全文获取类型
收费全文 | 3351篇 |
免费 | 490篇 |
国内免费 | 190篇 |
专业分类
化学 | 975篇 |
晶体学 | 8篇 |
力学 | 430篇 |
综合类 | 46篇 |
数学 | 1305篇 |
物理学 | 1267篇 |
出版年
2023年 | 41篇 |
2022年 | 117篇 |
2021年 | 103篇 |
2020年 | 106篇 |
2019年 | 85篇 |
2018年 | 80篇 |
2017年 | 146篇 |
2016年 | 152篇 |
2015年 | 120篇 |
2014年 | 167篇 |
2013年 | 259篇 |
2012年 | 138篇 |
2011年 | 176篇 |
2010年 | 183篇 |
2009年 | 177篇 |
2008年 | 191篇 |
2007年 | 189篇 |
2006年 | 190篇 |
2005年 | 140篇 |
2004年 | 124篇 |
2003年 | 157篇 |
2002年 | 135篇 |
2001年 | 130篇 |
2000年 | 116篇 |
1999年 | 85篇 |
1998年 | 86篇 |
1997年 | 62篇 |
1996年 | 59篇 |
1995年 | 48篇 |
1994年 | 34篇 |
1993年 | 34篇 |
1992年 | 35篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 7篇 |
1988年 | 13篇 |
1987年 | 3篇 |
1986年 | 12篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有4031条查询结果,搜索用时 15 毫秒
151.
Energy spectrum of multi-radiation of X-rays in a low energy Mather-type plasma focus device 下载免费PDF全文
The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device (operated with argon gas). The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 (J/Sr) and 0.04 ±0.01 (J/Sr), respectively. The total energy of the emitted hard X-ray (〉 15 keV) was around 0.12± 0.02 (J/Sr). 相似文献
152.
153.
C. R.H. Bahl J. Garde K. Lefmann T. B.S. Jensen P.-A. Lindgård D. E. Madsen S. Mørup 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):53-57
In magnetic nanoparticles the uniform precession
(q = 0 spin wave) mode gives the predominant contribution
to the magnetic excitations. We have calculated the energy of the
uniform mode in antiferromagnetic nanoparticles with uncompensated
magnetic moments, using the coherent potential approximation. In
the presence of uncompensated moments, an antiferromagnetic
nanoparticle must be considered as a kind of a ferrimagnet. Two
magnetic anisotropy terms are considered, a planar term confining
the spins to the basal plane, and an axial term determining an
easy axis in this plane. Excitation energies are calculated for
various combinations of these two anisotropy terms, ranging from
the simple uniaxial case to the planar case with a strong
out-of-plane anisotropy. In the simple uniaxial case, the
uncompensated moment has a large influence on the excitation
energy, but in the planar case it is much less important. The
calculations explain recent neutron scattering measurements on
nanoparticles of antiferromagnetic α-Fe2O3 and NiO. 相似文献
154.
Inverse scattering method and soliton solutionfamily for the Einstein--Maxwell theory with multiple Abelian gauge fields 下载免费PDF全文
A Hauser-Ernst-type extended hyperbolic complex linear system given in our previous paper [Gao Y J 2004 Chin. Phys. 13 602] is slightly modified and used to develop a new inverse scattering method for the stationary axisymmetric Einstein-Maxwell theory with multiple Abelian gauge fields. The reduction procedures in this inverse scattering method are found to be fairly simple, which makes the inverse scattering method be fine and effective in practical application. As an example, a concrete family of soliton solutions for the considered theory is obtained. 相似文献
155.
156.
157.
The multiple knapsack problem denoted by MKP (B,S,rn,n) can be defined as follows. A set B of n items and a set S of rn knapsacks are given such that each item j has a profit pi and weight wj,and each knapsack i has a capacity Ci. The goal is to find a subset of items of maximum profit such that they have a feasible packing in the knapsacks. MKP (B,S,m,n) is strongly NP-Complete and no polynomial time approximation algorithm can have an approximation ratio better than 0.5. In the last ten years,semi-definite programming has been empolyed to solve some combinatorial problems successfully. This paper firstly presents a semi-definite relaxation algorithm (MKPS) for MKP (B,S,rn,n). It is proved that MKPS have a approximation ratio better than 0. 5 for a subclass of MKP (B,S,m,n) with n≤100, m≤5 and max^nj=1{wj}/min^mi=1={Ci}≤2/3. 相似文献
158.
Yanheng Ding 《Proceedings of the American Mathematical Society》2002,130(3):689-696
We establish existence and multiplicity of solutions to a class of nonlinear Schrödinger equations with, e.g., ``atomic' Hamiltonians, via critical point theory.
159.
A subset of the -dimensional torus is called a set of uniqueness, or -set, if every multiple trigonometric series spherically converging to outside vanishes identically. We show that all countable sets are -sets and also that sets are -sets for every . In particular, , where is the Cantor set, is an set and hence a -set. We will say that is a -set if every multiple trigonometric series spherically Abel summable to outside and having certain growth restrictions on its coefficients vanishes identically. The above-mentioned results hold also for sets. In addition, every -set has measure , and a countable union of closed -sets is a -set.
160.