全文获取类型
收费全文 | 3033篇 |
免费 | 212篇 |
国内免费 | 227篇 |
专业分类
化学 | 795篇 |
晶体学 | 2篇 |
力学 | 221篇 |
综合类 | 34篇 |
数学 | 1940篇 |
物理学 | 480篇 |
出版年
2023年 | 32篇 |
2022年 | 31篇 |
2021年 | 36篇 |
2020年 | 72篇 |
2019年 | 73篇 |
2018年 | 71篇 |
2017年 | 77篇 |
2016年 | 80篇 |
2015年 | 81篇 |
2014年 | 146篇 |
2013年 | 287篇 |
2012年 | 134篇 |
2011年 | 174篇 |
2010年 | 146篇 |
2009年 | 204篇 |
2008年 | 230篇 |
2007年 | 214篇 |
2006年 | 165篇 |
2005年 | 185篇 |
2004年 | 126篇 |
2003年 | 116篇 |
2002年 | 101篇 |
2001年 | 93篇 |
2000年 | 80篇 |
1999年 | 71篇 |
1998年 | 101篇 |
1997年 | 62篇 |
1996年 | 46篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 31篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有3472条查询结果,搜索用时 14 毫秒
1.
Kenji Saijyou 《Applied Acoustics》2006,67(10):1031-1043
The relationship between the dominant mode of the submerged thin cylindrical shell and the flexural wave velocity is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, it is difficult to estimate the dominant mode, especially if two or more vibration modes are involved. To estimate the dominant mode of a thin shell in vacuo, the concept of “modified bending stiffness” has been introduced. In this paper, the concept of modified bending stiffness is extended to estimate the dominant mode of a submerged thin cylindrical shell. The dominant mode of a submerged thin cylindrical shell is theoretically discriminated from the other mode based on the smallness of the modified bending stiffness of the submerged shell. The validity of our theory is confirmed by a good agreement between theoretical and experimental results on flexural wave velocity. 相似文献
2.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
3.
We consider immersions: and construct a subspace of which corresponds to a set of embedded manifolds which are either parallel to f, tubes around f or, in general, partial tubes around f. This space is invariant under the action of the normal holonomy group, We investigate the case where is non-trivial and obtain some results on the number of connected components of .
Received 24 March 2000. 相似文献
4.
最速下降规则不失为一可用规则 总被引:5,自引:4,他引:1
本从统计意义上平均迭代次数的观点出发,指出求解线性规划的最速下降规则是可取的,好用的。 相似文献
5.
《Magnetic resonance in chemistry : MRC》2003,41(6):417-430
A systematic study of the one‐bond and long‐range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s‐functions used for coupled carbons and Sauer's sets augmented with tight s‐functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1–2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2–3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non‐additivity of ?14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ?5.5 Hz for J(C,H), in line with previous findings. Non‐additivity effects in the latter compound established at the SOPPA level should be attributed to the through‐space non‐bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non‐bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
James Murdock 《Journal of Differential Equations》2004,205(2):424-465
Hypernormal forms (unique normal forms, simplest normal forms) are investigated both from the standpoint of foundational theory and algorithms suitable for use with computer algebra. The Baider theory of the Campbell-Hausdorff group is refined, by a study of its subgroups, to determine the smallest substages into which the hypernormalization process can be divided. This leads to a linear algebra algorithm to compute the generators needed for each substage with the least amount of work. A concrete interpretation of Jan Sanders’ spectral sequence for hypernormal forms is presented. Examples are given, and a proof is given for a little-known theorem of Belitskii expressing the hypernormal form space (in the inner product style) as the kernel of a higher-order differential operator. 相似文献
7.
Stefan Weigert 《Czechoslovak Journal of Physics》2004,54(1):147-149
The eigenstates of a diagonalizable PT-symmetric Hamiltonian satisfy unconventional completeness and orthonormality relations. These relations reflect the properties of a pair of bi-orthonormal bases associated with non-hermitean diagonalizable operators. In a similar vein, such a dual pair of bases is shown to possess, in the presence of PT symmetry, a Gram matrix of a particular structure: its inverse is obtained by simply swapping the signs of some its matrix elements. 相似文献
8.
多小波子空间上的单小波表示 总被引:1,自引:0,他引:1
本文在较弱的条件下,建立了2重多小波子空间与单小波子空间的关系.即由2重多小波构造出单小波.一方面,这种单小波的平移伸缩与2重多小波的平移伸缩生成的子空间是完全相同的;另一方面,它具有插值性.因此通过构造出的单小波建立了多小波子空间上的Shannon型采样定理. 相似文献
9.
Banach空间上的框架与Riesz基 总被引:5,自引:0,他引:5
本文讨论Banach空间上框架、无冗框架与Riesz基之间的关系及它们的稳定性. 相似文献
10.