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21.
The applicability of ion-pair reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (IP-RP-HPLC/ESI-MS) and direct infusion/ESI-MS to the characterization of nucleic acid mixtures was evaluated by the analysis of the reaction products obtained from solid-phase synthesis of a 39-mer oligonucleotide. IP-RP-HPLC/ESI-MS was performed using 200 microm i.d. capillary columns packed with octadecylated, micropellicular poly(styrene-divinylbenzene) particles and applying gradients of acetonitrile in 50 mM triethylammonium bicarbonate (TEAB). Three different solvent systems were utilized for direct infusion/ESI-MS with removal of metal cations by on-line cation exchange: (1) 10 mM triethylamine (TEA) in 50% aqueous acetonitrile, (2) 2.2 mM TEA, 400 mM hexafluoro-2-propanol (HFIP) in 20% aqueous methanol and (3) 50 mM TEAB in 10% aqueous acetonitrile. Owing to its separation capability, the highest selectivity and specificity were achieved with IP-RP-HPLC/ESI-MS, which, apart form the 39-mer target sequence, allowed the identification of two isobutyryl-protected target sequences and a 10-mer and 20-mer failure sequence. Direct infusion/ESI-MS with TEA-acetonitrile or TEA-HFIP-methanol as solvent revealed signals for the 39-mer in the m/z range 700-1600. The presence of derivatives containing one, two, three and four isobutyryl groups indicated that the hydrolysis of the protecting groups after solid-phase synthesis was not complete. Failure sequences could not be identified by direct infusion/ESI-MS under conditions favoring multiple charging of the analytes owing to the high chemical background and coincidental overlapping of m/z signals. However, efficient charge state reduction upon addition of carbonic acid to the electrosprayed solvent shifted the signals of the 39-mer and derivatives to m/z values >2400 and allowed the detection of seven different failure sequences, ranging from the 8-mer to the 23-mer, in the mixture. 相似文献
22.
J. F. K. Huber und A. I. M. Keulemans 《Fresenius' Journal of Analytical Chemistry》1964,205(1):263-274
Zusammenfassung Es wird vorgeschlagen, für die Identifizierung von Stoffen Verteilungskoeffizienten zu verwenden und diese mit Hilfe der GLC in einem einfachen Verfahren, das auch die Kontrolle der Meßbedingungen erlaubt, zu bestmimen. Dieser Vorschlag kombiniert ein relatives Meßverfahren mit der Bestimmung absoluter Größen. Der Meßgenauigkeit, die für die Identifizierung von entscheidender Bedeutung ist, wurde besondere Aufmerksamkeit gewidmet und dabei herausgestellt, daß sie im allgemeinen durch die Trennleistung der Säule begrenzt wird. Für die Auswertung der Ergebnisse bei der Verwendung von Säulen mit verschiedenen stationären Phasen wurde ein Verfahren erprobt, bei dem die an den verschiedenen Säulen gemessenen Verteilungskoeffizienten miteinander kombiniert werden. Es wurde eine Tabelle der Verteilungskoeffizienten von etwa 80 Kohlenwasserstoffen bei 50,0° C mit Squalan und Dinonylphthalat als stationären Flüssigkeiten angefertigt. An Hand dieser Tabelle wurde die Identifizierung der C5–C7-Kohlenwasserstoffe eines Crackproduktes durchgeführt.
Summary It is recommended to use partition coefficients for the identification of compounds and to determine these by a simple gas-chromatographic procedure, which allows the control of the measuring conditions.This recommendation combines a relative method of measurement with the determination of absolute quantities. The accuracy of the measurement, which is decisive for the identification, was investigated and it was found that the accuracy in most cases will be limited by the resolving power of the column. For the evaluation of the results obtained with columns with different stationary phases a method was tested in which the partition coefficients measured on two different columns were combined. A table of partition coefficients of 80 hydrocarbons at 50,0° C on squalane and dinonylphthalate as stationary phases was compiled. On the basis of this table the identification of the C5-C7 hydrocarbons in a crack product was carried out.相似文献
23.
A high-performance liquid chromatographic method is described for the determination of the phosphodiesterase III/IV inhibitor zardaverine in serum by using fully automated clean-up of large-volume serum samples on a semi-preparative-scale precolumn followed by chromatography on two analytical columns operated with two different solvent systems. The switching of the analytical columns provides the necessary specificity and sufficient sensitivity for UV detection is obtained by the sample volume. The method was shown to give nearly quantitative recovery, allowing the use of external standard quantification. Good precision and linearity within the concentration range 1-50 ng/ml could be demonstrated. The method is suitable for routine measurements in support of kinetic studies of zardaverine in man. 相似文献
24.
Zusammenfassung Die Zersetzung von Pb(CH3COO)3 · 3 H3O wurde im Bereich von Raumtemperatur bis 450° unter N3 mittels TG, DTA verfolgt und die Produkte wurden analytisch charakterisiert. PbO ist das hauptsächliche feste Endprodukt, neben dem im wesentlichen nur Pb entsteht. Als feste Zwischenprodukte wurden neben Pb(CH3COO)3 die basischen Acetate Pb(CH3COO)2 · PbO und Pb(CH3COO)2 · 2 PbO gefunden und durch Röntgenpulveraufnahmen identifiziert; diese basischen Acetate wurden durch isotherme Zersetzung bei 240 bzw. 305° dargestellt. Unter den durch GC und MS erfaßten und quantitativ bestimmten flüchtigen Zersetzungsprodukten sind CO2 und Aceton Hauptbestandteile. Verschiedene Bildungsweisen der übrigen Produkte, CH3COOH, (CH3CO)2O, Acetylaceton und des Zwischenproduktes Keten werden aufgezeigt.
