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61.
Ramanathan R Zhong R Blumenkrantz N Chowdhury SK Alton KB 《Journal of the American Society for Mass Spectrometry》2007,18(10):1891-1899
The widely different LC-MS response observed for many structurally different compounds limits the use of LC-MS in full scan detection mode for quantitative determination of drugs and metabolites without using reference standard. The recently introduced nanospray ionization (NSI) technique shows comparable MS response for some compounds under non-LC-MS conditions. However, in the presence of numerous endogenous compounds commonly associated with biological samples such as urine, plasma, and bile, LC-MS is required to separate, detect, identify, and measure individual analytes. An LC-NSI-MS system was devised and the MS response obtained in this system for a variety of pharmaceutical drugs and their metabolites. The set-up involves two high-performance liquid chromatography (HPLC) systems, a chip-based NSI source and a quadrupole-time-of-flight (Q-TOF) mass spectrometer. Herein this is referred to as the response normalized-liquid chromatography NSI-MS (RNLC-NSI-MS) system. One HPLC unit performs the analytical separation, while the other unit adds solvent post-column with an exact reverse of the mobile phase composition such that the final composition entering the NSI source is isocratic throughout the entire HPLC run. The data obtained from four different structural classes of compounds [vicriviroc (VCV), desloratadine (DL), tolbutamide, and cocaine] and their metabolites indicate that by maintaining the solvent composition unchanged across the HPLC run, the influence of the solvent environment on the ionization efficiency is minimized. In comparison to responses obtained from radiochromatograms, responses from conventional LC-ESI-MS overestimated the VCV and DL responses, respectively, by 6- and 20-fold. Although VCV and DL responses obtained using LC-NSI-MS are within 2- to 6-fold from the respective radiochromatographic responses, the response normalization modification results in nearly uniform LC-NSI-MS response for all compounds evaluated. 相似文献
62.
L. F. Miranda A. B. Lugo L. D. B. Machado L. V. Ramanathan 《Radiation Physics and Chemistry》1999,55(5-6):709-712
Swelling was performed on dried membranes, normal ones and dried gel to unravel the role of crosslinking and degradation on polymeric structure during drying and hydration process. The comparison of the swelling results suggested that the network were formed only by PVP molecules. The complex mixture of macromolecules showed a irreversible behavior upon drying and hydration, probably as a function of PEG and/or agar entangling in effective physical crosslink. The best network regularity and useful properties was found at 20–30 kGy. 相似文献
63.
Investigation of calcium-induced, noncovalent association of calmodulin with melittin by electrospray ionization mass spectrometry 总被引:1,自引:0,他引:1
Olga V. Nemirovskiy Ragulan Ramanathan Michael L. Gross 《Journal of the American Society for Mass Spectrometry》1997,8(8):809-812
Noncovalent association of Ca2+-loaded calmodulin with a target peptide melittin was studied by electrospray ionization mass spectrometry (ESI-MS). ESI-MS does not reveal any binding of the apocalmodulin to the melittin. Partial loading of calmodulin with calcium leads to weak association with melittin. Upon binding of two calcium ions to the protein, changes in the conformation of calmodulin occur; these changes are sufficient to promote binding of melittin. Saturation of the protein with Ca2+ (a distribution of up to seven calcium ions is detected) induces a large increase of the binding to melittin. The stoichiometry of peptide binding to calmodulin is 1:1. 相似文献
64.
In electrospray ionization source hydrogen/deuterium exchange LC-MS and LC-MS/MS for characterization of metabolites 总被引:4,自引:0,他引:4
A new method is described for performing hydrogen/deuterium (H/D) exchange in an electrospray ionization (ESI) source. The use of liquid chromatography (LC)-mass spectrometer equipped with an ESI source and deuterium oxide (D2O) as the sheath liquid allows H/D exchange experiments to be performed on-line. This directly provides information for determining the number and position of exchangeable hydrogens, aiding in the elucidation of the structures of drug metabolites. To demonstrate the utility of this method, LC-mass spectrometry (MS) and LC-MS/MS experiments were performed using either H2O or D2O as sheath liquid on a matrix metalloprotease (MMP) inhibitor (PD 0200126) and its metabolites. Examination of the mass shift of the deuteriated molecule from that of the protonated molecule allowed the number of exchangeable protons to be determined. Interpretation of the production-spectra helped to determine the location of the exchanged protons and assisted in the assignment of the site(s) of modification for each metabolite. 相似文献
65.
