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71.
Yamagiwa N Qin H Matsunaga S Shibasaki M 《Journal of the American Chemical Society》2005,127(38):13419-13427
The full details of a catalytic asymmetric aza-Michael reaction of methoxylamine promoted by rare earth-alkali metal heterobimetallic complexes are described, demonstrating the effectiveness of Lewis acid-Lewis acid cooperative catalysis. First, enones were used as substrates, and the 1,4-adducts were obtained in good yield (57-98%) and high ee (81-96%). Catalyst loading was successfully reduced to 0.3-3 mol % with enones. To broaden the substrate scope of the reaction to carboxylic acid derivatives, alpha,beta-unsaturated N-acylpyrroles were used as monodentate, carboxylic acid derivatives. With beta-alkyl-substituted N-acylpyrroles, the reaction proceeded smoothly and the products were obtained in high yield and good ee. Transformation of the 1,4-adducts from enones and alpha,beta-unsaturated N-acylpyrroles afforded corresponding chiral aziridines and beta-amino acids. Detailed mechanistic studies, including kinetics, NMR analysis, nonlinear effects, and rare earth metal effects, are also described. The Lewis acid-Lewis acid cooperative mechanism, including the substrate coordination mode, is discussed in detail. 相似文献
72.
A. Kakuta M. Kuramoto M. Ohno H. Kushida A. Tanioka K. Ishikawa 《Journal of polymer science. Part A, Polymer chemistry》1980,18(11):3229-3243
A freeze-dried cellulose acetate membrane fine structure was observed with an ultrathin sectioning electron microscope. The fine structure for the top surface in this membrane could be seen by lead citrate staining ultrathin sectioning. This network structure was observed among pores, which existed in porous substrate. The pore diameter in the top surface was about 50 Å, a value that agrees approximately with the value estimated by gas permeation. 相似文献
73.
We report the observations of a new type of changing process in the Burgers vector of dislocations by in situ transmission electron microscopy. Small interstitial-type perfect dislocation loops in bcc iron with diameters less than approximately 50 nm are transformed from a 1/2<111> loop to another 1/2<111> one or an energetically unfavorable <100> one; furthermore, a <100> loop is transformed to a 1/2<111> one. These transformations occurred on high-energy electron irradiation or simple heating without contact with external dislocations. The origin of these phenomena is discussed. 相似文献
74.
Noriyuki Inoue 《Mathematical Thinking and Learning》2013,15(1):36-67
Studies report that students often fail to consider familiar aspects of reality in solving mathematical word problems. This study explored how different features of mathematical problems influence the way that undergraduate students employ realistic considerations in mathematical problem solving. Incorporating familiar contents in the word problems was found to have only a limited impact. Instead, removing contextual constraints from the problem goal was found to motivate students to validate their problem solving in terms of their everyday experiences. Based on these findings, what determines the authenticity and relevance of a mathematical problem seems to be whether the problem allows students to freely reconstruct the problem situation by making use of their imagination and everyday experiences. In short, the basic principle seems to be “less is more”; that is, fewer constraints in problem goals could function to help students personally associate problem solving with their everyday experiences. 相似文献
75.
Lulu Zhang Naoki Kuramoto Akira Kurokawa Kenichi Fujii 《Surface and interface analysis : SIA》2019,51(4):400-407
As density is one of the basic physical properties of materials, an accurate density standard is absolutely essential. To determine density with high accuracy and precision, two 1-kg single-crystal silicon spheres (NMIJ-S4 and NMIJ-S5) are used as the primary standard at the National Metrology Institute of Japan. For the accurate measurement of the mass and volume of the silicon spheres, the effects of the surface layer must be carefully considered. In this work, a surface layer model of NMIJ-S4 and NMIJ-S5 was proposed and the thicknesses of each surface layer were determined using X-ray photoelectron spectroscopy. A detailed uncertainty budget is presented to aid use of the density standard. 相似文献
76.
Kosuke Takeda Kazushi Fujimoto Noriyuki Yoshii Susumu Okazaki 《Journal of computational chemistry》2019,40(31):2722-2729
Molecular dynamics calculations of a mixed micelle composed of sodium dodecyl sulfate (SDS) and octaethylene glycol monododecyl ether (C12E8) were performed for six compositions (SDS/C12E8 = 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100) to investigate the composition dependence of the mixed micelle structure and solubilization of cyclohexane, benzene, and phenol molecules by the micelle. The radial density distribution of the hydrophilic polyoxyethylene (POE) group of C12E8 as a function of distance from the micelle center is very sharp for micelles with high SDS content because the POE group captures a Na+ ion in solution and wraps around it to form a compact crown-ether-like complex. The hydrophobic dodecyl groups of SDS and C12E8 were separately distributed in the mixed micelle core. ΔG(r) evaluated for each solute showed that despite the structural changes of the micelle the binding strength of the solute molecules to the micelle did not change significantly. © 2019 Wiley Periodicals, Inc. 相似文献
77.
