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31.
The first isolation of a phosphonium amide, (Ph3PEt)+(NPh2)−, obtained via the deprotonation of a secondary amine (diphenylamine) with a phosphorus ylide (triphenylphosphonium ethylide), is described. An X-ray crystal structure provides the first observation of an essentially ion-separated Ph2N− anion in the solid state, though weak association with Ph3PEt+ cations take plac through C---H…N hydrogen bonding. Cryoscopic and NMR spectroscopic data suggest that this association is not maintained in benzene solution. 相似文献
32.
Dehestani A Lam WH Hrovat DA Davidson ER Borden WT Mayer JM 《Journal of the American Chemical Society》2005,127(10):3423-3432
Osmium tetroxide is reduced by molecular hydrogen in the presence of ligands in both polar and nonpolar solvents. In CHCl3 containing pyridine (py) or 1,10-phenanthroline (phen), OsO4 is reduced by H2 to the known Os(VI) dimers L2Os(O)2(mu-O)2Os(O)2L2 (L2 = py2, phen). However, in the absence of ligands in CHCl3 and other nonpolar solvents, OsO4 is unreactive toward H2 over a week at ambient temperatures. In basic aqueous media, H2 reduces OsO4(OH)n(n-) (n = 0, 1, 2) to the isolable Os(VI) complex, OsO2(OH)4(2-), at rates close to that found in py/CHCl3. Depending on the pH, the aqueous reactions are exergonic by deltaG = -20 to -27 kcal mol(-1), based on electrochemical data. The second-order rate constants for the aqueous reactions are larger as the number of coordinated hydroxide ligands increases, k(OsO4) = 1.6(2) x 10(-2) M(-1) s(-1) < k(OsO4(OH)-) = 3.8(4) x 10(-2) M(-1) s(-1) < k(OsO4(OH)2(2-)) = 3.8(4) x 10(-1) M(-1) s(-1). The observation of primary deuterium kinetic isotope effects, k(H2)/k(D2) = 3.1(3) for OsO4 and 3.6(4) for OsO4(OH)-, indicates that the rate-determining step in each case involves H-H bond cleavage. Density functional calculations and thermochemical arguments favor a concerted [3+2] addition of H2 across two oxo groups of OsO4(L)n and argue against H* or H- abstraction from H2 or [2+2] addition of H2 across one Os=O bond. The [3+2] mechanism is analogous to that of alkene addition to OsO4(L)n to form diolates, for which acceleration by added ligands has been extensively documented. The observation that ligands also accelerate H2 addition to OsO4(L)n highlights the analogy between these two reactions. 相似文献
33.
A vibrational assignment for the trimethylenemethane molecule, in [C(CH2)3]Fe(CO)3, has been proposed for the first time. CC3 stretches were found at 1348 (E) and 918 cm−1 (A1), with skeletal deformations at 802 cm−1 (A1, out-of-plane), and 471 cm−1 (E, in plane). The Fe(CO)3 vibrations were closely similar to those in analogous complexes. 相似文献
34.
The local spin formalism ( 3 ) for computing expectation values 〈SA · SB〉 that appear in the Heisenberg spin model has been extended to semiempirical single determinant wave functions. An alternative derivation of expectation values in restricted and unrestricted cases is given that takes advantage of the zero differential overlap (ZDO) approximation. A formal connection between single determinant wave functions (which are not in general spin eigenfunctions) and the Heisenberg spin model was established by demonstrating that energies of single determinants that are eigenfunctions of the local spin operators with eigenvalues corresponding to high‐spin radical centers are given by the same Heisenberg coupling constants {JAB} that describe the true spin states of the system. Unrestricted single determinant wave functions for transition metal complexes are good approximations of local spin eigenfunctions when the metal d orbitals are local in character and all unpaired electrons on each metal have the same spin (although spins on different metals might be reversed). Good approximations of the coupling constants can then be extracted from local spin expectation values 〈SA · SB〉 energies of the single determinant wave functions. Once the coupling constants are obtained, diagonalization of the Heisenberg spin Hamiltonian provides predictions of the energies and compositions of the spin states. A computational method is presented for obtaining coupling constants and spin‐state energies in this way for polynuclear transition metal complexes using the intermediate neglect of differential overlap Hamiltonian parameterized for optical spectroscopy (INDO/S) in the ZINDO program. This method is referred to as ZILSH, derived from ZINDO, Davidson's local spin formalism, and the Heisenberg spin model. Coupling constants and spin ground states obtained for 10 iron complexes containing from 2 to 6 metals are found to agree well with experimental results in most cases. In the case of the complex [Fe6O3(OAc)9(OEt)2(bpy)2]+, a priori predictions of the coupling constants yield a ground‐state spin of zero, in agreement with variable‐temperature magnetization data, and corroborate spin alignments proposed earlier on the basis of structural considerations. This demonstrates the potential of the ZILSH method to aid in understanding magnetic interactions in polynuclear transition metal complexes. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
35.
