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101.
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
102.
C.?Buron C.?Filiatre F.?Membrey A.?FoissyEmail author J.?F.?Argillier 《Colloid and polymer science》2004,282(5):446-453
The interaction between sodium dodecyl sulphate (SDS) and gelatin was studied at pH 4.5 and 6.5 where the gelatin is positively charged (i.e.p. 8). At pH 4.5 a SDS/gelatin concentration range was found where gelatin precipitates. At pH 6.5 the SDS-gelatin complex remains soluble although three SDS concentration domains were distinguished where the SDS-gelatin complex had very different affinities for the solvent. Below C1 the complex was highly surface active but other measurements (viscosity, potentiometry, protons uptake) did not reveal any particular consequence of binding. Between C1 and C2 the molecular size decreased (viscosity lowering) upon charge neutralization and collapse about small SDS aggregates (17 SDS molecules per gelatin molecule). Above C2 a cooperative binding mechanism lead to the formation of SDS aggregates; the complex stretched out and turned strongly hydrophilic (the viscosity increases, low surface activity). At saturation one gelatin molecule bound about 200 SDS molecules. Above the overlap concentration (about 3 wt%) SDS aggregates formed between several gelatin molecules, the viscosity increased continuously with SDS concentration and the binding ratio was lower than in dilute gelatin solutions. A very good correspondence was found between the different analytical data including turbidity, viscosity, surface tension, protons uptake and direct potentiometric SDS binding measurements. 相似文献
103.
钾镁氯化物(硫酸盐)与脲、水体系的溶度研究 总被引:7,自引:0,他引:7
报导了KCl-MgCl2-CO(NH2)2-H2O和K2SO4-MgSO4-CO(NH2)2-H2O两个四元体系在25℃时的溶度及其饱和溶液的折光率、密度,相应的溶度图和组成-折光率、组成-密度图.前一体系中形成3个三元化合物:MgCl2·4CO(NH2)2·2H2O、MgCl2·CO(NH2)2·4H2O和KCl·MgCl2·6H2O溶度盐份图由9支共饱线、4个四元无变点组成.四元体系的水量图、性质-组成图有类似的变化.后一体系中有2个异成份溶解化合物MgSO4·CO(NH2)2·2H2O和K2SO4·MgSO4·6H2O形成,溶度等温图由7支双饱溶度线、3个四元无变点组成.对两个体系相图的相似性和差异点进行了讨论. 相似文献
104.
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
105.
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
106.
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
107.
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
108.
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
109.
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
110.
Jörg Kärger 《Adsorption》2003,9(1):29-35
A review is given on the main problems associated with the determination and interpretation of molecular diffusion in zeolites. It is shown that the diffusivities may most decisively depend on the relevant space and time scales of observation, as well as on the physical state under which the measurements are carried out. Special emphasis is given to the microscopic techniques and their most recent evidence on the existence of transport resistances distributed over the intracrystalline space. 相似文献