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71.
Kazuma Gotoh Takahiro Ueda Taro Eguchi Michihisa Miyahara Hiroyuki Ishida 《Journal of Physics and Chemistry of Solids》2008,69(1):147-152
The existence of micropores and the change of surface structure in pitch-based hard-carbon in xenon atmosphere were demonstrated using 129Xe NMR. For high-pressure (4.0 MPa) 129Xe NMR measurements, the hard-carbon samples in Xe gas showed three peaks at 27, 34 and 210 ppm. The last was attributed to the xenon in micropores (<1 nm) in hard-carbon particles. The NMR spectrum of a sample evacuated at 773 K and exposed to 0.1 MPa Xe gas at 773 K for 24 h showed two peaks at 29 and 128 ppm, which were attributed, respectively, to the xenon atoms adsorbed in the large pores (probably mesopores) and micropores of hard-carbon. With increasing annealing time in Xe gas at 773 K, both peaks shifted and merged into one peak at 50 ppm. The diffusion of adsorbed xenon atoms is very slow, probably because the transfer of molecules or atoms among micropores in hard-carbon does not occur readily. Many micropores are isolated from the outer surface. For that reason, xenon atoms are thought to be adsorbed only by micropores near the surface, which are easily accessible from the surrounding space. 相似文献
72.
A scalar finite-element method is used for investigating propagation characteristics of dual-mode highly elliptical-core fibers. The dispersion property, polarization modal birefringence, and spatial modal birefringence are calculated. To improve the accuracy of solutions, isoparametric curvilinear elements are introduced. The applicability of the scalar finite-element method for highly elliptical-core fibers is assessed by comparing the results obtained with the vector finite-element method. An approximate simple approach, in which an elliptical-core is replaced by an appropriate rectangular-core, is also examined 相似文献
73.
The 23Na NMR lineshapes are reported for the ionic mesophase and isotropic phase of the melts of sodium n-butyrate and sodium isovalerate. The powder pattern for the central transition typical for the second-order quadrupole effect observed in the mesophase melts is of particular interest. Some analogies to 23Na behavior in sodium β-alumina are pointed out. 相似文献
74.
Mitsuru Nakayama Hiroshi Yamaoka Shizuko Eguchi Terukiyo Hanafusa Shûichi Hayashi 《Journal of mass spectrometry : JMS》1977,12(6):416-417
For some homochromones, it was confirmed by labelling C-9 with deuterium that the CHO radical expelled from the molecular ion contains either the methine hydrogen or one of the methylene hydrogens of the cyclopropane ring. The origin of the CO group in the expelled CHO radical was also inferred, and a plausible mechanistic interpretation is presented. 相似文献
75.
The title compounds 1b and 1c were synthesized from manool. On treatment with either trifluoroacetic acid or formic acid 1b provided in nearly 100% yield 4a with a rearranged labdane skeleton. With sulfuric acid, however, 1b gave solely Δ8,9-isomer 5. Reduction of 4a with lithium diisobutylaluminum hydride afforded 4b. On treatment with sulfuric acid 4a reverted to 5. Rearrangement of the epoxide 6 with boron trifluoride- etherate led to a complex product mixture from which no pure substance was obtained. 相似文献
76.
Tatsuhiko Kanmera Sannamu Lee Haruhiko Aoyagi Nobuo Izumiya 《Tetrahedron letters》1979,20(46):4483-4486
A series of cyclo (Δaminoacyl-L-Ala) () (Δ=α,β-dehydro) were prepared from cyclo(Gly-L-Ala) and corresponding aldehyde, and hydrogenated with Pd black in MeOH. Chiral inductions producing cyclo (L-aminoacyl-L-Ala) () from were 96–99% in the case of L-Aba (2-aminobutanoic acid), L-Val, L-Leu, and L-App (2-amino-5-phenylpentanoic acid) as an L-aminoacyl moiety in . Pure L-Leu, L-Aba, and L-App were synthesized in preparative scale from corresponding through asymmetric hydrogenation and acid-hydrolysis. 相似文献
77.
Vapor—liquid equilibrium data for the ternary ethanol—2-butanone—benzene system and its constituent binary systems at 298.15 K are presented. The results are correlated with the Wilson, original and modified UNIQUAC equations and the UNIFAC group contribution method. 相似文献
78.
Scanning-tunneling spectroscopy at 5 K was used to investigate the electrostatic potential profile on the Si(111)-square root of 3 x square root of 3 Ag surface at subnanometer spatial resolution. The potential was measured from an energy-level shift of electronic states on the surface. The potential images obtained reveal that the potential drops around the steps and Ag adsorbates, upon which positive charges are presumably accumulated. The profiles of the reduced potentials are explained with the screening of potential due to the charges by two-dimensional electron gas (2DEG) existing on the surface. The Friedel oscillation, which results from the screening and has a period of the half Fermi wavelength of the 2DEG, was also observed in the potential images. 相似文献
79.
Observing the OT-for-OH exchange reaction between iron(II or III) hydroxide and tritiated water (HTO) leads to the following results: (1) isotope exchange as atomic group occurred between the OH group in each iron hydroxide (i.e., Fe(OH)2 or Fe(OH)3) and OT– resulted from the dissociation of HTO; (2) the ratio of the reactivity of the hydroxides is roughly [iron(III) hydroxide]: [iron(II) hydroxide]=1.21.0 and the result is related to a difference in electronegativity between Fe2+ and Fe3+. (In other words, if the reactivity depends on the number of the charge, the ratio should be 1.51.0). 相似文献
80.
2‐Deoxystreptamine (2DOS) is the unique chemically stable aminocyclitol scaffold of clinically important aminoglycoside antibiotics such as neomycin, kanamycin, and gentamicin, which are produced by Actinomycetes. The 2DOS core can be decorated with various deoxyaminosugars to make structurally diverse pseudo‐oligosaccharides. After the discovery of biosynthetic gene clusters for 2DOS‐containing aminoglycoside antibiotics, the function of each biosynthetic enzyme has been extensively elucidated. The common biosynthetic intermediates 2DOS, paromamine and ribostamycin are constructed by conserved enzymes encoded in the gene clusters. The biosynthetic intermediates are then converted to characteristic architectures by unique enzymes encoded in each biosynthetic gene cluster. In this Personal Account, we summarize both common biosynthetic pathways and the pathways used for structural diversification.