全文获取类型
收费全文 | 265篇 |
免费 | 8篇 |
专业分类
化学 | 181篇 |
晶体学 | 8篇 |
力学 | 18篇 |
数学 | 9篇 |
物理学 | 57篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 19篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有273条查询结果,搜索用时 62 毫秒
91.
R. Saravanan S. Israel Y. Ono K. Ohno M. Isshiki T. Kajitani R. K. Rajaram 《Crystal Research and Technology》2006,41(3):259-267
The bonding between the atoms in the II‐VI compound semiconductors has always been a subject of rigorous research because of their tremendous applications in a variety of fields. The bonding and ionic character in CdTe at 300 and 200 K have been determined quantitatively as well as qualitatively using single crystal X‐ray data sets and MEM (Maximum Entropy Method) as the tool for the reconstruction of the electron densities distributed within the unit cell. The ab‐initio band calculation of the total and valence charge densities have been carried out theoretically by means of the local density approximation (LDA) method in support of the experimentally derived MEM maps. The difference density maps show fewer errors between the theoretical and experimental charge density and thus gives credence to the results accordingly. Along the bonding direction [111], the mid‐bond electron densities are found to be 0.233 e/Å3 and 0.284 e/Å3 at 300 K and 200 K at distances 1.4026 Å and 1.4036 Å respectively. The densities along [100] and [110] show an increase in the charge concentration at the bond at lower temperatures. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
92.
Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel 总被引:1,自引:0,他引:1
A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2)
of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one
millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with
after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two
configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated
by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated
using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and
computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also
estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and
pitching moment components.
相似文献
93.
94.
95.
A three-component accelerometer balance system is used to study the drag reduction effect of an aerodisc on large angle blunt cones flying at hypersonic Mach numbers. Measurements in a hypersonic shock tunnel at a freestream Mach number of 5.75 indicate more than 50% reduction in the drag coefficient for a 120° apex angle blunt cone with a forward facing aerospike having a flat faced aerodisc at moderate angles of attack. Enhancement of drag has been observed for higher angles of attack due to the impingement of the flow separation shock on the windward side of the cone. The flowfields around the large angle blunt cone with aerospike assembly flying at hypersonic Mach numbers are also simulated numerically using a commercial CFD code. The pressure and density levels on the model surface, which is under the aerodynamic shadow of the flat disc tipped spike, are found very low and a drag reduction of 64.34% has been deduced numerically. 相似文献
96.
Abstract Thiazolidin-4-ones are known to exhibit diverse biological activities such as antimicrobial, anticancer, antidiarrheal, anticonvulsant, antidiabetic, antihistaminic, and antifungal activities. In the present investigation, a series of 2-haloacetamides was prepared by reacting chloroacetyl chloride with amines in dry benzene under reflux conditions. The formed 2-haloacetamides reacted with potassium thiocyanate in refluxing dry acetone to afford new 2-iminothiazolidin-4-ones. The 5-arylidene-2-imino-3 (napthalen-2yl)-thiazolidin-4-ones were prepared by condensing 2-iminothiazolidin-4-ones with substituted benzaldehydes. All the products were characterized by infrared, mass, and 1H and 13C NMR techniques. 相似文献
97.
Venlafaxine hydrochloride is a phenyl ethylamine derivative, used for the treatment of depression. During the process development of venlafaxine hydrochloride, six process-related potential impurities were detected in high-performance liquid chromatography. All these impurities were identified, synthesized, and subsequently characterized by their respective spectral data (IR, mass, 1H NMR, and 13C NMR) as described in this article. 相似文献
98.
Anju Chopra Dheer Singh R. Manna S. Saravanan M. I. S. Sastry M. B. Patel B. Basu 《Chromatographia》2014,77(11-12):845-851
A GC and IR based protocol was developed for monitoring the isobutene dimerisation process wherein the complete characterisation of the products was carried out by GC coupled with mass spectrometry. In the dimerisation process, LPG from FCC process comprising a mixture of saturated and unsaturated C4 hydrocarbons is subjected to a dimerisation process using a catalyst to produce C8 hydrocarbons. The reaction is carried out keeping in view the demand for high-octane blending components in gasoline. The isooctene generated in the process (mainly from the dimerisation of isobutene) is converted into isooctane having the RON and MON value 100. The monitoring process requires the use of two different column chemistries, viz., a 100 m CPSIL PONA CB non-polar column for C8 and its isomers and an Alumina PLOT column for C4 hydrocarbons. A 100 m non-polar column does not separate the C4 mixture since the column is meant for gasoline range products containing C5 and above hydrocarbons. Therefore, a need was felt for an improvised method which can handle both the analyses simultaneously. A cryogenic oven program starting from 0 °C was developed for separating the isomers of C4 hydrocarbons and C8 hydrocarbons on a single column during the single run by Detailed Hydrocarbon Analyzer. The data obtained using the cryo programme was validated with data obtained using Alumina PLOT column on C4 mixture since the Alumina PLOT column is the widely accepted column chemistry for separating the C4 hydrocarbons. An IR method for the estimation of the total olefin content was developed using 2,2,4-trimethyl pentene-1 as the reference standard. The total olefins generated during the process were identified by GC–MS, quantified by DHA-FID and validated by infrared spectroscopy. A good correlation was found between GC and IR spectral results (correlation coefficient R 2 = 0.99). 相似文献
99.
A group of novel 2-aryl imidazole derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis.
An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dmip and dmtip) have been studied using
emission spectroscopy and it was detected that the two distinct ground state rotamers of I and II are responsible for the
normal and the tautomer emission respectively. In hydrocarbon solvent, the tautomer emission predominates over the normal
emission for both dmip and dmtip. This reveal that rotamer II is responsible for the tautomer emission and it is stabler than
rotamer I which causes the normal emission. In alcoholic solvent like ethanol, a dramatic enhancement of normal emission is
observed which was due to increased solvation, the more polar rotamer I become stabler than rotamer II. In dioxane—water mixtures
it is observed that the addition of water inhibits the ESIPT process due to the formation of the intermolecular hydrogen bonding
involving water. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited
states of the imidazole derivatives were performed and discussed. PES calculation indicates that the energy barrier for the
interconversion of two rotamers is too high in the excited state than the ground state. 相似文献
100.
Patil NR Melavanki RM Kapatkar SB Ayachit NH Saravanan J 《Journal of fluorescence》2011,21(3):1213-1222
The absorption and fluorescence spectra of three Carboxamides namely (E)-2-(4-Chlorobenzylideneamino)-N-(2-chlorophenyl)-4,
5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C1), (E)-N-(3-Chlorophenyl)-2-(3, 4-dimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C2) and (E)-N-(3-Chlorophenyl)-2-(3, 4, 5-trimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C3) have been recorded at room temperature in solvents of different polarities using dielectric constant (ε) and refractive
index (n). Experimental ground (μg) and excited (μe) state dipole moments are estimated by means of solvatochromic shift method and also the excited dipole moments are estimated
in combination with ground state dipole moments. It was estimated that dipole moments of the excited state were higher than
those of the ground state of all three molecules. Further, the changes in dipole moment (Dm \Delta \mu ) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter
(ETN E_T^N ) and the values are compared. 相似文献