全文获取类型
收费全文 | 1684篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
化学 | 1101篇 |
晶体学 | 11篇 |
力学 | 24篇 |
数学 | 305篇 |
物理学 | 268篇 |
出版年
2022年 | 20篇 |
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 19篇 |
2017年 | 27篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 36篇 |
2013年 | 85篇 |
2012年 | 84篇 |
2011年 | 78篇 |
2010年 | 51篇 |
2009年 | 56篇 |
2008年 | 112篇 |
2007年 | 90篇 |
2006年 | 81篇 |
2005年 | 72篇 |
2004年 | 68篇 |
2003年 | 46篇 |
2002年 | 55篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1997年 | 12篇 |
1996年 | 26篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 30篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 19篇 |
1978年 | 28篇 |
1977年 | 18篇 |
1976年 | 21篇 |
1974年 | 15篇 |
1973年 | 30篇 |
1972年 | 13篇 |
1971年 | 12篇 |
排序方式: 共有1709条查询结果,搜索用时 15 毫秒
91.
Celecoxib belongs to a new NSAID family specifically inhibiting cyclooxygenase‐2 (COX‐2). The present formulations require high dosage since the transmembrane transport fluctuates and is very difficult to control. We solubilized celecoxib in micelles of nonionic microemulsions and hydrophilic surfactant. The supersaturated solubilized drug was precipitated from the nano‐droplets to form a new solid structure with improved dissolution properties. The selected microemulsion systems loaded with celecoxib were characterized by SAXS, SD‐NMR, viscosity, and electrical conductivity techniques. Precipitation was conducted from W/O as well as from O/W U‐type microemulsions. The crystals obtained by the precipitation were characterized by x‐ray powder scattering, differential scanning calorimetry, FTIR measurements, and microscopic scans. 相似文献
92.
The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H2SO4 and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG. 相似文献
93.
Amino acids have been widely used as green corrosion inhibitors for an array of metals. Considering its importance in corrosion chemistry, studies were undertaken with the objective to discovering the inhibitory effect of a sulfur-containing amino acid, l-cysteine, on copper in different concentrations of sulfuric acid (0.5, 1.0, and 1.5 M) at different temperatures. Techniques like the weight loss method, electrochemical impedance spectroscopy, potentiodynamic polarization (Tafel), and adsorption studies were employed. Results revealed that l-cysteine do offer an attractive inhibition efficiency. However, with an increase in the concentration of the inhibitor, corrosion rates decreased irrespective of the temperature gradients. This is due to surface adsorption of the inhibitor molecules on the metal which has contributed to a decreased double-layer capacitance and increased polarization resistance. With the increase in the concentration of the medium, the corrosion rate was also enhanced and this is due the liberation of a high quantum of H+ ions. Based on the results of Tafel polarization studies, it is evident that the amino acid, l-cysteine, could act as a mixed type inhibitor. The importance of l-cysteine in the corrosion of copper metal has been highlighted in this paper. 相似文献
94.
Physicomechanical properties of nanocomposites based on cellulose nanofibre and natural rubber latex 总被引:1,自引:0,他引:1
Eldho Abraham B. Deepa L. A. Pothan Maya John S. S. Narine S. Thomas R. Anandjiwala 《Cellulose (London, England)》2013,20(1):417-427
Cellulose nanofibres (CNF) with diameter 10–60 nm were isolated from raw banana fibres by steam explosion process. These CNF were used as reinforcing elements in natural rubber (NR) latex along with cross linking agents to prepare nanocomposite films. The effect of CNF loading on the mechanical and dynamic mechanical (DMA) properties of NR/CNF nanocomposite was studied. The morphological, crystallographic and spectroscopic changes were also analyzed. Significant improvement of Young’s modulus and tensile strength was observed as a result of addition of CNF to the rubber matrix especially at higher CNF loading. DMA showed a change in the storage modulus of the rubber matrix upon addition of CNF which proves the reinforcing effect of CNF in the NR latex. A mechanism is suggested for the introduction of the Zn–cellulose complex and its three dimensional network as a result of the reaction between the cellulose and the Zinc metal which is originated during the composite formation. 相似文献
95.
