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51.
Hudson CE McAdoo DJ Griffin LL Traeger JC 《Journal of the American Society for Mass Spectrometry》2003,14(2):136-142
How formation of CH3CH3+* competes with H* loss from C3H6O+* isomers with the CCCO framework has been a puzzle of gas phase ion chemistry because the first reaction has a substantially higher threshold and a supposedly tighter transition state. These together should make CH3CH3+* formation much the slower of the two reactions at all internal energies. However, the rates of the two reactions become comparable at about 20 kJ x mol(-1) above the threshold for CH3CH3+* formation. It was recently shown that losses of atomic fragments increase in rate much more slowly with increasing internal energy than do the rates of competing dissociations to two polyatomic fragments. This occurs because fewer frequencies are substantially lowered in transition states for the former type of reaction than for the latter. The resulting lower transition state sums of states cause the rates of dissociations producing atoms as fragments to increase much more slowly than competing processes with increasing energy. Here we show that this is why CH3CH3+* formation competes with H* loss from CH3CH2CHO+*. These results further establish that the dependence on energy of the rate of a simple unimolecular dissociation is usually directly related to the number of rotational degrees of freedom in the products, a newly recognized factor in determining the dependence of unimolecular reaction rates on internal energy. 相似文献
52.
Phase-shifting shearing interferometer 总被引:2,自引:0,他引:2
Griffin DW 《Optics letters》2001,26(3):140-141
A single-element phase-shifting interferometer has been developed based on the lateral shearing interferometer. This new interferometer requires no precise alignment, and the phase is continuously varied by changes in the voltage across a commercially available liquid-crystal phase retarder. 相似文献
53.
Reif B Jaroniec CP Rienstra CM Hohwy M Griffin RG 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,151(2):320-327
In this Communication, we demonstrate the use of deuteration together with back substitution of exchangeable protons as a means of attenuating the strong 1H-1H couplings that broaden 1H magic angle spinning (MAS) spectra of solids. The approach facilitates 15N-1H correlation experiments as well as experiments for the measurement of 1H-1H distances. The distance measurement relies on the excellent resolution in the 1H MAS spectrum and homonuclear double quantum recoupling techniques. The 1H-1H dipolar recoupling can be analyzed in an analytical fashion by fitting the data to a 2- or 3-spin system. The experiments are performed on a sample of the dipeptide N-Ac-Val-Leu-OH, which was synthesized from uniformly [2H, 15N] labeled materials and back-exchanged in H2O. 相似文献
54.
Vo-Dinh Tuan Griffin Guy D. Alarie Jean Pierre Cullum Brian Sumpter Bobby Noid Donald 《Journal of nanoparticle research》2000,2(1):17-27
We describe the development and application of nanosensors having bioreceptor probes for bioanalysis. The nanoprobes were fabricated with optical fibers pulled down to tips having distal end sizes of approximately 30–60nm. The use of two different types of receptors was investigated. Fiberoptic nanoprobes were covalently bound either with bioreceptors, such as antibodies, or with other receptors, such as cyclodextrins that are selective for the size and chemical structure of the analyte molecules. Theoretical calculations were performed to model the binding of beta-cyclodextrin with pyrene and 5,6-benzoquinoline, and to illustrate the possibility of comparing experimental data with theoretical data. The antibody-based nanoprobe was used for in situ measurements of benzopyrene tetrol in single cells. The performance of the nanosensor is illustrated by intracellular measurements performed on a rat liver epithelial cell line (Clone 9) used as the model cell system. The usefulness and potential of these nanotechnology-based biosensors in biological research and applications are discussed. 相似文献
55.
Summary It is shown that a boundary-value problem based on a holonomic elastic-plastic constitutive law may be formulated equivalently as a variational inequality of the second kind. A regularised form of the problem is analysed, and finite element approximations are considered. It is shown that solutions based on finite element approximation of the regularised problem converge. 相似文献
56.
57.
Lawrence L. Griffin Katherine Holden Charles E. Hudson David J. McAdoo 《Journal of mass spectrometry : JMS》1986,21(4):175-182
The isomerizations preceding the metastable decompositions in the mass spectrometer of a number of [C6H12O]+˙ ions with the oxygen on the third carbon are characterized utilizing deuterium labeling. Hydrogens are transferred in these ions by three-, five- and six-membered ring rearrangements, with propensities determined by features of the individual reactions. Three-membered ring hydrogen transfers between α and β-carbons are preferred to all five-membered ring hydrogen transfers. However, six-membered ring hydrogen transfers take place to the apparent exclusion of three-membered ring hydrogen transfers to enol carbons when the products are of comparable stability. The low-energy [C6H12O]+˙ isomerizations characterized are predictable from the behavior of their lower homologs. It is concluded that the determinants of these reactions are the same as those of other highly reactive organic intermediates. 相似文献
58.
N. N. Otwagin F. Moll W. E. Cohen E. E. Harris H. Fielder A. S. Gnedowski A. I. Ssolnze A. Petersen H. A. Czernotzky J. I. Vogelsohn N. W. Kalmykova M. M. Eiderman M. A. Weitzman M. Ilmenew H. K. Griffin H. H. Storch E. R. Bolton K. A. Williams M. Tonegutti E. Brandimarte E. Sauerbrei W. Scheruhn A. Goetz U. W. O. Gould Baxelite Corporation 《Analytical and bioanalytical chemistry》1939,117(5-6):235-240
59.
C. W. Griffin Margaretha v. Saaf F. C. Oppen 《Analytical and bioanalytical chemistry》1938,112(11-12):418-419
60.
Griffin JM Yates JR Berry AJ Wimperis S Ashbrook SE 《Journal of the American Chemical Society》2010,132(44):15651-15660
High-resolution (19)F magic angle spinning (MAS) NMR spectroscopy is used to study disorder and bonding in a crystalline solid. (19)F MAS NMR reveals four distinct F sites in a 50% fluorine-substituted deuterated hydrous magnesium silicate (clinohumite, 4Mg(2)SiO(4)·Mg(OD(1-x)F(x))(2) with x = 0.5), indicating extensive structural disorder. The four (19)F peaks can be assigned using density functional theory (DFT) calculations of NMR parameters for a number of structural models with a range of possible local F environments generated by F(-)/OH(-) substitution. These assignments are supported by two-dimensional (19)F double-quantum MAS NMR experiments that correlate F sites based on either spatial proximity (via dipolar couplings) or through-bond connectivity (via scalar, or J, couplings). The observation of (19)F-(19)F J couplings is unexpected as the fluorines coordinate Mg atoms and the Mg-F interaction is normally considered to be ionic in character (i.e., there is no formal F-Mg-F covalent bonding arrangement). However, DFT calculations predict significant (19)F-(19)F J couplings, and these are in good agreement with the splittings observed in a (19)F J-resolved MAS NMR experiment. The existence of these J couplings is discussed in relation to both the nature of bonding in the solid state and the occurrence of so-called "through-space" (19)F-(19)F J couplings in solution. Finally, we note that we have found similar structural disorder and spin-spin interactions in both synthetic and naturally occurring clinohumite samples. 相似文献