全文获取类型
收费全文 | 6240篇 |
免费 | 859篇 |
国内免费 | 278篇 |
专业分类
化学 | 2050篇 |
晶体学 | 20篇 |
力学 | 371篇 |
综合类 | 143篇 |
数学 | 2176篇 |
物理学 | 2617篇 |
出版年
2024年 | 23篇 |
2023年 | 96篇 |
2022年 | 288篇 |
2021年 | 325篇 |
2020年 | 171篇 |
2019年 | 142篇 |
2018年 | 134篇 |
2017年 | 207篇 |
2016年 | 251篇 |
2015年 | 172篇 |
2014年 | 316篇 |
2013年 | 510篇 |
2012年 | 376篇 |
2011年 | 339篇 |
2010年 | 383篇 |
2009年 | 412篇 |
2008年 | 412篇 |
2007年 | 442篇 |
2006年 | 309篇 |
2005年 | 273篇 |
2004年 | 232篇 |
2003年 | 254篇 |
2002年 | 173篇 |
2001年 | 150篇 |
2000年 | 131篇 |
1999年 | 117篇 |
1998年 | 118篇 |
1997年 | 113篇 |
1996年 | 109篇 |
1995年 | 74篇 |
1994年 | 56篇 |
1993年 | 59篇 |
1992年 | 45篇 |
1991年 | 28篇 |
1990年 | 23篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有7377条查询结果,搜索用时 656 毫秒
141.
Jorge Casas-Sanchez M. Asuncion Alsina Mathias K. Herrlein Concepció Mestres 《Colloid and polymer science》2007,285(12):1351-1360
Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties
is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol
(PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant
area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts
in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria.
The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers
with the lipids assayed at the air/water interface. 相似文献
142.
Harshad P. Patil Ronald C. Hedden 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):3267-3276
We examine the influence of structural imperfections on mechanical damping in polydomain smectic main-chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan δ = G″(ω)/G′(ω) exhibits a strong maximum (tan δ ≈ 1.0) near the smectic-isotropic (clearing) transition. “Optimal” elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling “imperfect elastomers” that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan δ is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan δ and its temperature dependence are similar for optimal and imperfect elastomers at ω = 1 Hz. The prominent loss peak near the clearing transition arises from segment-level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration-damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3267–3276, 2007 相似文献
143.
Modelling and prediction of retention in high-performance liquid chromatography by using neural networks 总被引:1,自引:0,他引:1
Y. L. Xie J. J. Baeza-Baeza J. R. Torres-Lapasió M. C. García-Alvarez-Coque G. Ramis-Ramos 《Chromatographia》1995,41(5-6):435-444
Summary Multi-layer feed-forward neural networks trained with an error back-propagation algorithm have been used to model retention
behaviour of liquid chromatography as a function of the composition of the mobile phases. Conventional hydro-organic and micellar
mobile phases were considered. Accurate retention modelling and prediction have been achieved using mobile phases defined
by two, three and four parameters. With micellar mobile phases, the parameters involved included the concentrations of surfactant
and organic modifier, pH and temperature. It is shown that neural networks provide a competitive tool to model varied inherent
nonlinear relationships of retention behaviour with respect to the mobile phase parameters. The soft models defined by the
weights of the networks are capable of accommodating all types of linear and nonlinear relationships, neural networks being
specially useful when the relationships between retention behaviour and the mobile phase parameters are unknown. However,
to train neural networks more experimental points than with hard-modelling methods are required, hence the use of the networks
is recommended only for those cases where adequate theoretical or empirical models do not exist. 相似文献
144.
