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991.
Optically Active 3-Amino-2H-azirines as Synthons for Enantiomerically Pure αα-Disubstituted α-Amino Acids: Synthesis of the α-Methylphenylalanine Synthons and Some Model Peptides The synthesis of a novel 2-benzyl-2-methyl-3-amino-2H-azirine derivative with a chiral amino group is described. Chromatographic separation of the diastereoisomer mixture yielded the pure diastereoisomers 9a and 9b (Scheme 4) which are the D - and L -2-methylphenylalanine ((α-Me)Phe) synthons, respectively. The reaction of 9a and 9b with thiobenzoic acid and with Z-leucine yielded the monothiodiamides 10a and 10b (Scheme 5) and the dipeptide derivatives 11a and 11b (Scheme 6), respectively. Methanolysis of 11b yielded 12b . The absolute configuration of 10a was established by X-ray crystallography. The absolute configuration of (α-Me)Phe in 12b has been deduced from the known configuration of L -leucine. 相似文献
992.
Maria Garrlda Victoria Garcia Matthias Kretschmer Paul S. Pregosin Heinz Ruegger 《Helvetica chimica acta》1981,64(4):1150-1157
The products of the reaction of [RhCl (NBD)]2 (NBD = norbornadiene), with four equivalents tertiary phosphine and two equivalents of tin (II) bromide have been studied by 119Sn- and 31P-NMR. spectroscopy. The solution data suggest that halogen scrambling occurs during the preparation and results in a mixture of complexes containing SnBr3, SnClBr2, and SnCl2Br and SnCl3 ligands, and this is confirmed by independent synthesis of the SnCl3 and SnBr3 complexes. The metalmetal coupling constants, 1J (119Sn, 103Rh), vary from 452 to 580 Hz and are linearly related to: (a) δ(119Sn) in the complexes [Rh (SnClnBr(3-n))NBD (PEtPh2)2] and (b) the sum of the Pauling electronegativities for the halogens on tin. 相似文献
993.
Bernd?Lackner Klaus?Bretterbauer Heinz?FalkEmail author 《Monatshefte für Chemie / Chemical Monthly》2005,136(9):1629-1639
Summary. Emodic amine could be synthesized in a five-step approach in excellent overall yield by following a modified Curtius rearrangement strategy, starting from the naturally occurring emodin. This unique emodin derived 6-amino substituted polyhydroxylated anthraquinone may serve as a promising synthon for a new class of amino functionalized photodynamically active hypericin derivatives. In addition, the partially O-methyl protected 6-amino- and 6-carboxy-anthraquinones could be synthesized in high yields via selective O-methyl ether cleavage from the corresponding tri-O-methyl derivatives. 相似文献
994.
Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L2 (L=Et2PS2?; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L3 (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal-metal interaction is observed even under electron impact. 相似文献
995.
Günther Kraft und Heinz Dosch 《Fresenius' Journal of Analytical Chemistry》1972,260(4):261-267
Zusammenfassung Wichtige Einflußgrößen für voltametrische Indikationen sind neben der Titrationsgeschwindigkeit die Polarisationsstromdichte, die Menge an zu titrierender Substanz und die Titranskonzentration. Als optimale Bedingungen werden ermittelt: 0,001 M Maßlösungen bei Polarisationsströmen von 1 A für Drahtelektroden von je 10 mm2 Oberfläche und Arbeiten in Titrationsvolumina von 30–50 ml. Wird in Volumina von etwa 2 ml titriert, können die Polarisationsströme etwa um den Faktor 5 höher sein. Der Titrationsverbrauch soll zwischen etwa 3 und 7 ml liegen, die Titrationsgeschwindigkeit kleiner als 0,2 ml/min sein. Für Titrationen von 250–500 g Zn werden so Genauigkeiten von 0,6 g erreicht.Die Optimierung der Versuchsbedingungen hat ferner Wege für Titrationen von wenigen Nanogramm Metall eröffnet und dazu geführt, daß voltametrische und amperometrische Indikationskurven mit voll vergleichbarem Habitus und korrespondierender Absolutlage erhalten werden.
