全文获取类型
收费全文 | 7570篇 |
免费 | 1145篇 |
国内免费 | 750篇 |
专业分类
化学 | 2085篇 |
晶体学 | 107篇 |
力学 | 1402篇 |
综合类 | 43篇 |
数学 | 616篇 |
物理学 | 2047篇 |
无线电 | 3165篇 |
出版年
2024年 | 31篇 |
2023年 | 86篇 |
2022年 | 188篇 |
2021年 | 222篇 |
2020年 | 258篇 |
2019年 | 259篇 |
2018年 | 216篇 |
2017年 | 315篇 |
2016年 | 386篇 |
2015年 | 356篇 |
2014年 | 472篇 |
2013年 | 539篇 |
2012年 | 499篇 |
2011年 | 529篇 |
2010年 | 406篇 |
2009年 | 460篇 |
2008年 | 473篇 |
2007年 | 480篇 |
2006年 | 445篇 |
2005年 | 352篇 |
2004年 | 320篇 |
2003年 | 323篇 |
2002年 | 227篇 |
2001年 | 224篇 |
2000年 | 190篇 |
1999年 | 146篇 |
1998年 | 131篇 |
1997年 | 122篇 |
1996年 | 145篇 |
1995年 | 94篇 |
1994年 | 72篇 |
1993年 | 92篇 |
1992年 | 75篇 |
1991年 | 59篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9465条查询结果,搜索用时 15 毫秒
21.
This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two‐equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k–εmodel, the realizable k–εmodel, the standard k–ωmodel and the shear‐stress‐transport (SST) k–ωmodel. It has found that the realizable k–εturbulence model used with enhanced wall functions and near‐wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
22.
Shuichi Ishida Keiki Takeda Atsushi Okamoto Ichiro Shibasaki 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):255
Magnetoresistance (MR) effects have been investigated in perpendicular and parallel magnetic fields at 300, 80 K and liquid He temperatures for undoped InSb thin films 0.1–2.3 μm thick grown on GaAs(1 0 0) substrates by MBE. At high temperatures, the intrinsic carriers show the parabolic negative MR observable only in magnetic fields parallel to the film. The skipping-orbit effect due to surface boundary scattering in the classical orbits in the plane vertical to the film has been argued to be responsible for the negative MR. At low temperatures (T=80 K), the transport is dominated by the two-dimensional (2D) electrons in the accumulation layers at the InSb/GaAs(1 0 0) hetero interface; MR is positive and shows a logarithmic increase with anisotropy between parallel and perpendicular field orientation, arising from the 2D weak anti-localization (WAL) that reflects the interplay between the spin-Zeeman effect and strong spin–orbit interaction caused by the asymmetric potential at the interface (Rashba term). The zero-field spin splitting energy of Δ013 meV, the electron effective mass of m*0.10m0 seven times of the band edge mass in bulk InSb and the effective g-factor of |g*|15 in the accumulation layer have been inferred from fits of MR for the 0.1 μm thick film to the 2D WL theory. 相似文献
23.
Bakul C. Dave Xiankui Hu Yogeeswari Devaraj Shirshak K. Dhali 《Journal of Sol-Gel Science and Technology》2004,32(1-3):143-147
There is a current need for alternative coatings that can provide corrosion resistance to metals or alloy surfaces due to the environmental hazards posed by conventional coatings. Herein, we report on novel organically-modified sol–gel coatings for the protection of metal and alloy surfaces. The basic concept of chemical conversion of metal surfaces is based on deposition of a hydrophobic, nonporous sol–gel barrier layer for surface protection and corrosion prevention. The properties of these organosilica coatings can be tuned by varying the composition of precursors. The evaluation of hydrophobicity, adhesive strength, and anticorrosion properties of organically-modified sol–gel derived coatings suggests their potential utility as technologically-compatible alternatives to conventional coatings. 相似文献
24.
Takayuki Abe 《Mathematical Methods in the Applied Sciences》2004,27(9):1007-1048
This paper is concerned with the standard Lp estimate of solutions to the resolvent problem for the Stokes operator on an infinite layer with ‘Neumann–Dirichlet‐type’ boundary condition. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
25.
A method to produce monodisperse magnetic composite spheres with diameters from less than 100 nm to more than 1 μm in water solution is reported. The spheres consist of a dielectric silica core and a cobalt/cobalt oxide shell which can be protected from further oxidation with an outer shell of silica or, alternatively, they can be covered with the polymer polyvinylpyrrolidone as a stabilizer. The formation of a uniform magnetic shell proceeds with the adsorption of metallic cobalt seeds, produced by the reduction of cobalt chloride with sodium borohydride, on a self‐assembled layer of polyelectrolytes on the silica core. In the second step, an outer silica shell can be formed by the hydrolysis and condensation of (3‐aminopropyl)trimethoxysilane and tetraethoxysilane. The double‐shell composite spheres show excellent sphericity, monodispersity, and a magnetic hysteresis loop at room temperature. 相似文献
26.
A. P. Prishivalko 《Journal of Applied Spectroscopy》1997,64(1):94-100
A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that
provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments
is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and
is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of
mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the
size distribution of the pigment particles.
B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997. 相似文献
27.
本文综述了广义谱域导抗法,直线法及直线法的快速算法,全波离散镜象法等主要方法,并对各种方法的特点进行了比较,这些方法可有效地处理平面分层介质结构问题,文中包括作者近期的研究成果。 相似文献
28.
As IC devices scale down to the submicron level, the resistance-capacitance (RC) time delays are the limitation to circuit
speed. A solution is to use low dielectric constant materials and low resistivity materials. In this work, the influence of
underlying barrier Ta on the electromigration (EM) of Cu on hydrogen silsesquioxane (HSQ) and SiO2 substrates was investigated. The presence of a Ta barrier not only improves the adhesion between Cu and dielectrics, but
also enhances the crystallinity of Cu film and improves the Cu electromigration resistance. The activation energy obtained
suggests a grain boundary migration mechanism and the current exponent calculated indicates the Joule heating effect. 相似文献
29.
Muhammet Yürüsoy 《Applied mathematics and computation》2004,150(3):775-783
Two dimensional unsteady boundary layer equations of a general model of non-Newtonian fluids were investigated in this study. In this model, the shear stress is taken as an arbitrary function of the velocity gradient. Group classification of the equations with respect to shear stress is done using two different approaches: (1) classical theory (2) equivalence transformations. Both approaches yield identical results. It is found that the principle Lie Algebra extends only for cases of Newtonian and Power-Law flows. 相似文献
30.
An analytical approach for vibration response analysis of a beam with single passive constrained layer damping (PCLD) patch is presented. The governing equation of motion of the beam is firstly derived on the basis of an energy approach and the Lagrange equation. The noval contribution is that a third admissible function is introduced to represent the longitudinal displacements of the constraining layer in the PCLD patch when the assumed-modes method is applied for discretizing the governing equation. In conventional analytical approaches, only two admissible functions are used together with a longitudinal static equilibrium equation of a section of base beam or constraining layer. Comparison of the computational results from the proposed analytical approach and the conventional analytical approach as well as a commercial FEM code reveals that the proposed analytical approach can describe the vibration responses of the damped beam more accurately for commonly used viscoelastic material (VEM) layer in the PCLD patch while the conventional analytical approach, in general, overestimates the damping effects of the PCLD patch. The advantages and disadvantages of the proposed analytical approach and conventional analytical approach are discussed through some case studies. 相似文献