全文获取类型
收费全文 | 47440篇 |
免费 | 1290篇 |
国内免费 | 42篇 |
专业分类
化学 | 28835篇 |
晶体学 | 244篇 |
力学 | 764篇 |
综合类 | 1篇 |
数学 | 8910篇 |
物理学 | 10018篇 |
出版年
2023年 | 336篇 |
2022年 | 326篇 |
2021年 | 512篇 |
2020年 | 697篇 |
2019年 | 632篇 |
2018年 | 950篇 |
2017年 | 870篇 |
2016年 | 1692篇 |
2015年 | 1413篇 |
2014年 | 1366篇 |
2013年 | 3081篇 |
2012年 | 2906篇 |
2011年 | 2743篇 |
2010年 | 1841篇 |
2009年 | 1561篇 |
2008年 | 2422篇 |
2007年 | 2199篇 |
2006年 | 1981篇 |
2005年 | 2022篇 |
2004年 | 1735篇 |
2003年 | 1450篇 |
2002年 | 1277篇 |
2001年 | 965篇 |
2000年 | 984篇 |
1999年 | 688篇 |
1998年 | 523篇 |
1997年 | 450篇 |
1996年 | 597篇 |
1995年 | 430篇 |
1994年 | 493篇 |
1993年 | 449篇 |
1992年 | 474篇 |
1991年 | 404篇 |
1990年 | 450篇 |
1989年 | 364篇 |
1988年 | 375篇 |
1987年 | 333篇 |
1986年 | 325篇 |
1985年 | 452篇 |
1984年 | 412篇 |
1983年 | 327篇 |
1982年 | 328篇 |
1981年 | 343篇 |
1980年 | 281篇 |
1979年 | 276篇 |
1978年 | 273篇 |
1977年 | 262篇 |
1976年 | 278篇 |
1974年 | 251篇 |
1973年 | 263篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The aim of the paper is to investigate the limit behaviour of the least squares estimator of the shift parameter of nearly unstable, nearly stable, and nearly explosive AR(1) models. Both zero start and stationary cases are treated. Connection with the maximum likelihood estimator of the shift parameter of continuous time AR(1) processes is also discussed. 相似文献
62.
I. Jánossy 《Pramana》2003,61(2):435-445
It is suggested that liquid crystal—polymer interfaces are coupled systems, in which the components mutually influence the
orientational state of each other. The photo-orientation process at liquid crystal-polymer interfaces provides a striking
example of such a coupling. Experiments show that the anisotropic structure generated by polarised light at a polymer surface
is strongly affected by the phase of the liquid crystal covering the polymer. Photo-orientation is significantly more efficient
when the liquid crystal is in the isotropic phase than when it exhibits orientational order. The observations are interpreted
by assuming that in the smectic and nematic phases the liquid crystal stabilises to a large extent polymer chain-segments
aligned parallel to the director, while it blocks the photo-induced formation of chain-segments in the perpendicular direction.
Other situations, in which the coupling between the liquid crystal and the polymer can be important, are also discussed briefly. 相似文献
63.
Periodica Mathematica Hungarica - 相似文献
64.
Under intrinsic and extrinsic curvature assumptions on a Riemannian spin manifold and its boundary, we show that there is
an isomorphism between the restriction to the boundary of parallel spinors and extrinsic Killing spinors of non-negative Killing constant. As a corollary, we prove that a complete Ricci-flat spin manifold with mean-convex boundary
isometric to a round sphere, is necessarily a flat disc.
Received: 2 February 2002; in final form: 1 August 2002 /
Published online: 1 April 2003
Mathematics Subject Classification (1991): 53C27, 53C40, 53C80, 58G25
The authors would like to thank Lars Andersson for helpful discussions and for bringing to our knowledge the information
regarding Remark 4. We are also grateful to the referee for pointing out that Corollary 5 and Corollary 6 are only valid when
the boundary is at least 2-dimensional.
Research of S. Montiel is partially supported by a Spanish MCyT grant No. BFM2001-2967 相似文献
65.
