全文获取类型
收费全文 | 2039篇 |
免费 | 241篇 |
国内免费 | 214篇 |
专业分类
化学 | 1217篇 |
晶体学 | 33篇 |
力学 | 90篇 |
综合类 | 45篇 |
数学 | 206篇 |
物理学 | 903篇 |
出版年
2024年 | 7篇 |
2023年 | 33篇 |
2022年 | 64篇 |
2021年 | 55篇 |
2020年 | 58篇 |
2019年 | 80篇 |
2018年 | 70篇 |
2017年 | 46篇 |
2016年 | 77篇 |
2015年 | 65篇 |
2014年 | 77篇 |
2013年 | 107篇 |
2012年 | 150篇 |
2011年 | 147篇 |
2010年 | 101篇 |
2009年 | 115篇 |
2008年 | 110篇 |
2007年 | 96篇 |
2006年 | 95篇 |
2005年 | 109篇 |
2004年 | 93篇 |
2003年 | 77篇 |
2002年 | 68篇 |
2001年 | 102篇 |
2000年 | 50篇 |
1999年 | 63篇 |
1998年 | 55篇 |
1997年 | 44篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 16篇 |
1991年 | 16篇 |
1990年 | 33篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 19篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有2494条查询结果,搜索用时 31 毫秒
881.
In this article, we investigate a nonlinear viscoelastic equation with nonlinear localized damping and velocity-dependent material density. We prove the global existence of weak solutions and general decay of the energy by using the Faedo–Galerkin method [Z.Y. Zhang and X.J. Miao, Global existence and uniform decay for wave equation with dissipative term and boundary damping, Comput. Math. Appl. 59 (2010), pp. 1003–1018; J.Y. Park and J.R. Kang, Global existence and uniform decay for a nonlinear viscoelastic equation with damping, Acta Appl. Math. 110 (2010), pp. 1393–1406] and the perturbed energy method [Zhang and Miao (2010); X.S. Han, and M.X. Wang, Global existence and uniform decay for a nonlinear viscoelastic equation with damping, Nonlinear Anal. TMA. 70 (2009), pp. 3090–3098], respectively. Furthermore, for certain initial data and suitable conditions on the relaxation function, we show that the energy decays exponentially or polynomially depending the rate of the decay of the relaxation function. This result is an improvement over the earlier ones in the literature. 相似文献
882.
This paper deals with the mean-square exponential stability of stochastic theta methods for nonlinear stochastic delay integro-differential equations. It is shown that the stochastic theta methods inherit the mean-square exponential stability property of the underlying system. Moreover, the backward Euler method is mean-square exponentially stable with less restrictions on the step size. In addition, numerical experiments are presented to confirm the theoretical results. 相似文献
883.
In this paper,we prove that the solutions of magnetic Zakharov system converge to those of generalized Zakharov system in Sobolev space H s,s > 3/2,when parameter β→∞.Further,when parameter (α,β) →∞ together,we prove that the solutions of magnetic Zakharov system converge to those of Schro¨dinger equation with magnetic effect in Sobolev space H s,s > 3/2.Moreover,the convergence rate is also obtained. 相似文献
884.
The self-demodulation characteristic of finite-amplitude ultrasonic sound waves can be applied with parametric loudspeaker to reproduce audible sound with highly directivity. But measuring the difference-frequency sound is still a problem due to the spurious sound generated as a result of nonlinearity caused by the product of the primary waves at the receiving system. In this paper, based on the phase-cancellation method and the Gaussian beam expansion technique, an alternative method is proposed to measure the on-axis difference-frequency sound accurately without using any traditional acoustic filter, where the spurious sound can be greatly reduced or even eliminated. The proposed method is more suitable for the case where the piston source in the parametric loudspeaker comprises multiple small piezoelectric transducers (PZTs) and each transducer element in the array may have different frequency response. The validity of the proposed method is confirmed both by simulations and experiments. 相似文献
885.
Zhijun Cheng Tingyu Liu Chenxing Yang Haixiu Gan Feiwu Zhang Jianyu Chen 《Journal of Physics and Chemistry of Solids》2012,73(2):302-307
Employing the first-principle calculations based on the density functional theory (DFT) and the Molecule Orbital theory (MO), we have researched the electronic structures of the reduced anatase TiO2 and its visible light photoactivity. The study is emphasized on the O vacancy, including the components of the defect states, the relationship with the bulk states and the way in which these electrons occupying the defect states are distributed in the real space. We find that the origin of the visible light photoactivity should be due to the transition of the excited electrons from the defect states σg orbital to the σu orbital in the upper conduction bands, rather than arising from the reduction of the band gap. The calculated results indicate that the localized defect states induced by the neutral and doubly ionized oxygen vacancies are all located in the band gap. 相似文献
886.
