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491.
We have discovered that an Ir‐23Nb binary alloy more effectively oxidizes hydrogen peroxide than Ir, Ir‐13Nb, Ir‐17Nb, Ir‐30Nb, Ir‐43Nb, Ir‐62Nb, or Nb. The oxidation capability was determined via cyclic voltammogram measurements of pH‐buffer and hydrogen peroxide. We ascertained that applying a 0.7 V potential produces hydrogen peroxide currents of 9.2 μA/mm2 Ir‐23Nb, 5.3 μA/mm2 Ir, 5.1 μA/mm2 Ir‐17Nb, 3.7 μA/mm2 Ir‐13Nb, 2.0 μA/mm2 Ir‐30Nb, 1.5 μA/mm2 Ir‐43Nb, 0.6 μA/mm2 Ir‐62Nb, and 0.13 μA/mm2 Nb. These results indicate that the effective oxidation of Ir‐23Nb for hydrogen peroxide might be due to its fcc+L12 two‐phase structure and that Ir‐23Nb can be used as an amperometric transducer material. 相似文献
492.
Amos B. Smith III Chris Sfouggatakis Christina A. Risatti Jeffrey B. Sperry Wenyu Zhu Victoria A. Doughty Takashi Tomioka Dimitar B. Gotchev Clay S. Bennett Satoshi Sakamoto Onur Atasoylu Shohei Shirakami David Bauer Makoto Takeuchi Jyunichi Koyanagi Yasuharu Sakamoto 《Tetrahedron》2009,65(33):6489-5984
Three syntheses of the architecturally complex, cytotoxic marine macrolide (+)-spongistatin 1 (1) are reported. Highlights of the first-generation synthesis include: use of a dithiane multicomponent linchpin coupling tactic for construction of the AB and CD spiroketals, and their union via a highly selective Evans boron-mediated aldol reaction en route to an ABCD aldehyde; introduction of the C(44)-C(51) side chain via a Lewis acid-mediated ring opening of a glucal epoxide with an allylstannane to assemble the EF subunit; and final fragment union via Wittig coupling of the ABCD and EF subunits to form the C(28)-C(29) olefin, followed by regioselective Yamaguchi macrolactonization and global deprotection. The second- and third-generation syntheses, designed with the goal of accessing 1 g of (+)-spongistatin 1 (1), maintain both the first-generation strategy for the ABCD aldehyde and final fragment union, while incorporating two more efficient approaches for construction of the EF Wittig salt. The latter combine the original chelation-controlled dithiane union of the E- and F-ring progenitors with application of a highly efficient cyanohydrin alkylation to append the F-ring side chain, in conjunction with two independent tactics to access the F-ring pyran. The first F-ring synthesis showcases a Petasis-Ferrier union/rearrangement protocol to access tetrahydropyrans, permitting the preparation of 750 mg of the EF Wittig salt, which in turn was converted to 80 mg of (+)-spongistatin 1, while the second F-ring strategy, incorporates an organocatalytic aldol reaction as the key construct, permitting completion of 1.009 g of totally synthetic (+)-spongistatin 1 (1). A brief analysis of the three syntheses alongside our earlier synthesis of (+)-spongistatin 2 is also presented. 相似文献
493.
Stefan Feil Greg K. Koyanagi Diethard K. Bohme 《International journal of mass spectrometry》2009,280(1-3):38
Room temperature rate coefficients and product distributions are reported for the reactions initiated in D2O with dications of the alkaline-earth metals Mg, Ca, Sr and Ba. The measurements were performed with a selected-ion flow tube (SIFT) tandem mass spectrometer and electrospray ionization (ESI). Mg2+ reacts with water by a fast electron transfer leading to charge separation with a rate coefficient of 1.4 × 10−9 cm3 molecule−1 s−1. Ca2+ reacts with D2O in a first step to form the adduct Ca2+(D2O), with an effective bimolecular rate coefficient of 2.3 × 10−11 cm3 molecule−1 s−1, which then undergoes rapid charge separation by deuteron transfer to form CaOD+ and D3O+ in a second step with k = 7.9 × 10−10 cm3 molecule−1 s−1. The CaOD+ ion reacts further by clustering up to five more D2O molecules. Sr2+ clusters up to eight D2O molecules and Ba2+ up to seven D2O molecules, with the first addition of D2O being rate determining in each case and the last addition being distinctly slower, as might be expected from a transition in the occupation of the added water molecules from an inner to an outer hydration shell. 相似文献
494.