Vortrag anläßlich der Analytikertagung in Düsseldorf am 3. und 4. 6. 1971. 相似文献
Optimization of experimental parameters for the voltametric indication of complexometric titrations
Essential factors of influence for voltametric indications are the titration rate, the polarization current density, the amount of substance to be titrated and the concentration of the titrating solution. Optimum conditions are: 0.001 M volumetric solutions, polarization currents of 1 A, wire electrodes of 10 sq. mm surface each and titration volumes of 30 to 50 ml. If the titration is performed in about 2 ml, the polarization currents may be about 5-fold higher. The consumption of titrating solution should be within the range of 3 to 7 ml and the titration rate inferior to 0.2 ml/min. In this way, accuracies of 0.6 g are reached for titrations of 250–500 g Zn.The optimization of the conditions has furthermore opened possibilities for titrations of a few ng of metal only and permits to obtain voltametric and amperometric indication curves, whose shapes and positions in the mV and A scale, respectively, are fully comparable.
Vortrag anläßlich der Analytikertagung in Düsseldorf am 3. und 4. 6. 1971. 相似文献
996.
The solubility constant of ZnCO3, smithsonite, in aqueous NaClO4 solutions hasbeen investigated as a function of temperature (288.15 T/K 338.15) atconstant ionic strength I = 1.00 mol-kg–1. In addition, the solubility of zinccarbonate has been determined at 2.00 and 3.00 mol-kg–1 NaClO4 (298.15 K).The solubility measurements have been evaluated by applying the Daviesapproximation, the specific ion-interaction theory, and the Pitzer model, respectively.The thermodynamic interpretation leads to an internally consistent set ofthermodynamic data for ZnCO3 (298.15 K): solubility constant log*K
p50
0
= 7.25 ± 0.10,standard Gibbs energy of formation i G (ZnCO3) = (–777.3±0.6)kJ-mol–1, standard enthalphy of formation f H (ZnCO3)= (–820.2±3.0) kJ-mol–1,and standard entropy S (ZnCO3) = (77±10)J-mol–1 K.–1. Furthermore, the DSCcurve for the thermal decarbonation of zinc carbonate has been recorded in orderto obtain the enthalpy of formation fH (ZnCO3) =(–820.2±2.0) from theheat of decomposition. Finally, our results are also consistent within theexperimental error limits with a recent determination of the standard entropy ofsmithsonite, leading to a recommended set of thermodynamic properties of ZnCO3:
相似文献
997.
Bester K Beernaert H Bernreuther A Harbeck S Konieczka P Linsinger TP Mertens I Schimmel H Sejerøe-Olsen B Pauwels J De Poorter G 《Analytical and bioanalytical chemistry》2002,374(2):305-313
During the Belgian PCB crisis (1999/2000) the quality of the data from the PCB monitoring were studied with a proficiency testing experiment. Pork fat that was spiked at the Institute for Reference Materials and Measurements (EC-JRC-IRMM) was sent out as unknown to all laboratories that participated in the monitoring. In parallel, the material was certified on the basis of the results of several leading PCB laboratories throughout Europe that did not participate in the monitoring. During the first round 15 to 25% deviation was experienced, while in the end of this multistep intercalibration procedure the average deviation for the respective PCBs was 10.9% (PCB 28), 13.1% (PCB 52), 10.1% (PCB 101), 10.7% (PCB 118), 10.7% (PCB 138), 9.1% (PCB 153), 8.1% (PCB 180) and 8.2% for the sum of the 7 PCBs. The concentrations measured for the higher volatile PCB 28 had a tendency to show lower levels, while for PCB 180 this was less pronounced. On the other hand, PCB 153 showed results rather to the higher side. During this exercise the material was also tested for stability by one of the certifying laboratories. 相似文献
998.
Franz L. Dickert Michael Vonend Heinz Kimmel Gert Mages 《Fresenius' Journal of Analytical Chemistry》1989,333(6):615-618
Summary The formation of highly coloured trityl ions from substituted phthalides can be utilized for the detection of solvent vapours in the air down to nearly ten ppm. These optochemical sensor materials were optimized with respect to their sensitivity, stability, linearity of the response and exclusion of the humidity influence. For this purpose the 4,4,4-substituents at the aromatic rings of the dyes must yield an appropriate carbenium ion stability. Thus even small amounts of absorbed solvent vapours lead to the reduction of the dye concentration in the sensor layers. The largest sensitivity can be achieved by applying dyes with two — N(CH3)2 substituents or, instead of one dimethylamino group, the — OCH3 group at the aryl rings. Further improvements to reduce the sensor response to moisture were possible by introducing into the phthalides large aromatic ring systems with a hydrophobic behaviour such as indolyl.
