全文获取类型
收费全文 | 51297篇 |
免费 | 5949篇 |
国内免费 | 4665篇 |
专业分类
化学 | 36215篇 |
晶体学 | 523篇 |
力学 | 1684篇 |
综合类 | 803篇 |
数学 | 6994篇 |
物理学 | 15692篇 |
出版年
2023年 | 415篇 |
2022年 | 946篇 |
2021年 | 2132篇 |
2020年 | 1736篇 |
2019年 | 1667篇 |
2018年 | 1281篇 |
2017年 | 1400篇 |
2016年 | 1666篇 |
2015年 | 1716篇 |
2014年 | 2100篇 |
2013年 | 3714篇 |
2012年 | 2627篇 |
2011年 | 2569篇 |
2010年 | 2283篇 |
2009年 | 2743篇 |
2008年 | 2835篇 |
2007年 | 2989篇 |
2006年 | 2521篇 |
2005年 | 1838篇 |
2004年 | 1755篇 |
2003年 | 1689篇 |
2002年 | 4194篇 |
2001年 | 1762篇 |
2000年 | 1315篇 |
1999年 | 1081篇 |
1998年 | 1007篇 |
1997年 | 755篇 |
1996年 | 770篇 |
1995年 | 710篇 |
1994年 | 684篇 |
1993年 | 652篇 |
1992年 | 640篇 |
1991年 | 409篇 |
1990年 | 336篇 |
1989年 | 286篇 |
1988年 | 318篇 |
1987年 | 260篇 |
1986年 | 248篇 |
1985年 | 344篇 |
1984年 | 260篇 |
1983年 | 154篇 |
1982年 | 310篇 |
1981年 | 493篇 |
1980年 | 443篇 |
1979年 | 478篇 |
1978年 | 377篇 |
1977年 | 284篇 |
1976年 | 247篇 |
1974年 | 78篇 |
1973年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
131.
132.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
133.
B. Sadashive Gowda G.S.V.L. Narasimham M.V. Krishna Murthy 《International Journal of Heat and Fluid Flow》1997,18(6):613-624
In this paper, a mathematical model for forced-air precooling of spherical food products in bulk is developed. The foods are arranged in horizontal layers stacked one above the other to form a rectangular parallelepiped with a vertical gap in between the product layers. The foods are cooled by chilled air blown along the height of the package. The governing equations for the conduction heat transfer in the foods, simultaneous heat and mass transfer at the food-air interface and in the air stream are solved numerically using finite-difference methods. A comprehensive numerical study is performed by varying the process parameters over a wide range. Typical results showing the variation of moist air properties along the height of the package and the effect of each parameter on the process time are presented. The ranges of parameters for advantageous operation of the precooling system are identified. Correlations are obtained for the process time based on the product center and mass-averaged temperatures in terms of process parameters. 相似文献
134.
以金刚石压腔高压装置为工具,用Ⅱ型金刚石作压砧兼红外窗口,对本征态聚苯胺进行了高压(0~8.4 GPa)就位红外光谱测试。结果表明:在4.8~5.2 GPa压力区间,代表醌环振动的吸收峰相对代表苯环振动的吸收峰变小,表明聚苯胺在此压力区间结构上发生了显著变化,且这种变化是不可逆的。聚苯胺的高压(0~14.5 GPa)电阻测量结果表明:当压力小于7.5 GPa时,电阻随压力升高而显著降低,据此认为聚苯胺为电子性导电物质;在7.5 GPa处电阻出现极小值,然后又缓慢升高,至10 GPa后基本不变。推测聚苯胺电阻极小值是由结构变化引起的。至于红外光谱与电阻测量结果反映聚苯胺结构变化的压力值不一致,可能是由于测试条件不同所致。 相似文献
135.
136.
Magnetic Properties of the Cobaltates Na6CoS4, Na6CoSe4, and K6CoS4 The alkali metal cobalt chalcogenides Na6CoS4, Na6CoSe4, and K6CoS4 crystallize in the space group P63mc with Z = 4. The structure is characterized by isolated [CoX4]-tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. The deviations at low temperatures are caused by antiferromagnetic interactions. The magnetic moments are discussed with regard to ligand-field parameters. 相似文献
137.
S. Albeverio S. N. Lakaev J. I. Abdullaev 《Functional Analysis and Its Applications》2002,36(3):212-216
A Hamiltonian describing four bosons that move on a lattice and interact by means of pair zero-range attractive potentials is considered. A stronger version of the Hunziker–Van Vinter–Zhislin theorem on the essential spectrum is established. It is proved that the set of eigenvalues lying to the left of the essential spectrum is finite for any interaction energy of two bosons and is empty if this energy is sufficiently small. 相似文献
138.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
139.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
140.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献