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981.
982.
Andreas Martin Christoph Tefehne Wolfram Gronski 《Macromolecular rapid communications》1996,17(5):305-311
Liquid-crystalline (LC) block copolymers of lamellar morphology were prepared via anionic polymerization of polystyrene-block-1,2-polybutadiene and subsequent introduction of a deuterated mesogen by polymer analogous reaction. Deuteron NMR measurements show that the first-order nematic/isotropic transition in the block copolymer is changed to a critical behaviour under the influence of shear. In the nematic phase the order parameter is reduced with respect to the homopolymer, and there is no evidence of an isotropic boundary layer of the LC-block at the nematic/isotropic interface. 相似文献
983.
984.
Klaus Eckart Max C. Holthausen Wolfram Koch Joachim Spiess 《Journal of the American Society for Mass Spectrometry》1998,9(10):1002-1011
B ions represent an important type of fragment ions derived from protonated peptides by cleavage of an amide bond with N-terminal charge retention. Such species have also been discussed as key intermediates during cyclic peptide fragmentation. Detailed structural information on such ion types can facilitate the interpretation of multiple step fragmentations such as the formation of inner chain fragments from linear peptides or the fragmentation of cyclic peptides. The structure of different b2 ion isomers was investigated with collision-induced dissociations (CID) in combination with hydrogen/deuterium (H/D) exchange of the acidic protons. Special care was taken to investigate fragment ions derived from pure gas-phase processes. Structures deduced from the results of the CID analysis were compared with structures predicted on the basis of quantum chemical density functional theory (DFT) calculations to be most stable. The results pointed to different types of structures for b2 ion isomers of complementary amino acid sequences. Either the protonated oxazolone structure or the N-terminally protonated immonium ion structure were proposed on the basis of the CID results and the DFT calculations. In addition, the analysis of different selectively N-alkylated peptide analogs revealed mechanistic details of the processes generating b ions. 相似文献
985.
Qin Qin Zhu Wolfram Schnabel 《Journal of photochemistry and photobiology. A, Chemistry》2000,130(2-3):119-125
Hindered amines such as 2,2,6,6-tetramethyl piperidines and N-methyl-2,2,6,6-tetramethyl piperidines and hindered amino ethers such as N-methoxy-2,2,6,6-tetramethyl piperidines were examined with respect to their reactivity towards triplet-excited benzophenone (3BP*) in Ar-saturated acetonitrile solution at room temperature. Upon measuring phosphorescence decay rates in the absence and presence of quencher it was found that the amines are two to three orders of magnitude more reactive than the amino ethers. For all amine/BP systems examined the generation of free ions was inferred from an increase in the electrical conductivity. This indicates that a charge transfer (CT) mechanism is operative in these cases. Notably, tertiary amines were found to be more reactive towards 3BP* and give higher free ion yields than secondary amines. In the case of amino ether/BP systems evidence for a CT mechanism was not obtained in spite of an increase in the electrical conductivity indicating the generation of free ions. The latter are formed much faster than the phosphorescence decays and very likely originate from triplet–triplet annihilation (3BP*+3BP*→BP√++BP√−). 相似文献
986.
987.
Distance algorithms are most frequently used in robotics to determine the distance between two obstacles in the environment of a robot or between a sensor point and an object. We extend the multibody simulation package MOBILE for an application of accurate algorithms for distance computation between objects represented by convex or non-convex polyhedra. These objects are represented by their vertices and oriented facets. As an application example, a multibody system is discussed where a sensor point moves close to a non-convex obstacle. The computed results show that the algorithms developed are suitable for accurate real-time multibody simulations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
988.
989.
Nils Wiberg Wolfgang Niedermayer Hans‐Wolfram Lerner Michael Bolte 《无机化学与普通化学杂志》2001,627(5):1043-1047
Disupersilylsilanides M(SiHR*2)2 of Metals of the Zinc Group (M = Zn, Cd, Hg; R* = Si t Bu3): Syntheses, Characterization, and Structures Bis(disupersilyl)silylmetals M(SiHR )2 (R* = Supersilyl = SitBu3) with M = Zn, Cd, Hg are obtained in tetrahydrofuran/benzene/pentane by the reaction of NaSiHR with ZnCl2, CdI2, HgCl2 in the molar ratio 2 : 1. The compounds form colorless, in organic media soluble, not hydrolysis‐ and air‐sensitive crystals, the stabilities of which for thermolysis or photolysis decrease in the row Zn > Hg > Cd compound. According to X‐ray structure analyses, the compounds M(SiHR )2 are monomeric with a – to date not observed – non‐linear framework –M– (angle SiMSi for M(SiHR )2 with M = Zn/Cd/Hg 170.7/174.2/174.4°). 相似文献
990.