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111.
Formation of inclusion complexes and controlled release of atrazine using free or silica-anchored β-cyclodextrin 总被引:1,自引:0,他引:1
Lucas Bragan?a de Carvalho Luciana de Matos Alves Pinto 《Journal of inclusion phenomena and macrocyclic chemistry》2012,74(1-4):375-381
Immobilization of cyclodextrin on the surface of silica was performed using citric acid as the bonding agent. Inclusion complexes of atrazine with free (CD) or anchored (CDSI) β-cyclodextrin were prepared and then characterized using infrared spectroscopy, X-ray diffraction and differential scanning calorimetry. The complexation reaction showed first order kinetics, with a rate constant (k) of 8.72?×?10?3 min?1. There was a rapid increase of absorbance in the first 40?min, followed by attainment of equilibrium after ~2?h. The stoichiometry of the reaction was 1:1, with both free and anchored β-cyclodextrin increasing the solubilization of atrazine in an aqueous medium (by around 1.5 and 3.4 times, respectively). The association constant (K a) of the complex was 28.93?L?mol?1 using CD and 130.68?L?mol?1 using CDSI. In release tests, 62% of the atrazine complexed with CDSI or β-CD was released after 40?h, while 83% of free atrazine was released during the same period. 相似文献
112.
A method for the simultaneous determination of benzodiazepines in binary mixtures is proposed, based on the acid hydrolysis of benzodiazepines to benzophenones and the spectrophotometric determination of the latter in the presence of Nemol K 1030, a non-ionic surfactant condensate of ethylene oxide with nonylphenol. The experimental conditions for the hydrolysis of several benzodiazepines in sealed Pyrex tubes were determined. The addition of Nemol K 1030 to acidic solutions of benzophenones modified the positions of the absorption bands and made possible the simultaneous analysis of binary mixtures of benzodiazepines. 相似文献
113.
S. Maurugeon B. Bureau C. Boussard-Pldel A.J. Faber X.H. Zhang W. Geliesen J. Lucas 《Journal of Non》2009,355(37-42):2074-2078
Te80−xGe20Sex glasses have been prepared along the GeSe4–GeTe4 axis using the classical method in silica tube under vacuum. A phase separation domain appears for composition around Te40Ge20Se40. Our attention was turned toward the Te-rich compositions corresponding to 1 < x < 5 at.%. These glasses are transparent from 4 to about 20 μm without any purification of the starting elements. Furthermore the difference ΔT between the crystallization temperature Tx and the vitreous transition temperature Tg lies at about 110 °C that is to say 30 °C higher than for the GeTe4 reference glass. Finally the introduction of a few percentages of Se makes the glasses much easier to prepare and more stable against crystallization, making them drawable as optical fibers for example. Taking into account their transparency window, encompassing the CO2 absorption band around 15 μm, the Te80−xGe20Sex with 1 < x < 5 at.% could become matchless composition for the CO2 infrared detection as planed by the Darwin mission of the European Space Agency. 相似文献
114.
We present an O(min(Kn,n2)) algorithm to solve the maximum integral multiflow and minimum multicut problems in rooted trees, where K is the number of commodities and n is the number of vertices. These problems are NP-hard in undirected trees but polynomial in directed trees. In the algorithm we propose, we first use a greedy procedure to build the multiflow then we use duality properties to obtain the multicut and prove the optimality. 相似文献
115.
van der Waals interactions between nanoclusters have been calculated with a self-consistent, coupled dipole method. The method accounts for all many-body (MB) effects. Comparison is made between the exact potential energy, V, and the values obtained with two alternative methods: the sum of two-body interactions and the sum of two-body and three-body interactions. For all cases considered, the three-body term alone does not accurately represent the MB contributions to V. MB contributions are especially large for shape-anisotropic clusters. 相似文献
116.
In the reaction of Reformatsky reagents (R-CHZnBr-CO2R') with aromatic β-aminoketones (C6H5-CO-CH2-CH2-NR″2, mixtures of erythro and threo diastereomeric amino-hydroxyesters, with the former predominating, were obtained.The proposed bicyclic transition states involve the participation of the neighbouring nitrogen atom, and support the direction and the magnitude of the observed asymmetric induction. The relative stabilities of diastereomeric transition states are discussed in terms of steric and electronic effects. 相似文献
117.
118.
Jonathan P. Blitz Nigel T. Lucas Mark G. Humphrey 《Journal of organometallic chemistry》2002,650(1-2):133-140
The 60-electron tetrahedral clusters W2Ir2(μ-L)(CO)8(η5-C5H4Me)2 [L=dppe (2), dppf (3)] have been prepared from reaction between W2Ir2(CO)10(η5-C5H4Me)2 (1) and the corresponding diphosphine in 52 and 66% yields, respectively. A structural study of 2 reveals that three edges of a WIr2 face are spanned by bridging carbonyls, that the iridium-ligated diphosphine coordinates diaxially and that the tungsten-bound methylcyclopentadienyls coordinate axially and apically with respect to the plane of bridging carbonyls. A structural study of 3 reveals that the dppf ligand bridges an Ir---Ir bond which is also spanned by a bridging carbonyl; tungsten-ligated methylcyclopentadienyl ligands and terminal carbonyls result in electronic asymmetry (17e and 19e iridium atoms) in the electron-precise cluster. Both clusters show two reversible one-electron oxidation processes and an irreversible two-electron reduction; the dppf-containing cluster 3 has a further, irreversible, one-electron oxidation process. UV–vis-NIR spectroelectrochemical studies of the 2→2+→22+ progression reveal the appearance of a low-energy transition on oxidation to 2+ which persists on further oxidation to 22+. 相似文献
119.
Gabriela Bar-Nes Radford Hall Vikashni Sharma Marianne Gaborieau David Lucas Patrice Castignolles Robert G. Gilbert 《European Polymer Journal》2009,45(11):3149-3163
A process for RAFT-controlled radical polymerization in emulsion [36] has been applied to the polymerizations of isoprene and of butadiene in emulsion systems, with the goal of producing latex particles containing block copolymers of acrylic acid (stabilizer and starting polymer), styrene (second polymer) and isoprene or butadiene (third polymer). The microstructure of the polymer chains was examined using dual-detection size-exclusion chromatography, and the nanostructure of the materials was investigated by differential scanning calorimetry and solid-state nuclear magnetic resonance. Reactions were always slow (although faster than the corresponding processes in solution), and exhibited limited reinitiation by isoprene when in emulsion. The materials containing isoprene exhibit a nanostructure with a phase separation into high-Tg polystyrene-rich domains and low-Tg polyisoprene-rich domains, revealed by DSC and NMR. This has the potential to lead to barrier materials with novel physical properties. 相似文献
120.
J. J. Whitmore F. Persi W. S. Toothacker P. A. Elcombe J. C. Hill W. W. Neale W. D. Walker W. Kowald P. Lucas L. Voyvodic R. Ammar D. Coppage R. Davis J. Gress S. Kanekal N. Kwak J. M. Bishop N. N. Biswas N. M. Cason V. P. Kenney M. C. K. Mattingly R. C. Ruchti W. D. Shephard 《Zeitschrift fur Physik C Particles and Fields》1994,62(2):199-227