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981.
Ekaterina V. Rastoltseva Vadim A. Bataev Alexander V. Abramenkov Vladimir I. Pupyshev Igor A. Godunov 《Journal of Molecular Structure》2010,939(1-3):14-21
Geometric parameters, harmonic and anharmonic vibrational frequencies, conformer energy differences and barriers to internal rotation were obtained for dicyclopropyl ketone (DCPK) in the ground electronic state through MP2, DFT, CCSD and CCSD(T) calculations. VFPA was used to improve the estimations of conformer energy differences and heights of barriers to internal rotation. The ab initio calculations demonstrated that there are three stable conformations of DCPK: the cis–cis, the cis–trans and the gauche–gauche. The energy of the gauche–gauche conformer is noticeably higher than the energy of the two other conformers, so this conformer was not found experimentally. To study the conformational dynamics of the DCPK molecule, one- and two-dimensional sections of the potential energy surface corresponding to the rotations of the cyclopropyl groups were calculated. These sections were used to calculate torsion transition energies and vibrational wave functions in anharmonic approach. It was found that there is a strong coupling of large-amplitude torsion motions in the area of the cis–cis and gauche–gauche conformers. 相似文献
982.
Vdovenko SI Gerus II Kukhar VP 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(3):779-785
Infrared spectroscopy studies of six beta-alkoxyvinyl methyl ketones, with common structure R(1)O-CR(2)CH-COR(3), where R(1)=R(3)=CH(3), R(2)=H (1); R(1)=C(2)H(5), R(2)=H (2); R(3)=CF(3); R(1)=R(2)=CH(3), R(3)=CF(3) (3); R(1)=C(2)H(5), R(2)=C(6)H(5), R(3)=CF(3) (4); R(1)=C(2)H(5), R(2)=4-O(2)NC(6)H(4), R(3)=CF(3) (5); R(1)=C(2)H(5), R(2)=C(CH(3))(3), R(3)=CF(3) (6) in 11 pure organic solvents of different polarity were undertaken to investigate the solute-solvent interactions and to correlate solvent properties by means of linear solvation energy relationships (LSER) with the carbonyl and vinyl stretching vibrations of existing stereoisomeric forms. It was shown that contrary to simple carbonyl-containing compounds where solvent HBD acidity (alpha) has the largest influence on the nu (CO) band shift to lower wavenumbers, the dipolarity/polarizability (pi) term plays the main role in the interactions of conjugated enones with solvent molecules leading to the nu (CO) and nu (CC) bathochromic band shifts. The trifluoroacetyl group possesses a reduced ability to form hydrogen bonds with solvents. For the nu (CC) band of non-fluorinated enone 1 solvent HBD acidity (alpha) and solvent HBA basicity term (beta) play a perceptible role, whereas for 2 these terms are not significant. beta-Substituents in fluorinated enones such as R(2)=H, C(6)H(5), and C(CH(3))(3) assist in the intermolecular hydrogen bond formation of the carbonyl moiety with HBD solvents, while beta-substituents such as CH(3) and 4-NO(2)C(6)H(4) prevent the CO group to form the H-bonds with HBD solvents (the solvent HBD acidity term (alpha) is not significant). The comparison of four conformers of the enone 1 reveals that (EEE) form is the most polarizable conformer; the influences of the solvent dipolarity/polarizability (pi) and solvent HBD acidity (alpha) term on the bathochromic nu (CO) band shift are opposite to one another. 相似文献
983.
Ekaterina A. Verochkina Nadezhda Victorovna Vchislo Igor B. Rozentsveig 《Molecules (Basel, Switzerland)》2021,26(14)
α-Functionalized α,β-unsaturated aldehydes is an important class of compounds, which are widely used in fine organic synthesis, biology, medicine and pharmacology, chemical industry, and agriculture. Some of the 2-substituted 2-alkenals are found to be the key metabolites in plant and animal cells. Therefore, the development of efficient methods for their synthesis attracts the attention of organic chemists. This review focusses on the recent advances in the synthesis of 2-functionally substituted 2-alkenals. The approaches to the preparation of α-alkyl α,β-unsaturated aldehydes are not included in this review. 相似文献
984.
