全文获取类型
收费全文 | 7753篇 |
免费 | 1491篇 |
国内免费 | 560篇 |
专业分类
化学 | 2295篇 |
晶体学 | 96篇 |
力学 | 674篇 |
综合类 | 47篇 |
数学 | 550篇 |
物理学 | 4038篇 |
无线电 | 2104篇 |
出版年
2024年 | 29篇 |
2023年 | 114篇 |
2022年 | 201篇 |
2021年 | 300篇 |
2020年 | 317篇 |
2019年 | 261篇 |
2018年 | 225篇 |
2017年 | 274篇 |
2016年 | 355篇 |
2015年 | 315篇 |
2014年 | 417篇 |
2013年 | 560篇 |
2012年 | 443篇 |
2011年 | 553篇 |
2010年 | 410篇 |
2009年 | 495篇 |
2008年 | 525篇 |
2007年 | 527篇 |
2006年 | 528篇 |
2005年 | 409篇 |
2004年 | 336篇 |
2003年 | 325篇 |
2002年 | 266篇 |
2001年 | 208篇 |
2000年 | 203篇 |
1999年 | 146篇 |
1998年 | 149篇 |
1997年 | 102篇 |
1996年 | 123篇 |
1995年 | 83篇 |
1994年 | 97篇 |
1993年 | 73篇 |
1992年 | 62篇 |
1991年 | 41篇 |
1990年 | 48篇 |
1989年 | 62篇 |
1988年 | 29篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有9804条查询结果,搜索用时 12 毫秒
41.
纳米通道的尺寸、结构和表面化学对其内部溶液的分布结构和输运性质有着重大影响.本文研究了一种全新的菱形石墨烯纳米通道.这种理想的通道与最近被广泛研究的金属有机框架材料(MOF)的内部结构类似,有着与传统的碳纳米管截然不同的内部结构.本文使用分子动力学模拟的方法研究在不同尺寸的菱形石墨烯纳米通道内的KCl溶液的性质,并将其与同尺寸的单壁碳纳米管进行了比较.研究结果表明在小孔道内(<20?)其内部的溶液结构呈现若干个密度极高的聚集区域,即出现了结晶化的趋势.这一研究结果,将为MOF的结构设计提供思路,从而有望实现类似于生物离子通道的高选择性和高传输能力. 相似文献
42.
43.
Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF3SO3) dispersed with various concentrations of aluminum oxide (Al2O3) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of
the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte.
The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T
g) whereas the degree of crystallization (X
c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of
all these samples has revealed the presence of absorption bands around 1,000 cm−1; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the
standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity
thereby revealing that the significant contribution to electrical conduction was due to ions only.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9,
2006 相似文献
44.
Peter Oberta Peter Mikulík Martin Kittler Jaromir Hrdý 《Journal of synchrotron radiation》2011,18(3):522-526
Two crystals with precise parabolic holes were used to demonstrate sagittal beam collimation by means of a diffractive–refractive double‐crystal monochromator. A new approach is introduced and beam collimation is demonstrated. Two Si(333) crystals with an asymmetry angle of α = 15° were prepared and arranged in a dispersive position (+,?,?,+). Based on theoretical calculations, this double‐crystal set‐up should provide tunable beam collimation within an energy range of 6.3–18.8 keV (ΘB = 71–18.4°). An experiment study was performed on BM05 at ESRF. Using 8.97 keV energy, the beam profile at various distances was measured. The experimental results are in good agreement with theoretical predictions. Owing to insufficient harmonic suppression, the collimated (333) beam was overlapped by horizontally diverging (444) and (555) beams. 相似文献
45.
We investigate the stochastic dynamics and the hopping transfer of electrons embedded into two‐dimensional atomic layers. First we formulate the quantum statistics of general atom ‐ electron systems based on the tight‐binding approximation and express ‐ following linear response transport theory ‐ the quantum‐mechanical time correlation functions and the conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the atom motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. In the last part we derive Pauli equations for the stochastic electron dynamics including nonlinear excitations of the atomic subsystem. We carry out Monte Carlo simulations and show that mean square displacements of electrons and transport properties are in a moderate to high temperature regime strongly influenced by by soliton‐type excitations and demonstrate the existence of percolation effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
46.
47.
We apply unrestricted Hartree-Fock to modelling two systems:
- (1)
- We calculate the spin structure and addition spectra of small symmetric quantum dots (often called 2D “artificial atoms”), improving the accuracy considerably by including, for the first time, second-order correlation corrections. We compare the results to experiment and to previous numerical works, and find that our spin structure in some cases disagrees with that calculated within mean-field theories, such as Hartree-Fock without correlation corrections, or density-functional theory [C. Sloggett, O.P. Sushkov, Phys. Rev. B 71 (2005) 235326].
- (2)
- We model the well-known 0.7 anomaly in the conductance of a quantum point contact. We calculate the conductance using direct calculation of scattering phases on a ring, within Hartree-Fock. We observe strong localisation of the Fermi electrons on the barrier, and suggest a mechanism for the observed temperature-dependent conductance anomaly.
48.
为在更高参数运行的HL-2A装置上实现等离子体芯部加料,设计了一套基于G-M循环制冷机的25管弹丸注入系统。描述了该系统的构成、工程参数,给出了系统的结构设计,并对各组成部件进行热力分析计算。对枪管温度梯度的建立及控制、弹丸注入方式等进行了讨论。 相似文献
49.
We present transport measurements of ferromagnetically contacted carbon nanotubes. In both single- and multi-walled nanotube devices, a spin valve effect is observed due to spin-polarized transport. In one single-walled nanotube device, the spin-valve effect is suppressed as the influence of Coulomb charging is observed at around 10 K. To help understand the interplay between the Coulomb charging and the spin-polarized transport we investigated the temperature dependence of the carbon nanotube magnetoresistance. 相似文献
50.