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61.
Adsorption of CF4 on the internal and external surfaces of opened single-walled carbon nanotubes: a vibrational spectroscopy study 总被引:1,自引:0,他引:1
Byl O Kondratyuk P Forth ST FitzGerald SA Chen L Johnson JK Yates JT 《Journal of the American Chemical Society》2003,125(19):5889-5896
Infrared spectroscopy has been used to make the first experimental discrimination between molecules bound by physisorption on the exterior surface of carbon single-walled nanotubes (SWNTs) and molecules bound in the interior. In addition, the selective displacement of the internally bound molecules has been observed as a second adsorbate is added. SWNTs were opened by oxidative treatment with O(3) at room temperature, followed by heating in a vacuum to 873 K. It was found that, at 133 K and 0.033 Torr, CF(4) adsorbs on closed SWNTs, exhibiting its nu(3) asymmetric stretching mode at 1267 cm(-1) (red shift relative to the gas phase, 15 cm(-1)). Adsorption on the nanotube exterior is accompanied by adsorption in the interior in the case of opened SWNTs. Internally bound CF(4) exhibits its nu(3) mode at 1247 cm(-1) (red shift relative to the gas phase, 35 cm(-1)). It was shown that, at 133 K, Xe preferentially displaces internally bound CF(4) species, and this counterintuitive observation was confirmed by molecular simulations. The confinement of CF(4) inside (10,10) single-walled carbon nanotubes does not result in the production of lattice modes that are observed in large 3D ensembles of CF(4). 相似文献
62.
With an excess of dithizone over tellurium, the extraction of Te(IV) from 1 M perchloric acid solutions into a carbon tetrachloride solution (o) of dithixone follows the relation When the acidity is varied, again with a sufficiently large excess of dithissone, the following relation seems to be approached; (μ=1.0). 相似文献
63.
The reaction of fluorenone ethyleneketal (9), diphenic anhydride as well as of biphenyls such as4 with Cr(CO)6 in refluxing di-n-butylether (BE) gives dimethylbenchrotrenes [xylene-Cr(CO)3,7] which are also formed by refluxing pureBE with Cr(CO)6—although with much lower yields. Similarily, from di-n-pentylether and Cr(CO)6 isobutyl- and 1-methyl-3-propyl-benchrotrene (13 and14) were obtained, whilst from di-n-propyl- and-hexylether, resp., and Cr(CO)6 no benchrotrenes could be isolated.Tentative assumptions on the catalytic action of certain functional groups were confirmed by the reaction ofBE and Cr(CO)6 in the presence of carbonamides, such as acetamide, urea and pyrrolidone, where 1,4-dimethylbenchrotrene (7 c) was formed with appreciable yields.Studies using dideuteratedBE showed that—at least for the reaction of9 with Cr(CO)6 (giving a much lower yield of7 than with undeuteratedBE)—a simple bimolecular mechanism can be excluded. 相似文献
64.
Radish plants were grown in the presence of three different herbicides that interfere with the formation of the normal range of cyclic carotenoids, leading to an accumulation of acyclic biosynthetic intermediates, mainly phytoene (SAN 6706 and amitrole) and zeta-carotene (3852). Plants were then irradiated by four different light programs in order to gain more insight into the first steps of carotenoid biosynthesis and their control by light and phytochrome. In all cases, herbicide-treated and control, carotenoid biosynthesis was greatly enhanced by red light consistent with an effect of phytochrome on the early steps of the pathway. However, similar enhancement was also obtained after treatment with far-red light. Indeed with SAN 6706-treated plants synthesis of phytoene was stimulated to a much greater extent by far-red light given alone, than by red light. The involvement of phytochrome in the regulation of carotenoid biosynthesis appears not to be as simple as previously supposed. 相似文献
65.
Some results of approximate ab initio calculations of the “correlation” contribution to the true parameters of the pi electron hamiltonian are presented for the ethylene molecule. In particular, by using sum-of-the-pairs type generalized perturbation theory, it is shown that there is a large core “correlation” contribution to singlet-triplet splittings within pi electron theories that results from the difference in the degree of ionicity of the isoconfigurational states. 相似文献
66.
