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121.
以 2,6-二叔丁基-4-甲基苯酚(BHT)为自由基捕捉剂,研究了四(五氟化苯基)-六,七溴-卟啉氯化铁选择性催化氧化超临界丙烷为丙醇的反应机理. 结果表明,添加少量的BHT能促进反应进行,过量的BHT则抑制反应进行. 反应产物中除有丙基自由基外,还有异丙氧自由基及其他微量反应产物(如异己烷、正己烷、双丙基过氧化物)存在. 超临界丙烷在催化剂的作用下形成更多的丙基自由基,进一步证明金属卟啉催化氧化超临界丙烷是链式自由基自氧化反应机理. 对于其他微量反应产物如乙醇、乙酸和丙酸的存在,不能用链式自由基自氧化反应机理进行解释. 相似文献
122.
Luci H. Fatori Tais O. Saito Mauricio Sepúlveda Renan Takahashi 《Mathematical Methods in the Applied Sciences》2020,43(1):225-241
We consider the classical Timoshenko system for vibrations of thin rods. The system has an indefinite damping mechanism, ie, it has a damping function a=a(x) possibly changing sign, present only in the equation for the vertical displacement. We shall prove that exponential stability depends on conditions regarding of the indefinite damping function a and a nice relationship between the coefficient of the system. Finally, we give some numerical result to verify our analytical results. 相似文献
123.
Radiation induced effects in glass-rods and fiberoptics have been studied to determine parameters affecting the application of these materials in nuclear technology, i.e. as fiberscopes for visual inspection in severe radiation environments. Different glass and fibertypes have been exposed to fission product gamma radiation. The radiation induced transmission loss was measured with a spectrophotometer and then different annealing methods were examined to improve the transmission properties again. Especially the changes in glass and fiber recovery vs. time as a function of radiation dose and annealing temperature were investigated. Annealing experiments were performed exposing the samples either to temperature treatment or to various light sources such as quartz lamp, arc lamp or UV-laser for optical annealing. The transmission recovery was then investigated either as a function of annealing temperature or of exposure time to the light sources. The results allow conclusions on the design and composition of optical fiber endoscopes to be used in severe radiation environment where image transmission is required in the presence of high level nuclear radiation. 相似文献
124.
125.
In1–x
Pd
x
films with 0.2x0.75 have been prepared by vapour quenching at 4.2 K or 77 K, respectively. To test whether amorphous (a-) phases can be obtained in this way, the resistance behavior and the electron diffraction patterns of the as-prepared and annealed films were studied insitu. For films withx=0.25 additional information could be acquired from their superconducting behavior. Combining these results one concludes that a-phases exist for the compositional range 0.2x0.6, which are stable up to crystallization temperaturesT
x within the range 250 KT
x
420 K. Irradiation of the crystallized films at low temperatures (4.2 K or 77 K) with heavy ions (350 keV Ar+ or Kr+) leads to complete re-amorphization. Forx=0.67 corresponding to InPd2 a nanocrystalline (n-) phase is obtained by vapour quenching at 77 K as inferred from x-ray diffraction. AtT
x
=700 K, thesen-films exhibit a drop of the electrical resistance indicating the beginning of significant grain growth. After recooling, Kr+ bombardment at 77 K does not restore the high electrical resistance of the as-quenchedn-film. This result can be used as a criterion when studying quenched films withx=0.625 corresponding to In3Pd5. In this case, a resistance drop is found atT
x
=600 K, but the diffraction techniques do not allow an uniquevocal distinction between amorphous and nanocrystalline. This becomes possible by low temperature ion irradiation after annealing atT>T
x
. The bombardment results in resistance changes, which saturate well-below the value of the as-quenched sample implying nanocrystallinity for the latter. Based on this criterion, a phase-diagram for quenched In1–x
Pd
x
is provided with 0x1 containing the newly detecteda- andn-phases. 相似文献
126.
