全文获取类型
收费全文 | 917篇 |
免费 | 44篇 |
专业分类
化学 | 663篇 |
晶体学 | 7篇 |
力学 | 22篇 |
数学 | 30篇 |
物理学 | 239篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 40篇 |
2019年 | 32篇 |
2018年 | 27篇 |
2017年 | 28篇 |
2016年 | 48篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 62篇 |
2012年 | 70篇 |
2011年 | 92篇 |
2010年 | 47篇 |
2009年 | 33篇 |
2008年 | 57篇 |
2007年 | 44篇 |
2006年 | 46篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有961条查询结果,搜索用时 15 毫秒
11.
Chakraborty S 《Physical review letters》2008,101(18):184501
A novel phase-field model is developed for the quantitative modeling of the complex electrochemical-hydrodynamic interactions in narrow fluidic confinements. Through an order parameter variation, this model captures the underlying excluded volume effects, solvation interactions, and preferential polarizabilities in a self-consistent fashion, without resorting to computationally prohibitive molecular dynamics simulations. Agreement with molecular dynamics predictions is found to be quantitative. 相似文献
12.
Jyotsnendu Giri Pallab Pradhan Vaibhav Somani Hitesh Chelawat Shreerang Chhatre Rinti Banerjee Dhirendra Bahadur 《Journal of magnetism and magnetic materials》2008
Nanomagnetic particles have great potential in the biomedical applications like MRI contrast enhancement, magnetic separation, targeting delivery and hyperthermia. In this paper, we have explored the possibility of biomedical applications of [Fe1−xBxFe2O4, B=Mn, Co] ferrite. Superparamagnetic particles of substituted ferrites [Fe1−xBxFe2O4, B=Mn, Co (x=0–1)] and their fatty acid coated water base ferrofluids have been successfully prepared by co-precipitation technique using NH4OH/TMAH (Tetramethylammonium hydroxide) as base. In vitro cytocompatibility study of different magnetic fluids was done using HeLa (human cervical carcinoma) cell lines. Co2+-substituted ferrite systems (e.g. CoFe2O4) is more toxic than Mn2+-substituted ferrite systems (e.g. MnFe2O4, Fe0.6Mn0.4Fe2O4). The later is as cytocompatible as Fe3O4. Thus, Fe1−xMnxFe2O4 could be useful in biomedical applications like MRI contrast agent and hyperthermia treatment of cancer. 相似文献
13.
Anup Pradhan Sakhya Alo Dutta T. P. Sinha 《Applied Physics A: Materials Science & Processing》2014,114(4):1097-1104
A ceramic SmAlO3 (SAO) sample is synthesized by the solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern has been done to find the crystal symmetry of the sample at room temperature. An impedance spectroscopy study of the sample has been performed in the frequency range from 50 Hz to 1 MHz and in the temperature range from 313 K to 573 K. Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The Cole–Cole model is used to analyze the dielectric relaxation mechanism in SAO. The temperature-dependent relaxation times are found to obey the Arrhenius law having an activation energy of 0.29 eV, which indicates that polaron hopping is responsible for conduction or dielectric relaxation in this material. The complex impedance plane plot of the sample indicates the presence of both grain and grain-boundary effects and is analyzed by an electrical equivalent circuit consisting of a resistance and a constant-phase element. The frequency-dependent conductivity spectra follow a double-power law due to the presence of two plateaus. 相似文献
14.
Ravinder Agarwal V. R. Singh M. M. Pradhan Ved Singh 《International Journal of Infrared and Millimeter Waves》1991,12(2):115-123
The occurance of the urinary stones varies according to the geographical regions. The presence of stones in the urinary system causes pain and discomfort. These generate colics and hence are sometimes life threatening. In the present study, infrared measurements have been made on several stone samples. It has been found that calcium oxalate, calcium phosphate, magnesiunm ammonium phosphate, calcium carbonate, uric acid, -cystine and xanthin are present, as expected. Also, silicon dioxide is found to be present in some of the stones but in small quantity, in addition to the above constituents. This constituent is responsible to exhibit piezoelectricity in the urinary calculi. 相似文献
15.
Anirudh Pradhan Purnima Pandey Kanti Jotania Mahesh Kumar Yadav 《International Journal of Theoretical Physics》2007,46(11):2774-2787
Plane symmetric viscous fluid cosmological models of the universe with a variable cosmological term are investigated. The
viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear
viscosity is to be proportional to rate of expansion in the model. We have also obtained a special model in which the shear
viscosity is assumed to be zero. The cosmological constant Λ is found to be a decreasing function of time and a positive which is supported by results from recent supernovae Ia observations.
Some physical and geometric properties of the models are also discussed. 相似文献
16.
