全文获取类型
收费全文 | 17401篇 |
免费 | 3672篇 |
国内免费 | 2829篇 |
专业分类
化学 | 13177篇 |
晶体学 | 298篇 |
力学 | 1777篇 |
综合类 | 180篇 |
数学 | 1437篇 |
物理学 | 7033篇 |
出版年
2024年 | 23篇 |
2023年 | 255篇 |
2022年 | 461篇 |
2021年 | 652篇 |
2020年 | 933篇 |
2019年 | 697篇 |
2018年 | 675篇 |
2017年 | 699篇 |
2016年 | 935篇 |
2015年 | 842篇 |
2014年 | 1123篇 |
2013年 | 1793篇 |
2012年 | 1241篇 |
2011年 | 1206篇 |
2010年 | 966篇 |
2009年 | 1053篇 |
2008年 | 1110篇 |
2007年 | 1179篇 |
2006年 | 1037篇 |
2005年 | 902篇 |
2004年 | 804篇 |
2003年 | 762篇 |
2002年 | 568篇 |
2001年 | 526篇 |
2000年 | 530篇 |
1999年 | 404篇 |
1998年 | 411篇 |
1997年 | 321篇 |
1996年 | 265篇 |
1995年 | 272篇 |
1994年 | 245篇 |
1993年 | 187篇 |
1992年 | 182篇 |
1991年 | 117篇 |
1990年 | 91篇 |
1989年 | 83篇 |
1988年 | 74篇 |
1987年 | 47篇 |
1986年 | 53篇 |
1985年 | 34篇 |
1984年 | 34篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1973年 | 6篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
971.
Xiaoyan Liu Karen L. Feilberg Wei Yan Erling H. Stenby 《Journal of Dispersion Science and Technology》2013,34(11):1611-1617
AbstractIn this study, the atomic force microscopy colloidal probe technique was employed to investigate the interaction between apolar, basic and acidic model oil probes and a calcite surface in solutions containing different concentrations of NaCl, CaCl2 and Na2SO4. In the presence of SO42?, hydration and structural forces were observed between apolar model oil probes and a calcite surface on approach. Relatively low adhesion forces were observed between the basic model oil probes and the calcite surface, while higher adhesion forces were observed between the acidic model oil probes and the calcite surface. Furthermore, the adhesion forces between the basic model oil probes and the calcite surface significantly increased in the presence of SO42?, while the adhesion force between the acidic model oil probes and the calcite surface decreased in the presence of Ca2+ or SO42?. The differences in the adhesion forces are related to electrostatic attraction and ion bridging forces between the model oil probes and the calcite surface. 相似文献
972.
The interactions between oppositely charged surfactant-polymer systems have been studied using surface tension and conductivity measurements and the dependence of aggregation phenomenon over the polyelectrolyte concentration and chain length of cationic ATAB surfactants, cetyltrimethyl ammonium bromide (CTAB), tetradecyltrimethyl ammonium bromide (TTAB), and dodecyltrimethyl ammonium bromide (DTAB) have been investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolyte at critical aggregation concentration (cac). The cac values of ATAB surfactants in the presence of anionic polyelectrolyte, sodium carboxy methyl cellulose (NaCMC), are considerably lower than their critical micelle concentration (cmc). After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in polyelectrolyte aqueous solution than in pure water. Among the cationic surfactants (i.e., CTAB, TTAB, and DTAB), DTAB was found to have least interaction with NaCMC. Surfactants with longer tail size strongly favor the interaction, indicating the dependence of aggregation phenomenon on the structure, morphology, and tail length of the surfactant. 相似文献
973.
Mohamed Nedjhioui Jean Paul Canselier Aicha Bensmaili 《Journal of Dispersion Science and Technology》2013,34(9):1333-1341
Aqueous solutions containing sodium dodecyl sulphate, xanthan gum, and salt were characterized by ionic conductivity, viscosity, and surface tension methods. A preliminary experimental study was performed to evaluate the effect of the mixture compositions on the surface behavior of the mixed polymer/surfactant systems under different solution conditions. An experimental design using response surface method (RSM) was then applied to assess factors interactions and empirical models regarding the physicochemical responses variables (i.e., conductivity, surface tension and viscosity). The main effects of the three independent factors: SDS concentration (x1), NaCl concentration (x2) and xanthan concentration (x3) were determined using in particular a D-optimal design. The results show an important effect of the factors on responses; they also indicate that the synergetic action of surfactant, electrolyte and biopolymer greatly influences these properties. Analysis of variance (ANOVA) showed high variance coefficient (R 2 ) values, thus, ensuring a satisfactory adjustment of the second-order regression model with the experimental data. 相似文献
974.
Madhumanchi Sreenu Rati Ranjan Nayak Yedla Poornachandra C. Ganesh Kumar 《Journal of Dispersion Science and Technology》2013,34(6):765-771
Synthesized sodium N-pamitoyl amino acids were evaluated for surface and antimicrobial properties and compared with sodium lauryl sulfate (SLS). Emulsion stability of the amino acid surfactants and calcium tolerance of the sodium N-palmitoyl isoleucine were better as compared to SLS. Wetting ability and foaming properties of the palmitic acid-based surfactants were inferior to SLS. N-Acyl amino acids exhibited better antibacterial activity compared to sodium salts of N-acyl amino acids and standard compounds against Staphylococcus aureus MLS-16 and Bacillus subtilis. These studies revealed that the palmitoyl amino acid surfactants can be exploited in household, skin care formulations, and industrial applications. 相似文献
975.