[MoCl(CO)3(η5-C5H5)] on photolysis with allyl or crotyl halides C5H4RX gives MoIV complexes [MoX2(CO)(η3-C3H4R)(η5-C5H5)] (R = H, X = Cl, Br, I; R = Me, X = Cl, Br). [WCl(CO)3(η5-C5H5)] under similar conditions gives trihalides [WX3(CO)2(η5-C5H5)] (X = Cl, Br) on reaction with C3H5Cl and C3H5Br while [WCl(CO)3(η5-C5H4SiMe3)] and [CrI(CO)3(η5-C5H5)] react with allyl chloride to give [WCl3(CO)2(η5-C5H4SiMe3)] and [CrCl2(η5-C5H5)] respectively. 相似文献
36.
Masson JF Battaglia TM Davidson MJ Kim YC Prakash AM Beaudoin S Booksh KS 《Talanta》2005,67(5):918-925
The elimination or minimization of non-specific protein adsorption from serum is critical for the use of surface plasmon resonance (SPR) sensors for in vitro and in vivo analysis of complex biological solutions. The ultimate goals in this application are to minimize non-specific adsorption of protein and to maximize analyte signal. A reduction of the non-specific protein adsorption from serum of up to 73% compared to carboxymethylated-dextran 500 kDa (CM-dextran) was achieved following a survey of eight biocompatible polymers and 10 molecular weights of CM-dextran. These coatings minimize non-specific adsorption on the sensor while also serving as immobilization matrices for antibody fixation to the probes. Polymers including polysaccharides: CM-dextrans, CM-hyaluronic acid, hyaluronic acid, and alginic acid were investigated. Humic acid, polylactic acid, polyacrylic acid, orthopyridyldisuldfide–polyethyleneglycol–N-hydroxysuccinimide (OPSS–PEG–NHS), and a synthesized polymer; polymethacrylic-acid-co-vinyl-acetate (PMAVA) were also used. The non-specific protein adsorption reduction was measured over a 14 day period at 0 °C for each polymer. Calibration curves using some of these polymers were constructed to show the performance and low detection limit possibilities of these new antibody supports. For many of the polymers, this is the first demonstration of employment as an antibody support for an optical or surface active sensor. CM-dextran is the polymer offering the largest signal for the antigen detection. However, the biocompatible polymers demonstrate a greater stability to non-specific binding in serum. These biocompatible polymers offer different alternatives for CM-dextran. 相似文献
37.
38.
Diane C. Rawlings Ernest R. Davidson Martin Gouterman 《International journal of quantum chemistry》1984,26(2):237-250
A new minimum basis set was developed for use in computing excitation energies of large molecules. It is particularly suited to calculating ionization potentials and Rydberg transitions. Pyrrole excitation energies and oscillator strengths calculated with this basis set are compared to larger basis set ab initio and semiempirical results. The 6-eV band in the experimental spectrum is predicted to be the result of three Rydberg absorptions, with no underlying (π, π*) absorption. The calculations also provide an explanation for the observed N? H stretch in the 6-eV region. 相似文献
39.
Rates of volatilisation and chain scission have been measured in the thermal degradation, photodegradation in solution, photodegradation in thin films and photothermal degradation of poly(methyl methacrylate) and a series of copolymers of methyl methacrylate with maleic anhydride. In each case the rate of volatilisation is depressed by the maleic anhydride units. On the other hand, rates of chain scission are accelerated by maleic anhydride except in the case of photothermal degradation. These results are discussed from a mechanistic point of view. 相似文献
40.
Stephen R. Langhoff Stephen T. Elbert Ernest R. Davidson 《International journal of quantum chemistry》1973,7(5):999-1019
The electron spin dipole-dipole contribution to the zero field splitting has been evaluated for the 3A2 (n → π*) and 3A1 (π → π*) states of formaldehyde using a CI wave function constructed from contracted Gaussian-lobe functions. The values D = 0.539 cm?1 and E = 0.031 cm?1 were obtained for the 3A2(n → π*) state and D = ?0.588 cm?1 and E = 0.058 cm?1 were obtained for the 3A1 (π → π*) state using the CI wave function constructed from SCF orbitals of the respective parent configurations. An analysis of the effect of CI on the parameters is given for the 3A2 (n n → π*) state of formaldehyde and the 3B1 ground state of methylene. Numerical results are given which show that internally consistent self-consistent field orbitals (ICSCF ) are superior to canonical SCF orbitals as a starting point for a CI calculation. Our CI wave function for the 1A1 ground state gave an energy of ?114.13658 hartrees which is significantly lower than any previously reported energy calculation. This wave function gives a dipole moment of 2.22 Debye (C+O?) in good agreement with the experimental value of 2.33 ± 0.02 Debye. 相似文献