全文获取类型
收费全文 | 279篇 |
免费 | 2篇 |
专业分类
化学 | 188篇 |
力学 | 1篇 |
数学 | 36篇 |
物理学 | 56篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 13篇 |
2012年 | 23篇 |
2011年 | 20篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 7篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有281条查询结果,搜索用时 0 毫秒
31.
D. T. Stoyanov 《Letters in Mathematical Physics》1986,12(2):93-96
In terms of Fueter analytic functions, a classical solution of the Liouville equation in a fourdimensional Euclidean space depending on two arbitrary complex functions is obtained and discussed. 相似文献
32.
33.
V. M. Stoyanov M. M. El'chaninov A. F. Pozharskii 《Chemistry of Heterocyclic Compounds》1991,27(10):1140-1144
We have synthesized 2-(thienyl-2)imidazole and its N-methyl derivative. The latter product was obtained by nitration, bromination, acylation, and formylation, occurring as a rule on the thiophene ring. A general method for methylating 2-R-imidazoles with methyl iodide KOH-dimethoxy ethane is proposed.For Communication 1 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1414–1418, October, 1991. 相似文献
34.
E. V. Vlasova V. M. Stoyanov M. M. El’chaninov B. S. Lukyanov 《Chemistry of Heterocyclic Compounds》2010,46(6):681-683
Bromination of 2-acetylfuran with copper(II) bromide in a mixture of ethyl acetate and chloroform leads selectively to furacyl
bromide, the nucleophilic substitution of bromine in which by OAc and subsequent use of the Weidenhagen reaction enabled the
synthesis of 4(5)-(2-furyl)imidazole. On N-methylation of this imidazole in KOH–acetone 2 isomers are formed, the 1-methyl-4-
and 1-methyl-5-(2-furyl)imidazoles. It was established that, unlike alkylation of 4(5)-phenylimidazole, the main product of
the reaction is 1-methyl-5-(2-furyl)imidazole. 相似文献
35.
M.H. Majles Ara SR. Hosseini M.H. Rezvani M. Abolhassani 《Journal of Physics and Chemistry of Solids》2011,72(11):1367-1372
In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO3 photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering. 相似文献
36.
A. A. Petukhov B. E. Zhurtanov S. S. Molchanov N. D. Stoyanov Yu. P. Yakovlev 《Technical Physics》2011,56(4):520-525
The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the
temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band
radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum
to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hν
max = 0.693 − 4.497 × 10−4
T). Based on the dependence E
g
= hν
max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, E
g
≅ 0.817 − 4.951 × 10−4
T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R
0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage U
cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U
cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout
the temperature interval. 相似文献
37.
G. Kofod H. Stoyanov R. Gerhard 《Applied Physics A: Materials Science & Processing》2011,102(3):577-581
A simple dip-coating technique was employed to manufacture coaxial actuators with multiple layers of alternating dielectric
and conducting layers. A thin rubber string was coated with an electrode–insulator–electrode structure, giving rise to a thin,
fiber-like actuator with coaxial geometry. The process was repeated to achieve a compact multilayer actuator with up to three
coaxial dielectric layers. Mechanical and electromechanical characterization of the actuators is presented, showing actuation
strains up to 8% and proper voltage–thickness scaling behavior. Also presented is a capacitance vs. extension plot, demonstrating
that these structures can be used for compact and accurate capacitive strain sensing. 相似文献
38.
The article discusses peculiar features of polymer tape coatings for protecting pipelines and main methods of applying them
in a field environment. It is shown that the design of polymer tape coating depends on operational conditions, the conditions
of the coating application, and the method of pipeline construction. The main Russian and Western insulating materials are
reviewed and some of the technical characteristics of these materials are presented. 相似文献
39.
Method of frustrated total reflection in spectroscopy of surface polaritons in almost perfectly conducting metals 总被引:1,自引:0,他引:1
The standard technique for surface polaritons excitation by a prism coupling in Otto configuration is applied for investigation of almost perfectly conducting (pec) metals like tantalum irradiated by a collimated He-Ne laser radiation (λ 0 = 632.8 nm). In pec metals the imaginary part of the relative dielectric permittivity (ɛ″) is quite larger than the modulus of the real part of the same quantity (ɛ′ < 0, ɛ″ ≫ | ɛ′ |). Under this condition the single Lorentz dip of the reflectivity coefficient is proven to exist and is given in an analytical form, which follows from simplification of the usual multilayer Fresnel formula. In the case of a deterministically curved metal surface an approximate solution to the reduced Rayleigh integral equation appropriate for the Otto configuration is also given. These two theoretical deductions are compared with experimental data that have been produced by us for the reflectivity into the prism region from a bulk tantalum sample. 相似文献
40.
Stanimirova R Marinova K Tcholakova S Denkov ND Stoyanov S Pelan E 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12486-12498
Extracts of the Quillaja saponaria tree contain natural surfactant molecules called saponins that very efficiently stabilize foams and emulsions. Therefore, such extracts are widely used in several technologies. In addition, saponins have demonstrated nontrivial bioactivity and are currently used as essential ingredients in vaccines, food supplements, and other health products. Previous preliminary studies showed that saponins have some peculiar surface properties, such as a very high surface modulus, that may have an important impact on the mechanisms of foam and emulsion stabilization. Here we present a detailed characterization of the main surface properties of highly purified aqueous extracts of Quillaja saponins. Surface tension isotherms showed that the purified Quillaja saponins behave as nonionic surfactants with a relatively high cmc (0.025 wt %). The saponin adsorption isotherm is described well by the Volmer equation, with an area per molecule of close to 1 nm(2). By comparing this area to the molecular dimensions, we deduce that the hydrophobic triterpenoid rings of the saponin molecules lie parallel to the air-water interface, with the hydrophilic glucoside tails protruding into the aqueous phase. Upon small deformation, the saponin adsorption layers exhibit a very high surface dilatational elasticity (280 ± 30 mN/m), a much lower shear elasticity (26 ± 15 mN/m), and a negligible true dilatational surface viscosity. The measured dilatational elasticity is in very good agreement with the theoretical predictions of the Volmer adsorption model (260 mN/m). The measured characteristic adsorption time of the saponin molecules is 4 to 5 orders of magnitude longer than that predicted theoretically for diffusion-controlled adsorption, which means that the saponin adsorption is barrier-controlled around and above the cmc. The perturbed saponin layers relax toward equilibrium in a complex manner, with several relaxation times, the longest of them being around 3 min. Molecular interpretations of the observed trends are proposed when possible. Surprisingly, in the course of our study we found experimentally that the drop shape analysis method (DSA method) shows a systematically lower surface elasticity, in comparison with the other two methods used: Langmuir trough and capillary pressure tensiometry with spherical drops. The possible reasons for the observed discrepancy are discussed, and the final conclusion is that the DSA method has specific problems and may give incorrect results when applied to study the dynamic properties of systems with high surface elasticity, such as adsorption layers of saponins, lipids, fatty acids, solid particles, and some proteins. The last conclusion is particularly important because the DSA method recently became the preferred method for the characterization of fluid interfaces because of its convenience. 相似文献