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71.
Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W 总被引:1,自引:0,他引:1
Dattatray J. Late Pankaj Misra B. N. Singh Lalit M. Kukreja Dilip S. Joag Mahendra A. More 《Applied Physics A: Materials Science & Processing》2009,95(2):613-620
Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition
method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm2 and 9.3 mA/cm2 has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar
emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87
and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear
behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×105 cm−1 and 2.16×105 cm−1 for pointed and 3.2×104 and 1.74×104 for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots
exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology
studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence
to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion
bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical
applications in field-emission-based electron sources. 相似文献
72.
Anuj Kumar Sapna Pathak Mahendra Singh Poonam Tandon V. D. Gupta 《Macromolecular Symposia》2009,277(1):51-61
Poly(4-methyl-2-pentyne) (PMP) is an amorphous glassy disubstituted acetylene based polymer. The excellent gas-separation and mechanical properties of these polymers have stipulated their use as membrane material for vapor and gas separation. PMP is among the hydrocarbon disubstituted polyacetylenes which have been synthesized to date. This polymer combines excellent gas and vapor permeability with good resistance to organic solvents. As was shown recently, PMP offers promise in the manufacture of nanocomposite membranes for the separation of various hydrocarbon mixtures. It is also of importance as its monomer, 4-methyl- 2-pentyne, can be easily derived from commercial compounds, 4-methyl-2-pentene or methyl isobutyl ketone, produced on a large scale. It is known that PMP exists in cis and trans configurations. Synthetic conditions, e.g., the used catalyst, temperature, solvent etc., of substituted polyacetylenes decide percentage of different configurations (cis or trans). Different geometries of macromolecules can influence the supramolecular structure of the polymer, which primarily defines its properties, such as solubility, permeability, sorption, etc. Qualitative assignments of few bands of IR spectra are reported earlier. We present here, complete normal mode analysis and dispersion curves for PMP using Wilson GF matrix method modified by Higgs using Urey-Bradley force field. Dispersion curves for PMP are drawn and salient features are discussed. Predicted values of specific heat via density-of-states are also reported. 相似文献
73.
Conductivities of some tetraalkylammonium halides, viz. tetrabutylammonium bromide (Bu4NBr), tetrapentylammonium bromide (Pen4NBr), tetrahexylammonium bromide (Hex4NBr) and tetraheptylammonium bromide (Hep4NBr) were measured at 298.15 K in THF + C6H6 mixtures with 10, 20, 30 and 40 mass% of C6H6. A minimum in the conductance values was observed as concentration increases, which dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M+ + X− ↔ MX, KP) and triple-ions (2 M+ + X− ↔ M2X+; M+ + 2X− ↔ MX2−, KT). A linear relationship between the triple-ion formation constants [log(KT/KP)] and the salt concentrations at the minimum conductivity (log Cmin) was given for all salts in C6H6 + THF mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R4N+ X−). 相似文献
74.
Mahendra Thunga Bhabani K. Satapathy Manfred Stamm Konrad Knoll 《European Polymer Journal》2009,45(2):537-314
The phase behaviour of symmetric (LN4) and asymmetric (LN3) triblock copolymers based on styrene-b-(styrene-co-butadiene)-b-styrene (S-SB-S) and their blends have been studied using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) and were correlated with rheological properties. A direct control over the final morphology and segregation strength for the block copolymer blends was achieved by blending of LN3 and LN4. The interaction parameter (χ) for LN4 is extracted by fitting the SAXS patterns at temperatures well above the ODT in consistency with Leibler mean-field structure-function for ABA triblock copolymers. A weak temperature dependency of χ has been observed which revealed that the phase behaviour in LN4 is mainly controlled by the entropic term. In the low frequency regime a non-terminal flow behaviour was observed in LN3 revealing the persistence of ordered structure within the experimental temperature range whereas a terminal flow behaviour with composition fluctuation was observed in LN4. G′ vs. G″ plots indicated a solid-like elastic melt behaviour for LN3 whereas presence of ODT over a broad temperature range was observed for LN4. ODT is observed to increase non-linearly with increase in LN3 content in the blends. ODT behaviour of the blends further reveals that the blends shift from weak-segregation to intermediate-segregation strength with the increase in LN3 content. The improvement in the state of ordering along with the change in morphology with the increase of LN3 content is attributed to co-surfactant effect between the PS end-blocks of LN3 and LN4 inside PS-rich phase. 相似文献
75.