Karl A. Gschneidner Jr. O. D. McMasters 《Monatshefte für Chemie / Chemical Monthly》1971,102(5):1499-1515
Zusammenfassung Das systematische Verhalten (sowie dessen Fehlen) der Seltenerdmetall-Blei-Legierungen wird untersucht. Es wurden 12 verschiedene Verbindungsstöchiometrien beobachtet. Fast alle dreiwertigen Lanthanidenelemente bilden die PhasenR
5Pb3,R
5Pb4 undRPb3. Von den anderen möglichen Stöchiometrien kommen, mit Ausnahme vonRPb2, nur von einigen Lanthaniden Verbindungen vor. Die bekannten kristallographischen Daten werden durchbesprochen und die Existenz und Nichtexistenz einiger Phasen auf Grund kristallchemischer Theorien diskutiert. Das Schmelzverhalten derR-reichen Eutektika und der PhasenR
5Pb3,RPb2 undRPb3 wird dargestellt. Die bekannten Informationen über diese Legierungen werden auf der Basis der relativen Volumskontraktionen und des 4f-Beitrags zur Bindung überprüft und die Ergebnisse zu Voraussagen über die relativen Stabilitäten der VerbindungenR
5Pb3,RPb2 undRPb3 verwertet.
Mit 8 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Die Arbeiten wurden im Ames-Laboratorium der US-Atomenergie-kommission durchgeführt (Beitrag Nr. 2972). 相似文献
Systematics of the rare earth-lead alloys
The systematic behavior (and also the lack of it) in the rare earth-lead alloys is examined. Twelve different compound stoichiometries have been observed. Nearly all of the trivalent lanthanide elements form theR 5Pb3,R 5Pb4, andRPb3 phases. For the other stoichiometries, except for possiblyRPb2, compounds exist for only a limited number of the lanthanide elements. The known crystallographic data are reviewed, and the existence and nonexistence of some of the phases are discussed on the basis of crystal chemistry theories. The melting behaviors of theR-rich eutectic and theR 5Pb3,RPb2 andRPb3 phases are presented. The known information on these alloys is examined on the basis of the relative volume contractions and the 4f contribution to the bonding, and the results are used to predict the relative stabilities of theR 5Pb3,RPb2, andRPb3 compounds.
Mit 8 Abbildungen
Herrn Prof. Dr.H. Nowotny gewidmet.
Die Arbeiten wurden im Ames-Laboratorium der US-Atomenergie-kommission durchgeführt (Beitrag Nr. 2972). 相似文献
67.
Solvent effects on the electrochemistry and spectroscopic properties of alkyl- and aryl-substituted corroles in nonaqueous media are reported. The oxidation and reduction of six compounds containing zero to seven phenyl or substituted phenyl groups on the macrocycle were studied in four different nonaqueous solvents (CH(2)Cl(2), PhCN, THF, and pyridine) containing 0.1 M tetra-n-butylammonium perchlorate. Dimers were formed upon oxidation of all corroles in CH(2)Cl(2), but this was not the case in the other three solvents, where either monomers or dimers were formed upon oxidation depending upon the solvent Gutmann donor number and the number or location of aryl substituents on the macrocycle. The half-wave potentials were analyzed as a function of the number of aryl substituents on the macrocycle as well as the concentration of added pyridine to PhCN solutions of the compound, and these data were combined with data from the spectroelectrochemistry experiments to determine the stoichiometry of the species actually in solution after the first oxidation or first reduction of each compound. The results of these experiments indicate that reduction of the bispyridine adduct (Cor)Co(III)(py)(2) proceeds via the monopyridine complex (Cor)Co(III)(py) to give in each case the unligated cobalt(II) corrole [(Cor)Co(II)](-). In contrast, pyridine remains coordinated after electrooxidation, and the final product was characterized as [(Cor)Co(III)(py)(2)](+). 相似文献
68.
69.
We compute the Hofer distance for a certain class of compactly supported symplectic diffeomorphisms of 2n. They are mainly characterized by the condition that they can be generated by a Hamiltonian flow
H
t
which possesses only constantT-periodic solutions for 0 <T 1. In addition, we show that on this class Hofer's and Viterbo's distances coincide. 相似文献
70.
Martin Anderle Herwig Schweng Karl E. Kürten Karl W. Kratky 《Journal of statistical physics》1995,81(3-4):843-849
We present evidence that the performance of the traditional fully connected Hopfield model can be dramatically improved by carefully selecting an information-specific connectivity structure, while the synaptic weights of the selected connections are the same as in the Hopfield model. Starting from a completely disconnected network we let genuine Hebbian synaptic connections grow, one by one, until a desired degree of stability is achieved. Neural pathways are thus fixed notbefore, butduring the learning phase. 相似文献