全文获取类型
收费全文 | 6473篇 |
免费 | 256篇 |
国内免费 | 46篇 |
专业分类
化学 | 4783篇 |
晶体学 | 24篇 |
力学 | 207篇 |
数学 | 883篇 |
物理学 | 878篇 |
出版年
2023年 | 67篇 |
2022年 | 87篇 |
2021年 | 126篇 |
2020年 | 118篇 |
2019年 | 148篇 |
2018年 | 91篇 |
2017年 | 82篇 |
2016年 | 197篇 |
2015年 | 166篇 |
2014年 | 205篇 |
2013年 | 369篇 |
2012年 | 465篇 |
2011年 | 500篇 |
2010年 | 271篇 |
2009年 | 239篇 |
2008年 | 424篇 |
2007年 | 435篇 |
2006年 | 391篇 |
2005年 | 361篇 |
2004年 | 338篇 |
2003年 | 299篇 |
2002年 | 249篇 |
2001年 | 84篇 |
2000年 | 80篇 |
1999年 | 65篇 |
1998年 | 56篇 |
1997年 | 60篇 |
1996年 | 74篇 |
1995年 | 49篇 |
1994年 | 36篇 |
1993年 | 27篇 |
1992年 | 32篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 18篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 39篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 25篇 |
1980年 | 37篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 37篇 |
1976年 | 27篇 |
1975年 | 28篇 |
1974年 | 16篇 |
1973年 | 18篇 |
排序方式: 共有6775条查询结果,搜索用时 8 毫秒
21.
We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spinor self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields. 相似文献
22.
We consider the 3D Navier–Stokes equation with generalized impermeability boundary conditions. As auxiliary results, we prove the local in time existence of a strong solution (‘strong’ in a limited sense) and a theorem on structure. Then, taking advantage of the boundary conditions, we formulate sufficient conditions for regularity up to the boundary of a weak solution by means of requirements on one of the eigenvalues of the rate of deformation tensor. Finally, we apply these general results to the case of an axially symmetric flow with zero angular velocity. 相似文献
23.
We construct division algebras with involution containing a Baer ordering with noninvariant order ring. This gives a negative
answer to a question of Holland, whether the order ring is always invariant under inner automorphisms. Furthermore, we give
examples of any index. Previously, the only known examples of division algebras containing Baer orderings were of index 2
n
or of indexp forp a prime of the form 4m + 3.
Supported in part by the National Science Foundation. 相似文献
24.
Justina Grabowska Karuna Kar Nanda R.T. Rajendra Kumar J.P. Mosnier M.O. Henry Simon B. Newcomb Patrick McNally Lisa OReilly Xu Lu Enda McGlynn 《Superlattices and Microstructures》2007,42(1-6):327
Self-organized ZnAl2O4 nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed c-sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on c-sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl2O4, formed by the reaction of Zn and O with the sapphire substrate. 相似文献
25.
Patrick Mather Nino Grizzuti Glenn Heffner Mathias Ricker Willie E. Rochefort Markus Seitz Hans-Werner Schmidt Dale S. Pearson 《Liquid crystals》1994,17(6):811-826
In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a 'model' polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range-from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations. 相似文献
26.
Paul A. Binding Patrick J. Browne Bruce A. Watson 《Journal of Mathematical Analysis and Applications》2004,291(1):246-261
Three inverse problems for a Sturm-Liouville boundary value problem −y″+qy=λy, y(0)cosα=y′(0)sinα and y′(1)=f(λ)y(1) are considered for rational f. It is shown that the Weyl m-function uniquely determines α, f, and q, and is in turn uniquely determined by either two spectra from different values of α or by the Prüfer angle. For this it is necessary to produce direct results, of independent interest, on asymptotics and oscillation. 相似文献
27.
Heinz H. Bauschke Patrick L. Combettes 《Proceedings of the American Mathematical Society》2003,131(12):3757-3766
An iterative method is proposed to construct the Bregman projection of a point onto a countable intersection of closed convex sets in a reflexive Banach space.
28.
Patrick Pruja Sauveur Bnet Bernard Claudet Olivier Faugeroux Jean-Jacques Serra 《Superlattices and Microstructures》2004,35(3-6):409
Modeling the behavior of a protective coating during a thermal shock not only requires the knowledge of its own thermophysical characteristics, but also those of the coating–substrate discontinuity. According to its nature, this discontinuity can be modeled as a zero-thickness interface (thermal contact resistance) or a finite thickness layer (thermal third body). This paper presents an experimental device and two associated thermal transfer models developed in view of the microscale characterization of such discontinuities. 相似文献
29.
We review the proof of a conjecture concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems, obtained via a connection between the theories of ordinary differential equations and integrable models. Spectral equivalences inspired by the correspondence are also discussed. 相似文献
30.
Recent successes in applying tabu search to a wide variety of classical optimization problems have motivated the investigation of applying tabu search to the well-known general fixed charge problem (GFCP). In this paper, an adaptation of tabu search to GFCP is described and computational results are given. In addition, the computational results are compared with those obtained from SWIFT-2, the most well-known and frequently used heuristic method for GFCP. As will be shown, the results are very encouraging. 相似文献