Ashok B. Bhise Dattatray J. Late Bhaskar R. Sathe Mahendra A. More Imtiaz S. Mulla Vijayamohanan K. Pillai Dilip S. Joag 《Solid State Sciences》2009,11(6):1114-1117
Tin oxide submicronwires doped with Fe element were prepared by the thermal evaporation method. Morphological and structural characterizations revealed wires with sub micron size and crystalline in nature. The field electron emission from the single Fe:SnO2 wire was carried out in conventional field emission microscope. The Fowler–Nordheim plot obtained from I–V characteristics of the wire showed a linear behavior typical that of metal. The field enhancement factor estimated from the slope of the F–N plot is 7455 cm?1, indicating that the field emission is from nanometric features of the emitter. A current density of 10 A/cm2 has been obtained at an applied field of 4.845 × 103 V/μm. The field emission current–time record at a current level of 1 μA for more than 3 h duration is promising for various field emissions based applications. 相似文献
76.
We report an accurate method to measure the group-velocity dispersion (GVD) of transparent materials by use of spectrally resolved phase-shifting interferometry. The GVD of silica glass slide measured using an eight-step phase-shifting algorithm agrees well with that calculated using the Sellmeier dispersion equation over the entire visible wavelength region, with a rms error of < or =0.0036 microm(-2), better than that of other measurement methods reported so far. 相似文献
77.
Vijay Singh Jun-Jie Zhu Manoj Tiwari Manish Soni Mahendra Aynayas Seok-Hee Hyun R. Narayanan Manoj Mohapatra V. Natarajan 《Journal of Non》2009,355(50-51):2491-2495
Strong blue-green light emitting Eu doped SrAl2O4 phosphor was synthesized by a low-temperature initiated, self-propagating and gas producing combustion process in a very short time (<5 min). The prepared powder was characterized by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy. The excitation spectrum shows a peak at 397 nm. Upon excitation at 397 nm, the emission spectrum exhibits a well defined broad band with maximum at 493 nm corresponding to 4f65d → 4f7 transition. Electron paramagnetic resonance (EPR) measurements at X-band showed low field signals due to Eu2+ ions in SrAl2O4:Eu. 相似文献
78.
Qualitative and quantitative analyses of molecular interaction prevailing in ionic liquid tetrabutylphosphonium methanesulfonate [Bu4PMS] in dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF) and N,N-dimethyl acetamide (DMA) probed by electrical conductances and Fourier transform infrared (FT-IR) measurements have been reported at 298.15 K. Corresponding conductance data have been analysed using the Fuoss conductance-concentration equation (1978) for ion pair formation. The limiting ionic conductances (λ o ± ) have been estimated from the appropriate division of the limiting molar conductivity value of tetrabutylammonium tetraphenylborate [Bu4NBPh4] as the ‘reference electrolyte’. The diffusion coefficient (D) has been obtained from Stokes-Einstein relation and the ionic mobility (i) for [Bu4P]+ and MS? using appropriate equation. The results have been discussed in terms of dipole-dipole interactions, hydrogen bond formation and structural aspect of the solvents and configurational theory. The FT-IR spectra have also been studied to predict the interactions occurring in the system. Figure
Exploration of significant interaction of ionic liquid in some liquid systems having a wide range of industrial application 相似文献
79.
Ranjan K. Bhatt Satyasheel Sharma Mahendra Nath 《Monatshefte für Chemie / Chemical Monthly》2012,54(1):309-316
Abstract
An improved synthetic procedure is developed for the regioselective nitration of a phenyl group of meso-tetraphenylporphyrin by using NaNO2 in a mixture of trichloroacetic acid and AcOH. The meso-(4-nitrophenyl)porphyrins are successfully reduced to corresponding meso-(4-aminophenyl)porphyrins by SnCl2 under acidic conditions. In addition, an efficient one-pot methodology for synthesizing a series of novel meso-substituted porphyrinic thiazolidinone conjugates is developed by reacting meso-(4-aminophenyl)porphyrins with various aromatic aldehydes and mercaptoacetic acid in refluxing toluene using La(OTf)3 as a catalyst. The products obtained are characterized on the basis of their spectral data. Preliminary photophysical properties of the newly synthesized compounds are reported. 相似文献80.
Kanchan Verma Yogesh Kumar Tailor Sarita Khandelwal Monu Agarwal Esha Rushell Sakshi Pathak Yogita Kumari Kamlendra Awasthi Mahendra Kumar 《应用有机金属化学》2020,34(10):e5836
An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated indolo[3,2-c]quinolines involving three component sequential reaction of phenylhydrazine, o-aminoacetophenone and cyclic ketones using nanostructured terbium doped TiO2 as recyclable and reusable heterogeneous catalyst. The nanostructured catalyst was synthesized successfully and characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), EDX and Fourier transform infra-red spectroscopy (FTIR). The substitution of Ti+4 with Tb+3 and the formation of Ti-O-Tb bonds as a result of doping of Terbium with TiO2 NPs increases the catalytic efficiency and facilitates the reaction to provide the products in excellent yields. The present protocol with special features; operational simplicity, atom-economy, mild reaction conditions, environmental sustainability and high synthetic efficiency with recyclability and reusability of catalyst has been reported for the first time to synthesize spiroannulated indoloquinolines and expecting to provide the library of promising new leads in drug discovery research. 相似文献