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排序方式: 共有233条查询结果,搜索用时 15 毫秒
81.
Mabel C. Chou Mahmut Parlar Yun Zhou 《Journal of Optimization Theory and Applications》2017,175(1):194-217
In this paper, we consider the problem of the optimal timing to initiate a medical treatment. In the absence of treatment, we model the disease evolution as a semi-Markov process. The optimal time to initiate the treatment is a stopping time, which maximizes the total expected reward for the patient. We propose a stochastic dynamic programming formulation to find this stopping time. Under some plausible conditions, we show that the maximum total expected reward at the start of a health state will be smaller when the patient is in a more severe state. We then prove that the optimal policy for initializing the treatment is determined by a time threshold for each given health state. That is, in each health state, the treatment should be planned to start, when the patient’s duration time in the health state reaches (or exceeds, in the case of a late observation of the patient’s health status) a certain threshold level. We also present numerical examples to illustrate our model and to provide managerial insights. 相似文献
82.
Atilla D Durmuş M Gürek AG Ahsen V Nyokong T 《Dalton transactions (Cambridge, England : 2003)》2007,(12):1235-1243
The synthesis, photophysical and photochemical properties of the tetra- and octa-poly(oxyethylene)substituted zinc (II) phthalocyanines are reported for the first time. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet oxygen, triplet state and fluorescence quantum yields, and triplet and fluorescence lifetimes of these compounds in dimethylsulfoxide (DMSO). Photophysical and photochemical properties of phthalocyanine complexes are very useful for PDT applications. The effects of the substituents on the photophysical and photochemical parameters of the zinc(II) phthalocyanines (3a, 5a and 6a) are also reported. The singlet oxygen quantum yields (Phi(Delta)), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.60 to 0.72. Thus, these complexes show potential as Type II photosensitizers. The fluorescence of the complexes was quenched by benzoquinone (BQ). 相似文献
83.
Microdevices in mass spectrometry 总被引:1,自引:0,他引:1
Miniaturization of laboratory instrumentation is becoming critical in achieving the speed and throughput required by the current revolutionary progress in biology. This mini review critically summarizes the present status of microfluidic devices designed for use in mass spectrometry. 相似文献
84.
85.
Characteristics of charge traps in TlInS2 single crystals are investigated by the use of thermally stimulated current (TSC) technique. The TSC spectra of the sample from 80 K to 300 K are recorded at a constant heating rate. The spectra reveal that there are several trapping levels associated with the complex structure of overlapping peaks. The experimental results indicate that the traps in TlInS2 associated with the spectra in the measuring range of temperature obey the monomolecular (first order) kinetics. Thus, the spectra are resolved into first order shaped peaks by the use of computerized best fit procedure. The trapping parameters; such as the energy depth, temperature dependent frequency factor and capture cross section, together with concentrations of the corresponding six discrete levels are computed. These centers all having low capture cross sections with strong temperature dependence are found to be at the energies of 0.11 eV, 0.22 eV, 0.25 eV, 0.26 eV, 0.29 eV and 0.30 eV with high concentrations of 6.6 × 1016, 2.0 × 1017, 3.3 × 1017, 9.6 × 1016, 2.3 × 1017 and 4.0 × 1017 cm?3, respectively. 相似文献
86.
In this study, the synthesis of Ce0.8Sm0.2O1.9 (SDC) solid electrolyte by the ultrasound assisted co-precipitation method was accomplished to explore the effects of ultrasound power, ultrasound pulse ratio and probe type upon the ionic conductivity of SDC as well as the lattice parameter, the microstructure and the density. Fine powders of uniform crystallite sizes (average 11.70 ± 0.62 nm) were obtained, needing lower sintering temperature. The SDC powders were successfully sintered to a relative density of over 95% at 1200 °C (5 °C min?1) for 6 h. The micrograph of SDC pellets showed non-agglomerated and well-developed grains with average size of about 200 nm. X-ray diffraction analysis showed that the lattice parameter increased with increasing acoustic intensity and reached a maximum for the 14.94 W cm?2. Further, a linear relationship was detected between the lattice parameter and the ionic conductivity, inspiring a dopant like effect of US on the electrolyte properties. The highest ionic conductivity as σ800°C = 3.07 × 10?2 S cm?1 with an activation energy Ea = 0.871 kJ mol?1 was obtained with pulsed ultrasound for an acoustic intensity of 14.94 W cm?2, using 19 mm probe and 8:2 pulse ratio. 相似文献
87.
Mahmut Işik 《Mathematica Slovaca》2011,61(5):779-788
The purpose of this paper is to introduce the spaces of sequences that are strongly almost (ω, λ, q)-summable with respect to a modulus function. We give some relations related to these sequence spaces. It is also shown that
if a sequence is strongly (ω, λ, q)-summable with respect to a modulus function, then it is S(λ
q
)-statistically convergent. 相似文献
88.
In [10] one-parameter planar motion was first introduced and the relations between absolute, relative, sliding velocities
(and accelerations) in the Euclidean plane
\mathbb E2{{\mathbb E}^2} were obtained. Moreover, the relations between the complex velocities of one-parameter motion in the complex plane were provided
by [10]. One-parameter planar homothetic motion was defined in the complex plane, [9]. In this paper, analogous to homothetic
motion in the complex plane given by [9], one-parameter planar homothetic motion is defined in the hyperbolic plane. Some
characteristic properties about the velocity vectors, the acceleration vectors and the pole curves are given. Moreover, in
the case of homothetic scale h identically equal to 1, the results given in [15] are obtained as a special case. In addition, three hyperbolic planes, of
which two are moving and the other one is fixed, are taken into consideration and a canonical relative system for one-parameter
planar hyperbolic homothetic motion is defined. Euler-Savary formula, which gives the relationship between the curvatures
of trajectory curves, is obtained with the help of this relative system. 相似文献
89.
Sait Eren San Mustafa OkutanTebello Nyokong Mahmut Durmu?Birol Ozturk 《Polyhedron》2011,30(6):1023-1026
The effects of introducing gallium and indium metals into phthalocyanine molecules were investigated via temperature and frequency dependent dielectric spectroscopy. The dielectric properties of Ga(III) and In(III) phthalocyanine pellets were measured at frequencies from 1 kHz to 1 MHz in the temperature range 300-530 K. The temperature dependence of the real part of the dielectric constant suggested that these compounds exhibit semiconductor behavior. The activation energy values were calculated from the Arrhenius plots at different frequencies. A distinct transition in these plots indicated the activation of ionic conductivity at higher temperatures. 相似文献
90.
R?za Bayrak Mahmut Durmu? ?smail De?irmencio?lu 《Journal of organometallic chemistry》2011,696(23):3807-3815
The synthesis and characterization of new peripherally tetra-3,5-dimethylpyrazole-1-methoxy substituted metal-free (4), zinc (5), nickel (6), cobalt (7), copper (8) and lead (9) phthalocyanines are described for the first time in this study. The photophysical (fluorescence quantum yields and fluorescence lifetimes) and photochemical (photodegradation and singlet oxygen quantum yields) properties of metal-free (4), zinc (5) and lead (9) phthalocyanines are studied in dimethylsulfoxide (DMSO). Nickel (6), cobalt (7) and copper (8) phthalocyanines (6-8) did not evaluate for this purpose due to transition metal and paramagnetic behavior of central metals in the phthalocyanine cavity. The fluorescence quenching behavior of metal-free (4), zinc (5) and lead (9) phthalocyanines are also investigated. The fluorescence emissions of these phthalocyanines are effectively quenched by 1,4-benzoquinone in DMSO. 相似文献