全文获取类型
收费全文 | 1162篇 |
免费 | 322篇 |
国内免费 | 206篇 |
专业分类
化学 | 248篇 |
晶体学 | 27篇 |
力学 | 131篇 |
综合类 | 16篇 |
数学 | 212篇 |
物理学 | 1056篇 |
出版年
2024年 | 8篇 |
2023年 | 24篇 |
2022年 | 32篇 |
2021年 | 25篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 10篇 |
2017年 | 27篇 |
2016年 | 25篇 |
2015年 | 35篇 |
2014年 | 60篇 |
2013年 | 36篇 |
2012年 | 67篇 |
2011年 | 76篇 |
2010年 | 65篇 |
2009年 | 66篇 |
2008年 | 173篇 |
2007年 | 107篇 |
2006年 | 72篇 |
2005年 | 123篇 |
2004年 | 90篇 |
2003年 | 72篇 |
2002年 | 92篇 |
2001年 | 61篇 |
2000年 | 44篇 |
1999年 | 29篇 |
1998年 | 32篇 |
1997年 | 27篇 |
1996年 | 31篇 |
1995年 | 19篇 |
1994年 | 28篇 |
1993年 | 11篇 |
1992年 | 24篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1690条查询结果,搜索用时 15 毫秒
951.
952.
层状类钙钛矿结构新铌酸盐KSr2Nb3O10 总被引:3,自引:0,他引:3
A new niobate compound KSr2Nb3O10 was synthesized for the first time. The chemical compositions, crystal structure, optical property, density and melting point of the new compound were characterized by EPMA, TEM, XRD, DTA and so on. KSr2Nb3O10 crystallizes the orthorhombic system with unit cell parameters a=0.7816(1) nm, b=0.7764(2) nm, c=2.9995(2) nm, V=1.8114(4) nm3, and space group P212121, Z=8. The structure may be described as treble perovskite sheets [Sr2Nb3O10]- interleaved with K+. Further, it was found that KSr2Nb3O10 has intercalation phenomenon. Na+, Li+, H+, NH+4 could exchange the interlayer cations K+ of KSr2Nb3O10, and n-hexylamine also could intercalate into the place between the layers of [Sr2Nb3O10]-. 相似文献
953.
In this paper the nonlinear dynamical behaviour of a quantum cellular neural network (QCNN)
by coupling Josephson circuits was investigated and it was shown that the
QCNN using only two of them can cause the onset of chaotic oscillation. The
theoretical analysis and simulation for the two Josephson-circuits-coupled
QCNN have been done by using the amplitude and phase as state variables. The
complex chaotic behaviours can be observed and then proved by calculating
Lyapunov exponents. The study provides valuable information about QCNNs for
future application in high-parallel signal processing and novel chaotic
generators. 相似文献
954.
955.
Arrhenius law implicates that only those molecules which possess the internal energy greater than the activation energy Ea can react. However, the internal energy will not be proportional to the gas temperature if the specific heat ratio y and the gas constant R vary during chemical reaction processes. The varying y may affect significantly the chemical reaction rate calculated with the Arrhenius law under the constant γ assumption, which has been widely accepted in detonation and combustion simulations for many years. In this paper, the roles of variable γ and R in Arrhenius law applications are reconsidered, and their effects on the chemical reaction rate are demonstrated by simulating one- dimensional C-J and two-dimensional cellular detonations. A new overall one-step detonation model with variable γ and R is proposed to improve the Arrhenius law. Numerical experiments demonstrate that this improved Arrhenius law works well in predicting detonation phenomena with the numerical results being in good agreement with experimental data. 相似文献
956.
ZHANG Li-Hua CAO Zhuo-Liang 《理论物理通讯》2008,49(3):595-598
We present a scheme for generation of two-atomic entangled state by using the interference of polarized photons. The scheme does not require complete mapping between the atomic state and the photonic state, nor does it require the establishment of maximal entanglement between the atom and the cavity. And the atom-cavity coupling strength is smaller than the cavity decay rate. This greatly relaxes the requirement on the cavity quality. The scheme is for non-post-selection results and all the steps of the scheme are within the current technologies. 相似文献
957.
阐述了二氧化硫性质演示实验的改进方法,从实验的设计意图、实验装置的准备、实验的具体操作与实验现象、实验过程中应注意的事项等方面将自己的经验及做法作了一个完整的介绍. 相似文献
958.
研究了转子和定子碰摩时振幅的跳跃现象,利用响应相位特征解释了接触诱发‘刚度增加'的机理.当转子与定子之间的间隙足够大时,转子在临界转速达到最大振幅,然后迅速衰减.如果与定子发生接触或碰撞,它们之间的接触将在很宽的速度范围得以维持,即便是转速已经远离临界转速.这一现象也称为‘刚度增加'或‘硬化'(stiffness increase Or stiffening).研究结果表明,形成该现象的机理足由于接触的作用,使得激励与振动响应的相位差保持在小于π/2的范围内.并且振幅跳跃与相位跃迁相伴出现.实验结果也验证了这一结论. 相似文献
959.
In this paper, the investigation is focused on a (3+1)-dimensional variable-coefficient Kadomtsev- Petviashvili (vcKP) equation, which can describe the realistic nonlinear phenomena in the fluid dynamics and plasma in three spatial dimensions. In order to study the integrability property of such an equation, the Painlevé analysis is performed on it. And then, based on the truncated Painlevé expansion, the bilinear form of the (3+1)-dimensionaJ vcKP equation is obtained under certain coefficients constraint, and its solution in the Wronskian determinant form is constructed and verified by virtue of the Wronskian technique. Besides the Wronskian determinant solution, it is shown that the (3+1)-dimensional vcKP equation also possesses a solution in the form of the Grammian determinant. 相似文献
960.
用数值方法研究铁-铍介质界面上的激波折射现象.运用激波极曲线理论分析不同强度的激波从正规折射过渡到非正规折射的临界角变化.运用一个具有二阶精度和波传播性质的激波捕捉法,数值求解激波折射运动的流体力学方程组.对正规折射,数值结果与激波极曲线理论一致;对非正规折射,不同强度的激波大都存在前驱的折射激波,并且入射激波的强度不同、入射角度不同,激波折射的图像也不同. 相似文献