Anna?Maria?A.?P.?FernandesEmail author Pedro?H.?Vendramini Renan?Galaverna Nicolas?V.?Schwab Luciane?C.?Alberici Rodinei?Augusti Roger?F.?Castilho Marcos?N.?EberlinEmail author 《Journal of the American Society for Mass Spectrometry》2016,27(12):1944-1951
Mass spectrometry imaging (MSI) of neurotransmitters has so far been mainly performed by matrix-assisted laser desorption/ionization (MALDI) where derivatization reagents, deuterated matrix and/or high resolution, or tandem MS have been applied to circumvent problems with interfering ion peaks from matrix and from isobaric species. We herein describe the application of desorption electrospray ionization mass spectrometry imaging (DESI)-MSI in rat brain coronal and sagittal slices for direct spatial monitoring of neurotransmitters and choline with no need of derivatization reagents and/or deuterated materials. The amino acids γ-aminobutyric (GABA), glutamate, aspartate, serine, as well as acetylcholine, dopamine, and choline were successfully imaged using a commercial DESI source coupled to a hybrid quadrupole-Orbitrap mass spectrometer. The spatial distribution of the analyzed compounds in different brain regions was determined. We conclude that the ambient matrix-free DESI-MSI is suitable for neurotransmitter imaging and could be applied in studies that involve evaluation of imbalances in neurotransmitters levels. 相似文献
127.
Richelly Cardoso Renan Valente Clauber Henrique Souza da Costa Joo Lidio da S. Gonalves Vianez Jr. Kauê Santana da Costa Fbio Alberto de Molfetta Cludio Nahum Alves 《Molecules (Basel, Switzerland)》2021,26(10)
Tyrosinases belong to the functional copper-containing proteins family, and their structure contains two copper atoms, in the active site, which are coordinated by three histidine residues. The biosynthesis of melanin in melanocytes has two stages depending on the actions of the natural substrates L-DOPA and L-tyrosine. The dysregulation of tyrosinase is involved in skin cancer initiation. In the present study, using molecular modeling tools, we analyzed the inhibition activity of tyrosinase activity using kojic acid (KA) derivatives designed from aromatic aldehydes and malononitrile. All derivatives showed conformational affinity to the enzyme active site, and a favorable distance to chelate the copper ion, which is essential for enzyme function. Molecular dynamics simulations revealed that the derivatives formed promising complexes, presenting stable conformations with deviations between 0.2 and 0.35 Å. In addition, the investigated KA derivatives showed favorable binding free energies. The most stable KA derivatives showed the following binding free energies: −17.65 kcal mol−1 (D6), −18.07 kcal mol−1 (D2), −18.13 (D5) kcal mol−1, and −10.31 kcal mol−1 (D4). Our results suggest that these derivatives could be potent competitive inhibitors of the natural substrates of L-DOPA (−12.84 kcal mol−1) and L-tyrosine (−9.04 kcal mol−1) in melanogenesis. 相似文献
128.
Carlos Alberto Galeano Suarez Inti Doraci Cavalcanti-Montaño Renan Gustavo da Costa Marques Felipe Fernando Furlan Pedro Luiz da Mota e Aquino Roberto de Campos Giordano Ruy de Sousa Jr. 《Applied biochemistry and biotechnology》2014,173(5):1083-1096
Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, and lignin. Fuzzy logic, in turn, is a branch of many-valued logic based on the paradigm of inference under vagueness. This paper presents a methodology, based on computational intelligence, for modeling the kinetics of a complex reactional system. The design of a fuzzy interpolator to model cellulose hydrolysis is reported, within the perspective of applying kinetic models in bioreactor engineering. Experimental data for various types of lignocellulosic materials were used to develop the interpolator. New experimental data from the enzymatic hydrolysis of a synthetic substrate, on the other hand, were used to validate the methodology. The accuracy of the results indicates that this is a promising approach to extend the application of models fitted for specific situations to different cases, thus enhancing their generality. 相似文献
129.
H.A. Radovan H.H. Wen P. Ziemann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):533-540
Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a
ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100
Oe at different temperatures is determined. The j
c
(
T
) data show a field-dependent anomalous kink close to Tc pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S
(
T
) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase
for increasing T-values, while an anomalous decrease of S
(
T
) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also
reflected by the activation barriers for flux creep U
(
j
), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .
Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998 相似文献
130.
M. Nittmann P. Ziemann W. Buckel G. Linker 《Zeitschrift für Physik B Condensed Matter》1981,41(3):205-209
Al-films were evaporated from Al2O3-crucibles or W-boats onto substrates held at 4.2 K or at room temperature (R.T.). The superconducting transition temperatureT
c
was measured in situ, while the oxygen contentC
o of the films was determined by Rutherford-backscattering. Layers evaporated at R.T. from Al2O3-crucibles exhibit aT
c
vs.C
o-relation like granular Al-films. For layers quench-condensed from W-boats without an external oxygen source typicalT
c
-values of 2.5 K and oxygen concentrations of 10 at % were found. In case of quench-condensation from Al2O3-crucibles it is concluded from theT
c
vs.C
o-relation that oxygen is incorporated into the films in the form of Al2O-molecules. The different behavior of theT
c
vs.C
o-curves will be discussed. 相似文献