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991.
Marniev Luiggi Rosa M. Dominguez Alexandra Rotinov Armando Herize Mary Cordova Gabriel Chuchani 《国际化学动力学杂志》2002,34(1):67-71
The elimination kinetics of ethyl N‐benzyl‐N‐cyclopropylcarbamate and ethyl diphenylcarbamate were investigated over the temperature range of 349.9–440.0°C and the pressure range of 31–106 Torr. These reactions have been found to be homogeneous, unimolecular, and obey a first‐order rate law. The products are ethylene, carbon monoxide, and the corresponding secondary amine. The rate coefficient is expressed by the following Arrhenius equations: For ethyl N‐benzyl‐N‐cyclopropylcarbamate log k1 (s?1) = (12.94 ± 0.09) ? (198.5 ± 0.9) kJ mol?1 (2.303RT)?1 For ethyl diphenylcarbamate log k1 (s?1) = (12.91 ± 0.18) ? (208.2 ± 2.4) kJ mol?1 (2.303RT)?1 The presence of phenyl and bulky groups at the nitrogen atom of the ethylcarbamate showed a decrease in the rate of elimination. Steric factor may be operating during the process of decomposition of these substrates. These reactions appear to undergo a semipolar six‐membered cyclic transition type of mechanism.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 67–71, 2002 相似文献
992.
Max Ziegler 《Fresenius' Journal of Analytical Chemistry》1958,164(4):387-390
Zusammenfassung Es wird ein photometrisches Verfahren zur Bestimmung von Kupfer in Leichtmetall-Legierungen mittels Violursäure beschrieben, das sich als Schnellverfahren zur Bestimmung von Kupfergehalten von 0,02 bis 10% Cu eignet. Nickelgehalte bis 4% stören die Bestimmung nicht. Die Messung kann sofort oder nach längerer Zeit erfolgen.Herrn Prof. Dr. O. Glemser, Direktor des Anorganisch-chemischen Instituts, danke ich für die Unterstützung der vorliegenden Arbeit durch Institutsmittel.Der techn. Assistentin, Frl. U. Hartje, danke ich für die unermüdliche Hilfe bei der analytischen Arbeit. 相似文献
993.
The relationship between one-bond 13C-1H coupling constants and internuclear CCC bond angles (n) in hydrocarbons of the type R2CH2 is best approximated by a quadratic expression. 相似文献
994.
St. Becker G. Dietrich H. -U. Hasse N. Klisch H. -J. Kluge D. Kreisle St. Krückeberg M. Lindinger K. Lützenkirchen L. Schweikhard H. Weidele J. Ziegler 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,30(4):341-348
The stability of gold cluster ions Au
n
+
(2n23) has been investigated via collision induced dissociation in a Penning trap. Threshold energies and dissociation channels have been determined. The cluster stability exhibits a pronounced odd — even alternation: Clusters with an odd number of atoms,n, are more stable than the even-numbered ones. Enhanced stabilities are found for Au
3
+
, Au
9
+
, and Au
19
+
in accordance with the Clemenger-Nilsson and the deformed jellium model of delocalized valence electrons. Excited odd cluster ions withn15 predominantly decay by evaporation of dimers; all others decay by monomer evaporation. From the dissociation channels estimates of the binding energies are deduced.This publication comprises part of the thesis of St. Becker 相似文献
995.
A rapid, sensitive and selective method is described for the determination of chromium(VI) in presence of 100-fold amounts of chromium(III) by flame atomic absorption spectrometry (FAAS) in conjunction with coprecipitative preconcentration of its ethyl xanthate complex onto naphthalene. The solid mixture consisting of the chromium(VI) complex together with naphthalene is dissolved in 8.0 ml of dimethyl formamide (DMF) and chromium(VI) content was established by FAAS. Calibration graphs were rectilinear over the chromium(VI) concentration in the range 0-200 μg l−1. Five replicate determinations of 20 μg of chromium(VI) present in 1.0 l of sample solution gave a relative standard deviation of 3.1%. The detection limit corresponding to three times the standard deviation of the blank was found to be 0.5 μg l−1. The developed procedure has been successfully utilized for the estimation of chromium(VI), chromium(total) (after oxidation with bromate) and chromium(III) (by subtracting chromium(VI) content from chromium(total) value contents of several tannery industries. 相似文献
996.
Amberlite XAD-4 has been functionalized by coupling it with 5-aminoquinoline-8-ol after acetylation. The resulting resin has been characterized by elemental analysis and IR spectra and has been used for preconcentrating uranyl ions prior to its determination by spectrophotometry. The optimum pH value for quantitative sorption is 4-6, and desorption can be achieved by using 5 mL of 1 mol L(-1) HCl. The sorption capacity of the resin is 11.5 mmol g(-1). The effect of various cations and anions on the preconcentration of uranium in conjunction with the determination procedure has been studied and we have found that none of the ions interfere except thorium. The enrichment factor for preconcentration of uranium was found to be 200. Ten replicate determinations of 40 micro g of uranium present in 1 L of sample gave a mean absorbance of 0.185 with a relative standard deviation of 2.64%. The detection limit corresponding to three times the standard deviation of the bank was found to be 2 micro g L(-1). The validation of the developed preconcentration procedure was carried out by successfully analyzing standard marine sediment reference material. The uranyl content of sediment and soils is estimated by spectrophotometry after its preconcentration with the above chelating resin. 相似文献
997.
