全文获取类型
收费全文 | 10739篇 |
免费 | 352篇 |
国内免费 | 74篇 |
专业分类
化学 | 6437篇 |
晶体学 | 65篇 |
力学 | 216篇 |
数学 | 1688篇 |
物理学 | 2278篇 |
无线电 | 481篇 |
出版年
2024年 | 13篇 |
2023年 | 56篇 |
2022年 | 220篇 |
2021年 | 274篇 |
2020年 | 203篇 |
2019年 | 279篇 |
2018年 | 274篇 |
2017年 | 250篇 |
2016年 | 410篇 |
2015年 | 321篇 |
2014年 | 362篇 |
2013年 | 732篇 |
2012年 | 667篇 |
2011年 | 777篇 |
2010年 | 542篇 |
2009年 | 477篇 |
2008年 | 679篇 |
2007年 | 607篇 |
2006年 | 537篇 |
2005年 | 513篇 |
2004年 | 444篇 |
2003年 | 361篇 |
2002年 | 315篇 |
2001年 | 165篇 |
2000年 | 167篇 |
1999年 | 153篇 |
1998年 | 106篇 |
1997年 | 93篇 |
1996年 | 146篇 |
1995年 | 123篇 |
1994年 | 104篇 |
1993年 | 101篇 |
1992年 | 96篇 |
1991年 | 63篇 |
1990年 | 48篇 |
1989年 | 45篇 |
1988年 | 25篇 |
1987年 | 33篇 |
1986年 | 37篇 |
1985年 | 42篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 37篇 |
1981年 | 34篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1975年 | 17篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We study the chiral behavior of the nucleon and Δ-isobar masses within a manifestly covariant chiral effective-field theory, consistent with the analyticity principle. We compute the πN and πΔ one-loop contributions to the mass and field-normalization constant, and find that they can be described in terms of universal relativistic loop functions, multiplied by appropriate spin, isospin and coupling constants. We show that these manifestly relativistic one-loop corrections, when properly renormalized, obey the chiral power-counting and vanish in the chiral limit. The results including only the πN-loop corrections compare favorably with the lattice QCD data for the pion-mass dependence of the nucleon and Δ masses, while inclusion of the πΔ loops tends to spoil this agreement. 相似文献
42.
Phase transmittance RBF neural networks 总被引:1,自引:0,他引:1
Presented is a new complex valued radial basis function (RBF) neural network with phase transmittance between the input nodes and output, which makes it suitable for channel equalisation on quadrature digital modulation systems. 相似文献
43.
Detection of hepatocarcinoma in rats by integration of the fluorescence spectrum: Experimental model
J. C. Marcassa J. Ferreira S. Zucoloto O. de Castro e Silva Jr. L. G. Marcassa V. S. Bagnato 《Laser Physics》2006,16(5):827-832
The incorporation of spectroscopic techniques into diagnostic procedures may greatly improve the chances for precise diagnostics. One promising technique is fluorescence spectroscopy, which has recently been used to detect many different types of diseases. In this work, we use laser-induced tissue fluorescence to detect hepatocarcinoma in rats using excitation light at wavelengths of 443 and 532 nm. Hepatocarcinoma was induced chemically in Wistar rats. The collected fluorescence spectrum ranges from the excitation wavelength up to 850 nm. A mathematical procedure carried out on the spectrum determines a figure of merit value, which allows the detection of hepatocarcinoma. The figure of merit involves a procedure which evaluates the ratio between the backscattered excitation wavelength and the broad emission fluorescence band. We demonstrate that a normalization allowed by integration of the fluorescence spectra is a simple operation that may allow the detection of hepatocarcinoma. 相似文献
44.
Beginning with the most general fractal strings/sprays construction recently expounded in the book by Lapidus and Frankenhuysen, it is shown how the complexified extension of El Naschie's cantorian-fractal spacetime model belongs to a very special class of families of fractal strings/sprays whose scaling ratios are given by suitable pinary (pinary, p prime) powers of the Golden Mean. We then proceed to show why the logarithmic periodicity laws in Nature are direct physical consequences of the complex dimensions associated with these fractal strings/sprays. We proceed with a discussion on quasi-crystals with p-adic internal symmetries, von Neumann's Continuous Geometry, the role of wild topology in fractal strings/sprays, the Banach-Tarski paradox, tesselations of the hyperbolic plane, quark confinement and the Mersenne-prime hierarchy of bit-string physics in determining the fundamental physical constants in Nature. 相似文献
45.
Characterization of spherical particles using high-order neural networks and scanning flow cytometry
Vladimir V. Berdnik Alexander Shvalov Valeri Maltsev Valery A. Loiko 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(1):62-72
We retrieve the radius R, real n and imaginary k parts of the refractive index of homogeneous spherical particles using angular distribution of the light-scattering intensity. To solve the inverse light-scattering problem we use a high-order neural-network technique. The effect of network parameters on optimization is examined. The technique is evaluated for noise-corrupted input data at 0.6 μm<R<10.6 μm, 1.02<n<1.38, and 0<k<0.03. The errors of retrieval for nonabsorbing particles do not exceed 0.05 μm for radius and 0.015 for refractive index. The experimental verification is fulfilled by experimental data retrieved by means of a scanning flow cytometer. The light-scattering profiles of polystyrene beads and spherized red blood cells are processed with the high-order neural networks and a non-linear regression at Mie theory. The parameters retrieved by the high-order neural networks correlate well with the parameters retrieved by the least-square method. 相似文献
46.
47.
48.
Magnetization measurements in the (Dy
x
Y1−x
)Fe2 intermetallic compounds show evidence of blocking of domain wall motion. This effect is a function of concentrationx. The direction of magnetization is also dependent on the Dy concentration. We have used the Mossbauer spectroscopy of57Fe to verify the direction of magnetization in the series as a function ofx and temperature. The results show that this change in easy direction occurs at higher temperatures than those where the blocking
is detected through DC magnetization measurements.
supported by RHAE/SCT. 相似文献
49.
M. Alves Da Silva M. Helena Gil A. P. Piedade J. S. Redinha A. M. Oliveira Brett J. M. Caridade Costa 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):269-274
The immobilization of catalase on grafted membranes of poly(ethylene)-g-co-acrylic acid and poly(tetrafluoroethylene)-g-co-acrylic acid and their application in hydrogen peroxide electrochemical sensors is described. The introduction of carboxylic acid groups onto a hydrophobic support provides a good environment for subsequent enzyme immobilization. This single membrane, hydrogen peroxide sensor showed significant improvement with respect to the double membrane versions. The response is very rapid, the linear range being from 10 μM up to 6 mM, with a detection limit of 4.7 μM, and a lifetime of more than 4 months. 相似文献
50.
In this article we propose efficient scan path and BIST schemes for RAMs. Tools for automatic generation of these schemes have been implemented. They reduce the design effort and thus allow the designer to select the more appropriate scheme with respect to various constraints. 相似文献