全文获取类型
收费全文 | 861篇 |
免费 | 26篇 |
国内免费 | 11篇 |
专业分类
化学 | 578篇 |
晶体学 | 1篇 |
力学 | 76篇 |
数学 | 112篇 |
物理学 | 131篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 30篇 |
2021年 | 37篇 |
2020年 | 51篇 |
2019年 | 49篇 |
2018年 | 46篇 |
2017年 | 45篇 |
2016年 | 51篇 |
2015年 | 34篇 |
2014年 | 50篇 |
2013年 | 78篇 |
2012年 | 70篇 |
2011年 | 68篇 |
2010年 | 49篇 |
2009年 | 35篇 |
2008年 | 45篇 |
2007年 | 34篇 |
2006年 | 25篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有898条查询结果,搜索用时 15 毫秒
31.
In the current communication, the problem of plane wave diffraction by a conductible plate of finite length in the presence of cold plasma is investigated. The boundary-value problem corresponding to this model is formulated by Fourier transform which then leads to the Wiener?Hopf equation. The resulting equation has been solved by the Wiener?Hopf procedure in a standard way. The separated field (diffracted field) is analyzed in an anisotropic medium using asymptotic expansion and modified stationary phase method. The problem can be made simple by assuming ε2→0, where ε2 is the element of permittivity tensor. This happens, if the operating frequency is assumed to be very large as compared to ωc (cyclotron frequency) while it is of same order of ωp (the plasma frequency). The case ε1 =1, ε2→0 leads to the results for soft plate of finite length in an isotropic medium. Graphical study is performed to investigate the behavior of separated field for various physical parameters for isotropic and anisotropic media. 相似文献
32.
Hosseini Seyed Ghorban Khodadadipoor Zahra Mahyari Mojtaba Zinab Javad Mohebbi 《Journal of Thermal Analysis and Calorimetry》2019,135(2):963-979
Journal of Thermal Analysis and Calorimetry - The present study reports numerical simulations of water-based Al2O3 nanofluid flowing in a 2D channel with a heated wall-mounted obstacle. The... 相似文献
33.
AbstractThis article contains the nonlocal elasticity theory to capture size effects in functionally graded (FG) nano-rod under magnetic field supported by a torsional foundation. Torque effect of an axial magnetic field on an FG nano-rod has been defined using Maxwell’s relation. The material properties were assumed to vary according to the power law in radial direction. The Navier equation and boundary conditions of the size-dependent FG nano-rod were derived by the Hamilton’s principle. These equations were solved by employing the generalized differential quadrature method (GDQM). Presented model has the ability to turn into the classical model if the material length scale parameter is taken to be zero. The effects of some parameters, such as inhomogeneity constant, magnetic field and small-scale parameter, were studied. As an important result of this study can be stated that an FG nano-rod model based on the nonlocal elasticity theory behaves softer and has smaller natural frequency. 相似文献
34.
We study the Klein-Gordon oscillator in commutative, noncommutative space, and phase space with psudoharmonic potential under magnetic field hence the other choice is studying the Klein-Gordon equation oscillator in the absence of magnetic field. In this work, we obtain energy spectrum and wave function in different situations by NU method so we show our results in tables. 相似文献
35.