Itaru Okamoto Dr. Kenji Iwamoto Yuko Watanabe Yoko Miyake Dr. Akira Ono Dr. 《Angewandte Chemie (International ed. in English)》2009,48(9):1648-1651
DNA duplexes containing 5‐modified uracil pairs (5‐bromo, 5‐fluoro, and 5‐cyanouracil) bind selectivity to metal ions. Their selectivity is sensitive to the pH value of the solution (see picture), as the acidities of the modified uracil bases vary according to the electron‐withdrawing properties of the substituents.
495.
In this series of studies, we systematically apply the analytical energy gradients of the direct symmetry-adapted cluster-configuration interaction singles and doubles nonvariational method to calculate the equilibrium geometries and vibrational frequencies of excited and ionized states of molecules. The harmonic vibrational frequencies were calculated using the second derivatives numerically computed from the analytical first derivatives and the anharmonicity was evaluated from the three-dimensional potential energy surfaces around the local minima. In this paper, the method is applied to the low-lying valence singlet and triplet excited states of HAX-type molecules, HCF, HCCl, HSiF, HSiCl, HNO, HPO, and their deuterium isotopomers. The vibrational level emission spectra of HSiF and DSiF and absorption spectra of HSiCl and DSiCl were also simulated within the Franck-Condon approximation and agree well with the experimental spectra. The results show that the present method is useful and reliable for calculating these quantities and spectra. The change in geometry in the excited states was qualitatively interpreted in the light of the electrostatic force theory. The effect of perturbation selection with the localized molecular orbitals on the geometrical parameters and harmonic vibrational frequencies is also discussed. 相似文献
496.
Hirai K Furukawa S Kondo M Meilikhov M Sakata Y Sakata O Kitagawa S 《Chemical communications (Cambridge, England)》2012,48(52):6472-6474
Spatiospecific functionalisation of a shell crystal was performed in a core-shell crystal of a porous coordination polymer (PCP) via post-synthetic modification (PSM). The shell crystal allowed the core crystal to selectively accumulate N,N-dimethylaniline (DMA) and afford the intense exciplex fluorescence. 相似文献
497.
498.
Masahiro Kasai Yuzoo Kozono Yoko Kanke Toshiyuki Ohno Masanobu Hanazono Yutaka Sugita 《Phase Transitions》2013,86(1-2):59-63
A novel proximity effect between superconductor and magnetic manganese oxide has been found. To investigate interactions between superconductor and magnetic materials, we have fabricated both trilayered-type and coplanar-type junctions and investigated their current-voltage characteristics. The magnetic material was La1-x Ca x MnO z (LCMO) or La1-x Sr x MnO z (LSMO) manganese oxide. In YBCO/LCMO/YBCO junctions, supercurrents were observed through a magnetic barrier as thick as 500 nm. This phenomenon was also confirmed by coplanar junctions. The effect of magnetism of the barrier material was investigated. It was found that this proximity effect occurred only in a limited region where spin fluctuations are considered to exist. 相似文献
499.
500.
Usui T Nagumo Y Watanabe A Kubota T Komatsu K Kobayashi J Osada H 《Chemistry & biology》2006,13(11):1153-1160
Lymphocytes in T cell activation require extracellular nutrients to provide energy for cellular proliferation and effector functions. Therefore, inhibitors of nutrient transporters are expected to be a new class of immunosuppressant. Here, we report that the molecular target of brasilicardin A (BraA), an immunosuppressive compound, is the amino acid transporter system L. BraA inhibited the cell-cycle progression of murine T cell lymphocyte CTLL-2 cells in G1 phase, and potently inhibited the uptake of amino acids that are substrates for amino acid transport system L. Moreover, BraA stimulated the GCN2 activation and, subsequently, the phosphorylation of eIF2alpha. These results suggest that the immunosuppressive activity of BraA is induced by amino acid deprivation via the inhibition of system L and that the amino acid transporter is a target for immunosuppressant. 相似文献