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31.
Siya Ram William Evans Dean S. Wise Leroy B. Townsend John W. Mccall 《Journal of heterocyclic chemistry》1989,26(4):1053-1059
A series of methyl 2-substituted purine 8-carbamates was prepared and evaluated for antifilarial activity. These purines were synthesized as aza congeners of benzimidazole carbamates which have shown significant anthelmintic activity to determine the effect that this modification might have on anthelmintic activity. The compounds were tested against the filarial infection, B. pahangi, in jirds. None of the compounds prepared in this study demonstrated antifilarial activity. 相似文献
32.
Robert J. Evans Thomas A. Milne Michael N. Soltys Hans-Rolf Schulten 《Journal of Analytical and Applied Pyrolysis》1984,6(3):273-283
Pyrolysis-mass spectrometric studies of cellulose indicate low abundances of levoglucosan in the product spectrum compared to the yield values determined in more conventional types of pyrolysis studies. To examine the reason for these conflicting observation, levoglucosan was examined under different ion source conditions and ionization modes to ascertain the relative contributions of thermal degradation and ionization fragmention to the low abundances of the levoglucosan molecular ion. Low-energy electron ionization using conventional sample volatilization and molecular-beam sampling is compared to chemical ionization using methane, isobutane, and ammonia as reagent gases, and to field ionization and desorption. The mass spectrometric fragmentation patterns under the various systems indicate that studies of cellulose pyrolysis underestimate the amount of levoglucosan formed due to ionization fragmentation and thermal rearrangement reactions in the ion source. Several peaks, including m/z 126 and 144, are dominated by the contribution from the fragmentation of levoglucosan. 相似文献
33.
The displacements of the methyl substituents away from the metal and out of the cyclopentadienyl ring plane are compared in sterically crowded (C(5)Me(5))(3)M complexes vs sterically normal f-element complexes in an attempt to evaluate the utility of this parameter in predicting unusual (C(5)Me(5))(1-) ring reactivity. The out-of-plane displacements of 16 sterically crowded tris(cyclopentadienyl) complexes of general formula (C(5)Me(5))(3)M, (C(5)Me(4)R)(3)M (R = Et, (i)Pr, (t)()Bu, SiMe(3)), (C(5)Me(5))(3)MX (X = anion), and (C(5)Me(5))(3)ML (L = neutral ligand) are compared with [(C(5)Me(5))(2)U](2)(C(6)H(6)), (C(5)Me(5))(2)Sm(PC(4)H(2)(t)Bu(2)), and 33 representative examples of f-element bis(cyclopentadienyl) complexes with normal cyclopentadienyl behavior and coordination numbers ranging from 6 to 10. In general, the methyl displacement values of sterically crowded complexes overlap with those in the other complexes, which demonstrates that the basis of the structural distortions is complex. However, if the most extreme out-of-plane displacement in each of the sterically crowded complexes is examined vs the analogous maximum out-of-plane displacement in less crowded systems, there appears to be a basis for predicting cyclopentadienyl reactivity. 相似文献
34.
D. Fennell Evans Martin Allen B. W. Ninham Abdel Fouda 《Journal of solution chemistry》1984,13(2):87-101
Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol–1. 相似文献
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Heterogeneous fluorescence immunoassays have been automated using flow injection manifolds incorporating thiophilic gel solid phase reactors to separate antibody-bound and unbound analyte molecules. Antibody elution is achieved by changes in ionic strength, thus allowing the use of pH sensitive fluorescent labels. This facilitates the development of dual analyte systems, in which two competitive immunoassays with separate labels are monitored in parallel. Detection of the fluorophores by high speed synchronous fluorescence scanning while the flow is briefly stopped utilises either one synchronous interval which detects both fluorophores, or two separate scans at different wavelength intervals, one for each fluorophore. Simultaneous analyses of serum albumin and transferrin exemplify these novel approaches. Spectroscopic interferences are very small, analyte recoveries are close to 100%, with a relative standard deviation of 5-6% and a sampling rate of 20 h-1. 相似文献
37.
