全文获取类型
收费全文 | 1634篇 |
免费 | 105篇 |
国内免费 | 50篇 |
专业分类
化学 | 1265篇 |
晶体学 | 12篇 |
力学 | 77篇 |
综合类 | 2篇 |
数学 | 167篇 |
物理学 | 266篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 28篇 |
2021年 | 48篇 |
2020年 | 61篇 |
2019年 | 88篇 |
2018年 | 84篇 |
2017年 | 69篇 |
2016年 | 125篇 |
2015年 | 82篇 |
2014年 | 114篇 |
2013年 | 202篇 |
2012年 | 138篇 |
2011年 | 134篇 |
2010年 | 108篇 |
2009年 | 87篇 |
2008年 | 119篇 |
2007年 | 56篇 |
2006年 | 56篇 |
2005年 | 26篇 |
2004年 | 46篇 |
2003年 | 16篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
1941年 | 1篇 |
1937年 | 2篇 |
1927年 | 3篇 |
排序方式: 共有1789条查询结果,搜索用时 15 毫秒
951.
Lin P Turner CW Gantz BJ Djalilian HR Zeng FG 《The Journal of the Acoustical Society of America》2011,130(2):858-865
Residual acoustic hearing can be preserved in the same ear following cochlear implantation with minimally traumatic surgical techniques and short-electrode arrays. The combined electric-acoustic stimulation significantly improves cochlear implant performance, particularly speech recognition in noise. The present study measures simultaneous masking by electric pulses on acoustic pure tones, or vice versa, to investigate electric-acoustic interactions and their underlying psychophysical mechanisms. Six subjects, with acoustic hearing preserved at low frequencies in their implanted ear, participated in the study. One subject had a fully inserted 24 mm Nucleus Freedom array and five subjects had Iowa/Nucleus hybrid implants that were only 10 mm in length. Electric masking data of the long-electrode subject showed that stimulation from the most apical electrodes produced threshold elevations over 10 dB for 500, 625, and 750 Hz probe tones, but no elevation for 125 and 250 Hz tones. On the contrary, electric stimulation did not produce any electric masking in the short-electrode subjects. In the acoustic masking experiment, 125-750 Hz pure tones were used to acoustically mask electric stimulation. The acoustic masking results showed that, independent of pure tone frequency, both long- and short-electrode subjects showed threshold elevations at apical and basal electrodes. The present results can be interpreted in terms of underlying physiological mechanisms related to either place-dependent peripheral masking or place-independent central masking. 相似文献
952.
953.
Volkov VS Han Z Nielsen MG Leosson K Keshmiri H Gosciniak J Albrektsen O Bozhevolnyi SI 《Optics letters》2011,36(21):4278-4280
We report on the realization of long-range dielectric-loaded surface plasmon polariton waveguides (LR-DLSPPWs) consisting of straight and bent subwavelength dielectric ridges deposited on thin and narrow metal stripes supported by a dielectric buffer layer covering a low-index substrate. Using imaging with a near-field optical microscope and end-fire coupling with a tapered fiber connected to a tunable laser at telecommunication wavelengths (1425-1545?nm), we demonstrate low-loss (propagation length ~500?μm) and well-confined (mode width ~1?μm) LR-DLSPPW mode guiding and determine the propagation and bend loss. 相似文献
954.
Hamid OmidvarSaba Goodarzi Ahmad SeifAmir R. Azadmehr 《Superlattices and Microstructures》2011,50(1):26-39
TiO2 nanotube arrays can be fabricated by electrochemical anodization in organic and inorganic electrolytes. Morphology of these nanotube arrays changes when anodization parameters such as applied voltage, type of electrolyte, time and temperature are varied. Nanotube arrays fabricated by anodization of commercial titanium in electrolytes containing NH4F solution and either sulfuric or phosphoric acid were studied at room temperature; time of anodization was kept constant. Applied voltage, fluoride ion concentration, and acid concentrations were varied and their influences on TiO2 nanotubes were investigated. The current density of anodizing was recorded by computer controlled digital multimeter. The surface morphology (top-view) of nanotube arrays were observed by SEM. The nanotube arrays in this study have inner diameters in range of 40-80 nm. 相似文献
955.
Analytic solution to the problem of scattering by an infinitely long perfect electromagnetic conducting (PEMC) strip is obtained
using the method of separation of variables. The scattering widths can be enhanced/reduced by choosing appropriate values
of PEMC admittance. 相似文献
956.
