Bernhard W. Adams Anil U. Mane Jeffrey W. Elam Razib Obaid Matthew Wetstein Matthieu Chollet 《Journal of synchrotron radiation》2015,22(5):1202-1206
X‐ray detectors that combine two‐dimensional spatial resolution with a high time resolution are needed in numerous applications of synchrotron radiation. Most detectors with this combination of capabilities are based on semiconductor technology and are therefore limited in size. Furthermore, the time resolution is often realised through rapid time‐gating of the acquisition, followed by a slower readout. Here, a detector technology is realised based on relatively inexpensive microchannel plates that uses GHz waveform sampling for a millimeter‐scale spatial resolution and better than 100 ps time resolution. The technology is capable of continuous streaming of time‐ and location‐tagged events at rates greater than 107 events per cm2. Time‐gating can be used for improved dynamic range. 相似文献
952.
Emergence of the sub‐THz central peak at phase transitions in artificial BaTiO3/(Ba,Sr)TiO3 superlattices 下载免费PDF全文
Yu. A. Tikhonov A. G. Razumnaya V. I. Torgashev I. N. Zakharchenko Yu. I. Yuzyuk M. El Marssi N. Ortega A. Kumar R. S. Katiyar 《固体物理学:研究快报》2015,9(1):68-71
A prominent central peak in the sub‐THz frequency range was observed in the Raman spectra of BaTiO3/(Ba,Sr)TiO3 (BT/BST) superlattice grown on (001)MgO substrate. Both soft and central mode show an anomaly around 200 K and 280 K, which can be correlated with orthorhombic to monoclinic phase transition of BST and BT, respectively. The observed temperature dependence of the central mode enabled us to explain rather broad temperature dependence of the dielectric permittivity previously observed in BT/BST superlattices. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
953.
In spite of large spin coherence length in graphene due to small spin–orbit coupling, the created potential barrier and antiferromagnetic coupling at graphene/transition metal (TM) contacts strongly reduce the spin transport behavior in graphene. Keeping these critical issues in mind in the present work, ferromagnetic (Co, Ni) nanosheets are grown on graphene surface to elucidate the nature of interaction at the graphene/ferromagnetic interface to improve the spin transistor characteristics. Temperature dependent magnetoconductance shows unusual behavior exhibiting giant enhancement in magnetoconductance with increasing temperature. A model based on spin–orbit coupling operated at the graphene/TM interface is proposed to explain this anomalous result. We believe that the device performance can be improved remarkably tuning the spin–orbit coupling at the interface of graphene based spin transistor. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
954.
Betha?Saineelima?B.?Kasibabu Stephanie?L.?D’souza Sanjay?Jha Suresh?Kumar?KailasaEmail author 《Journal of fluorescence》2015,25(4):803-810
In this paper, we have described a simple hydrothermal method for preparation of fluorescent carbon dots (C-dots) using Carica papaya juice as a precursor. The synthesized C-dots show emission peak at 461 nm with a quantum yield of 7.0 %. The biocompatible nature of C-dots was confirmed by a cytotoxicity assay on E. coli. The C-dots were used as fluorescent probes for imaging of bacterial (Bacillus subtilis) and fungal (Aspergillus aculeatus) cells and emitted green and red colors under different excitation wavelengths, which indicates that the C-dots can be used as a promising material for cell imaging. 相似文献
955.
956.
Baishali Chakraborty Kumar S. Gupta Siddhartha Sen 《The European Physical Journal B - Condensed Matter and Complex Systems》2015,88(6):155
We analyze the screening of an external Coulomb charge in gapless graphene cone, which is taken as a prototype of a topological defect. In the subcritical regime, the induced charge is calculated using both the Green’s function and the Friedel sum rule. The dependence of the polarization charge on the Coulomb strength obtained from the Green’s function clearly shows the effect of the conical defect and indicates that the critical charge itself depends on the sample topology. Similar analysis using the Friedel sum rule indicates that the two results agree for low values of the Coulomb charge but differ for the higher strengths, especially in the presence of the conical defect. For a given subcritical charge, the transport cross-section has a higher value in the presence of the conical defect. In the supercritical regime we show that the coefficient of the power law tail of polarization charge density can be expressed as a summation of functions which vary log periodically with the distance from the Coulomb impurity. The period of variation depends on the conical defect. In the presence of the conical defect, the Fano resonances begin to appear in the transport cross-section for a lower value of the Coulomb charge. For both sub and supercritical regime we derive the dependence of LDOS on the conical defect. The effects of generalized boundary condition on the physical observables are also discussed. 相似文献
957.
958.
Gold Decorated Graphene by Laser Ablation for Efficient Electrocatalytic Oxidation of Methanol and Ethanol 下载免费PDF全文
V. Lakshman Kumar R. S. Sai Siddhardha Adarsh Kaniyoor Ramakrishna Podila Muralikrishna Molli Sai Muthu Kumar V K. Venkataramaniah S. Ramaprabhu A. M. Rao Sai Sathish Ramamurthy 《Electroanalysis》2014,26(8):1850-1857
A well‐known limitation in the fabrication of metal‐graphene composite has been the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. We demonstrate here a novel one‐pot synthesis of gold nanoparticles by laser ablation of gold strip and in‐situ decoration on graphene substrate. Not only the impregnation of nanoparticles was linker free, but also the synthesis by itself was surfactant‐free. The composite materials were well characterized morphologically and functionally using electron microscopy, X‐ray and electron diffraction, Raman spectroscopy, Zeta potential, electrochemical measurements and UV‐Visible spectroscopic techniques. This linker‐free gold‐graphene based composite has been employed for catalytic applications pertaining to electrooxidation. We have explored the use of this composite as a binder‐free electrode in electrocatalytic oxidation of methanol and ethanol in alkaline medium. Additionally, the onset potential for ethanol oxidation was found to be more negative, ?100 mV, an indication of its promising application in direct ethanol fuel cells. 相似文献
959.
M. G. Sankar V. Ponneri K. S. Kumar Sivarambabu Sakamuri 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1821-1827
Measurement of densities ρ, viscosities η, and ultrasonic speeds u has been carried out for binary mixtures of N,N-diethylaniline (N,N-DEA) with acetophenone, cyclopentanone, cyclohexanone (CH), and 2-methylcyclohexanone (Me-CH) and their pure liquids at (303.15 and 308.15) K. These experimental data have been used to calculate the excess molar volume V E, deviation in ultrasonic velocity ?u, deviation in isentropic compressibility ?κ s , and deviation in viscosity ?η. The variation of these properties with composition of the mixtures suggests dipole–dipole interactions and charge-transfer complex formation between N,N-diethylaniline and dipolar ketones. The magnitude of the property is found to depend on the chain length of the ketones’ molecule. The viscosity data have been correlated using three equations: Grunberg and Nissan (Nature 164:799–800, 1949), Katti and Chaudhri (J Chem Eng Data 9:442–443, 1964), and Hind et al. (Trans Faraday Soc 56:328–330, 1960). These results have been fitted to the Redlich–Kister polynomial using multiparametric nonlinear regression analysis to estimate the binary coefficients and standard errors. 相似文献
960.