全文获取类型
收费全文 | 455篇 |
免费 | 27篇 |
专业分类
化学 | 284篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 18篇 |
物理学 | 173篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 45篇 |
2010年 | 24篇 |
2009年 | 16篇 |
2008年 | 26篇 |
2007年 | 23篇 |
2006年 | 30篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有482条查询结果,搜索用时 15 毫秒
51.
A method to study domain structure in ferroelectrics, using pyroelectric effect is described. Variation of pyroelectric signal
from the surface of a triglycine sulphate crystal plate has been studied by scanning the surface of the crystal with a low
wattage He-Ne laser beam. The integrated pyroelectric signal is due to two components, namely, (1) the primary component arising
out of the change in spontaneous polarization with temperature and (2) the delayed component arising out of the possible polarization
reversal. The component of an electric field along the ferroelectric axis due to thermal hemisphere within the crystal plate
formed by the laser beam has been calculated and shown to exceed coercive field, making polarization reversal possible. The
delayed pyroelectric signal is a measure of polarization reversal within the patch illuminated and its observed variation
over the surface yields information of the domain structure. 相似文献
52.
53.
Mandira Sinha H. Majumdar P. Basu Subinit Roy R. Bhattacharya M. Biswas M. K. Pradhan R. Palit I. Mazumdar S. Kailas 《The European Physical Journal A - Hadrons and Nuclei》2010,44(3):403-410
Fusion excitation functions are measured for the system 6Li + 28Si using the characteristic $ \gamma$ -ray method, encompassing both the sub-barrier and above-barrier regions, viz, E lab = 7-24 MeV. Two separate experiments were performed, one for the above-barrier region ( E lab = 11-24 MeV) and another for the below-barrier region ( E lab = 7-10 MeV). The results were compared with our previously measured fusion cross-section for the 7Li + 28Si system. We observed the enhancement of the fusion cross-section at sub-barrier regions for both 6Li and 7Li , but the yield was substantially larger for 6Li . However, for well-above-barrier regions, a similar type of suppression was identified for both the systems. 相似文献
54.
Shailaja J Kaanumalle LS Sivasubramanian K Natarajan A Ponchot KJ Pradhan A Ramamurthy V 《Organic & biomolecular chemistry》2006,4(8):1561-1571
Photochemistry of 17 aryl alkyl ketones included within cation exchanged zeolites has been examined. In solution five of the 17 ketones undergo intramolecular hydrogen abstraction reaction even in the presence of a chiral amine and the rest are photoreduced to the corresponding alcohol. Within zeolites all 17 ketones yielded in presence of a chiral amine, the corresponding alcohol as the major product. When a chiral amine was used as the coadsorbent within alkali ion exchanged zeolites, enantiomerically enriched alcohol was formed in all cases. The best chiral induction was obtained with phenyl cyclohexyl ketone (enantiomeric excess: 68%). 1H-13C Cross Polarization Magic Angle Spinning (CP-MAS) experiments, with a model ketone (perdeuterated acetophenone) and chiral amine (pseudoephedrine) included within MY zeolites, suggested that the cation brings the reactant and the chiral amine closer. The role of the cation in such a process is also revealed by the computation results. The results presented here highlight the importance of a supramolecular structure in forcing a closer interaction between a reactant and a chiral inductor that could be used to achieve asymmetric induction in photoproducts. 相似文献
55.
56.
Pabitra Kumar Pradhan Manoj Kumar Pandey 《Mathematical Methods in the Applied Sciences》2020,43(9):6081-6092
The system of generalized Chaplygin gas equations with a coulomblike friction term has been investigated by using the famous Lie symmetry method. A direct and systematic algorithm based on the adjoint transformation and invariants of the admitted Lie algebras is then used to construct one- and two-dimensional optimal system of the Chaplygin gas equations. Inequivalent classes of group invariant solutions are then obtained using the one-dimensional optimal system. Further, the evolutionary behaviour of the weak discontinuity wave within the state characterized by one of the group invariant solutions is investigated in detail, and certain observations are noted in respect to their contrasting behaviour. 相似文献
57.
M. Sinha H. Dutta S.K. Pradhan 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):367-369
Nanocrystalline Mg–Zn-ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe2O3. A non-stoichiometric ferrite phase is noticed to form after 3 h of milling when particles of starting materials became nano-sized. After 25 h of milling, stoichiometric ferrite phase is formed with 9 nm particle size. Post annealing study of ball-milled sample reveals that the nanocrystalline ferrite phase is stable up to 873 K and then starts to decompose into individual starting phases. However, heat treatment of unmilled stoichiometric powder mixture even at 1473 K for 1 h duration does not result in formation of stoichiometric Mg–Zn-ferrite phase. 相似文献
58.
59.
Pradhan Susanta Kumar Ambade Balram 《Journal of Radioanalytical and Nuclear Chemistry》2019,320(2):459-466
A modified LED fluorimetry determination of uranium in Nb/Ta minerals has been developed. The mineral is brought into solution by fusion with mixed phosphate flux (NaH2PO4, H2O and Na2HPO4). Iron quenches uranium fluorescence when it is present above the ratio of (iron to uranium) 100. Uranium is separated in ethyl acetate by solvent extraction and then stripped back into pyrophosphate buffer (pH ~ 7) prior to its LED fluorimetry determination. This modified method has been applied for the determination of uranium in synthetic mixtures and Nb/Ta minerals including Certified Reference Materials (X1807) with high degree of accuracy and precision.
相似文献60.
Tanmay Gupta Ambikeya Pradhan Sanchita Bandyopadhyay‐Ghosh Subrata Bandhu Ghosh 《先进技术聚合物》2019,30(9):2392-2401
Lightweight and flexible biosensors that can sustain mechanical deformation and can be adhered to human skin is an interesting field of study. In the current article, a systematic study on development of thermally exfoliated graphene oxide (TEGO)–reinforced poly(vinyl alcohol) (PVA)–based conductive hydrogel nanocomposites has been reported. The free‐standing hydrogels were synthesized using controlled and repetitive freeze‐thaw cycles. The samples were then studied for their mechanical as well as electrical properties. The hydrogels were characterized for their microstructural, chemical, and rheological properties to understand the observed macroscopic properties. Additionally, a study on the behavior of hydrogels immersed in phosphate‐buffered saline (PBS) was carried out to investigate their hydrolytic stability within simulated biological environment. Overall, the nanocomposite hydrogels demonstrated excellent static and dynamic mechanical performance, stability in PBS, considerable electrical conductivity, and significant electrical response to applied external stress, establishing their potential for use as flexible biosensors. 相似文献