Béziau A Baudron SA Hosseini MW 《Dalton transactions (Cambridge, England : 2003)》2012,41(24):7227-7234
Using ligands based on either an acetylacetonate or a dipyrrin moiety appended with pyridyl groups, a series of novel heteroleptic copper(II) and cobalt(III) complexes combining both chelate units such as (acacpy(2))Cu(dpm-py) and (acacpy(2))Co(dpm-py)(2) (acacpy(2) = 1,3-bis(4-pyridyl)-1,3-propanedionate; dpm-py = 5-(4-pyridyl)dipyrrin) have been prepared and fully characterized. These two complexes were obtained upon reaction of dpm-py with the (acacpy(2))M homoleptic species (M = Cu(II), Co(II)). In the solid state, the (acacpy(2))Cu(dpm-py) complex behaves as a self-complementary metallatecton and leads to the formation of a 1D coordination polymer (CP) through the coordination of a peripheral pyridyl group to the copper centre. Contrastingly, the octahedral (acacpy(2))Co(dpm-py)(2) complex featuring a coordinatively saturated Co(III) centre crystallizes as an isolated mononuclear species. In order to generate heterometallic CPs, both complexes have been used as metallatectons upon their combination with different silver(I) salts. Upon reaction of (acacpy(2))Cu(dpm-py) with Ag(BF(4)) or Ag(TfO), 2- and 3-D heterometallic networks were obtained, respectively. In both cases, sheet type arrangements resulting from the binding of Ag(+) cations by three peripheral pyridyl groups were observed. These 2D sheets are further interconnected through Ag-π interactions with the pyrrolic rings. Under the same conditions, the combination of (acacpy(2))Co(dpm-py)(2) with Ag(TfO) leads to two networks differing by their connectivity patterns and dimensionality. Interestingly, whereas no Ag-π interactions were observed for the 2D network, a combination of coordination bonding with the pyridyl moieties and Ag-π interactions was detected for the 1D architecture. 相似文献
36.
S. Masoud Hosseini A. R. Moghadassi D. Henneke Ali Elkamel 《Journal of Thermal Analysis and Calorimetry》2010,101(1):113-118
Changes in the thermal conductivities of paraffin and mono ethylene glycol (MEG) as a function of β-SiC nanoparticle concentration
and size was studied. An enhancement in the effective thermal conductivity was found for both fluids (i.e., both paraffin
and MEG) upon the addition of nanoparticles. Although an enhancement in thermal conductivity was found, the degree of enhancement
depended on the nanoparticle concentration in a complex way. An increase in particle-to-particle interactions is thought to
be the cause of the enhancement. However, the enhancement became muted at higher particle concentrations compared to lower
ones. This phenomenon can be related to nanoparticles interactions. An improvement in the thermal conductivities for both
fluids was also found as the nanoparticle size shrank. It is believed that the larger Brownian motion for smaller particles
causes more particle-to-particle interactions, which, in turn, improves the thermal conductivity. The role that the base-fluid
plays in the enhancement is complex. Lower fluid viscosities are believed to contribute to greater enhancement, but a second
effect, the interaction of the fluid with the nanoparticle surface, can be even more important. Nanoparticle-liquid suspensions
generate a shell of organized liquid molecules on the particle surface. These organized molecules more efficiently transmit
energy, via phonons, to the bulk of the fluid. The efficient energy transmission results in enhanced thermal conductivity.
The experimentally measured thermal conductivities of the suspensions were compared to a variety of models. None of the models
proved to adequately predict the thermal conductivities of the nanoparticle suspensions. 相似文献
37.
S. Hosseini A. B. Mohamad A. H. Kadhum W. R. Wan Daud 《Journal of Thermal Analysis and Calorimetry》2010,99(1):197-202
A study concerned to thermogravimetric analysis is performed in cesium dihydrogen phosphate (CsH2PO4) that was synthesized, using cetyltrimethylammonium-bromide (CTAB), polyoxyethylene-polyoxypropylene (F-68) and mixture of
(F-68:CTAB) with two mole ratio 0.06 and 0.12 as surfactant. The dehydration behavior of particles was studied using thermal
gravimetric analysis and differential scanning calorimetric. Subsequently, the experimental results indicated that the first
dehydration temperature in the range of 237–239 °C upon heating, the second peaks occur at temperature range 290–295 °C and
overlapping in the thermogravimetric events is observed. The mass loss values are obtained in the range of 6.62–6.97 wt% that
is less than reported theoretical value 7.8 wt%. These values show well compatibility of reaction CsH2PO4 to Cs2H2P2O7 with 3.92 wt% whereas mass loss value of CsH2PO4 to CsPO3 is less than theoretical value 7.8 wt%. The activation energy of two steps dehydration are calculated using Kissinger equation
for the samples synthesized via CTAB and (F-68) with minimum value mass loss 6.62% and maximum value mass loss 6.97%, respectively.