A Proposal for a Low-Frequency Axion Search in the 1–2 μ eV Range and Below with the BabyIAXO Magnet
Saiyd Ahyoune Alejandro Álvarez Melcón Sergio Arguedas Cuendis Sergio Calatroni Cristian Cogollos Jack Devlin Alejandro Díaz-Morcillo David Díez-Ibáñez Babette Döbrich Javier Galindo Juan Daniel Gallego Jose María García-Barceló Benito Gimeno Jessica Golm Yikun Gu Louis Herwig Igor Garcia Irastorza Antonio Jose Lozano-Guerrero Chloé Malbrunot Jordi Miralda-Escudé Juan Monzó-Cabrera Pablo Navarro Jose Ramón Navarro-Madrid Javier Redondo José Reina-Valero Kristof Schmieden Tim Schneemann Marc Siodlaczek Stefan Ulmer Walter Wuensch 《Annalen der Physik》2023,535(12):2300326
In the near future BabyIAXO will be the most powerful axion helioscope, relying on a custom-made magnet of two bores of 70 cm diameter and 10 m long, with a total available magnetic volume of more than 7 m3. In this document, it proposes and describe the implementation of low-frequency axion haloscope setups suitable for operation inside the BabyIAXO magnet. The RADES proposal has a potential sensitivity to the axion-photon coupling down to values corresponding to the KSVZ model, in the (currently unexplored) mass range between 1 and 2 eV, after a total effective exposure of 440 days. This mass range is covered by the use of four differently dimensioned 5-meter-long cavities, equipped with a tuning mechanism based on inner turning plates. A setup like the one proposed will also allow an exploration of the same mass range for hidden photons coupled to photons. An additional complementary apparatus is proposed using LC circuits and exploring the low energy range ( eV). The setup includes a cryostat and cooling system to cool down the BabyIAXO bore down to about 5 K, as well as an appropriate low-noise signal amplification and detection chain. 相似文献
985.
Gennady Evtugyn Anna Porfireva Rusal Sitdikov Vladimir Evtugyn Ivan Stoikov Igor Antipin Tibor Hianik 《Electroanalysis》2013,25(8):1847-1854
An electrochemical aptasensor for ochratoxin A (OTA) detection has been developed on the base of a gold electrode covered with electropolymerized neutral red and silver nanoparticles obtained by chemical reduction with macrocyclic ligands bearing catechol fragments. Thiolated aptamers against OTA were covalently attached to silver nanoparticles via Ag? S bonding. The interaction with OTA induced the conformational switch of the aptamer, which caused increase of the charge transfer resistance measured by EIS in the presence of ferricyanide ions. The LOD achieved (0.05 nM) was comparable to other electrochemical aptasensors employing sophisticated assembling technique and enzyme amplification of the signal. The aptasensor was validated in spiked beer samples. The recovery of the OTA determination was found to be 66.3±14.1 % for light beer and 64.3±1.8 % for dark beer. 相似文献
986.
Golenya IA Gumienna-Kontecka E Boyko AN Haukka M Fritsky IO 《Dalton transactions (Cambridge, England : 2003)》2012,41(31):9427-9430
An unprecedented encapsulation of an exogenous sodium ion by iron(III) tris(hydroxamate)s was observed upon crystallization of an iron(III) complex with isonicotinylhydroxamic acid. The sodium cation is bound by bridging coordination of the amide oxygen atoms from two mononuclear iron(III) fac-tris(hydroxamate)s. 相似文献
987.
Vladimir G. Neudatchin Igor T. Obukhovsky Ludmila L. Sviridova Nikolai P. Yudin 《Central European Journal of Physics》2004,2(3):511-522
The pion momentum distributions (MDs) in four channels of virtual decay p→B+π, B = N, Δ, N
1/2-(1535), N
1/2+(1440) are calculated in two models, the microscopic model of 3
P
0 scalar q−q fluctuation with the pion as a composite q−q-system and the chiral semi-microscopic model of πq interaction with the pion as a structureless Goldstone boson. The results of the above models are similar for the baryon
states B = N, Δ, N
1/2-(1535) but are rather different for the Roper resonance N
1/2+(1440) which corresponds to excitation of two oscillator quanta in the nucleon. The experimental investigation of pion MDs
by means of the reaction of quasi-elastic knockout of pion by an electron of a few GeV energy p(e, e′ π)B may be very suitable for Jefferson Laboratory, Virginia (JLab). 相似文献
988.
