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931.
Analytical fractionation of aquatic humic substances and their metal species by means of multistage ultrafiltration 总被引:2,自引:0,他引:2
Brit Aster P. Burba Jose A. C. A. C. Broekaert 《Fresenius' Journal of Analytical Chemistry》1996,354(5-6):722-728
The molecular-size fractionation of aquatic humic substances (HS) and their metal species by means of a novel sequential-stage ultrafiltration (UF) device equipped with five appropriate ultramembranes (1, 5, 10, 50 and 100 kD) is described. First of all, the concentration dynamics of macromolecules, particulary HS, during five-stage UF and its subsequent washing step has been modelled. Based on these results, the fractionation of aquatic HS (from ground and bog water) by means of multistage UF has been optimized for an analytical scale (10 ml sample, 1 mg/ml HS, 10 ml washing solution, pH 6.0). The molecular size-distribution of selected aquatic HS (BOC 1/2 from the DFG-Versuchsfeld Bocholt, VM 5 from Venner Moor, Germany) studied by five-stage UF exhibited strong systematic influences of the procedure used for their isolation. The molecular-size distribution of HS obtained by on-line UF and gel permeation chromatography (GPC) showed a satisfactory agreement in the range 1–50 kD. Moreover, when interrupting multistage UF for > 48 h a slow transformation in the HS samples has been found as gradually additional HS fractions of < 1 kD have been formed. Besides unloaded HS molecules, the molecular-size distribution of freshly formed metal species of HS (1.0 mg metal/g HS of Al(III), Cd(II), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Zn(II), each) has been characterized by multistage UF as a function of pH-value, degree of loading and complexation time. Metal determinations as carried out by flame AAS, showed that considerable metal fractions in HS especially are present in molecules > 50 kD, which seemed to be rather acid-inert. With complexation times of < 2 days a transient shift of the molecular size distribution of both HS and their metal species (e.g., Al(III), Fe(III) to higher values (> 10 kD) has been found. 相似文献
932.
Conclusions On the basis of UV, IR, and NMR spectroscopy, and the preparation of derivatives, the most probable structures of ursinoic acid and ursinin, aromatic oxo acids isolated previously from the roots ofAngelica ursina Rupr. et Schmalh., have been established. It has been shown that the former has the structure 2,2-dimethylpyrano-5, 6:5, 6-(2, 4-dimethoxy)benzoylacetic acid while the second is 2,2-dimethylpyrano-5,6:5, 6-(2-methoxy)benzoylacetic acid.Khimiya Prirodnykh Soedinenii, Vol. 6, No. 4, pp. 421–424, 1970 相似文献
933.
Summary Polarographic studies have been made of the reaction between Cerium(IV) and potassium thiocyanate in acidic medium. CeIVin the concentration range 2 · 10–4 M to 5 · 10–3 M was found to be reduced to CeIII by thiocyanate ion. One equivalent of thiocyanate reduced 4–6 equivalents of CeIV in the concentration range studied.
Zusammenfassung Die Reaktion zwischen CerIV und Kaliumthiocyanat wurde in saurem Medium polarographisch untersucht. CerIII wurde im Bereich von 2 · 10–4 m bis 5 · 10–3 m von Thiocyanat zu CerIII reduziert. In diesem Konzentrationsbereich entsprachen einem Äquivalent Thiocyanat 4–6 Äquivalente CerIV.相似文献
934.
In an earlier study we showed that a blend of thermoresponsive and nonthermoresponsive hydroxyalkylcelluloses could be used to create a thermally tunable polymer network for double-stranded (ds) DNA separation. Here, we show the generality of this approach using a family of polymers suited to a wider range of DNA separations: a blended mixture of N,N-dialkylacrylamide copolymers with different thermoresponsive behaviors. A mixture of 47% w/w N,N-diethylacrylamide (DEA)/53% w/w N,N-dimethylacrylamide (DMA) (DEA47; thermoresponsive, transition temperature = 55 degrees C in water) and 30% w/w DEA/70% w/w DMA (DEA30; nonthermoresponsive, transition temperature > 85 degrees C in water) copolymers in the ratio of 1:5 w/w DEA47:DEA30 was used to separate a dsDNA restriction digest (PhiX174-HaeIII). We investigated the effects of changing mesh size on dsDNA separation, as controlled by temperature. We observed good DNA separation performance with the copolymer blend at temperatures ranging from 25 degrees C to 48 degrees C. The separation selectivity was evaluated quantitatively for certain DNA fragment pairs as a function of temperature. The results were compared with those obtained with a control matrix consisting only of the nonthermoresponsive DEA30. Different DNA fragment pairs of various sizes show distinct temperature-dependent selectivities. Over the same temperature range, no significant temperature dependence of selectivity is observed for these DNA fragment pairs in the nonthermoresponsive control matrix. Overall, the results show similar trends in the temperature dependency of separation selectivity to what was previously observed in hydroxyalkylcellulose blends, for the same DNA fragment pairs. Finally, we showed that a ramped temperature scheme enables improved separation in the blended copolymer matrix for both small and large DNA fragments, simultaneously in a single capillary electrophoresis (CE) run. 相似文献
935.
