全文获取类型
收费全文 | 226篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 140篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 31篇 |
物理学 | 58篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 14篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有238条查询结果,搜索用时 62 毫秒
161.
An efficient and operationally simple method for C3-alkylation of 4-hydroxycoumarins has been developed under acidic medium giving good yields of the products. In the present method, a reusable Amberlite® IR-120 (H+ form) was used as an acid catalyst and secondary benzyl alcohols were used as alkylating agents. The obtained 3-alkylated-4-hydroxycoumarins offered an easy access for the synthesis of 3,4-disubstituted coumarins by way of Pd-catalyzed coupling reactions. 相似文献
162.
Raman scattering studies on 1–4 dihydroxyanthraquinone (DHAQ) at Ag electrode have been carried out to investigate the enhancement
in the spectral line intensity after adsorption. Charge transfer between the adsorbate and the substrate is more pronounced
for certain normal modes of vibration. It is found that the DHAQ molecules are lying with their molecular plane on the top
of the metal surface. Laser induced fluorescence spectra of DHAQ have also been analysed with a view to assign the relative
orientation of absorption and emission dipoles. 相似文献
163.
By making a combination of both point contact and barrier type tunnel junctions on a single sample of the highT
c superconductor BSCCO (2212) single crystal, we have shown that as the tunneling tip is slowly retracted from the surface
a point contact junction gradually evolves from a N-S short to a high resistance tunnel junction. The scaled dynamic conductance
(dI/dV) of this point contact tunnel junction becomes almost identical to that of a conventional barrier type tunnel junction and
both show a linear dI/dV —V curve. The observation implies that at high resistance a point contact junction behaves in the same way as a barrier type
tunnel junction. We suggested that the almost linear tunneling conductance obtained in both the cases most likely arises due
to an intrinsic characteristic of the surface of the crystal comprising of a mosaic of superconducting regions of the order
of a few nanometers. We also conclude that the barrierless (N-S) point contact obtained by piercing the surface oxide layer
of the crystal shows Andreev reflection which we suggest as the origin of the zero bias anomaly often observed in point contact
junctions. 相似文献
164.
Shaikshavali Petnikota Naresh K. Rotte Vadali V. S. S. Srikanth Bhanu S. R. Kota M. V. Reddy Kian P. Loh B. V. R. Chowdari 《Journal of Solid State Electrochemistry》2014,18(4):941-949
Few-layered graphene (FLG) with specific surface area of only ~8.2 m2 g?1 was synthesized from graphene oxide (GO) using microwave-assisted exfoliation. GO was prepared using modified Hummers method. Few-layered nature of the exfoliated material was confirmed by electron microscopy, X-ray and electron diffraction, and Raman spectroscopy. Coin cells were fabricated using FLG as an anode and lithium metal as a counter electrode. The cells were tested using cyclic voltammetry and galvanostatic cycling techniques. FLG showed reversible capacity values of ~400 and ~250 mAh g?1 at current rates of 0.1 and 1 C, respectively. Columbic efficiency was more than 98 % while cycle to cycle capacity fading was less than 2 %. Maximum discharge or charging capacity was below 0.3 V, a preferable characteristic for achieving ideal anodic behavior. 相似文献
165.
Velázquez F Arasappan A Chen K Sannigrahi M Venkatraman S McPhail AT Chan TM Shih NY Njoroge FG 《Organic letters》2006,8(4):789-792
[reaction: see text] A highly stereoselective synthesis of beta-amino sulfones and sulfonamides via addition of sulfonyl anions to chiral N-sulfinyl imines is described. The addition reaction proceeds in good yield (75-99%) and stereoselectivity. 相似文献
166.
We study the dynamics of entanglement in a two-qubit system interacting with a squeezed thermal bath via a dissipative system-reservoir interaction with the system and reservoir assumed to be in a separable initial state. The resulting entanglement is studied by making use of concurrence as well as a recently introduced measure of mixed state entanglement via a probability density function which gives a statistical and geometrical characterization of entanglement by exploring the entanglement content in the various subspaces spanning the two-qubit Hilbert space. We also make an application of the two-qubit dissipative dynamics to a simplified model of quantum repeaters. 相似文献
167.
Hans-Christian Herbig Srikanth B. Iyengar Markus J. Pflaum 《Letters in Mathematical Physics》2009,89(2):101-113
We discuss BFV deformation quantization (Bordemann et al. in A homological approach to singular reduction in deformation quantization,
singularity theory, pp. 443–461. World Scientific, Hackensack, 2007) in the special case of a linear Hamiltonian torus action.
In particular, we show that the Koszul complex on the moment map of an effective linear Hamiltonian torus action is acyclic.
We rephrase the nonpositivity condition of Arms and Gotay (Adv Math 79(1):43–103, 1990) for linear Hamiltonian torus actions.
It follows that reduced spaces of such actions admit continuous star products.
相似文献
168.
We study the local decodability and (tolerant) local testability of low‐degree n‐variate polynomials over arbitrary fields, evaluated over the domain {0,1}n. We show that for every field there is a tolerant local test whose query complexity depends only on the degree. In contrast we show that decodability is possible over fields of positive characteristic, but not over the reals. 相似文献
169.
6-Arylidene-3-methyl-6,7,8,9-tetrahydro-5H-benzo[a]cyclohepten-5-ones (2a-h), obtained by the condensation of 3-methylbenzocyclohepten-5-one 1 with appropriate aromatic aldehydes, on reaction with Lawesson's reagent in xylene yielded phosphorus containing compounds 3a-h. A number of these compounds showed promising anti-inflammatory activity. 相似文献
170.
A novel route towards chiral trans-fused polyether lactones 7 and 12 has been developed starting with commercially available furfural. Sharpless kinetic resolution and ring-closing metathesis reactions served as key steps in the strategy. 相似文献