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841.
Shubina LK Kalinovsky AI Makarieva TN Fedorov SN Dyshlovoy SA Dmitrenok PS Kapustina II Mollo E Utkina NK Krasokhin VB Denisenko VA Stonik VA 《Natural product communications》2012,7(4):487-490
Three new sulfated meroterpenoids containing sesquiterpene and hydroquinone moieties, namely siphonodictyal A sulfate (1), akadisulfate A (2) and akadisulfate B (3), along with the known siphonodictyal B3 and bis(sulfato)-cyclosiphonodictyol A were isolated from the sponge Aka coralliphaga. Their structures were elucidated on the basis of spectroscopic data. Akadisulfate B and siphonodictyal B3 showed a radical-scavenging activity comparable with that of the known lipophylic antioxidant BHT. 相似文献
842.
Artem A. Babaryk Alexandra N. Kozachkova Natalia V. Tsaryk Anatolij V. Dudko Vasily I. Pekhnyo 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(9):m242-m245
The asymmetric unit of the title compound, dipotassium bis[hexaaquanickel(II)] tris(μ2‐methylenediphosphonato)tripalladium(II) hexahydrate, K2[Ni(H2O)6]2[Pd3{CH2(PO3)2}3]·6H2O, consists of half a {[Pd{CH2(PO3)2}]3}6− anion [one Pd atom (4e) and a methylene C atom (4e) occupy positions on a twofold axis] in a rare `handbell‐like' arrangement, with K+ and [Ni(H2O)6]2+ cations to form the neutral complex, completed by three solvent water molecules. The {[Pd{CH2(PO3)2}]3}6− units exhibit close Pd...Pd separations of 3.0469 (4) Å and are packed via intermolecular C—H...Pd hydrogen bonds. The [KO9] and [NiO6] units are assembled into sheets coplanar with (011) and stacked along the [100] direction. Within these sheets there are [K4Ni4O8] and [K2Ni2O4] loops. Successive alternation of the sheets and [Pd{CH2(PO3)2}]3 units parallel to [001] produces the three‐dimensional packing, which is also supported by a dense network of hydrogen bonds involving the solvent water molecules. 相似文献
843.
Garcia I Vior NM Braña AF González-Sabin J Rohr J Moris F Méndez C Salas JA 《Chemistry & biology》2012,19(3):399-413
The gene cluster for the bipyridyl compound collismycin was characterized from Streptomyces sp. CS40. Sequence analysis of a 46.7 kb DNA region revealed 27 open reading frames, 23 of which are involved in collismycin biosynthesis. Eight insertional inactivation mutants were generated in the sequenced region to prove its involvement in collismycin biosynthesis, define the boundaries of the cluster, functionally characterize some genes, and isolate two biosynthetic intermediates. A model for collismycin biosynthesis--which includes the conversion of lysine into picolinic acid, participation of a polyketide synthase-non-ribosomal peptide synthetase system, and some further modifications--is proposed. The biosynthetic pathway would include an unusual NRPS-mediated incorporation of a cysteine residue, possibly through a Michael addition and followed by the extension of the peptide chain by leucine incorporation and later removal by amidohydrolase. 相似文献
844.
Igor Sharf Andrii Tykhonov Grygorii Sokhrannyi Maksym Deliyergiyev Natalia Podolyan Vitaliy Rusov 《Central European Journal of Physics》2012,10(4):858-887
We demonstrate a new method to calculate inelastic scattering cross-sections, which in contrary to the Regge-based methods takes into account the energy momentum conservation law. It is shown that the main contribution to integral expressing inelastic scattering cross-sections does not come from the multi-Regge domain. In particular, accounting for the longitudinal momenta contribution to virtualities is sufficient and results in the new mechanism of cross-section growth. The reasons for taking into account the sufficiently high number of interference contributions are shown and the approximate method for this purpose is developed. By fitting single free parameter of the model achieved a qualitative agreement of the total and inelastic cross sections with experimental data. 相似文献
845.
Dr. Denis V. Anokhin Dr. Jānis Lejnieks Dr. Ahmed Mourran Dr. Xiaomin Zhu Dr. Helmut Keul Prof. Martin Möller Dr. Oleg Konovalov Dr. Natalia Erina Dr. Dimitri A. Ivanov 《Chemphyschem》2012,13(6):1470-1478
This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules. 相似文献
846.
847.
A family of nonlinear conservative finite difference schemes for the multidimensional Boussinesq Paradigm Equation is considered.
A second order of convergence and a preservation of the discrete energy for this approach are proved. Existence and boundedness
of the discrete solution on an appropriate time interval are established. The schemes have been numerically tested on the
models of the propagation of a soliton and the interaction of two solitons. The numerical experiments demonstrate that the
proposed family of schemes is about two times more accurate than the family of schemes studied in [Kolkovska N., Two families
of finite difference schemes for multidimensional Boussinesq paradigm equation, In: Application of Mathematics in Technical
and Natural Sciences, Sozopol, June 21–26, 2010, AIP Conf. Proc., 1301, American Institute of Physics, Melville, 2010, 395–403]. 相似文献
848.
Szemik-Hojniak A Deperasiñska I Jerzykiewicz L Sobota P Hojniak M Puszko A Haraszkiewicz N van der Zwan G Jacques P 《The journal of physical chemistry. A》2006,110(37):10690-10698
The crystal structure of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) was resolved on the basis of X-ray diffraction. Solid 2B6M occurs in the form of a doubly hydrogen-bonded dimer with squarelike hydrogen-bonding network composed of two intra- (2.556(2) A) and two intermolecular (2.891(2) A) N-H...O type hydrogen bonds. The molecule thus has both a protonable and a deprotonable group that led us to investigate the possibility of an excited-state proton transfer (ESIPT) reaction in different solvents by means of experimental absorption, steady state, and time-resolved emission spectroscopy. The results were correlated with quantum mechanical TD-DFT and PM3 calculations. Experimental and theoretical findings show the possibility of an ESIPT reaction in polar solvents. It is demonstrated that in particular the emission spectra of 2B6M are very sensitive to solvent properties, and a large value of the Stokes shift (about 8000 cm(-1)) in acetonitrile is indicative for an ESIPT process. This conclusion is further supported by time-resolved fluorescence decay measurents that show dual exponential decay in polar solvents. Vertical excitation energies calculated by TD-DFT reproduce the experimental absorption maxima in nonpolar solvents well. The majority of electronic transitions in 2B6M is of pi --> pi* character with a charge shift from the electron-donating to the electron-accepting groups. The calculations show that, due to the charge redistribution on excitation, the acidity of the amino group increases significantly, which facilitates the proton transfer from the amino to the N-oxide group in the excited state. 相似文献
849.
850.