全文获取类型
收费全文 | 2197篇 |
免费 | 63篇 |
国内免费 | 17篇 |
专业分类
化学 | 1748篇 |
晶体学 | 17篇 |
力学 | 44篇 |
数学 | 240篇 |
物理学 | 228篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 20篇 |
2020年 | 31篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 47篇 |
2015年 | 49篇 |
2014年 | 59篇 |
2013年 | 97篇 |
2012年 | 129篇 |
2011年 | 195篇 |
2010年 | 68篇 |
2009年 | 72篇 |
2008年 | 117篇 |
2007年 | 157篇 |
2006年 | 172篇 |
2005年 | 154篇 |
2004年 | 116篇 |
2003年 | 78篇 |
2002年 | 109篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有2277条查询结果,搜索用时 15 毫秒
91.
Neil A. Watling 《Communications in Mathematical Physics》1990,134(2):321-345
Monodromy fields on ?2 are a family of lattice fields in two dimensions which are a natural generalization of the two dimensional Ising field occurring in theC *-algebra approach to Statistical Mechanics. A criterion for the critical limit one point correlation of the monodromy field σa(M) at a ∈ ?2, $$\mathop {\lim }\limits_{s \uparrow 1} \left\langle {\sigma _a (M)} \right\rangle ,$$ is deduced for matrices M ∈ GL(p,?) having non-negative eigenvalues. Using this criterion non-identity 2×2 matrices are found with finite critical limit one point correlation. The general set ofp×p matrices with finite critical limit one point correlations is also considered and a conjecture for the critical limitn point correlations postulated. 相似文献
92.
Mathias Beiglbö ck Vitaly Bergelson Neil Hindman Dona Strauss 《Transactions of the American Mathematical Society》2008,360(2):819-847
There are several notions of largeness that make sense in any semigroup, and others such as the various kinds of density that make sense in sufficiently well-behaved semigroups including and . It was recently shown that sets in which are multiplicatively large must contain arbitrarily large geoarithmetic progressions, that is, sets of the form , as well as sets of the form . Consequently, given a finite partition of , one cell must contain such configurations. In the partition case we show that we can get substantially stronger conclusions. We establish some combined additive and multiplicative Ramsey theoretic consequences of known algebraic results in the semigroups and , derive some new algebraic results, and derive consequences of them involving geoarithmetic progressions. For example, we show that given any finite partition of there must be, for each , sets of the form together with , the arithmetic progression , and the geometric progression in one cell of the partition. More generally, we show that, if is a commutative semigroup and a partition regular family of finite subsets of , then for any finite partition of and any , there exist and such that is contained in a cell of the partition. Also, we show that for certain partition regular families and of subsets of , given any finite partition of some cell contains structures of the form for some .
93.
94.
We consider a problem related to Hadwiger's Conjecture. Let D=(d1, d2, …, dn) be a graphic sequence with 0?d1?d2?···?dn?n?1. Any simple graph G with D its degree sequence is called a realization of D. Let R[D] denote the set of all realizations of D. Define h(D)=max{h(G): G∈R[D]} and χ(D)=max{χ(G): G∈R[D]}, where h(G) and χ(G) are Hadwiger number and chromatic number of a graph G, respectively. Hadwiger's Conjecture implies that h(D)?χ(D). In this paper, we establish the above inequality for near regular degree sequences. © 2009 Wiley Periodicals, Inc. J Graph Theory 64: 175–183, 2010 相似文献
95.
We report a study of the 4 A 2g →2 T 1g absorption band of Mn4+ in Cs2SiF6. The band shows several lines or groups of lines associated with transitions from the 4 A 2g ground state to the spin-orbit components (2 T 1g )Γ8 and (2 T 1g )Γ6 coupled to the three odd-parity vibrations v 6(t 2u ), v 4(t 1u ) and v 3(t 1u ). The absorptions associated with the (2 T 1g )Γ8 electronic state have structure whereas those associated with the (2 T 1g )Γ6 do not. It is shown that the structure is a consequence of splitting of the Γ8 × v vibronic multiplets by electron-vibration interaction. The intensity of the 4 A 2g →(2 T 1g )Γ i + vj vibronic transitions are expressed in terms of a small number of parameters; two parameters for v(t 1u ) modes and three for v(t 2u ) modes. Plausible but not good fits to the low temperature Zeeman data and vibronic splitting patterns are obtained. The excitation spectrum of the Cs2SiF6 : Mn4+ in the region of the 4 A 2g →2 Eg and 4 A 2g →2 T 1g is recorded using a c.w. dye laser. This reveals numerous weaker lines involving combinational modes and even-parity modes v5 (t 2g ), v 2(eg ) and v 1(a 1g ). Several interesting electron-vibrational effects are observed. These are illustrated and discussed qualitatively. 相似文献
96.
