全文获取类型
收费全文 | 11042篇 |
免费 | 2200篇 |
国内免费 | 1682篇 |
专业分类
化学 | 2773篇 |
晶体学 | 202篇 |
力学 | 619篇 |
综合类 | 98篇 |
数学 | 784篇 |
物理学 | 3503篇 |
无线电 | 6945篇 |
出版年
2024年 | 67篇 |
2023年 | 157篇 |
2022年 | 289篇 |
2021年 | 345篇 |
2020年 | 391篇 |
2019年 | 423篇 |
2018年 | 349篇 |
2017年 | 497篇 |
2016年 | 552篇 |
2015年 | 626篇 |
2014年 | 771篇 |
2013年 | 906篇 |
2012年 | 787篇 |
2011年 | 829篇 |
2010年 | 696篇 |
2009年 | 684篇 |
2008年 | 682篇 |
2007年 | 688篇 |
2006年 | 671篇 |
2005年 | 570篇 |
2004年 | 532篇 |
2003年 | 561篇 |
2002年 | 454篇 |
2001年 | 385篇 |
2000年 | 375篇 |
1999年 | 313篇 |
1998年 | 202篇 |
1997年 | 182篇 |
1996年 | 166篇 |
1995年 | 131篇 |
1994年 | 114篇 |
1993年 | 85篇 |
1992年 | 99篇 |
1991年 | 73篇 |
1990年 | 51篇 |
1989年 | 47篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Extended Fisher-Kolmogorov系统的渐近吸引子 总被引:2,自引:0,他引:2
考虑了ExtendedFisher-Kolmogorov系统的解的长时间行为,构造了一个有限维解序列即该系统的渐近吸引子,证明了它在长时间后无限趋于方程的整体吸引子,并给出了渐近吸引子的维数估计. 相似文献
82.
Four-wave mixing in semiconductor laser amplifiers enables various applications in photonic switching including wavelength conversion, space and time switching, optical phase conjugation, and demultiplexing. Switching times faster than 1 ps are possible. 相似文献
83.
在70-300K温度范围内测量了组分x为0.01和0.04的Cd1-xFexTe及CdTe的法拉第效应随入射光子能量的变化,首次获得了Cd1-xFexTe在布里渊区Γ点和L点的有效g因子及其与温度的关系。给出了Fe2+离子与载流子间的sp-d交换作用常数N0(β-α)=(-1.57±0.03)eV。 相似文献
84.
High-voltage super-junction lateral double-diffused metal-oxide semiconductor with a partial lightly doped pillar 下载免费PDF全文
A novel super-junction lateral double-diffused metal-oxide semiconductor(SJ-LDMOS) with a partial lightly doped P pillar(PD) is proposed.Firstly,the reduction in the partial P pillar charges ensures the charge balance and suppresses the substrate-assisted depletion effect.Secondly,the new electric field peak produced by the P/P-junction modulates the surface electric field distribution.Both of these result in a high breakdown voltage(BV).In addition,due to the same conduction paths,the specific on-resistance(R on,sp) of the PD SJ-LDMOS is approximately identical to the conventional SJ-LDMOS.Simulation results indicate that the average value of the surface lateral electric field of the PD SJ-LDMOS reaches 20V/μm at a 15μm drift length,resulting in a BV of 300V. 相似文献
85.
New (3+1)‐dimensional nonlinear equations with KdV equation constituting its main part: multiple soliton solutions 下载免费PDF全文
Abdul‐Majid Wazwaz 《Mathematical Methods in the Applied Sciences》2016,39(4):886-891
In thiswork,we present two new(3+1)‐dimensional nonlinear equationswith Korteweg‐de Vries equation constituting its main part. We show that the dispersive relation is distinct for each model, whereas the phase shift remains the same. We determine multiple solitons solutions, with distinct physical structures, for each established equation. The architectures of the simplified Hirota's method is implemented in this paper. The constraint conditions that fall out which must remain valid in order for themultiple solitons to exist are derived.Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
86.
Quantum dots (3–4?nm) of Zn1? x Cd x S (both free of Mn2+ and with Mn2+ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn1? x Cd x S and Zn1? x Cd x S:Mn2+ (x?=?0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5?nm. The optical energy gap for Zn1? x Cd x S was found to vary from 3.878 to 2.519?eV and for Zn1?x Cd x S:Mn2+ it varies from 3.830 to 2.442?eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442?eV to a maximum of 3.878?eV. DC conductivity analysis (from 40°C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn1? x Cd x S solid solutions varies from 0.3840?×?10?10 to 8.7782?×?10?10?mho/m at 150°C and for Zn1? x Cd x S:Mn2+ it varies from 0.5751?×?10?10 to 9.8078?×?10?10 mho /m at 150°C (for x?=?0 to x?=?1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study. 相似文献
87.
Jian Tong Duncan L. MacFarlane Issa Panahi L. Roberts Hunt Govind Kannan Gary A. Evans 《Fiber and Integrated Optics》2013,32(4):201-215
Abstract An integrated photonic architecture is introduced and used to realize an optical filter with direct form I realization. The architecture offers gain from semiconductor optical amplifiers, and this gain results in an active optical filter whose filter response depends on the individual gains. The presence of gain provides advantages in filter performance, and tunable and adaptive functionality. The optical filter is modeled as a discrete time system and the z-transform is used in its analysis and design. A low-pass filter design example is presented and the filter coefficients are derived in terms of gains and coupler splitting ratios. The region of stable operations is derived by applying the Schur-Cohn stability test. 相似文献
88.
Luc Molinet Didier Pilod Stéphane Vento 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2018,35(7):1719-1756
We show that the Cauchy problem for a class of dispersive perturbations of Burgers' equations containing the low dispersion Benjamin–Ono equation is locally well-posed in when . As a consequence, we obtain global well-posedness in the energy space as soon as , i.e. . 相似文献
89.
Starting from a field theory action that describes a Dirac fermion, we propose and analyze a model based on a low‐relativistic Pauli equation coupled to a torsion‐like term to study Spin Hall Effect (SHE). We point out a very particular connection between the modified Pauli equation and the (SHE), where what we refer to torsion as field playing an important role in the spin‐orbit (SO) coupling process. In this scenario, we present a proposal of a spin‐type current, considering the tiny contributions of torsion in connection with intrinsic anisotropy of the crystal electric field. 相似文献
90.
Nonlinear spin excitations in ferromagnetic spin chains are studied for spintronic and magnetic devices including magnetic‐field sensors and for high‐density data storage. Here, (2+1)‐dimensional nonlinear Schrödinger equation is investigated, which describes the nonlinear spin dynamics for a Heisenberg ferromagnetic spin chain. Lie point symmetry generators and Lie symmetry groups of that equation are derived. Lie symmetry groups are related to the time, space, scale, rotation transformations, and Galilean boosts of that equation. Certain solutions, which are associated with the known solutions, are constructed. Based on the Lie symmetry generators, the reduced systems of such an equation are obtained. Based on the polynomial expansion and through one of the reduced systems, group‐invariant solutions are constructed. Soliton‐type group‐invariant solutions are graphically investigated and effects of the magnetic coupling coefficients, that is, α1, α2, α3, and α4, on the soliton's amplitude, width, and velocity are discussed. It is seen that α1, α2, α3, and α4 have no influence on the soliton's amplitude, but can affect the soliton's velocity and width. Lax pair and conservation laws of such an equation are derived. 相似文献