全文获取类型
收费全文 | 476061篇 |
免费 | 5948篇 |
国内免费 | 2570篇 |
专业分类
化学 | 244049篇 |
晶体学 | 6557篇 |
力学 | 23221篇 |
综合类 | 78篇 |
数学 | 76457篇 |
物理学 | 134217篇 |
出版年
2020年 | 2731篇 |
2019年 | 2632篇 |
2018年 | 12516篇 |
2017年 | 12255篇 |
2016年 | 10725篇 |
2015年 | 5020篇 |
2014年 | 5966篇 |
2013年 | 17912篇 |
2012年 | 16868篇 |
2011年 | 26318篇 |
2010年 | 15573篇 |
2009年 | 15763篇 |
2008年 | 21172篇 |
2007年 | 23367篇 |
2006年 | 15198篇 |
2005年 | 15074篇 |
2004年 | 13866篇 |
2003年 | 12899篇 |
2002年 | 11746篇 |
2001年 | 12509篇 |
2000年 | 9698篇 |
1999年 | 7710篇 |
1998年 | 6366篇 |
1997年 | 6136篇 |
1996年 | 6234篇 |
1995年 | 5704篇 |
1994年 | 5295篇 |
1993年 | 5102篇 |
1992年 | 5663篇 |
1991年 | 5520篇 |
1990年 | 5150篇 |
1989年 | 4997篇 |
1988年 | 5263篇 |
1987年 | 4979篇 |
1986年 | 4793篇 |
1985年 | 6852篇 |
1984年 | 6967篇 |
1983年 | 5710篇 |
1982年 | 6348篇 |
1981年 | 6240篇 |
1980年 | 6028篇 |
1979年 | 6093篇 |
1978年 | 6235篇 |
1977年 | 6133篇 |
1976年 | 6098篇 |
1975年 | 5928篇 |
1974年 | 5656篇 |
1973年 | 5942篇 |
1972年 | 3511篇 |
1971年 | 2635篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
962.
J.E. Lorenzo H. Requardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):185-186
Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K0.3MoO3 and (TaSe4)2I. We have shown that the anomaly in the C
P
/
T
3
data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds.
Received 21 February 2002 Published online 19 July 2002 相似文献
963.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(4):517-520
A generalization of theG-theory defined by A. Heilet al. is presented. 相似文献
964.
J. Sładkowski 《International Journal of Theoretical Physics》1991,30(8):1075-1078
The possibility of inflation without any genuine scalar is discussed. It is suggested that drops of primordial plasma may drive inflation. The model, although naive, is consistent with observational data. 相似文献
965.
We study the superextension of the semi-infinite cohomology theory of the Virasoro Algebra. In particular, we examine the BRST complex with coefficients in the Fock Space of the RNS superstring. We prove a theorem of vanishing cohomology, and establish the unitary equivalence between a positive definite transversal space, a physical subspace and the zeroth cohomology group. The cohomology of a subcomplex is identified as the covariant equivalent of the well-known GSO subspace. An exceptional case to the vanishing theorem is discussed.Supported by NSF Grant DMS-8703581 相似文献
966.
Jan J. Dijkstra 《Topology and its Applications》2006,153(15):2948-2951
In 1988 A. Gutek proved that there exist one-point connectifications of hereditarily disconnected spaces that do not have the fixed point property. We improve on this result by constructing a one-point connectification of a totally disconnected space without the fixed point property. 相似文献
967.
Detection of hepatocarcinoma in rats by integration of the fluorescence spectrum: Experimental model
J. C. Marcassa J. Ferreira S. Zucoloto O. de Castro e Silva Jr. L. G. Marcassa V. S. Bagnato 《Laser Physics》2006,16(5):827-832
The incorporation of spectroscopic techniques into diagnostic procedures may greatly improve the chances for precise diagnostics. One promising technique is fluorescence spectroscopy, which has recently been used to detect many different types of diseases. In this work, we use laser-induced tissue fluorescence to detect hepatocarcinoma in rats using excitation light at wavelengths of 443 and 532 nm. Hepatocarcinoma was induced chemically in Wistar rats. The collected fluorescence spectrum ranges from the excitation wavelength up to 850 nm. A mathematical procedure carried out on the spectrum determines a figure of merit value, which allows the detection of hepatocarcinoma. The figure of merit involves a procedure which evaluates the ratio between the backscattered excitation wavelength and the broad emission fluorescence band. We demonstrate that a normalization allowed by integration of the fluorescence spectra is a simple operation that may allow the detection of hepatocarcinoma. 相似文献
968.
969.
J. Globevnik 《Inventiones Mathematicae》1989,98(2):331-350
Dedicated to the memory of my father 相似文献
970.
J. Kogan 《Journal of Optimization Theory and Applications》1989,63(2):225-260
In this paper, we study intersections of extremals in a linear-quadratic Bolza problem of optimal control. The structure of the inter-sections is described. We show that this structure implies the semipositive definiteness of the quadratic cost functional. In addition, we derive necessary and sufficient conditions for the existence of minimizers. 相似文献