The dynamic surface elasticity of the solution of carboxymethylchitosan (CMCH) and cetyltrimethylammonium bromide (C16TAB) was measured as a function of the surfactant concentration and the surface age by the oscillating drop method. The results showed that the surface layer of the CMCH/C16TAB solution transformed from loose to structured with the increase in the surfactant concentration. The surface elasticity versus the surface pressure curve during the adsorption showed different features at different surfactant concentration ranges, which was connected with the structural transformation of the surface layer. Our results show that the measurement of dynamic surface dilational properties is a powerful tool for studying the surface kinetics, which is helpful for dealing non-equilibrium systems in industry. 相似文献
976.
Different experimental methods including ellipsometry, zeta potential measurements, imbibition studies, and contact angle measurements were used to study the mechanism and influencing factors of wettability alteration of water-wet sandstone surface caused by CTAB (hexadecyl trimethyl ammonium bromide). Results show that when the concentration of CTAB reaches a certain level (below CMC), due to the electrostatic attraction between the positively charged head groups of CTAB and the negatively charged sandstone surface, the monolayer of CTAB is formed and hydrophobic chains of CTAB molecules are toward the aqueous phase, making the solid surface oil-wet. When the concentration of CTAB continues to increase (above CMC), due to the hydrophobic interaction, the compact bilayer of CTAB is formed and hydrophilic head groups of CTAB molecules are toward the aqueous phase, rendering the solid surface water-wet. The contact angles between the oil–water interface and the surface treated with CTAB increase with the increase of the concentration of NaCl and CaCl2. Compared to NaCl, the inorganic salt CaCl2 has a greater impact on the contact angle. In addition, the contact angles increase with the increase of temperature and decrease with the increase of pH value of the aqueous solution. 相似文献
977.
Milindkumar S. Kalekar 《Journal of Dispersion Science and Technology》2013,34(7):1027-1034
Adsorption of various surfactants at the gas liquid interface is studied with equilibrium and dynamic surface tension measurements. The Wilhelmey plate method and maximum bubble pressure method are used for this study. Dynamic surface tension of solutions of different surfactants, sodium lauryl sulfate (SLS), polyoxyethylene glycol 4‐tert‐octyl phenyl ether (Triton X 100), poly‐oxyethylene(20) cetyl ether (Brij 58), and tetraethylene glycol mono‐n‐dodecyl ether (Brij 30), is measured at different concentrations. Adsorption of different surfactants is compared on the basis of equilibrium and dynamic behavior. Effectiveness and efficiency of different surfactants is found from equilibrium surface tension measurement. A new parameter is defined to quantify the dynamic behavior of adsorption, which gives the concentration of surfactant needed to reduce surface tension to half of its maximum reduction within a defined time available for adsorption. The dynamics of surfactant solution is quantified by using this parameter. 相似文献
978.
The morphology of different ratio K/V catalysts supported on porous α‐alumina substrate was investigated by atomic force microscopy (AFM). Changes in the particle size distribution, pore size distribution were analyzed respectively using AFM software. In addition, their catalytic activities and compositions for carbon oxidation were studied by x‐ray diffraction (XRD), differential scanning calorimetry (DSC), and temperature‐programmed reactions (TPR). As a result, with the increase of K concentration, the mean particle size gradually increased and the mean pore size decreased. According to the catalytic activity studies, the catalytic activity of the KVO3 and K3V5O14 phases are more effective than KCl. 相似文献
979.
Andrew M. Bodratti Jiahui Wu Ruksana Jahan Biswajit Sarkar Marina Tsianou 《Journal of Dispersion Science and Technology》2013,34(12):1806-1815
Colloidal stabilization of nanoparticle dispersions is central to applications including coatings, mineral extraction, and dispersion of oil spills in oceanic environments, which often involves oil-mineral-aggregates (OMAs). We have an ongoing interest in the modulation of amphiphile micellization and adsorption behavior in aqueous colloidal dispersions in the presence of various additives. Here we evaluate the effect of added salts CaCl2, MgCl2, and NaCl on the micellization and adsorption behavior of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer Pluronic P105 (EO37PO56EO37). In 0.10 wt% silica nanoparticle (10.6 nm average diameter) dispersion, adsorbed block copolymer layer formation begins at a critical surface micelle concentration (csmc) of 0.02 wt%, well below the critical micellization concentration of Pluronic P105 in water. Dye solubilization experiments demonstrate an increase in the csmc upon addition of each salt. Each added salt reaches a level of maximum effectiveness in its ability to disfavor Pluronic P105 adsorption at the silica surface. These peak levels occur at concentrations of 0.005, 0.03, and 0.05 M for CaCl2, MgCl2, and NaCl, respectively, in the presence of 0.10 wt% silica nanoparticles. We explain these results in the context of an electrostatic displacer mechanism and discuss possible connections to OMA-dispersant formation. 相似文献
980.
Interaction of sodium dodecyl sulfate (SDS) with the cationic polyelectrolyte poly(ethyleneimine) (PEI) was investigated in this study. Turbidity measurements were performed in order to analyze the interaction and complex formation in bulk solution as a function of polymer concentration and pH. Surface tension measurements were made to investigate the properties of SDS/PEI/water mixtures at air/solution interface. Results revealed that SDS/PEI complexes form in solution depending on the surfactant and polymer concentration. A decrease was observed in surface tension values in the presence of SDS/PEI mixtures compared to the values of pure SDS solutions. Both solution and interfacial properties exhibited pH dependent behavior. A shift was seen in the critical micelle concentration of SDS solutions as a function of PEI concentration and solution pH. Monovalent and divalent salt additions showed some influence on the interfacial properties of SDS solutions in the presence of PEI. 相似文献