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61.
Jacques Vervoort Dennis J. O'Kane Lionel A. Carreira John Lee 《Photochemistry and photobiology》1983,37(1):117-119
The vibrational fingerprint in the frequency region 1700-1100 cm-1 has been obtained for a fluorescent protein purified from the bioluminescent bacterium Photobacterium leiognathi. using the technique of resonance coherent anti-Stokes Raman scattering. The frequencies of the 4 prominent modes are the same as for lumazine protein purified from Photobacterium phosphoreum , and for an authentic sample of 6,7-dimethyl-8-ribityllumazine. The fluorophore in the new protein, therefore, must have the same chemical structure. The absence of frequency shifts between the free and bound ligand, in contrast to observations of fiavoproteins, implies that the lumazine ring undergoes no changes in hydrogen bonding between the free and protein-bound ligand in its ground electronic state. However, changes in relative intensities of two modes are seen, arising from differences in interactions in the excited state, and this is also reflected by differences in fluorescence properties. 相似文献
62.
According to the subsequent treatment, azepines , , or 1,2-dihydro derivatives and are obtained in the photolysis in basic medium of β-anthracenic azides and and provide strong evidence for the intermediate formation of bicyclic aziridines. 相似文献
63.
Clémence Guillaume Jacques Le Calvé Iliana Dimicoli Michel Mons 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,32(1):157-165
The intensity distribution of benzene+-Arn cluster ions formed by laser ionization of neutral clusters has been investigated: two main intensity anomalies (magic numbers atn=20 and 45) have been observed in the 15–60 size range. The evaporation dynamics of these species in the 2–50 microsecond time window following ionization has been studied using the electrostatic mirror of a reflectron time-of-flight mass spectrometer as a kinetic energy analyser capable to distinguish parent and daughter ions. The magic numbers are interpreted in terms of size dependent evaporation behaviors: beyondn=20, a sudden decrease of the evaporation energy is observed; in then=45–47 size range, the magic number is accounted for by the specific dynamics of then=46 and 47 clusters, in particular the possible loss of two argon atoms forn=47 within the experimental time window. These results and their implications on the cluster structure are discussed in the light of the evaporative ensemble model and compared to the evaporation characteristics of similar species, in particular the neat rare gas clusters. 相似文献
64.
A unique process of chemical oxidation polymerization of aniline using manganese dioxide (MnO2) as the oxidizing agent in an aqueous medium is described. The reaction between aniline and MnO2 follows a mechanism by which the organic monomer is oxidized while the metal oxide undergoes reductive dissolution. The effects of the amount of oxidizing agent and aniline, pH and temperature of the reactive system, type of acid on the yield and conductivity of polyaniline are discussed. The resulting polyaniline was characterized by [R and UV-Vis spectrometry. Polyaniline with a conductivity of 12.5 S/cm was obtained using 0.033 tool of aniline oxidized by 0.023 tool MnO2 in the presence of 100 mL of 2.7 mol/L HCI at 25℃ for 4 h. 相似文献
65.
D. Zorrilla Cuenca J. Sánchez Márquez M. Fernández Núñez R. Rodríguez Huertas 《International journal of quantum chemistry》2007,107(4):879-893
This project consists of two parts. In the first part, a series of test calculations is performed to verify that the integrals involved in the determination of atomic and molecular properties by standard self‐consistent field (SCF) methods can be obtained through Halton, Korobov, or Hammersley quasi‐random integration procedures. Through these calculations, we confirm that all three methods lead to results that meet the levels of precision required for their use in the calculation of properties of small atoms or molecules at least at a Hartree–Fock level. Moreover, we have ensured that the efficiency of quasi‐random integration methods that we have tested is Halton=Korobov>Hammersley?pseudo‐random. We also find that these results are comparable to those yielded by ordinary Monte Carlo (pseudo‐random) integration, with a calculation effort of two orders of smaller magnitude. The second part, which would not have been possible without the integration method previously analyzed, contains a first study of atoms constrained in spherical boxes through SCF calculations with basis functions adapted to the features of the problem: Slater‐type orbitals (STOs) trimmed by multiplying them by a function that yields 1 for 0 < r < (R‐δ), polynomial values for (R‐δ) < r < R and null for r > R, R being the radius of the box and δ a variationally determined interval. As a result, we obtain a equation of state for electrons of small systems, valid just in the limit of low temperatures, but fairly simple. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
66.
The silver nitrate assisted cyclization of the entitled diols leads, depending on the substitution of the allenic linkage, specifically to dihydropyranes , when R is alkyl or to an equimolecular mixture of and its tetrahydrofuranyl isomer when R is hydrogen. 相似文献
67.
Optimal performance laminar chromatography and automated multiple development chromatography are relatively recent techniques of planar chromatography that can be applied with success in plant material analysis. Therefore, these methods are used to study plant extracts and constituents belonging to different chemical classes of secondary metabolism: heterocyclic oxygen compounds (coumarins, flavonoids, and anthocyanins), alkaloids and quaternary ammonium salts, cannabinoids, essential oils, ginsenosides, and cardiac heterosides. Generally, the results obtained with these methods are good, and in most cases they compare with those of thin-layer chromatography. 相似文献
68.
Christians Ferradini Jacques Foos Chantal Houee Jacques Pucheault 《Photochemistry and photobiology》1978,28(4-5):697-700
Abstract— In order to obtain a better understanding of the kinetics of the Haber-Weiss reaction
often proposed as a source of OH radicals, we have measured the decomposition rate of H2 O2 in aqueous solutions by y rays and for different pH values. This decomposition proceeds by a chain reaction involving the preceding one as the propagating step.
The rate constant found is to be
相似文献
often proposed as a source of OH radicals, we have measured the decomposition rate of H
The rate constant found is to be
相似文献
69.
Structural basis for thrombin activation of a protease-activated receptor: inhibition of intramolecular liganding 总被引:3,自引:0,他引:3
Seeley S Covic L Jacques SL Sudmeier J Baleja JD Kuliopulos A 《Chemistry & biology》2003,10(11):1033-1041
Protease-activated G protein-coupled receptors (PAR1-4) are tethered-ligand receptors that are activated by proteolytic cleavage of the extracellular domain (exodomain) of the receptor. PAR1, the prototypic member of the PAR family, is the high-affinity thrombin receptor of platelets and vascular endothelium and plays a critical role in blood coagulation, thrombosis, and inflammation. Here, we describe the solution structure of the thrombin-cleaved exodomain of PAR1. The side chains of a hydrophobic hirudin-like (Hir) sequence and adjacent anionic motif project into solution. Docking of the exodomain Hir sequence to exosite I of thrombin reveals that the tethered ligand in the cleaved exodomain bends away from thrombin, leaving its active site available to another large macromolecular substrate. The N-terminal ligand is longer than anticipated and forms an intramolecular complex with a region located in the C terminus of the exodomain. Mutational analysis confirmed that this C-terminal region is a ligand binding site for both intra- and intermolecular ligands. A lipidated-ligand binding site peptide was found to be an effective inhibitor of thrombin-induced platelet aggregation. 相似文献
70.
Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)
A new bixbyite family, Cu1?xTi1?xFe2xO3 (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ~ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)2O3 compounds. There is a disordered distribution of CuII, TiIV, and FeIII over the two cyrstallographic sites: PI and PII. PII is highly distorted (two long MO distances) by the Jahn-Teller effect of CuII. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM2O3 family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu1?xTi1?xFe2xO3 compounds. The electrical properties (σ ~ 10?5(Ω cm)?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism. 相似文献