全文获取类型
收费全文 | 5067篇 |
免费 | 728篇 |
国内免费 | 1373篇 |
专业分类
化学 | 3378篇 |
晶体学 | 230篇 |
力学 | 1397篇 |
综合类 | 73篇 |
数学 | 524篇 |
物理学 | 1566篇 |
出版年
2024年 | 16篇 |
2023年 | 69篇 |
2022年 | 151篇 |
2021年 | 174篇 |
2020年 | 220篇 |
2019年 | 185篇 |
2018年 | 169篇 |
2017年 | 275篇 |
2016年 | 275篇 |
2015年 | 189篇 |
2014年 | 278篇 |
2013年 | 518篇 |
2012年 | 314篇 |
2011年 | 379篇 |
2010年 | 269篇 |
2009年 | 305篇 |
2008年 | 333篇 |
2007年 | 338篇 |
2006年 | 340篇 |
2005年 | 344篇 |
2004年 | 289篇 |
2003年 | 259篇 |
2002年 | 197篇 |
2001年 | 208篇 |
2000年 | 180篇 |
1999年 | 149篇 |
1998年 | 122篇 |
1997年 | 130篇 |
1996年 | 89篇 |
1995年 | 88篇 |
1994年 | 76篇 |
1993年 | 62篇 |
1992年 | 36篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有7168条查询结果,搜索用时 15 毫秒
891.
小波变换特征提取的复合材料损伤检测 总被引:3,自引:0,他引:3
论述了小波变换及其快速算法,基于小波变换的波形模量极大点来构造全局的相似性度量,并将此应用于复合材料损伤类型的检测 相似文献
892.
本实验选用TiH2及其它微量元素做粘结剂,在DS-029B型六面顶压机上烧结人造金刚石与硬质合金复合材料。实验中,采取TiH2脱氢与金刚石净化同时进行的工艺,在高真空和一定温度下脱氢,得到高活性的新鲜钛,使其具有更强的粘结作用,以获得高磨耗比的金刚石复合材料。实验中比较了不同净化温度对磨耗比的影响;同一种粘结剂不同含量与磨耗比之间的关系;同时还测试了其耐热性及时间极限。结果表明,这种复合材料在850 ℃下,加热3 min,磨耗比没有明显改变。 相似文献
893.
The interaction of four parallel non-symmetric permeable cracks in a piezoelectric/piezomagnetic composite plane subjected to anti-plane shear stress loading was studied by the Schmidt method. The problem was formulated through a Fourier transform into four pairs of dual integral equations, in which unknown variables are jumps of displacements across the crack surfaces. To solve the dual integral equations, the jumps of displacements across the crack surfaces were directly expanded as a series of Jacobi polynomials. Finally, the relationships among the electric displacement, magnetic flux and stress fields near the crack tips were obtained. The results show that the stress, the electric displacement and the magnetic flux intensity factors at the crack tips depend on the lengths and spacing of cracks. It was also revealed that the crack shielding effect is present in piezoelectric/piezomagnetic composites. 相似文献
894.
Lead-free ferroelectric ceramics with a morphotropic phase boundary (MPB) composition 85.4% (Bi0.5Na0.5)TiO3–2.6%BaTiO3–12.0% (Bi0.5K0.5)TiO3 (BNT-BT-BKT at a molar ratio of 85.4: 2.6: 12.0) doped with 0.8?mol% Nb2O5 were studied for their crystalline phases and microstructure. The crystalline phases were identified using X-ray diffractometry (XRD) with the contents determined using the Rietveld refinement technique. The phase-transformation-induced microstructure was analyzed using transmission electron microscopy (TEM) and the crystal symmetries were determined using the convergent-beam electron diffraction (CBED) technique. Samples sintered at 1200°C contain a mixture of cubic (C-), tetragonal (T-) and rhombohedral (R-) phases at a ratio of C/T/R?=?56.6: 28.4: 15.0?wt%. Two types of grains are produced: one characterized by a featureless contrast consisting of nano-scale T-domains dispersed in a C-phase matrix; the other a core-shell structure with a shell containing twin and anti-phase-boundary (APB) domains coexisting with a (C?+?T)-phase mixture core. The T- and R-twin boundaries are determined to {111}T and {110}R, respectively, and the fault vector for T-APB to R?=?1/2?110]T. The characteristic microstructure is discussed in terms of the reduction in the point group symmetry and changes in the unit cell volume or the Bravais lattice upon phase transformation among the C-, T- and R-phases. The twin and the APB domains are induced and explained. 相似文献
895.
