全文获取类型
收费全文 | 450篇 |
免费 | 10篇 |
国内免费 | 10篇 |
专业分类
化学 | 136篇 |
晶体学 | 2篇 |
力学 | 110篇 |
综合类 | 2篇 |
数学 | 26篇 |
物理学 | 194篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 22篇 |
2012年 | 11篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 28篇 |
2008年 | 30篇 |
2007年 | 36篇 |
2006年 | 29篇 |
2005年 | 19篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 22篇 |
2000年 | 12篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有470条查询结果,搜索用时 730 毫秒
91.
Aqueous suspensions of silicon dioxide porous nanoparticles (average size 10–30 nm, average pore size 5.8 nm) were obtained via ultrasonic dispersing. As was shown through recording SiO molecular lines in a moving single-bubble sonoluminescence spectrum, these nanoparticles penetrate into the bubble and then undergo decay. Similarly, suspensions of SiO2 nanoparticles, the pores of which were saturated with ruthenium dodecacarbonyl or elemental sulfur, were obtained by impregnation of the initial powder with solutions of these reagents in chloroform followed by evaporation of the solvent. Single-bubble sonoluminescence spectra of these suspensions contain more intense lines of Ru or S and Sn+ as compared with the SiO lines. This also proves the involvement of water insoluble ruthenium and sulfur compounds into bubble sonoluminescent reactions in the heterogenic aqueous medium. Using the method of comparing the experimentally obtained and computer simulated luminescent spectra, we determined the effective electronic temperature TeRu, which was 9000 ± 500 K, in non-equilibrium plasma of a bubble levitating in the ultrasonic field. 相似文献
92.
Katarzyna Kaahurska Pawel P. Ziemiaski Wieslaw J. Roth Barbara Gil 《Molecules (Basel, Switzerland)》2021,26(7)
We investigated the properties and catalytic activity of zeolites with MWW topology obtained by unprecedented liquid exfoliation of the MCM-56 zeolite into solutions of monolayers and isolation/reassembly of the dispersed layers by various methods, with optional purification by dialysis or ammonium exchange. The layers were recovered by flocculation with alcohol or ammonium nitrate and freeze-drying. Flocculation alone, even with ammonium nitrate, did not ensure removal of residual sodium cations resulting in catalysts with low activity. Dialysis of the solutions with dispersed monolayers proved to be efficient in removing sodium cations and preserving microporosity. The monolayers were also isolated as solids by freeze-drying. The highest BET area and pore volume obtained with the freeze-dried sample confirmed lyophilization efficiency in preserving layer structure. The applied test reaction, Friedel–Crafts alkylation of mesitylene, showed high benzyl alcohol conversion due to increased concentration of accessible acid centers caused by the presence of secondary mesoporosity. The applied treatments did not change the acid strength of the external acid sites, which are the most important ones for converting bulky organic molecules. Zeolite acidity was not degraded in the course of exfoliation into monolayers, showing the potential of such colloid dispersions for the formation of active catalysts. 相似文献
93.
Gerald G. Fuller Kaye Smith Wesley R. Burghardt 《Journal of statistical physics》1991,62(5-6):1025-1039
This paper presents experimental results on the use of spectroscopic optical polarimetry to study structure in dense systems of rigid particles and rigid polymer liquid crystals. These measurements probe microstructural anisotropy induced by the application of electric fields in the case of dense suspensions of rigid spheres, or flow fields in the case of polymer liquid crystals. It is demonstrated that conservative linear dichroism can measure moments of the particle pair distribution function in dense suspensions. In liquid crystals, the dichroism is a result of field-induced anisotropy in the defect structure of the material. 相似文献
94.
Hendryk Pfeiffer 《Annals of Physics》2003,308(2):447-477
In conventional gauge theory, a charged point particle is described by a representation of the gauge group. If we propagate the particle along some path, the parallel transport of the gauge connection acts on this representation. The Lagrangian density of the gauge field depends on the curvature of the connection which can be calculated from the holonomy around (infinitesimal) loops. For Abelian symmetry groups, say G=U(1), there exists a generalization, known as p-form electrodynamics, in which (p−1)-dimensional charged objects can be propagated along p-surfaces and in which the Lagrangian depends on a generalized curvature associated with (infinitesimal) closed p-surfaces. In this article, we use Lie 2-groups and ideas from higher category theory in order to formulate a discrete gauge theory which generalizes these models at the level p=2 to possibly non-Abelian symmetry groups. An important feature of our model is that it involves both parallel transports along paths and generalized transports along surfaces with a non-trivial interplay of these two types of variables. Our main result is the geometric picture, namely the assignment of non-Abelian quantities to geometrical objects in a coordinate free way. We construct the precise assignment of variables to the curves and surfaces, the generalized local symmetries and gauge invariant actions and we clarify which structures can be non-Abelian and which others are always Abelian. A discrete version of connections on non-Abelian gerbes is a special case of our construction. Even though the motivation sketched so far suggests applications mainly in string theory, the model presented here is also related to spin foam models of quantum gravity and may in addition provide some insight into the role of centre monopoles and vortices in lattice QCD. 相似文献
95.
