全文获取类型
收费全文 | 207篇 |
免费 | 9篇 |
专业分类
化学 | 155篇 |
力学 | 3篇 |
数学 | 10篇 |
物理学 | 48篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 16篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 23篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有216条查询结果,搜索用时 15 毫秒
21.
A straightforward method has been developed for the synthesis of 1-amidomethyl-imidazo[1,2-a]pyridines by Yb(OTf)3 catalyzed three-component reaction of aldehydes, acetamide, and imidazo[1,2-a]pyridines. A series of substituted 3-substituted imidazo[1,2-a]pyridines were synthesized in moderate to good yield (21–74%) under mild reaction condition and the catalyst was recycled for four cycles. 相似文献
22.
Q.M. Zhang Z.-Y. Cheng V. Bharti 《Applied Physics A: Materials Science & Processing》2000,70(3):307-312
This paper presents experimental results showing that in a certain composition range and under a proper electron-irradiation treatment, a normal ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer can be converted into a material exhibiting many typical features of relaxor ferroelectrics, suggesting that this is a new class of relaxor ferroelectric material. Furthermore, the irradiated copolymer can generate giant electrostriction (ƽ%) with a high elastic energy density. The X-ray diffraction results obtained from the irradiated copolymer under electric field, indicate that the observed polarization and strain responses are mainly due to the local phase transformation from a non-polar phase to a polar phase. 相似文献
23.
Neelesh Bharti Shukla 《Polymer Degradation and Stability》2009,94(8):1238-1244
The oxidative degradation of poly(acrylic acid) (PAA), a water soluble polymer, was studied at various temperatures with different concentrations of persulfates, potassium persulfate (KPS), ammonium persulfate (APS) and sodium persulfate (SPS). The photodegradation of PAA was also examined with APS as oxidizer. The degraded samples were analyzed for the time evolution of molecular weight distribution by gel permeation chromatography. A theoretical model based on the continuous distribution kinetics was developed that accounted for the polymer degradation and the dissociation of persulfate. The rate coefficients for the oxidative and photooxidative degradation of PAA were determined from the parametric fit of the model with experimental data. The rate of degradation increased with increasing amount of persulfate in both oxidative and photooxidative degradation. The rate of degradation also increased with increasing temperature in the case of oxidative degradation. 相似文献
24.
Sanjay K. Bharti Saurabh K. Patel Gopal Nath Ragini Tilak Sushil K. Singh 《Transition Metal Chemistry》2010,35(8):917-925
Six Cu(II) complexes of Schiff base ligands of arylidene-2-(4-(4-bromo/methoxy-phenyl)thiazol-2-yl) hydrazines have been synthesized,
characterized and screened for DNA cleavage and antimicrobial activities. The chemical structures of the complexes were deduced
by physicochemical and spectroscopic methods. Elemental analyses indicated that the stoichiometry of the complexes is CuL2 (L = Schiff base ligand). The DNA cleavage activities of the complexes were evaluated by agarose gel electrophoresis in the
presence and absence of oxidant (H2O2) and free radical scavenger (DMSO). All the six complexes showed significant nuclease activity in the presence of H2O2, and two of the complexes showed moderate nuclease activity even in the absence of oxidant. The complexes did not show nuclease
activity in the presence of free radical scavenger. The compounds were tested for activity against selected bacteria and fungi. 相似文献
25.
A polycrystalline rare earth double perovskite oxide, strontium cerium antimonate, Sr2CeSbO6 (SCS), is synthesized by solid-state reaction technique. The X-ray diffraction pattern at room temperature of SCS shows orthorhombic phase with the lattice parameters, a = 8.84 Å, b = 6.22 Å, and c = 5.83 Å. Fourier transform infrared spectrum shows two phonon modes of the sample at around 550 cm?1 and 670 cm?1 due to the antisymmetric SbO6 stretching vibration. The compound shows significant frequency dispersion in its dielectric properties. The complex impedance plane plots show that the relaxation (conduction) mechanism in SCS is purely a bulk effect arising from the semiconductive grains having the grain resistance = 3.8 × 106 Ω and the grain capacitance = 1.03 × 10?10 F at 603 K. The frequency-dependent conductivity spectra follow the universal power law. The conductivity at 100 Hz varies from 2 × 10?7 Sm?1 to 1.97 × 10?5 Sm?1 with the increase of temperature from 303 K to 703 K, respectively. The relaxation mechanism of the sample in the framework of electric modulus formalism is modelled by Davidson–Cole equation. The activation energy of the sample, calculated from both conductivity and modulus spectra is found to be ~0.15 eV. Such a value of activation energy indicates that the conduction mechanism for SCS is due to electron hopping. The scaling behaviour of imaginary electric modulus suggests that the relaxation describes the same mechanism at various temperatures. 相似文献
26.
27.
Singh AK Chawla R Rai A Yadav LD 《Chemical communications (Cambridge, England)》2012,48(31):3766-3768
NHC-catalysed azalactone ring-opening and piperidine ring-closing cascade with α,β-unsaturated aldehydes (enals) in a one-pot operation is reported. The present reaction cascade offers a convenient method for a highly diastereoselective synthesis of multifunctionalised piperidines in excellent yields under mild conditions. 相似文献
28.
29.
A numerical study of the steady forced convection heat transfer from an unconfined circular cylinder
Forced convection heat transfer from an unconfined circular cylinder in the steady cross-flow regime has been studied using
a finite volume method (FVM) implemented on a Cartesian grid system in the range as 10 ≤ Re ≤ 45 and 0.7 ≤ Pr ≤ 400. The numerical results are used to develop simple correlations for Nusselt number as a function of the pertinent dimensionless
variables. In addition to average Nusselt number, the effects of Re, Pr and thermal boundary conditions on the temperature field near the cylinder and on the local Nusselt number distributions
have also been presented to provide further physical insights into the nature of the flow. The rate of heat transfer increases
with an increase in the Reynolds and/or Prandtl numbers. The uniform heat flux condition always shows higher value of heat
transfer coefficient than the constant wall temperature at the surface of the cylinder for the same Reynolds and Prandtl numbers.
The maximum difference between the two values is around 15–20%. 相似文献
30.
Expedient Protocols for the Installation of 1,5‐Benzoazepino‐Based Privileged Templates on the 2‐Position of 1,4‐Benzodiazepine Through a Phenoxyl Spacer 下载免费PDF全文
An efficient novel strategy for the hetero‐annulation of 2‐chloro‐1,4‐benzodiazepine ring, substituted on its 5‐position with a carboxamido group ( 5 ), has been developed to allow the incorporation of 1,5‐benzodiazepine, 1,5‐benzothiazepine, and 1,5‐benzoxazepine ( 8 , 9 , 10 , 11 , 12 , 13 ) rings through their dimethylaminomethylene ketone intermediate ( 7 ). 相似文献