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21.
Stevenson S Mackey MA Thompson MC Coumbe HL Madasu PK Coumbe CE Phillips JP 《Chemical communications (Cambridge, England)》2007,(41):4263-4265
The yield of Sc3N@C80 metallofullerene and fullerene extract is dramatically increased via filling cored graphite rods with copper and Sc2O3 only; when compared to 100% Sc2O3 packed rods, improvements of factors of approximately 3 and approximately 5 have been achieved for Sc3N@C80 and fullerene extract produced, respectively, with the weight percent of Cu added to the rod affecting the type and amount of fullerene produced. 相似文献
22.
The spectroscopic properties of Calcium Green 2 (CG-2), a dual-fluorophore Ca(2+) indicator dye, were characterized by a combination of steady state and time-resolved ensemble spectroscopic measurements, molecular mechanics calculations and single-molecule fluorescence spectroscopy. It was found that in Ca(2+) free solutions, CG-2 exists primarily as a highly quenched intramolecular dimer, but when bound to Ca(2+), the molecule adopts an extended, fluorescent conformation. The difference in emission properties of these two CG-2 conformations is explained in terms of simple exciton theory. Through single-molecule fluorescence measurements, we have shown that the bulk increase in ensemble fluorescence intensity correlates with a simple statistical increase in the number of fluorescent molecules in solution. In addition, we have also observed that the majority of CG-2 molecules photobleach in a single step, despite the molecule possessing two distinct fluorophores. A small fraction of molecules photobleach in multiple steps or show a series of transitions between emissive and nonemissive fluorescent states ("blinking"). We rationalize these photophysical phenomena using a simple model based on dipole-dipole F?rster coupling between fluorophores in conjunction with irreversible photodamage to one of the constituent chromophores. 相似文献
23.
A new derivation is given for the generalized singular value decomposition of two matrices X and F having the same number of rows. It is shown how this decomposition reveals the structure of the general Gauss-Markov linear model (y, Xβ, σ2FF′), and exhibits the structure and solution of the generalized linear least squares problem used to provide the best linear unbiased estimator for the model. The decomposition is used to prove optimality of the estimator and to reveal the structure of the covariance matrix of the error of the estimator. 相似文献
24.
25.
Chahma M Li X Phillips JP Schwartz P Brammer LE Wang Y Tanko JM 《The journal of physical chemistry. A》2005,109(15):3372-3382
By using direct and indirect electrochemical methods, rate constants (ko) for cyclopropane ring opening of radical anions derived from the one-electron reduction of trans-1-benzoyl-2-phenylcyclopropane, trans-1-benzoyl-2-vinylcyclopropane, 2-methylenecyclopropyl phenyl ketone, spiro[anthracene-9,1'-cyclopropan-10-one], 3-cyclopropylcyclohex-2-en-1-one, and 3-(1-methylcyclopropyl)cyclohex-2-en-1-one were determined. Qualitatively, rate constants for ring opening of these (and other cyclopropyl- and cyclobutyl-containing radical anions) can be rationalized on the basis of the thermodynamic stability of the radical anion, the ability of substituents on the cyclopropyl group to stabilize the radical portion of the distonic radical anion, and the stability of the enolate portion of the distonic radical anion. On the basis of this notion, a thermochemical cycle for estimating deltaG(o) for ring opening was presented. For simple cyclopropyl-containing ketyl anions, a reasonable correlation between log(ko) and deltaG(o) was found, and stepwise dissociative electron transfer theory was applied to rationalize the results. Activation energies calculated with density functional theory (UB3LYP/6-31+G*) correlate reasonably well with measured log(ko). The derived log(ko) and deltaG(o) and log(ko) vs E(a) plots provide the basis for a "calibration curve" to predict rate constants for ring opening of radical anions derived from carbonyl compounds, in general. 相似文献
26.
27.
Bashore CG Vetelino MG Wirtz MC Brooks PR Frost HN McDermott RE Whritenour DC Ragan JA Rutherford JL Makowski TW Brenek SJ Coe JW 《Organic letters》2006,8(26):5947-5950
[Structure: see text] The development of a concise enantioselective synthesis of nicotinic alkaloid 1 is presented. The route features the synthesis and use of a "stable" aliphatic triflate 21 in an alkylation step to generate Heck precursor 24 and an enantioselective cyclization to establish a compound with the key [3.2.1]-bicyclic core, 29. 相似文献
28.
Johnson ED Rogachev GV Mukhamedzhanov AM Baby LT Brown S Cluff WT Crisp AM Diffenderfer E Goldberg VZ Green BW Hinners T Hoffman CR Kemper KW Momotyuk O Peplowski P Pipidis A Reynolds R Roeder BT 《Physical review letters》2006,97(19):192701
The reaction 13C(alpha,n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2+ 6.356 MeV subthreshold resonance in (17)O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The alpha-particle ANC for the subthreshold state has been measured using the sub-Coulomb alpha-transfer reaction ((6)Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates. 相似文献
29.
Stevenson S Phillips JP Reid JE Olmstead MM Rath SP Balch AL 《Chemical communications (Cambridge, England)》2004,(24):2814-2815
The X-ray crystal structure of Gd(3)N@C(80).Ni(II)(OEP).1.5(benzene) shows that the Gd(3)N unit within the I(h) C(80) cage is pyramidal, whereas Sc(3)N@C(80), Sc(3)N@C(78), Sc(3)N@C(68), Lu(3)N@C(80) and Sc(2)ErN@C(80) have planar M(3)N units. 相似文献
30.
C. le Paige 《Mathematische Annalen》1879,15(2):206-210
Sans résumé 相似文献