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741.
McKeown NB Budd PM Msayib KJ Ghanem BS Kingston HJ Tattershall CE Makhseed S Reynolds KJ Fritsch D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2610-2620
Novel types of microporous material are required for chemoselective adsorptions, separations and heterogeneous catalysis. This concept article describes recent research directed towards the synthesis of polymeric materials that possess microporosity that is intrinsic to their molecular structures. These polymers (PIMs) can exhibit analogous behaviour to that of conventional microporous materials, but, in addition, may be processed into convenient forms for use as membranes. The excellent performance of these membranes for gas separation and pervaporation illustrates the unique character of PIMs and suggests immediate technological applications. 相似文献
742.
A sensitive and selective luminescence quenching method is developed and used for manual and flow injection analysis (FIA) of chromium(VI) by reaction with [Ru(bpy)3]2+. The emission peak of ruthenium(II) at 595 nm is linearly decreased as a function of Cr(VI) concentration. This permits determination of chromium(VI) ion over the concentration range 0.1-20 μg ml−1 with a detection limit of 33 ng ml−1. The quenching process is due to an electron transfer from the luminescent [Ru(bpy)3]2+ complex ion to Cr(VI) resulting in the formation of the non-luminescent [Ru(bpy)3]3+ complex ion. Selectivity for Cr(VI) over many anions and transition, alkali and alkaline earth metal cations is demonstrated. High concentration levels of sulphate, chloride, borate, acetate, phosphate, nitrate, cyanide, Pb2+, Zn2+, Hg2+, Cu2+, Cd2+, Ni2+ and Mn2+ ions are tolerated. The effects of solution pH and [Ru(bpy)3]2+ reagent concentration are examined and the reaction conditions are optimized. Validation of the method according to the quality assurance standards show suitability of the proposed method for use in the quality control assessment of Cr(VI) in complex matrices without prior treatment. The method is successfully applied to determine chromium(VI) in electroplating baths using flow injection analysis. Results with a mean standard deviation of ±0.6% are obtained which compare fairly well with data obtained using atomic absorption spectrometry. 相似文献
743.
Substituent effects on reactivity are compared for base hydrolysis of tris-ligand-iron(II) complexes of Schiff base ligands derived from 2–acetylpyridine and substituted benzylamines and their aniline analogues. The methylene spacer in the former effectively isolates the iron from substituent effects in the phenyl ring, as indicated by the almost equal rate constants for base hydrolysis of the complexes derived from benzylamine and its 4–methyl, 4–fluoro, and 4– trifluoromethyl derivatives. Rate constants for base hydrolysis of the (substituted) benzylamine derivatives are also reported for some Me2CO-H2O and DMSO-H2O solvent mixtures. Reaction is faster in all these binary aqueous mixtures, mainly due to the higher chemical potentials of hydroxide ion. 相似文献
744.
Two novel membrane sensors sensitive and reasonably selective for Cu2+ ions are described. These are based on the use of newly synthesized cyclic tetrapeptide derivatives as neutral ionophores and sodium tetraphenylborate (NaTPB) as an anionic excluder in plasticized PVC membranes. The sensors exhibit fast and stable near-Nernstian response over the concentration range 1.0 × 10−6 mol l−1 to 1.0 × 10−2 mol l−1 Cu2+ with a cationic slope of 30.2-25.9 mV per decade at pH 4.5-7 with a lower detection limit of 0.05-0.13 μg ml−1. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors display long life-span, long term stability, high reproducibility, and short response time. Selectivity of both sensors is significantly high for Cu2+ over Fe3+, Al3+, Zn2+, Cd2+, Hg2+, Ni2+, Co2+, Mn2+, alkaline earth and alkali metal ions. The sensors are used for direct measurement of copper content in different rocks and industrial wastewater samples from electroplating factories. The results agree fairly well with data obtained using atomic absorption spectrometry. 相似文献
745.