I. Zvára 《Physics of Atomic Nuclei》2003,66(6):1125-1130
Studies of chemistry of the transactinoid elements, which are available only as single atoms, by gas (thermo)chromatographic techniques can provide the adsorption enthalpies of the atoms or molecules. These values serve the ultimate goal—to characterize bulk volatility of the species in terms like sublimation enthalpies. The paper attempts an in-depth discussion of the statistical significance of the adsorption enthalpies derived in such experiments. Usually, the counting statistics are very poor and one faces nonstandard problems in evaluating the confidence intervals for the values of parameters. Here, a most efficient way seems to be the Bayesian approach, realized, when necessary, by Monte Carlo simulations of the counting results. Necessarily, the adsorption enthalpy is not evaluated based on the second law of thermodynamics but through accepting an a priori value of the adsorption entropy. More additional assumptions about the mechanisms and parameters involved are needed. This may produce systematic errors in the quantitative conclusions; the analysis of some recent works with elements 106 and 108 corroborates this concern. Despite such problems, it is possible to reveal qualitative differences in the adsorption behavior of a transactinoid and its expected known congeners as well as to use chemistry for an independent assignment of the atomic numbers of transactinoid nuclides. 相似文献
66.
Essam Totry Carlos González Javier LLorca 《International Journal of Solids and Structures》2008,45(6):1663-1675
The influence of the loading path on the failure locus of a composite lamina subjected to transverse compression and out-of-plane shear is analyzed through computational micromechanics. This is carried out using the finite element simulation of a representative volume element of the microstructure, which takes into account explicitly fiber and matrix spatial distribution within the lamina. In addition, the actual failure mechanisms (plastic deformation of the matrix and interface decohesion) are included in the simulations through the corresponding constitutive models. Two different interface strength values were chosen to explore the limiting cases of composites with strong or weak interfaces. It was found that failure locus was independent of the loading path for the three cases analyzed (pseudo-radial, compression followed by shear and shear followed by compression) in the composites with strong and weak interfaces. This result was attributed to the fact that the dominant failure mechanism in each material was the same in transverse compression and in shear. Failure is also controlled by the same mechanisms under a combination of both stresses and the failure locus depended mainly on the magnitude of the stresses that trigger fracture rather than in the loading path to reach the critical condition. 相似文献
67.
The vertical migration of 85Sr, 137Cs and 131I in some arable and undisturbed single-contaminated soils was studied by gamma-spectrometry measurements under lysimetric laboratory conditions during irrigation of the soil profiles with wet atmospheric precipitation for about one year, except 131I. A new simple exponential compartment (box) model was derived, which makes it possible to calculate the migration rate constants and migration rates in the individual soil layers (vertical sections) as well as the total vertical migration rate constants and total vertical migration rates of radionuclides in the bulk soil horizon. The relaxation times of radionuclides in respective soil horizons can also be evaluated. 相似文献
68.
In this paper an automatic technique for handling discontinuous IVPs when they are solved by means of adaptive Runge–Kutta codes is proposed. This technique detects, accurately locates and passes the discontinuities in the solution of IVPs by using the information generated by the code along the numerical integration together with a continuous interpolant of the discrete solution. A remarkable feature is that it does not require additional information on the location of the discontinuities. Some numerical experiments are presented to illustrate the reliability and efficiency of the proposed algorithms. 相似文献
69.
We consider a discretized volume V consisting of finite, congruent and attached copies of a tile t. We find a group L
V
the orbit of which, when applied to t, is just V. We show the connection between the structural matrixQ in the formal solution of a boundary value problem formulated for volume V and the so called auxiliary matrix of the graph Γ
v
associated with V. We show boundary value problems to be isomorphic if the graphs associated with the volumes are isomorphic, or, if the covering
groups are Sunada pairs. 相似文献
70.
András Sütő 《Journal of statistical physics》2003,112(1-2):375-396
We study condensation of trapped bosons in the limit when the number of particles tends to infinity. For the noninteracting gas we prove that there is no phase transition in any dimension, but in any dimension, at any temperature the system is 100% condensated into the one-particle ground state. In the case of an interacting gas we show that for a family of suitably scaled pair interactions, the Gross–Pitaevskii scaling included, a less-than-100% condensation into a single-particle eigenstate, which may depend on the interaction strength, persists at all temperatures. 相似文献