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排序方式: 共有476条查询结果,搜索用时 15 毫秒
341.
Priscila M. Lalli Bernardo A. Iglesias Henrique E. Toma Gilberto F. de Sa Romeu J. Daroda Juvenal C. Silva Filho Jan E. Szulejko Koiti Araki Marcos N. Eberlin 《Journal of mass spectrometry : JMS》2012,47(6):712-719
Travelling wave ion mobility mass spectrometry (TWIM‐MS) with post‐TWIM and pre‐TWIM collision‐induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM‐MS. CID performed after TWIM separation (post‐TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N‐protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH3, whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co‐existing protomers of two isomeric porphyrins were also separated and characterized via post‐TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO2 loss, but a CID‐resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
342.
Dr. Prabhpreet Singh Dr. Cécilia Ménard‐Moyon Dr. Alessia Battigelli Dr. Francesca Maria Toma Dr. Jesus Raya Dr. Jitendra Kumar Nagapradeep Nidamanuri Prof. Sandeep Verma Dr. Alberto Bianco 《化学:亚洲杂志》2013,8(7):1472-1481
Herein, we have developed a synthetic strategy for the covalent double functionalization of single‐walled carbon nanotubes (SWCNTs) with a combination of purine–pyrimidine and purine–purine nucleobase systems. The nucleobases were introduced on the sidewall of oxidized SWCNTs through 1,3‐dipolar cycloaddition and by amidation of the carboxylic acids located at the tips and defect sites of the nanotubes. The new nanohybrids were characterized by transmission electron microscopy, thermogravimetric analysis, FTIR and Raman spectroscopy, magic‐angle spinning NMR spectroscopy, and Kaiser test. The nucleobase/SWCNT conjugates can be envisaged for the modulation of the interactions with nucleic acids by means of base pairing, thereby opening new possibilities in the development of DNA/CNT nanobioconjugates. 相似文献
343.
M. Prokešová I. Prokeš M. Hudeček Š. Toma 《Monatshefte für Chemie / Chemical Monthly》1994,125(8-9):901-908
Summary The effect of 8 solvents on the rate as well as the yields of complexation of toluene with Cr(CO)6 has been studied. It has been found that the intensity of boiling has a profound effect on the rate of complexation in some cases (whenn-hexanol, cyclohexanone or diglyme is used as solvent). The rates of complexation are highest in these cases, but a considerable extent of decomposition results in lower yields. Butyl acetate, dibutyl ether and decalin have been found to be the most feasible solvents. Additionally, 27 different catalysts have been tested for the complexation of toluene in decalin solution, their effect being quantified by rate constants and the isolated yields of the reaction. The rate constants have been obtained from the rate of CO evolution and vary from 6.6·10–5 s–1 for formic acid to 6.5·10–4 s–1 for ethyl acetamidomalonate. Cycloalkanones proved to be more efficient catalysts than acyclic ketones with a close boiling point. Lactones are more efficient than esters, both cyclic and acyclic ketones, and diesters, all having a similar boiling point.
Lösungsmittel- und katalytische Effekte bei der Komplexierung von Toluol mit Cr(CO)6
Zusammenfassung Es wurde der Effekt von 8 Lösungsmitteln auf Komplexierungsgeschwindigkeit und Ausbeute der Komplexbildung von Toluol mit Cr(CO)6 untersucht. Dabei wurde festgestellt, daß die Intensität der Erhitzung beim Sieden in einigen Fällen einen wesentlichen Effekt auf die Komplexierungsgeschwindigkeit hat (bein-Hexanol, Cyclohexanon und Diglyme). Die Komplexierungsgeschwindigkeit ist in diesen Fällen die größte, die bereits beträchtlich einsetzende Zersetzung ergibt aber geringere Ausbeuten. Butylacetat, Dibutylether und Decalin erwiesen sich als die günstigsten Lösungsmittel. Außerdem wurden 27 verschiedene Katalysatoren für die Komplexierungsreaktion in Decalin als Lösungsmittel getestet und ihre Effizienz durch Geschwindigkeitskonstanten und isolierbare Ausbeute charakterisiert. Die Geschwindigkeitskonstanten wurden aus der Entwicklung von CO berechnet; sie liegen zwischen 6.5·10–5 s–1 für Ameisensäure bis zu 6.5·10–4 s–1 für Ethylacetamidomalonat. Cycloalkanone erwiesen sich als die besseren Katalysatoren gegenüber acyclischen Ketonen vergleichbaren Siedepunkts. Lactone sind effektvoller als Ester, cyclische sowohl als auch acyclische Ketone und Diester mit ähnlichen Siedepunkten.相似文献
344.
