全文获取类型
收费全文 | 308篇 |
免费 | 17篇 |
专业分类
化学 | 214篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 31篇 |
物理学 | 67篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 4篇 |
2013年 | 10篇 |
2012年 | 22篇 |
2011年 | 16篇 |
2010年 | 6篇 |
2009年 | 14篇 |
2008年 | 27篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有325条查询结果,搜索用时 15 毫秒
171.
We propose a compact compound-eye projector using superresolved projection. The optics are composed of multiple small suboptics (units) to reduce their thickness in the projector. Each of the suboptics adds a subpixel shift to a projected image for superresolved projection and has a color filter or a dispersive element for multicolor projection. The projected images in the units are determined via a model of the system in preprocessing. The images are projected by the suboptics and superimposed on a screen. In this Letter, we describe the system model and show the simulation results. 相似文献
172.
Yu Shiratsuchi Shin-ichi KawaharaHayato Noutomi Kazuto ArakawaHirotaro Mori Ryoichi Nakatani 《Journal of magnetism and magnetic materials》2011,323(5):579-586
The effect of the crystalline quality of ultrathin Co films on perpendicular exchange bias (PEB) has been investigated using a Au/Co/Au/α-Cr2O3 thin film grown on a Ag-buffered Si(1 1 1) substrate. Our investigation is based on the effect of the Au spacer layer on the crystalline quality of the Co layer and the resultant changes in PEB. An α-Cr2O3(0 0 0 1)layer is fabricated by the thermal oxidization of a Cr(1 1 0) thin film. The structural properties of the α-Cr2O3(0 0 0 1) layer including the cross-sectional structure, lattice parameters, and valence state have been investigated. The fabricated α-Cr2O3(0 0 0 1) layer contains twin domains and has slightly smaller lattice parametersthan those of bulk-Cr2O3. The valence state of the Cr2O3(0 0 0 1) layer is similar to that of bulk Cr2O3. The ultrathin Co film directly grown on the α-Cr2O3(0 0 0 1) deposited by an e-beam evaporator is polycrystalline. The insertion of a Au spacer layer with a thickness below 0.5 nm improves the crystalline quality of Co, probably resulting in hcp-Co(0 0 0 1). Perpendicular magnetic anisotropy (PMA) appears below the Néel temperature of Cr2O3 for all the investigated films. Although the PMA appears independently of the crystallinequality of Co, PEB is affected by the crystalline quality of Co. For the polycrystalline Co film, PEB is low, however, a high PEB is observed for the Co films whose in-plane atom arrangement is identical to that of Cr3+ in Cr2O3(0 0 0 1). The results are qualitatively discussed on the basis of the direct exchange coupling between Cr and Co at the interface as the dominant coupling mechanism. 相似文献
173.
Ryoichi Horisaki Yoshizumi Nakao Takashi Toyoda Keiichiro Kagawa Yasuo Masaki Jun Tanida 《Optical Review》2009,16(3):241-246
A compact system of the thin observation module by bound optics (TOMBO) imager based on compound-eye imaging has been constructed
to demonstrate its advantages over single-eye imaging systems such as thinner hardware. To reconstruct a high-resolution image
from low resolution images captured by the compound-eye optics, we propose an image restoration scheme based on the iterative
back-projection algorithm with depth map estimated from the disparities on the captured image. The scheme includes suppression
of unit-by-unit color shift caused by the offset microlenses and the color filters on the commercial image sensors and deblurring
of defocus by geometrical optics using the depth map. In the experiment, three-dimensional objects were captured by the TOMBO
imager and reconstructed with the scheme. After the processing, the power spectrum of the captured image was improved by up
to 19 dB, and the power spectrum of the effect of the color shift was reduced by 7 dB. 相似文献
174.
O.M. Lyulin A.V. Nikitin V.I. Perevalov Isamu Morino Tatsuya Yokota Ryoichi Kumazawa Takeshi Watanabe 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(9-10):654-668
The absorption spectra of mixtures of methane (CH4) with N2 and O2 at different partial pressures of both CH4 and buffer gases for three temperatures 240, 267, and 296 K have been recorded using the Bruker IFS 125 HR FTIR spectrometer in the 5550–6236 cm?1 region. The multispectrum fitting procedure has been applied to these spectra to recover the spectral line parameters. The main goal of this procedure was the determination of the N2- and O2-broadening and shifting coefficients and the exponents of their temperature dependences. These parameters have been derived for 452 assigned lines with good values of the signal to noise ratio. The rotational dependence of the mean values of these parameters is discussed. The temperature dependence exponents were observed for both N2 and O2 buffer gases. 相似文献
175.
