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891.
892.
Evidence for a proposed activation mechanism is summarized. The low rate of ATP cleavage in the resting state of muscle is considered to result from the formation of a stable ring structure involving the two essential sulfhydryl groups on each myosin head and MgATP. Activation is thought to occur by interaction of actin in the vicinity of one of the essential sulfhydryl groups. Thus opening the stable ring leading to rapid dissociation of split products. This idea is consistent with the kinetic scheme of ATP cleavage developed recently by other workers and allows a prediction of the shift in population of intermediate states with changes in solvent conditions. It is also supported by our recent studies on the spatial geometry of the ring. The possibility that other nucleophilic groups may replace the sulfhydryl groups in other contractile systems is considered. The relevance of the ring structure to the tension generating event is discussed on the basis of recent measurements of the rate of contraction of modified (SH1-blocked) actomyosin threads. Results indicate the ability to form the ring structure is an essential requirement of the contractile process in these systems, and, moreover, that single, modified heads of myosin can act independently to produce the same rate of contraction as native myosin. This latter finding suggests that the myosin duplex exhibits some type of negative cooperativity in the contractile process. 相似文献
893.
W. J 《Journal of Molecular Structure》1973,15(2):319-320
The infrared and Raman spectra of trimethylarsine sulfide, trimethylarsine selenide, and their perdeuterated analogues have been recorded. An assignment of 22 of the 24 fundamental vibrational frequencies (exclusive of the methyl torsions) has been made for each molecule. Assignments were made on the basis of symmetry selection rules and comparison with structurally similar molecules.A normal coordinate analysis for each of these molecules was carried out to reinforce the assignments. Assuming a valence force field for each molecule of C3v symmetry, a set of 24 force constants was refined to give a least squares fit of the calculated frequencies to the observed frequencies. Calculations of the potential energy distribution for each molecule show that there exists little coupling between the different modes. 相似文献
894.
Gustav Zigeuner W.-Bernd Lintschinger Alfred Fuchsgruber Krystyna Kollmann 《Monatshefte für Chemie / Chemical Monthly》1976,107(1):171-181
2- and 3-aminoalcohols, o-aminobenzylalcohol, o-hydroxybenzylamine and o-amino(thio)-phenol react with 4-isothiocyanato-4-methyl-2-pentanone (1) to yield derivatives of condensed heterocycles (oxazolopyrimidines7, pyrimidooxazine8, pyrimidobenzoxazines9, 10, pyrimidobenzoxazole11 a and pyrimidobenzothiazole11 c respectively). Ethylenediamine or 1,3-diaminopropane react with1 to yield either imidazo-pyrimidine13 and pyrimidopyrimidine14 respectively or the 1,2-ethylene- and trimethylenebisdihydro-2(1H)-pyrimidinethione15 a, b respectively, according to the molar ratio of the reactants. o-Phenylenediamine gives pyrimidobenzimidazole11 d. 11a undergoes ring cleavage in boiling dimethylformamide followed by methylpyrimidine-pyridine rearrangement to dihydrohydroxyphenylamino-2(1H)-pyridinethione12, while15 a is converted into the bis-4-(ethanediimino)-pyridinthione16. 相似文献
895.
van Duynhoven JP Broekmann I Sein A van Kempen GM Goudappel GJ Veeman WS 《Journal of colloid and interface science》2005,285(2):703-710
Monoglyceride coagels consist of a network of plate-like crystals and are formed from a swollen gel state (alpha-gel). In order to resolve the transition mechanism, coagels were prepared with monoglycerides that differ in fatty acid composition (monomyristate and palmitate/stearate, respectively). Rheology provided information on kinetics of coagel formation and the strength of the resulting crystal network. From NMR measurements, the surface-to-volume ratio, tortuosity, and dimensionality of the network were obtained. These findings were in line with qualitative and quantitative structural information obtained from CryoSEM. As a model for the behaviour of non-monoglyceride species, the dynamics of (perdeuterated) palmitic acid was monitored in both alpha-gels and coagels. The experimental data support a two-stage mechanism. In the first stage, two-dimensional separation of D- and L-isomers in the monoglyceride bilayers of the alpha-gel occurs. This process depends primarily on lateral diffusion rate of the monoglycerides. Palmitic acid can be accommodated in the alpha-gel bilayer, but in the coagels it is separated into relative mobile and mechanically weak junction zones between the crystal plates. In the second stage of coagel formation, the crystal plates also grow in the third dimension. Both monoglyceride type and concentration determine the kinetics of this process. 相似文献
896.
