全文获取类型
收费全文 | 2260篇 |
免费 | 142篇 |
国内免费 | 13篇 |
专业分类
化学 | 1575篇 |
晶体学 | 10篇 |
力学 | 65篇 |
数学 | 321篇 |
物理学 | 282篇 |
无线电 | 162篇 |
出版年
2024年 | 7篇 |
2023年 | 15篇 |
2022年 | 36篇 |
2021年 | 45篇 |
2020年 | 35篇 |
2019年 | 51篇 |
2018年 | 38篇 |
2017年 | 47篇 |
2016年 | 96篇 |
2015年 | 56篇 |
2014年 | 121篇 |
2013年 | 143篇 |
2012年 | 177篇 |
2011年 | 190篇 |
2010年 | 118篇 |
2009年 | 122篇 |
2008年 | 150篇 |
2007年 | 147篇 |
2006年 | 126篇 |
2005年 | 121篇 |
2004年 | 118篇 |
2003年 | 85篇 |
2002年 | 74篇 |
2001年 | 37篇 |
2000年 | 34篇 |
1999年 | 25篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有2415条查询结果,搜索用时 15 毫秒
91.
92.
Roy Abi Zeid Daou Xavier Moreau Clovis Francis 《Signal, Image and Video Processing》2012,6(3):463-478
In this paper, we deal with the effects of the uncertainties on a fractional system of the first kind, mainly on the frequency-domain and the time-domain responses. For the structural uncertainties, two main aspects are studied: the nonlinearities of the physical components used to realize the fractional system and the consideration of the previously neglected dynamics of the system. Both uncertainties are introduced for the hydropneumatic CRONE suspension, previously synthesized and realized without taking into consideration these uncertainties. So, the novel approach treated in this work is to find whether the uncertainties, which were previously neglected in the synthesis and the realization phases, alter the behaviour of the system or not. The results show that the fractional order system behaviour is not affected. 相似文献
93.
Xavier L��pez Pere Mir�� Jorge J. Carb�� Antonio Rodr��guez-Fortea Carles Bo Josep M. Poblet 《Theoretical chemistry accounts》2011,128(4-6):393-404
Computational chemistry applied to the study of polyoxometalates has achieved its maturity in the last years. During two decades, important advances have been made using theoretical tools in the comprehension and interpretation of many relevant issues. In the present mini-review, we want to stress that different techniques have been incorporated to the routine of computation: from the very first Hartree?CFock LCAO-SCF calculation on the decavanadate anion, followed by numerous density functional theory?Cbased studies on increasingly complex systems, also applying correlated ab initio techniques for magnetism and, more recently, using molecular dynamics to analyse properties in liquid media, the information provided by computational chemistry gets more and more relevant. 相似文献
94.
Xavier Solans‐Monfort Dr. Roser Pleixats Prof. Mariona Sodupe Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(24):7331-7343
The catalytic activity and catalyst recovery of two heterogenized ruthenium‐based precatalysts ( H and NO2(4) ) in diene ring‐closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs–Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered. DFT calculations suggest that either for the homogeneous and heterogenized systems the activity of the catalysts mainly depends on the ability of the precursor to generate the propagating carbene. This ability does not correlate with the traditionally identified key factor, the Ru???O interaction strength. In contrast, precatalysts with lower alkoxy‐dissociation energy barriers and lower stabilities compared with the propagating carbene also present larger C1? C2 bond length (i.e., lower π character of the C? C bond that exists between the metal–carbene (Ru?C) and the phenyl ring of the Hoveyda ligand). Catalyst recovery, regardless of whether a release–return mechanism occurs or not, is also mainly determined by the π delocalization. Therefore, future Grubbs–Hoveyda‐type catalyst development should be based on fine‐tuning the π‐electron density of the phenyl moiety, with the subsequent effect on the metalloaromaticity of the ruthenafurane ring, rather than considering the modification of the Ru???O interaction. 相似文献
95.
96.
97.
A?ta Thior Anne-Claire Lepage Xavier Begaud Olivier Maas 《Applied Physics A: Materials Science & Processing》2012,109(4):1095-1101
This paper presents an analytical model for CRLH (Composite Right-Left Handed) antennas preliminary design. The objective of this work is to develop a tool to estimate quickly the scattering and radiating characteristics of these CRLH-based structures. The analytical model provides thus a set of parameters which roughly fulfill desired requirements. Afterwards, the antenna designer can refine the CRLH-based antenna performances with full 3D electromagnetic simulation software. 相似文献
98.
N. K. Leite J. G. Santos R. F. Souza G. M. Cabianchi F. O. Xavier B. M. Gomes L. B. Silveira A. C. Oliveira A. F.R. Rodriguez P. C. Morais 《The European physical journal. Special topics》2008,153(1):45-48
In this study we demonstrate the usefulness of the
Photoacoustic Spectroscopy (PAS) in the investigation of water collected
from a natural site located within the Amazon region, Brazil, during the wet
to dry seasons transition (May/2006). The water samples were collected from
different stages along a hydrologic pathway including precipitation water
(Prec), groundwater (GW), through flow water (TF), overland flow water (OF),
and stream flow water (SW). The observed photoacoustic spectral features, in
the 0.3 to 1.0 μm wavelength region, fall within three distinct bands
(C, S, and L). We found band-C, band-S and band-L occurring in the spectral
range of 0.30 to 0.40 μm, 0.40 to 0.45 μm and 0.45 to 1.0 μm
regions, respectively. The photoacoustic features shift peak positions and
change intensities for all samples investigated, thus supporting the
proposal of PAS as a useful technique to investigate water samples from
natural environments. 相似文献
99.
Sandie Souchet Xavier Guyon 《Annales de l'Institut Henri Poincaré (B) Probabilités et Statistiques》2002,38(6):1093
Let (X(lδ), l=0,n) be a discrete observation at mesh δ>0 of X, a CAR(p). Classical Yule–Walker estimation are biased and must be corrected. Resultant estimators converge if T=nδ→+∞, are asymptotically normal with rate
, and efficient. The diffusion coefficient is also estimated, with rate
. 相似文献
100.
We prove a uniform bound for the density, p
t
(x), of the solution at time t(0, 1] of a 1-dimensional stochastic differential equation, under hypoellipticity conditions. A similar bound is obtained for an expression involving the distributional derivative (with respect to x) of p
t
(x). These results are applied to extend the Itô formula to the composition of a function (satisfying slight regularity conditions) with a hypoelliptic diffusion process in the spirit of the work of Föllmer et al.
(5) 相似文献