全文获取类型
收费全文 | 19199篇 |
免费 | 570篇 |
国内免费 | 711篇 |
专业分类
化学 | 4104篇 |
晶体学 | 859篇 |
力学 | 468篇 |
综合类 | 69篇 |
数学 | 12382篇 |
物理学 | 2598篇 |
出版年
2023年 | 77篇 |
2022年 | 201篇 |
2021年 | 166篇 |
2020年 | 167篇 |
2019年 | 451篇 |
2018年 | 481篇 |
2017年 | 331篇 |
2016年 | 330篇 |
2015年 | 311篇 |
2014年 | 654篇 |
2013年 | 1004篇 |
2012年 | 625篇 |
2011年 | 1309篇 |
2010年 | 1337篇 |
2009年 | 1435篇 |
2008年 | 1452篇 |
2007年 | 1431篇 |
2006年 | 1181篇 |
2005年 | 870篇 |
2004年 | 839篇 |
2003年 | 667篇 |
2002年 | 555篇 |
2001年 | 427篇 |
2000年 | 353篇 |
1999年 | 334篇 |
1998年 | 317篇 |
1997年 | 266篇 |
1996年 | 380篇 |
1995年 | 318篇 |
1994年 | 340篇 |
1993年 | 289篇 |
1992年 | 229篇 |
1991年 | 133篇 |
1990年 | 134篇 |
1989年 | 123篇 |
1988年 | 84篇 |
1987年 | 101篇 |
1986年 | 100篇 |
1985年 | 141篇 |
1984年 | 83篇 |
1983年 | 59篇 |
1982年 | 84篇 |
1981年 | 70篇 |
1980年 | 45篇 |
1979年 | 22篇 |
1978年 | 37篇 |
1977年 | 54篇 |
1976年 | 43篇 |
1975年 | 9篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
We investigate several versions of a cardinal characteristic defined by Frankiewicz. Vojtáš showed , and Blass showed . We show that all the versions coincide and that is greater than or equal to the splitting number. We prove the consistency of and of .
Received: 2 October 1996 / Revised version: 22 May 1997 相似文献
12.
Intense multi- and single-line laser operation is reported from semiconductively preionised atomic fluorine lasers employing an optimised capacitor transfer excitation circuitry. The performance and spectral characteristics of these lasers are discussed and compared to the characteristics of previously described atomic fluorine lasers. The efficiency of one of these lasers described, at optimum conditions, is reaching a value as high as 0.14%. To the best of our knowledge, this is the highest efficiency reported up date, for an atomic fluorine laser. 相似文献
13.
Lévy processes in matrix Lie groups are studied. Subordination (random time change) is used to show that quasi-invariance of the Brownian motion in a Lie group induces absolute continuity of the laws of the corresponding pure jump processes. These results are applied to several examples which are discussed in detail. 相似文献
14.
The main results of the paper are as follows: covering characterizations of wQN-spaces, covering characterizations of QN-spaces and a theorem saying that Cp(X) has the Arkhangel'ski?ˇ property (α1) provided that X is a QN-space. The latter statement solves a problem posed by M. Scheepers [M. Scheepers, Cp(X) and Arhangel'ski?ˇ's αi-spaces, Topology Appl. 89 (1998) 265-275] and for Tychonoff spaces was independently proved by M. Sakai [M. Sakai, The sequence selection properties of Cp(X), Preprint, April 25, 2006]. As the most interesting result we consider the equivalence that a normal topological space X is a wQN-space if and only if X has the property S1(Γshr,Γ). Moreover we show that X is a QN-space if and only if Cp(X) has the property (α0), and for perfectly normal spaces, if and only if X has the covering property (β3). 相似文献
15.
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
16.
The authors give a consistent affirmative response to a question of Juhász, Soukup and Szentmiklóssy: If GCH fails, there are (many) extraresolvable, not maximally resolvable Tychonoff spaces. They show also in ZFC that for ω<λ?κ, no maximal λ-independent family of λ-partitions of κ is ω-resolvable. In topological language, that theorem translates to this: A dense, ω-resolvable subset of a space of the form (DI(λ)) is λ-resolvable. 相似文献
17.
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
18.
19.
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
20.
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