Hong Yu Wenwen Zi Shi Lan Shucai Gan Haifeng Zou Xuechun Xu Guangyan Hong 《Optics & Laser Technology》2012,44(7):2306-2311
Sr3MgSi2O8:Ce3+, Tb3+ phosphor samples were prepared using a solid-state reaction technique, and the photoluminescence properties and energy transfer were investigated. Effective energy transfer occurred in Ce3+/Tb3+ co-doped Sr3MgSi2O8 phosphors. Co-doping of Ce3+ was found to enhance the emission intensity of Tb3+ to a certain extent by transferring energy to Tb3+. The Ce3+/Tb3+ energy transfer was thoroughly investigated through its emission/excitation spectra and photoluminescence decay behavior. The color emitted by Sr3MgSi2O8:Ce3+, Tb3+ phosphors varied from blue to green and can be controlled by altering the concentration ratio of Ce3+ to Tb3+. These results indicate that Sr3MgSi2O8:Ce3+, Tb3+ may be useful as a green-emitting phosphor for ultraviolet whitelight-emitting diodes. 相似文献
887.
Comparing values of trace elements determined by external‐beam proton‐induced X‐ray emission (PIXE) and inductively coupled plasma atomic emission spectrometry (ICP‐AES) is important to find the provenience of raw materials of ancient nephrite artifacts, because most previous elemental characterizations of nephrite minerals were obtained by ICP‐AES, but PIXE presents the possibility of nondestructive analysis for largely and integrally ancient nephrite artifacts. In this work based on 12 nephrite minerals, it shows that the distribution of trace elements of nephrite samples both in PIXE and ICP‐AES data are generally consistent, although large differences exist in some elements. According to the trace elements, the two types of nephrite mineralization origins can be distinguished, determined by PIXE and ICP‐AES, respectively. Moreover, depending on the PIXE and ICP‐AES data, Sr can be regarded as fingerprint element of Xiaomeiling nephrite minerals, and the differentiation of Sr content between Xiaomeiling nephrite minerals and ancient nephrite artifacts from Liangzhu culture (3300–2300 bc ) is clear evidence that the raw materials of the artifacts are not from Xiaomeiling deposit. The nephrite minerals from Wenchuan deposit can be distinguished from other samples because of their high values of Mn/Fe. Therefore, the PIXE can be used with ICP‐AES to judge mineralization mechanism and find fingerprint elements of raw materials of ancient nephrite artifacts. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
888.
Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n+-layer 下载免费PDF全文
A novel silicon-on-insulator (SOI) high-voltage device based on epitaxy-separation by implantation oxygen (SIMOX) with a partial buried n+-layer silicon-on-insulator (PBN SOI) is proposed in this paper. Based on the proposed expressions of the vertical interface electric field, the high concentration interface charges which are accumulated on the interface between top silicon layer and buried oxide layer (BOX) effectively enhance the electric field of the BOX (EI), resulting in a high breakdown voltage (BV) for the device. For the same thicknesses of top silicon layer (10 μm) and BOX (0.375 upmum), the EI and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI, respectively. 相似文献
889.
景德镇早期制瓷工艺一直是学术界所关注的焦点问题之一。采用能量色散X射线荧光法分析了景德镇五代时期湘湖窑出土白瓷和青瓷样品的胎釉元素组成,并据此探讨其原料和配方。研究表明,五代时期景德镇湘湖窑白瓷胎体所用原料为瓷石,而青瓷瓷胎应是采用瓷石配以紫金土的二元配方;白瓷和青瓷瓷釉皆使用釉果加釉灰的配方,且青瓷瓷釉配方中釉灰的用量高于白瓷瓷釉。 相似文献
890.
运用拉曼光谱技术研究了Na2O(K2O)—CaO(MgO)—SiO2,Na2O(K2O)—Al2O3—SiO2,Na2O(K2O)—B2O3—SiO2,Na2O(K2O)—PbO—SiO2和PbO—BaO—SiO2五个系统的玻璃。结果表明,阳离子对玻璃近程结构的改造会引起拉曼特征的变化。部分样品是根据古玻璃平均成分在实验室烧制的,这项研究对于运用激光拉曼光谱区分不同系统的古代硅酸盐玻璃有重要意义。 相似文献