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31.
Derivatives of benzyl 2-[1-(benzyloxy)formamido]-2-deoxy-α-D-glucopyranoside with various protecting groups at C(3) (benzoyl, benzyl and N-phenylcarbamoyl) and C(6) (benzoyl, benzylsulfonyl, N-phenylcarbamoyl and tosyl) have been synthesized as starting materials for disaccharides. The C(4) and C(6) hydroxyl groups of the amino sugar were initially blocked by an acetal group. After introduction of the protecting group at C(3), the acetal group was removed by acid hydrolysis, and the C(6) hydroxyl group was selectively acylated or sulfonylated. The 3,6-di-O-benzoate has also been prepared by dimolar benzoylation of the amino sugar, whereby the 4,6-isomer was obtained as a by-product. 相似文献
32.
Correia I Costa Pessoa J Duarte MT Henriques RT Piedade MF Veiros LF Jakusch T Kiss T Dörnyei A Castro MM Geraldes CF Avecilla F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(9):2301-2317
The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds. 相似文献
33.
Emil W. Kiss 《Algebra Universalis》1992,29(4):455-476
First a problem of Ralph McKenzie is answered by proving that in a finitely directly representable variety every directly indecomposable algebra must be finite. Then we show that there is no local proof of the fundamental theorem of Abelian algebras nor of H. P. Gumm's permutability results. This part may also be of interest for those investigating non-modular Abelian algebras. Finally we provide a Gumm-type characterization of the situation when twonot necessarily comparable congruences centralize each other. In doing this, we introduce a four variable version of the difference term in every modular variety. A two-terms condition is also investigated.Dedicated to the memory of András HuhnPresented by R. W. Quackenbush. 相似文献
34.
T. Szitó J. G. Kiss GY. I. Garab L. A. Mustárdy Á. Faludi-Dániel 《Photochemistry and photobiology》1984,40(1):113-117
Abstract Orientation pattern of the Qy absorption and emission dipoles of chlorophyll a were studied in wild type Scenedesmus obliquus and in mutants deficient in chlorophyll b and carotenoids. Fluorescence polarization ratio at –140°C and linear dichroism at 25°C were measured in whole cells and thylakoids aligned in polyacrylamide gel. Unlike normal thylakoids, mutants displayed fluorescence polarization ratios significantly lower than 1.0 and showed a negative LD signal around 672 nm, indicating the tendency of the Qy dipoles to tilt out from the membrane plane. Such an orientation pattern can also be artificially induced by treating normal thylakoids with linolenic acid. 相似文献
35.
Tibor A. Kiss 《Fresenius' Journal of Analytical Chemistry》1965,208(5):334-337
Zusammenfassung Eine Studie über die Deblockierung von Metallindicatoren bei chelometrischen Titrationen in Gegenwart von organischen Lösungsmitteln wurde unternommen. Als Beispiele dienten die Bestimmungen von Kobalt, Eisen(III), Kupfer, Mckel und Aluminium in Gegenwart der in der Tabelle angegebenen organischen Lösungsmittel. Dazu versetzte man mit überschüssiger ÄDTA-Lösung und titrierte gegen Eriochromschwarz T als Indicator zurück. Eine Erklärung des Einflusses der organischen Lösungsmittel auf den Titrationsverlauf wurde versucht.
Mein ganz besonderer Dank gilt an dieser Stelle Herrn Prof. Dr. L.Erdey, nicht nur für sein Interesse an dieser Arbeit und seine fördernden Ratschläge, sondern auch für freundliche Aufnahme an seinem Institut.
Für wertvolle Hilfe danke ich den Herren Dr. Dipl.-Ing.Gy. Rády, Dr. Dipl.-Ing. F.Szabadváry und Dipl.-Ing. O.Weber. 相似文献
Summary The deblocking of metal indicators in chelometric titrations in the presence of organic solvents has been studied. As examples the titrations of cobalt, iron(III), copper, nickel and aluminium have been performed in the presence of the organic solvents mentioned in the table. The sample solution was mixed with an excess of EDTA solution and backtitrated with Eriochrome Black T as an indicator. It has been tried to elucidate the effect of the organic solvents on the titration.
Mein ganz besonderer Dank gilt an dieser Stelle Herrn Prof. Dr. L.Erdey, nicht nur für sein Interesse an dieser Arbeit und seine fördernden Ratschläge, sondern auch für freundliche Aufnahme an seinem Institut.
Für wertvolle Hilfe danke ich den Herren Dr. Dipl.-Ing.Gy. Rády, Dr. Dipl.-Ing. F.Szabadváry und Dipl.-Ing. O.Weber. 相似文献
36.
Krisztina Sebk‐Nagy Lszl Biczk Akimitsu Morimoto Tetsuya Shimada Haruo Inoue 《Photochemistry and photobiology》2004,80(1):119-126
Effects of solvent, pH and hydrogen bonding with N‐methylimidazole (MIm) on the photophysical properties of 1‐hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet‐excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pKa of 1HOF decreased from 10.06 to 5.0 on light absorption, and H3O+ quenched the singletexcited molecules in a practically diffusion‐controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen‐bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady‐state and the time‐resolved fluorescence results. 相似文献
37.
The aim of the present work was to provide arguments to the almost ‘hystorical’ problem of what β-tungsten is.
WO3was reduced in dry H2gas atmosphere in order to examine, whether β-tungsten formed in such a way contains oxygen as part of the lattice described
as WxO (e.g. W20O) or is a pure metallic phase of tungsten.
As a result of thermoanalytical measurements and of chemical analysis for oxygen, the assumption is supported that in the
600-800°C temperature range of metal formation not the WxO (β-W)→W(α-W) transformation but the β-W→α-W structural rearrangement of materials with identical chemical composition is
the most probable process.
The earlier opinion that the formation of the β-W structure requires the presence of oxygen atoms was not verified by our
results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
38.
In the last two decades protection against electrostatic hazards became a very important topic. The increase in the range of possible faults fast automated systems and complex fault analysis is required.The tools of artificial intelligence and expert systems have been applied successfully on this field and this paper aims to take a step further. While giving some insight to the currently used tools, another AI method, the 'support vector machines' are introduced in this paper. Besides a brief review on SVMs they are introduced to the SCOUT system, a novel approach to electrostatic hazard management. 相似文献
39.
Truong Son Pham Katalin Gönczi György Kardos Krisztina Süle László Hegedűs Mihály Kállay Miklós Kubinyi Pál Szabó Imre Petneházy László Tőke Zsuzsa Jászay 《Tetrahedron: Asymmetry》2013,24(24):1605-1614
Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation. 相似文献
40.
Dávid Illés Nagy Alajos Grün Krisztina Lévay Sándor Garadnay István Greiner 《合成通讯》2018,48(6):663-671
The reaction of 1H-imidazol-1-ylacetic acid and two equivalents of phosphorus trichloride/phosphorous acid at 75?°C in sulfolane, or in the presence of catalytic amounts of [bmim][BF4] afforded zoledronic acid in yields up to 75%. The joint use of the ionic liquid additive and sulfolane as the solvent was synergetic affording highly valuable zoledronic acid in a record yield of 93%. 相似文献