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41.
A graph G is dot-critical if contracting any edge decreases the domination number. Nader Jafari Rad (2009) [3] posed the problem: Is it true that a connected k-dot-critical graph G with G′=0? is 2-connected? In this note, we give a family of 1-connected 2k-dot-critical graph with G′=0? and show that this problem has a negative answer. 相似文献
42.
43.
The forcing number or the degree of freedom of a perfect matching M of a graph G is the cardinality of the smallest subset of M that is contained in no other perfect matchings of G. In this paper we show that the forcing numbers of perfect matchings in a fullerene graph are not less than 3 by applying the 2-extendability and cyclic edge-connectivity 5 of fullerene graphs obtained recently, and Kotzig’s classical result about unique perfect matching as well. This lower bound can be achieved by infinitely many fullerene graphs. 相似文献
44.
The title compound crystallizes in space group P 21/c of the monoclinic system in a cell of dimensions: a = 9.231(2), b = 15.931(2), c = 12.420(2) Å, β = 108.37(1)°. The observed density is 1.60 g/cm3 and the density calculated for four molecules in the cell is 1.58 g/cm3. The refinement converged with R = 0.029 and Rw = 0.028 based on 2569 reflections with I > 2.5 σ. The molecule has approximate Cs symmetry with a mirror plane roughly containing the central Mo atom and two cis-carbonyls, C(1)O(1) and C(4)O(4), while bisecting the bidentate, H2CPz2, and two trans-carbonyls. The four carbonyls and tine bidentate adopt a quasi-octahedral arrangement around the Mo atom. The C(NN)2Mo linkage of the (H2CPz′2)Mo fragment is observed to be in the boat form. The two cis-carbonyls are bent away by the bulky H2CPz′2 bidentate giving ∠C(1)-Mo-C(4) ? 167.3(1)°. The distortion explains the facile allyl bromination and decarbonylation observed for the title compound. 相似文献
45.
Three new η2-acyl complexes, TMo(CO)2(η2-COR) (T = Tp', Tp'; R= Me, Bun; Tp' = hydridotris(3,5-dimethyl-pyrazol-1-yl)borate; Tp' = hydridotris(3,4,5-trimethylpyrazol-l-yl)borate) prepared from the corresponding alkyl iodides, RI, and the anions, TMo(CO)?3. The preparation of Et4N+Tp Mo(CO)3? is also described. Using solution IR spectra to monitor the reactions between RI and TMo(CO)3?, it was found that Tp'Mo(CO)2(η2-COMe) was formed more readily than Tp'Mo(CO)2(η2-COMe) which was obtained more easily than Tp'Mo(CO)2(η2-COBun). This finding suggests that the mechanism is probably an ionic substitution rather than a radical mechanism. The different times required for the complete conversion from the anions to TMo(CO)2(η2-COR) is rationalized in terms of the electronic and steric influences of T and RI. 相似文献
46.
Kom-Bei Shiu Li-Yuan Yeh
Shie-Ming Peng
Ming-Chu Cheng 《Journal of organometallic chemistry》1993,460(2):203-211The neutral nitrogen-bidentate ligand, diphenylbis(3,5-dimethylpyrazol-1-yl)methane, Ph2CPz′2, can readily be obtained by the reaction of Ph2CCl2 with excess HPz′ in a mixed-solvent system of toluene and triethylamine. It reacts with [Mo(CO)6] in 1,2-dimethoxyethane to give the η2-arene complex, [Mo(Ph2CPz′2)(CO)3] (1). This η2-ligation appears to stabilize the coordination of Ph2CPz′ 2 in forming [Mo(Ph2CPz′2)(CO)2(N2C6H4NO2-p)][BPh4] (2) and [Mo(Ph2CPz′2)(CO)2(N2Ph)] [BF4] (3) from the reaction of 1 with the appropriate diazonium salt but the stabilization seems not strong enough when [Mo{P(OMe)3} 3(CO)3] is formed from the reaction of 1 with P(OMe)3. The solid-state structures of 1 and 3 have been determined by X-ray crystallography: 1-CH2Cl2, monoclinic, P21/n, a = 11.814(3), b = 11.7929(12), c = 19.46 0(6) Å, β = 95.605(24)°, V = 2698.2(11) Å3, Z = 4, Dcalc = 1.530 g/cm3 , R = 0.044, Rw = 0.036 based on 3218 reflections with I > 2σ(I); 2 (3)-1/2 hexane-1/2 CH3OH-1/2 H2O-1 CH2Cl2, monoclinic, C2/c, a = 41.766(10), b = 20.518(4), c = 16.784(3) Å, β = 101.871(18)°, V = 14076(5) Å3, Z = 8, Dcalc = 1.457 g/cm3, R = 0.064, Rw = 0.059 based on 5865 reflections with I > 2σ(I). Two independent cations were found in the asymmetric unit of the crystals of 3. The average distance between the Mo and the two η2-ligated carbon atoms is 2.574 Å in 1 and 2.581 and 2.608 Å in 3. The unfavourable disposition of the η2-phenyl group with respect to the metal centre in 3 and the rigidity of the η2-arene ligation excludes the possibility of any appreciable agostic C---H → Mo interaction. 相似文献
47.