Lucio Toma Pierangela Ciuffreda Diego Colombo Fiamma Ronchetti Luigi Lay Luigi Panza 《Helvetica chimica acta》1994,77(3):668-678
The conformational space of the trisaccharide α-L -Fuc-(1→2)-β- D -Gal-(1→3)-β -D -GalNAc-1-OPr ( 2 ) and of its component disaccharide moieties α -L -Fuc-(1→2)-β -D -Gal-1-OMe ( 3 ) and β -D -Gal-(1→3)-β- D -GalNAc-1-OPr ( 4 ) was investigated with the aid of molecular-mechanics energy minimizations and molecular-dynamics simulations. These calculations suggested the occurrence of two conformations for each compound characterized by different ? and Ψ glycosidic angles. However, 1H-NMR investigation of D2O solutions of 2–4 indicated a sure preference for one of the two conformers with a contribution of the other one ranging from negligible to low. 相似文献
345.
Detection of Plasmon Coupling between Silver Nanowires Based on Hyperspectral Darkfield and SERS Imaging and Supported by DDA Theoretical Calculations
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Dr. Jonnatan J. Santos Evandro Ivanov Prof. Dr. Diego P. dos Santos Prof. Dr. Henrique E. Toma Prof. Dr. Paola Corio 《Chemphyschem》2016,17(4):463-467
We report the unprecedented observation of plasmon coupling between silver nanowires, showing how the surface‐enhanced Raman scattering depends upon this interaction and how the spectrum can be shaped by the hot spot. Such observations were accomplished by Raman spectroscopy mapping of silver nanowires modified with rhodamine. The local spectra on the hot spots were measured by darkfield hyperspectral microscopy, a powerful but uncommonly used technique that is capable of determining the location, structure, and spectra of the hot spots. The result obtained by the simulation of two parallel nanowires based on the discrete dipole approximation (DDA) method was in excellent agreement with the results obtained experimentally. 相似文献
346.
Justin Claude Kemmegne-Mbouguen Henrique Eisi Toma Koiti Araki Vera Regina Leopoldo Constantino Emmanuel Ngameni Lúcio Angnes 《Mikrochimica acta》2016,183(12):3243-3253
A new hybrid material has been prepared by intercalating the supramolecular cationic complex [μ-meso-tetra(4-pyridyl)porphyrinatecobalt(II) tetrakis[bis(bipyridine)(chlorido)ruthenium(II)], referred to as [CoTPyP{Ru(bipy)2Cl}4]4+ into a Cameroonian smectite clay (from Bagba hill, denoted Ba). The intercalated material (named CoTPyPRu(bipy)2–Ba) was used to modify glassy carbon electrodes (GCE), which were successfully applied to the simultaneous determination of acetaminophen (AC) and tyrosine (Tyr). The CoTPyPRu(bipy)2–Ba material was characterized by UV/Vis absorption spectroscopy, X-ray diffractometry and FT-IR spectroscopy. The intercalation of [CoTPyP{Ru(bipy)2Cl}4]4+ into the Ba interlayer endowed large surface area to the material. Electrodes modified with CoTPyPRu(bipy)2–Ba display good compatibility and stability, high selectivity and sensitivity, even with real samples. Working at pH?7.0, AC was oxidized at +0.42 V and Tyr at 0.72 V (vs Ag/AgCl). Linear calibration plots for AC and Tyr were obtained in the 1 to 50 μM and 1 to 24 μM range, with detection limits of 0.1 μM and 0.5 μM, respectively. The modified electrode was successfully applied to the determination of tyrosine in urine, and of acetaminophen in a pharmaceutical product. 相似文献
347.
