全文获取类型
收费全文 | 12204篇 |
免费 | 990篇 |
国内免费 | 1341篇 |
专业分类
化学 | 3601篇 |
晶体学 | 28篇 |
力学 | 1028篇 |
综合类 | 137篇 |
数学 | 7131篇 |
物理学 | 2610篇 |
出版年
2024年 | 16篇 |
2023年 | 105篇 |
2022年 | 177篇 |
2021年 | 264篇 |
2020年 | 304篇 |
2019年 | 352篇 |
2018年 | 373篇 |
2017年 | 401篇 |
2016年 | 363篇 |
2015年 | 356篇 |
2014年 | 491篇 |
2013年 | 1689篇 |
2012年 | 490篇 |
2011年 | 596篇 |
2010年 | 528篇 |
2009年 | 638篇 |
2008年 | 748篇 |
2007年 | 727篇 |
2006年 | 666篇 |
2005年 | 607篇 |
2004年 | 580篇 |
2003年 | 605篇 |
2002年 | 523篇 |
2001年 | 411篇 |
2000年 | 418篇 |
1999年 | 319篇 |
1998年 | 368篇 |
1997年 | 320篇 |
1996年 | 205篇 |
1995年 | 145篇 |
1994年 | 109篇 |
1993年 | 105篇 |
1992年 | 83篇 |
1991年 | 71篇 |
1990年 | 65篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 37篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings. 相似文献
42.
Marianne Gerny Burkhard Alpers 《International Journal of Computers for Mathematical Learning》2004,9(1):25-57
In this article we describe a mathematical microworld for investigating car motion on a racing course and its use with a group of grade 12 students. The microworld is concerned with the mathematical construction of courses and functions which describe car motion. It is implemented in the computer algebra system, Maple®, which provides the means to represent courses and functions symbolically and graphically. We describe the learning opportunities offered by the microworld in relation to the research literature on functions. Various facets and layers of the function concept are addressed in the microworld, and we suggest how work in the microworld might help in overcoming some well-known misconceptions.This revised version was published online in September 2005 with corrections to the Cover Date. 相似文献
43.
Akhlesh Lakhtakia 《Optik》2004,115(4):151-158
44.
Using two different types of the laddering equations realized simultaneously by the associated Gegenbauer functions, we show that all quantum states corresponding to the motion of a free particle on AdS
2 and S
2 are splitted into infinite direct sums of infinite-and finite-dimensional Hilbert subspaces which represent Lie algebras u(1, 1) and u(2) with infinite- and finite-fold degeneracies, respectively. In addition, it is shown that the representation bases of Lie algebras with rank 1, i.e., gl(2, C), realize the representation of nonunitary parasupersymmetry algebra of arbitrary order. The realization of the representation of parasupersymmetry algebra by the Hilbert subspaces which describe the motion of a free particle on AdS
2 and S
2 with the dynamical symmetry groups U(1, 1) and U(2) are concluded as well. 相似文献
45.
In this paper we extend a result of Semrl stating that every 2-local automorphism of the full operator algebra on a separable infinite dimensional Hilbert space is an automorphism. In fact, besides separable Hilbert spaces, we obtain the same conclusion for the much larger class of Banach spaces with Schauder bases. The proof rests on an analogous statement concerning the 2-local automorphisms of matrix algebras for which we present a short proof. The need to get such a proof was formulated in Semrl's paper.
46.
Sylvia Pulmannová 《International Journal of Theoretical Physics》2003,42(5):907-919
Tensor products of quantum logics and effect algebras with some known problems are reviewed. It is noticed that although tensor products of effect algebras having at least one state exist, in the category of complex Hilbert space effect algebras similar problems as with tensor products of projection lattices occur. Nevertheless, if one of the two coupled physical systems is classical, tensor product exists and can be considered as a Boolean power. Some applications of tensor products (in the form of Boolean powers) to quantum measurements are reviewed. 相似文献
47.
Mathematical Notes - 相似文献
48.
Teimuraz Pirashvili 《Central European Journal of Mathematics》2003,1(2):169-183
In this paper we consider duplexes, which are sets with two associative binary operations. Dimonoids in the sense of Loday
are examples of duplexes. The set of all permutations carries a structure of a duplex. Our main result asserts that it is
a free duplex with an explicitly described set of generators. The proof uses a construction of the free duplex with one generator
by planary trees. 相似文献
49.
Chi-Kwong Li Ilya M. Spitkovsky 《Journal of Mathematical Analysis and Applications》2003,282(1):329-340
Existence of the fractional powers is established in Banach algebra setting, in terms of the numerical ranges of elements involved. The behavior of the spectra and (for Hermitian ∗-algebras satisfying some additional hypotheses) the ∗-numerical range under taking these powers also is investigated. 相似文献
50.
Anna Avallone 《Mathematica Slovaca》2007,57(2):129-140
We prove the existence of separating points for every countable family of nonatomic σ-additive modular measures on a σ-complete lattice ordered effect algebra.
相似文献