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51.
We study functors underlying derived Hochschild cohomology, also called Shukla cohomology, of a commutative algebra S essentially of finite type and of finite flat dimension over a commutative noetherian ring K. We construct a complex of S-modules D, and natural reduction isomorphisms for all complexes of S-modules N and all complexes M of finite flat dimension over K whose homology H(M) is finitely generated over S; such isomorphisms determine D up to derived isomorphism. Using Grothendieck duality theory we establish analogous isomorphisms for any essentially finite-type flat map of noetherian schemes, with f!OY in place of D. 相似文献
52.
Krishna B. Athreya Siva R. Athreya Srikanth K. Iyer 《Proceedings Mathematical Sciences》2010,120(3):363-385
This paper studies: (i) the long-time behaviour of the empirical distribution of age and normalized position of an age-dependent
critical branching Markov process conditioned on non-extinction; and (ii) the super-process limit of a sequence of agedependent
critical branching Brownian motions. 相似文献
53.
Thermolysis or Me3NO activation of the hexaruthenium cluster Ru6(μ6-C)(CO)17 in the presence of the diphosphine ligand 1,2-bis(diphenylphosphino)benzene (dppbz) does not furnish the expected dppbz-substituted cluster Ru6(μ6-C)(CO)15(dppbz) but rather HRu6(μ5-C)(μ3-P)(CO)14(dppbz), whose edge-bridged square-pyramidal structure has been established by X-ray crystallography. Accompanying the opening of the original closo Ru6 polyhedron is the dephosphination of a second dppbz ligand through three rapid P-C bond cleavages, leading to the capture of the phosphorus atom as a face-capping phosphido ligand. This unprecedented reactivity between Ru6(μ6-C)(CO)17 and the dppbz ligand is discussed relative to other diphosphine ligands. 相似文献
54.
Mettath S Srikanth GS Dangerfield BS Castle SL 《The Journal of organic chemistry》2004,69(19):6489-6492
The Cinchona alkaloid derived chiral ammonium salt developed by Park and Jew functions as an effective catalyst for the synthesis of beta-hydroxy alpha-amino acids via asymmetric aldol reactions under homogeneous conditions. The syn diastereomers are obtained in good ee, and aryl-substituted aliphatic aldehydes are the best substrates for the reaction. These results represent the highest ee's obtained to date in direct aldol reactions of glycine equivalents catalyzed by inexpensive, readily prepared chiral ammonium salts. 相似文献
55.
[reaction: see text] The tricyclic core of the bioactive natural product acutumine has been synthesized. Key steps include an oxidative phenolic coupling to form a masked o-benzoquinone, an anionic oxy-Cope rearrangement to construct an all-carbon quaternary center, and a Michael-type cyclization to form an amine-bearing quaternary carbon. The target compound exists in solution as an enol, in contrast to related compounds that are ketones. A model explaining these observations is presented. 相似文献
56.
[reaction: see text] Beta-substituted alpha,beta-unsaturated alpha-nitro esters and amides undergo radical conjugate additions when treated with an appropriate Lewis acid. Deuterium studies revealed that the acidic alpha-stereocenter of the alpha-nitro ester products does not racemize under strictly controlled workup conditions. The alpha-nitro amides did racemize significantly during chromatography, but this could be greatly minimized by subjecting the crude adducts to subsequent transformations. The conjugate addition products can be elaborated into beta-substituted alpha-amino acids in two simple steps. 相似文献
57.
