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51.
The reaction of 2 equiv of LiSeCC-n-C(5)H(11) (1) with cis-PtCl(2)(Ph(3)P)(2) (2) gives a mixture of the cis and trans isomers of Pt(Ph(3)P)(2)(SeCC-n-C(5)H(11))(2) (3), which slowly isomerizes in CH(2)Cl(2) to the preferred trans form trans-3. The closely related cis-[Pt(dppf)(2)(SeCC-n-C(5)H(11))(2)] (4) (dppf = bis(diphenylphosphino)ferrocene) was prepared by a similar metathetical reaction using the platinum chloride complex of the chelating dppf to impose the cis geometry. The structures of the cis and trans complexes have been investigated in solution by heteronuclear NMR ((31)P, (77)Se, and (195)Pt) and, in the cases of trans-3 and 4, characterized in the solid state by single-crystal X-ray diffraction. Changing the coordination geometry from cis to trans induces significant changes in the structural and spectroscopic parameters, which do not comply with the previously anticipated donor-acceptor properties of selenolate ligands. 相似文献
52.
Zusammenfassung Es wird eine rasche Methode zur Bestimmung von Magnesium in Aluminium und Aluminiumlegierungen beschrieben. Magnesium wird als CMAB-Oxin-Komplex mit Chloroform extrahiert und nach Rückschüttelung mit einer Boratpufferlösung spektralphotometrisch unter Verwendung von Calmagit als Reagens bestimmt.
Herrn Prof. Dr. W. Leithe danken wir für wertvolle Anregungen und Hinweise, der Direktion der Österreichischen Stickstoffwerke AG für die Erlaubnis zur Veröffentlichung. 相似文献
Summary A quick method is described for the determination of magnesium in aluminium and aluminium alloys. Magnesium is first separated as CMAB-oxine complex in chloroform and after back-extraction into a borate-buffer solution determined spectrophotometrically using Calmagite as reagent.
Herrn Prof. Dr. W. Leithe danken wir für wertvolle Anregungen und Hinweise, der Direktion der Österreichischen Stickstoffwerke AG für die Erlaubnis zur Veröffentlichung. 相似文献
53.
Rudolf Tannenberger 《Fresenius' Journal of Analytical Chemistry》1956,152(1-3):193-203
Zusammenfassung Das Studium der Fällungsbedingungen für Asphalte aus Teeren und Hydrierprodukten hat zur Entwicklung einer Bestimmungsmethodik mit Vorfällung des Asphaltes durch Erdölschmieröle geführt. Die Verwendung des Schmieröles ermöglicht die Abscheidung der Asphaltstoffe in einer für die nachfolgende Extraktion sehr günstigen, großoberflächigen, pulvrigen Form, wenn man dafür sorgt, daß ein Schmelzen oder Klebrigwerden durch zu hohe Temperaturen beim Fällungsvorgang vermieden wird. Die Dispergierung des zu fällenden Produktes wird durch die gute Lösefähigkeit des Erdölschmieröles für die Nichtasphaltstoffe sehr gefördert und ermöglicht eine gute Verteilung. Auf die Zusammensetzung der Teer- bzw. Entschlammungsasphalte wird näher eingegangen und ihre Bedeutung für die Weiterverarbeitung kurz gestreift.Herrn Professor Dr. A. Kurtenacker zum 70. Geburtstag gewidmet.Herrn Friedrich Ganteför und Fräulein Reiher sei an dieser Stelle für die umfangreiche Mitarbeit bei der praktischen Durchführung der Versuche herzlichst gedankt. 相似文献
54.
For symmetry-constrained boranes B10H, B12H, and their valence isoelectronic analogues containing a single hetero atom, completely optimized geometries were obtained using Hartree–Fock SCF calculations with the 3-21G and 6-31G* basis sets. For the anionic and dianionic species, the geometry optimization was also carried out using the 6-31 + G* basis set. Harmonic vibrational frequencies were obtained at HF/3-21G level. The results compare well with experiment where available. 相似文献
55.
Dana Kubies Jaroslav Š?udla Rudolf Puffr Antonín Sikora Josef Baldrian Jana Ková?ová Miroslav Šlouf František Rypá?ek 《European Polymer Journal》2006,42(4):888-899
Poly(ε-caprolactone) (PCL) masterbatches with the intercalated and the exfoliated morphology were prepared by ring opening polymerization of ε-caprolactone in the presence of organomodified montmorillonite (MMT) Cloisite 30B. Poly(l-lactide) (PLLA) nanocomposites with Cloisite 30B or PCL masterbatches were prepared by melt blending. The effects of the silicate type, MMT content and the nanocomposite morphology on thermal and mechanical properties of PLLA nanocomposites were examined. The montmorillonite particles in PLLA/Cloisite 30B and PLLA/intercalated masterbatch nanocomposites were intercalated. In contrary to expectations, the exfoliated silicate layers of exfoliated masterbatch were not transferred into the PLLA matrix. Due to a low miscibility of PCL and PLLA, MMT remained in the phase-separated masterbatch domains. The stress-strain characteristics of PLLA nanocomposites, Young modulus E, yield stress σy and yield strain εy, decreased with increasing MMT concentration, which is associated with the increase in PCL content. The expected stiffening effect of MMT was low due to a low aspect ratio of its particles and was obscured by both plastifying effects of PCL and low PLLA crystallinity. Interestingly, in contrast to the neat PLLA, ductility was enhanced in all PLLA/Cloisite 30B materials and in PLLA/masterbatch nanocomposites with low MMT concentrations. 相似文献
56.
