全文获取类型
收费全文 | 77篇 |
免费 | 1篇 |
专业分类
化学 | 32篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 8篇 |
物理学 | 32篇 |
综合类 | 2篇 |
出版年
2022年 | 2篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 5篇 |
2011年 | 7篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2007年 | 3篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 2篇 |
1998年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1987年 | 2篇 |
1984年 | 4篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有78条查询结果,搜索用时 218 毫秒
1.
A new method for the preparation of the synthon (±)-2,6,7,7a-tetrahydro-1β-hydroxy-4-formyl-7aβ-methylindene (1,a) for the
total synthesis of steroids in both (±) and (+) forms, starting from the known β-ketoester, (±)-methyl 1β-t-butoxy-5,6,7,7a-tetrahydro-7aβ-methyl-5-keto-4-indancarboxylate (2,a) has been described. An alternative route to (1,a) has
been investigated. Although the compound, (±)-1β-hydroxy-5,6,7,7a-tetrahydro-7aβ-methyl-5-keto-4-methoxymethylindan (2,b)
could not be prepared, interesting pathways leading to two unexpected products, (±)-5,6,7,7a-tetrahydro-4,7a-dimethyl-5H-indene-1,5-dione
and (±)-2,6-diketo-3-methyltricyclo-(5,2,1,0)decan-8-ol (3 and 4), were encountered during an attempted annelation reaction
of the ketone, N-diethylamino-5-methoxypentan-3-one (6), with 2-methylcyclopentan-1,3-dione (5). Trapping of the intermediate,
(±)-3a,4,5,6,7,7a-hexahydro-3a-hydroxy-4-methylene-7a-methylindene-1,5-dione (7), through the formation of the adduct, (±)-3a,4,5,6,7,7a-hexahydro-3a-hydroxy-4-(1′,
3′-diketo-2′-methylcyclopentano-2′-methylene)-7a-methylindene-1,5-dione (8), established the mechanism of the formation of
the products (3 and 4). 相似文献
2.
3.
The structure of the abnormal product 1a formed in the Knoevenagel condensation of 2-carbethoxycyclohexanone and malononitrile has been further confirmed. Oxidation of the tetrahydroisoquinoline 3b using Na2Cr2O-AcOH-H2SO4 gave the keto isoquinoline 3d and the isoquinoline-1-carboxylic acid 5a. The acid chloride of 5a was condensed with diethyl ethoxymagnesiomalonate to afford after decarbethoxylation the methyl ketone 5d which on Baeyer-Villiger oxidation gave a mixture of the acetate 1g and the title compound 1b. The unambiguous synthesis of 1b confirms the structure assigned earlier to the title compound also formed during the partial hydrolysis of the diethoxy compound 1c. Condensation of 2-acetylcyclohexane-1,3-dione with malononitrile gave the quinoline derivative 4c which on ethylation yielded the ketoquinoline 4d. The present studies have confirmed that the quinoline compound 4a is also formed in the condensation of 2-acetylcyclohexanone and cyanoacetamide. 相似文献
4.
Programming the magnitude and persistence of antibody responses with innate immunity 总被引:1,自引:0,他引:1
Kasturi SP Skountzou I Albrecht RA Koutsonanos D Hua T Nakaya HI Ravindran R Stewart S Alam M Kwissa M Villinger F Murthy N Steel J Jacob J Hogan RJ García-Sastre A Compans R Pulendran B 《Nature》2011,470(7335):543-547
Many successful vaccines induce persistent antibody responses that can last a lifetime. The mechanisms by which they do so remain unclear, but emerging evidence indicates that they activate dendritic cells via Toll-like receptors (TLRs). For example, the yellow fever vaccine YF-17D, one of the most successful empiric vaccines ever developed, activates dendritic cells via multiple TLRs to stimulate proinflammatory cytokines. Triggering specific combinations of TLRs in dendritic cells can induce synergistic production of cytokines, which results in enhanced T-cell responses, but its impact on antibody responses remain unknown. Learning the critical parameters of innate immunity that program such antibody responses remains a major challenge in vaccinology. Here we demonstrate that immunization of mice with synthetic nanoparticles containing antigens plus ligands that signal through TLR4 and TLR7 induces synergistic increases in antigen-specific, neutralizing antibodies compared to immunization with nanoparticles containing antigens plus a single TLR ligand. Consistent with this there was enhanced persistence of germinal centres and of plasma-cell responses, which persisted in the lymph nodes for >1.5 years. Surprisingly, there was no enhancement of the early short-lived plasma-cell response relative to that observed with single TLR ligands. Molecular profiling of activated B cells, isolated 7 days after immunization, indicated that there was early programming towards B-cell memory. Antibody responses were dependent on direct triggering of both TLRs on B cells and dendritic cells, as well as on T-cell help. Immunization protected completely against lethal avian and swine influenza virus strains in mice, and induced robust immunity against pandemic H1N1 influenza in rhesus macaques. 相似文献
5.
6.
Shalini Bagchi Kasturi Roychowdhury A.P. Mishra A. Roy Chowdhury 《Communications in Nonlinear Science & Numerical Simulation》2010,15(2):275-280
Excitation of nonlinear waves in a quantum dusty plasma with various effects is analyzed when the geometry is cylindrical.This introduces the effect of finite boundary conditions on the solitary waves so generated. it is observed that the nonlinear equation deduced is cylindrical KP–Burger type leading to the generation of Shock Wave. Different situations which arises in various parameter regions are considered separately and the form of the nonlinear excitations are obtained explicitly. 相似文献
7.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
8.
We show that any k-fold covering using translates of an arbitrary convex polygon can be decomposed into Ω(k) covers. Such a decomposition can be computed using an efficient (polynomial-time) algorithm. 相似文献
9.
Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
10.
Molar extinction coefficients of some carbohydrates viz. l-arabinose (C5H10O5), d-glucose (C6H12O6), d-mannose (C6H12O6), d-galactose (C6H12O6), d(-) fructose (C6H12O6) and maltose (C12H24O12) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a
narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter
polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying
within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well. 相似文献