A sugar-based photoresponsive supergelator, N-glycosylazobenzene that shows selective gelation of aromatic solvents is described. The partial trans-cis isomerization of the azobenzene moiety allows photoinduced chopping of the entangled gel fibers to short fibers, resulting in controlled fiber length and gel-sol transition. The gelator is useful for the selective removal of toxic aromatic solvents from water. 相似文献
66.
The aim of this study is to investigate the antitumour and antioxidant activities of the ethanol extract of Scutia myrtina (EESM) against Ehrlich's ascites carcinoma (EAC) in mice. Twenty-four hours after tumour inoculation, EESM was administered at doses 100, 200 and 300?mg?kg?1 bodyweight/mice/day for 21 days. EESM caused a significant (p?0.01) decrease in ascites volume, packed cell volume and viable cell count, and also prolonged the life span of EAC tumour-bearing mice. Haematological profiles reverted to near-normal levels in extract-treated mice (p?0.01). EESM also produced protective effects by significantly decreasing the activity of serum enzymes and bilirubin and increasing the protein and uric acid levels (p?0.05). EESM significantly (p?0.05) decreased the levels of lipid peroxidation, while it significantly (p?0.05) increased the levels of enzymatic and non-enzymatic antioxidants. The results indicate that EESM exhibited significant antitumour and antioxidant activities in EAC-bearing mice. 相似文献
67.
Sankaranarayanan SK Subbaraman R Ramanathan S 《Physical chemistry chemical physics : PCCP》2012,14(10):3360-3368
Atomistic simulations employing dynamic charge transfer between atoms are used to investigate ultra-thin oxide growth on Al(100) metal substrates in the presence of an ac electric field. In the range of 1-10 GHz frequencies, the enhancement in oxidation kinetics by ~12% over natural oxidation can be explained by the Cabrera-Mott mechanism. At field frequencies approaching 0.1-1 THz, however, we observe a dramatic lowering of the kinetics of oxygen incorporation by ~35% compared to the maximum oxidation achieved, which results in oxygen non-stoichiometry near the oxide-gas interface (O/Al ≈ 1.0). This is attributed to oxygen desorption from the oxide surface. These results suggest a general strategy to tune oxygen concentration at oxide surfaces using ac electric fields that could be of interest in diverse fields related to surface chemistry and applications such as tunnel barriers, thin dielectrics and oxide interfaces. 相似文献
68.
JM Taylor R Vaidhyanathan SS Iremonger GK Shimizu 《Journal of the American Chemical Society》2012,134(35):14338-14340
A new porous metal-organic framework (MOF), barium tetraethyl-1,3,6,8-pyrenetetraphosphonate (CALF-25), which contains a new phosphonate monoester ligand, was synthesized through a hydrothermal method. The MOF is a three-dimensional structure containing 4.6 ? × 3.9 ? rectangular one-dimensional pores lined with the ethyl ester groups from the ligand. The presence of the ethyl ester groups makes the pores hydrophobic in nature, as determined by the low heats of adsorption of CH(4), CO(2), and H(2)O (14.5, 23.9, and 45 kJ mol(-1), respectively) despite the polar and acidic barium phosphonate ester backbone. The ethyl ester groups within the pores also protect CALF-25 from decomposition by water vapor, with crystallinity and porosity being retained after exposure to harsh humid conditions (90% relative humidity at 353 K). The use of phosphonate esters as linkers for the construction of MOFs provides a method to protect hydrolytically susceptible coordination backbones through kinetic blocking. 相似文献
69.
In this paper an alternative approach for measurement of στ product for 4
F
3/2→4
I
11/2 transition of Nd3+ doped YVO4 crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator
and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable.
The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is
measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO4 crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple
method for direct measurement of στ product of laser crystals. 相似文献
70.
A recently reported anomalous behaviour of the positronium annihilation rate with temperature in certain super-cooled organic liquids is explained in terms of a simple free-volume model modified in the presence of molecular cluster formation. This model apart from showing the entropic origin of the phenomenon accounts for the existence of the transition temperature “Tr” much above the glass-transition temperature Tg. It also predicts for the threshold temperature “Tr” fo clusters to commence formation a value of 310-7.0+8.0 K as against the experimental value of 304 K for ortho-terphenyl. 相似文献