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81.
Herein, we discuss the analyses and quantification of the different components in porphyrin mixtures, prepared from p-anisaldehyde, p-tolualdehyde, and 5-(4-bromophenyl)-dipyrromethane with acid catalysis, using NMR and HPLC. The advantages and disadvantages of these analytical methods are emphasized. Due to the similar size of a bromine atom and a methyl group it was possible to grow crystals suitable for X-ray crystallographic studies from a mixture of porphyrins, where the 4-position of the meso-phenyl rings was either substituted with methyl groups or bromine atoms. We also show that X-ray studies are inferior to NMR analysis for determining the components in a porphyrin mixture. 相似文献
82.
Lenice de Loureno Marques Ernesto Schulz Lang Herton Fenner Eduardo Ernesto Castellano 《无机化学与普通化学杂志》2005,631(4):745-748
[Hg(sulfamethoxazolato)2]·2DMSO ( 1 ) and [Cu2(CH3COO)4(sulfa‐methoxazole)2] ( 2 ) can be obtained by the reaction of sulfamethoxazole with mercury acetate or copper acetate in methanol. The structures of the two complexes were characterized by single crystal X—ray diffractometry. Compound 1 consists of sulfamethoxazolato ligands bridging the metal ions building an unidimensional chain. Two solvent dimethylsulfoxide molecules are involved via N‐H···O hydrogen bridges. The mercury atom shows a linear primary coordination arrangement formed by two trans deprotonated sulfonamidic nitrogen atoms. The overall coordination around the metal atom may be regarded as a strongly distorted octahedron when the interactions of mercury with four sulfonamidic oxygen atoms [bond distances of 2.761(4) Å—2.971(4) Å] are also considered to build an equatorial plane and the N1 and N1′ atoms [bond distance of 2.037(5) Å] occupy the apical positions. Compound 2 is a dinuclear complex in which the copper ions are bridged by four syn‐syn acetate ligands which are related by a symmetry centre located in the centre of the complex. Each copper atom presents a nearly octahedral coordination where the equatorial plane is formed by four oxygen atoms and an isoxazolic nitrogen atom and the second copper atom occupy the apical positions. 相似文献
83.
Grigorii G. Sivets Elena N. Kalinichenko Igor A. Mikhailopulo 《Helvetica chimica acta》2007,90(9):1818-1836
Convergent syntheses of the 9‐(3‐X‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranosyl)adenines 5 (X=N3) and 7 (X=NH2), as well as of their respective α‐anomers 6 and 8 , are described, using methyl 2‐azido‐5‐O‐benzoyl‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranoside ( 4 ) as glycosylating agent. Methyl 5‐O‐benzoyl‐2,3‐dideoxy‐2,3‐difluoro‐β‐D ‐ribofuranoside ( 12 ) was prepared starting from two precursors, and coupled with silylated N6‐benzoyladenine to afford, after deprotection, 2′,3′‐dideoxy‐2′,3′‐difluoroadenosine ( 13 ). Condensation of 1‐O‐acetyl‐3,5‐di‐O‐benzoyl‐2‐deoxy‐2‐fluoro‐β‐D ‐ribofuranose ( 14 ) with silylated N2‐palmitoylguanine gave, after chromatographic separation and deacylation, the N7‐β‐anomer 17 as the main product, along with 2′‐deoxy‐2′‐fluoroguanosine ( 15 ) and its N9‐α‐anomer 16 in a ratio of ca. 42 : 24 : 10. An in‐depth conformational analysis of a number of 2,3‐dideoxy‐2‐fluoro‐3‐X‐D ‐ribofuranosides (X=F, N3, NH2, H) as well as of purine and pyrimidine 2‐deoxy‐2‐fluoro‐D ‐ribofuranosyl nucleosides was performed using the PSEUROT (version 6.3) software in combination with NMR studies. 相似文献
84.
