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41.
Hansen R Måsøy SE Tangen TA Angelsen BA 《The Journal of the Acoustical Society of America》2011,129(2):1117-1127
A method of acoustic imaging is discussed that potentially can improve the diagnostic capabilities of medical ultrasound. The method, given the name second order ultrasound field imaging, is achieved by the processing of the received signals from transmitted dual frequency band pulse complexes with at least partly overlapping high frequency (HF) and low frequency (LF) pulses. The transmitted HF pulses are used for image reconstruction whereas the transmitted LF pulses are used to manipulate the elastic properties of the medium observed by the HF imaging pulses. In the present paper, nonlinear propagation effects observed by a HF imaging pulse due to the presence of a LF manipulation pulse is discussed. When using dual frequency band transmit pulse complexes with a large separation in center frequency (e.g., 1:10), these nonlinear propagation effects are manifested as a nonlinear HF propagation delay and a HF pulse distortion different from conventional harmonic distortion. In addition, with different transmit foci for the HF and LF pulses, nonlinear aberration will occur. 相似文献
42.
The objective of this paper is ultrasonic measurement and characterization of solid particles in liquid (20–40 μm glass beads in water) in high shear flow (1.5–2 m/s). Ultrasonic time dependent signals as well as frequency spectra are analyzed, for simultaneous determination of average particle concentration and average flow speed. As a result, the distribution of sound energy in such concentrated systems at given flow speeds is measured. Influence of flow turbulence is demonstrated in measurements. Also, characteristic behaviors of liquid–particle mixtures like particle clustering and influence of gas bubbles have been investigated. Experimental results are complemented with a discussion of factors that influence measurement uncertainty. 相似文献
43.
Dietzel PD Johnsen RE Blom R Fjellvåg H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(8):2389-2397
Porous metal-organic framework compounds with coordinatively unsaturated metal sites on the inner surface of the pores promise to be valuable adsorbents and catalyst systems, either in industrial applications or as model systems to study interactions with guest molecules. The dehydration process of two isostructural microporous coordination polymers, [M2(dhtp)(H2O)2].8 H2O, termed CPO-27-M (M=Co, Zn; H(4)dhtp=2,5-dihydroxyterephthalic acid) was investigated by in situ variable temperature X-ray diffraction. Both compounds contain accessible coordination sites at the metal after complete removal of the solvent. However, despite the analogy of their crystal structures, they behave differently during dehydration. For CPO-27-Co, water desorption is a smooth topotactic process of second order with no concomitant space group change and no increase in microstrain, which is beneficial for the applicability of the material. Removal of the water propagates from the center of the channels outwards. The coordinating water molecule at the metal desorbs only when almost all the bulk water in the pores has disappeared. In contrast, discontinuities in the powder pattern of CPO-27-Zn indicate the occurrence of first-order transitions. The crystal structures of four of the five individual phases could be determined. The structure of the intermediate phase occurring just before the framework is completely evacuated was elusive in respect to full structure solution and refinement, but it is most probably related to the removal of the axis of threefold symmetry. The zinc-based material experiences a significant amount of strain. 相似文献
44.
Seidler-Egdal RK Nielsen A Bond AD Bjerrum MJ McKenzie CJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(15):3849-3858
Capillary electrophoresis (CE) and electrospray ionisation (ESI) mass spectra of aqueous solutions of manganese(II) complexes of the monoanions of the pentadentate ligands N-methyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (mcbpen(-)) and N-benzyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (bcbpen(-)), show the presence of a mixture of closely related Mn(II) species, assigned to the mono, di-, tri- and poly-cationic complexes [Mn(II)(L)(H(2)O)](n)(n+), L = mcbpen(-) or bcbpen(-) with n = 1, 2, 3, etc. In solution, these complexes are reversibly oxidized by tert-butyl hydrogen peroxide (TBHP), (NH(4))(2)[Ce(NO(3))(6)], Ce(ClO(4))(4), oxone and [Ru(bipy)(3)](3+) to form metastable (t(?) = min to h) higher valent (hydr)oxide species, showing a collective maximum absorbance at 430 nm. The same species can be produced by [Ru(bipy)(3)](2+)-mediated photooxidization in the presence of an electron acceptor. TBHP oxidation of the complexes, in large excesses of the TBHP, is concurrent with an O(2) evolution with turnovers of up to 1.5 × 10(4) mol of O(2) per mol of [Mn] and calculated rate constants from two series of experiments of 0.039 and 0.026 mol[O(2)] s(-1) M(-2). A 1:1 reaction of TBHP with [Mn] is rate determining and the resultant species is proposed to be the mononuclear, catalytically competent, [Mn(IV)(O)(mcbpen)](+). At very close m/z values [Mn(III)(OH)(mcbpen)](+), [Mn(2)(III/IV)(O)(2)(mcbpen)(2)](+) and [Mn(IV)(2)(O)(2)(mcbpen)(2)](2+) are detected by ESI MS and CE when the concentration of TBHP is comparable to or lower than that of [Mn]. These are conditions that occur post catalysis and these species are derived from [Mn(IV)(O)(mcbpen)](+) through condensation reactions. 相似文献
45.