Rudolf Schmid Joseph Foricher Marco Cereghetti Peter Schnholzer 《Helvetica chimica acta》1991,74(2):370-389
The new axially dissymmetric diphosphines (R)- and (S)-(6,6′-dimethoxybiphenyl-2,2′-diyl)bis(diphenyl phosphine) ((R)- and (S)- 5a ; ‘MeO-BIPHEP’) and the analogues (R)- and (S)- 5b and 5c have been synthesized in enantiomerically pure form. These ligands have become readily available by a synthetic scheme which employs, as key steps, an ortho-lithiation/iodination reaction of the (m-methoxyphenyl)diprienylphosphine oxides 8 and a subsequent Ullmann reaction of the resulting iodides 9 to provide the racemic bis(phosphine oxides) 10 . The bis(phosphine oxides) 10 subsequently are resolved with (?)-(2R,3R)- and (+)-(2S,3S)-O-2,3-dibenzoyltartaric acid and reduced to diphosphines 5 . The Ullmann reaction constitutes a new and efficient route to 2,2′-bis(phosphinoyl)-substituted biphenyl systems. Absolute configurations were established for (R)- 5a by X-ray analysis of the derived Pd complex (R,R)- 17a , and for 5b and 5c by means of 1H-NMR comparisons of the derived Pd complexes 16 or 17 , respectively, and by means of CD comparisons. The MeO-BIPHEP diphosphine 5a proved to be as efficient as the previously described BIPHEMP diphosphine ((6,6′-dimethylbiphenyl-2,2′-diyl)bis(diphenylphosphine)) in enantioselective isomerizations and hydrogenations. 相似文献
57.
We have theoretically examined the reaction course of the butadiene insertion into the arylNiII bond in the [NiII(η5-Cp)(η1-phenyl)(η2-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η1-σ→η3-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η3- and syn-η3-allyl isomers of the [NiII(η5-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η3-allyl isomer. Butadiene preferably inserts in η2-mode into the η1-phenylNiII bond, initially giving rise to the η1(C3)-allyl product species, 3σ. The direct formation of the η3-allyl product species, 3π, along the alternative path for η4-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η2-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η3-allylNiII coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η3-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η3-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η3-allyl→syn-η3-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η3-allylNiII coordination. 相似文献
58.
Rudolf F. X. Bauer Ikhlas A. Khan Hermann Lotter Hildebert Wagner Victor Wray 《Helvetica chimica acta》1985,68(8):2355-2358
The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities. 相似文献
59.
Paul Richard Jenkins Rudolf Gut Hansjürg Wetter Albert Eschenmoser 《Helvetica chimica acta》1979,62(6):1922-1931
Note on a preparation of β, γ-unsaturated carboxylic acid derivatives using the amide acetal Claisen rearrangement 3-(Trimethylsilyl)allyl alcohols smoothly undergo the amide acetal Claisen rearrangement furnishing allyl silanes. Subsequent protolysis with HF at ?20° provides a convenient, stereoselective method for the preparation of β, γ-unsaturated carboxylic acid derivatives. Three model examples illustrate the procedure. 相似文献
60.
Douglas A. Livingston Andreas Pfaltz Jakob Schreiber Albert Eschnmoser Dorothe Ankel-Fuchs Johanna Moll Rolf Jaenchen Rudolf K. Thauer 《Helvetica chimica acta》1984,67(1):334-351
Factor F430 from Methanogenic Bacteria: Structure of the Protein-free Factor Factor F430, the porphinoid nickel-containing coenzyme of the methylcoenzyme-M reductase of metanogenic bacteria is shown to be the 33,83,122,133,182-pentaacid derivative of the pentamethylester F430M, the structure of which had been determined previously (see structural formulae 1 and 2 ). The structure assignment rests on chromatographic, UV/VIS-, CD-, IR-, and 13C-NMR-spectroscopic as well as FAB-mass spectral comparision of F430 with F430M and the pentaacid prepared by acid-catalyzed hydrolysis of F430M. In the cells of Methanobacterium thermoautotrophicum, factor F430 is present in a ‘bound’ and also, depending on the growth conditions, in ‘free’ form, the latter being defined as the part of total F430 that can be extracted from the cells under extremely mild conditions (80% EtOH at 0–4°). From the (protein)-‘bound’ form, F430 is extracted by subsequently treating the cells at 0–4° with 80% EtOH containing (e.g.), 2m LiCi. From both sources, the extracted factor is the same pentaacid, and there is no indication for the existence of a protein-free F430 species that would contain additional (covalently bound) structural elements. 相似文献