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81.
Mathew D. Halls Julia Velkovski H. Bernhard Schlegel 《Theoretical chemistry accounts》2001,105(6):413-421
Scaling factors for obtaining fundamental vibrational frequencies from harmonic frequencies calculated at six of the most
commonly used levels of theory have been determined from regression analysis for the polarized-valence triple-zeta (pVTZ)
Sadlej electric property basis set. The Sadlej harmonic frequency scaling factors for first- and second-row molecules were
derived from a comparison of a total of 900 individual vibrations for 111 molecules with available experimental frequencies.
Overall, the best performers were the hybrid density functional theory (DFT) methods, Becke's three-parameter exchange functional
with the Lee–Yang–Parr fit for the correlation functional (B3-LYP) and Becke's three-parameter exchange functional with Perdew
and Wang's gradient-corrected correlation functional (B3-PW91). The uniform scaling factors for use with the Sadlej pVTZ basis
set are 0.9066, 0.9946, 1.0047, 0.9726, 0.9674 and 0.9649 for Hartree–Fock, the Slater–Dirac exchange functional with the
Vosko–Wilk–Nusair fit for the correlation functional (S-VWN), Becke's gradient-corrected exchange functional with the Lee–Yang–Parr
fit for the correlation functional (B-LYP), B3-LYP, B3-PW91 and second-order M?ller–Plesset theory with frozen core (MP2(fc)),
respectively. In addition to uniform frequency scaling factors, dual scaling factors were determined to improve the agreement
between computed and observed frequencies. The scaling factors for the wavenumber regions below 1800 cm−1 and above 1800 cm−1 are 0.8981 and 0.9097, 1.0216 and 0.9857, 1.0352 and 0.9948, 0.9927 and 0.9659, 0.9873 and 0.9607, 0.9844 and 0.9584 for
Hartree–Fock, S-VWN, B-LYP, B3-LYP, B3-PW91 and MP2(fc), respectively. Hybrid DFT methods along with the Sadlej pVTZ basis
set provides reliable theoretical vibrational spectra in a cost-effective manner.
Received: 22 May 2000 / Accepted: 30 August 2000 / Published online: 28 February 2001 相似文献
82.
J. Tomkinson 《Pramana》2008,71(4):745-754
The role that model compounds can play in understanding the vibrational eigenvectors of molecules is discussed. Assigning
the spectra of model compounds is of particular importance and the individual-scaling approach, that has been used with isolated
molecule ab-initio calculations, is outlined. Special emphasis is given to recent work on assigning the spectra of three 5–6 heterobicyclic
systems; indole, benzimidazole and isatin.
相似文献
83.
K. Sreejith 《Applied Surface Science》2005,252(2):321-329
Carbon nitride (CNx) films were deposited from acetonitrile at low voltage (150-450 V) through electrodeposition. The films were characterized by atomic force microscopy (AFM), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. AFM investigations revealed that the grain size was ∼200 nm and roughness was ∼10 nm. The films were found to be continuous and close packed. IR spectra revealed existence of strong sp3, sp2 type bonding and weak sp type carbon nitrogen bonds and these bonds were found to increase with voltage. The fraction of sp3-bonded species in the sample increased in low voltage range and after reaching maximum at 350 V, decreased for higher voltages. However, the concentration of sp2 CN ring structures in the film increased with increasing voltage. Also, the peak width decreased at low voltages reaching a minimum and increased thereafter. It was observed that the voltage dependent increase in the concentration of polymeric type sp2 CN (chain) structures was much more pronounced than that of graphitic type sp2 CN (ring) structures. Raman spectra showed the presence of both the D and G bands. The shift in the G band indicated the presence of nitrogen in the film. The ID/IG ratio was found to increase with the incorporation of nitrogen. Auger electron spectroscopy (AES) showed a clear increase in the nitrogen content with increase in the voltage. The formation of the film could be explained on the basis of dissociation of electrolyte under applied voltage. 相似文献
84.
Ikram Dhouib Philippe Guionneau Zakaria Elaoud 《Journal of Coordination Chemistry》2017,70(21):3585-3597
An organic-inorganic compound of tetraethylammonium dihydrogenarsenate bis(arsenic acid) salts of formula (NEt4)(H2AsO4)(H3AsO4)2, a potential new nonlinear optical material, was prepared by a slow evaporation technique and characterized by IR and Raman spectroscopy accomplished with DFT calculation and electrical-dielectrical measurements. The structure has been solved using direct method and refined by least-squares analysis. In this case, the structure consists of infinite parallel two-dimensional planes built of mutually H2AsO4?, H3AsO4 tetrahedra connected by strong O–H?O hydrogen bonding giving birth to trimers. The geometry, first hyperpolarizability and harmonic vibrational wavenumbers were calculated by means of density functional theory (DFT) with the B3LYP/6-31G(d) level of theory. Good consistency was found between the calculated and the experimental structure, IR, and Raman results. The first hyperpolarizability βtot of the title compound is about 1.75 times more than that of the reference crystal KDP. The complex impedance has been investigated in relation to the temperature and frequency ranges 297 and 373 K and 1 to 100 KHz, respectively. The conductivity temperature variation shows a typical Arrhenius-type behavior with a linear dependence on logarithm of conductivity. Transport properties in this material appear to be due to proton hopping mechanism. 相似文献
85.
