全文获取类型
收费全文 | 144篇 |
免费 | 2篇 |
专业分类
化学 | 124篇 |
物理学 | 22篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 1篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 1篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1990年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1903年 | 1篇 |
1902年 | 2篇 |
1893年 | 1篇 |
1890年 | 1篇 |
1886年 | 2篇 |
1876年 | 2篇 |
1873年 | 2篇 |
排序方式: 共有146条查询结果,搜索用时 15 毫秒
1.
With the help of a commercial heat-flux calorimeter the enthalpy change was measured as a function of the interlamellar spacing for lamellar precipitated Cu-In samples. This is related to the replacement of the two-phase structure (α + δ) by the homogeneous solid solution (α0. From this, the specific interfacial enthalpy of the α-δ interface was determined to be ΔHδ = 1100 ± 550 mJ m?2. A value of ΔHc = 1320 ± 60 J mol?1 results for the chemical part of the total measured transformation enthalpy. A value of ΔSδ = 0.66 mJ m?2 K?1 was estimated for the specific interfacial entropy and using the Gibbs-Helmholtz equation the specific interfacial free energy was calculated as ΔGδ = 700 ± 400 mJ m?2 at 600 K. 相似文献
2.
Clorobiocin (clo) and novobiocin (nov) are potent inhibitors of bacterial DNA gyrase. The two substances differ in the substitution pattern at C-8' of the aminocoumarin ring, carrying a chlorine atom or a methyl group, respectively. By gene inactivation, clo-hal was identified as the gene of the halogenase responsible for the introduction of the chlorine atom of clorobiocin. Inactivation of cloZ did not affect clorobiocin formation, showing that this ORF is not essential for clorobiocin biosynthesis. Expression of the methyltransferase gene novO in the clo-hal(-) mutant led to the very efficient formation of a hybrid antibiotic containing a methyl group instead of a chlorine atom at C-8'. Comparison of the antibacterial activity of clorobiocin analogs with -Cl, -H, or -CH(3) at C-8' showed that chlorine leads to 8-fold higher activity than hydrogen and to 2-fold higher activity than a methyl group. 相似文献
3.
Krasnovsky AA Cheng P Blankenship RE Moore TA Gust D 《Photochemistry and photobiology》1993,57(2):324-330
Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen. 相似文献
4.
Di Valentin M Bisol A Agostini G Fuhs M Liddell PA Moore AL Moore TA Gust D Carbonera D 《Journal of the American Chemical Society》2004,126(51):17074-17086
Photoinduced charge separation and recombination in a carotenoid-porphyrin-fullerene triad C-P-C(60)(1) have been followed by multifrequency time-resolved electron paramagnetic resonance (TREPR) at intermediate magnetic field and microwave frequency (X-band) and high field and frequency (W-band). The electron-transfer process has been characterized in the different phases of two uniaxial liquid crystals (E-7 and ZLI-1167). The triad undergoes photoinduced electron transfer, with the generation of a long-lived charge-separated state, and charge recombination to the triplet state, localized in the carotene moiety, mimicking different aspects of the photosynthetic electron-transfer process. Both the photoinduced spin-correlated radical pair and the spin-polarized recombination triplet are observed starting from the crystalline up to the isotropic phase of the liquid crystals. The W-band TREPR radical pair spectrum has allowed unambiguous assignment of the spin-correlated radical pair spectrum to the charge-separated state C(.+)-P-C(60)(.-). The magnetic interaction parameters have been evaluated by simulation of the spin-polarized radical pair spectrum and the spin-selective recombination rates have been derived from the time dependence of the spectrum. The weak exchange interaction parameter (J = +0.5 +/- 0.2 G) provides a direct measure of the dominant electronic coupling matrix element V between the C(.+)-P-C(60)(.-) radical pair state and the recombination triplet state (3)C-P-C(60). The kinetic parameters have been analyzed in terms of the effect of the liquid crystal medium on the electron-transfer process. Effects of orientation of the molecular triad in the liquid crystal are evidenced by simulations of the carotenoid triplet state EPR spectra at different orientations of the external magnetic field with respect to the director of the mesophase. The order parameter (S = 0.5 +/- 0.05) has been evaluated. 相似文献
5.
6.
Bicrystals of Fe-6 at.% Si alloy containing <001> 5 tilt grain boundaries with a deposited zinc layer have been annealed at various hydrostatic pressure at four temperatures between 700° and 905°C. After the anneals the dihedral angle of the grain boundary groove formed at the site of the grain boundary intersection with the solid-melt interphase boundary has been measured. The transition from complete to incomplete wetting of the grain boundary by the zinc-rich melt (dewetting phase transition) has been found to occur as the pressure increased at all temperatures studied. The temperature dependence of the dewetting transition pressure p
w
has been determined. That dependence has a minimum at a temperature of 790°C, which is close to the peritectic temperature in the Fe–Zn system (782°C). A thermodynamic analysis of the wetting phenomena in the two-component system, based on Becker's regular solution model for the surface tension of the interphase boundary, explains the minimum in the p
w
(T) dependence. 相似文献
7.
8.
An integrated solid-phase spectrophotometry/flow injection analysis (FIA) method is proposed for the determination of the
synthetic colorant matter Ponceau 4R (P4R) in the presence of its unsulfonated derivative 2-hydroxy-1-[(naphthalenyl)azo]
naphthalene (N2N). The procedure is based on the measurement of P4R at λ = 508, followed by retention and preconcentration
of the low level concentration of N2N on a C18 silica gel minicolumn and subsequent measurement of the absorbance of N2N at λ = 508 nm after its elution. The applicable
concentration range, the detection and the relative standard were the following: for P4R, from 0.30 to 20.0 mg/L; 0.052 mg/L
1.1%; and for N2N, between 0.020 to 3.0 mg/L 0.003 mg/L and 1.1%. The method was applied to the determination of small amounts
of N2N present in P4R in food and cosmetic products. Percentages of recovery between 95 and 105% were obtained in all instances.
The method was applied satisfactorily to the determination of the compounds P4R and N2N in samples of sweets and cosmetic
products when compared to results offered by a HPLC reference method.
Received April 5, 2001. Revision July 25, 2001. 相似文献
9.
The paper demonstrates conceptual parallels and relationships between intellectual capital measurement methods and the evaluation
of quality in clinical laboratories in the Slovak Republic. It explores further the contextual links of those parallels with
the tangibility (or intangibility) of quality indicators of laboratory diagnostics. It also highlights the problems which
laboratory staff in Slovakia are confronted with.
Presented at the conference Quality in the Spotlight, March 2007, Antwerp, Belgium. 相似文献
10.