全文获取类型
收费全文 | 13456篇 |
免费 | 2273篇 |
国内免费 | 1698篇 |
专业分类
化学 | 3713篇 |
晶体学 | 41篇 |
力学 | 1039篇 |
综合类 | 190篇 |
数学 | 5393篇 |
物理学 | 7051篇 |
出版年
2024年 | 9篇 |
2023年 | 133篇 |
2022年 | 216篇 |
2021年 | 258篇 |
2020年 | 366篇 |
2019年 | 351篇 |
2018年 | 316篇 |
2017年 | 353篇 |
2016年 | 420篇 |
2015年 | 390篇 |
2014年 | 614篇 |
2013年 | 1135篇 |
2012年 | 776篇 |
2011年 | 865篇 |
2010年 | 713篇 |
2009年 | 898篇 |
2008年 | 1003篇 |
2007年 | 963篇 |
2006年 | 917篇 |
2005年 | 779篇 |
2004年 | 698篇 |
2003年 | 647篇 |
2002年 | 618篇 |
2001年 | 521篇 |
2000年 | 492篇 |
1999年 | 449篇 |
1998年 | 398篇 |
1997年 | 323篇 |
1996年 | 269篇 |
1995年 | 195篇 |
1994年 | 170篇 |
1993年 | 165篇 |
1992年 | 134篇 |
1991年 | 110篇 |
1990年 | 100篇 |
1989年 | 66篇 |
1988年 | 86篇 |
1987年 | 62篇 |
1986年 | 49篇 |
1985年 | 63篇 |
1984年 | 48篇 |
1983年 | 29篇 |
1982年 | 52篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 32篇 |
1978年 | 24篇 |
1977年 | 24篇 |
1976年 | 16篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
2.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2020,37(2):417-456
We study the energy-critical nonlinear wave equation in the presence of an inverse-square potential in dimensions three and four. In the defocussing case, we prove that arbitrary initial data in the energy space lead to global solutions that scatter. In the focusing case, we prove scattering below the ground state threshold. 相似文献
3.
Two novel 2′-hydroxychalcone derivatives (i.e., M1 and M2) are explored in this work. We mainly focus on investigating the effects of photoexcitation on hydrogen bonds and on the excited-state intramolecular proton transfer (ESIPT) process. On the basis of calculations of electrostatic potential surface and intramolecular interactions, we verify the formation of hydrogen bond O1 H2···O3 in both S0 and S1 states. Exploring the ultraviolet–visible spectra in the liquid phase, our simulated results reappear in the experimental phenomenon. Analyzing molecular geometry and infrared stretching vibrational spectra, we confirm O1 H2···O3 is strengthened for both M1 and M2 in the S1 state. We further confirm that charge redistribution facilitates ESIPT tendency. Constructing potential energy curves, we find the ultrafast ESIPT behavior for M1, which is because of the deficiency of side hydroxyl moiety comparing with M2. This work makes a reasonable affiliation of the ESIPT mechanism for M1 and M2. We wish this paper could facilitate understanding these two novel systems and promote their applications. 相似文献
4.
The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent
state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour
of the nuclear ground states using the coherent states. 相似文献
5.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
6.
7.
采用Cundari和Stevens等推导的有效芯势对镧系金属一氢化物进行了理论计算,以探讨镧系金属元素与氢的相互作用。结果表明所有镧系金属一氢化物基态时理论上是稳定的,最稳定的是SmH,最不稳定的是DyH;键长计算结果显示,基态时镧系金属一招兵买马花物有独立王国 收缩现象发生;红外振动频率理论计算值与实验结果一致;成键轨道中,金属原子轨道的贡献主要是s轨道和d轨道:从CeH至ErH(GdH)例外)随着外层电子的增加s轨道成分逐渐增大d轨道成分逐渐减小;从TmH和LuH(包括GdH),成键轨道中金属原子轨道的贡献主要是d轨道,约为90%;约大多数镧系金属一氧化物的成键轨道中金属原子轨道f成分小于1%。 相似文献
8.
Zhong-Qing Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):374-403
An orthogonal system of rational functions is discussed. Some inverse inequalities, imbedding inequalities and approximation results are obtained. Two model problems are considered. The stabilities and convergences of proposed rational spectral schemes and rational pseudospectral schemes are proved. The techniques used in this paper are also applicable to other problems on the whole line. Numerical results show the efficiency of this approach. 相似文献
9.
Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak
estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum,
minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity
networks is considered.
Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002 相似文献
10.
LI Yu-qiong SUN Zhen-rong ZHANG Shi-an YANG Xi-hua WANG Zu-geng. Key Laboratory of Optical Magnetic Resonance Spectroscopy 《光谱学与光谱分析》2006,26(8):1395-1395
The authors achieved the temporal coherent control in an Er^3+ doped telluride glass, one kind of disordered solids. The upconversion at 670 nm was modulated and the dephasing time was simulated as 300 fs. Moreover, the photon echo signal gave the dephasing time due to the phonon interaction. The agreement between the two data indicates that the interaction between the wavepacket and the phonon leads to the fast disappearance of wavepackets interference, which is helpful for the tech- nique to be applied to the disordered solids. 相似文献