全文获取类型
收费全文 | 8571篇 |
免费 | 1016篇 |
国内免费 | 513篇 |
专业分类
化学 | 2363篇 |
晶体学 | 72篇 |
力学 | 910篇 |
综合类 | 41篇 |
数学 | 2663篇 |
物理学 | 2802篇 |
无线电 | 1249篇 |
出版年
2024年 | 22篇 |
2023年 | 120篇 |
2022年 | 150篇 |
2021年 | 208篇 |
2020年 | 274篇 |
2019年 | 261篇 |
2018年 | 217篇 |
2017年 | 250篇 |
2016年 | 305篇 |
2015年 | 238篇 |
2014年 | 362篇 |
2013年 | 778篇 |
2012年 | 382篇 |
2011年 | 431篇 |
2010年 | 354篇 |
2009年 | 453篇 |
2008年 | 501篇 |
2007年 | 528篇 |
2006年 | 457篇 |
2005年 | 411篇 |
2004年 | 423篇 |
2003年 | 352篇 |
2002年 | 328篇 |
2001年 | 299篇 |
2000年 | 265篇 |
1999年 | 234篇 |
1998年 | 201篇 |
1997年 | 204篇 |
1996年 | 135篇 |
1995年 | 124篇 |
1994年 | 124篇 |
1993年 | 101篇 |
1992年 | 83篇 |
1991年 | 95篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 40篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 44篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 32篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1974年 | 5篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
131.
Taking soil colloid and hydrated silica (quartz sand) as the experimental material, the comparative study has been made on the kinetics of ion diffusion and ion exchange in charged colloid and charged coarse disperse systems. The results showed that ion exchange kinetics in the two systems conform to the kinetic law of ion diffusion. Besides, through this comparative study on the kinetics of ion exchange and ion diffusion, a method has been advanced theoretically to estimate the quantity of adsorbed ion that is located in the inner of the Helmholtz layer. As far as hydrated silica is concerned , there were about 33 per cent of the total adsorbed quantity of Mg2+that were located in the inner of the Helmholtz layer under the given experimental conditions, bu tfor soil colloid the percentage was only 7.5. 相似文献
132.
The concentration fields, Nusselt number distributions along the electrode, and ratios of concentrations of electrochemically active components at the entrance into and exit out of an electrochemical cell are determined by numerical integration of the convective-diffusion equation for a broad range of rate constants of electrode reactions, Peclet numbers, and geometrical parameters of channels. Three regions of parameter values are revealed. At low reaction rates (K
l
< 0.5), mass transfer is completely determined by electrode kinetics; at high rates (K
l
> 20), it is completely determined by the diffusion in the gas phase; and in the intermediate region of values of K
l
it is necessary to allow for both the diffusion processes and the electrode reactions.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 317–324.Original Russian Text Copyright © 2005 by Ezin, Somov. 相似文献
133.
A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH+ + Cl- Gly + H+ + Cl-. Diffusion in this system is, therefore, a ternary process described by the equations J
1(GlyHCl) = – D
11C
1 – D
12C
2 and J
2(HCl) = –D
21C
1 – D
22C
2 for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D
21/D
11 of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl– counterions, the main diffusion coefficient of glycine hydrochloride, D
11, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids. 相似文献
134.
Yossef A. Elabd Marco Giacinti Baschetti Timothy A. Barbari 《Journal of Polymer Science.Polymer Physics》2003,41(22):2794-2807
Over the past 2 decades, the use of time‐resolved Fourier transform infrared/attenuated total reflection (ATR) spectroscopy for the measurement of diffusion in polymers has grown. ATR is a powerful technique for the measurement of diffusion in polymers because it is an in situ technique that is relatively inexpensive, provides reliable short‐time data, and provides a wealth of information at the molecular level. This article highlights the technique and its application to numerous studies, ranging from the diffusion of drugs in human skin to chemical warfare agents in barrier materials. In addition to these topics, recent studies with ATR to quantify and model molecular interactions during the diffusion process are reviewed. In the future, the ATR technique may have an impact on a variety of emerging fields in which diffusion in polymers plays an important role, such as fuel cells, membrane separation, sensors, and drug delivery. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2794–2807, 2003 相似文献
135.