The calculation results reveal that the reaction rate in the first step (CsH2PO4 → Cs2H2P2O7) is faster than the second step (CsH2PO4 → CsPO3). The weight loss values of the samples demonstrate that existence of CTAB can be considered as effective factor which prevents
more weight loss during the dehydration process. 相似文献
38.
A solvent-controlled four-component reaction has been described for the preparation of either hydroxy-tetrahydro-thiaza-cyclopenta[c]fluoren-6-one or dihydro-thiaza-cyclopenta[c]fluoren-6-one from nitroketene dithioacetals, cysteamine hydrochloride, 1,3-indandione and aromatic aldehydes starting materials by changing solvent systems. These reactions proceed under catalyst-free conditions affording a range of two types of skeletally distinct thiazolo[3,2-a]pyridines-based heterocycles. Hydroxy-tetrahydro-thiaza-cyclopenta[c]fluoren-6-one was obtained in H2O/EtOH (3:1, v/v) in high yield and diastereoselectivity but in contrast dihydro-thiaza-cyclopenta[c]fluoren-6-one was synthesised in EtOH in moderate to good yields and in the longer reaction time. The structural diversities have been confirmed spectroscopically, by IR 1H and 13C NMR, and EI-MS spectra, which agree with the proposed structures. 相似文献
39.
Meghdad Pirsaheb Hiva Hosseini Hasan Mohamadi Sorkali Negar Noori 《International journal of environmental analytical chemistry》2019,99(2):112-123
In the present study, a new method for extraction and preconcentration of amoxicillin and ceftriaxone was used in hospitalised sewage samples, called vortex-assisted liquid-phase microextraction based on the solidification of deep eutectic solvent. Samples were analysed by high-performance liquid chromatography–ultraviolet detection after preparation and extraction. In this method, the new deep eutectic solvent is used as the extraction solvent, which is obtained from the combination of 1-decyl-3-methylimidazolium chloride and n-butanoic acid. The important advantages of this novel extraction solvent include material stability, low density and good freezing point near room temperature. Under the optimum conditions, enrichment factors are in the range of 164–172. Repeatability and reproducibility of the method based on seven replicate measurements of 50.0 µg L?1 of the target analytes in analysed samples were in the range of 2.1–3.5% and 3.8–5.2%, respectively. The limit of detections and linearity are in the range of 0.005–0.10 and 3–600 µg L?1, respectively. The method was successfully applied for the determination of amoxicillin and ceftriaxone in the real sewage samples. The relative recoveries of sewage samples spiked with amoxicillin and ceftriaxone are 91–107%. 相似文献
40.
Sanaz Rezaei Afsaneh Valipouri Seyed Abdolkarim Hosseini Ravandi Monireh Kouhi Laleh Ghasemi Mobarakeh 《先进技术聚合物》2019,30(9):2447-2457
Pigmented purpuric dermatosis (PPD) is a skin disorder mainly seen in the lower limbs. The nanofibrous web has been shown to be an appropriate alternative for the treatment of skin diseases as a drug delivery vehicle. In this study, sodium alginate (SA)/polyethylene oxide (PEO) nanofibers containing vitamin C (VC) were fabricated using both blended electrospinning and core/shell electrospinning. The resultant nanofibers were characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. Enhancing the VC content resulted in increasing the nanofibers diameter. Also, the degradation rate and drug release were investigated. Drug release was evaluated using the in vitro dissolution and permeation method. The degradation rate and the drug release of the core/shell nanofibers were found to be lower than those of the blended nanofibers. The drug release of the extended nanofibers followed a different pattern, indicating that the extension of the nanofibers could be a promising way to control the drug release. 相似文献