全文获取类型
收费全文 | 103篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 69篇 |
晶体学 | 9篇 |
力学 | 1篇 |
数学 | 15篇 |
物理学 | 18篇 |
出版年
2023年 | 4篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有112条查询结果,搜索用时 15 毫秒
21.
22.
Coupling normal-phase LC separation methods to atmospheric pressure ionization (API)-mass spectrometry (MS) for detection can be problematic because of the possible detonation hazard and because nonpolar solvents do not support ionization of the analyte. Unlike achiral separations, enantiomeric separations can be very sensitive to small changes in the separation environment. Thus, completely substituting the main mobile phase component of a normal-phase LC solvent for an environmentally friendly, nonflammable fluorocarbon-ether as a safe and effective solvent must be thoroughly evaluated before it can be recommended for enantioselective separations with API-MS detection. Ethoxynonafluorobutane (ENFB) was used as a normal-phase solvent for the enantioselective separation of 15 compounds on two macrocyclic glycopeptide chiral stationary phases (CSPs) and a new polymeric chiral stationary phase. The chromatographic figures of merit were compared between results obtained with the ENFB mobile phases and traditional heptane-based mobile phases. In addition, the limits of detection (LOD) using the API-MS compatible ENFB were examined, as well as flow rate sensitivities and compatibilities with common polar organic modifier. ENFB is a safe and effective solvent for enantioselective normal-phase/API-MS analyses. 相似文献
23.
The surface acidity/basicity of perovskite-type mixed oxides (LaCrO3, PrCrO3, SmCrO3, LaMnO3, PrMnO3, SmMnO3, LaFeO3, PrFeO3, SmFeO3, LaCoO3, PrCoO3, SmCoO3, LaNiO3, PrNiO3 and SmNiO3) are reported. These properties have been correlated with the catalytic activity of these oxides towards esterification of
acetic acid usingn-butanol. 相似文献
24.
25.
S. Grace V. Meera S. A. Balakrishnan H. D. Sarma 《Journal of Radioanalytical and Nuclear Chemistry》1997,224(1-2):83-87
A study for separation and sequential recovery of uranium and plutonium from nitric acid solutions by extraction chromatography using tributyl phosphate (TBP)/Amberlite XAD7 as stationary phase is presented. Distribution ratios of actinides, lanthanides and fission products were obtained. The column capacity was investigated and actinides retention conditions were established. Finally, U-Pu sequential separation was studied as well as the U and Pu recovery yields from nitric solutions containing Am/fission products were determined. 相似文献
26.
We report the infrared and Raman studies of titanium doped vitreous silica glasses for a number of titanium concentrations. The vibrational modes associated with the randomly oriented chains of SiO4 tetrahedra show broadenings and shifts. The LO-TO splitting of some Raman active modes decreases with increasing titanium concentration. This is attributed to the decrease in long-range coulomb fields associated with the chains of SiO4 tetrahedra which are broken by the titanium atoms. The results are discussed in the context of random network models. An increase in the average intertetrahedral angle of the SiO4 network is calculated from the data. This explains the anomalous decrease in the density of TiO2---SiO2 glasses with increasing titanium content. We identify two new modes associated with the distorted titanium tetrahedra. A polarized Raman mode at 1115 cm−1 which is infrared inactive and an unpolarized Raman mode at 945 cm−1 which is infrared active are observed. 相似文献
27.
The well-studied X-ray-edge problem is revisited using the sea-boson method. This approach is contrasted with the well-known theories of Mahan, Nozières and De Dominicis (MND). The present approach does not use the sudden approximation and the holes carry a momentum label unlike in the MND theory. We focus on the case of doped semiconductors rather than metals. The problem of electrons in a partially filled conduction band and holes in the initially hole-depleted valence band is recast in the sea-boson language. The resulting hamiltonian is shown to be equivalent to the electron-phonon hamiltonian with the excitons taking on the role of electrons and intra-conduction band particle-hole excitations known as ‘conductrons’ taking on the role of phonons. It is shown that the excitonic pole in the computed absorption spectra is replaced by a branch cut with a simple radical leading to a broadening of the exicton line due to these many-body effects. A critical comparison is made with the MND theory as well as with relevant experiments. 相似文献
28.
Generation of fluorescent adducts of malondialdehyde and amino acids: toward an understanding of lipofuscin 总被引:2,自引:0,他引:2
Chowdhury PK Halder M Choudhury PK Kraus GA Desai MJ Armstrong DW Casey TA Rasmussen MA Petrich JW 《Photochemistry and photobiology》2004,79(1):21-25
Lipofuscin is a yellow-brown, highly fluorescent pigment that undergoes an age-related progressive accumulation in animal cells, mainly in postmitotic cells. It is a heterogeneous, high-molecular weight material associated with proteins, lipids and nucleic acids. Lipofuscin is implicated in many aspects of human health, including aging, oxidative stress, macular degeneration, lipid peroxidation, atherosclerosis, dementia (Alzheimer's Disease) and diseases associated with prions. Although the fluorescent properties of lipofuscin have long been recognized, neither histologists nor chemists have yet isolated the pigments themselves or characterized their optical properties. We have prepared lipofuscinlike species by reacting malondialdehyde (MDA) with cysteine (Cys). MDA:Cys adducts 3:2 and 2:2 are two of those that have been identified among the many that were present in the reaction. Whereas previous attempts to synthesize lipofuscinlike species resulted in compounds that were either nonfluorescent or emitted principally in the blue, the MDA:Cys adducts reported in this study are not only fluorescent but also emit over a broader range. 相似文献
29.
This paper is motivated by a link between algebraic proof complexity and the representation theory of the finite symmetric groups. Our perspective leads to a new avenue of investigation in the representation theory of Sn. Most of our technical results concern the structure of “uniformly” generated submodules of permutation modules. For example, we consider sequences
of submodules of the permutation modules M(n−k,1k) and prove that if the sequence Wn is given in a uniform (in n) way – which we make precise – the dimension p(n) of Wn (as a vector space) is a single polynomial with rational coefficients, for all but finitely many “singular” values of n. Furthermore, we show that dim(Wn)<p(n) for each singular value of n≥4k. The results have a non-traditional flavor arising from the study of the irreducible structure of the submodules Wn beyond isomorphism types. We sketch the link between our structure theorems and proof complexity questions, which are motivated by the famous NP vs. co-NP problem in complexity theory. In particular, we focus on the complexity of showing membership in polynomial ideals, in various proof systems, for example, based on Hilbert's Nullstellensatz. 相似文献
30.