全文获取类型
收费全文 | 37700篇 |
免费 | 6202篇 |
国内免费 | 3077篇 |
专业分类
化学 | 24988篇 |
晶体学 | 145篇 |
力学 | 303篇 |
综合类 | 120篇 |
数学 | 950篇 |
物理学 | 12842篇 |
综合类 | 7631篇 |
出版年
2024年 | 128篇 |
2023年 | 529篇 |
2022年 | 1352篇 |
2021年 | 1374篇 |
2020年 | 1868篇 |
2019年 | 1522篇 |
2018年 | 1295篇 |
2017年 | 1228篇 |
2016年 | 1932篇 |
2015年 | 1803篇 |
2014年 | 2169篇 |
2013年 | 2557篇 |
2012年 | 2240篇 |
2011年 | 2481篇 |
2010年 | 1959篇 |
2009年 | 2100篇 |
2008年 | 2231篇 |
2007年 | 2205篇 |
2006年 | 2084篇 |
2005年 | 1889篇 |
2004年 | 1746篇 |
2003年 | 1499篇 |
2002年 | 2107篇 |
2001年 | 965篇 |
2000年 | 928篇 |
1999年 | 758篇 |
1998年 | 753篇 |
1997年 | 558篇 |
1996年 | 430篇 |
1995年 | 397篇 |
1994年 | 276篇 |
1993年 | 247篇 |
1992年 | 217篇 |
1991年 | 174篇 |
1990年 | 180篇 |
1989年 | 160篇 |
1988年 | 117篇 |
1987年 | 103篇 |
1986年 | 124篇 |
1985年 | 52篇 |
1984年 | 31篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 24篇 |
1978年 | 19篇 |
1976年 | 13篇 |
1973年 | 11篇 |
1972年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A. A. Dokukin 《Computational Mathematics and Mathematical Physics》2006,46(5):914-918
To validate approximate optimization schemes for estimate calculation algorithms (ECAs), it is necessary to compute the optimal height, which cannot be done in a reasonable amount of time. A variety of samples are built for which the optimal height of the ECAs is known by construction. 相似文献
42.
The influence of the electron-LO-phonon coupling on energy spectrum of the low-lying states ofan exciton inparabolic quantum dots is investigated as a function of dot size. Calculations are made by using the method of few-bodyphysics within the effective-mass approximation. A considerable decrease of the energy in the stronger confinement rangeis found for the low-lying states of an exciton in quantum dots, which results from the confinement of electron-phononcoupling. 相似文献
43.
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
44.
S. Zschocke G. Plunien G. Soff 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):147-156
The renormalization method of Bogoljubov-Parasiuk-Hepp-Zimmermann (BPHZ) is used in order to derive the renormalized energy
shift due to the gauge invariant K?llén-Sabry diagram of the two-photon vacuum polarization (VPVP) as well as the self energy
vacuum polarization S(VP)E beyond the Uehling approximation. It is outlined, that no outer renormalization is required for
the two-photon vacuum polarization and that only the inner renormalization has to be accomplished. It is shown that the so-called
nongauge invariant spurious term is absent for a wide class of vacuum polarization (VP) diagrams if one applies the widely
used spherical expansion of bound and free-electron propagator. This simplifies significantly calculations in bound state
quantum electrodynamics. As one result of our paper the use of the BPHZ-approach in bound state QED is established.
Received 28 September 2001 相似文献
45.
用三个关系式与Mathematica软件求第二类自然数幂和公式 总被引:1,自引:1,他引:0
首先介绍三个第二类自然数幂和关系式并对其中的两式给出证明,接着利用这些关系式与数学软件M athem atica4.0,给出求解第二类自然数幂和公式的若干机械计算方法. 相似文献
46.
本文叙述了倍半萜类化合物——β-桉烯、衍生物Neointermedeol以及1,2,3,4,7,8-六氢-5,8-二甲基-3-异丙烯基萘的合成。初步药理筛选结果表明,这三个化合物均具有一定的抗生育活性。化合物还未见报道,它的化学结构在本文得到证实。 相似文献
47.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure,
over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative
measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique
of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained
quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely
different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms
of cyclic coarse-grained quantum logics. 相似文献
48.
Ahmad Afaq DU Meng-Li 《理论物理通讯》2006,46(1):119-122
The photodetachment of a negative molecular ion is studied theoretically using a two-center model. The detached electron wave function is obtained as a superposition of two coherent waves originating from each center. The photo-detached electron flux is evaluated on a screen placed at a large distance from the negative molecular ion. The electron flux on the screen displays strong interferences, the peak positions are related to the distance between the two centers in the negative molecular ion. We a/so obtained a simple analytical formula for the total photodetachment cross section. It approaches one and two times of the cross section for the one-center system in the high and lowphoton energy limits respectively. 相似文献
49.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献
50.
关于非平行板电容器电容计算的讨论 总被引:4,自引:3,他引:1
用串联方法计算非平行板电容器的电容,简便地得到与其他方法相同的结果。 相似文献