全文获取类型
收费全文 | 1948篇 |
免费 | 705篇 |
国内免费 | 764篇 |
专业分类
化学 | 1191篇 |
晶体学 | 57篇 |
力学 | 211篇 |
综合类 | 95篇 |
数学 | 491篇 |
物理学 | 1372篇 |
出版年
2024年 | 14篇 |
2023年 | 64篇 |
2022年 | 72篇 |
2021年 | 52篇 |
2020年 | 54篇 |
2019年 | 80篇 |
2018年 | 97篇 |
2017年 | 60篇 |
2016年 | 79篇 |
2015年 | 111篇 |
2014年 | 170篇 |
2013年 | 137篇 |
2012年 | 116篇 |
2011年 | 123篇 |
2010年 | 131篇 |
2009年 | 159篇 |
2008年 | 133篇 |
2007年 | 115篇 |
2006年 | 116篇 |
2005年 | 123篇 |
2004年 | 106篇 |
2003年 | 124篇 |
2002年 | 70篇 |
2001年 | 96篇 |
2000年 | 85篇 |
1999年 | 105篇 |
1998年 | 59篇 |
1997年 | 65篇 |
1996年 | 46篇 |
1995年 | 66篇 |
1994年 | 45篇 |
1993年 | 42篇 |
1992年 | 65篇 |
1991年 | 51篇 |
1990年 | 32篇 |
1989年 | 47篇 |
1988年 | 44篇 |
1987年 | 62篇 |
1986年 | 35篇 |
1985年 | 47篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1963年 | 4篇 |
1959年 | 4篇 |
1958年 | 4篇 |
1956年 | 4篇 |
排序方式: 共有3417条查询结果,搜索用时 15 毫秒
961.
962.
963.
964.
Calculation of the surface energy of fcc metals with modified embedded-atom method 总被引:1,自引:0,他引:1 下载免费PDF全文
The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, A1, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, A1, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy. 相似文献
965.
We study theoretically the low-temperature electronic transport property of a straight quantum wire under the irradiation of a finite-range transversely polarized external terahertz (THz) electromagnetic (EM) field. Using the freeelectron model and the scattering matrix approach, we show an unusual behaviour of the electronic transmission of this system. A sharp step-structure appears in the electronic transmission probability as the EM field strength increases to a threshold value when a coherent EM field is applied. We demonstrate that this effect physically comes from the inelastic scattering of electrons with lateral photons through intersubband transitions. 相似文献
966.
Quantum interference effects on the probe amplification without and with inversion in a four-level system 下载免费PDF全文
A four-level system driven by two coherent fields is considered. It is shown that in the presence of an incoherent pump, the probe gain at a short wavelength can be achieved due to the quantum interference. Our density matrix calculation provides the conditions for probe amplification from different origins, including gain without population inversion on any state basis, gain with population inversion on the dressed-state basis, and gain with population inversion on the bare-state basis. Also, by controlling the Rabi frequency of the coupling field a total change from non-inversion to inversion can be achieved which does not depend on the intensity of the incoherent pump. 相似文献
967.
Bursty events and incremental diffusion in a local diffusion and multi—scale convection system 下载免费PDF全文
A one-dimensional cellular automaton is defined without the critical gradient rule (Δh>Δh_c) which is essential to the existence of avalanches in self-organized criticality (SOC) models. Instead, only the local diffusion rule is used, however, the characteristics of SOC, such as the bursty behaviour, power-law decay in fluctuation spectra, self-similarity over a broad range of scales and long-time correlations, are still observed in these numerical experiments. This numerical model is established to suggest that the bursty events and the incremental diffusion observed universally in fusion experiments do not necessarily imply the submarginal dynamics. 相似文献
968.
969.
Yield strengths and stress induced crackles in copper films:effects of substrate and passivated layer 总被引:4,自引:0,他引:4 下载免费PDF全文
Yield strengths in unpassivated and 530 nm TiN passivated Cu films deposited on Ti, high-speed steel and Ni substrates have been measured by x-ray diffraction (XRD) in combination with the four-point bending method. The results show that, although the texture and average grain size, investigated by XRD and transmission electron microscopy respectively, do not vary with different substrate, the yield strength of the Cu film increases obviously when a thin passivated layer is present and varies slightly with substrates. Many crackles appear in the passivated Cu film on Ti substrate but do not appear in other samples. The experimental results have been explained satisfactorily with an expression for the yield strength of thin films given previously. 相似文献
970.
A 2× 2 electro-optic switch is experimentally demonstrated
using the optical structure of a Mach--Zehnder interferometer (MZI) based
on a submicron rib waveguide and the electrical structure of a PIN diode on
silicon-on-insulator (SOI). The switch behaviour is achieved through
the plasma dispersion effect of silicon. The device has a modulation arm
of 1~mm in length and cross-section of 400~nm× 340~nm. The
measurement results show that the switch has a VπLπ
figure of merit of 0.145~V\cdot cm and the extinction ratios of two
output ports and cross talk are 40~dB, 28~dB and -28~dB,
respectively. A 3~dB modulation bandwidth of 90~MHz and a switch
time of 6.8~ns for the rise edge and 2.7~ns for the fall edge are also
demonstrated. 相似文献