Franci Bajd Anton Gradišek Tomaž Apih Igor Serša 《Magnetic resonance in chemistry : MRC》2016,54(10):827-834
Fast field cycling (FFC) and quantitative magnetization transfer (qMT) NMR methods are two powerful tools in NMR analysis of biological tissues. The qMT method is well established in biomedical NMR applications, while the FFC method is often used in investigations of molecular dynamics on which longitudinal NMR relaxation times of the investigated material critically depend. Despite their proven analytical potential, these two methods were rarely used in NMR studies of food, especially when combined together. In our study, we demonstrate the feasibility of a combined FFC/qMT‐NMR approach for the fast and nondestructive characterization of dry‐curing ham tissues differing by protein content. The characterization is based on quantifying the pure quadrupolar peak area (area under the quadrupolar contribution of dispersion curve obtained by FFC‐NMR) and the restricted magnetization pool size (obtained by qMT‐NMR). Both quantities correlate well with concentration of partially immobilized, nitrogen‐containing and proton magnetization exchanging muscle proteins. Therefore, these two quantities could serve as potential markers for dry‐curing process monitoring. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
348.
Mária Me?iarová Katarína Hubinská ?tefan Toma Burkhard Koch Albrecht Berkessel 《Monatshefte für Chemie / Chemical Monthly》2007,14(1):1181-1186
N-Toluensulfonyl-l-prolin amide was tested as catalyst in the enantioselective Michael addition of carbonyl compounds to (E)-β-nitrostyrene in nine ionic liquids under different reaction conditions. The reaction rates and enantioselectivities were
strongly dependent on the ionic liquids. Change of enantioselectivity was observed too and it is attributed to both the cation
and the anion of ionic liquid. The best yields (up to 98%) and enantioselectivity (70% ee) of product were obtained in a basic ionic liquid [bmim]BF4 at room temperature. 相似文献
349.
Synthesis of a Naphthalimide Functionalized Calix[4]arene; A Host Type Fluorophore for Inclusion Compounds in Organic Medium 总被引:1,自引:0,他引:1
Izilda?A.?Bagatin Alexandre?T.?Cruz Henrique?E.?Toma Mário?J.?Politi Grégoire?J.?-F.?DemetsEmail author 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(3-4):189-193
This article reports the synthesis and the properties of 5,11,17,23-tetra(t-butyl)-25,27-bis-(ethoxy-1,8-naphthalimide)-26,28-hidroxy-calix[4]arene and the formation of an inclusion compound in organic medium. This functionalized calix[4]arene was conceived as the association of a potential host species with a good fluorophore for optical sensoring purposes. Calix[4]-NI as we will call it, maintains its ‘cone-pinched’ configuration and exhibits typical naphthalimide fluorescence bands in non-polar solvents. Its ability to interact with guest species via hydrogen bonding in its endo-hydrophilic cavity to form inclusion compounds was verified with absorption and fluorescence measurements using N-ethanol-1,8-naphthalimide as guest species, which was projected to fit exactly the host cavity and to interact with its naphthalimide π electrons. For this reason, it was possible to follow the formation of the inclusion compound with electronic spectroscopy.in final form: 17 November 2004.This revised version was published online in July 2005 with a corrected issue number. 相似文献
350.
Satoshi Toma Koji Asaka Masaru Irita Yahachi Saito 《Surface and interface analysis : SIA》2019,51(1):131-135
Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm. 相似文献