全文获取类型
收费全文 | 4365篇 |
免费 | 815篇 |
国内免费 | 491篇 |
专业分类
化学 | 3306篇 |
晶体学 | 40篇 |
力学 | 216篇 |
综合类 | 44篇 |
数学 | 485篇 |
物理学 | 1580篇 |
出版年
2024年 | 5篇 |
2023年 | 74篇 |
2022年 | 112篇 |
2021年 | 123篇 |
2020年 | 176篇 |
2019年 | 193篇 |
2018年 | 154篇 |
2017年 | 125篇 |
2016年 | 237篇 |
2015年 | 202篇 |
2014年 | 254篇 |
2013年 | 299篇 |
2012年 | 363篇 |
2011年 | 367篇 |
2010年 | 271篇 |
2009年 | 291篇 |
2008年 | 307篇 |
2007年 | 268篇 |
2006年 | 254篇 |
2005年 | 225篇 |
2004年 | 163篇 |
2003年 | 143篇 |
2002年 | 181篇 |
2001年 | 153篇 |
2000年 | 92篇 |
1999年 | 104篇 |
1998年 | 64篇 |
1997年 | 61篇 |
1996年 | 70篇 |
1995年 | 43篇 |
1994年 | 56篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 43篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有5671条查询结果,搜索用时 15 毫秒
981.
Cheng Shao Hong-Jie Yu Chen-Guo Feng Rui Wang Guo-Qiang Lin 《Tetrahedron letters》2012,53(22):2733-2735
A variety of novel C1-symmetric chiral diene ligands based on the dicyclopentadiene (DCP) skeleton were easily prepared from commercially available DCP. The application of these diene ligands in the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds has been examined and excellent enantioselectivities (up to 97% ee) as well as good yields were achieved under mild reaction conditions. 相似文献
982.
A novel technique in controlling the size of SiO2 nano‐particles in the preparation of Nafion/SiO2 composite membranes via in situ sol–gel method, as well as the effects of nano‐particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO2 composite membranes containing SiO2 nano‐particles with four different diameters (5 ± 0.5, 7 ± 0.5, 10 ± 1, and 15 ± 2 nm) are fabricated by altering the reactant concentrations during in situ sol–gel reaction. Sequentially, size effects of SiO2 nano‐particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10 nm is a critical diameter for SiO2 incorporated into Nafion matrix, exhibiting desirable physico‐chemical properties for operation at elevated temperature and low humidity. At 110°C and 59% RH, the output voltage of the cell equipped with Nafion/SiO2 (10 nm) obtains an output voltage of 0.625 V at 600 mA/cm2, which is 50 mV higher than that of unmodified Nafion. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
983.
In a recent letter [E. Proynov, Y. Shao, and J. Kong, Chem. Phys. Lett. 493, 381 (2010)], Becke's B05 model of nondynamic electron correlation in density functional theory was implemented self-consistently with computational efficiency (the "SCF-RI-B05" scheme). Important modifications of the algorithm were done in order to make the self-consistency feasible. In the present work, we give a complete account of the SCF-RI-B05 algorithm, including all the formulae for the analytical representation of the B05 functional and for its self-consistent field (SCF) potential. The average performance of the SCF-RI-B05 method reported in the above letter was somewhat less accurate, compared to the original B05 implementation, mainly because the parameters of the original B05 model were optimized with post-local-spin-density calculations. In this work, we report improved atomization energies with SCF-RI-B05, based on a SCF re-optimization of its four linear parameters. The re-optimized SCF-RI-B05 scheme is validated also on reaction barriers, and on the subtle energetics of NO dimer, an exemplary system of strong nondynamic correlation. It yields both the binding energy and the singlet-triplet splitting of the NO dimer correctly, and close to the benchmarks reported in the literature. 相似文献
984.
Modelling of spall damage in ductile materials and its application to the simulation of the plate impact on copper
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A statistical model of dynamic spall damage due to void nucleation and growth is proposed for ductile materials under intense loading, which takes into account inertia, the elastic-plastic effect, and initial void size. To some extent, void interaction could be accounted for in this approach. Based on this model, the simulation of spall experiments for copper is performed by using the Lagrangian finite element method. The simulation results are in good agreement with experimental data for the free surface velocity profile, stress record behind copper target, final porosity, and void concentrations across the target. The influence of elastic-plastic effect upon the damage evolution is explored. The correlation between the damage evolution and the history of the stress near the spall plane is also analyzed. 相似文献
985.
