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81.
Zvjezdana Lazarević Jasna Vorkapić-Furač Jasenka Mühl 《Monatshefte für Chemie / Chemical Monthly》1992,123(12):1175-1179
Summary Stable enolic isomers of 2-aroyl-4-aracyl-1,3-cyclopentanediones such as3 and4 were prepared by condensation of aryl methyl ketones and diethyl maleate using an excess of sodium ethoxide (Aryl=C6H5, 4-C6H4CH3, 4-C6H4Br and 4-C6H4Cl).
-Tricarbonyl Verbindungen. I. 2,4-Disubstituierte 1,3-Cyclopentandione
Zusammenfassung Stabile Enol-Isomere von 2-Aroyl-4-aracyl-1,3-cyclopentandionen wie3 und4 wurden durch Kondensation von Arylmethylketonen und Diethylmaleat mit einem Überschuß von Natriumethoxid dargestellt (Aryl=C6H5, 4-C6H4CH3, 4-C6H4Br und 4-C6H4Cl).相似文献
82.
Peptides represent an extensive class of biologically active molecules. They may be used as leads in the development of novel therapeutic agents provided the pharmacophoric information present within them can be translated into non-peptide analogs that lack the peptide backbone and are stable to proteolysis. This is the rationale for peptidomimetic drug design. Frequently, the -turn has been implicated as a conformation important for biological recognition of peptides. Empirical evidence from known peptidomimetics, coupled with a theoretical model of peptide binding and the observation that glycine and proline residues are common within the -turn, has suggested the design of molecules to mimic placement of between two and four of the side-chains. The moderate number of different -turn conformations, combined with the combinatoric nature of side-chain selection complicates the procedure. In this paper, cluster analysis has been used to classify the arrangement of C_ atoms about the various fragments of the -turn. Recombination of the observed patterns provides a general model for the -turn which may be used as an effective screen for potential peptidomimetic scaffolds in chemical databases. 相似文献
83.
Hoebbel Dagobert Reinert Thomas Schmidt Helmut Arpac Ertugrul 《Journal of Sol-Gel Science and Technology》1997,10(2):115-126
The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H
84.
Summary Two -cyclodextrin (-CD)-containing polymers have been prepared either by condensation of -CD molecules with a bifunctional reagent or by grafting a -CD derivative on to a linear polymer (polyvinylimidazole). HPLC stationary phases were obtained by adsorption of the -CD polymers on to silica. The ability of these chromatographic supports to resolve racemic mixtures of organic compounds such as amino acid derivatives, phenylhydantoins, barbiturates, and hydroxycoumarin derivatives has been investigated. Results were found to depend on the chemical structure of the -CD polymers 相似文献
85.
Ali Taha Viktor Gutmann Wolfgang Linert 《Monatshefte für Chemie / Chemical Monthly》1991,122(5):327-339
Summary The solvatochromic and thermochromic behaviour of a series of mixed Ni(II) complexes with unsubstituted and substituted -diketones and diamines in the solvents 1,2-dichloroethane (DCE), acetonitrile (An), acetone (AC),n-butanol (n-BuOH), formamide (FA), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine (PY) has been studied and characterized on the basis of electronic spectra. Spectrophotometric methods have been used to evaluate equilibrium constants and their enthalpic and entropic terms for the formation of Ni(-dik)(diam)L
+ and Ni(-dik)(diam)L
2
+
. Increasing donor strength of the donor-solvents (L) and (or) increasing electronwithdrawing parameters of the substituents at the -diketone and the diamine ligands lead to increasing formation constants, paralleled by relative increase in the stability of the five-coordinated species Ni(-dik)(diam)L
+. The results are discussed in terms of the extended donor-acceptor concept.On leave of absence from the Faculty of Education, Ain Schams University, Roxy, Cairo, Egypt 相似文献
86.
Bromination of -aminovinyl ketones (AVK) with geminal arrangement of the fluoroalkyl and amino groups gives N-bromo derivatives. Regioisomeric AVK with the amino groups in the -position relative to the fluoroalkyl group undergo bromination under analogous conditions to give a mixture of the -bromo and ,N-dibromo derivatives. -Bromo derivatives of AVK disproportionate upon storage.Division of Fine Chemical Synthesis, Institute of Organic Chemistry, Urals Branch, Russian Academy of Sciences, 620219 Ekaterinburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 746–749, March, 1992. 相似文献
87.
