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441.
The reduction of diphenyl ditelluride by the Sm/CrCl3(cat.) system led to a telluride anion.This species reacted with acid chlorides,alkyl halides,and α,β-unsaturated enoates or α,β-unsaturated ene nitriles to afford telluroesters and unsymmetrical phenyltellurides,respectively,in moderate to good yields under mild and neutral conditions. 相似文献
442.
David A. Babb Richard A. Bartsch James J. Collier Dhimant H. Desai Sadik Elshania Mi‐Ja Goo Johnny L. Hallman Gwi Suk Heo Xiaowu Huang Vincent J. Huber Hong‐Sik Hwang Russell J. Johnson Yung Liu Michael J. Pugia Qiang Zhao 《Journal of heterocyclic chemistry》2004,41(5):659-675
Structurally related dibenzo‐16‐crown‐5 lariat ethers with pendant ester and ether groups are prepared. Structural variations within the series of alkyl lariat ether esters include changes in the O‐alkyl group, attachment site and nature of the lipophilic group, and length of the spacer, which connects the ester group to the polyether framework. Also synthesized are bis(crown ether) diesters with two dibenzo‐16‐crown‐5 or two dicyclohexano‐16‐crown‐5 units and two ester groups connected to each other by a linker of varying length. Synthetic strategies for the preparation of these lariat ethers with pendant ester‐ and ether‐containing side arms are described. 相似文献
443.
The dissociative photoionization of molecular‐beam cooled CH2CO in a region of ?10–20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH2CO+ and of observed fragment ions CH2+, CHCO+, HCO+, C2O+, CO+, and C2H2+ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH2CO are computed with the Gaussian‐3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C‐H bonds to form CH2+ + CO and CHCO+ + H, respectively; at greater energies, dissociation involving H migration takes place. 相似文献
444.
Choong S. Kim Kee J. Lee Hong S. Kim Yung B. Chae 《Journal of heterocyclic chemistry》1983,20(5):1417-1418
4(5)-Hydroxymethylimidazoles were prepared by hydroxymethylation and decarboxylation of imidazole-4(5)-carboxylic acid esters. The reaction was simply carried out with aqueous formaldehyde solution in the presence of base. 相似文献
445.
446.
In order to explore whether hydrophobicity or charge at the 71th residue is important for chaperone‐like activity, wild type (wt) and two mutant αA‐crystallins, F71W and F71R, with an extra 11 residues including 6 histidines tagged at the N‐terminal were prepared. Chaperone‐like activity toward dithiotreitol (DTT) induced insulin aggregation showed the 11 extra residues had little effect. The activity for F71W was as active as the wild type, while F71R was much less active. For the wild type and F71W, the activity increased with the increase of molar quantity; surprisingly, for F71R it caused a drastic decline. ANS fluorescence measurements showed F71R had the highest surface hydrophobicity, suggesting positive charge at this site caused the conformational alteration leading to the increase of hydrophobicity and this hydrophobicity resulted in the formation of high molecular weight aggregates (> 2000 kDa) observed from the thermal stability study. The thermal stability study revealed F71W was the most thermally stable crystallin. Chaperone‐like activity studies at various temperatures suggested the monomer and oligomer, 650 kDa, were responsible for chaperone function and surface hydrophobicity was not the prerequisite for activity. Near‐UV CD studies showed β‐sheet was the major secondary structure for all three crystallins and F71R had a higher percentage of random coil. 相似文献
447.
RuShan Chen Edward K. N. Yung Ke Wu DaoXiang Wang 《International Journal of Infrared and Millimeter Waves》1999,20(6):1143-1153
In this paper, a novel numerical technique to solve electromagnetic boundary value problem is described. This finite element based method of lines is developed by combining finite element method and the method of lines, so that it not only has high flexibility to treat geometrically and compositionally complex problems but also maintains high accuracy of semi-analytical technique. The geometry discretization, element mapping, element trial function and standard ordinary differential equation construction are discussed in details. Our numerical result demonstrates that this method can successfully solve the complex problems with fewer mesh lines when compared with conventional method of lines. 相似文献
448.
A simplified predictive model for high-fluence ultra-short pulsed laser ablation of semiconductors and dielectrics 总被引:1,自引:0,他引:1
Ultra-short pulsed laser ablation is a very complicated process and a predictive model is very desirable for process design and optimization in practical applications. However, the molecular dynamics or hydrodynamic models, although they are powerful and necessary tools for the study of the fundamental physics, are time-consuming and difficult to apply for practical applications. In this paper, a predictive, simplified and easy to apply model has been developed for high-fluence ultra-short laser ablation of semiconductors and dielectrics. Unlike many other simplified models, this model does not involve any free adjustable variables. The model predictions agree well with experimental measurements for femtosecond laser ablation, while the model is not very applicable for pulse durations more than ∼10 ps. 相似文献
449.
A numerical method is employed to examine the flow in symmetrical, two‐dimensional branches of Y shape and Tee shape. The methodology is based on a pressure‐correction procedure within the frame of unstructured grids. Specified pressures are imposed at the outlets of the two branches. The area ratio of the branch is allowed to vary in the range of 2–3. Separation of the flow in the bifurcating region is inevitable. With equal outlet pressures, symmetrical flow patterns prevail except for the Y type branch under the conditions of high Reynolds numbers and large area ratios. This implies that the Y‐branch flow is more sensitive to small disturbances. It is shown that with a slightly higher pressure imposed on one of the two branches the structure of the recirculating flow for the Y type is greatly affected and the flow rate is reduced dramatically in the high‐pressure branch channel. In contrast, the influence on the Tee type branch is much lower since the flow behaves like a jet impinging on a confined duct. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
450.
Fine silica-like fines with 11 nm width are successfully fabricated using x-ray Fresnel diffraction exposure. X-rays pass a mask of 175-nm-wide lines and 125-nm-wide spaces and form sharp peaks on a wafer coated with a layer of hydrogen silsesquioxane resist (HSQ). By precisely controlling the mask-wafer gap at 10μm using the laser interferogram method, the fine structures are defined on HSQ. Experimental images are reproduced by a simulation using the one-dimensional beam propagation method. This lithographic technique presents a novel and convenient way to fabricate fine silica-like structures and devices in nano-optical and nanoelectronic applications. 相似文献