全文获取类型
收费全文 | 14651篇 |
免费 | 2894篇 |
国内免费 | 1009篇 |
专业分类
化学 | 3622篇 |
晶体学 | 113篇 |
力学 | 3638篇 |
综合类 | 164篇 |
数学 | 2596篇 |
物理学 | 8421篇 |
出版年
2024年 | 30篇 |
2023年 | 133篇 |
2022年 | 242篇 |
2021年 | 303篇 |
2020年 | 459篇 |
2019年 | 350篇 |
2018年 | 382篇 |
2017年 | 460篇 |
2016年 | 523篇 |
2015年 | 428篇 |
2014年 | 814篇 |
2013年 | 922篇 |
2012年 | 829篇 |
2011年 | 1048篇 |
2010年 | 872篇 |
2009年 | 931篇 |
2008年 | 980篇 |
2007年 | 1031篇 |
2006年 | 933篇 |
2005年 | 881篇 |
2004年 | 858篇 |
2003年 | 772篇 |
2002年 | 610篇 |
2001年 | 564篇 |
2000年 | 490篇 |
1999年 | 413篇 |
1998年 | 357篇 |
1997年 | 287篇 |
1996年 | 241篇 |
1995年 | 217篇 |
1994年 | 163篇 |
1993年 | 161篇 |
1992年 | 132篇 |
1991年 | 145篇 |
1990年 | 96篇 |
1989年 | 85篇 |
1988年 | 79篇 |
1987年 | 64篇 |
1986年 | 36篇 |
1985年 | 34篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 23篇 |
1977年 | 6篇 |
1973年 | 11篇 |
1971年 | 8篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献
32.
We study nonlinear dynamics of optical pulse propagation in the spectral region inside the polariton gap. It is shown that the Kerr nonlinearity can lead to formation of solitary waves in this region of frequencies. 相似文献
33.
Jeong Ryeol Choi 《International Journal of Theoretical Physics》2004,43(4):947-958
We derived the WKB wave function for the general time-dependent quadratic Hamiltonian system using a unitary transformation method. We applied our research to sinusodially drived Caldirola–Kanai oscillator and confirmed that the time evolution of our approximated WKB wave function is similar to that of the exact one. This wave function can be used to analyze the interference between the probability amplitudes contributed by the area of overlap in phase space of quantum states. 相似文献
34.
35.
Andrey Pereverzev 《Foundations of Physics Letters》2003,16(5):411-428
We argue that it may be possible to consistently explain the quantum measurement by assuming that the wave function is in one-to-one correspondence with objective physical reality and has no probabilistic interpretation. In the context of such approach we consider the model of a harmonic oscillator linearly coupled to a heat bath and treat the oscillator as the system being measured. Three classes of initial pure states for the bath are considered. Exact expressions for the average values and variances of the oscillator coordinate and momentum as functions of time are considered for each class of pure states. It is shown that these quantities exhibit different asymptotic behavior for different classes of initial states of the bath. In particular, if each mode of the bath is initially in a coherent state, then for an arbitrary initial state of the oscillator the variances of the oscillator coordinate and momentum asymptotically approach the same values as for a coherent state of the free oscillator, while the averages of coordinate and momentum show a Brownian-like behavior. We argue that such behavior shows several features of the quantum measurement and supports our interpretation of the wave function. 相似文献
36.
研究了具有非线性项|u|~αu的半线性波动方程的Cauclly问题,利用仿积分解及交换子估计等技术,证明了当α为一般的实数且满足一定的限制时,Cauchy问题自相似解的存在性。本文的结果回答了Planchon在其工作中所遗留的问题。 相似文献
37.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
38.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
39.
提出了一种比较系统的求解非线性发展方程精确解的新方法, 即试探方程法. 以一个带5阶 导数项的非线性发展方程为例, 利用试探方程法化成初等积分形式,再利用三阶多项式的完 全判别系统求解,由此求得的精确解包括有理函数型解, 孤波解, 三角函数型周期解, 多项 式型Jacobi椭圆函数周期解和分式型Jacobi椭圆函数周期解
关键词:
试探方程法
非线性发展方程
孤波解
Jacobi椭圆函数
周期解 相似文献
40.
M. Akbari A. Behzadmehr F. Shahraki 《International Journal of Heat and Fluid Flow》2008,29(2):545-556
Fully developed laminar mixed convection of a nanofluid consists of water and Al2O3 in horizontal and inclined tubes has been studied numerically. Three-dimensional elliptic governing equations have been solved to investigate the flow behaviors over a wide range of the Grashof and Reynolds numbers. Comparisons with previously published experimental and numerical works on mixed convection in a horizontal and inclined tube are performed and good agreements between the results are observed. Effects of nanoparticles concentration and tube inclinations on the hydrodynamics and thermal parameters are presented and discussed. It is shown that the nanoparticles concentration does not have significant effects on the hydrodynamics parameters. Heat transfer coefficient increases by 15% at 4 Vol.% Al2O3. Skin friction coefficient continually increases with the tube inclination, but the heat transfer coefficient reaches a maximum at the inclination angle of 45°. 相似文献