W. Herr und R. Wölfle 《Fresenius' Journal of Analytical Chemistry》1965,209(1):213-226
Zusammenfassung Aufgrund ihrer komplexen und charakteristischen Zerfallsschematalassen sich eine Reihe von beispielsweise durch Neutroneneinfang entstandenen Radionukliden selektiv durch ,-Koinzidenz-Messungen nachweisen und quantitativ bestimmen. Die Methode wird hier besonders auf die Elemente Selen (75Se) und Iridium (192Ir) angewendet. Sie bietet den Vorzug extrem hoher Nachweisempfindlichkeit (etwa 10–10 g) und gestattet es darüber hinaus, in geeigneten Grundmaterialien wie Eisen und Platin zerstörungsfrei zu arbeiten. Eine Beeinflussung durch die Gegenwart anderer -Strahler kann durch diskrete Wahl und Einstellung der Koinzidenzbereiche weitgehend verhindert werden. Die besonderen Vorteile der Methode liegen in einer beachtlichen Vereinfachung und Verkürzung der chemischen Aufbereitung.
Es ist uns eine angenehme Pflicht, der Reaktorbetriebsgruppe des FRJ 1 in Jülich für die freundlicherweise durchgeführten Bestrahlungen zu danken; Herrn Heinz Ollig möchten wir für seine Hilfe bei der Durchführung der Messungen Dank sagen. 相似文献
Summary On the basis of their complex and characteristic decay schemes, a number of radionuclides formed for example by neutron capture can be selectively detected and quantitatively determined by means of ,-coincidence measurements. The method is specifically applied to the elements selenium (75Se) and iridium (192Ir). It offers the advantage of extremely high sensitivity of detection (ca. 10–10 gram) and permits in addition the performance of non-destructive analyses in suitable matrix materials, such as iron and platinum. Disturbances due to the presence of other -emitters can largely be prevented by discrete choice and adjustment of the coincidence ranges. The influence of the sample composition and dimensions are discussed. The particular advantage of the method consists in a considerable simplification and reduction of the time of chemical treatment.
Es ist uns eine angenehme Pflicht, der Reaktorbetriebsgruppe des FRJ 1 in Jülich für die freundlicherweise durchgeführten Bestrahlungen zu danken; Herrn Heinz Ollig möchten wir für seine Hilfe bei der Durchführung der Messungen Dank sagen. 相似文献
897.
A synthesis of all possible N-alkylated 2-n-butyl-imidazo[4,5]pyridine isomers is described as well as their structural assignment by 1H NMR spectroscopy. One of these derivatives, 2,-n-butyl-3-[2′- (1H-tetrazol-5-yl)-4-biphenylylmethyl]-3H-imidazo[4,5-b]pyridine 9 is a potent angiotensin II receptor antagonist. 相似文献
898.
C.S. Hoad R.W. Matthews M.M. Thakur D.G. Gillies 《Journal of organometallic chemistry》1977,124(3):c31-c36
Thallium-205, carbon-13 and proton NMR spectra have been determined for some monomethylthallium(III) derivatives CH3TlX2 (X anion) permitting comparison of NMR parameters in the series CH3TlX2, (CH3)2TlX, (CH3)3Tl. 相似文献
899.
900.