Analysis of selected ionic liquid cations by ion exchange chromatography and reversed-phase high performance liquid chromatography 总被引:1,自引:0,他引:1
The chromatographic behavior of 8 ionic liquids - 7 homologues of 1-alkyl-3-methylimidazolium and 4-methyl-N-butylpyridinium - has been investigated with a strong cation exchange adsorbent. In particular, the dependence of the retention properties of these solutes on mobile phase composition, pH, and buffer concentration was evaluated with the aim of optimizing and improving the selectivity and retention of solute separation. While using the SCX stationary phase, several interactions occurred with varying strengths, depending on the mobile phase composition. Cation exchange, nonspecific hydrophobic interactions, and adsorption chromatography behavior were observed. Reversed phase chromatography occurred at low concentrations of acetonitrile, electrostatic and adsorption interactions at higher organic modifier concentrations. Elevated buffer concentrations lowered the retention factors without affecting the selectivity of ionic liquids. Obtained results were further compared to the chromatographic behaviour of ionic liquids in the reversed phase system. All analyzed ionic liquids follow reversed-phase behavior while being separated. Much lower selectivity in the range of highly hydrophilic compounds is obtained. This suggests preferred use of ion chromatography for separation and analysis of compounds below 4 carbon atoms in the alkyl side chain. 相似文献
85.
A piezoelectric chemical sensor array was developed using four quartz crystals. Gas chromatographic stationary phases were used as sensing materials and the array was connected to an artificial neural network (ANN). The application of the ANN method proved to be particularly advantageous if the measured property (mass, concentration, etc.) should not be connected exactly to the signal of the transducers of the piezoelectric sensor. The optimum structure of neural network was determined by a trial and error method. Different structures were tried with several neurons in the hidden layer and the total error was calculated. The optimum values of primary weight factors, learning rate (η=0.15), momentum term (μ=0.9), and the sigmoid parameter (β=1) were determined. Finally, three hidden neurons and 900 training cycles were applied. After the teaching process the network was used for identification of taught analytes (acetone, benzene, chloroform, pentane). Mixtures of organic compounds were also analysed and the ANN method proved to be a reliable way of differentiating the sensing materials and identifying the volatile compounds. 相似文献
86.
Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable. 相似文献
87.
Simutaneous analysis of seven commonly used herbicides, 2,4-D methyl ester, 2,4-D methyl ester, 2,4,5-T methyl ester, silvex methyl ester, ramrod, CIPC and DEF, by gas-liquid chromatography with an electron capture detector was attempted. Two packed columns (which are generally used for the analysis of chlorinated pesticides) and two chemically bonded fused silica capillary columns were used for the analysis. When the packed columns were used, ramrod always interfered with the analysis of 2,4-D methyl ester and/or silvex methyl ester. Complete separation with reasonable analysis time can be achieved using one of the chemically bonded fused silica capillary columns. 相似文献
88.
89.
Summary A preliminary study has been carried out to evaluate a new adsorbent, Thermosorb, for trace level organic contaminants. For this purpose, a comparison was made with a well-characterized adsorbent, Tenax GC, using a prepared aqueous solution of trace organic components. In addition, a comparison was made of chromatograms of air contaminants obtained using both of these adsorbents, under equivalent conditions. The results clearly indicated the potential of this thermally stable, inorganic adsorbent for many trace organic substances of environmental interest. 相似文献
90.
L. I. Andersson M. Abdel-Rehim L. Nicklasson L. Schweitz S. Nilsson 《Chromatographia》2002,56(1):S65-S68
Summary
Solidago canadensis L., Canadian goldenrod (Asteraceae) has been used in European phytotheraphy for centuries as a component of urological and
antiphlogistical remedies. High-performance liquid chromatography (HPLC) coupled with diode-array detection (DAD) and online
mass spectrometry (MS) has been used for the separation and quantification of phenolics (chlorogenic acid, caffeic acid, kaempferol-3-O-α-L-rutinoside
(nicotiflorin), quercetin-3-O-β-D-rutinoside (rutin), quercetin-3-O-β-D-galactoside (hyperoside), quercetin-3-O-β-D-glucoside
(isoquercitrin), quercetin-3-O-β-D-rhamnoside (quercitrin), kaempferol-3-O-α-L-rhamnoside (afzelin) and quercetin from Solidaginis
herba. Extracts have been obtained using different technologies. Three aqueous and three alcoholic extracts were studied separately.
Reversedphase high-performance liquid chromatography separation of polyphenols on octadecyl sorbent Hypersil was performed,
using acetonitrile: acetic acid 2.5 v/v % as eluent in gradient elution. Our results confirm previous reports concerning the
presence of several flavonoids. Quantification of the main quercetin glycosides in pharmaceuticals is also reported.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献