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411.
Takahiko Taniguchi Kunio Ogasawara 《Angewandte Chemie (International ed. in English)》1998,37(8):1136-1137
Child's play! Allyl ethers as protecting groups for hydroxyl functions can be removed readily with a combination of DIBAL and catalytic amounts of [NiCl2(dppp)]. Propene is expelled in this remarkably selective reaction, and a nickel-catalyzed hydroalumination–elimination pathway is proposed [Eq. (a)]. dppp=propane-1,3-diylbis(diphenylphosphane). 相似文献
412.
413.
Keita Sakamoto Akihiro Hakamata Dr. Arihiro Iwasaki Prof. Dr. Kiyotake Suenaga Prof. Dr. Masashi Tsuda Prof. Dr. Haruhiko Fuwa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(36):8528-8542
Iriomoteolide-2a is a marine macrolide metabolite isolated from a cultured broth of the benthic dinoflagellate Amphidinium sp. HYA024 strain. This naturally occurring substance was reported to show remarkable cytotoxic activity against human cancer cell lines HeLa and DG-75 and in vivo antitumor activity against murine leukemia P388 cell line. Herein, the total synthesis, stereochemical revision, and biological assessment of iriomoteolide-2a are reported in detail. Total synthesis of the proposed structure 1 of iriomoteolide-2a featured a late-stage convergent assembly of three components by a Suzuki–Miyaura coupling, an esterification, and a ring-closing metathesis. However, the NMR data of synthetic 1 were not identical to those of the natural product. Careful analysis of the NMR data of the authentic material and synthesis/NMR analysis of appropriately designed model compounds led to consideration of four possible stereoisomers 2 – 5 as candidates for the correct structure. Accordingly, total syntheses of 2 – 5 were achieved by taking advantage of the convergent strategy, and comparison of the NMR spectra of synthetic 2 – 5 with those of the natural product led to the conclusion that 5 shows the correct relative configuration of iriomoteolide-2a. The absolute configuration of this natural product was finally established through chiral HPLC analysis of synthetic 5 /ent- 5 with the authentic sample. The antiproliferative activity of the synthetic compounds was assessed against HeLa and A549 cells to show that, in contrast to expectation, synthetic 5 and ent- 5 were only marginally active in these cell lines. This work clearly underscores the vital role of total synthesis in the establishment of the structure and biological activity of natural products. 相似文献
414.
Haruhiko Ogasawara 《Computational Statistics》2012,27(4):661-683
Asymptotic approximations to the distributions of the ability estimator and its transformations in item response theory are derived beyond the usual normal one when associated item parameters are given as in tailored testing. For the approximations, the asymptotic cumulants of the estimators up to the fourth order with the higher-order asymptotic variances are obtained under possible model misspecification. For testing and interval estimation of abilities, the asymptotic cumulants of the pivots studentized in four ways are derived. Numerical examples with simulations including those for confidence intervals for abilities are given using the three-parameter logistic model. 相似文献
415.
Naofumi Naga Nobuo Tano Haruhiko Tomoda 《Journal of polymer science. Part A, Polymer chemistry》2012,50(20):4223-4229
Copolymerization of ethylene and diallyl‐bis(pyren‐1‐yl)‐silane (APyS) was investigated with zirconocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride ( 1 ) and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride ( 2 ), using methylaluminoxane as a cocatalyst. APyS was copolymerized via both 1,2‐insertion and cyclization insertion, and cyclization selectivity, ratio of cyclized insertion unit, of APyS in the copolymers obtained with Catalyst 1 was higher than that obtained with Catalyst 2 . Catalyst 2 showed a higher reactivity for APyS than Catalyst 1 . Photophysical properties of the copolymer were investigated by UV–vis and photoluminescence (PL) spectroscopy, and absorption and fluorescence derived from pyrenyl groups were detected in the copolymers. Chloroform solution of the copolymer showed emission derived from both monomer and eximer of pyrenyl units. Only the emission derived from eximer of pyrenyl units was observed in the cast film. The polarized PL spectrum of an oriented film showed anisotropy, and the polarization excitation parallel to the drawing direction showed high fluorescence intensity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
416.
Prof. Dr. Haruhiko Fuwa Takashi Muto Kumiko Sekine Prof. Dr. Makoto Sasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1848-1860
Didemnaketal B, a structurally complex spiroacetal that exhibits potent HIV‐1 protease inhibitory activity, was originally discovered by Faulkner and his colleagues from the ascidian Didemnum sp. collected at Palau. Its absolute configuration was proposed on the basis of degradation/derivatization experiments of the authentic sample. However, our total synthesis of the proposed structure of didemnaketal B questioned the stereochemical assignment made by Faulkner et al. Here we describe in detail our first total synthesis of the proposed structure 2 of didemnaketal B, which features 1) a convergent synthesis of the C7–C21 spiroacetal domain by means of a strategy exploiting Suzuki–Miyaura coupling, 2) an Evans syn‐aldol reaction and a vinylogous Mukaiyama aldol reaction for the assembly of the C1–C7 acyclic domain, and 3) a Nozaki–Hiyama–Kishi reaction for the construction of the C21–C28 side chain domain. The NMR spectroscopic discrepancies observed between synthetic 2 and the authentic sample as well as careful inspection of the Faulkner’s stereochemical assignment led us to postulate that the absolute configuration of the C10–C20 domain of 2 has been erroneously assigned. Accordingly, the total synthesis of the revised structure 65 was achieved to show that the NMR spectroscopic properties of synthetic 65 were in good agreement with those of the authentic sample. Furthermore, application of the phenylglycine methyl ester (PGME) method to the C7–C21 spiroacetal domain enabled us to establish the absolute configuration of didemnaketal B. 相似文献
417.