Patmore NJ Hague C Cotgreave JH Mahon MF Frost CG Weller AS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(9):2088-2098
Four Lewis acidic silver phosphane complexes partnered with [1-closo-CB(11)H(12)](-) and [1-closo-CB(11)H(6)Br(6)](-) have been synthesised and studied by solution NMR and solid-state X-ray diffraction techniques. In the complex [Ag(PPh(3))(CB(11)H(12))] (1), the silver is coordinated with the carborane by two stronger 3c-2e B-H-Ag bonds, one weaker B-H-Ag interaction and a very weak Ag.C(arene) contact in the solid state. In solution, the carborane remains closely connected with the [Ag(PPh(3))](+) fragment, as evidenced by (11)B chemical shifts. Complex 2 [Ag(PPh(3))(2)(CB(11)H(12))](2) adopts a dimeric motif in the solid state, each carborane bridging two Ag centres. In solution at low temperature, two distinct complexes are observed that are suggested to be monomeric [Ag(PPh(3))(2)][CB(11)H(12)] and dimeric [Ag(PPh(3))(2)(CB(11)H(12))](2). With the more weakly coordinating anion [CB(11)H(6)Br(6)](-) and one phosphane, complex 3 [Ag(PPh(3))(CB(11)H(6)Br(6))] is isolated. Complex 4, [Ag(PPh(3))(2)(CB(11)H(6)Br(6))], has been characterised spectroscopically. All of the complexes have been assessed as Lewis acids in the hetero-Diels-Alder reaction of N-benzylideneaniline with Danishefsky's diene. Exceptionally low catalyst loadings for this Lewis acid catalysed reaction are required (0.1 mol %) coupled with turnover frequencies of 4000 h(-1) (quantitative conversion to product after 15 minutes using 3 at room temperature). Moreover, the reaction does not occur in rigorously dry solvent as addition of a substoichiometric amount of water (50 mol %) is necessary for turnover of the catalyst. It is suggested that a Lewis assisted Br?nsted acid is formed between the water and the silver. The effect of changing the counterion to [BF(4)](-), [OTf](-) and [ClO(4)](-) has also been studied. Significant decreases in reaction rate and final product yield are observed on changing the anion from [CB(11)H(6)Br(6)](-), thus demonstrating the utility of weakly coordinating carborane anions in organic synthesis. 相似文献
998.
Zusammenfassung 4-Benzoyl-5-phenyl-2.3-dihydrofuran-2.3-dion (1) wandelt sich beim Erhitzen auf 120–140° unter Abgabe von CO und CO2 in 3.5-Dibenzoyl-2.6-diphenyl-4-pyron (2, 79% d. Th.) um. Nimmt man die therm. Zers. in Toluol in Gegenwart katalyt. Mengen Säure vor, so bildet sich 3.7-Dibenzoyl-4.8-diphenyl-1.5-dioxocin-2.6-dion (3, 90% d. Th.). Als gemeinsame Zwischenstufe wird das Dibenzoyl-keten (4) postuliert.
Herrn Prof. Dr.M. Pailer, Univ. Wien, mit freundschaftlichen Grüßen und besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
Syntheses of heterocycles, CLIV (reactions of cyclic oxalyl compounds, V)
4-Benzoyl-5-phenyl-2.3-dihydrofuran-2.3-dione (1) is converted at 120–140° under the loss of CO and CO2 to yield 3.5-dibenzoyl-2.6-diphenyl-4-pyrone (2, 79%). However, 3.7-dibenzoyl-4.8-diphenyl-1.5-dioxocin-2.6-dione (3) is formed in 90% yield, if1 is decomposed in boiling toluene in the presence of acids. The dibenzoyl ketene4 is postulated as the common intermediate.
Herrn Prof. Dr.M. Pailer, Univ. Wien, mit freundschaftlichen Grüßen und besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
999.
Helga Wittmann P. Sroka H. Sterk E. Ziegler 《Monatshefte für Chemie / Chemical Monthly》1969,100(2):734-738
Zusammenfassung Die Malonsäurediamid-N,N-disulfochloride1–4 übertragen beim Erhitzen in Benzol oder Toluol die SO2Cl-Gruppe auf den Aromaten, wobei das Diamiddisulfochlorid in gasförmige Bruchstücke zerfällt. Das Massenspektrum von Isopropylmalonsäurediamid-N,N-disulfochlorid (1) wird diskutiert.
Chlorosulfonation of aromatic hydrocarbons by means of malondiamide disulfochlorides
Malonamide-N,N-disulfochlorides (1–4) transfer their SO2Cl-group to aromatic solvents if heated to reflux. Under these conditions the malonamide-N,N-disulfochlorides are cleaved into gaseous fragments. The mass spectrum of isopropylmalonamide-N,N-disulfochloride (1) is discussed.相似文献
1000.
Max Ziegler und Hartmut Schroeder 《Fresenius' Journal of Analytical Chemistry》1967,226(5):405-408
Zusammenfassung Unter den Verbindungen [Pd · Thioxan2 X2] (X=Cl, Br, J) eignet sich das Chlorid zur extraktiv-photometrischen Bestimmung geringer Palladium-Mengen neben größeren Überschüssen an Gold und Platinmetallen, sowie neben den meisten Übergangsmetallen bei Verhältnissen Pd: Übergangsmetall=110000.
Der Deutschen Forschungsgemeinschaft danken wir für die Förderung der Arbeit durch Sachhilfen. 相似文献
Summary Within the compounds of the type [Pd · Thioxan2X2] (X=Cl, Br, J) the chloride may be used for extractive-photometric determination of small amounts of palladium in the presence of larger quantities of gold and platinum metals, and also of most of the transition metals (Pd: transition metal=110000).
Der Deutschen Forschungsgemeinschaft danken wir für die Förderung der Arbeit durch Sachhilfen. 相似文献