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51.
Rachel R. Ogorzalek Loo Brian E. Winger Richard D. Smith 《Journal of the American Society for Mass Spectrometry》1994,5(12):1064-1071
Proton transfer reaction of multiply charged ions at high mass-to-charge ratios were explored with a low frequency quadrupole mass spectrometer. This instrument enabled a qualitative comparison of proton transfer reaction rates at low charge states for ions generated by electrospray ionization (ESI) from different solution conformations and for disulfide-linked versus disulfide-reduced protein ions. Proton transfer reactions that efficiently reduced the number of charges for ESI-generated ions to approximately the number of arginines in the polypeptide sequence were observed. No significant differences in gas-phase reaction rates were noted between different solution conformers. Differences in reaction rates between “native” and disulfide-reduced proteins were much smaller than those observed below m/z 2000 with lower proton affinity reagents or by using lower reagent concentrations. These smaller differences in reaction rates are thought to reflect the reduced electrostatic contributions from widely spaced charge sites and thus, the reduced sensitivity to an ion's three-dimensional structure or “compactness.” 相似文献
52.
This paper describes the application of a novel broadband acoustic sensor to evaluating the acoustic emissions from cavitation produced by a typical commercial 20 kHz sonochemical horn processor. Investigations of the reproducibility of the processor, and of the variation in cavitation emissions as a function of output setting and sensor location are described, and resulting trends discussed in terms of the broadband integrated power in the megahertz frequency range. Companion studies with a conventional membrane hydrophone have illustrated for the first time that cavitation emissions produced by a sonochemical horn processor can extend to frequencies beyond 20 MHz, and the sensor shows that significant nonlinearity can be seen in measured cavitation activity with increasing nominal output power. 相似文献
53.
54.
Lauren M. Gehman Kalyan V. Vasudevan Rachel R. Butorac Salem S. Al-Deyab Alan H. Cowley 《Journal of chemical crystallography》2011,41(7):998-1001
Abstract
The coordination of decamethyleuropocene to a “clamshell” 1,2-bis(imino)acenaphthene (BIAN) ligand is accompanied by a one-electron redox process. The crystal structure of the Eu3+ product has been determined. The complex crystallizes in the triclinic space group P-1, with a = 12.065(2), b = 15.391(3), c = 17.266(4) ?, α = 73.71, β = 73.93(3), γ = 81.40(3)°, V = 2948.3(10) ?3 and Z = 2. The pyridine moiety of the clamshell ligand is not coordinated to the Eu3+ center. 相似文献55.
56.
This paper presents a new method for studying the surface of a heterogeneous solid by inverse gas chromatography at infinite dilution (IGC-ID). After saturating the high-energy sites by impregnation with a suitable polymer, the chromatographic probes visit the low energy sites, which are not visible by conventional IGC-ID. This method has been used to study the two types of surface of talc: lateral and basal surfaces. In the second part of the paper the influence of the structure of the polymer on the impregnation is examined. In particular it is shown that a polymer with a linear structure is more able to fit a rough surface than is a branched or a cyclic polymer. 相似文献
57.
Woerdeman DL Parnas RS Giunta RK Wilkerson AL 《Journal of colloid and interface science》2002,249(1):246-252
We employ a direct method, time-of-flight secondary ion mass spectroscopy (ToF-SIMS), to determine experimentally the chemical compositions of the wetted and dewetted regions of an uncured epoxy thin film. Determining the composition of the dewetted region indicated the presence of a very thin sublayer of resin in what was thought to be a region devoid of resin. The capability of ToF-SIMS to probe small 65 x 65 microm(2) areas of the surface has permitted us to directly compare the SIMS spectra of the wetted and dewetted regions to the survey spectra of the reactants. This may indicate the strength of resin/silica interactions, which determine interface formation and properties. 相似文献
58.
A series of derivatisation reactions between p-t-butyl calix[4]arene and ethyl bromoacetate were carried out in order to prepare 1,3 diester substituted calix[4]arene. Mass spectral data, obtained from direct injection of samples, indicated that the reactions were rich in the desired product. Since the ultra violet (UV) spectra of the desired product and possible impurities are very similar, liquid chromatography (LC) chromatographic data seemed to corroborate these results. However, when on-line LC-UV-MS was carried out and each LC peak subjected to MS analysis as it eluted, a very different picture emerged. It was found that many of these reactions actually contained high levels of the monoester product which, having less affinity for sodium in the MS, is therefore seriously underestimated in any direct injection assay. LC-diode array detection (DAD) methods were also used to help successfully identify and characterise the compounds being formed in these complex reactions. The overall results obtained in this paper allowed the optimal reaction conditions to be determined for this reaction. LC-MS analysis of the chromatographic peaks also identified the presence of two isomers of the diester substituted calix[4]arene (1,3 and 1,2 diesters). The combination of LC and UV/MS detection is required for accurate analysis of the products of such reactions. 相似文献
59.
60.
Andrianasolo EH Gross H Goeger D Musafija-Girt M McPhail K Leal RM Mooberry SL Gerwick WH 《Organic letters》2005,7(7):1375-1378
[structure: see text] Chemical investigation of two field collections of marine cyanobacteria has led to the discovery of two new cytotoxic natural products, ankaraholides A (2) and B (3), along with the known compound swinholide A (1). Since swinholide-type compounds were previously localized to the heterotrophic bacteria of sponges, these findings raise intriguing questions about their true metabolic source. 相似文献