Rodriguez-Garcia V Hirata S Yagi K Hirao K Taketsugu T Schweigert I Tasumi M 《The Journal of chemical physics》2007,126(12):124303
The authors present a first-principles prediction of the energies of the eight lowest-lying anharmonic vibrational states of CO(2), including the fundamental symmetric stretching mode and the first overtone of the fundamental bending mode, which undergo a strong coupling known as Fermi resonance. They employ coupled-cluster singles, doubles, and (perturbative) triples [CCSD(T) and CCSDT] in conjunction with a range of Gaussian basis sets (up to cc-pV5Z, aug-cc-pVQZ, and aug-cc-pCVTZ) to calculate the potential energy surfaces (PESs) of the molecule, with the errors arising from the finite basis-set sizes eliminated by extrapolation. The resulting vibrational many-body problem is solved by the vibrational self-consistent-field and vibrational configuration-interaction (VCI) methods with the PESs represented by a fourth-order Taylor expansion or by numerical values on a Gauss-Hermite quadrature grid. With the VCI, the best theoretical estimates of the anharmonic energy levels agree excellently with experimental values within 3.5 cm(-1) (the mean absolute deviation). The theoretical (experimental) anharmonic frequencies of the Fermi doublet are 1288.9 (1285.4) and 1389.3 (1388.2) cm(-1). 相似文献
989.
Langhals H Esterbauer AJ Walter A Riedle E Pugliesi I 《Journal of the American Chemical Society》2010,132(47):16777-16782
We investigate the ultrafast resonant energy transfer of a perylene bisimide dyad by pump-probe spectroscopy, chemical variation, and calculations. This dyad undergoes transfer with near-unit quantum efficiency, although the transition dipole moments of the donor and acceptor are in a perfectly orthogonal arrangement to each other in the equilibrium geometry. According to the point dipole approximation used in Fo?rster theory, no energy transfer should occur. Experimentally we do, however, find an ultrafast transfer time of 9.4 ps. With the transition density cube approach we show that in the orthogonal arrangement the Coulombic interactions do not contribute to the electronic coupling. Through the change of the spacer in both length and chemical character, we can clearly exclude any Dexter-type energy transfer. The temperature effects on the Fo?rster resonant energy transfer rate demonstrate that energy transfer is enabled through low-frequency ground-state vibrations, which break the orthogonal arrangement of the transition dipole moments. The dyads presented here therefore are a first example that shows with extreme clarity the decisive role vibrational motion plays in energy transfer processes. 相似文献
990.
Sikorska E Khmelinskii I Hoffmann M Machado IF Ferreira LF Dobek K Karolczak J Krawczyk A Insińska-Rak M Sikorski M 《The journal of physical chemistry. A》2005,109(51):11707-11714
Experimental time-resolved spectral and photon counting kinetic results confirm formation of an isoalloxazinic excited state via excited-state double proton transfer (ESDPT) catalyzed by a carboxylic acid molecule that forms a hydrogen-bond complex with the parent alloxazine molecule. This isoalloxazinic tautomer manifests itself as a distinct long-lived emissive species formed only in such alloxazine derivatives that were not substituted at the N1 nitrogen atom, being a product of the excited-state reaction occurring from the alloxazinic excited state. Theoretical calculations support the idea that the ESDPT occurs by the concerted mechanism. The calculated activation barrier in the excited state is much lower than the same barrier in the ground state and even disappears for the HOMO-1 to LUMO excitation, which explains the fact that the reaction takes place in the excited-state only. The reaction rate estimated from the emission kinetics is ca. 1.4 x 10(8) dm3 mol(-1) s(-1) in ethanolic solutions of lumichrome with added acetic acid. 相似文献