全文获取类型
收费全文 | 4948篇 |
免费 | 779篇 |
国内免费 | 428篇 |
专业分类
化学 | 1605篇 |
晶体学 | 25篇 |
力学 | 151篇 |
综合类 | 19篇 |
数学 | 381篇 |
物理学 | 3974篇 |
出版年
2024年 | 8篇 |
2023年 | 49篇 |
2022年 | 60篇 |
2021年 | 108篇 |
2020年 | 158篇 |
2019年 | 132篇 |
2018年 | 131篇 |
2017年 | 119篇 |
2016年 | 191篇 |
2015年 | 152篇 |
2014年 | 182篇 |
2013年 | 313篇 |
2012年 | 220篇 |
2011年 | 304篇 |
2010年 | 237篇 |
2009年 | 323篇 |
2008年 | 364篇 |
2007年 | 407篇 |
2006年 | 332篇 |
2005年 | 249篇 |
2004年 | 230篇 |
2003年 | 279篇 |
2002年 | 243篇 |
2001年 | 189篇 |
2000年 | 206篇 |
1999年 | 141篇 |
1998年 | 142篇 |
1997年 | 86篇 |
1996年 | 48篇 |
1995年 | 63篇 |
1994年 | 48篇 |
1993年 | 47篇 |
1992年 | 44篇 |
1991年 | 28篇 |
1990年 | 34篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1974年 | 8篇 |
排序方式: 共有6155条查询结果,搜索用时 375 毫秒
31.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance). 相似文献
32.
对溴分子在68800-7200cm^-1范围内的两个被观察到的[^2Π3/2]4d偶宇称里堡态的转动光谱进行了计算模拟,确定了转动常数,并且证实了原先对实验光谱的传动结构和电子角动量的标识。 相似文献
33.
与q形变玻色算符逆算符相关的相干态及其量子统计性质 总被引:1,自引:1,他引:0
讨论了q形变玻色算符的广义逆算符作用于q-相干态所得到的两类量子态的数学及量子统计性质。结果表明,q-相干态的光子激发态不存在压缩但呈现反聚束效应,而q-相干态的光子湮灭态却存在压缩但不呈现反聚束效应。 相似文献
34.
一类Narcissistic反应过渡态的优化 总被引:1,自引:0,他引:1
我们对一类narcissistic 反应XCH_2-CH_2Y→[过渡态TS]→YCH_2—CH_2X (1)进行了研究,结果表明其过渡态能在对称性限制下由能量极小化方法较容易地给出. 采用IMSPAK分子轨道从头算程序,在IBM VM/370计算机系统上用STO—3G极小基组以平衡几何构型的能量梯度优化方法,在对称性限制下对反应(1)的几种反应体系的过渡态构型进行了优化,其结果列于表1. 相似文献
35.
Electronic properties of model quantum-dot structures in zero and finite magnetic fields 总被引:1,自引:0,他引:1
H. Saarikoski E. Räsänen S. Siljamäki A. Harju M.J. Puska R.M. Nieminen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):241-252
We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral
dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional
theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method.
The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions
which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic
field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability
of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained
for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking
solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed.
Received 16 October 2001 and Received in final form 17 January 2002 相似文献
36.
导出了类Kerr介质中双模SU(1,1)相干态场与Λ型三能级原子相互作用系统的态函数,研究了Kerr效应对Λ型三能级原子布居概率、双模SU(1,1)相干态场的互关联函数、Cauchy-Schwartz不等式及二阶相干度的影响.结果表明:Kerr效应使原子与光场的耦合减弱,原子布居的崩塌与复苏的周期缩短;在初始光场较弱和较强两种情况下,类Kerr介质对双模SU(1,1)相干态场两模间的相关性、相关程度以及光子的聚束与反聚束效应产生的作用有明显的区别. 相似文献
37.
N.-K. Lee T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):451-465
We study the elastic properties of single A/B random copolymer chains, with a specific sequence and use them as theoretical
model for so called HP proteins. HP proteins carry hydrophilic (P) and hydrophobic (H) monomers. We predict a rich structure
in the force-extension relations which can be attributed to the information in the sequence. The variational method is used
to probe local minima on the path of stretching and releasing for the chain molecules. At a given force, we find multiple
configurations which are separated by energy barriers. A collapsed globular configuration consists of several domains which
unravel cooperatively. Upon stretching, the unfolding path shows a stepwise pattern corresponding to the unfolding of each
domain. While releasing, several cores can be created simultaneously in the middle of the chain, resulting in a different
path of collapse. The long-range interactions and stiffness of the chain simplify the potential landscape given by the disorder
in sequence.
Received 5 March 2002 / Received in final form 16 May 2002 Published online 13 August 2002 相似文献
38.
39.
The possibility that pairs of quarks will form diquark clusters in the regime above deconfinement transition for hadron matter
at finite density is revisited. Here we present the results on the diquark-diquark (dq-dq) interaction in the framework of
constituent quark model taking account of spin, isospin and color degrees of freedom in the spirit of generalized Pauli principle.
By constructing the appropriate spin and color states of the dq-dq clusters we compute the expectation values of the interaction
Hamiltonian involving pairwise quark—quark interaction. We find that the effective interaction between two diquark clusters
is quite sensitive to different configurations characterized by color and spin states, obtained after the coupling of two
diquark states. The value of the coupling parameter for a particular color—spin state, i.e., -3, 1 is compared to the one
obtained earlier by Donoghue and Sateesh,Phys. Rev.
D38, 360 (1988) based on the effective Φ4-theory. This new value of λ derived for different color-spin dq-dq states, may lead to several important implications in
the studies of diquark star and diquark gas. 相似文献
40.
Maria Mamalui Chien-Yueh Huang 《Physica E: Low-dimensional Systems and Nanostructures》2004,22(4):912-920
We present the theoretical study of the effect of external random field characterized by a Gaussian probability distribution function on the continuous phonon spectrum of one-dimensional (1D) chain, based on the Jacobian matrix method. The cumulative effect of the random field and simple isotopic defect is studied analytically and numerically. The Gaussian random field removes a square-root divergence appearing in the phonon spectrum of ideal 1D chain. The impurity phonon DOS shows strong dependence on the variance and the mean of the random field and exhibits very different behavior from the non-random case: the continuous spectrum is expanded and the δ-peak, describing discrete impurity vibrations in the non-random chain with the impurity, falls into a continuous zone. 相似文献