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991.
Erhard Heinz Ralf Beyerstedt 《Calculus of Variations and Partial Differential Equations》1994,2(2):241-247
Letz=z(x, y) be a real-valued twice continuously differentiable solution of the elliptic Monge-Ampère equationAr+2Bs+Ct+rt – s
2=E in the punctured disk 0<(x–x
0)2+(y–y
0)2<2. Assume thatq is continuous at (x0, y0). Our aim is to give sufficient conditions on the coefficientsA,..., E which ensure that the singularity (x
0,y
0) is removable. This generalizes an earlier result of Jörgens (Math. Ann. 129 (1955), 330–344). 相似文献
992.
Tarek A. Salama Bernd Lackner Heinz Falk 《Monatshefte für Chemie / Chemical Monthly》2003,32(5):1113-1119
An efficient synthesis of tri-O-methylemodin aldehyde was achieved via bromination of tri-O-methylemodin utilizing N-bromosuccinimide yielding the monobromo and dibromo derivatives. Sommelet reaction of the monobromomethyl derivative as well as hydrolysis of the dibromomethyl analog with aqueous silver nitrate afforded the protected aldehyde in good yield. Accordingly, both bromo derivatives can be used even when they are obtained as a mixture of the bromination reaction, which could not be controlled easily to yield the bromo products selectively. From the aldehyde the tri-O-methylemodin nitrile was prepared in a one-pot reaction using hydroxylamine-O-sulfonic acid. 相似文献
993.
Wilhelm Berger und Heinz Elvers 《Fresenius' Journal of Analytical Chemistry》1959,171(3):185-193
Zusammenfassung 1-(2-Pyridyl-azo)-2-naphthol gibt mit einer Reihe von Metallkationen gefärbte Chelatkomplexe, die sich zum Teil mit organischen Lösungsmitteln extrahieren lassen. Durch systematische Prüfung wurden die für die Chelatbildung günstigsten pH-Bereiche ermittelt. Durch Maskierung und/oder durch Zerlegung der gebildeten Chelate mit spezifischen Reagentien lassen sich selektive Nachweise im Mikrogrammbereich durchführen. Es werden spezifische Bestimmungen für Zink, Cadmium, Mangan, Indium, Gallium, Uranyl und Kobalt mitgeteilt. Auch Kupfer, Palladium und Nickel lassen sich gut nachweisen.I. Mitteilung: diese Z. 154, 114 (1957). 相似文献
994.
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
995.
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
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