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51.
52.
The pressure shift of S excitons in the rutile-type semiconductor tin oxide (SnO2) is measured by two-photon absorption. From these data the pressure coefficients of the band gap (62.0 meV/GPa) and of the exciton binding energy (0.87 meV/GPa) are determined. 相似文献
53.
An analysis of the temperature dependence of the line width variation of topoisomers (I) and (II) of La@C82 revealed that both molecules exhibit practically identical rotational correlation times from room temperature down to the freezing point of CS2. Although this result indicates confinement of the metal ion, from the increased line width of13C satellites in isomer (II) we conclude that in this molecule there might be increased mobility within a confine volume. Three stable topoisomers of La@C90 were identified for the first time. One of these topoisomers was separated by HPLC technique. We were unable, however, to detect any nuclear spin dependence of the EPR line width even at low temperatures. This might indicate that in this case the ion is no longer confined to a specific binding site, although a more trivial explanation assuming small anisotropies of all hyperfine interactions cannot yet be ruled out. 相似文献
54.
55.
Chen Q Schweitzer D Kane J Davisson VJ Helquist P 《The Journal of organic chemistry》2011,76(13):5157-5169
Iejimalide B, a structurally unique 24-membered polyene macrolide having a previously underutilized mode of anticancer activity, was synthesized according to a strategy employing Julia-Kocienski olefinations, a palladium-catalyzed Heck reaction, a palladium-catalyzed Marshall propargylation, a Keck-type esterification, and a palladium-catalyzed macrolide-forming, intramolecular Stille coupling of a highly complex cyclization substrate. The overall synthesis is efficient (19.5% overall yield for 15 linear steps) and allows for more practical scaled-up synthesis than previously reported strategies that differed in the order of assembly of key subunits and in the method of macrocyclization. The present synthesis paves the way for efficient preparation of analogues for drug development efforts. 相似文献
56.
The presumably "small molecule structure" of the organopalladium complex rac-PdCl(C(6)H(3)-4-OMe-CHMeNH(2))(py) crystallizes with 16 molecules in the asymmetric unit, a highly unusual situation according to the CSD database. The symmetrically independent residues differ with respect to soft conformational degrees of freedom. Packing in the acetonitrile solvate of the same compound is unexceptional. 相似文献
57.
Irmgard Kalf Ulli Englert 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(6):o206-o208
The crystal structure of cholic acid–pentan‐3‐one (1/1), C5H10O·C24H40O5, has been determined in order to deduce the molecular conformation of the small volatile ketone. Data were collected at 100 K to a resolution of (sin θ)/λ = 0.91 Å−1. The structure contains a hydrogen‐bonded cholic acid host network, forming only van der Waals interactions with the guest pentan‐3‐one molecules. The ketone molecules are disordered on general positions, with two clearly identifiable conformations. The majority conformer exhibits approximate C2 symmetry and is similar to that recently observed by microwave spectroscopy in the gas phase. 相似文献
58.
A unified quantum <Emphasis Type="Italic">SO</Emphasis>(3) invariant for rational homology 3-spheres
Given a rational homology 3-sphere M with |H
1(M,ℤ)|=b and a link L inside M, colored by odd numbers, we construct a unified invariant I
M,L
belonging to a modification of the Habiro ring where b is inverted. Our unified invariant dominates the whole set of the SO(3) Witten–Reshetikhin–Turaev invariants of the pair (M,L). If b=1 and L=∅, I
M
coincides with Habiro’s invariant of integral homology 3-spheres. For b>1, the unified invariant defined by the third author is determined by I
M
. Important applications are the new Ohtsuki series (perturbative expansions of I
M
) dominating quantum SO(3) invariants at roots of unity whose order is not a power of a prime. These series are not known to be determined by the
LMO invariant. 相似文献
59.
Nathan A. Stump George K. Schweitzer Lester L. Pesterfield Joseph R. Peterson George M. Murray 《光谱学快报》2013,46(8):1421-1432
Abstract Salts of the [Eu(2,6-pyridinedicarboxylate)3]3- complex anion and various monovalent inorganic and organic counterions (Li+, Na+, K+, Rb+, Cs+, NH4 +, and pyridinium+) have been synthesized and studied by emission spectroscopy. The Eu3+ ion emission spectra exhibited by these salts have been observed with high resolution (less than 1.0 cm?1) and at low temperature (77 K). The emission spectra of these compounds indicate that changing the attached counterion does not affect the site symmetry observed by the europium ion beyond slight distortions indicated by small shifts in the energies of the Eu3+ electronic levels. 相似文献
60.