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排序方式: 共有792条查询结果,搜索用时 15 毫秒
721.
Yoshinori Niwa Shigeki Kouno Wakako Sayama Nobukatsu Nemoto 《Journal of polymer science. Part A, Polymer chemistry》2008,46(2):692-701
Novel poly(tetramethyl‐1,3‐silphenylenesiloxane) derivative with phenol moiety in the main chain, that is, poly(tetramethyl‐5‐hydroxy‐1,3‐silphenylenesiloxane) ( P1 ), was synthesized and the thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). P1 was obtained via deprotective hydrogenation of poly(tetramethyl‐5‐benzyloxy‐1,3‐silphenylenesiloxane) ( Pre‐P1 ) catalyzed by 10% palladium on charcoal as well as via direct polycondensation of 3,5‐bis(dimethylhydroxysilyl)phenol ( M2 ). Pre‐P1 was obtained by polycondensation of 1,3‐bis(dimethylhydroxysilyl)‐5‐benzyloxybenzene ( M1 ), catalyzed by 1,1,3,3‐tetramethylguanidinium 2‐ethylhexoate. M1 was prepared by the Grignard reaction using chlorodimethylsilane and 1,3‐dibromo‐5‐benzyloxybenzene followed by the hydrolysis catalyzed by 5% palladium on charcoal. M2 was prepared by deprotective hydrogenation of M1 catalyzed by 10% palladium on charcoal. The obtained P1 was soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and so forth as well as in highly polar solvents as ethanol and methanol in which poly(tetramethyl‐1,3‐silphenylenesiloxane) is insoluble. The glass transition temperature (Tg) of P1 was determined to be 40 °C from DSC, which was much higher than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (?52 °C), indicating that the intermolecular and/or intramolecular hydrogen bondings based on hydroxyl groups restricted the mobility of the main chain. The temperature at 5% weight loss (Td5) of P1 (393 °C) determined by TG was lower than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (ca. 500 °C), indicating that the phenol moieties decline the thermal stability; however, the obtained P1 would promise to be a new reactive‐polymer with phenolic–hydroxyl moieties to develop new functional materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 692–701, 2008 相似文献
722.
Shigeki Kudo Takashi Mitsui Hideaki Sakai Hiroyuki Murata Masahiro Kanazawa 《Optical Review》2009,16(2):66-73
A new measuring technique that can measure retardation and can output magnitude and direction of plane stress in each glass
of a panel composed of double transparent pieces of glass has been developed using reflective confocal optics. The linear
polarized probe beam is incident to the glass and we can detect a reflected beam converted to orthogonal polarization caused
by the photoelastic phenomenon. Using the high extinction ratio (106) beam-displacing prism as a polarization discriminator, we can measure the photoelasticity by rotating the polarization of
the probe beam from 0 to π rad without disturbing the optical axis. This system has the ability to measure retardation. The lowest one is estimated
as nearly 0.066 nm for 700 μm thickness glass which corresponds to 0.03 MPa stress from our calibration line. 相似文献
723.
724.
Tomohisa Temma Shigeki Habaue 《Journal of polymer science. Part A, Polymer chemistry》2005,43(24):6287-6294
The asymmetric oxidative coupling polymerization of methyl 6,6′‐dihydroxy‐2,2′‐binaphthalene‐7‐carboxylate with the copper‐diamine catalysts under an O2 atmosphere was carried out. As is the case with the CuCl‐2,2′‐(S)‐isopropylidenbis(4‐phenyl‐2‐oxazoline) [(S)IPhO] catalyst, a polymer with a high cross‐coupling selectivity of 96% was obtained in 71% yield, whose THF‐soluble part had a number‐average molecular weight of 4.5 × 103. To estimate the enantioselectivity with respect to the cross‐coupling linkage in the obtained polymer, the model asymmetric oxidative cross‐coupling reaction with CuCl‐(S)IPhO was also conducted, and the products showed a 94% cross‐coupling selectivity and enantioselectivity of 31% ee (S). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6287–6294, 2005 相似文献
725.