Zaia J Li XQ Chan SY Costello CE 《Journal of the American Society for Mass Spectrometry》2003,14(11):1270-1281
Chondroitin sulfate (CS) is a glycosaminoglycan consisting of repeating (HexA-GalNAc sulfate) disaccharides, the functions of which depend on patterns of sulfation and uronic acid epimerization. The correlation of biological activities with structure requires a strategy to determine the sequences of CS oligosaccharides without the need for total isolation. Tandem mass spectrometry has enabled the development of proteomics, based on CID fragmentation of ions produced from complex mixtures of proteolytic peptides, and has the potential for rapid sequencing of CS and other glycosaminoglycan classes. The most challenging aspects of CS sequencing are to distinguish GalNAc residues sulfated at the 4- versus the 6-position and uronic acid epimers. This work describes the utility of (1) reducing terminal derivatives and (2) control of precursor ion charge state for tandem mass spectrometric strategies for determining GalNAc sulfation positional isomers of CS. The capability of tandem MS to differentiate uronic acid epimers is also shown, providing evidence that complete or nearly complete information on CS covalent structure may be obtained using tandem MS. 相似文献
48.
Six new 2-(2-phenylethyl)chromones from Agarwood 总被引:1,自引:0,他引:1
Six new chromones, 6-methoxy-2-[2-(3-methoxy-4-hydroxyphenyl)ethyllchromone (2), 6,8-dihydroxy-2-(2-phenylethyl)chromone (3), 6-hydroxy-2-[2-(4-hydroxyphenyl)ethyl]chromone (4), 6-hydroxy-2-[2-(2-hydroxyphenyl)ethyl]chromone (5), 7-hydroxy-2-(2-phenylethyl)chromone (6), and 6-hydroxy-7-methoxy-2-(2-phenylethyl)chromone (7) were isolated from the ether extract of agarwood in addition to a known compound, 2-(2-phenylethyl)chromone or flidersiachromone (1). Their structures were determined by spectroscopic methods including UV, IR, and NMR spectral data and comparisons with the calculated values using the hydroxyl and methoxyl substituent increments of the chromone ring. 相似文献
49.
A complete characterization for <Emphasis Type="Italic">k</Emphasis>-resonant Klein-bottle polyhexes
A hexagonal tessellation K(p, q, t) on Klein bottle, a non-orientable surface with cross-cap number 2, is a finite-sized elemental benzenoid which can be produced
from a p × q-parallelogram of hexagonal lattice with usual identifications of sides and with torsion t. Unlike torus, Klein bottle polyhex K(p, q, t) is not transitive except for some degenerated cases. We shall show, however, that K(p, q, t) does not depend on t. Accordingly, criteria for K(p, q, t) to be k-resonant for every positive integer k will be given. Moreover, we shall show that K(3, q, t) of 3-resonance are fully-benzenoid.
相似文献
50.
In this study, a variational approach to the settlement analysis of an axially loaded pier embedded in a multi-layered soil
profile is presented. In this method, the soil profile and the embedded pier are divided into a number of sub-layers according
to the actual number of soil layers observed in the field. The displacement shape function of each soil layer is given as
a product of an exponential equation along the pier depth and the Bessel's solution in the radial direction. The displacement
relationship among the layers can be derived through the transformation matrices. One of the major features of this method
is that the total number of pier elements is the same as that of soil sub-layers. All the field components, such as the displacement,
stress, and strain in the soil, can be calculated by closed-form solutions except that the only unknown variable is the value
β which can be determined by iteration techniques. Comparisons were made with the results of finite element analysis and the
field observation in pile-loaded tests. 相似文献