A density-functional theory investigation on desorption of O2 on Sn(111) and its comparison with initial oxidation on the X(111) (X=Si,Ge, Sn,Pb) surfaces
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
<正>The first-principles calculations are performed to investigate the adsorption of O2 molecules on an Sn(111) 2×2 surface.The chemisorbed adsorption precursor states for O2 are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn(lll) induced by oxygen adsorption are studied.Based on this,the adsorption behaviours of O2 on X(111)(X=Si,Ge,Sn,Pb) surfaces are analysed,and the most stable adsorption channels of O2 on X(111)(X=Si,Ge,Sn,Pb) are identified.The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared.The results show that the O2 adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity. 相似文献
986.
Y. Zhang C. Zheng Y Liu L. Shao · C. Gou School of Mechanical Vehicular Engineering Beijing Institute of Technology Beijing China Y.Liu School of Mechanical-Electronic Automobile Engineering Beijing University of Civil Engineering Architecture Beijing China 《Acta Mechanica Sinica》2009,25(2):205-210
This paper presents two exact explicit solutions for the three dimensional dual-phase lag (DLP) heat conduction equation, during the derivation of which the method of trial and error and the authors' previous experiences are utilized. To the authors' knowledge, most solutions of 2D or 3D DPL models available in the literature are obtained by numerical methods, and there are few exact solutions up to now. The exact solutions in this paper can be used as benchmarks to validate numerical solutions and to develop numerical schemes, grid generation methods and so forth. In addition, they are of theoretical significance since they correspond to physically possible situations. The main goal of this paper is to obtain some possible exact explicit solutions of the dual-phase lag heat conduction equation as the benchmark solutions for computational heat transfer, rather than specific solutions for some given initial and boundary conditions. Therefore, the initial and boundary conditions are indeterminate before derivation and can be deduced from the solutions afterwards. Actually, all solutions given in this paper can be easily proven by substituting them into the governing equation. 相似文献
987.
Semi-analytical solutions for bending and free vibration of composite laminated plates have been derived based on three-dimensional elasticity theory using a newly developed hybrid analysis, which perfectly combines the state space approach (SSA) and the technique of differential quadrature (DQ). The thickness direction of laminates is selected as the transfer direction in SSA, and the DQ technique is employed to discretize the in-plane domains. This actualizes the transformation of the original partial differential equations into a state equation consisting of first-order ordinary differential equations. In particular, the use of DQ technique makes ease of the treatment of various boundary conditions, which cannot be considered in the conventional exact SSA. To avoid numerical instabilities in the conventional transfer matrix method, artificial interfaces are introduced to divide each layer into several sub-layers to reduce the transfer distance and the joint coupling matrices are established according to the continuity conditions at actual and artificial interfaces to implement the global analysis. Comprehensive numerical examples are preformed to validate the present hybrid method. Effects of some parameters on mechanical properties of the laminates are discussed. 相似文献
988.
塑性损伤本构模型的自由能势函数研究 总被引:1,自引:1,他引:0
自由能势函数是不可逆热力学量及其共轭量的标量泛函,是广义标准材料模型的重要组成.论文根据损伤状态、过程、作用和伪势的定义和定理,分析了损伤耗散势的数学和物理含义,探讨了损伤耗散势的理论基础和描述耗散势的一般理论方法.研究了耗散势、损伤作用和自由能势函数的相互关系,给出了满足上述基本原理的自由能表达式,基于增量最小原理的变分形式得到了损伤理论基本方程的数值离散方程,实验模拟验证了该文理论和数值方法的正确性和有效性. 相似文献
989.
Graded index broadband antireflection coating prepared by glancing angle deposition for a high-power laser system
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper reports that SiO2 is selected to fabricate
broadband antireflection (AR) coatings on fused silica substrate by
using glancing angle deposition and physical vapour deposition.
Through accurate control of the graded index of the SiO2 layer,
transmittance of the graded broadband AR coating can achieve an average
value of 98% across a spectral range of 300--1850~nm. Moreover,
a laser-induced damage threshold measurement of the fabricated AR
coating is performed by using a one-on-one protocol according to
ISO11254-1, resulting in an average damage threshold of
17.2~J/cm$^{2}$. 相似文献
990.
Junhai Liu Chenlin Du Zhengping Wang Li Zhu Huaijin Zhang Xianlin Meng Jiyang Wang Zongshu Shao Minhua Jiang 《Optics & Laser Technology》2001,33(3)
A diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:GdVO4/KTP green laser formed with a flat–flat resonator was demonstrated. 3.05 W of average green output power at pulse repetition frequency (PRF) of 40 kHz was obtained with an optical conversion efficiency of 18.4%, the effective intracavity frequency-doubling efficiency was 57%. At the incident pump power of 15 W, the shortest laser pulse occurred at PRF of 25 kHz with FWHM width of 14 ns, yielding the highest peak power of 7.44 kW; while the largest pulse energy of 0.14 mJ was achieved at PRF of 15 kHz. 相似文献