Dem Fonds der Chemischen Industrie danken wir für finanzielle Unterstützung. 相似文献
The decomposition of Pb(CH3COO)3 · 3 H2O under N2 has been studied by TG and DTA between room temperature and 450° and the products have been characterized analytically. PbO is the main solid product, besides which essentially only Pb is produced. As solid intermediates, aside from Pb(CH3COO)3 the basic acetates Pb(CH3COO)2 · PbO and Pb(CH3COO)2 · 2 PbO have been found and identified via their X-ray powder diagrams; these basic acetates have been prepared by isothermal decomposition at 240 and 305°, respectively. Among the volatile decomposition products analyzed by GC and MS and determined quantitatively, CO2 and acetone are the main products. Different routes for the formation of the other products, CH3COOH, (CH3CO)2O, acetylacetone and the intermediate ketene are shown.
Résumé On a suivi, par TG et ATD sous N2, dans l'intervalle de températures allant de l'ambiante jusqu'à 450°, la décomposition de Pb(CH3COO)2 · 3 H2O dont on a caractérisé les produits par des méthodes analytiques. PbO est le principal produit final solide, en dehors duquel il ne se forme essentiellement que du Pb. Comme produits intermédiaires solides, on a trouvé, à part Pb(CH3COO)2, les acétates basiques Pb(CH3COO)3. PbO et Pb(CH3COO)2 · · 2 PbO qui ont été identifiés par analyse de poudres aux rayons X. Ces acétates basiques se sont formés, par décomposition isotherme, respectivement à 240 et à 305°. Parmi les produits de décomposition volatils décelés par GC et MS et dosés par des méthodes quantitatives, CO3 et l'acétone sont les composants principaux. On montre les différents modes de formation des autres produits, comme CH3COOH, (CH3CO)3O, l'acétylacétone et le cétène formé transitoirement.
Pb(CH3COO)2. 32O 450°. . PbO , , . , Pb(CH3COO)2, Pb(CH3COO)2. PbO Pb(CH3COO)2. 2PbO, . , , 240 305°. , -, CO2 . , CH3COOH, (CH3CO)2O, .
Dem Fonds der Chemischen Industrie danken wir für finanzielle Unterstützung. 相似文献
25.
John M. Kane Christopher R. Dalton Michael A. Staeger Edward W. Huber 《Journal of heterocyclic chemistry》1995,32(1):183-187
Several 1,2,4-triazole derivatives containing a 2-fluorophenyl substituent at either the 3- or 5-position and a methyl group at the 4-position were synthesized. These derivatives exhibit long-range 19F-1H and 19F-13C through-space coupling in their 1H and 13C nmr spectra between the fluorine and the 4-methyl group. The close spatial proximity of these nuclei was confirmed by X-ray analysis and by fluorine irradiated proton observe ({19F}-1H) NOE difference spectroscopy. 相似文献
26.
Ansgar Schäfer Christian Huber Jürgen Gauss Reinhart Ahlrichs 《Theoretical chemistry accounts》1993,87(1-2):29-40
Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu2Se and Cu4Se2. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested. 相似文献
27.
Capillary reversed-phase high-performance liquid chromatography (RP-HPLC) utilizing monolithic poly(styrene-divinylbenzene) columns was optimized for the coupling to electrospray ionization mass spectrometry (ESI-MS) by the application of various temperatures and mobile phase additives during peptide and protein analysis. Peak widths at half height improved significantly upon increasing the temperature and ranged from 2.0 to 5.4 s for peptide and protein separations at 70 degrees. Selectivity of peptide elution was significantly modulated by temperature, whereas the effect on proteins was only minor. A comparison of 0.10% formic acid (FA), 0.050% trifluoroacetic acid (TFA), and 0.050% heptafluorobutyric acid (HFBA) as mobile phase additives revealed that highest chromatographic efficiency but poorest mass spectrometric detectabilities were achieved with HFBA. Clusters of HFBA, water, and acetonitrile were observed in the mass spectra at m/z values >500. Although the signal-to-noise ratios for the individual peptides diverged considerably both in the selected ion chromatograms and extracted mass spectra, the average mass spectrometric detectabilities varied only by a factor of less than 1.7 measured with the different additives. Limits of detection for peptides with 500 nl sample volumes injected onto a 60 mm x 0.20 mm monolithic column were in the 0.2-13 fmol range. In the analysis of hydrophobic membrane proteins, HFBA enabled highest separation selectivity at the cost of lower mass spectral quality. The use of 0.050% TFA as mobile phase additive turned out to be the best compromise between chromatographic and mass spectrometric performance in the analysis of peptides and proteins by RP-HPLC-ESI-MS using monolithic separation columns. 相似文献
28.
A total synthesis of the optically active tetrahydroesterastin β -lactam analogue 2 using Miller's hydroxamate approach is described (Scheme 2). Significant modification of published procedures has resulted in a short and facile stereospecific preparation of the N-[(benzyloxycarbonyl)methyl]-β -lactam 17 starting from the readily available D -serine. This material served as intermediate for the preparation of a variety of N-[(benzyloxycarbonyl)methyl]tetrahydroesterastin β-lactam analogues (Scheme 5). 相似文献
29.
30.
Roland Huber 《Geometriae Dedicata》1995,58(3):291-311
We show some topological properties of semianalytic subsets of rigid analytic varieties: curve selection lemma, the closure
of a semianalytic subsetS is semianalytic,
for every quasi-compact morphismf. As an application we show that a morphismf: X Y of rigid analytic varieties is open at a pointx X if and only if SpecO
X,x SpecO
Y,f(x) is surjective. 相似文献