Traceless synthesis of 2-aminoimidazoquinoxalinones has been performed on soluble polymer support under open-vessel microwave
dielectric heating. The reaction progression is monitored directly by the conventional proton NMR which indicated no release
of the substrate from the support. Fmoc-deprotected amino acid polymer conjugates react with 1,5-difluoro-2,4-dinitro benzene
to yield polymer bound dinitro fluoro amines, which are further substituted by various primary amines to yield PEG-immobilized
dinitrodiamines. Simultaneous reduction of aromatic meta-dinitro group leads to the traceless release of 2-quinoxalinones, followed by N-hetero cyclization with various isothiocyanates
in the presence of mercury(II)chloride to furnish 2-aminoimidazoquinolinone rings with three points of diversity at rapid
pace. 相似文献
17.
Anterior cingulate and cerebellar GABA and Glu correlations measured by ¹H J-difference spectroscopy
Waddell KW Zanjanipour P Pradhan S Xu L Welch EB Joers JM Martin PR Avison MJ Gore JC 《Magnetic resonance imaging》2011,29(1):19-24
Gamma-aminobutyric acid (GABA) and glutamate (Glu) levels, normalized to total creatine (tCr), were measured in the anterior cingulate and cerebellar vermis in healthy adults (n=19, age=24.6±6.4 years) using 1H MRS at 3 T, and metabolite correlations across regions and subjects were determined. Mean anterior cingulate and cerebellar GABA/tCr ratios were 0.31 (0.08) and 0.23 (0.06), respectively, while corresponding Glu levels were 1.16 (0.10) and 0.70 (0.07), respectively. Anterior cingulate and cerebellar glutamate levels were correlated (r=0.6103, P=.0140), although it is noted that when adjusted for multiple comparisons, all correlations reported here cluster to a P value of .0583. It is unlikely that this correlation is driven by correlations in tCr, since interregional correlations were not observed for other metabolites referenced to tCr. Correlations were also observed among metabolites in both the anterior cingulate and cerebellar vermis. In the former, N-acetylasparate was linearly dependent on glutamate (r=0.6577, P=.0063) and, at or below this significance threshold, four metabolites were correlated in the cerebellar vermis (Ins/tCh: r=0.6261, P=.0109. NAA/tCh: r=0.6426, P=.0082. NAA/Glu: r=0.6412, P=.0085. tCh/Glu: r=0.6193, P=0.0122). 相似文献
18.
Hassan Amirhashchi Anirudh Pradhan Rekha Jaiswal 《International Journal of Theoretical Physics》2013,52(8):2735-2752
Some new exact solutions of Einstein’s field equations have come forth within the scope of a spatially homogeneous and anisotropic Bianchi type-III space-time filled with barotropic fluid and dark energy by considering a variable deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution of the universe, the equation of state (EoS) for dark energy ω (de), in both cases, tends to ?1 (cosmological constant, ω (de)=?1), by displaying various patterns as time increases, which is consistent with recent observations. The cosmic jerk parameter in our derived models are in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed Statefinder parameters, the behaviour of different stages of the universe has been studied. The physical and geometric properties of cosmological models are also discussed. 相似文献
19.
We report successful fabrication of Ag doped Hg:1223 films by reacting Ba2Ca2.3Cu3.3Oz(Agy): y=0, 0.02, 0.025, 0.05, 0.1 and 0.2 precursors deposited by spray pyrolysis on SrTiO3 (100) substrates, in controlled Hg+Pb ambient, in an evacuated sealed quartz tube at 820 °C for 4 h. The effects of AgNO3 addition on the superconducting properties of Hg/(Pb):1223 films are studied. The addition of low concentration of silver e.g. y≈0.025 results in a slight increase in Tc (R=0) from 125 to 126 K and the dc critical current density (Jc) decreases with the increasing Ag in Hg(Pb):1223 (Agy) films. The microstructural details exhibit the curious characteristics of spiral like features for lower concentrations of silver i.e. up to y=0.05. These improvements are believed to be due to the liberation of oxygen through the dissociation of AgNO3 at higher temperature and passivation of weak link effects through the segregation of silver at these grain boundaries. The addition of silver content y≥0.05 resulted in the decrease in transition temperature. The Jc is observed to decrease steadily with increasing Ag content. The microstructural features, e.g. spiral are also found to deteriorate with increasing silver content. The deterioration in superconducting properties at high Ag content is believed to be mainly due to the formation of Ag-Hg amalgam. 相似文献
20.
Solid immersion lenses (SIL) facilitate high numerical aperture (NA) and consequent sub-wavelength diffraction limited focusing in near-field optics based systems. Such systems are in commercial and research use for various applications including near-field scanning optical microscopy, ultra-high-density magneto-optic data storage and near-field nanolithography. Here, we present a novel manufacturing method using SIL-based near-field optics for laser-induced patterning on silicon wafers. The near-field effect of SILs was investigated by using hemispherical lenses made of three different materials (BK7, Sapphire, LaSFN9) to superfocus an incident Q-switched, 532 nm Nd:YAG laser beam transmitted through a focusing objective. This optical arrangement achieved a laser-processed feature resolution near the diffraction limit in air. Results of experiments that were conducted at various processing conditions to investigate the effects of varying incident laser power (with peak pulse power less than 1 W), pulse width, number of pulses and size of SIL on processed feature size and resolution are presented. Experimental results are compared with numerical simulations using the simplified model. 相似文献