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851.
852.
H. P. Qi M. Berglund P. D. P. Taylor F. Hendrickx A. Verbruggen P. De Bièvre 《Fresenius' Journal of Analytical Chemistry》1998,361(8):767-773
Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016,
requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were
prepared by weighing and mixing of two well characterised, isotopically enriched, Li2CO3 compounds. The starting materials, 99.9981% enriched 6Li, and 99.9937% enriched 7Li, were purified by ion exchange, and the purified materials converted from LiOH to Li2CO3 by reaction with CO2. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li2CO3 carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(6Li)/n(7Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically
2 · 10–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.
Received: 6 November 1997 / Revised: 22 December 1997 / Accepted: 24 January 1998 相似文献
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An RP-HPLC method was developed for the first time to simultaneously determine five major compounds in Polygonum cuspidatum, namely resveratrol, polydatin, anthraglycoside B, emodin and physcion with UV detection at 306 nm. The column was an Agilent Zorbax SB-C18 (250 × 4.6 mm i.d., 5 μm). The separation was carried out with a gradient program. The mobile phase was acetonitrile–water (containing 0.1% formic acid) at a flow rate of 1.0 mL min?1. The standard curve was rectilinear in the range of 2.04–62.96 μg mL?1 (r = 0.9998) for resveratrol, 20.13–239.7 μg mL?1 (r = 0.9998) for polydatin, 7.19–71.92 μg mL?1 (r = 1.0000) for anthraglycoside B, 2.68–83.68 μg mL?1 (r = 0.9998) for emodin and 0.60–14.37 μg mL?1 (r = 0.9997) for physcion. The recoveries of the markers were 96.0, 106.5, 97.8, 97.9 and 98.1%, respectively. The relative standard deviation of intra-day and inter-day were less than 5.0 and 2.3%. This method was simple, accurate and reproducible. The developed method was successfully applied to analyze five compounds in P. cuspidatum of 20 commercial brands. 相似文献
857.
Yun‐Mei Bi Xu‐Bin Bi Qian‐Rong Zhao Yuan‐Teng Chen Jin‐Lun Xie 《Helvetica chimica acta》2004,87(11):2890-2895
Four novel dihydroisocoumarin (=3,4‐dihydro‐1H‐2‐benzopyran‐1‐one) glucosides were isolated from a culture broth of a strain of the fungus Cephalosporium sp. AL031. Their structures were elucidated as (2E,4E)‐5‐[(3S)‐5‐acetyl‐8‐(β‐D ‐glucopyranosyloxy)‐3,4‐dihydro‐6‐hydroxy‐1‐oxo‐1H‐2‐benzopyran‐3‐yl]penta‐2,4‐dienal ( 1 ), (2E,4E)‐5‐[(3S)‐5‐acetyl‐8‐(β‐D ‐glucopyranosyloxy)‐3,4‐dihydro‐6‐methoxy‐1‐oxo‐1H‐2‐benzopyran‐3‐yl]penta‐2,4‐dienal ( 2 ), (3S)‐8‐(β‐D ‐glucopyranosyloxy)‐3‐[(1E,3E,5E)‐hepta‐1,3,5‐trienyl]‐3,4‐dihydro‐6‐hydroxy‐5‐methyl‐1H‐2‐benzopyran‐1‐one ( 3 ), and (3S)‐8‐[(6‐O‐acetyl‐β‐D ‐glucopyranosyl)oxy]‐3‐[(1E,3E,5E)‐hepta‐1,3,5‐trienyl]‐3,4‐dihydro‐6‐methoxy‐5‐methyl‐1H‐2‐benzopyran‐1‐one ( 4 ) by spectroscopic methods, including 2D‐NMR techniques and chemical methods. 相似文献
858.
Ting-ting Wang Hao Jin Qing Li Wei-ming Cheng Qing-qing Hu Xiao-hui Chen Kai-shun Bi 《Chromatographia》2007,65(7-8):477-481
For the first time simple, rapid, and systematic methods have been established for preparative isolation and purification
of coumarin compounds in an important traditional Chinese Medicine, Radix Angelica dahurica, and for simultaneous determination of several of the compounds in the medicine. Bergapten, imperatorin, and cnidilin, three
of the biologically active coumarin compounds, were isolated from the chloroform-soluble fraction of the ethanol extract of
Radix Angelica dahurica. After further purification by open column ODS chromatography the purified components were simultaneously determined, with
two other coumarins (osthole and isoimperatorin), by reversed phase high-performance liquid chromatography (RP-HPLC) on a
C18 column, with methanol–water, 66:34 (v/v), as mobile phase at a flow rate of 0.8 mL min−1. The compounds were detected by UV absorption at 310 nm. Calibration plots for all the coumarins had correlation coefficients
close to unity. Limits of detection (S/N = 3) were <92 ng mL−1 and limits of quantification (S/N = 10) were <259 ng mL−1. Mean recovery of the coumarins was in the range 96.7–101.9% and the intra-day and inter-day precision, as relative standard
deviation, was <2.3 and <2.9%, respectively. This simple, sensitive, and reproducible method can be used for quality control
of Radix Angelica dahurica. 相似文献
859.
Our previous study has revealed that para-substituents have opposite electronic effects on the C-S bond lengths of thiophenols and thiophenolic radicals. Although a theoretical elucidation has been given, it has not been supported by theoretically calculated atomic charges. To give an alternative explanation, we calculated the C-S bond lengths, C-S bond electron densities, and Mulliken charges on the carbon and sulfur atoms for thiophenols, thiophenolic radicals, and thiophenolic radical cations by means of the B3LYP density functional theory method using the 6-31G(d, p) basis set. It was revealed that the C-S bond length is adequately defined in terms of C-S bond electron density. The distinct electronic effects on the C-S bond lengths of thiophenols, thiophenolic radicals and thiophenolic radical cations are well elucidated by the different electronic states (electron-deficient or-rich) of the phenyl ring and SH group. 相似文献
860.
Cong Ding Guo‐Hua Han Bi‐Zhou Lin Ling Bai 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(6):m256-m258
The crystal structure of the title compound, {(C3H12N2)[Mo3O10]·2H2O}n, is composed of [Mo3O10]2− anionic chains, propane‐1,3‐diammonium cations and solvent water molecules. The [Mo3O10]2− chain is constructed from edge‐sharing MoO6 octahedra. The protonated propane‐1,3‐diamine cations and solvent water molecules are located between the chains and are linked to the O atoms of the inorganic chains by hydrogen bonds. 相似文献