全文获取类型
收费全文 | 174篇 |
免费 | 6篇 |
国内免费 | 23篇 |
专业分类
化学 | 83篇 |
晶体学 | 1篇 |
力学 | 46篇 |
综合类 | 4篇 |
数学 | 19篇 |
物理学 | 50篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 23篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
排序方式: 共有203条查询结果,搜索用时 171 毫秒
51.
A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary (GB) and the average tensile stress within A1203 grains caused by SiC nanoparticles. The normal compressive stress strengthens the GB, and the average tensile stress weakens the grains. The model gives a reasonable interpretation of the strength changes of A1203-SiC nanocomposites with the number of SiC particles. 相似文献
52.
A two-dimensional numerical model is used to study the nonlinear behavior of density gradients on transverse dispersion. Numerical
simulations are conducted using d
3
f, a computer code for simulation of density-dependent flow in porous media. Considering a density-stratified horizontal flow
in a heterogeneous porous media, a series of simulations is carried out to examine the effect of the density gradient on macro-scale
transverse dispersivity. Changing salt concentration significantly affects fluid properties. This physical behavior of the
fluid involves a non-linearity in modeling the interaction between salt and fresh water. It is concluded that the large-scale
transport properties for high density flow deviate significantly from the tracer case due to the spatial variation of permeability,
described by statistical parameters, at the local-scale. Indeed, the presence of vertical flow velocities induced by permeability
variations is responsible for the reduction of the mixing zone width in the steady state in the case of a high density gradient.
Uncertainties in the model simulations are studied in terms of discretization errors, boundary conditions, and convergence
of ensemble averaging. With respect to the results, the gravity number appears to be the controlling parameter for dispersive
flux. In addition, the applicability and limitations of the nonlinear model of Hassanizadeh (1990) and Hassanizadeh and Leijnse
(1995) (Adv Water Resour 18(4):203–215, 1995) in heterogeneous porous media are investigated. We found that the main cause
of the nonlinear behavior of dispersion, which is the interaction between density contrast and vertical velocity, needs to
be explicitly accounted for in a macro-scale model. 相似文献
53.
Microalloying additions of Ag (0.1 at.%) increase the hardening response of Al–Zn–Mg alloys to elevated temperature ageing in the range 100–200°C due to the formation of a high density of very fine η′ precipitate plates. The present study employed transmission electron microscopy (TEM) and three-dimension atom probe (3DAP) to study the early stages of ageing in the alloy Al–1.8Zn–3.4Mg–0.1Ag (at.%) in an attempt to identify the role of Ag in stimulating precipitation hardening. During isothermal ageing at 90°C, the hardening response is attributed to a high density of Zn–Mg–Ag rich solute clusters and GP zones. During ageing at 150°C, η′ precipitates nucleate at Zn–Mg–Ag rich solute clusters, the former growing as {111} platelets with an average composition of approximately 20 at.% Zn, 20 at.% Mg and 1.4 at.% Ag. The 3DAP data indicates that the co-segregation of Zn and Ag and subsequently Zn and Mg atoms precedes the formation of the Zn–Mg–Ag rich solute clusters. The GP zones and η′ precipitates were observed to possess a Zn:Mg ratio close to 1:1, whereas the equilibrium η precipitates possessed compositions consistent with MgZn2. Furthermore, partitioning of Ag was observed inside all precipitate phases, viz. G.P. zones, η′ and η. 相似文献
54.
新型橡塑助剂NRF901补强性能的研究 总被引:2,自引:0,他引:2
研究了以廉价的烟煤 ,煤矸石为原料加工而成的橡塑补强助剂NRF90 1的性能。其化学、物理和机械性能优于常用的补强炭黑N770 ,补强性能接近于高耐磨炭黑N330 ,是代替炭黑的新型助剂。 相似文献
55.
56.