Srikanth R Reddy PN Srinivas R Sharma GV Reddy KR Krishna PR 《Rapid communications in mass spectrometry : RCM》2004,18(24):3041-3050
Electrospray tandem mass spectrometry was used to study the dissociation reactions of [M+Cat]+ (Cat = Na+ and Li+) of Boc-carbo-beta3-peptides. The collision-induced dissociation (CID) spectra of [M+Cat-Boc]+ of these peptides are found to be significantly different from those of [M+H-Boc]+ ions. The spectra are more informative and display both C- and N-terminus metallated ions in addition to characteristic fragment ions of the carbohydrate moiety. Based on the fragmentations observed in the CID spectra of the [M+Cat-Boc]+ ions, it is suggested that the dissociation involves complexes in which the metal ion is coordinated in a multidentate arrangement involving the carbonyl oxygen atoms. The CID spectra of [M+Cat-Boc]+ ions of the peptide acids show an abundant N-terminal rearrangement ion [b(n)+17+Cat]+ which is absent for esters. Further, two pairs of positionally isomeric Boc-carbo-beta3-peptide acids, Boc-NH-Caa(S)-beta-hGly-OH (11) and Boc-NH-beta-hGly-Caa(S)-OH (12), and [Boc-NH-Caa(S)-beta-hGly-Caa(S)-beta-hGly-OH] (13) and [Boc-NH-beta-hGly-Caa(S)-beta-hGly-Caa(S)-OH] (14), were differentiated by the CID of [M+Cat-Boc]+ ions. The CID spectra of compounds 11 and 13 are significantly different from those of 12 and 14, respectively. The abundance of [b(n)+17+Cat]+ ions is higher for peptide acids 12 and 14 with a sugar group at the C-terminus when compared to 11 and 13 which contain a sugar moiety at the N-terminus. The observed differences between the CID spectra of these isomeric peptides are attributed to the difference in the preferential site of metal ion binding and also on the structure of the cyclic intermediate involved in the formation of the rearrangement ion. 相似文献
58.
K. Srikanth V. R. Marathe Manoj K. Mishra 《International journal of quantum chemistry》2002,89(6):535-549
ZINDO/S calculations on cis‐Ru(4,4′‐dicarboxy‐2,2′‐bipyridine)2(X)2 and cis‐Ru(5,5′‐dicarboxy‐2,2′‐bipyridine)2(X)2 complexes where X = Cl?, CN?, and NCS? reveal that the highest occupied molecular orbital (HOMO) of these complexes has a large amplitude on both the nonchromophoric ligand X and the central ruthenium atom. The lowest‐energy metal to ligand charge transfer (MLCT) transition in these complexes involves electron transfer from ruthenium as well as the halide/pseudohalide ligand to the polypyridyl ligand. The contribution of the halide/pseudohalide ligand(X) to the HOMO affects the total amount of charge transferred to the polypyridyl ligand and hence the photoconversion efficiency. The virtual orbitals involved in the second MLCT transition in 4,4′‐dicarboxy‐2,2′‐bipyridine complexes have higher electron density on the ? COOH group compared to the lowest unoccupied molecular orbital and hence a stronger electronic coupling with the TiO2 surface and higher injection efficiency at shorter wavelengths. In comparison, the virtual orbitals involved in the second MLCT transition in 5,5′‐dicarboxy‐2,2′‐bipyridine complexes have lesser electron density on the ? COOH group, leading to a weaker electronic coupling with the TiO2 surface and therefore lower efficiency for electron injection at shorter wavelengths for these complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
59.
S. Aravamudhan K. Luongo P. Poddar H. Srikanth S. Bhansali 《Applied Physics A: Materials Science & Processing》2007,87(4):773-780
We report the fabrication and characterization of porous silicon templates for electrodeposition of high aspect ratio one-dimensional
metallic nanostructures (nanowires/nanoparticles) in them. Even though nanostructures/nanowires in the past have been fabricated
in alumina, polymer or silica templates, the advantages of this approach are the possibility for seamless integration of nanostructures
with other silicon components, and silicon based sensors because of better physical and electrical interconnection between
the nanostructure and the silicon substrate. In this work, fabrication and characterization of nanowires/nanostructures such
as single-segment Ni–Fe and Au and two-segment Ni–Fe/Au electrodeposited in the porous silicon template are presented. The
templates with ordered and controlled nanometer-sized pores, 40 nm and 290 nm in diameter, were created through porous Si
etching. The morphology, composition and structural characteristics of the template and of the single-segment Ni–Fe and Au
and two-segment Ni–Fe/Au nanostructures of diameter 275±25 nm, length up to 100 μm and pitch of 1 μm were analyzed using scanning
electron microscopy and X-ray diffraction techniques. The micrographs confirm that the plating parameters have a strong influence
on morphology and composition of the structures. Further, the Ni–Fe images show the formation of both vertical and branched
nanowires along with nanoparticles, from breakage/discontinuous growth of nanowires. Ni–Fe nanostructures were further analyzed
for temperature-dependent magnetization and magnetization vs. magnetic field measurements using a commercial physical property
measurement system. They reveal no magnetic anisotropy of the nanostructures probably due to a balance between ‘reduced’ shape
anisotropy from branched and rough pore surfaces and magnetocrystalline anisotropy.
PACS 61.46.+w; 75.75.+a; 81.07.-b; 81.16.Be 相似文献
60.