46.
Sakhi AK Russnes KM Smeland S Blomhoff R Gundersen TE 《Journal of chromatography. A》2006,1104(1-2):179-189
A method for the simultaneous quantification of reduced and oxidized glutathione in human plasma employing a two-dimensional chromatographic system with parallel porous graphitized carbon (PGC) columns coupled with fluorescence (FLD) and coulometric electrochemical detection (ED) has been developed. Post-sampling oxidation of reduced glutathione (GSH) was prevented by derivatizing the -SH group with monobromobimane (MBB) and the glutathione-bimane adduct (GSMB) was detected by FLD. Oxidized glutathione (GSSG) was detected by ED optimized to give lowest possible limits of detection (LOD). The method is fully validated and is currently used for determination of GSH, GSSG and its redox potential in different clinical studies. 相似文献
47.
Nonlinear propagation acoustics of dual-frequency wide-band excitation pulses in a focused ultrasound system 总被引:1,自引:0,他引:1
Måsøy SE Standal Ø Deibele JM Näsholm SP Angelsen B Johansen TF Tangen TA Hansen R 《The Journal of the Acoustical Society of America》2010,128(5):2695-2703
In this article, acoustic propagation effects of dual-frequency wide-band excitation pulses in a focused ultrasound system are demonstrated in vitro. A designed and manufactured dual-frequency band annular array capable of transmitting 0.9/7.5 MHz center frequency wide-band pulses was used for this purpose. The dual-frequency band annular array, has been designed using a bi-layer piezo-electric stack. Water tank measurements demonstrate the function of the array by activating the low- and high-frequency layers individually and simultaneously. The results show that the array works as intended. Activating the low- and high-frequency layers individually, results in less than -50 dB signal level from the high- and low-frequency layers respectively. Activating both layers simultaneously, produce a well defined dual-frequency pulse. The presence of the low-frequency pulse leads to compression, expansion, and a time delay of the high-frequency pulse. There is a phase shift between the low- and high-frequency pulse as it propagates from the array to the focus. This makes the latter described effects also dependent on the array configuration. By varying the low-frequency pressure, a shift of up to 0.5 MHz in center frequency of a 8.0 MHz transmitted high-frequency pulse is observed at the array focus. The results demonstrate the high propagation complexity of dual-frequency pulses. 相似文献
48.
Jeppe Byskov-Nielsen Allan H. Holm Rune H?jsholt Pedro Sá Peter Balling 《Applied Physics A: Materials Science & Processing》2011,104(3):975-979
Micro-mechanical interlocking (MMI) can be applied to create new and interesting composite materials. We have employed laser structuring to achieve MMI between stainless steel and plastic with extremely high joint strength. However, the water permeability and corrosion resistance of the joint must be examined. For many industrially relevant applications it is important to keep water away from certain parts and to prevent the sample from corroding. A thorough study of the permeability of the interconnected samples at different temperatures and after employing different laser-structuring techniques is conducted. The permeability seems to be consistent with the Hagen–Poiseuille equation independent of the laser structuring technique and is orders of magnitudes larger than the diffusion rate through the plastic. Two different types of corrosion tests have been undertaken, and we show that care must be taken in order not to degrade the corrosion resistance of the sample to an unacceptable level. 相似文献
49.
Practical radical cyclizations using organoboronic acids and trifluoroborates take place in water, open to air, and in a scalable fashion employing catalytic silver nitrate and stoichiometric potassium persulfate. Both Pschorr-type cyclizations and tandem radical cyclization/trap cascades are described, illustrating the utility of these mild conditions for the generation of polycyclic scaffolds. 相似文献
50.
Encapsulation and handling methods for hygroscopic, volatile, oily and other kinds of difficult samples for analysis are described. Hermetical encapsulation is achieved with an electrical spot welder. 相似文献