Dr. M. A. Llorente Dr. A. L. Andrady Professor J. E. Mark 《Colloid and polymer science》1981,259(11):1056-1061
Summary Elastomeric networks of high extensibility were prepared by end-linking mixtures of vinyl-terminated polydimethylsiloxane chains having molecular weights of approximately 600 and 11,000 g mol–1, with silanes chosen to give junction functionalities ranging from 3 to 8. The resulting bimodal networks were studied in elongation, at 25 °C, to their rupture points, and in swelling equilibrium in benzene at room temperature. The elongation moduli [f
*] were found to be in satisfactory agreement with previous results obtained by end-linking hydroxyl-terminated polydimethylsiloxane chains. Values of [f
*] at low and moderate deformations gave relatively low values of the ratio of elasticity constants 2C
2/2C
1, which is a measure of the extent to which the elongation changes from approximately affine to nonaffine as the elongation increases. The low values obtained for this ratio are presumably due to diminished interpenetration of configurational domains in the case of very short chains. In spite of its small magnitude, 2C
2/2C
1 does show some decrease with increase in , as predicted by the recent molecular theory of rubberlike elasticity developed by Flory. The swelling equilibrium results were also found to be in satisfactory agreement with theory. The elongation moduli increased significantly at high elongations, and the values of the elongation at which the upturn was first discernible were very nearly independent of , This is consistent with the interpretation of this anomalous behaviour in terms of limited chain extensibility. The maximum extensibility generally decreased somewhat with increase in and this caused a decrease in both the ultimate strength and the toughness of the elastomer, as measured by the energy required for rupture. 相似文献
145.
An artificial neural network (ANN) procedure was used in the development of a catalytic spectrophotometric method for the determination of Cu(II) and Ni(II) employing a stopped-flow injection system. The method is based on the catalytic action of these ions on the reduction of resazurin by sulfide. ANNs trained by back-propagation of errors allowed us to model the systems in a concentration range of 0.5-6 and 1-15 mg l−1 for Cu(II) and Ni(II), respectively, with a low relative error of prediction (REP) for each cation: REPCu(II) = 0.85% and REPNi(II) = 0.79%. The standard deviations of the repeatability (sr) and of the within-laboratory reproducibility (sw) were measured using standard solutions of Cu(II) and Ni(II) equal to 2.75 and 3.5 mg l−1, respectively: sr[Cu(II)] = 0.039 mg l−1, sr[Ni(II)] = 0.044 mg l−1, sw[Ni(II)] = 0.045 mg l−1 and sw[Ni(II)] = 0.050 mg l−1. The ANNs-kinetic method has been applied to the determination of Cu(II) and Ni(II) in electroplating solutions and provided satisfactory results as compared with flame atomic absorption spectrophotometry method. The effect of resazurin, NaOH and Na2S concentrations and the reaction temperature on the analytical sensitivity is discussed. 相似文献
146.
Interpenetrating Polymer Networks (IPNs) based on Poly n-vinyl 2-pyrrolidone (PVP) and Acrylonitrile (AN) were prepared by irradiating PVP solutions prepared in AN. PVP/AN mixtures were irradiated by 60Co-γ rays at room temperature at a dose rate of 0.5 kGy/hour. IPNs were characterized by using FT-IR and Thermal Analysis techniques. The chelating adsorbents containing amidoxime groups were prepared by the reaction of these IPNs with hydroxylamine in aqueous NaOH solution at 50°C. These amidoxime containing adsorbents were used in adsorption studies for the recovery of uranium from aqueous systems. The adsorption capacity of an IPN with equivolume fraction of PVP and amidoximated PAN was found to be 750mg UO22+/g dry amidoximated IPN. 相似文献
147.
148.
R. M. Masegosa M. A. Llorente M. G. Prolongo I. Hernández-Fuentes A. Horta 《Colloid and polymer science》1984,262(11):862-866
Measurements of preferential sorption,(
3), determined by refractometry, and swelling equilibrium,
3
–1, of PMMA networks have been carried out in the cosolvent mixture MeCN+BuOH at 25 and 49 C. With an intermediate mixture composition,
3
–1 passes through a maximum at both temperatures. At 25 C MeCN is preferentially adsorbed by the network over most of the composition range, but a small inversion is detected. At 49 C MeCN is preferentially adsorbed over all the composition range.The behavior of the system crosslinked PMMA/MeCN + BuOH is compared with the results obtained for solutions of linear PMMA in mixtures formed by the same two solvents, MeCN and BuOH. 相似文献
149.
150.
Two groups of polymer networks (polymer resins) are investigated by selective liquid sorption fromn-propanol-water mixtures. Group 1 consists of gel polymerized polar (hydrophilic) ion exchangers which swell in the binary liquid mixture. Group 2 consists of non-polar, non-swelling, macroporous resins. The free energy isotherms accompanying the sorption processes are calculated from the excess isotherms and the bulk activities. The adsorption excess free energies reveal the differences in polarity of the polymer network. 相似文献