In this study, densified wood was prepared by hot pressing after partial lignin and hemicellulose were removed through alkaline solution cooking. The tensile strength and elastic modulus of densified wood were improved up to 398.5 MPa and 22.5 GPa as compared with the original wood, and the characterization of its supramolecular structures showed that the crystal plane spacing of the densified wood decreased, the crystallite size increased, and the maximum crystallinity (CI) of cellulose increased by 15.05%; outstandingly, the content of O(6)H⋯O(3′) intermolecular H-bonds increased by approximately one-fold at most. It was found that the intermolecular H-bond content was significantly positively correlated with the tensile strength and elastic modulus, and accordingly, their Pearson correlation coefficients were 0.952 (p < 0.01) and 0.822 (p < 0.05), respectively. This work provides a supramolecular explanation for the enhancement of tensile strength of densified wood. 相似文献
57.
Wenbo Li Wenyao Zhang Fang Qian Deng Huang Qiuwang Wang Cunlu Zhao 《Electrophoresis》2021,42(3):257-268
This paper utilizes a combined approach of the convection-diffusion theory and the moment analysis to conduct a comprehensive investigation of the solute dispersion under the influence of the interphase transport in finitely long inner coated microchannels. The present work has threefold novel contributions: (1) The 2D solute concentration contours in the stationary phase are calculated for the first time to facilitate the understanding the role of the interphase transport in the solute dispersion in the mobile phase. (2) The skewness of the elution curves is investigated to guide the control of solute band shape at the channel outlet. (3) The 2D diffusion-convection theory and zero-dimensional (0D) moment analysis complement each other to present a characterization of the solute dispersion behaviors more comprehensive than that by either of the two methods alone. Parametric studies are performed to clarify the effects of four major parameters related to the interphase transport (i.e., stationary phase Péclet number, interphase transport rate, partition coefficient, and stationary phase thickness) on the solute dispersion characteristics. The results from this study provide a straightforward understanding of the effects of interphase transport on the solute dispersion in finitely long microchannels and are of potential relevance to the design and operation of the microfluidics-based analytical devices. 相似文献
58.
David L. Olmsted Louis G. Hector Jr. 《Journal of the mechanics and physics of solids》2006,54(8):1763-1788
The strengthening of Al by Mg solute atoms is investigated using molecular dynamics (MD) studies of single dislocations moving through a field of randomly placed solutes. The MD method permits explicit treatment of “core” effects, dislocation pinning and deceleration, and dislocation unpinning by thermal activation, all under an applied load. Choice of an appropriate MD simulation cell size is assessed using analytic concepts developed by Labusch. The interaction energy of a single Mg atom with straight edge and screw dislocations is computed and compared with continuum models. Using the single Mg energies, a one-dimensional energy landscape for the motion of a straight edge dislocation through a random field of Mg solutes is computed. The minima in this landscape match well with those found in the MD simulations at zero temperature. The stress to unpin a straight edge dislocation trapped in a local energy minimum generated by the solutes is then predicted semi-analytically using the energy landscape, and good agreement is obtained with the MD results. At temperatures of 300 and 500 K, the thermally activated rate of unpinning vs. stress and temperature is calculated semi-analytically, and agreement with the full MD results is again obtained with the fitting of a single attempt frequency in a transition state model. The agreement of the semi-analytical models provides a basis for calculating yield stress vs. strain rate and temperature, resulting from statistical pinning, for the case of non-interacting dislocations on a single slip system, and for extending the analysis to study dynamic strain aging effects resulting from diffusion of Mg atoms around a pinned dislocation. 相似文献
59.
One of the greatest challenges in structural engineering nowadays is the strengthening, upgrading, and retrofitting of existing
structures. The use of fibre-reinforced polymers (FRPs) bonded to the tension face of a structural member is an attractive
technique in this field of application. The strengthening of reinforced concrete structures by means of an externally bonded
reinforcement (EBR) is achieved by gluing a FRP laminate to the concrete substrate. For an efficient utilization of the FRP
EBR systems, an effective stress transfer is required between the FRP and concrete. The paper discusses the bond behaviour
between a FRP and concrete in the case of flexural strengthening of continuous beams. With respect to this type of beams,
only a few studies have been reported, though continuous members often occur in concrete constructions. The structural behaviour
of statically indeterminate elements is typically characterized by redistributions of the internal forces. These distributions
are related to the nonlinear deformations of the beams and has also a distinct influence on the bond behaviour between the
FRP and concrete.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 389–402, May–June, 2008. 相似文献
60.