全文获取类型
收费全文 | 18757篇 |
免费 | 580篇 |
国内免费 | 749篇 |
专业分类
化学 | 4277篇 |
晶体学 | 863篇 |
力学 | 456篇 |
综合类 | 76篇 |
数学 | 11720篇 |
物理学 | 2694篇 |
出版年
2023年 | 77篇 |
2022年 | 206篇 |
2021年 | 170篇 |
2020年 | 162篇 |
2019年 | 456篇 |
2018年 | 473篇 |
2017年 | 330篇 |
2016年 | 333篇 |
2015年 | 316篇 |
2014年 | 616篇 |
2013年 | 974篇 |
2012年 | 585篇 |
2011年 | 1236篇 |
2010年 | 1273篇 |
2009年 | 1431篇 |
2008年 | 1465篇 |
2007年 | 1454篇 |
2006年 | 1146篇 |
2005年 | 886篇 |
2004年 | 846篇 |
2003年 | 651篇 |
2002年 | 568篇 |
2001年 | 413篇 |
2000年 | 351篇 |
1999年 | 345篇 |
1998年 | 312篇 |
1997年 | 263篇 |
1996年 | 370篇 |
1995年 | 300篇 |
1994年 | 322篇 |
1993年 | 282篇 |
1992年 | 220篇 |
1991年 | 135篇 |
1990年 | 120篇 |
1989年 | 124篇 |
1988年 | 82篇 |
1987年 | 90篇 |
1986年 | 97篇 |
1985年 | 129篇 |
1984年 | 74篇 |
1983年 | 55篇 |
1982年 | 70篇 |
1981年 | 64篇 |
1980年 | 39篇 |
1979年 | 21篇 |
1978年 | 35篇 |
1977年 | 47篇 |
1976年 | 33篇 |
1974年 | 15篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
32.
Valery Agoshkov Paola Gervasio Alfio Quarteroni 《Mediterranean Journal of Mathematics》2006,3(2):147-176
New domain decomposition methods (DDM) based on optimal control approach are introduced for the coupling of first and second
order equations on overlapping subdomains. Several cost functionals and control functions are proposed. Uniqueness and existence
results are proved for the coupled problem, and the convergence of iterative processes is analyzed.
The work was supported by the Russian Foundation for Basic Research (04-01-00615) and it was partly carried out while the
first author was visiting the IACS at EPFL. 相似文献
33.
Christos Kravvaritis Marilena Mitrouli Jennifer Seberry 《Linear and Multilinear Algebra》2007,55(5):471-490
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k × k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
34.
35.
Norbert Poschadel 《Mathematische Semesterberichte》2002,49(1):45-54
Zusammenfassung. Eine Abbildung zwischen metrischen R?umen hei?t abstandsvertr?glich, wenn der Abstand der Bilder zweier Punkte nur vom Abstand der Punkte selbst abh?ngt. Wir zeigen, dass eine Abbildung genau dann abstandsvertr?glich ist, wenn der Cauchyschen Funktionalgleichung genügt, also ein Endomorphismus der Gruppe ist. Ein entsprechendes Resultat gilt auch für die abstandsvertr?glichen Abbildungen des Kreises (mit der Multiplikation komplexer Zahlen als Gruppenverknüpfung). Damit kann man sowohl alle messbaren abstandsvertr?glichen Abbildungen von bzw. in sich angeben, als auch einen Nachweis für die Existenz nichtmessbarer abstandsvertr?glicher Abbildungen auf und erbringen.
Eingegangen am 20. Juni 2001 / Angenommen am 13. September 2001 相似文献
36.
37.
The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keV and grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated.For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations. 相似文献
38.
In this paper, we report that the phase transformation of Ni-B, Ni-P diffusion barriers deposited electrolessly on Cu, for the reason that the Ni-P layer is a more effective diffusion barrier than the Ni-B layer. The Ni3B crystallized was decomposed to Ni and B2O3 above 400 °C and the Ni3P crystallized was decomposed to Ni and P2O5 above 600 °C respectively in Ar atmosphere. Also, the Ni3B was decomposed to Ni and free B above 400 °C and the Ni3P was decomposed to Ni and free P above 600 °C respectively in H2 atmosphere. The decomposed Ni formed a solid solution with Cu. The Cu diffusion occurred above 400 °C for Ni-B layer and above 600 °C for Ni-P layer, respectively. Because the decomposition temperature of Ni-P layer is about 200 °C higher than that of Ni-B layer, the Ni-P layer is a more effective barrier for Cu than the Ni-B layer. 相似文献
39.
Consider the problem of three point vortices (also called Helmholtz’ vortices) on a plane, with arbitrarily given vorticities.
The interaction between vortices is proportional to 1/r, where r is the distance between two vortices. The problem has 2 equilateral and at most 3 collinear normalized relative equilibria.
This 3 is the optimal upper bound. Our main result is that the above standard statements remain unchanged if we consider an
interaction proportional to r
b, for any b < 0. For 0 < b < 1, the optimal upper bound becomes 5. For positive vorticities and any b < 1, there are exactly 3 collinear normalized relative equilibria. The case b = −2 of this last statement is the well-known theorem due to Euler: in the Newtonian 3-body problem, for any choice of the
3 masses, there are 3 Euler configurations (also known as the 3 Euler points). These small upper bounds strengthen the belief
of Kushnirenko and Khovanskii [18]: real varieties defined by simple systems should have a simple topology. We indicate some
hard conjectures about the configurations of relative equilibrium and suggest they could be attacked within the quasi-polynomial
framework. 相似文献
40.
Piotr Ko?cielniak 《Topology and its Applications》2007,154(9):1951-1955
Let M be a compact manifold with dimM?2. We prove that some iteration of the generic homeomorphism on M is semiconjugated to the shift map and has infinite topological entropy (Theorem 1.1). 相似文献