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991.
Yibin Wei 《Liquid crystals》2017,44(2):303-311
Detection of amino acid (AA) is an essential step to understand various biological processes. In this study, we used innovative optical birefringent patterns of nematic liquid crystals (LCs) for the detection of several AAs. We attempted to use capillary-confined nematic LCs as sensor for AA analysis because their three-dimensional micro-scale architecture of LCs allowed better performance than that of mainly reported LC thin film sensors owing to the effect on the formation and dynamics of point defect. The sensing system was built by disrupting the alignment of a nematic LC, 4-cyano-4′-pentylbiphenyl (5CB), using the dopant of dodecyl aldehyde. Detection principle is based on the chemical analytical method of aldehyde titration for AAs, wherein the reaction between AAs and aldehyde group generates Schiff bases that could alter the configuration of nematic LCs at the aqueous/LC interface. The patterns generated in the reaction are captured by polarising optical microscopy (POM) and are visible to the naked eye. The functionalised LCs detected glycine at concentrations as low as 1 pM. There was a surprising result that it can selectively detect D-AAs against their L-isomers, however, further efforts are required to explain the mechanism. 相似文献
992.
Szymon Kapuściński Agata Wojciechowska Katarzyna Urbaniak Piotr Kaszyński 《Liquid crystals》2017,44(7):1093-1103
A series of hockey-stick shaped 6-oxoverdazyl radicals 1[n]–3[n], containing CH3 (a), CF3 (b) and CN (c) groups in the short ‘arm’, were prepared and their physical properties were investigated. Mesogenic behaviour was found only in the CN derivatives with the COO (1[n]c) and N=N (2[12]c) linking groups, which exhibited a nematic phase. Analysis of binary mixtures of selected compounds with bent-core nematic host 4[12] gave virtual nematic-isotropic transition temperatures, [TNI], which follow the order 1[12]b < 1[12]c < 1[12]a in one series and 1[12]c < 2[12]c < (3[12]c) in another. The observed effectiveness of the short-arm substituent, CF3 < CN < CH3, was related to the magnitude and orientation of the molecular dipole moment calculated with density functional theory methods. 相似文献
993.
994.
Roman Dabrowski Katarzyna Garbat Stanisław Urban Tomasz R. Woliński Jerzy Dziaduszek Tomasz Ogrodnik 《Liquid crystals》2017,44(12-13):1911-1928
ABSTRACTSeries of low-birefringence liquid crystal mixtures composed of alkyl alkylbicyclohexyl carbonates and modified mixtures with other compounds have been formulated, their refractive indices and electric permittivity measured upon temperature. They exhibit the ordinary refraction index no lower than the refractive index of silica glass in a different range of temperature. This enables to observe in photonic liquid crystal fibres (PLCFs) a change in the light propagation mechanism from photonic band gap guiding to modified total internal reflection at different temperatures. Selected applications of PLCFs are also discussed. 相似文献
995.
Peng Lin Nan-Xiang Zhang Jing-Jing Li Jing Zhang Jia-Hui Liu Bao Zhang Jian Song 《中国化学快报》2017,28(4):771-776
The gelation behaviours of low molecular weight gelators 1,3:2,5:4,6-tris(3,4-dichlorobenzylidene)-D-mannitol(G1)and 2,4-(3,4-dichlorobenzylidene)-N-(3-aminopropyl)-D-gluconamide(G2)in 34 solvents have been studied.We found that sample dissolved at low concentrations may become a gel or precipitate at higher concentrations.The Hansen solubility parameters(HSPs)and a Teas plot were employed to correlate the gelation behaviours with solvent properties,but with no success if the concentration of the tests was not maintained constant.Instead,on the basis of the gelation results obtained for the G1 and G2 in single solvents,we studied the gelation behaviours of G1 and G2 in 23 solvent mixtures and found that the tendency of a gelator to form a gel in mixed solvents is strongly correlated with its gelation behaviours in good solvents.If the gelation occurs in a good solvent at higher concentrations,it will take place as well in a mixed solvent(the good solvent plus a poor solvent)at a certain volume ratio.In contrast,if the gelator forms a precipitate in a good solvent at higher concentrations,no gelation is to be observed in the mixed solvents.A gelation rule for mixed solvents is thus proposed,which may facilitate decision making with regard to solvent selection for gel formation in the solvent mixtures in practical applications. 相似文献
996.