Summary A volumetric method has been developed for the determination of thorium salts with Titriplex III (disodium EDTA) using a mixture of ferrous salt and cacotheline as indicator. The titration of the thorium salt is carried out in a buffered solution ofph 2.72 in carbon dioxide atmosphere with magnetic stirring until a pink color appears. The reduction of cacotheline to the pink compound occurs only when all the thorium is complexed by EDTA. The end point is sharp and the method has been found to give results accurate to 0.2 to 0.3%. Ferric iron, zirconium and phosphates are found to interfere while ferrous iron does not interfere. Walpole sodium acetate-HCl buffers are to be employed since phosphate-citrate buffers interfere, due to the presence of phosphate and citrate.In conclusion one of us, Mr. V. Narayana Rao, desires to express his grateful thanks to the Ministry of Education, Government of India, for the award of Senior Research Fellowship which has enabled him to take part in this investigation. 相似文献
936.
A new and original method of synthesizing difficultly accessible 1-hydrosilatranes, is developed. It is based on transesterification of the appropriate boratranes in the presence of aluminum alkoxide catalyst. The method is used to prepare four compounds of the type stated, only one of which (R=R=R"=H) was previously known.For Part X see [1]. 相似文献
937.
Jan Vorlíek Milan Fara Frantiek Vydra 《Fresenius' Journal of Analytical Chemistry》1968,241(5):314-318
Summary Conditions for the magnesium determination in alkaline solution by EDTA titration with biamperometric indication were examined. The most preferable pH range was found to be above 9.6. A reliable determination can be carried out in the presence of Ca, Ni, Cu and Co up to the ratio of 11. In the case of higher concentrations of Cu and Ni masking with potassium cyanide can be used. In this case, however, a change of the titration curves occurs.A new method for the determination of water-hardness by biamperometric indication is proposed. It is rapid and accurate and meets the requirements of routine and research work (error: ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
Zusammenfassung Die Bedingungen für die Magnesiumbestimmung in alkalischer Lösung durch Titration mit ÄDTA bei biamperometrischer Endpunktsanzeige wurden untersucht. Der günstigste pH-Bereich liegt über 9,6. Zuverlässige Bestimmungen können in Gegenwart von Ca, Ni, Cu und Co bis zum Verhältnis 11 ausgeführt werden. Höhere Konzentrationen an Cu oder Ni können mit KCN maskiert werden, wobei allerdings eine Umkehrung der Kurven auftritt.Ein Verfahren zur Wasserhärtebestimmung mit biamperometrischer Indikation wird vorgeschlagen, das schnell durchzuführen ist und genaue Werte liefert (Fehler ±1%).
Part XV: Vorlíek, J., and P. Peták: Microchem. J. 12, 466–471 (1967). 相似文献
938.
羧甲基壳聚糖/聚乙烯醇/甘油环氧树脂蛇笼型复合螯合膜的制备及对金属离子的吸附性能 总被引:4,自引:0,他引:4
以交联甘油环氧树脂交联的聚乙烯醇(PVA)为笼树脂,羧甲基壳聚糖(CCTS)为蛇树脂制备了具有蛇笼结构的复合螯合膜,研究了其对Cu^2 、Ni^2 、Pb^2 、Fe^3 、Zn^2 ,Hg”^2 、Cd^2 等金属离子的吸附性能,研究表明,该树脂对Cu^2 、Ni^2 、Pb^2 有较好的吸附性能,其中PVA是对Cu^2 的吸附的主要贡献者,而CCTS则是在对Ni^2 的吸附中起主要作用。该树脂可以用于含Cu^2 废水的处理。 相似文献
939.
M. A. Aramendía V. Borau C. Jiménez J. M. Marinas A. Moreno F. J. Urbano 《Reaction Kinetics and Catalysis Letters》1995,56(1):87-96
We have studied the activity of Pd/sepiolite and Pd/SiO2–AlPO4 catalysts in cyclohexane aromatization. The catalysts were characterized by H2 chemisorption measurements. The influence of support and reduction temperature on the metal surface properties and activity of the catalysts is discussed. 相似文献
940.
1- and 2-Methoxy-heptafluorophenazine and 1- and 2-bromoheptafluorophenazine have been obtained by anodic oxidation of appropriately substituted 2-amino-octafluorodiphenylamines, the synthesis of which is described. By reaction of octofluorophenazine with suitable nucleophiles, 2-methoxy-, 2-hydroxy and 2-N,N1-dimethylamino-heptafluorophenazine were formed; some of their reactions are described. 相似文献