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101.
In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio. 相似文献
102.
103.
Kirsten Werner Volker Steinert Steffi Reinhardt 《Macromolecular rapid communications》1995,16(9):673-678
The polarographic behaviour of hydrolyzed propene-maleic anhydride copolymers in the interval pH 2.0–11.0 has been investigated by differential pulse polarography in aqueous lithium chloride solution at 25°C. In dependence on the pH-value, one, two or three signals, belonging to the acid groups in the copolymer, appear in the polarograms. Three apparent polarographic acid constants have been determined graphically from the changes in the half-wave potential of the separate peaks in correlation with pH. 相似文献
104.
Based on the Michael reaction of multifunctional acetoacetates with multiacrylates, in the presence or absence of dimethacrylates, tailor made matrix materials can be prepared. This can be achieved in a one- or two-step process. The Michael addition (first step) can be followed by radiation curing of excessive acrylate (second step). 相似文献
105.
End group analysis is the most important absolute method of obtaining number-average molar mass values for polymers of the step-growth polymerization type. A great number of methods are available which primarily differ in the detection of the end group concerned. Special chemical methods based on the formation of covalent derivatives of the end groups (e.g. introduction of UV/VIS chromophores) are important if there is a need to demonstrate, with the aid of gel permeation chromatography, that damage to the polymer (e.g. onset of cross-linking) has occurred. In the case of fibre-forming polycondensation products, the applicability of end group analysis is often restricted by the lack of suitable reagents and solvents. This is also true of the determination of amino end groups in polyamides by means of 1-fluoro-2,4-dinitrobenzene, as is already contained in the German Standards specification (DIN 54 274) - albeit only for polyamide 6 and 6,6. This contribution describes a modified version of the 1-fluoro-2,4-dinitrobenzene method. The analytical principle and practical procedure correspond to those of DIN 54 274, but the solvent used for the reaction with the reagent is benzyl alcohol, and that for the photometric evaluation is 1,1,1,3,3,3-hexafluoro-2-propanol. The scope of the method is thus increased. Examples of applications for this method are commercial products based on aliphatic polyamides (6; 11; 12; 6,6; 6, 12), partially aromatic polyamides (2,4,4-trimethylhexamethylenediamine, terephthalic acid; copolyamides with bis-(4-aminocyclohexyl)propane(2), isophthalic acid, ω-aminododecanoic acid) and multicomponent systems with the abovementioned polyamides (bicomponent fibres, blends). It is shown that large differences may arise between the value determined by titration and the actual amino end group content. In addition, the presence of secondary amino groups can be demonstrated in polyamides of the Trogamid T type. 相似文献
106.
Volker Schubert 《Nachrichten aus der Chemie》1992,40(12):1339-1339
107.
108.
M. Häser R. Ahlrichs H. P. Baron P. Weis H. Horn 《Theoretical chemistry accounts》1992,83(5-6):455-470
Summary The ab initio SCF computation of second-order properties of large molecules (with 50 atoms or more) on workstation computers is demonstrated for static dipole polarizabilities and nuclear magneting shieldings. The magnetic shieldings are calculated on the basis of gauge including atomic orbitals (GIAO). Algorithmic advances (semi-direct algorithms with efficient integral pre-screening, and use of a quadratically convergent functional for the polarizabilities) are presented together with an illustrative application to the fullerenes C60 and C70. 相似文献
109.
110.
I. K. Bensafa P. Achenbach M. Ases Antelo C. Ayerbe D. Baumann R. Böhm D. Bosnar E. Burtin X. Defaÿ N. D'Hose M. Ding M. O. Distler L. Doria H. Fonvieille J. M. Friedrich J. Friedrich J. García Llongo P. Janssens G. Jover Mañas M. Kohl G. Laveissière M. Lloyd M. Makek J. Marroncle H. Merkel P. Merle U. Müller L. Nungesser B. Pasquini R. Pérez Benito J. Pochodzalla M. Potokar G. Rosner S. Sánchez Majos M. Seimetz S. Širca T. Spitzenberg G. Tamas R. Van de Vyver L. Van Hoorebeke Th. Walcher M. Weis 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):69-75
The beam-helicity asymmetry has been measured simultaneously for the reactions
p→epγ and
p→epπ
0 in the Δ(1232)-resonance region at Q
2 = 0.35(GeV/c)2. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The
results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model
for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining
discrepancies may be ascribed to an imperfect parametrization of some γ
(*)
N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π
0) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization. 相似文献