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51.
Josef Edinger Heinz Falk Walter Jungwirth Norbert Müller Ulrich Zrunek 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):1081-1099
From an investigation of the ICD of bilatrienes-abc and 2,3-dihydrobilatrienes-abc induced by mixtures of CCl4 with (+)-cis-Pinane, (–)-lactic and (+)-tartaric acid esters it is concluded that specific interactions between chromophore and the chiral reagents afford a partial resolution of the labile racemate of helices. Attaching chiral residues covalently to the chromophore induces very low resolution of the same kind in case of apolar ligands like a cholesteryl-residue. However, with polar ligands as in the case ofBoc-lysyl derivatives enantiomeric excesses up to 90% are achieved depending on the solvent used.
Herrn Prof. Dr.Karl Schlögl zu seinem 60. Geburtstag gewidmet. 相似文献
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Katsufumi Hashimoto Jií íek Josef Paldus 《International journal of quantum chemistry》1988,34(5):407-415
The ground state energies of finite Hubbard molecules are calculated by numerically solving the Lieb–Wu equations for a complex Hubbard repulsion parameter U. From the positions of the singular points located in the complex plane, the radii of convergence of the perturbation expansions for the ground state energies are determined. 相似文献
54.
In Nd-Fe-B based permanent magnets a high magnetocrystalline anisotropy of the hardmagnetic phase is necessary for a high intrinsic coercivity. In fact, metallurgical parameters (distribution of phases, chemical composition and crystal structures of phases) and processing parameters (alloy preparation, size and shape of particles, sintering and annealing treatments) determine the value of the coercive force of each sintered Nd-Fe-B magnet. Our analytical electron microscope study shows that melt-spun and sintered Nd-Fe-B based magnets contain more or less a distribution of nucleation centres for reversed domains, such as iron-rich phases and-iron precipitates within the hardrnagnetic 2141-grains. A continuous non-magnetic layer phase between the hardrnagnetic 2141-grains increases the expansion field of reversed domains and increase the coercivity. In melt-spun magnets the contribution of the pinning of magnetic domain walls becomes effective during the magnetization reversal process. 相似文献
55.
The model of two interacting ethylene molecules having D
2h symmetry was studied using generalized Hückel method. The validity of - separation was tested on this model. The general character of the ground state and lower lying excited states of the model was discussed and the implications drawn concerning transannular interaction and excimer formation. The values obtained for the dissociation energy of the first excited state of our model and corresponding equilibrium intermolecular distance are of right order of magnitude.
Zusammenfassung Mittels der verallgemeinerten Hückel-Methode wurde das Modell von zwei Äthylenmolekülen mit der Symmetrie D 2h studiert. An diesem Modell wurde die Gültigkeit der - -Separation geprüft. Der allgemeine Charakter des Grundzustandes und der niedriger liegenden angeregten Zustände des Modells wird erörtert und die Folgerungen in Bezug auf transannulare Wechselwirkung und Excimer-Entstehung diskutiert. Die erhaltenen Werte für die Dissoziationsenergie des ersten angeregten Zustandes von unserem Modell und den entsprechenden intermolekularen Gleichgewichtsabstand haben die richtige Größenordnung.
Résumé Le modèle à symétrie D 2h de deux molécules d'éthylène en interaction a été étudié en utilisant la méthode généralisée de Hückel. On a examiné la validité de la séparation - sur ce modèle. Le caractère général de l'état fondamental et celui des états excités inférieurs du modèle furent discutés et on a fait des déductions sur l'interaction transannulaire et sur la formation d'«excimères». Les valeurs obtenues pour l'énergie de dissociation du premier état excité de notre modèle et la distance intermoléculaire d'équilibre corréspondante ont l'ordre de magnitude correct.相似文献
56.
Rearrangements of (2′-Propinyl)cyclohexadienols and -semibenzenes The acid-catalyzed dienol-benzene rearrangement of 3- and 5-methyl-substituted (2′-propinyl)cyclohexadienols has been investigated. Treatment of the dienols with CF3COOH in CCl4 yields allenyl- and (2′-propinyl)benzenes via [3,4]- and [1,2]-sigmatropic rearrangements, respectively. The reaction with H2SO4 in Et2O leeds to a mixture of allenyl-, 2′-propinyl-, 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 3). The latter are products of a thermal semibenzene-benzene rearrangement (cf. Scheme 9). The corresponding semibenzenes have been prepared by dehydration of the cyclohexadienols with H2SO4 or POCl3 (Schemes 6 and 7). Under acidic conditions, the p-(2′-propinyl)semibenzenes 33–35 (Scheme 8) undergo [3,4]- and [1,2]-sigmatropic rearrangements to give again allenyl- and (2′-propinyl)benzenes, whereas the thermal rearrangements to the 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 9) involves a radical mechanism. In contrast, the o-(2′-propinyl)semibenzene b (Scheme 7) leads to (2′,3′-butadienyl)benzene 32 via a thermal [3,3]-sigmatropic rearrangement. 相似文献
57.
Shelby E. Thames Josef F. McClesky Phillip L. Kelly 《Journal of heterocyclic chemistry》1968,5(6):749-752
The preparation of several 2-furyl-, 2-thienyl-, benzyl-, and allylsubstituted silanes is reported. Such derivatives, when treated with aziridine in the presence of a metal catalyst, afford good yields of silylaziridines and silyldiaziridines. A qualitative study of electronic and steric requirements of the displacement reaction is reported. 相似文献
58.
A fast and effective method to study the aquation of rhodium(III) chlorocomplex in hydrochloric solutions using capillary zone electrophoresis (CZE) is developed. At least five species, some of which seem to be oligomeric, are formed in solution during the aquation process at pH>1. The fast hydration of RhCl63− makes this species impossible to detect. The first species detected in the optimised conditions is RhCl5(H2O)2− although RhCl4(H2O)2− is the main species during the first stage of the aquation process. When equilibrium is reached either RhCl3(H2O)3 or a cationic complex, RhCl2(H2O)4+, is formed as the main species. Matrix Assisted Laser Desorption Ionisation Time of Flight Mass Spectrometry (MALDI-TOF MS) is used as a novel technique to elucidate the structure of the rhodium aqua/chloro complexes formed in solution. Results obtained by CZE are confirmed by spectrophotometry. 相似文献
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60.