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171.
M. Takeshi Nakata Grant W. Hart Bryan G. Peterson 《Journal of the American Society for Mass Spectrometry》2010,21(10):1712-1719
Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is often limited by space-charge effects. Previously,
particle-in-cell (PIC) simulations have been used to understand these effects on FTICR-MS signals. However, none have extended
fully into the space-charge dominated (plasma) regime. We use a two-dimensional (2-D) electrostatic PIC code, which facilitates
work at very high number densities at modest computational cost to study FTICR-MS in the plasma regime. In our simulation,
we have observed peak coalescence and the rapid loss of signal coherence, two common experimental problems. This demonstrates
that a 2-D model can simulate these effects. The 2-D code can handle a larger numbers of particles and finer spatial resolution
than can currently be addressed by 3-D models. The PIC method naturally takes into account image charge and space charge effects
in trapped-ion mass spectrometry. We found we can quantify the relative abundances of two closely spaced (such as 7Be+ and 7Li+) species in the plasma regime even when their peaks have coalesced. We find that the frequency of the coalesced peak shifts
linearly according to the relative abundances of these species. Space charge also affects more widely spaced lines. Singly-ionized
7BeH and 7Li have two separate peaks in the plasma regime. Both the frequency and peak area vary nonlinearly with their relative abundances.
Under some conditions, the signal exhibited a rapid loss of coherence. We found that this is due to a high order diocotron
instability growing in the ion cloud. 相似文献
172.
Hart SR Lau KW Hao Z Broadhead R Portman N Hühmer A Gull K McKean PG Hubbard SJ Gaskell SJ 《Journal of the American Society for Mass Spectrometry》2009,20(2):167-175
The use of electron-transfer dissociation as an alternative peptide ion activation method for generation of protein sequence
information is examined here in comparison with the conventional method of choice, collisionally activated dissociation, using
a linear ion trapping instrument. Direct comparability between collisionally and electron-transfer-activated product ion data
were ensured by employing an activation-switching method during acquisition, sequentially activating precisely the same precursor
ion species with each fragmentation method in turn. Sequest (Thermo Fisher Scientific, San Jose, CA) searching of product
ion data generated an overlapping yet distinct pool of polypeptide identifications from the products of collisional and electron-transfer-mediated
activation products. To provide a highly confident set of protein recognitions, identification data were filtered using parameters
that achieved a peptide false discovery rate of 1%, with two or more independent peptide assignments required for each protein.
The use of electron transfer dissociation (ETD) has allowed us to identify additional peptides where the quality of product
ion data generated by collisionally activated dissociation (CAD) was insufficient to infer peptide sequence. Thus, a combined
ETD/CAD approach leads to the recognition of more peptides and proteins than are achieved using peptide analysis by CAD- or
ETD-based tandem mass spectrometry alone. 相似文献
173.
Estrogen receptor beta is differentially regulated by alternative O-GlcNAcylation/O-phosphorylation at Ser(16). NMR, CD, and molecular dynamics analyses of model peptides show that these alternative modifications induce different peptide conformations, providing a molecular basis for their differential regulation of protein function. 相似文献
174.
We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt transitions between areas of micrometer-thick tangled CNT films and millimeter-scale aligned CNT structures are manipulated by changing the duration of pretreatment by H2/Ar prior to introduction of C2H4 and by changing the configuration of the substrate sample in the furnace tube. This demonstrates that the flow profile over the sample mediates the supply of reactants to the catalyst and that pretreatment using H2 significantly affects the initial activity of the catalyst. 相似文献
175.
For X a compact Abelian group and B an infinite subset of its dual , let CB be the set of all x∈X such that converges to 1. If F is a free filter on , let . The sets CB and DF are subgroups of X. CB always has Haar measure 0, while the measure of DF depends on F. We show that there is a filter F such that DF has measure 0 but is not contained in any CB. This generalizes previous results for the special case where X is the circle group. 相似文献
176.
Aubert B Barate R Bona M Boutigny D Couderc F Karyotakis Y Lees JP Poireau V Tisserand V Zghiche A Grauges E Palano A Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Charles E Gill MS Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Orimoto TJ Pripstein M Roe NA Ronan MT Wenzel WA del Amo Sanchez P Barrett M Ford KE Harrison TJ Hart AJ Hawkes CM Morgan SE Watson AT Held T Koch H Lewandowski B 《Physical review letters》2006,97(20):201801
We report searches for B-meson decays to the charmless final states rhoK* and f0(980)K* with a sample of 232x10(6) BB pairs collected with the BABAR detector at the PEP-II e+e- collider. We measure in units of 10(-6) the following branching fractions, where the first error quoted is statistical and the second systematic, or upper limits are given at the 90% confidence level: B(B+-->rho0K*+)<6.1, B(B+-->rho+K*0)=9.6+/-1.7+/-1.5, B(B0-->rho-K*+)<12.0, B(B0-->rho0K*0)=5.6+/-0.9+/-1.3, B(B+-->f0(980)K*+)=5.2+/-1.2+/-0.5, and B(B0-->f0(980)K*0)<4.3. For the significant modes, we also measure the fraction of longitudinal polarization and the charge asymmetry: fL(B+-->rho+K*0)=0.52+/-0.10+/-0.04, fL(B0-->rho0K*0)=0.57+/-0.09+/-0.08, ACP(B+-->rho+K*0)=-0.01+/-0.16+/-0.02, ACP(B0-->rho0K*0)=0.09+/-0.19+/-0.02, and ACP(B+-->f0(980)K*+)=-0.34+/-0.21+/-0.03. 相似文献
177.
