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91.
I. G. Gazarian G. A. Ashby R. N. F. Thorneley L. M. Lagrimini 《Applied biochemistry and biotechnology》1996,61(1-2):1-12
Anionic tobacco peroxidase (TOP) (mol wt 36 kDa, pI 3.5) was purified from transgenic tobacco plants with the yield of 60
mg/1 kg leaves. The enzyme exhibits unusual properties, i.e., Compound I is less reactive than Compound II. The enzyme was
investigated in oxidation of indole-3-acetic acid (IAA) oxidation by oxygen in the air. The aerobic steady-state spectral
studies reveal that Compound II is the key intermediate of the reaction mechanism. This was confirmed in the anaerobic stopped-flow
experiments. No reaction between the enzyme and IAA is observed under anaerobic conditions. The data obtained are interpreted
in terms of a ternary complex formation (ferric enzyme-IAA-oxygen) at the initiation step resulting in production of IAA radicals.
The latter interacts with the ferric enzyme and oxygen producing Compound II. The oxidative cycle involves the ferric enzyme
and Compound II, and is independent from the peroxidative one. 相似文献
92.
This report provides spectroscopic evidence to support a single electron transfer pathway to describe the reaction of metal hydrides with alkyl halides by direct EPR observation of the radical formed in the reaction. 相似文献
93.
The use of chemical shift imaging for fat and water quantitation and differential measurement of relaxation times for the fat and water component is demonstrated using a hybrid technique. The efficacy of the imaging technique for fat and water quantitation has been tested by comparing the results of imaging to the results of volumetric measurements in phantoms with oil and water homogeneously mixed, fat extraction in ground meat of different grades, and biopsy in preliminary clinical studies. Good correlation is found between the fat and water content measured by imaging and that measured by other means except for the inability to differentiate unsaturated fat protons from water protons. Longitudinal (T1) and transverse (T2) relaxation times for water and fat are also shown to be measurable independently when fat and water signal are suppressed accordingly. The independently measured relaxation times correspond closely to those of the pure samples except that unsaturated protons give decreased water relaxation estimates. 相似文献
94.
A knowledge of the sugar content of molasses is of commercial importance to a number of industrial fermentations. Hence the feasibility of using a glucose oxidase biosensor to determine the glucose content of molasses samples was investigated. This method was compared with standard high-performance liquid chromatographic (HPLC) and gas-liquid chromatographic (GLC) procedures and with the use of a commercially available glucose analyser. A good correlation was obtained between the standard acetic anhydride GLC and glucose oxidase biosensor results (correlation coefficient = 0.98). Rapid and accurate measurements could be carried out using the biosensor without the need to employ the sample preparation step required in standard GLC methods. It was concluded that the use of the biosensor technique for the determination of glucose in molasses samples has distinct advantages over conventional methods. 相似文献
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98.
Ashby N Heavner TP Jefferts SR Parker TE Radnaev AG Dudin YO 《Physical review letters》2007,98(7):070802
We report the most sensitive tests to date of the assumption of local position invariance (LPI) underlying general relativity, based on a 7 yr comparison of cesium and hydrogen atomic clocks (frequency standards). The latest results place an upper limit that is over 20 times smaller than the previous most sensitive tests; this is consistent with the null shift predicted by LPI. The result is based on precise comparisons of frequencies of four hydrogen masers maintained by NIST, with four independent Cs fountain clocks--one at NIST and three in Europe--as the Sun's gravitational potential at Earth's surface varies due to Earth's orbital eccentricity. 相似文献
99.
Fortier TM Ashby N Bergquist JC Delaney MJ Diddams SA Heavner TP Hollberg L Itano WM Jefferts SR Kim K Levi F Lorini L Oskay WH Parker TE Shirley J Stalnaker JE 《Physical review letters》2007,98(7):070801
We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8x10(-6) per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |alpha/alpha|<1.3x10(-16) yr-1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards yield a coupled constraint of -1.5x10(-15)相似文献
100.
Hypothiocyanite (OSCN-) hydrolyzes under alkaline conditions to give thiocarbamate-S-oxide (H2NC(=O)SO-, the conjugate base of carbamothioperoxoic acid) via a mechanism that involves rate-limiting nucleophilic attack of OH- on OSCN-, followed by fast protonation (with no net consumption of H+/OH- at pH 11.7). Thiocarbamate-S-oxide has been characterized by 13C NMR, 15N NMR, UV spectroscopy, and ion chromatography. It has also been independently synthesized by the reaction of thiocarbamate (H2NC(=O)S-) and hypochlorite (OCl-). The properties of thiocarbamate-S-oxide that is produced by hydrolysis of OSCN- and by oxidation of H2NC(=O)S- are the same. The possible relevance of thiocarbamate-S-oxide in human peroxidase defense mechanisms remains to be explored. 相似文献