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991.
The temperature dependences of the equilibrium constants of two chain reversible reactions in quinonediimine (quinonemonoimine)—2,5-dichlorohydroquinone
systems in chlorobenzene were studied. The enthalpy of equilibrium of the reversible reaction of quinonediimine with 4-hydroxydiphenylamine
was estimated from these data (ΔH = − 14.4±1.6 kJ mol−1) and a more accurate value of the N-H bond dissociation energy in the 4-anilinodiphenylaminyl radical was determined (D
NH = 278.6±3.0 kJ mol−1). A chain mechanism was proposed for the reaction between quinonediimine and 2,5-dichlorohydroquinone, and the chain length
was estimated (ν = 300 units) at room temperature. Processing of published data on the rate constant of the reaction of styrylperoxy
radicals with 2,5-dichlorohydroquinone in the framework of the intersecting parabolas method gave the O-H bond dissociation
energy in 2,5-dichlorohydroquinone: D
OH = 362.4±0.9 kJ mol−1. Taking into account these data, the O-H bond dissociation energy in the 2,5-dichlorosemiquinone radical was found: D
OH = 253.6±1.9 kJ mol−1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1661–1666, October, 2006. 相似文献
992.
Accurate lower and upper bounds for the nonrelativistic lowest energies1
E
0 and3
E
0 of the singlet and triplet-system of the4He-Isotop are calculated with the linearized method of variance minimization. The same was done for1
E
1 the energy of the first excitedS-state 21
S.
The results especially for1
E
0 and3
E
0 in a.u. are −2.90330769975 ≤1
E
0 ≤ −2.90330769218 −2.17493242637 ≤3
E
0 ≤ −2.17493242459 i.e. the values are determined with an absolute error smaller than 0.00167 cm−1 for1
E
0 and 0.00039 cm−1 for3
E
0. 相似文献
993.
S. Nygren 《Journal of separation science》1979,2(6):319-323
The technique of programming the carrier gas flow rate in gas chromatography, especially in connection with the use of capillary columns shorter than 10 m can significantly accelerate GC analyses. Equations for calculation of the parameters of the exponential flow function and retention data are described. The effects of flow programming in a short capillary column are shown in a few chromatograms. Different programming rates are tested and compared with temperature programming. 相似文献
994.
P. Burba und K. H. Lieser 《Fresenius' Journal of Analytical Chemistry》1978,291(3):205-209
Zusammenfassung Trennröhrchen, die Celluloseaustauscher mit SalicylsÄure als Ankergruppe enthalten, werden für die chromatographische Bestimmung von Fe3+-, UO2
2+- und Cu2+-Ionen in wÄ\rigen Lösungen verwendet. Die Herstellung des Austauschers und das Trennverfahren werden beschrieben. Die Nachweisgrenzen liegen bei etwa 0,2 g Fe, 5 g U und 10 g Cu. In bestimmten Konzentrationsbereichen ist die chromatographische Trennung und gleichzeitige Bestimmung mehrerer Ionen möglich, wie an den Beispielen Fe3+/Cu2+ und UO2
2+/Cu2+ gezeigt wird.
Chromatography on cellulose exchangers — Microdetermination of Fe3+, Uo2 2+ and Cu2+ ions in aqueous solutions by means of small separation columns
Summary Small separation columns filled with a cellulose exchanger containing salicylic acid as anchor group are used for chromatographic determination of Fe3+, UO2 2+, and Cu2+ in aqueous solutions. The preparation of the cellulose exchanger and the separation procedure are described. The detection limits are approximately 0.2 g Fe, 5 g U and 10 g Cu. Within certain concentration ranges chromatographic separation und simultaneous determination of several ions is possible, as shown by the examples Fe3+/Cu2+ and UO2 2+/Cu2+.
Der chromatographisch ermittelte Analysenwert wurde durch Röntgenfluorescenzanalyse überprüft. Zu diesem Zweck wurde das Fe aus 100 ml 10%iger NaCl p. a. Löung bei pH 7 in einem Schüttelversuch an 100 mg SalicylsÄure-Austauscher quantitativ fixiert. Der Austauscher wurde anschlie\end als gleichmÄ\ige Filterschicht abgetrennt und das Fe, wie an anderer Stelle beschrieben [2] durch Röntgenfluorescenzanalyse bestimmt. Das Analysenergebnis von 7,2 g zeigte innerhalb der Fehlergrenze gute übereinstimmung mit der chromatographischen Bestimmung. 相似文献
995.
Anab initio crystal orbital method is used to calculate the energies of an infinite chain of H atoms and of linear arrangements of H2 molecules with different interatomic distances. The H2 arrangements are not stable in respect to isolated molecules. The cohesive energy of an optimized arrangement of H atoms chain is 0.0354 a.u. 相似文献
996.
《Surface and interface analysis : SIA》2003,35(2):216-225
Catalysts of Co,K/La2O3 have been prepared by wet impregnation. The samples have been calcined at 400°C and 700°C and have been characterized for phase composition using x‐ray diffraction and Fourier transform infrared spectroscopy. The XPS analysis of the samples has been obtained by examination of the O 1s, K 2p, C 1s and La 3d spectral regions. The XPS data are discussed with respect to the calcination temperatures and the soot combustion performed in the spectrometer reaction chamber. Analysis of the XPS data indicates considerable carbonation of the surfaces of all samples, even after burning the soot. The K/La2O3 solid presents the highest content of surface carbonated species, showing the highest catalytic activity for soot combustion. Interaction of the catalysts with CO2 is studied by temperature‐programmed desorption and microbalance experiments. Kinetic studies and surface characterization of the potassium‐containing samples suggest that an appropriate surface potassium concentration is necessary for a synergetic action between potassium and lanthanum. In the cobalt‐containing catalysts calcined at 700°C, an increase is observed in the concentration of the outer‐layer perovskite species when the potassium content increases, following the same tendency observed in the bulk. Such LaCoO3 species would limit the reaction of lanthanum with CO2. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
997.
The basicities of aluminated zeolites βhave been investigated by FTIR spectra of chemisorbed pyrrole. The NH-stretching frequency of pyrrole adsorbed on the samples shifts towards lower wavenumber as the St/Al ratio is decreased and correlates well with the negative charge on the framework oxygen calculated from the Sanderson electronegativity equalization principle, revealing zeolite β to possess a stronger overall basicity after alumination and, therefore, the alumination to be an effective method to improve the basicity. It is also found that the heterogeneity of basic strength occurs and some stronger basic sites appear after alumination. 相似文献
998.
Analysis of alpha-amino acids, proteins, and phenolic compounds was simultaneously performed using three capillaries in capillary electrophoresis with chemiluminescence detection, taking advantage of the micro-space area for reaction/detection at the tip of the capillary. The three capillaries included usual, polymer-containing, and sodium docley sulfate (SDS)-containing migration buffers for separation. The eluted samples from the capillaries, which were inserted into the chemiluminescence detection cell, were mixed with chemiluminescence reagent at the tips of the capillaries to generate visible light. The specific micro-space area for reaction/detection at the tips of the capillaries enabled the simultaneous operation of the three separation modes in the present system. 相似文献
999.
The activity coefficients at infinite dilution have been measured at 25°C for cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, benzene, n-hexane, 1-hexene, 1-hexyne, n-heptane, 1-heptene and 1-heptyne in decahydronaphthalene, bicyclohexyl, 1,2,3,4-tetrahydronaphthalene and cyclohexylbenzene. These results, together with previously determined H
m
E
and V
m
E
have been used to calculate the partial molar excess thermodynamic properties of mixing at infinite dilution. 相似文献
1000.