We study quantum dynamics of the multichannel reactions of H(2)CO including the molecular and radical dissociation channels as well as the isomerization ones, H(2)CO-->trans-HCOH and trans-HCOH-->cis-HCOH. For this purpose, the previously developed potential energy function [T. Yonehara and S. Kato, J. Chem. Phys. 117, 11131 (2002)] is refined to give accurate transition state energies and to describe the radical dissociation channel. The cumulative reaction probabilities for the molecular dissociation and two isomerization channels are calculated by using the full Watson Hamiltonian. We also carry out wave packet dynamics calculations starting from the transition state region for the molecular dissociation. A contracted basis set for the angular coordinates is constructed to reduce the size of dynamics calculations. The intramolecular vibrational relaxation dynamics is found to be fast and almost complete within 300 fs. Using the energy filtered wave functions, the time propagation of HCOH population is obtained in the energy range from 81 to 94 kcal/mol. The branching ratio of the radical product is estimated by calculating the time dependent reactive fluxes to the molecular and radical dissociation products. 相似文献
726.
Kentarou Imamura Masao Takahashi Shigeki Imai Hikaru Kobayashi 《Surface science》2009,603(7):968-5756
A relatively thick (i.e., ∼9 nm) SiO2 layer can be formed by oxidation of Si with nitric acid (HNO3) vapor below 500 °C. In spite of the low temperature formation, the leakage current density flowing through the SiO2 layer is considerably low, and it follows the Fowler-Nordheim mechanism. From the Fowler-Nordheim plots, the conduction band offset energy at the SiO2/Si interface is determined to be 2.57 and 2.21 eV for HNO3 vapor oxidation at 500 and 350 °C, respectively. From X-ray photoelectron spectroscopy measurements, the valence band offset energy is estimated to be 4.80 and 4.48 eV, respectively, for 500 and 350 °C oxidation. The band-gap energy of the SiO2 layer formed at 500 °C (8.39 eV) is 0.68 eV larger than that formed at 350 °C. The higher band-gap energy for 500 °C oxidation is mainly attributable to the higher atomic density of the SiO2 layer of 2.46 × 1022/cm3. Another reason may be the absence of SiO2 trap-states. 相似文献
727.
Shigeki Yoshida Koji Suizu Yoichi Nakagomi Kodo Kawase 《Journal of Molecular Spectroscopy》2009,256(1):146-198
Metallic meshes work as band-pass filters in the terahertz (THz) region, with their transmission spectra acutely affected by the refractive index of the material inside and above the metallic-mesh openings. We used a metallic mesh for high-sensitivity observations by focusing on the “dip,” that is, a sudden change in transmittance that only appeared when the THz wave was obliquely incident onto the metallic mesh. Here we consider the interference between apertures of the metallic mesh in the diagonal direction and explain the dip using finite-difference time-domain (FDTD) electromagnetic simulations. 相似文献
728.
Motivated by the anomalous positron flux recently reported by the PAMELA Collaboration, we study the cosmic-ray positron produced by the pair annihilation and the decay of superparticle dark matter. We calculate the cosmic-ray positron flux and discuss implications of the PAMELA data. We show that the positron excess observed by the PAMELA can be explained with some of the superparticle dark matter. 相似文献
729.
Multiple Zeta Values at Non-Positive Integers 总被引:2,自引:0,他引:2
Values of Euler-Zagier's multiple zeta function at non-positive integers are studied, especially at (0,0,...,–n) and (–n,0,...,0). Further we prove a symmetric formula among values at non-positive integers. 相似文献
730.
Koji Takizawa Tomoyuki Sekino Shunta Sato Tatsuhiko Yoshino Masahiro Kojima Shigeki Matsunaga 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9297-9301
Co‐catalyzed allylic substitution reactions have received little attention, arguably because of the lack of any known advantage of Co catalysis over either Rh or Ir catalysis. Described here is a general and regioselective Co‐catalyzed allylic alkylation using an in situ catalyst activation by organophotoredox catalysis. This noble‐metal‐free catalytic system exhibits unprecedentedly high reactivities and regioselectivities for the allylation with an allyl sulfone, for the first time, representing the unique synthetic utility of the Co‐catalyzed method compared to the related Rh‐ and Ir‐catalyzed reactions. 相似文献