Dr. Kilian Colas A. Catarina V. D. dos Santos Dr. Stefanie V. Kohlhepp Dr. Abraham Mendoza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202104053
The synthesis of ketones through addition of organometallic reagents to aliphatic carboxylic acids is a straightforward strategy that is limited to organolithium reagents. More desirable Grignard reagents can be activated and controlled with a bulky aniline-derived turbo-Hauser base. This operationally simple procedure allows the straightforward preparation of a variety of aliphatic and perfluoroalkyl ketones alike from functionalized alkyl, aryl and heteroaryl Grignard reagents. 相似文献
96.
This study is attempted to develop a green corrosion inhibitor from a waste material of Jack fruit (Artocarpus heterophyllus). This method is therefore quite valuable to health, environment, and economic point of view. Pectin is isolated from the jackfruit peel waste using 0.05 ?N oxalic acid and used as an inhibitor for mild steel corrosion in acidic environment as it is highly water soluble. 250–1000 ?ppm of pectin was used in this study at a temperature range of 303–323 ?K. The protection efficiency of jack fruit pectin (JP) in 0.5 ?M HCl was evaluated by conventional weight loss and electrochemical techniques. The potentiodynamic polarization results revealed that JP could effectively reduce the corrosion of mild steel in acidic medium at 1000 ?ppm concentration with an inhibition efficiency of 89.75% and corrosion rate of 2.392 mpy. The mixed type behavior of the inhibitor is identified from Tafel polarization studies. Electrochemical impedance spectroscopy (EIS) measurements suggest that the corrosion inhibition process is kinetically controlled. adsorption and kinetic behavior of the inhibitor also have been studied. Surface manifestations were followed using FESEM and AFM techniques. DFT calculations and Monte Carlo simulations were also carried out to corroborate the experimental results with theoretical outputs and succeeded to a great extent. 相似文献
97.
Shady Farah Oren Aviv Natalia Laout Stanislav Ratner Nurit Beyth Abraham J. Domb 《先进技术聚合物》2014,25(6):689-692
Silica particles functionalized with quaternary ammonium groups were prepared by interpenetrating polyethylenimine (PEI) into silica particles and crosslinking with diiodopentane, followed by octyliodide alkylation and methyliodide quaternarization (S‐QA‐PEI). The synthesized S‐QA‐PEI particles were identified with a slight particle size increase of 2–3 µm. Different ratios of PEI:silica particles were prepared and analyzed. While silica particles are negatively charged, ?16.7 ± 5.11 mV, the prepared S‐QA‐PEI particles are positively charged, +50–60 mV. These particles were embedded in poly(ethylene vinyl acetate) and poly(ethylene methacrylic acid) coatings which exhibited strong antibacterial activity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
98.
Qualitative and semiquantitative study of the Liesegang rings formed by the reaction of oxalic acid and cadmium chloride in the acidic range of pH in silica hydrogel is made. The behaviour of Jablczynski's space constant and Morce-Pierce's time constant at various temperatures, pH and concentration of outer electrolyte is studied. The possible mechanisms for the above observed behaviour are suggested. The deviations from Isemura's general obserations are interprerted by considering two particular aspects, viz., comparatively larger crystals constituting the rings and the irreversibility of inner and outer electrolytes. 相似文献
99.
100.
D. B. Abraham 《Studies in Applied Mathematics》1971,50(1):71-88
The eigenvalue problem for the transfer matrix of the two-dimensional Ising lattice, with free boundaries perpendicular to the transfer direction, is solved. The mathematical mechanism which produces the asymptotic degeneracy of the eigenvalue spectrum below the bulk transition temperature is different from the case with cyclic boundary conditions. The results are used to calculate the two-spin correlation function between two spins in the same edge of the lattice, and between two spins in opposite edges. 相似文献