全文获取类型
收费全文 | 94247篇 |
免费 | 2678篇 |
国内免费 | 1601篇 |
专业分类
化学 | 60342篇 |
晶体学 | 611篇 |
力学 | 1726篇 |
综合类 | 14篇 |
数学 | 16386篇 |
物理学 | 19447篇 |
出版年
2023年 | 611篇 |
2022年 | 975篇 |
2021年 | 1325篇 |
2020年 | 1342篇 |
2019年 | 1414篇 |
2018年 | 1669篇 |
2017年 | 1587篇 |
2016年 | 3114篇 |
2015年 | 2560篇 |
2014年 | 2703篇 |
2013年 | 5941篇 |
2012年 | 5975篇 |
2011年 | 6245篇 |
2010年 | 3922篇 |
2009年 | 3755篇 |
2008年 | 5272篇 |
2007年 | 5103篇 |
2006年 | 4577篇 |
2005年 | 4385篇 |
2004年 | 4111篇 |
2003年 | 3303篇 |
2002年 | 2890篇 |
2001年 | 1960篇 |
2000年 | 1814篇 |
1999年 | 1325篇 |
1998年 | 1065篇 |
1997年 | 961篇 |
1996年 | 1164篇 |
1995年 | 856篇 |
1994年 | 891篇 |
1993年 | 902篇 |
1992年 | 863篇 |
1991年 | 683篇 |
1990年 | 730篇 |
1989年 | 584篇 |
1988年 | 588篇 |
1987年 | 554篇 |
1986年 | 548篇 |
1985年 | 758篇 |
1984年 | 721篇 |
1983年 | 545篇 |
1982年 | 556篇 |
1981年 | 556篇 |
1980年 | 511篇 |
1979年 | 463篇 |
1978年 | 431篇 |
1977年 | 416篇 |
1976年 | 428篇 |
1974年 | 376篇 |
1973年 | 394篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Bernardo Lafuerza-Guillén Donal O’regan Reza Saadati 《Proceedings Mathematical Sciences》2007,117(1):61-70
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness
of a quotient. 相似文献
52.
Márton Kiss 《Acta Mathematica Hungarica》2006,110(3):253-259
Summary New results for the eigenvalue ratios of vibrating strings are presented partially in connection with previous results concerning
Schr?dinger operators. 相似文献
53.
In this note we study uncertainty sequencing situations, i.e., one-machine sequencing situations in which no initial order
is specified. We associate cooperative games with these sequencing situations, study their core, and provide links with the
classic sequencing games introduced by Curiel et al. (Eur J Oper Res 40:344–351, 1989). Moreover, we propose and characterize
two simple cost allocation rules for uncertainty sequencing situations with equal processing times. 相似文献
54.
N. Hegyvári 《Acta Mathematica Hungarica》1989,53(1-2):149-154
55.
In [3] it was shown that a (real) signed measure on a cyclic coarse-grained quantum logic can be extended, as a signed measure,
over the entire power algebra. Later ([9]) this result was re-proved (and further improved on) and, moreover, the non-negative
measures were shown to allow for extensions as non-negative measures. In both cases the proof technique used was the technique
of linear algebra. In this paper we further generalize the results cited by extending group-valued measures on cyclic coarse-grained
quantum logics (or non-negative group-valued measures for lattice-ordered groups). Obviously, the proof technique is entirely
different from that of the preceding papers. In addition, we provide a new combinatorial argument for describing all atoms
of cyclic coarse-grained quantum logics. 相似文献
56.
We study the spectral properties of a large class of compact flat Riemannian manifolds of dimension 4, namely, those whose
corresponding Bieberbach groups have the canonical lattice as translation lattice. By using the explicit expression of the
heat trace of the Laplacian acting on p-forms, we determine all p-isospectral and L-isospectral pairs and we show that in this class of manifolds, isospectrality on functions and isospectrality on p-forms for all values of p are equivalent to each other. The list shows for any p, 1 ≤ p ≤ 3, many p-isospectral pairs that are not isospectral on functions and have different lengths of closed geodesics. We also determine
all length isospectral pairs (i.e. with the same length multiplicities), showing that there are two weak length isospectral
pairs that are not length isospectral, and many pairs, p-isospectral for all p and not length isospectral.
Mathematics Subject Classifications (2000): 58J53, 58C22, 20H15. 相似文献
57.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
58.
Generally, in homotopy theory a cylinder object (or, its dual, a path object) is used to define homotopy between morphisms,
and a cone object is used to build exact sequences of homotopy groups. Here, an axiomatic theory based on a cone functor is
given. Suspension objects are associated to based objects and cofibrations, obtaining homotopy groups referred to an object
and relative to a cofibration, respectively. Exact sequences of these groups are built. Algebraic and particular examples
are given. We point out that the main results of this paper were already stated in [3], and the purpose of this article is
to give full details of the foregoing. 相似文献
59.
E. Liénard G. Ban J. Blieck D. Durand F. Duval X. Fléchard M. Herbane M. Labalme Y. Lemière F. Mauger A. Méry O. Naviliat-Cuncic D. Rodríguez J. C. Thomas 《Hyperfine Interactions》2006,172(1-3):29-33
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller
decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The
6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to
deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this
experiment. Up to 105 coincidences were recorded during a second run in 2006. 相似文献
60.
Elena Larraz Carlos Elvira Julio San Romn 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1641-1649
This article explores the synthesis of a novel methacrylic macromonomer with an amphiphilic character derived from poly(ethylene glycol) tert‐octylphenyl ether (MT) and its respective homopolymer. To know their reactivity in radical copolymerization reactions with methyl methacrylate (MMA), a model monomer (MTm) was synthesized to determine the reactivity ratios and compare them with the low molar fractions of copolymers of MT with MMA because they were difficult to isolate. They were rMTm = 0.97 and rMMA = 0.95. The compositional diagrams when representing the weight fraction of MT and MTm in the feed and the copolymer suggested that a clear correlation exists between the experimental points of the model monomer MTm and the macromonomer MT ones, suggesting that the length of the side poly(ethylene oxide) chain does not affect the reactivity of the methacrylic double bond in the prepared monomers for this type of polymerization reaction. The reactivity ratios of the copolymers have a tendency for the formation of random or Bernoullian copolymers. The glass‐transition temperatures (Tg's) of the prepared copolymers were determined by differential scanning calorimetry, deviated from the Fox equation, and discussed on the basis of treatments that consider the influence of the monomeric units along the copolymer chains, determining the Tg of the corresponding alternating dyads. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1641–1649, 2003 相似文献