报道了调制n型掺杂ZnSe/BeTe/ZnSe Ⅱ型量子阱(type-II QW)在极低温至室温(14—296K)条件下的各种光学性质. 反射光谱显示了对于非掺杂样品,激子(X)的跃迁起着支配作用,而只有在掺杂样品的光谱里展示了一个典型的负的带电激子(X-)的跃迁特征. PL光谱及其直线偏振度Pl都显著地依赖于n型掺杂量和平行于QW生长方向的外加电场. 这个特征被认为是由n型掺杂导致了内秉电场(built
关键词:
光致发光
二维电子气
带电激子
Ⅱ型量子阱 相似文献
176.
Cha-Yeol Lee Ryoichi Yamashita Masaru Masuzaki 《International Journal of Infrared and Millimeter Waves》1997,18(2):519-535
We present, based on the cold fluid theory, linear analysis of the Cherenkov and cyclotron-Cherenkov instabilities which are
driven when a linear electron beam is injected into a dielectric-loaded waveguide immersed in an axial magnetic field. In
the analysis we consider azimuthally symmetric TM0n modes. We derive dispersion relations for three types of waveguide, and compare computationally obtained linear growth rates
of both instabilities. For the type A, which consists of a metallic cylinder with dielectric liner on its inner surface, the
growth rate of the Cherenkov instability is larger than that of the cyclotron-Cherenkov instability. For the type B, which
consists of a dielectric core and an outer metallic cylinder, both growth rates are comparable. And for the type C, which
consists of a metallic core with dielectric liner on its surface and an outer metallic cylinder, the growth rate of the latter
instability is higher than that of the former instability. Finally, for the type C, obtained are dependences of the oscillation
frequency and the growth rates of both instabilities on the following parameters: the beam energy, the beam current, the axial
magnetic field, the dielectric constant, and the thickness of the dielectric. 相似文献
177.
We analyze the numerical stability of Finite Difference Lattice Boltzmann Method (FDLBM) by means of von Neumann stability analysis. The stability boundary of the FDLBM depends on the BGK relaxation time, the CFL number, the mean flow velocity, and the wavenumber. As the BGK relaxation time is increased at constant CFL number, the stability of the central difference LB scheme may not be ensured. The limits of maximum stable velocity are obtained around 0.39, 0.43, and 0.43 for the central difference, for the explicit upwind difference, and for the semi-implicit upwind difference schemes, respectively. We derive artificial viscosities for every difference scheme and investigate their influence on numerical stability. The requirements for artificial viscosity is consistent with the conditions derived from von Neumann stability analysis. This analysis elucidates that the upwind difference schemes are suitable for simulation of high Reynolds number flows. 相似文献
178.
Yamada K Unno M Kobayashi K Oku H Yamamura H Araki S Matsumoto H Katakai R Kawai M 《Journal of the American Chemical Society》2002,124(43):12684-12688
An X-ray crystallographic analysis of the bis-Ndelta-Boc-tetra-Nalpha-methyl derivative of gramicidin S, cyclo(-Val-MeOrn(Boc)-Leu-d-MePhe-Pro-)2, was undertaken successfully (R-factor = 0.088). As expected, the main chain adopts an antiparallel pleated beta-sheet conformation, but the pleated sheet is slightly twisted, and the sense of twisting is opposite to that found in the reported crystal structures of the gramicidin S-urea complex and the bis-Ndelta-(trichloroacetyl) and bis-Ndelta-(m-bromobenzoyl) derivatives of gramicidin S. In agreement with the observed resistance toward N-methylation, the urethane NH groups of the protected Orn side chains are hydrogen bonded to the carbonyl groups of the d-Phe residues. However, the side-chain-main-chain hydrogen bonding is in the i --> i - 3 mode, although hydrogen bonding in the i --> i + 2 mode was deduced from a 1H NMR study of protected gramicidin S derivatives and was actually found in the crystal structures of the diacylated gramicidin S. 相似文献
179.
180.