Pham Duc Chinh 《哲学杂志》2013,93(4):609-627
A randomly inhomogeneous material may have macroscopic properties (elasticity, conductivity) scattered over some uncertainty intervals, despite the idealistic uniqueness assumption of homogenization theory. Based on minimum energy principles and certain statistical isotropy-symmetry hypotheses, our partly third-order bounds on the effective properties of random polycrystals are expected to estimate those scatter ranges. Explicit expressions are given and calculated for the elastic moduli of the random aggregates of some known monoclinic and triclinic crystals, which yield results in agreement with those calculated for higher-symmetry crystals: the moduli are determinable within an accuracy of two or three significant digits in most cases. It is shown, however, that with some real-world exotic crystals the bounds may fall far apart, and further theoretical and experimental studies on them deserve attention. 相似文献
896.
897.
The microstructure of a composite containing a quasicrystal phase, i.e. so-called crystal–quasicrystal (CQ) composite, was studied. The CQ composite was obtained by the Bridgman method via solidification of Al61Cu27Fe12 alloy (numbers indicate at%). The process was conducted at a pull out rate of v = 0.07 mm/min. The average temperature gradient in the heating zone was 43 K/cm. The composite matrix consisted of cubic β phase Al(Fe, Cu), with reinforcement of λ-phase rod-shaped fibres surrounded by a quasicrystal icosahedral ψ phase, which also existed in the fibre core. The fibres were rhomboidal in cross-section. The composite was studied using X-ray and electron diffraction, light-optical and scanning electron microscopy (SEM), X-ray topography and Laue diffraction. 相似文献
898.
Zhihang Peng Qiang Chen Dan Liu Yadan Wang Dinquan Xiao Jianguo Zhu 《Current Applied Physics》2013,13(7):1183-1187
Aurivillius type (NaBi)0.5?x(LiCe)xBi2Nb2O9 ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce4+ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb5+ ions by the Ce4+ ions. 相似文献
899.
Ali Hussain Jin Soo Kim Tae Kwon Song Myong Ho Kim Won Jong Kim Sang Su Kim 《Current Applied Physics》2013,13(6):1055-1059
Lead-free non-stoichiometric (K0.470Na0.545)(Nb0.55Ta0.45)O3 (KNNT) textured ceramics were prepared by a reactive templated grain growth method using NaNbO3 (NN) templates. The Plate-like NaNbO3 (NN) templates were synthesized from bismuth layer-structured Bi2.5Na3.5Nb5O18 (BNN) particles by a topochemical microcrystal conversion (TMC) method. Using 5 wt% of NN templates, textured KNNT ceramics were fabricated, and their crystal structure, microstructure, dielectric and piezoelectric properties were compared with non-textured KNNT ceramics prepared by a conventional solid state reaction method. The textured KNNT ceramics exhibited high grain orientation and high dielectric constant. In addition, piezoelectric properties of textured KNNT ceramics were improved, giving a high piezoelectric coefficient d33 = 390 pC/N and piezoelectric coupling coefficient kp = 0.60. 相似文献
900.
Bu-Won Son Seok-Joo Park Seung-Bok Lee Tak-Hyoung Lim Rak-Hyun Song Jong-Won Lee 《Current Applied Physics》2013,13(9):1906-1913
In a segmented-in-series solid oxide fuel cell (SIS-SOFC), an interconnect (IC) provides electrical contact and sealing between the anode of one cell and the cathode of the next. A metallic silver-glass composite (SGC) is considered a promising alternative to ceramic IC materials in SIS-SOFCs. In this work, a simulation study is performed on a tubular SIS-SOFC to assess the effectiveness of the SGC-IC design and to predict the SOFC performance characteristics for various IC geometries and conductivities. The developed model provides detailed information on cell behavior, such as the internal resistance, the potential/current distribution, and the local gas species concentration. The results demonstrate that the SGC material greatly reduces a potential drop across the IC film. Thus, it provides the following substantial advantages over conventional ceramic IC materials: (i) increased power density and (ii) a larger degree of flexibility in the cell design. Moreover, the validation test, i.e., comparison of the simulated results with the experimental data, indicates that the model could serve as a valuable tool for design optimization to achieve the required SOFC performance. 相似文献