An efficient 1-methylimidazole-catalyzed synthesis of dialkyl 2-[(4-methylphenyl)sulfonyl]-1H-pyrrole-3,4-dicarboxylates is described.The reactive 1:1 zwitterionic intermediate formed by the addition of 1-methylimidazole to dialkyl acetylenedicarboxylates is trapped by tosylmethyl isocyanide(TOSMIC) to afford the title compounds in excellent yields. 相似文献
957.
Hamid RD Swedlund PJ Song Y Miskelly GM 《Langmuir : the ACS journal of surfaces and colloids》2011,27(21):12930-12937
The effect of ionic strength on reactions at aqueous interfaces can provide insights into the nature of the chemistry involved. The adsorption of H(4)SiO(4) on iron oxides at low surface silicate concentration (Γ(Si)) forms monomeric silicate complexes with Fe-O-Si linkages, but as Γ(Si) increases silicate oligomers with Si-O-Si linkages become increasingly prevalent. In this paper, the effect of ionic strength (I) on both Γ(Si) and the extent of silicate oligomerization on the ferrihydrite surface is determined at pH 4, 7, and 10, where the surface is, respectively, positive, nearly neutral, and negatively charged. At pH 4, an increase in ionic strength causes Γ(Si) to decrease at a given H(4)SiO(4) solution concentration, while the proportion of oligomers on the surface at a given Γ(Si) increases. At pH 10, the opposite is observed; Γ(Si) increases as I increases, while the proportion of surface oligomers at a given Γ(Si) decreases. Ionic strength has only a small effect on the surface chemistry of H(4)SiO(4) at pH 7, but at low Γ(Si) this effect is in the direction observed at pH 4 while at high Γ(Si) the effect is in the direction observed at pH 10. The pH where the surface has zero charge decreases from ≈8 to 6 as Γ(Si) increases so that the surface potential (Ψ) is positive at pH 4 for all Γ(Si) and at pH 7 with low Γ(Si). Likewise, Ψ < 0 at pH 10 for all Γ(Si) and at pH 7 with high Γ(Si). The diffuse layer model is used to unravel the complex and subtle interactions between surface potential (Ψ) and chemical parameters that influence interfacial silicate chemistry. This analysis reveals that the decrease in the absolute value of Ψ as I increases causes Γ(Si) to decrease or increase where Ψ is, respectively, positive or negative. Therefore, at a given Γ(Si), the solution H(4)SiO(4) concentration changes with I, and because oligomerization has a higher H(4)SiO(4) stoichiometry coefficient than monomer adsorption, this results in the observed dependence of the extent of silicate oligomerization on I. 相似文献
958.
A.S. Hamid 《哲学杂志》2013,93(34):4302-4310
The Fermi surface (FS) and spin-dependent momentum space density distribution of ferromagnetic Gd was studied via longitudinally polarised positrons. The measurements were performed using a 2D angular correlation of the annihilation radiation experiments with the reversal magnetic field direction parallel and anti-parallel to the polarisation direction of the positron. It was found that the minority-spin states were concentrated in the basal plane and majority-spin states were concentrated around the A, L and H points. The analysis confirmed that the main contributions to the FS of Gd were influenced by the mixing of both the 5d–6s and the 4f–5d hybrid bands. The general layout of this FS was observed as two hole-like surfaces running along the [ΓA] axis and one electron-like surface running along the [MK] direction. In general, the experimental results showed good agreement with earlier investigations. 相似文献
959.
In this work, two different maximum likelihood approaches for multivariate curve resolution based on maximum likelihood principal component analysis (MLPCA) and on weighted alternating least squares (WALS) are compared with the standard multivariate curve resolution alternating least squares (MCR‐ALS) method. To illustrate this comparison, three different experimental data sets are used: the first one is an environmental aerosol source apportionment; the second is a time‐course DNA microarray, and the third one is an ultrafast absorption spectroscopy. Error structures of the first two data sets were heteroscedastic and uncorrelated, and the difference between them was in the existence of missing values in the second case. In the third data set about ultrafast spectroscopy, error correlation between the values at different wavelengths is present. The obtained results confirmed that the resolved component profiles obtained by MLPCA‐MCR‐ALS are practically identical to those obtained by MCR‐WALS and that they can differ from those resolved by ordinary MCR‐ALS, especially in the case of high noise. It is shown that methods that incorporate uncertainty estimations (such as MLPCA‐ALS and MCR‐WALS) can provide more reliable results and better estimated parameters than unweighted approaches (such as MCR‐ALS) in the case of the presence of high amounts of noise. The possible advantage of using MLPCA‐MCR‐ALS over MCR‐WALS is then that the former does not require changing the traditional MCR‐ALS algorithm because MLPCA is only used as a preliminary data pretreatment before MCR analysis. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
960.