Yoshihiko Ooka Fumihiko Kanai Shinichiro Okabe Takuya Ueda Ryota Shimofusa Sadahisa Ogasawara Tetsuhiro Chiba Yasunori Sato Masaharu Yoshikawa Osamu Yokosuka 《Magnetic resonance imaging》2013
Purpose
To assess the value of gadoxetic acid-enhanced magnetic resonance imaging (MRI) for the pre-therapeutic detection of hepatocellular carcinoma (HCC) using receiver operating characteristic (ROC) analysis with the combination of computed tomography (CT) arterial portography and CT hepatic arteriography (CTAP/CTHA).Materials and Methods
A total of 54 consecutive patients with 87 nodular HCCs were retrospectively analyzed. All HCC nodules were confirmed pathologically. Three blinded readers independently reviewed 432 hepatic segments, including 78 segments with 87 HCCs. Each reader read two sets of images: Set 1, CTAP/CTHA; Set 2, gadoxetic acid-enhanced MRI including a gradient dual-echo sequence and diffusion-weighted imaging (DWI). The ROC method was used to analyze the results. The sensitivity, specificity, positive predictive value, negative predictive value and sensitivity according to tumor size were evaluated.Results
For each reader, the area under the curve was significantly higher for Set 2 than for Set 1. The mean area under the curve was also significantly greater for Set 2 than for Set 1 (area under the curve, 0.98 vs. 0.93; P = .0009). The sensitivity was significantly higher for Set 2 than for Set 1 for all three readers (P = .012, .013 and .039, respectively). The difference in the specificity, positive predictive values and negative predictive values of the two modalities for each reader was not significant (P > .05).Conclusion
Gadoxetic acid-enhanced MRI including a gradient dual-echo sequence and DWI is recommended for the pre-therapeutic evaluation of patients with HCC. 相似文献418.
M. G. Brik K. Ogasawara H. Ikeno I. Tanaka 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):345-355
Fully relativistic multielectron method based on the numerical solution of
the Dirac equation was used to calculate the L2,3-edge X-ray absorption
near edge structure (XANES) spectra of VO2, V2O3, and
V2O5 crystals. The key-points of the method are: i) usage of the
molecular orbitals (MO); ii) absence of any fitting parameters; iii) wide
area of application: to any ion in any symmetry; iv) possibility of
numerical analysis of the MO composition. The calculated spectra are in a
satisfactory agreement with experimental data available in the literature,
including the absolute values of the transitions energy, the shape of the
absorption bands, and polarization dependence. The assignment of the
absorption bands in terms of the electronic configurations was done. The
structure of the absorption bands is attributed to the splitting of the
vanadium p- and d-orbitals; the magnitude of this splitting is estimated from
the spectra. Covalency effects were considered for all hosts; it was shown
that the contribution of the oxygen wave functions increases with increasing
the vanadium oxidation state. Dependence of the relative positions of the
vanadium 3d and oxygen 2p levels and energies of the “ligand–metal” charge
transfer transitions on the vanadium oxidation state was analysed. 相似文献
419.
The surface chemical compositions of solid samples from environmental and geological sources can differ from the bulk or average compositions, because of changes caused by adsorption, dissolution, oxidation, etc. Accordingly, analytical information on surface layers is important for a better understanding of the environmental chemistry involving solid surfaces. The rapid development of surface-analytical techniques has enabled us to probe the surface chemistry of environmental and geological solid samples of complex composition. This article demonstrates some examples of important items of information that can be obtained by applying surface-analytical techniques, such as X-ray photoelectron spectroscopy and secondary ion mass spectrometry, to environmental and geological samples. The surface analysis of fly ashes, soils, sediments and weathered silicate minerals is reviewed. 相似文献
420.
Keisuke Sakurai Prof. Dr. Makoto Sasaki Prof. Dr. Haruhiko Fuwa 《Angewandte Chemie (International ed. in English)》2018,57(18):5143-5146
Total synthesis of (?)‐enigmazole A, a marine macrolide natural product with cytotoxic activity, has been accomplished. The tetrahydropyran moiety was constructed by means of a domino olefin cross‐metathesis/intramolecular oxa‐Michael addition of a δ‐hydroxy olefin. After coupling of advanced intermediates, the macrocycle was formed through gold‐catalyzed rearrangement of a propargylic benzoate, followed by ring‐closing metathesis of the resultant α,β‐unsaturated ketone. 相似文献