Mariko Kitajima Tomomi Yanagisawa Mari Tsukahara Yasuka Yamaguchi Noriyuki Kogure Ruri Kikura-Hanajiri Yukihiro Goda Osamu Iida Yasushi Sugimura Nobuo Kawahara Hiromitsu Takayama 《Tetrahedron》2018,74(4):441-452
Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions. 相似文献
78.
Heteroisotope and heteroatom tagging with [34S]-enriched methionine (Met), selenomethionine (SeMet), and telluromethionine (TeMet) was applied to in vitro translation.
Green fluorescent protein (GFP) and JNK stimulatory phosphatase-1 (JSP-1) genes were translated with wheat germ extract (WGE)
in the presence of Met derivatives. GFPs containing Met derivatives were subjected to HPLC coupled with treble detection,
i.e., a photodiode array detector, a fluorescence detector, and an inductively coupled plasma mass spectrometer (ICP-MS).
The activities of JSP-1-containing Met derivatives were also measured. GFP and JSP-1 containing [34S]-Met and SeMet showed comparable fluorescence intensities and enzyme activities to those containing naturally occurring
Met. TeMet was unstable and decomposed in WGE, whereas SeMet was stable throughout the experimental period. Thus, although
Te was the most sensitive to ICP-MS detection among S, Se, and Te, TeMet was less incorporated into the proteins than Met
and SeMet. Finally, the potential of heteroisotope and heteroatom tagging of desired proteins in in vitro translation followed
by ICP-MS detection was discussed.
Figure TeMet was less incorporated into GFP than Met and SeMet due to its instability in WGE 相似文献
79.
Kang JH Kuramoto M Tsuchiya A Toita R Asai D Sato YT Mori T Niidome T Katayama Y 《European journal of mass spectrometry (Chichester, England)》2008,14(4):261-265
To identify the correlation between the phosphorylation ratios by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-ToF MS) analysis and enzyme kinetics (K(m), V(max), and V(max)/K(m)) is important to understand whether MALDI-TOF MS can be applied for monitoring the properties of peptides that are substrates of protein kinases. The correlation between phosphorylation ratios and enzyme kinetics was examined using peptides for protein kinase C (PKC) and for 60 kDa phosphoprotein, encoded by the cellular sarcoma gene (c-Src). Phosphorylation ratios, analyzed by MALDI-ToF MS, showed higher correlation coefficient (r = > +0.7) for V(max)/K(m) compared with that (r = < -/+0.6) for K(m) or V(max). For ion modes, a higher correlation coefficient between phosphorylation ratios and V(max)/K(m) was identified in the positive mode (r = > +0.7) compared to that in the negative mode (r = < +0.5). These results suggest that MALDI-ToF MS is a useful tool to evaluate V(max)/K(m) of peptides for protein kinases. 相似文献
80.
Ohishi Y Kimura K Yamaguchi M Uchida N Kanayama T 《The Journal of chemical physics》2008,128(12):124304
We report the formation of icosahedral B(12)H(8) (+) through ion-molecule reactions of the decaborane ion [B(10)H(x)(+) (x=6-14)] with diborane (B(2)H(6)) molecules in an external quadrupole static attraction ion trap. The hydrogen content n of B(12)H(n)(+) is determined by the analysis of the mass spectrum. The result reveals that B(12)H(8)(+) is the main product. Ab initio calculations indicate that B(12)H(8)(+) preferentially forms an icosahedral structure rather than a quasiplanar structure. The energies of the formation reactions of B(12)H(14)(+) and B(12)H(12)(+) between B(10)H(x)(+) (x=6,8) ions, which are considered to be involved in the formation of B(12)H(n)(+), and a B(2)H(6) molecule are calculated. The calculations of the detachment pathway of H(2) molecules and H atoms from the product ions, B(12)H(14)(+) and B(12)H(12) (+), indicate that the intermediate state has a relatively low energy, enabling the detachment reaction to proceed owing to the sufficient reaction energy. This autodetachment of H(2) accounts for the experimental result that B(12)H(8)(+) is the most abundant product, even though it does not have the lowest energy among B(12)H(n)(+). 相似文献