997.
Fleming Martínez Abolghasem Jouyban William E. Acree Jr 《Physics and Chemistry of Liquids》2017,55(3):291-303
Preferential solvation parameters of etoricoxib in several aqueous cosolvent mixtures were calculated from solubilities and other thermodynamic properties by using the IKBI method. Cosolvents studied were as follows: 1,4-dioxane, N,N-dimethylacetamide, 1,4-butanediol, N,N-dimethylformamide, ethanol and dimethyl sulfoxide. Etoricoxib exhibits solvation effects, being the preferential solvation parameter δx1,3, negative in water-rich and cosolvent-rich mixtures but positive in mixtures with similar proportions of both solvents. It is conjecturable that the hydrophobic hydration in water-rich mixtures plays a relevant role in drug solvation. In mixtures of similar solvent proportions where etoricoxib is preferentially solvated by the cosolvents, the drug could be acting as Lewis acid with the more basic cosolvents. Finally, in cosolvent-rich mixtures the preferential solvation by water could be due to the more acidic behaviour of water. Nevertheless, the specific solute–solvent interactions in the different binary systems remain unclear because no relation between preferential solvation magnitude and cosolvent polarities has been observed. 相似文献
998.
999.
Glow discharge mass spectrometry (GD-MS) is an excellent technique for fast multi-element analysis of pure metals. In addition
to metallic impurities, non-metals also can be determined. However, the sensitivity for these elements can be limited due
to their high first ionization potentials. Elements with a first ionization potential close to or higher than that of argon,
which is commonly used as discharge gas in GD-MS analysis, are ionized with small efficiency only. To improve the sensitivity
of GD-MS for such elements, the influence of different glow-discharge parameters on the peak intensity of carbon, chlorine,
fluorine, nitrogen, phosphorus, oxygen, and sulfur in pure copper samples was investigated with an Element GD (Thermo Fisher
Scientific) GD-MS. Discharge current, discharge gas flow, and discharge gas composition, the last of which turned out to have
the greatest effect on the measured intensities, were varied. Argon–helium mixtures were used because of the very high potential
of He to ionize other elements, especially in terms of the high energy level of its metastable states. The effect of different
Ar–He compositions on the peak intensity of various impurities in pure copper was studied. With Ar–He mixtures, excellent
signal enhancements were achieved in comparison with use of pure Ar as discharge gas. In this way, traceable linear calibration
curves for phosphorus and sulfur down to the μg kg−1 range could be established with high sensitivity and very good linearity using pressed powder samples for calibration. This
was not possible when pure argon alone was used as discharge gas.
This contribution is based on a presentation given at the Colloquium for Analytical Atomic Spectroscopy (CANAS ’07) held March
18–21, 2007 in Constance, Germany. 相似文献
1000.
Martín A Menéndez A Pereiro R Bordel N Sanz-Medel A 《Analytical and bioanalytical chemistry》2007,388(8):1573-1582
An overview of the effects produced by the presence of hydrogen in a glow discharge (GD), generated either in argon or in
neon, is given. Extensive work related to the addition of hydrogen to GDs, coupled with optical emission spectrometry (OES)
and mass spectrometry (MS), has been published in the last few years in an attempt to explain the processes involved in the
discharge of mixed gases. Although numerous experimental results have already been explained theoretically, a complete understanding
of the effects brought about by mixing hydrogen with argon (or another discharge inert gas) has not been reported yet. The
use of theoretical models implemented using a computer has allowed the importance of some collisional and radiative processes
in the inert gas plasma when hydrogen is present to be evaluated. This review shows, however, that both experimental work
and theoretical work are still needed. The influence of small quantities of hydrogen on discharge parameters, such as electrical
current or dc bias voltage, on crater shapes and on sputtering rates is thoroughly reviewed along with the effect on the analytical
signals measured by OES and MS. Also, hydrogen-effect corrections needed to carry out proper calibrations for direct solid
quantitative analyses are discussed.
Figure Hydrogen induced changes in the Ar glow discharge reactions. 相似文献