全文获取类型
收费全文 | 5869篇 |
免费 | 111篇 |
专业分类
化学 | 3215篇 |
晶体学 | 30篇 |
力学 | 130篇 |
数学 | 1346篇 |
物理学 | 1259篇 |
出版年
2021年 | 33篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 140篇 |
2017年 | 128篇 |
2016年 | 200篇 |
2015年 | 143篇 |
2014年 | 193篇 |
2013年 | 480篇 |
2012年 | 293篇 |
2011年 | 398篇 |
2010年 | 210篇 |
2009年 | 181篇 |
2008年 | 335篇 |
2007年 | 330篇 |
2006年 | 304篇 |
2005年 | 223篇 |
2004年 | 197篇 |
2003年 | 141篇 |
2002年 | 134篇 |
2001年 | 95篇 |
2000年 | 78篇 |
1999年 | 56篇 |
1998年 | 49篇 |
1997年 | 48篇 |
1996年 | 47篇 |
1995年 | 46篇 |
1994年 | 28篇 |
1993年 | 41篇 |
1992年 | 54篇 |
1991年 | 42篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 47篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 60篇 |
1984年 | 67篇 |
1983年 | 65篇 |
1982年 | 61篇 |
1981年 | 43篇 |
1980年 | 53篇 |
1979年 | 48篇 |
1978年 | 68篇 |
1977年 | 39篇 |
1976年 | 53篇 |
1975年 | 40篇 |
1974年 | 48篇 |
1973年 | 40篇 |
1972年 | 33篇 |
排序方式: 共有5980条查询结果,搜索用时 15 毫秒
1.
N. S. Simonović 《Few-Body Systems》2006,38(2-4):139-145
In agreement with the Kohn theorem the relative motion (rel) of three electrons in a two-dimensional parabolic trap separates
from the centre-of-mass (CM) motion. By introducing new coordinates the Hamiltonian for relative motion in the approximation
of non-interacting electrons can be taken to the normal form. The eigenstates of the normalized Hamiltonian are products of
the Fock-Darwin states for normal modes. The energy levels for relative motion are obtained by diagonalizing the exact Hamiltonian
in the eigenbasis for the non-interacting case. In this basis the interaction matrix elements can be obtained in the analytical
form. Since the rank of the Hamiltonian matrix is significantly reduced, the calculations are faster and more accurate than
those for the full (CM + rel) motion. This advantage is especially important for the calculations of excited states and the
analysis of energy spectra. 相似文献
2.
3.
In this paper a new definition of a lattice valued intuitionistic fuzzy set (LIFS) is introduced, in an attempt to overcome
the disadvantages of earlier definitions. Some properties of this kind of fuzzy sets and their basic operations are given.
The theorem of synthesis is proved: For every two families of subsets of a set satisfying certain conditions, there is an
lattice valued intuitionistic fuzzy set for which these are families of level sets.
The research supported by Serbian Ministry of Science and Technology, Grant No. 1227. 相似文献
4.
S. Mentus Dijana Jelić Veselinka Grudić 《Journal of Thermal Analysis and Calorimetry》2007,90(2):393-397
Thermal decomposition of lanthanum nitrate to lanthanum oxide was carried out by both temperature programmed heating (TPH)
and citrate-gel combustion. The temperature programmed heating was carried out under flow of oxidizing (air), neutral (nitrogen)
and reducing (25 vol.% hydrogen+argone mixture) gases, and the processes were controlled by simultaneous thermogravimetry
and differential thermal analysis. It was shown that hydrogen atmosphere helps to reduce temperatures of all decomposition
steps. The results of TPH were utilized to check the nature of residues in the products of lanthanum nitrate-to-oxide conversion
performed via citrate-gel combustion technique. 相似文献
5.
6.
7.
Marijana ?aković Zora Popović 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):m507-m509
In the title compound, [Ni(N3)2(C6H6N2O)2], the NiII atom lies on an inversion centre. The distorted octahedral nickel(II) coordination environment contains two planar trans-related N,O-chelating picolinamide ligands in one plane and two monodentate azide ligands perpendicular to this plane. Molecules are linked into a three-dimensional framework by N—H...N hydrogen bonds. 相似文献
8.
Miodrag M. Spalević 《Numerical Algorithms》2007,46(3):253-264
We have recently proposed a very simple numerical method for constructing the averaged Gaussian quadrature formulas. These
formulas exist in many more cases than the real positive Gauss–Kronrod formulas. In this note we try to answer whether the
averaged Gaussian formulas are an adequate alternative to the corresponding Gauss–Kronrod quadrature formulas, to estimate
the remainder term of a Gaussian rule. 相似文献
9.
We consider a four-dimensional generalization of Hess–Appel’rot system and costruct its Lax pair. Both classical and algebro-geometric integration procedure are proceeded. The algebro-geometric integration is based on deep facts from geometry of Prym varieties such as the Mumford relation and Mumford-Dalalyan theory. The integration is similar to the integration of Lagrange bitop which has recetly been performed by the authors. 相似文献
10.
Monoclinic (N2H6)3Zr2F13·F crystallizes in space group P21-C
2
2
(No. 4) with unit cell dimensionsa=5.670(1),b=10.984(2),c=10.601(2) Å,=93.88(1)°,V=658.7(4) Å3 andZ=2. Two different types of N2H6
2+ ions are present. One is involved in strong H-bonds to F– ions in infinite chains running along the a axis (the shortest N-F distance is 2.437(5) Å), and the other links the structure through weaker bi- and trifurcated H-bonds to fluorine ligands of the Zr2F13
5– ions. The N-N bond lengths range from 1.430(5) to 1.446(5) Å with apparently no meaningful correlation to the type of N2H2
2+ ions. The Zr2F13
5– ions have very nearly C2 point symmetry and are formed by joining two distorted bicapped trigonal prisms of ZrF8-units through a common face. Distances of Zr-F terminal bonds range from 2.015(2) to 2.112(2) Å and of bridging bonds from 2.133(2) to 2.212(2) Å. (N2H6)3Hf2F13·F is isomorphous. The vibrational spectra of the two compounds are nearly identical, with the exception of a strong infrared band, which is assigned to a stretching mode with the moving central atom within the anion. The anion part of the spectrum is simple, showing broad unresolved bands. The cation part shows two types of N2H6
– ions. H-Bonding is strongly present in the spectra, but no simple correlations with the H-bond strength is evident. 相似文献