Dedicated to Prof. Dr. Hans Hofmann on the occasion of his 60th birthday 相似文献
Farbstoffe vom Triphenylmethan-Typus als Sensormaterial für LösungsmitteldÄmpfe
Dedicated to Prof. Dr. Hans Hofmann on the occasion of his 60th birthday 相似文献
999.
Heinz Falk Gerhard Kapl Walter Medinger Norbert Müller 《Monatshefte für Chemie / Chemical Monthly》1987,118(8-9):973-985
A strategy for the synthesis of bilatrienes-abc bridged between rings A and C has been developed and tested in case of a bibenzylethane bridging fragment. This strategy was then applied to the synthesis of a 2,3-dihydrobilatriene-abc bridged by a (S)-lysine moiety from ring A to ring C (positions 3 and 12) by means of peptide bonds between the two amino groups of lysine and the acetic and propionic acid side chains of the chromophoric unit. The two diastereomers resulting from the two chiral centers of the lysine residue and at position 3 of the chromophore were separated by chromatography. 相似文献
1000.
E. Heinz 《Fresenius' Journal of Analytical Chemistry》1965,212(1):99-109
Zusammenfassung Nach kurzer Charakterisierung der in den Körperflüssigkeiten gelösten starken Elektrolyte und ihrer biologischen Bedeutung wird die Frage erörtert, wie die spezifischen Wirkungen dieser Ionen auf biologische Systeme zu erklären sind. Es ist anzunehmen, daß derartige Wirkungen über nicht-kovalente Bindungen der betreffenden Ionen an spezifische Gruppen von Enzymen oder anderen Wirkstoffen zustandekommen, obgleich über solche Bindungen im biologischen Milieu noch wenig bekannt ist. Diese Bindungsreaktionen müssen, da sie enzymatisch nicht katalysierbar oder steuerbar sind, spontan bis zum Gleichgewicht fortschreiten. Daraus ergibt sich die Notwendigkeit der Homöostase, d. h. die Aktivitäten der einzelnen Ionen müssen konstant bleiben, um optimale Bedingungen für biologische Vorgänge zu gewährleisten. An den homöostatischen Regulationen sind aktive Transportmechanismen für Ionen maßgebend beteiligt. Es folgt eine Besprechung der wichtigsten analytischen Probleme, die bei der Untersuchung des Elektrolythaushaltes auftreten können, z.B. bei der Bestimmung von Ionenkonzentrationen innerhalb der Zelle oder in kleinsten Flüssigkeitsproben, bei der elektrometrischen Messung von Ionenaktivitäten usw. Dabei wird auf die Fortschritte bei der Herstellung spezifischer Glaselektroden für Alkali- und Erdalkaliionen hingewiesen. Das Kernproblen des Elektrolythaushaltes betrifft jedoch die oben erwähnten Bindungen von Elektrolytionen an organische Molekülgruppen, die wegen ihrer geringen Stabilität und ihres geringen Ausmaßes analytisch nur schwer faßbar sind. Fortschritte werden erwartet bei der Anpassung moderner Methoden der Komplexchemie an die Besonderheiten der Elektrolytionen.
Summary Following a short characterisation of the strong electrolytes present in body fluids and of their biological significance the question is discussed in which way these ions specifically affect biological systems. It is assumed that these effects involve non-covalent attachments of ions to specific sites of enzymes or other effectors, although little is known about such interactions in biological environment. Since ionic reactions are not subject to enzymatic catalysis or control they must proceed spontaneously towards the equilibrium. Hence, the ionic levels in the body fluids must be kept constant (homeostasis) in order to maintain proper conditions for biological processes. These homeostatic levels are primarily maintained by active transport mechanisms for ions. Furthermore, the most important analytical problems of the investigation of electrolyte metabolism are discussed, such as those concerning the determination of ionic concentrations of ions within cells or in small fluid samples, the electrometric measurement of ion activities etc. Reference is made to the progress made in this field owing to the manufacturing of specific glass electrodes for alkali and alkaline earth ions. The main problem of electrolyte metabolism, however, concerns the above mentioned binding of electrolytes to organic groups, since these bindings are unstable and often too minute to be analytically accessible. Progresses are to be expected if modern methods of complex chemistry are adapted to the complexes of alkali and alkaline earth ions.相似文献