Barium tetrametaphosphate hydrate Ba2(P4O12)∙3.5H2O was synthesized as a single‐phase crystalline powder starting from an aqueous solution of barium hydroxide and phosphorus pentoxide at 300 K. Ba2(P4O12)∙3.5H2O crystallizes in a new structure type in which the Ba2+ ions form a distorted hexagonal diamond‐like arrangement with the (P4O12)4– anions in the trigonal prismatic voids (Ba2(P4O12)∙3.5H2O, C2/c, Z = 4, a = 777.3(2), b = 1297.6(2), c = 1346.1(3) pm, b = 95.38(2)°, wR2 = 0.071, R1 = 0.018, 1180 reflections, 118 parameters). The vibrational spectra of Ba2(P4O12)∙3.5H2O and its thermal behavior up to 720 K are also reported. 相似文献
86.
Bis(tetraphenylphosphonium) hexachloridodiberyllate, (Ph4P)2[Be2Cl6], reacts with excess trimethylsilyl‐iso‐thiocyanate to give a mixture of colourless single crystals of (Ph4P)2[Be(NCS)4] ( 1 ) and (Ph4P)4[{Be2(NCS)4(μ‐NCS)2}{Be2(NCS)6(μ‐H2N2C2S2)}] ( 2 ), which can be separated by selection. Both complexes were characterized by X‐ray diffraction. Compound 1 can be prepared without by‐products by treatment of (Ph4P)2[BeCl4] with excess Me3SiNCS in dichloromethane solution. 1 : Space group I41/a, Z = 4, lattice dimensions at 100(2) K: a = b = 1091.2(1), c = 3937.1(3) pm, R1 = 0.0474. The [Be(NCS)4]2– ion of 1 forms tetragonally distorted tetrahedral anions with Be–N distances of 168.4(2) pm and weak intermolecular S ··· S contacts along [100] and [010]. 2 ·4CH2Cl2: Space group P , Z = 1, lattice dimensions at 100(2) K: a = 919.5(1), b = 1248.3(1), c = 2707.0(2) pm, α = 101.61(1) °, β = 95.08(1) °, γ = 94.52(1) °, R1 = 0.103. Compound 2 contains two different anionic complexes in the ratio 1:1. In {Be2(NCS)4(μ‐NCS)2}2–, the beryllium atoms are connected by (NCS)– bridging groups forming centrosymmetric eight‐membered Be2(NCS)2 rings with distances Be–N of 168(1) pm and Be–S of 235.2(9) pm. The second anion {Be2(NCS)6(μ‐H2N2C2S2)}2– consists of two {Be(NCS)3}– units, which are linked by the nitrogen atoms of the unique dimeric cyclo‐addition product of HNCS with Be–N distances of 179(1) pm. 相似文献
87.
Isabel C. Henao Castañeda Carlos O. Della Védova Oscar E. Piro Nils Metzler-Nolte Jorge L. Jios 《Polyhedron》2010
Structural and conformational properties of S-benzyl ferrocenecarbothioate (I) and S-(2-methoxyphenyl) ferrocenecarbothioate (II) are analyzed using data obtained from X-ray diffraction, vibrational data and theoretical calculations. According to chemical quantum calculations, the synperiplanar and antiperiplanar forms are found as the first and second more stable conformations, respectively, for the title compounds. The geometric parameters and normal modes of vibration were calculated using a density functional theory method (B3LYP) and the 6-31+G∗∗ basis set for all atoms except for iron. For this atom the calculations were carried out with the Lanl2dz basis set. The calculated parameters are in good agreement with the corresponding X-ray diffraction values. The combined experimental and theoretical approach allows a consistent assignment for most of the fundamental modes. 相似文献
88.
89.
Arthur G. Maki 《Journal of Molecular Spectroscopy》2011,269(2):166-174
The high-resolution spectrum of cyanogen (14N12C12C14N) has been measured from 500 to 4900 cm−1. For this isotopomer many combination levels with both degenerate fundamentals, ν4 and ν5, have been measured for the first time and the effects of vibrational l-type resonance are observed as well as rotational l-type resonance. The effects of the vibrational resonance coupling ν2 and 2ν4 have also been studied. The data have been combined with earlier measurements below 500 cm−1 to give a comprehensive catalog of the vibrational energy levels and the rovibrational constants for the normal isotopomer of cyanogen. A comparison of the term value constants for the three major symmetric isotopomers is given and they are compared with a recent ab initio calculation. The present data were combined with earlier work on the two symmetric isotopomers, 13C214N2 and 12C215N2, to obtain the equilibrium bond lengths, rCC = 138.109(60) pm and rCN = 115.976(40) pm. 相似文献
90.
《Communications in Nonlinear Science & Numerical Simulation》2014,19(10):3913-3926
The problem of re-stabilization via parametric excitation of statically unstable linear Hamiltonian systems is addressed. An n-degree-of-freedom dynamical system is considered, at rest in a critical equilibrium position, possessing a pair of zero-eigenvalues and n − 1 pairs of distinct purely imaginary conjugate eigenvalues. The response of the system to a small static load, making the zero eigenvalues real and opposite, simultaneous to a harmonic parametric excitation of small amplitude, is studied by the Multiple Scale perturbation method, and the stability of the equilibrium position is investigated. Several cases of resonance between the excitation frequency and the natural non-zero frequencies are studied, calling for standard and non-standard applications of the method. It is found that the parametric excitation is able to re-stabilize the equilibrium for any value of the excitation frequencies, except for frequencies close to resonant values, provided a sufficiently large excitation amplitude is enforced. Results are compared with those provided by a purely numerical approach grounded on the Floquet theory. 相似文献