This paper presents a mathematical model of a potentiometric biosensor based on a potentiometric electrode covered with an
enzyme membrane. The model is based on the reaction–diffusion equations containing a non-linear term related to theMichaelis–Menten
kinetics of the enzymatic reaction. Using computer simulation the influence of the thickness of the enzyme membrane on the
biosensor response was investigated. The digital simulation was performed using the finite difference technique. Results of
the numerical simulation were compared with known analytical solutions.
相似文献
136.
In this paper, the chronoamperometry was used to study the charging processes of polyethylenedioxythiophene (PEDOT) modified electrodes in the potential range where PEDOT was in the oxidized state. The results show that the charging behaviors of the PEDOT films are well agreed with the exhausted finite diffusion model. The dependence of the capacitance values of the films on potential and concentration of solution was also studied in this potential range. 相似文献
137.
Using well-cycled, thin composite graphite electrodes we analyze carefully the limitations of potentiostatic and galvanostatic intermittent titration techniques (PITT and GITT, respectively) for determination of the differential (incremental) intercalation capacitance, Cdif, and the chemical diffusion coefficient, D, of Li ions in these ion-insertion electrodes (IIEs). We demonstrate the superiority of the GITT over PITT to determine these quantities as the former technique allows for a more accurate determination of Cdif and hence D which closely approach to the spinodal domain related to the first-order phase transition during ion-insertion. We show that GITT is also more effective in eliminating the parasitic contributions of background currents to the total measured response. A pronounced difference in the initial, intrinsic kinetics of formation of a new phase in the bulk of the old one has been observed depending on the direction of titration (phases less saturated with Li are formed faster during deintercalation than the Li-rich phases in the course of intercalation). 相似文献
138.
A model is developed to express the solute diffusion coefficient through semicrystalline polymeric networks. The crystallites create impermeable diffusional barriers around the amorphous regions. Solute diffusion is determined by applying a transport model to the amorphous phase and incorporating the crosslinked polymer structure characteristics. This model is tested with theophylline and vitamin B12 permeation experiments through semicrystalline poly(vinyl alcohol) membranes prepared by annealing of amorphous PVA membranes. The degree of crystallinity varies between 23.1 % and 40.5 % on a dry basis. The solute diffusion coefficients correlate well with various parameters of the model. 相似文献
139.
The diffusion length of charge carriers in the active layer of a perovskite solar cell (PSC) of the structure Glass/PEDOT: PSS/CH3NH3PbI3/PC60BM/Al is modelled. It is found that the diffusion length depends on the position x in the active layer measured from the PEDOT: PSS interface, Urbach energy and temperature. By varying the voltage in the range from zero to , it is shown that the dependence of diffusion length on the position x in the active layer reduces at higher voltage. The combined influence of applied voltage and temperature on the diffusion length of charge carriers is investigated and it is found that in the low voltage range the diffusion length is temperature independent, but it becomes significantly temperature dependent at higher voltages. Also, it is found that the diffusion length decreases as the applied voltage increases and this reduction becomes much more significant at higher voltage and temperatures. The combined influence of applied voltage and Urbach energy on diffusion length of charge carriers reveals that the diffusion length decreases when both the applied voltage and Urbach energy increase. However, the reduction in the diffusion length due to the increase in Urbach energy becomes less significant at higher voltage. 相似文献
140.
Takao Masuda 《Catalysis Surveys from Asia》2003,7(2-3):133-144
The diffusion mechanisms within zeolite catalysts, such as resistance to diffusion at pore mouths, configurational diffusion, adsorption-controlled diffusion, influence of co-existing molecules and pore blocking, were overviewed. Two kinds of diffusivities, the intracrystalline diffusivity and the effective diffusivity, were discussed separately to clarify the diffusion mechanism. 相似文献