Christopher H. Evans Morgan Partyka Jan Van Stam 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):381-396
Naphthalene forms 1 : 1 complexes with -cyclodextrin (-CD)in water. The binding constant is 377 ± 35 M-1. Addition of linear or branched alcohols causes a reduction in the apparent strength of naphthalene binding (Kapp) compared to the value in the absence of additives. For example, 1% 1-pentanol reduces Kapp to 184 ± 31 M-1. Branching does not alter Kapp much for a given number of carbon atoms, e.g., it is 113 ± 9 M-1for 2-pentanol and 116 ± 8 M-1for 3-pentanol. The exception to this is tert-butanol for which Kapp is 577 ± 40 M-1. The variation in Kapp as a function of [1-pentanol] yields values for the individual equilibrium constants contributing to Kapp. This reveals that a ternary complex forms involving naphthalene, the CD and 1-pentanol. The constant for formation of the ternary complex is 99 ± 29 M-2. NaI quenching of naphthalene fluorescence indicates that the CD cavity partially protects the naphthalene excited state fromthis water phase quencher. Interestingly, the Stern–Volmer constant is lower in the presence of 1-pentanol than in its absence, although there should be more unbound (and therefore more NaI accessible) naphthalene in the former system than in the latter. These apparently contradictory results are discussed in terms of ternary complex formation. 相似文献
38.
D. L. Evans 《Mikrochimica acta》1967,55(2):385-388
Summary The preliminary tests for organic radicals, which are based on charring by strong heating or by hot concentrated sulphuric acid are examined. Even when both these tests are applied some organic acids escape identification. Two alternative procedures based upon oxidation of organic matter with potassium dichromate in dilute sulphuric have been examined. The first procedure involves a reduction of the dichromate ion to the distinctive green chromium(III) ion. This occurs with all organic radicals commonly encountered in qualitative inorganic analysis, except acetate and salicylate. Interference due to inorganic reducing agents is overcome by a preliminary oxidation with hydrogen peroxide. The second procedure involves decomposition of carbonates, bicarbonates, and cyanates with dilute sulphuric acid, followed by oxidation of organic matter with potassium dichromate in sulphuric acid to carbon dioxide, which is detected with lime water. Of the radicals commonly encountered in qualitative inorganic analysis only acetate gives a negative result.
Zusammenfassung Die Vorprobe auf organische Anionen auf Grund ihrer Verkohlung durch kräftiges Erhitzen oder durch Einwirkung konz. Schwefelsäure wurde überprüft. Auch bei Anwendung beider Arbeitsweisen entziehen sich einige organische Säuren dem Nachweis. Zwei andere Verfahren auf der Grundlage der Oxydation des organischen Materials mit Kaliumbichromat in verd. Schwefelsäure wurden untersucht. Das erste führt zur Reduktion des Bichromats zu deutlich grün gefärbtem Cr(III) mit allen bei der anorganischen Analyse üblicherweise auftretenden organischen Anionen, ausgenommen Acetat und Salicylat. Störungen durch reduzierende anorganische Substanzen werden durch deren vorherige Oxydation mit Wasserstoffperoxid umgangen. Das zweite Verfahren sieht die vorherige Zersetzung anwesender Carbonate, Bicarbonate oder Cyanate mit verd. Schwefelsäure vor, wonach das organische Material mit Kaliumbichromat-Schwefelsäure zu Kohlendioxid oxydiert wird, das mit Kalklösung nachgewiesen wird. Von den in der anorganischen Analyse üblichen organischen Anionen gibt nur Acetat ein negatives Resultat.
Résumé On examine les essais préliminaires pour radicaux organiques, fondés sur la carbonisation par chauffage à température élevée ou sur l'action de l'acide sulfurique concentré chaud. Même en appliquant ces deux modes de recherche, certains des acides organiques échappent à l'identification. On a étudié deux autres procédés susceptibles d'être utilisés. Ils reposent sur l'oxydation de la matière organique par le bichromate de potassium en milieu sulfurique dilué. Le premier met en jeu la réduction de l'ion bichromate en ion chrome-III vert caractéristique. Cette réaction se produit avec tous les radicaux organiques habituellement rencontrés en analyse minérale qualitative, sauf avec les acétates et les salicylates. On élimine l'interférence due aux agents réducteurs minéraux par oxydation préliminaire par l'eau oxygénée. Le second procédé met en jeu la décomposition des carbonates, hydrogénocarbonates et cyanates par l'acide sulfurique dilué, suivie d'une oxydation de la matière organique par le bichromate de potassium dans l'acide sulfurique, en gaz carbonique que l'on met en évidence par l'eau de chaux. Seul l'ion acétate donne un résultat négatif parmi tous les radicaux rencontrés habituellement en analyse minérale qualitative.相似文献
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