The purpose of this paper is to introduce, for a finite Coxeter groupW, the mod 2 boundary operator on the space of all Coxeter matroids (also known asWP-matroids) forWandP, wherePvaries through all the proper standard parabolic subgroups ofW(Theorem 3 of the paper). A remarkably simple interpretation of Coxeter matroids as certain sets of faces of the generalized permutahedron associated with the Coxeter groupW(Theorem 1) yields a natural definition of the boundary of a Coxeter matroid. The latter happens to be a union of Coxeter matroids for maximal standard parabolic subgroupsQiofP(Theorem 2). These results have very natural interpretations in the case of ordinary matroids and flag-matroids (Section 3). 相似文献
97.
We show that, if E is a commutative MU-algebra spectrum such that is Landweber exact over , then the category of -comodules is equivalent to a localization of the category of -comodules. This localization depends only on the heights of E at the integer primes p. It follows, for example, that the category of -comodules is equivalent to the category of -comodules. These equivalences give simple proofs and generalizations of the Miller-Ravenel and Morava change of rings theorems. We also deduce structural results about the category of -comodules. We prove that every -comodule has a primitive, we give a classification of invariant prime ideals in , and we give a version of the Landweber filtration theorem. 相似文献
98.
Neil N. Katz 《Differential Geometry and its Applications》2005,22(3):297-313
We study a broad class of problems where volume is minimized among metrics on a smooth, compact Riemannian manifold that keep the length of a fixed set of curves bounded below. They can be seen as a generalization of isosystolic inequalities. Necessary and sufficient conditions are given for continuous minima in a conformal class and necessary conditions are given for local minima. 相似文献
99.
Lafon C Murillo-Rincon A Goldenstedt C Chapelon JY Mithieux F Owen NR Cathignol D 《Ultrasonics》2009,49(2):172-178
Miniature flat ultrasound transducers have shown to be effective for a large variety of thermal therapies, but the associated superficial heating implicates developing original strategies in order to extend therapeutic depth. The goal of the present paper is to use ultrasound contrast agents (UCA) to increase remote attenuation and heating. Theoretical simulations demonstrated that increasing attenuation from 0.27 to 0.8 Np/cm at 10 MHz beyond a distance of 18 mm from the transducer should result in longer thermal damages due to protein coagulation in a tissue mimicking phantom. Contrast agents (BR14, Bracco, Plan-les-Ouates, Switzerland) were embedded in thermo-sensitive gel and attenuations ranging from 0.27 to 1.33 Np/cm were measured at 10 MHz for concentrations of BR14 between 0 and 4.8%. Thermal damages were then induced in several gels, which had different layering configurations. Thermal damages, 12.8 mm in length, were obtained in homogeneous gels. When mixing contrast agents at a concentration of 3.2% beyond a first 18 mm-thick layer of homogeneous gel, the thermal damages reached 21.5 mm in length. This work demonstrated that contrast agents can be used for increasing attenuation remotely and extending therapeutic depth induced by a non-focused transducer. Additional work must be done in vivo in order to verify the remote-only distribution of bubbles and associated increase in attenuation. 相似文献
100.
John R. Britnell Neil Saunders Tony Skyner 《Journal of Pure and Applied Algebra》2017,221(11):2647-2665
A finite group G is exceptional if it has a quotient Q whose minimal faithful permutation degree is greater than that of G. We say that Q is a distinguished quotient.The smallest examples of exceptional p-groups have order . For an odd prime p, we classify all pairs where G has order and Q is a distinguished quotient. (The case has already been treated by Easdown and Praeger.) We establish the striking asymptotic result that as p increases, the proportion of groups of order with at least one exceptional quotient tends to 1/2. 相似文献