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101.
Zusammenfassung Aluminiumoxid, das mit Wasser vorbelegt ist, gibt an organische Lösungsmittel einen Teil davon ab und ändert dadurch seine Aktivität. In einer chromatographischen Trennsäule können sich hieraus ernste Störungen ergeben. Man vermeidet sie durch die Anwendung von Fließ-mitteln mit passendem Wasserzusatz. Auf die Trocknung von Pyridin an aktivem Aluminiumoxid wird kurz eingegangen.
Ein Teil der Ergebnisse wurde bereits in verschiedenen Vorträgen mitgeteilt.
Roscher, G.: Diss. Univ. Erlangen 1960. 相似文献
Summary Aluminium oxide containing a certain amount of water transfers it in part to organic solvents, thus changing its activity. Serious interferences in chromatographic column separations can arise from that fact. They can be prevented by use of solvents with adjusted water content. The use of active aluminium oxide for desiccation of pyridine is described shortly.
Ein Teil der Ergebnisse wurde bereits in verschiedenen Vorträgen mitgeteilt.
Roscher, G.: Diss. Univ. Erlangen 1960. 相似文献
102.
Frank?WendlerEmail author Gerhard?Grane? Thomas?Heinze 《Cellulose (London, England)》2005,12(4):411-422
The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements
by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of
stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions
with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared
with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating
rate autocatalysis can be proved by dynamic caloric measurements as well. 相似文献
103.
Vass S Grimm H Bányai I Meier G Gilányi T 《The journal of physical chemistry. B》2005,109(24):11870-11874
Slowly diffusing water molecules were found by quasi-elastic neutron scattering (QENS) in a sodium dodecyl sulfate (SDS) micellar solution, and both their diffusion coefficient (4.33 x 10(-6) cm2 x s(-1)) and mole fraction (0.057) were determined. After successfully checking the mean slowing down of solvent molecules by the gradient compensated stimulated spin-echo (GCSTE) pulse sequence NMR method, a similar effect was observed with this technique in the solvent phase of dodecyl trimethylammonium bromide (DTAB) and differing chain length (X = 12, 20, 30, and 40) ethoxylated nonyl phenol (9NX) micellar systems. Following the literature, the experimental results are qualitatively explained by assuming that, apart from ionic hydration, H-bonds may form between the solvent molecules and the O or N atoms present in the hydrophilic (head)groups of the micelle-forming monomers. 相似文献
104.
Zusammenfassung Zur Bestimmung von Coffein in Erfrischungsgetränken (Cola), Kaffee und Tee wird die Differential-Pulsvoltammetrie verwendet. Bei dieser Methode wird Coffein bei pH 1,2 an einer glasartigen Kohlenstoffelektrode oxydiert und quantitativ bestimmt. Die voltammetrisch ermittelten Analysenergebnisse werden mit den Resultaten der Flüssigkeistchromatographie verglichen. Um einen weiteren Einblick in den Reaktionsverlauf zu erhalten, wurde Coffein anodisch bei pH 1,2, 2,3 und pH 6 oxydiert. Die Reaktionsprodukte wurden kathodisch durch Differential-Pulspolarographie identifiziert.
Voltammetric determination of caffeine in coffee, tea, and soft drinks
Summary Differential pulse voltammetry is used for the determination of caffeine in soft drinks, coffee, and tea. In this method caffeine is oxidised at a glassy carbon electrode at pH 1.2 and determined quantitatively. The voltammetric results are compared with those found by HPLC. To elucidate the mechanism of the electrode processes the reaction products were produced by anodic oxidation of caffeine at pH 1.2, 2.3 und pH 6 and then identified by cathodic differential pulse polarography.相似文献
105.
The radical yields and rate constants in the quenching reaction of thionine triplet with the complete series of monohalogen substituted anilines as electron donors were determined by flash spectroscopy. Whereas the quenching rate constants show little and unsystematic variation, the radical yields decrease with increasing spin—orbit coupling constant of the halogen substituent. This effect is very sensitive to the position of the halogen in the donor. The results are explained in terms of a heavy atom effect on the intersystem crossing rate constant in a triplet exciplex. 相似文献
106.
Gerhard BringmannStefan Busemann 《Tetrahedron》2003,59(8):1245-1253
The first quantum chemical calculation of the circular dichroism (CD) spectra of michellamines has been achieved, based on a complete quantum chemical conformational analysis. Michellamines are dimeric naphthylisoquinoline alkaloids and thus naturally occurring quateraryls, with a large molecular size and flexibility and equipped with stereogenic centers and axes. 相似文献
107.
Gustav Kortüm und Gerhard Herzog 《Fresenius' Journal of Analytical Chemistry》1962,190(2):239-242
Zusammenfassung Pulvergemische von zwei verschiedenen Modifikationen eines Stoffes oder von zwei Pigmenten lassen sich mit Hilfe diffuser Reflexionsmessungen quantitativ analysieren, wenn die Reflexionsspektren sich in einem zugänglichen Spektralgebiet genügend stark unterscheiden. Die Methode wird am Beispiel der Titandioxyde Rutil und Anatas im einzelnen beschrieben.
Summary Mixtures of two modifications of solid powdered material can be quantitatively analyzed by diffuse reflectance measurements, if the reflectance spectra are sufficiently different in some wavelength range. The method is described with the example of the titanium dioxides rutile and anatase.相似文献
108.
109.
Burghard Grüning Gerhard Holze Albert Gossauer Ludger Ernst 《Helvetica chimica acta》1985,68(6):1771-1781
The transformation of the c-acetic-acid chain of hexamethyl Coα, Coβ-dicyanocobyrinate into an ethyl group (→ 2 ) as well as the synthesis of the pentadecaalkyl-cobalticorrin 6d from commercial cyanocobalamin are described. On reaction of 2 or 6d with O2 in the presence of ascorbic acid, migration of the CH3 group at C(5) to the vicinal position C(6) takes place concomitantly with the introduction of a carbonyl group at C(5). 相似文献
110.
A New Approach to Bicyclo[4.1.0]heptane Derivatives The reaction of the dienone 1 with ethyl α-bromoacetate does not furnish the expected glycidic acid ester 2 but leads to the bicyclo[4.1.0]heptenone derivative 3 . The structure of this new compound has been proved by means of spectroscopic methods (1R, 1H-NMR, 13C-NMR, MS). The elucidation of the configuration at C(7) could be realized by measuring a NOE effect. Other α-alkylated α-bromoacetates react with 1 in the same manner. 相似文献