全文获取类型
收费全文 | 144篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 87篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 21篇 |
物理学 | 39篇 |
出版年
2021年 | 3篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2013年 | 8篇 |
2012年 | 2篇 |
2011年 | 3篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 2篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1924年 | 1篇 |
1905年 | 2篇 |
1899年 | 1篇 |
1898年 | 1篇 |
1897年 | 1篇 |
1888年 | 2篇 |
1885年 | 1篇 |
1884年 | 1篇 |
排序方式: 共有149条查询结果,搜索用时 250 毫秒
21.
22.
J.G. Morley 《Physics Reports》1976,28(3):245-302
The physical properties of solids determine their usefulness as structural materials. Metals have some disadvantageous characteristics which reduce their effectiveness in critical engineering applications. These limitations can be overcome by the use of certain types of fibrous reinforced composites which have become available over the last few years. However, these materials in turn have their own inherent limitations, particularly in their mode of fracture under overload conditions. In this review the basic properties of conventional fibrous composites are discussed, particular emphasis being given to physics of these failure processes.In an attempt to overcome some of these limitations a new type of fibre reinforced composite has been designed and preliminary research data on the physical properties of these systems has now been obtained. The primary reinforcing elements extend throughout the whole length of the composite but differ from others in that they do not fracture when the composite is subjected to a wide ranged of loading and deformation conditions.These characteristics are achieved because the interface between the primary reinforcing members and the rest of the composite structure is responsive to the local stress carried by the reinforcing members. This stress controlled decoupling/recoupling process is very broadly analogous to the transition between elastic and plastic deformation in metals and the physical principles underlying the design of the reinforcing members are outlined.Because the reinforcing members do not fracture any failure process is confined to the rest of the composite structure. Various interactions occur between the non-fracturing and fracturable parts of the system and these suppress crack growth in the latter, thus producing a structure possessing very considerable damage tolerance. A preliminary analysis of the basic physics of these interactions is given.Possible future developments of these materials are outlined. Also ways are discussed in which the simple analytical models, developed in the study of the fracture processes occuring these materials, amy be applied to more conventional fibrous composites. 相似文献
23.
ADOLFO V. T. CARTAXO JOÃO L. REBOLA NATAŠA B. PAVLOVIĆ PEDRO M. A. CHARRUA DANIEL D. T. FONSECA JOSÉ A. P. MORGADO 《Fiber and Integrated Optics》2013,32(3-4):331-352
Abstract This article introduces the main achievements resulting from the DWDM/ODC project. The five areas of research activity within the DWDM/ODC project cover some of the main issues of design and development of dense wavelength division multiplexing systems for transparent optical networks. These issues are: performance assessment with arbitrary optical filtering; performance of signaling formats; dispersion compensation strategies for directly and externally modulated systems in presence of nonlinear transmission-induced degradation; and the impact of noise and crosstalk in the extent of transparent optical networks. All five areas of research activity have contributed significantly to a better understanding of the limitations present in dense wavelength division multiplexing systems. 相似文献
24.
Background
Scripting languages such as Python are ideally suited to common programming tasks in cheminformatics such as data analysis and parsing information from files. However, for reasons of efficiency, cheminformatics toolkits such as the OpenBabel toolkit are often implemented in compiled languages such as C++. We describe Pybel, a Python module that provides access to the OpenBabel toolkit. 相似文献25.
Benny PD Fugate GA Barden AO Morley JE Silva-Lopez E Twamley B 《Inorganic chemistry》2008,47(7):2240-2242
Reaction of [NEt4]2[ReBr3(CO)3] with 2,4-pentanedione (acac) yields a complex of the type fac-Re(acac)(OH2)(CO)3 (1) under aqueous conditions. 1 was further reacted with a monodentate ligand (pyridine) to yield a fac-Re(acac)(pyridine)(CO)3 complex (2). Complex 1 was found to react with primary amines to generate a Schiff base (imine) in aqueous solutions. When a mixed-nitrogen donor bidentate ligand, 2-(2-aminoethyl)pyridine, that has different coordination affinities for fac-Re(acac)(OH2)(CO)3 was utilized, a unique tridentate ligand was formed in situ utilizing a metal-assisted Schiff base formation to yield a complex fac-Re(CO)3(3[(2-phenylethyl)imino]-2-pentanone) (3). Tridentate ligand formation was found to occur only with the Re-coordinated acac ligand. Reactions of acac with fac-Re(CO)3Br(2-(2-aminoethyl)pyridine) (4) or a mixture of [NEt4]2[ReBr3(CO)3], acac, and 2-(2-aminoethyl)pyridine did not yield the formation of complex 3 in water. 相似文献
26.
27.
Hafiz T.Ali MRamzan M Imran Arshad Nicola A.Morley M.Hassan Abbas Mohammad Yusuf Atta Ur Rehman Khalid Mahmood Adnan Ali Nasir Amin MAjaz-un-Nabi 《中国物理 B》2022,31(2):27502-027502
We investigate the impact of Ni insertion on the structural,optical,and magnetic properties of Ba0.8La0.2Fe12-xNixO19hexaferrites(Ni substituted La-BaM hexaferrites).Samples were prepared using the conventional co-precipitation method and sintered at 1000℃for 4 hours to assist the crystallization process.An analysis of the structure of the samples was carried out using an x-ray diffraction(XRD)spectrometer.The M-type hexagonal structure of all the samples was confirmed using XRD spectra.The lattice parameters a and c were found to be in the ranges of 5.8925±0.001 nm–5.8952±0.001 nm and 23.2123±0.001 nm–23.2219±0.001 nm,respectively.The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra,respectively.EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio.A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm–1100 nm.The optical energy bandgap of the samples was found to be in the range of 1.21 eV–3.39 eV.The M–H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe–60 kOe.A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz.This high value of saturation magnetization is due to the substitution of La3+ions at the spin-up(12k,2a,and 2b)sites.The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites.Therefore,we suggest that the prepared samples are suitable for use in magneto-optic applications. 相似文献
28.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献
29.
Eigenvalues of the Laplacian of a graph 总被引:24,自引:0,他引:24
Let G be a finite undirected graph with no loops or multiple edges. We define the Laplacian matrix of G,Δ(G)by Δij= degree of vertex i and Δij-1 if there is an edge between vertex i and vertex j. In this paper we relate the structure of the graph G to the eigenvalues of A(G): in particular we prove that all the eigenvalues of Δ(G) are non-negative, less than or equal to the number of vertices, and less than or equal to twice the maximum vertex degree. Precise conditions for equality are given. 相似文献
30.
Glawe DD Rodríguez F Stone MO Naik RR 《Langmuir : the ACS journal of surfaces and colloids》2005,21(2):717-720
Herein, we describe the formation of silica structures on indium tin oxide (ITO) surfaces using poly-L-lysine (PLL) to template the condensation of silicic acid. Precisely controlled electrostatic fields were used to preposition PLL onto ITO surfaces. Subsequent polypeptide-mediated silicification resulted in the formation of silica with concentration gradients that followed the pattern of the externally applied electrostatic field used in the deposition of the PLL. The resulting silica structures were securely attached to the ITO surface. The technique described here offers an inexpensive and rapid method for the deposition of polypeptides on surfaces. 相似文献