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841.
Gas chromatography (GC) was investigated for the determination of residual methyl methacrylate (MMA) in heat-processed poly(methyl methacrylate) (PMMA) denture base material emphasizing recovery and validation. Standard solutions of MMA and emulsion-polymerized PMMA in dichloromethane were analysed, before and after distillation by a room-temperature air stream into a liquid nitrogen trap, and in the presence of PMMA by direct injection. Quantitative NMR analysis using dimethyl sulphoxide as internal calibration standard in deuterated chloroform solutions provided validation. Good concordance was observed between results under all conditions; no problems arose from direct injection of PMMA solution for GC. Good straight line responses in log-log plots were generally observed. For GC and MMA: log-log calibration curve (slope: 0.9552 +/- 0.0051, r2: 0.9992, n = 32) indicated some non-linearity (t = 8.875, p approximately 4 x 10(-10)). Distillation gave slope: 0.9751 +/- 0.0213 (NS versus unity; t = 1.172, p > 0.25). For PMMA solutions, distillation (r2: 0.9301) gave greater scatter than direct injection (r2: 0.9704). For NMR: log-log plot of calculated versus actual MMA (slope: 0.9363 +/- 0.0157, r2: 0.9969, n = 13) again indicated non-linearity (t = 4.0682, p = 0.0019). PMMA solutions gave slope: 0.9477 +/- 0.0328, r2 = 0.9858 (NS versus unity; t = 1.5941, p = 0.13). Determination of MMA in PMMA by GC is recommended. 相似文献
842.
Correlation times for rotation of deuterated methyls in crystalline leucine, valine, and cyclo-L-alanyl-L-alanine are calculated with molecular dynamics and compared with NMR data. The simulations distinguish between methyls having different steric environments in the crystal, yielding correlation times differing by a factor of up to 30 for methyls within a given crystal. MD and NMR correlation times agree to within a factor of 2. However, averaging over nonequivalent methyls can yield correlation functions that, although actually multiexponential, are well fit by single exponentials. This may have significance for interpreting NMR data; previous NMR data did not distinguish between the methyls in these crystals. Adiabatic rotational barriers calculated with the X-ray structure differ from effective barriers during simulation by up to +/-1 kcal/mol; the difference indicates that dynamical effects have a significant role in determining rotational correlation times. 相似文献
843.
844.
The title compound (1) was treated with NaH at room temperature in anhydrous DMF to give a sodium salt (containing nitrogen anion)which could shift the methyl group from oxygen to nitrogen atom to form N-methyl phosphinic acid as the reaction temperature was increased to 120 ℃.Three nitro derivatives containing 5,10-dihydrophenophosphazine ring system were prepared for the investigation on the above reaction mechanism which would be possible regarded as a special inter-molecular substitution.viz.,the nucleophilic nitrogen anion from one molecule of 1 attacked the cabon atom of the O-methyl of another 1.In addition,the chemical structures of seven compounds containing 5,10-dihydrophenophosphazine ring system involved in the experiment were confirmed by IR,^1 H NMR,^31P NMR and mass spectroscopy. 相似文献
845.
Piperonyl methyl ketone was obtained by oxidizing isosafrole with hydrogen peroxide and formic acid.Dianion of ethyl acetoacetate reacted with piperonyl methyl ketone and 5,6-dihydro-6-methyl-6-piperonyl-2H-pyran-2,4-dione was prepared,which reacted with substituted anilines in the presence of ethyl orthoformate to obtain 3-anilinomethylene-5,6-dihydro-6-methyl-6-piperonyl-2H-pyran-2,4-diones.Their structure were confirmed by ^1HNMR and elemental analysis. 相似文献
846.
The electrolytic conductances of NaClO4, NaB(C6H5)4, (n-C4H9)4NClO4 and (n-C4H9)4NPF6 have been measured in methyl acetate at 25°C. A dominating feature of these electrolyte solutions is, as expected, strong ion pairing. In addition it is found that the formation of triple ions makes an important contribution to the overall molar conductivities. The data suggest that there are strong ion-solvent interactions leading to structure-enhanced (after Diamond) ion association and triple ion formation which has an exact analogy in the phenomena of salting-in. The effects of increasing solution permittivity and viscosity are discussed, particularly in regard to comparing two models of treating conductivity data. The first model includes ion pairs and triple ions, and the second model ignores triple ion formation ascribing the anomalous increase in molar conductivities to a decrease in the ion association equilibrium constant caused by increasing solution permittivity. 相似文献
847.
848.
V. N. Khrustalev O. V. Shishkin S. V. Lindeman Yu. T. Struchkov M. A. Galkina Yu. G. Gololobov 《Russian Chemical Bulletin》1996,45(9):2172-2176
I-Adamantylmethyl 2-cyanoacrylate (1) was prepared by the reaction of 2-cyanoacryloyl chloride with 1-adamantylmethanol . 1,10-Decanediol bis-2-cyanoacrylate (2) was synthesized by transesterification of methyl 2-cyanoacrylate with 1,10-decanediol. Esters1 and2 were studied by X-ray structural analysis.Deceased in 1995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2288–2292, September, 1996. 相似文献
849.
Dungelová J Lehotay J Krupcík J Cizmárik J Armstrong DW 《Journal of separation science》2004,27(12):983-990
The enantiomers of thirteen 2-, 3-, and 4-alkoxyphenylcarbamic acid 2-methoxy-1-[(4-methylpiperazino)methyl]ethyl ester were separated on a (S,S) Whelk-O 1 CSP column isothermally in the range of 0-50 degrees C at 10 degrees C increments, using methanol/ water (90/10, v/v) containing 17.5 mmol L(-1) acetic acid and 14.36 mmol L(-1) triethylamine as a mobile phase. The dependence of the natural logarithms of retention and selectivity factors (In k, In alpha, respectively) on the inverse of temperature, 1/T, was used to determine thermodynamic data of enantiomers of alkoxysubstituted phenylcarbamic acid 2-methoxy-1-[(4-methylpiperazino) methyl]ethyl esters. Enthalpyentropy compensation plots showed that all of the compounds in this study separate via the same enthalpy-driven chiral recognition mechanism. 相似文献
850.
The poly(methyl methacrylate) (PMMA)/montmorillonite (MMT) nanocomposite was prepared by emulsifier-free emulsion technique and its structure and properties were characterized with infra red, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and cone calorimetry. The highly exfoliated MMT layers with dimension 1-2 nm in thickness were randomly dispersed in the polymer matrix containing MMT lower than 5% w/v, whereas the intercalated structure was predominant with MMT content higher than 5% w/v. Consequently, the fine dispersion of the MMT and the strong interactions between PMMA and MMT created significant improvement of the thermo-stability and fire retardancy of the nanocomposite. The combustion behavior has been evaluated using oxygen consumption cone calorimetry. In addition, a scheme was proposed to describe fire retardancy of PMMA and MMT as well as the correlation between the interaction and structure in polymer/clay systems. The biodegradability of the nanocomposite fire-retardant was tested for its better commercialization. 相似文献