全文获取类型
收费全文 | 91篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 49篇 |
力学 | 1篇 |
数学 | 7篇 |
物理学 | 21篇 |
无线电 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1973年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有96条查询结果,搜索用时 15 毫秒
1.
2.
In developing a method for possible low level isotopic enrichment, which uses to advantage the equilibrium isotope effect
observed during U(1V)-U(VI) electron exchange reaction in sulphate solutions, details of a solvent extraction process involving
high concentration of a mixture of U(IV) and U(VI) and at low acid concentrations, are described. The extraction behaviour
of uranium under these conditions is discussed. During the extraction with amines, U(IV) tended to get oxidised in sulphate
solutions. 相似文献
3.
K. L. N. Rao J. P. Shukla B. Venkataramani 《Journal of Radioanalytical and Nuclear Chemistry》1995,189(1):107-114
Ammonium molybdophosphate (AMP) was irradiated with electrons up to a dose of 1 MGy. X-ray diffraction patterns and FT-IR of irradiated and control AMP samples were recorded. Uptake of137Cs from nitric acid in the range of 0.2 to 10 mol·dm–3 was estimated by a batch equilibration technique. AMP undergoes perceptible changes in its physico-chemical characteristics on irradiation with electrons. Uptake of137Cs from nitric acid by irradiated AMP was nearly the same as the control AMP in the nitric acid concentration range of 6 to 10 mol·dm–3 and relatively higher in the range of 0.2 to 6 mol·dm–3. The results are discussed in terms of available information on the physicochemical properties of 12-heteropoly acids and their salts. 相似文献
4.
G. Manasa Arvind K. Bhakta Zineb Mekhalif Ronald J. Mascarenhas 《Electroanalysis》2019,31(7):1363-1372
Increased concern over the risk resorcinol (RS) pose to ecology and humans, led to its position in European Union Category 1 list of endocrine disruptors. Legal measures restricted RS utilization and hence crucial to monitor its levels in the environment. Herein we report development of highly efficient and economically viable electrochemical sensor for quantitative determination of RS based on 77Maghemite/MultiWall Carbon Nanotube (M/MWCNT) modified carbon paste electrode. M/MWCNT was synthesized via strategic IR irradiation for the first time, a promising approach to overcome other complicated chemical routes. Powder X‐ray diffraction (PXRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and Energy dispersive X‐ray (EDX) were used for characterization. Using Differential Pulse Voltammetry (DPV), we report the lowest detection limit at 0.02 μM. The potential application of the sensor was accomplished as a result of excellent recoveries made from real samples fortified with RS. Results indicated the proficiency of the sensor reliable for rapid, onsite monitoring of RS water contamination and in biological matrices. 相似文献
5.
Barium Manganate Oxidation in Organic Synthesis: Part—IV: Oxidation of Aldehydes to Carboxylic Acids
The oxidation of aldehydes to corresponding carboxylic acids by barium manganate under heterogeneous conditions is described. Aromatic aldehydes were smoothly converted to carboxylic acids while aliphatic aldehydes underwent polymerisation. 相似文献
6.
The oxidative cyclisation of bsenzylideneamino anilines, phenols and thiophenols to benzimidazoles, benzoxazoles and benzthiazoles respectively using barium manganate is described. 相似文献
7.
Semen B. Kharchenko Rangaramanujam M. Kannan Jeff J. Cernohous Shivshankar Venkataramani Gaddam N. Babu 《Journal of Polymer Science.Polymer Physics》2001,39(21):2562-2571
With the increase in sophisticated synthesis methods, it appears that polymer architecture may be a tunable property. Therefore, the role of architecture in rheological and processing properties has received renewed attention, mainly because of dendrimer synthesis and metallocene‐catalyst technology. Linear polymers and hyperbranched polymers represent two ends of branching complexity. Some previous studies have suggested that hyperbranched polymers may behave like unentangled polymers, whereas others have proposed that they exhibit the properties of soft colloids. In an effort to compare the responses of linear and hyperbranched polymers, we synthesized starlike hyperbranched polystyrenes (HBPSs) of various branch lengths and numbers of branches. The HBPSs used in this study were unentangled or weakly entangled, allowing us to study the effect of branch density more readily. Two linear polystyrene (L‐PS) melts and two HBPSs were studied. Using a custom‐built rheooptical apparatus, we characterized the rheology and flow birefringence of these materials. To our knowledge, these are the first flow birefringence measurements on highly branched polymer melts. Our results suggest that the flow behavior of HBPS is significantly different from that of L‐PS: (1) HBPS shows nonterminal behavior in the low‐frequency rheological response; (2) when the stress‐optical rule (SOR) holds, the stress‐optical coefficient of HBPS is much lower than those of analogous linear polymers; and (3) when the branch density is high and the branch length is sufficiently low, the SOR fails for these homopolymer melts. A significant increase in the birefringence for a given amount of stress in the low‐frequency region suggests that there may be a soft core in these materials due to the strong preferential radial orientation of chain segments near the center of a molecule versus those near the periphery. The predominantly elastic response of the soft structures may be responsible for the enhanced form birefringence. Our preliminary results indicate that these materials may exhibit both polymeric and soft‐colloid natures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2562–2571, 2001 相似文献
8.
We address the problem of finite impulse response (FIR) filter design for uniform multiple-input multiple-output (MIMO) sampling. This scheme encompasses Papoulis' generalized sampling and several nonuniform sampling schemes as special cases. The input signals are modeled as either continuous-time or discrete-time multiband input signals, with different band structures. We present conditions on the channel and the sampling rate that allow perfect inversion of the channel. Additionally, we provide a stronger set of conditions under which the reconstruction filters can be chosen to have frequency responses that are continuous. We also provide conditions for the existence of FIR perfect reconstruction filters, and when such do not exist, we address the optimal approximation of the ideal filters using FIR filters and a minmax l/sub 2/ end-to-end distortion criterion. The design problem is then reduced to a standard semi-infinite linear program. An example design of FIR reconstruction filters is given. 相似文献
9.
A new construction of 16-QAM Golay complementary sequences 总被引:2,自引:0,他引:2
Chan Vee Chong Venkataramani R. Tarokh V. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(11):2953-2959
We present a new construction of 16-QAM Golay sequences of length n = 2/sup m/. The number of constructed sequences is (14 + 12m)(m!/2)4/sup m+1/. When employed as a code in an orthogonal frequency-division multiplexing (OFDM) system; this set of sequences has a peak-to-mean envelope power ratio (PMEPR) of 3.6. By considering two specific subsets of these sequences, we obtain new codes with PMEPR bounds of 2.0 and 2.8 and respective code sizes of (2 + 2m)(m!/2)4/sup m+1/ and (4 + 4m)(m!/2)4/sup m+1/. These are larger than previously known codes for the same PMEPR bounds. 相似文献
10.
Anasuya Datta C. M. Srivastava N. Venkataramani 《Physica C: Superconductivity and its Applications》1993,210(3-4):408-412
We have examined the DC electrical resistivity of RE-123 superconductors (where RE is a rare earth element) on the basis of a model of correlated electron transfer arising from the electron-phonon interaction. The small polaron stabilization energy (εp) has been obtained from the fitting of the normal state resistivity data. A correlation between the lattice parameters of the unit cell and εp has been observed which is explained on the basis of fermiology. 相似文献