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81.
Electron attachment spectroscopy is employed to study the formation of negative ions from the chloroethylenes. It is found that the resonances recently observed in the total electron scattering cross section are predominantly associated with the formation of Cl?. Only in tetrachloroethylene is a long-lived parent negative ion observed. 相似文献
82.
Helmut Trutnovsky 《Mikrochimica acta》1968,56(1):97-105
Zusammenfassung Es wird über die Weiterentwicklung des bereits beschriebenen Verfahrens der gravimetrischen C-H-Bestimmung mit direkter Zuleitung der Verbrennungsprodukte zur Waage berichtet. Die Trennung von Wasser und Kohlendioxid erfolgt weiterhin durch eine Kühlfalle. Durch eine neuartige Konstruktion wurde eine durch vollständige Durchströmung der Absorptionsmittelschicht gewährleistete quantitative Absorption erreicht. Trotzdem kann das Absorptionsgefäß dauernd mit der hier verwendeten elektronischen Waage verbunden bleiben und ohne Manipulationen gewogen werden.
Herrn Prof. Dr.H. Lieb in Verehrung zum 80. Geburtstag gewidmet. 相似文献
Summary A report is given of the further development of the gravimetric determination of carbon-hydrogen in which the combustion products are led directly to the balance. The separation of the water and carbon dioxide is accomplished furthermore by a cooling trap. A new type of construction guaranteed quantitative absorption because of total passage through the layer of the absorbing agent. Nevertheless, the absorption vessel can remain permanently connected with the electronic balance employed and weighed without manipulation.
Herrn Prof. Dr.H. Lieb in Verehrung zum 80. Geburtstag gewidmet. 相似文献
83.
Egon Fanghnel Hagen Bartossek Ute Baumeister Matthias Biedermann Helmut Hartung 《Journal of heterocyclic chemistry》1998,35(6):1449-1454
The first synthesis of substituted 2,2-dioxo-1-phenyl-1H-thieno[3,4-c][1,2]thiazines 2 and some of their reactions are achieved. Compounds 2 were prepared from the 3,5-dimethyl-1,1-dioxo-1,2-thiazine-4-carbaldehydes 1 by reaction with sulfur and triethyl amine in dimethylformamide under mild conditions. They were characterized spectroscopically and by X-ray structure analysis. The formylation, chlorination and oxidation of 2 are reported. 相似文献
84.
Fausto Elisei Gian Gaetano Aloisi Helmut Görner 《Research on Chemical Intermediates》1995,21(7):725-734
The properties of the triplet state of five styrylphenanthrene (StPh) trans isomers were studied in 2-methyltetrahydrofuran (MTHF) as a function of temperature. At room temperature the T-T absorption was observed only for 4- and 9-StPh, while under these conditions 1-, 2-, and 3-StPh have too low a quantum yield of triplet formation (ΦT <0.02); their T-T absorption spectra were obtained at low temperature. ΦT of 1- and 2-StPh increases more than tenfold on going from 293 to 77 K, and the triplet lifetime (τT) increases by four orders of magnitude and approaches values of 5–40 ms at 77 K. The change in τT is explained in terms of an equilibrium between trans and perpendicular (perp) conformations of the lowest triplet state in fluid solution and temperature and viscosity effects on the trans → perp rotation. Evidence is presented for the existence of two conformeric trans triplet states of 3-StPh at 77 K. Semi-empirical calculations were performed to obtain the energy of the triplet state, the wavelengths of several T-T absorption maxima (λT), and the oscillator strength. The calculated λT values coincide with those measured in n-hexane. 相似文献
85.
Bis-(2,4,5-triphenylimidazolyls) result from the dimerization of 2,4,5-triphenylimidazolyls and from the nucleophilic attack of 2,4,5-triphenylimidazole anions upon 2,4,5-triphenylimidazolylium cations. The isomeric bis-imidazolyls consist of imidazole and isoimidazole systems. Imidazoles undergo only anodic oxidation, isoimidazoles only cathodic reduction. Therefore the bis-imidazolyls may be analyzed from their electrochemical behaviour. Bis-(2,4,5-triphenylimidazolyl)-1,2′ and bis-(2,4,5-triphenylimidazolyl)-1,4′ undergo reductive bond cleavage in an ē.c?.ē. mechanism from which 2,4,5-triphenyl-imidazole anions result. The electrochemical properties of one of the bis-imidazolyls agree with that of 1,4,5-triphenyl-2-(2,4,5-triphenylisoimidazolyl-4)-imidazole and not with that of bis-(2,4,5-triphenylimidazolyl)-2,4′ as reported in literature. 相似文献
86.
87.
Adenosine 5'-triphosphate (ATP(4-)) and related nucleoside 5'-triphosphates (NTP(4-)) serve as substrates in the form of metal ion complexes in enzymic reactions taking part thus in central metabolic processes. With this in mind, the coordination chemistry of NTPs is critically reviewed and the conditions are defined for studies aiming to describe the properties of monomeric complexes because at higher concentrations (>1 mM) self-stacking may take place. The metal ion (M(2+)) complexes of purine-NTPs are more stable than those of pyrimidine-NTPs; this stability enhancement is attributed, in accord with NMR studies, to macrochelate formation of the phosphate-coordinated M(2+) with N7 of the purine residue and the formation degrees of the resulting isomeric complexes are listed. Furthermore, the formation of mixed-ligand complexes (including also those with buffer molecules), the effect of a reduced solvent polarity on complex stability and structure (giving rise to selectivity), the use of nucleotide analogues as antiviral agents, and the effect of metal ions on group transfer reactions are summarized. 相似文献
88.
Sonnenschein H Kreher T Gründemann E Krüger RP Kunath A Zabel V 《The Journal of organic chemistry》1996,61(2):710-714
The first compounds of a new series of redox-active cyclophanes were prepared by dehydrocyclization of bridged indolizines of type 1. The bridged dipyridino-compounds 2a and 2b obtained by reaction of 2 mol of lithiated alpha-picolines with dihalides were used as starting materials. Subsequent treatment of 2a,b with 2 mol of alpha-bromo ketones gave quaternary pyridinium halides. Ring closure in an alkaline medium (Chichibabin reaction) yielded the starting material for the synthesis of the macrocycles. Oxidative C-C coupling gave the diastereomeric cyclophanes of type 3. In all cases one pair of the enantiomers was obtained in excess. CV-investigations have shown that the main products are reversible redox systems. To clarify their conformations, compounds 3c, 3d/1, and3d/2 were subjected to X-ray analysis. 相似文献
89.
Helmut Meyn 《Designs, Codes and Cryptography》1995,6(2):107-116
For an odd prime powerq the infinite field GF(q
2 )=
n0 GF (q
2n
) is explicitly presented by a sequence (f
n)1 ofN-polynomials. This means that, for a suitably chosen initial polynomialf
1, the defining polynomialsf
nGF(q)[x] of degrees2
n are constructed by iteration of the transformation of variablexx+1/x and have linearly independent roots over GF(q). In addition, the sequences are trace-compatible in the sense that the relative traces map the corresponding roots onto each other. In this first paper the caseq1 (mod 4) is considered and the caseq3 (mod 4) will be dealt with in a second paper. This specific construction solves a problem raised by A. Scheerhorn in [11]. 相似文献
90.
We give a necessary and sufficient condition for a Bell-type inequality to hold in a horizontal sum of finitely many finite Boolean algebras. 相似文献