Saad EF El-Hegazy FE Mahmoud ME Hamed EA 《Rapid communications in mass spectrometry : RCM》2000,14(14):1208-1213
The electron impact tandem mass spectrometry of 3- and 5-nitropyridinylaryl sulfides are reported and discussed. The [M-1](+) ion is observed as the base peak for all the 5-nitropyridinylaryl sulfides, series I, whereas the 2-mercapto-3-nitrosopyridine fragment at m/z 139 represents the base peak for the 3-nitro isomers, series II, with the exception of the 3-substituted derivatives and the unsubstituted parent sulfide. The proposed fragmentation processes are substantiated by tandem mass spectrometry (MS/MS). Hammett correlation analysis of the substituent effect on the formation of fragments [RH(4)C(6)S](+), [C(6)H(4)R](+) and [M-HNO(2)](+) is discussed. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
746.
Summary Rate constants for dissociation, in aqueous solution at 25° C, of [Fe(phen)3]2+, [Fe(bipy)3]2+, and [Fe(4,4-Me2bipy)3]2+ in the presence of cyanide, and of the last-named complex also in the presence of hydroxide, are significantly decreased by the application of pressure (up to 1 kbar). Kinetic measurements were carried out using a high pressure cell of improved design to that used in our earlier investigations. Volumes of activation, V
*, are scarcely sensitive to ligand or to attacking nucleophile, being in the range of 10–12 cm3 mol–1. An explanation of these results resides in an associative mechanism, a scheme invoked for similar reactions reported previously. 相似文献
747.
Budd PM Ghanem BS Makhseed S McKeown NB Msayib KJ Tattershall CE 《Chemical communications (Cambridge, England)》2004,(2):230-231
Microporous materials can be derived directly from soluble polymers whose randomly contorted shapes prevent an efficient packing of the macromolecules in the solid state. 相似文献
748.
A simple, sensitive and fairly rapid method for the determination of noscapine is described, based on the measurement of the absorbance of the organic soluble ion-association complex formed between the noscapine monocation and a bulky counter anion. Methyl Orange, Bromothymol Blue and Bromocresol Green (BCG) were examined as counter ions. The effect of few solvents, the counter-ion concentration and pH on the extraction were also investigated. The most suitable system was based on BCG (pH 3.0) with chloroform as the extraction solvent. The use of the other counter ions, in conjunction with their respective solvents, was found to be less sensitive. The BCG system exhibits negligible or no interference when used for the determination of 38 ppm of noscapine in the presence of several drug excipients, thus lending itself as a possible procedure for the determination of this alkaloid in pharmaceutical preparations. 相似文献
749.
Summary LiAlH4 reduction of 1, 1-ferrocene-bis(dimethyldithiocarbamates) gives 1, 1-dithiolatoferrocene [Fc(SH)2] in high yield. The dithiol reacts with first-row transition metals to give polymeric products but with [ReOCl3–(PPh3)2] the complex [ReO(FcS2)2]–, can be isolated as a tetraphenylphosphonium salt in good yield. 相似文献
750.
Mohamed Hilmy Elnagdi Mohamed Mohamed Mohamed Sallam Hussein Mahmoud Fahmy Saad Abdel-Motteleb Ibrahim Mohamed Ajmal Mohamed Elias 《Helvetica chimica acta》1976,59(2):551-557
Analysis of the IR., UV., and polarographic data of a variety of 2-arylhydrazono-3-ketimino-nitriles indicated that these derivatives exist mainly in the intramolecularly chelated hydrazone structure 1 . Compounds 1 reacted with hydrazine hydrate to yield the corresponding 5-amino-4-arylazopyrazoles ( 3 ). Compounds 3a reacted with acetylacetone, ethyl acetoacetate, and diethyl malonate to yield the pyrazolo[1, 5-a]pyrimidine derivatives 4, 5 , and 7 respectively. Compound 3a also reacted with benzoylisothiocyanate to yield the pyrazolyl thiourea derivative 8 . 相似文献