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51.
Hans Petersson 《Archiv der Mathematik》1985,44(2):152-158
Ohne ZusammenfassungHerrn Curt Meyer (Köln) zur Vollendung seines 65. Lebensjahres am 19. November 1984 gewidmet. 相似文献
52.
Nadine S Simons-Weidenmaier Maruschka Weber Claudia F Plappert Peter KD Pilz Susanne Schmid 《BMC neuroscience》2006,7(1):38
Background
Short-term habituation of the startle response represents an elementary form of learning in mammals. The underlying mechanism is located within the primary startle pathway, presumably at sensory synapses on giant neurons in the caudal pontine reticular nucleus (PnC). Short trains of action potentials in sensory afferent fibers induce depression of synaptic responses in PnC giant neurons, a phenomenon that has been proposed to be the cellular correlate for short-term habituation. We address here the question whether both this synaptic depression and the short-term habituation of the startle response are localized at the presynaptic terminals of sensory afferents. If this is confirmed, it would imply that these processes take place prior to multimodal signal integration, rather than occurring at postsynaptic sites on PnC giant neurons that directly drive motor neurons. 相似文献53.
The water-forming reaction on Pd has been studied on a PdSiO2Si (Pd-MOS) structure in the temperature range 323–473 K. The reaction is found to be of the Langmuir-Hinshelwood type with the formation of OH beeing rate limiting. Since the Pd-MOS structure works as a sensitive hydrogen detector unique information on the behaviour of hydrogen during this catalytic reaction has been obtained. The reaction can be described in a model where the hydrogen atoms on the Pd surface have a large temperature activated lateral mobility and with no evidence of beeing in hot precursor states. At T = 473 K this means that for oxygen coverages ? 0.01 monolayers all hydrogen adsorbed will also react with oxygen. For smaller oxygen coverages unreacted hydrogen will not initially desorb towards the vacuum but towards the internal Pd surface of the Pd-MOS structure. Futhermore, hydrogen adsorption is blocked by adsorbed oxygen. The sticking coefficient for hydrogen on the bare Pd surface is, however, close to one and only weakly temperature dependent. An effect giving rise to a hysteresis in the work function versus oxygen coverage curve during oxygen adsorption - desorption is also discussed. 相似文献
54.
A flow-injection system is described for on-line conversion of a soluble species to an insoluble compound by means of a tag-material which subsequently can be determined. This approach is used for the determination of sulphide by flame atomic absorption spectrometry, cadmium(II) ions being used as the precipitating tag-reagent. Excess of cadmium(II) is collected on a chelating ion-exchanger and later eluted. The detection limit for sulphide was 10 μg l?1 and the sampling rate was 100 h?1. Typical relative standard deviation was 1.2%. Of the potential interferences tested, only phosphate had any effect. 相似文献
55.
Summary. We prove existence and uniqueness of reduced models for arbitrary Albert algebras and relate them to the Tits process. This
relationship yields explicit noncohomological realizations of the invariants mod 2 due to Serre and Rost. We also construct
nontrivial examples of Albert division algebras with nonvanishing invariants mod 2.
Received 29 August 1994 / in final form 22 February 1995 相似文献
56.
57.
Nilsson SL Andersson C Sjöberg PJ Bylund D Petersson P Jörntén-Karlsson M Markides KE 《Rapid communications in mass spectrometry : RCM》2003,17(20):2267-2272
Capillary electrophoresis (CE) has been combined with atmospheric pressure photoionization (APPI) and electrospray ionization (ESI) for mass spectrometric (MS) detection. Separation conditions using potassium phosphate buffer and ammonium formate buffer have been compared for analysis of eleven pharmaceutical bases. The results showed improvements in separation efficiency and peak symmetry when phosphate buffer was used. The low flow in CE may enable utilization of these advances with MS detection. Compared with ESI, the APPI technique provided a cluster-free background. The enhanced signal-to-noise ratio in the total ion current (TIC) and the reduced spectral background indicated that the APPI process is less affected by non-volatile salts in the CE buffers. This results in a wider range of choice of CE buffers in CE/MS analysis when APPI is the ionization method. 相似文献
58.
Direct coupling of micellar electrokinetic chromatography (MEKC) to mass spectrometry (MS) without employing partial filling is considered to be a challenge. One way of solving the problem would be the use of an MS-compatible surfactant. In the present study, the applicability of a series of surfactants (sodium dodecyl sulfate (SDS), lauric acid, cholic acid and perfluorated carboxylic acids) have been investigated both in terms of separation performance and MS compatibility. It was found that a MEKC system based on perfluorooctanoic acid (PFOA) and ammonia gave excellent results. The separation performance of the suggested system is comparable to the one obtained with standard systems based on SDS and sodium borate buffer although the selectivity is different. The electrospray ionization MS signal of the analytes is not seriously suppressed even at a PFOA concentration of 100 mM. Clusters are formed but their intensities are relatively low and comparable to those obtained with acetic acid. PFOA is volatile enough to allow long-term use, 30 h of continuous use has been recorded without any signs of decreasing performance. After use residual PFOA is easily removed from the ion-source (no memory effects). Furthermore, quantitation of trace impurities is possible at 25 ppb level when employing selected ion monitoring. 相似文献
59.
Characterization of sixty alkenes in a cat-cracked gasoline naphtha by gas chromatography 总被引:3,自引:0,他引:3
Summary The alkene-rich petrol fraction from refinery fluid catalytic cracking (FCC) has been characterized by GC and GC-MS. Quantitative proportions and retention data of 52 acyclic and 11 cyclic C5–C7 alkenes are given. Relative retentions are reported for methylsilicone and aluminium oxide stationary phases as methylene units (MU). Applications of mass spectra, single-ion GC-MS monitoring and retention data for identifications are demonstrated. 相似文献
60.