Baptiste Mary Charles Dubois Pierre J. Carreau Patrick Brousseau 《Rheologica Acta》2006,45(5):561-573
Ultrafine aluminum powder was identified as very promising fuels for novel energetic materials formulations. However, the large specific surface area of this powder facilitates its oxidation and greatly reduces its shelf life. Therefore, different coating processes were proposed to solve this problem. The rheology of viscous suspensions of nanoparticles still remains poorly understood and the effect of the coating of such particles on the flow behavior is even more difficult to assess. We have studied the rheology of ultrafine aluminum suspensions in three low molecular weight polymers of different viscosities: a hydroxy-terminated polybutadiene, a polypropylene glycol, and a polysiloxane. The nanosize aluminum powder was previously coated by a thin layer of high-density polyethylene using an in situ polymerization process. The rheological characterization of the suspensions was conducted by the means of steady and oscillatory shear flow measurements for noncoated and coated particles. The effect of the coating process on the rheology of the suspensions is discussed in terms of the interactions between the particles and the suspending fluids. 相似文献
96.
This paper reviews current fibre laser technology and new directions that will improve their performances. Grating technology and the ability to provide high power operation has driven their maturity and growing commercialisation. The range of applications they are being used is reviewed, providing a platform for researchers and technologists to determine how such fibre lasers may benefit their work. 相似文献
97.
F. Abdullah B. Bouzid M. A. Mahdi C. L. Cheah M. Z. Jamaludin M. K. Abdullah 《Optics & Laser Technology》2004,36(3):1793-190
This paper reports the design of a dual wavelength fibre laser system using a dumbbell shaped configuration. The oscillation of the lasing wavelength is completed via fibre loop mirrors with a tuneable bandpass filter. The output power, side mode suppression ratio and wavelength spacing of the lasers were investigated against the pump power for forward and backward pumping schemes. The output powers of 4.99 and 3.69 dBm at 1545.08 and 1547.28 nm, respectively, for forward pumping scheme. On contrary, the output powers of 1.93 and 2.14 dBm at 1546.12 and 1551.48 nm, respectively, for backward pumping scheme. The peak output powers of less than 1 dB difference are obtained without any adjustment of the intra-cavity loss over a wider spectral range. 相似文献
98.
Xiaoli Wang Lucun Guo 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,324(1-3):126-130
The role of tetramethyl ammonium hydroxide (TMAH) in determining the rheological properties of aqueous zirconia suspensions containing polyacrylate (PANH4) was investigated. At acidic pH, the addition of TMAH after PANH4 could result in a much higher stability in zirconia slurries than that with only polymer as dispersant. While in alkaline media, it was more easily realized to lower yield stress of suspensions by adding TMAH before PANH4. Moreover, the both TMAH and PANH4 contained systems were found to need the less polyacrylate for obtaining complete dispersion than those stabilized with PANH4 alone. 相似文献
99.
Realisation of an effective dual-parameter sensor employing a single fibre Bragg grating structure 总被引:1,自引:0,他引:1
A novel technology for simultaneous and independent measurement of dual parameters is proposed and experimented. The length of a single fibre Bragg grating (FBG) is divided into two parts. The temperature variation and another measurand can be measured independently and simultaneously, and the thermal effect can be erased with great ease. 相似文献
100.
F.R. Molino J.-F. Berret G. Porte O. Diat P. Lindner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):59-72
We study the behavior under flow of soft spherical micelles forming a fcc phase at high volume fraction. Due to the size (300 ?) of the elementary objects, the structure can be investigated through
X-rays and neutron scattering, at rest and under flow in a Couette cell. Using scattering in two perpendicular directions,
different mechanisms of flow are identified. At intermediate shear (around 100 s-1) the system exhibits the so called layer sliding mechanism where two dimensional hexagonal compact planes of spheres align
themselves with the Couette cell walls. At lower shear rate, the fcc structure is locally preserved, and the flow is mediated by defects between crystallites. At high shear rate, we observe
the melting of the structure and a liquid-like structure factor. Moreover, we were able to use the existence of the layer
sliding regime to generate a fcc monocrystal by annealing the satcking faults between the decorrelated planes created by the layer sliding.
Received: 7 July 1997 / Received in final form: 16 January 1998 / Accepted: 5 March 1998 相似文献