Measurement of branching fractions and charge asymmetries in B decays to an eta meson and a K* meson
Aubert B Bona M Boutigny D Couderc F Karyotakis Y Lees JP Poireau V Tisserand V Zghiche A Grauges E Palano A Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Ofte I Stugu B Abrams GS Battaglia M Brown DN Button-Shafer J Cahn RN Charles E Gill MS Groysman Y Jacobsen RG Kadyk JA Kerth LT Kolomensky YG Kukartsev G Lynch G Mir LM Orimoto TJ Pripstein M Roe NA Ronan MT Wenzel WA del Amo Sanchez P Barrett M Ford KE Hart AJ Harrison TJ Hawkes CM Watson AT Held T Koch H Lewandowski B Pelizaeus M Peters K 《Physical review letters》2006,97(20):201802
We present measurements of branching fractions and charge asymmetries for the decays B-->etaK*, where K* indicates a spin 0, 1, or 2 Kpi system. The data sample corresponds to 344x10(6) BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+ e- collider at SLAC. We measure the branching fractions (in units of 10(-6): B(B0-->etaK*0(892))=16.5+/-1.1+/-0.8, B(B+-->etaK*+(892))=18.9+/-1.8+/-1.3, B(B0-->eta(Kpi)0*0)=11.0+/-1.6+/-1.5, B(B+-->eta(Kpi)0*+)=18.2+/-2.6+/-2.6, B(B0-->etaK2*0(1430))=9.6+/-1.8+/-1.1, and B(B+-->etaK2*+(1430))=9.1+/-2.7+/-1.4. We also determine the charge asymmetries for all decay modes. 相似文献
178.
Lucy Gilbert Simon Browning Andrew T. A. Jenkins John P. Hart 《Mikrochimica acta》2010,170(3-4):331-336
An amperometric biosensor for phosphate ion is described that is based on a cobalt phthalocyanine modified screen-printed carbon electrode (CoPC-SPCE). The biosensor operation is based on the enzyme pyruvate oxidase (PyOd) which catalyses the oxidative decarboxylation of pyruvate, in the presence of inorganic phosphate and O2, to acetyl phosphate, hydrogen peroxide (H2O2) and CO2. The transducer allows the electrocatalytic oxidation of H2O2 in order to generate the analytical signal. The enzyme was immobilised onto the CoPC-SPCE using a sandwich format. The inner membrane was formed in situ by depositing an acetone solution containing cellulose acetate first onto the transducer surface. The enzyme and cofactors were then deposited onto this layer and allowed to dry; finally a second aliquot of the cellulose acetate solution was deposited onto the enzyme layer and allowed to dry. The biosensor was characterised by amperometry in stirred solution to produce current-voltage curves and for calibration studies. From these it was deduced that a reliable electrocatalytic response was obtained for phosphate ion; an operating potential of +0.4 V was selected for the analysis of urine samples. The precision of the response for urine analysis and recovery data for potable water suggests that the biosensor could have applications in clinical and environmental monitoring. 相似文献
179.
Ryan Hart Dominique J. Hahne Veronica Llopis-Mestre Hillary Huttenhower Charles A. Eckert Charles L. Liotta 《Tetrahedron》2010,66(5):1082-52
Reversible ionic liquids are a novel class of solvents that combine an effective medium where reactions occur with a ‘built-in’ separation ability for facile recovery of the products and catalysts, making the solvent available for recycle. We report the utility of these solvents in a number of reactions (Claisen-Schmidt condensation, Heck C-C coupling, and CO2 capture) and discuss the effectiveness of the separation. We also provide insight into the challenges and limitations of using these unique solvent systems to couple reactions and separations. 相似文献
180.
The Vredefort impact structure in South Africa is the largest and oldest remnant impact structure on Earth. Observations from above the crater reveal lower than average magnetic field intensities, but the rocks in the crater have been shown to possess much higher magnetic intensities than the regional average that varies on a centimeter scale. Various mechanisms, including the presence of single domain magnetite structures, have been proposed for this anomaly. Mössbauer spectroscopy has been applied to study the Fe-mineralogy of samples from near the centre of the Vredefort crater. Transmission Mössbauer measurements on bulk and microtomics sections of samples showed that the magnetic minerals were magnetite and hematite, and we suggest that oxidation of olivine during the impact is responsible for the magnetic properties of the rocks. 相似文献