Günter M. Ziegler 《Journal of Algebraic Combinatorics》1992,1(3):283-300
The broken-circuit complex is fundamental to the shellability and homology of matroids, geometric lattices, and linear hyperplane arrangements. This paper introduces and studies the -system of a matroid, nbc(M), whose cardinality is Crapo's -invariant. In studying the shellability and homology of base-pointed matroids, geometric semilattices, and afflne hyperplane arrangements, it is found that the -system acts as the afflne counterpart to the broken-circuit complex. In particular, it is shown that the -system indexes the homology facets for the lexicographic shelling of the reduced broken-circuit complex
, and the basic cycles are explicitly constructed. Similarly, an EL-shelling for the geometric semilattice associated with M is produced,_and it is shown that the -system labels its decreasing chains.Basic cycles can be carried over from
The intersection poset of any (real or complex) afflnehyperplane arrangement is a geometric semilattice. Thus the construction yields a set of basic cycles, indexed by nbc(M), for the union of such an arrangement. 相似文献
88.
Summary The photogalvanic effect of ferrousbis-(acetylacetonate) (Fe(II)(acac)2) and ferrousbis-(trifluoroacetylacetonate) (Fe(II)(tfac)2) complexes in aqueous acetonitrile thionine dye solutions has been studied in a photogalvanic cell of 70 cm3 capacity with identical platinum electrodes (area: 0.25 cm2) using visible light (80 mW/cm2) at 25°C. The theoretical Sunlight Engineering Efficiency (SEE) was determined for both complexes and it was found that the best SEE was obtained when Fe(II)(tfac)2 was used at a concentration of 1.5×10–4 mol/dm3 with a thionine concentration of 1×10–4 mol/dm3 atpH=4 in 40% aqueous acetonitrile. Effects of incident light intensity and temperature on the photogalvanic performance and the action spectrum of the present system were also investigated. A mechanism of the photoredox reaction between the Fe(II)-complex and the dye molecule is proposed.
Der photogalvanische Effekt von Fe(II)--Diketonat/Thionin-Systemen in wäßrigem Acetonitril
Zusammenfassung Der photogalvanische Effekt von Eisen(II)-bis-(acetonylacetonat) (Fe(II)(acac)2) und Eisen(II)-bis-(trifluoracetylacetonat) (Fe(II)(tfac)2 in wäßriger acetonitrilischer Thioninlösung wurde in einer photogalvanischen Zelle (70 cm3) mit identischen Platinelektroden (Fläche: 0.25 cm2) mit sichtbarem Licht (80 mW/cm2) bei 25°C untersucht. Für beide Komplexe wurde die theoretische Sunlight Engineering Efficiency (SEE) bestimmt; der beste SEE-Wert wurde für Fe(II)(tfac)2 bei einer Konzentration von 1.5×10–4 mol/dm3 beipH=4 in 40%igem Acetonitril gefunden (Thioninkonzentration: 1.0×10–4 mol/dm3). Effekte, die durch Änderung der Lichtintensität und der Temperatur hervorgerufen werden, werden diskutiert. Ein Mechanismus für die Photoredoxreaktion zwischen dem Fe(II)-Komplex und dem Farbstoffmolekül wird vorgeschlagen.相似文献
89.
The influence of simulation methods, cutoff based and particle mesh Ewald (PME) on the accuracy by which experimentally derived nuclear Overhauser effect (NOE) data are reproduced, has been investigated using 500-ns-long molecular dynamics simulations on a model -sheet peptide in explicit solvent. The structural and conformational features under the different conditions were evaluated in terms of flexibility, secondary structure content, hydrogen-bonding pattern and percent of native contacts as a function of time. It was found that the different simulation methods strongly influence the dynamics of the peptide, confirming previous observations based on ideal peptide models simulated for much shorter times. Moreover, the results of our simulations prove once more that it is necessary to reach extremely long time scales to obtain enough statistics to accurately reproduce experimental NOE restraints even in the case of the PME method, despite its tendency to the stabilization of conformations which are structurally closely related to the ones derived through experiment. Possible implications regarding the stabilization and folding mechanisms, together with their relationship to the experimental study of peptide models, are discussed. 相似文献
90.
A seven-step synthesis ofS-(+)-hydroprene (S-1) in 20 % overall yield starting fromS-(+)-3,7-dimethyl-1,6-octadiene (2) of 55+-10 % optical purity is described. The introduction of an optical enhancement step in the synthetic sequence at the stage ofS-(–)-3,7-dimethyl-1-octanol (9) raises the optical purity ofS-1 from 50 % to 80 %.For part 13, see. ref.1
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 342–348, February, 1993. 相似文献