全文获取类型
收费全文 | 287篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
化学 | 255篇 |
晶体学 | 7篇 |
力学 | 2篇 |
数学 | 3篇 |
物理学 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2020年 | 2篇 |
2019年 | 7篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 27篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 11篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 4篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 15 毫秒
121.
Continuous Determination of Trace Amounts of Humic Acid in Natural Water by Chemiluminescence Method
A chemiluminescence (CL) method for the determination of humic acid (HA) based on the oxidation of HA with hydrogen peroxide in the presence of formaldehyde in alkaline solution is described. This method is sensitive and selective for the determination of HA in natural water. HA produces strong CL in the oxidation of HA with MnO4−, Br2, ClO−, and Cr2O72−, and the H2O2. HA-H2O2-HCHO system is suitable for the determination of HA because of its high sensitivity and high selectivity. The detection limit was 50 ppb and relative standard deviation for five measurements of 0.5 ppm (w/w) HA was 1.8%. Cations such as Na+, K+, Mg2+, Cu2+, and Fe3+ and anions such as PO43−, NO3−, CO32−, SO42−, Cl−, and Y− (EDTA-Na) did not interfere with the determination of HA. Addition of Mn(II) increased the CL intensity. The concentration of HA in natural water determined with this method is in good agreement with that determined by fluorometric analysis. 相似文献
122.
A new method for the measurement of trace amounts of HONO has been developed. Nitrous acid in the ambient air is absorbed in an aqueous solution by an air-dragged aqua-membrane-type denuder. The absorbed nitrite is reacted with 2,3-diaminonaphthalene, and the formed 1-naphthotriazol is measured using a fluorescence method. The calibration curve of HONO shows a straight line from 0 to 4000 ppt, and the detection limit is estimated to be 8.1 ppt calculated as being three times of the base line noise. The time resolution, which is defined as the time required to become a constant value by changing from 0 to ca. 1000 ppt was 2 min. The present method is not affected by NO(2), NO, SO(2), O(3) NH(3) or mixtures of these gases and organic nitrate, organic carboxylic acids, alcohols and aldehydes. The determination results of HONO concentrations in the ambient air by the present method are in good agreement with those by the annular denuder system and the differential optical absorption method. 相似文献
123.
A wide range of NCN pincer palladium complexes, [4-tert-butyl-2,6-bis(N-alkylimino)phenyl]chloropalladium (alkyl = n-butyl, benzyl, cyclohexyl, tert-butyl, adamantyl, phenyl, 4-methoxyphenyl), were readily prepared from trans-(4-tert-butyl-2,6-diformylphenyl)chlorobis(triphenylphosphine)palladium via dehydrative introduction of the corresponding alkylimino ligand groups (ligand introduction route) in excellent yields (71-98%). NMR studies on this route for forming pincer complexes revealed the intermediacy of [4-tert-butyl-2,6-bis(N-alkylimino)phenyl]chlorobis(triphenylphosphine)palladium which is in equilibrium with the corresponding NCN pincer complexes via coordination/dissociation of the intramolecular imino groups and triphenylphosphine ligands. A series of chiral NCN pincer complexes bearing pyrroloimidazolone units as the trans-chelating donor groups, [4-tert-butyl-2,6-bis{(3R,7aS)-2-phenylhexahydro-1H-pyrrolo[1,2-c]imidazol-1-on-3-yl}phenyl]chloropalladium, were also prepared from the same precursor via condensation with proline anilides in high yields. The catalytic properties of the NCN imino and the NCN pyrroloimidazolone pincer palladium complexes were examined in the Heck reaction and the asymmetric Michael reaction to demonstrate their high catalytic activity and high enantioselectivity. 相似文献
124.
Alkali-ion-modified silica-supported vanadium oxides are photocatalysts available in the field of photooxidation of light alkanes using molecular oxygen. The photooxygenated reaction was promoted over the catalyst under irradiation at steady state. Acetone formation on the photooxidation of propane was investigated over a rubidium-ion-modified silica-supported vanadium oxide that is the most effective catalyst. The kinetic analysis demonstrated that the rate-determining step is the reaction of propane on the lattice oxygen of the photoexcited VO4Rb species to yield the vanadium isopropoxide species. It was suggested that the photocatalytic active sites are occupied by photogenerated acetone during photoreaction at 333 K. Heating the photocatalyst bed drastically enhanced not only product yield but also the selectivity to propionaldehyde that is a minor product in the photooxidation at 333 K. The product distribution of photoassisted oxidation of propane was described by Boltzmann's distribution of stabilization energy of the intermediates: an isopropoxide-like one for the precursor of acetone and an n-propoxide-like one for the precursor of propionaldehyde. 相似文献
125.
Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO2, H2O and O2 were overviewed. Supported Ni catalysts (Ni/SiO2, Ni/TiO2 and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO2, H2O and O2 into CO, synthesis gas and CO2, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition. 相似文献
126.
127.
Optical conductivity measurements on the organic metal theta-(BEDT-TTF)2I3 revealed that the system crosses over rapidly from a coherent quasiparticle state to an incoherent state with temperature. Despite the metallic temperature dependence of resistivity, a well-defined Drude peak at low temperatures turns into a far-infrared peak with temperature. The peak energy shifts to higher frequencies and, simultaneously, the spectral weight is transferred to high frequencies beyond the electron band width. These characteristics imply that theta-(BEDT-TTF)2I3, so far believed to be a typical metal, is in fact a strongly correlated electron system with "bad-metal" character. 相似文献
128.
Effects of pu-erh tea on lipid metabolism in rats 总被引:2,自引:0,他引:2
M Sano Y Takenaka R Kojima S Saito I Tomita M Katou S Shibuya 《Chemical & pharmaceutical bulletin》1986,34(1):221-228
129.
LO phonon kink in the hot electron distribution function has been observed for the first time by photoluminescence measurement in n-GaAs. A detailed comparison between the experiment and the calculation is made on the distribution function and electron mean energy. 相似文献
130.
A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO2 Nanosheet
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Shintaro Ida Kenta Sato Tetsuya Nagata Prof. Hidehisa Hagiwara Prof. Motonori Watanabe Namhoon Kim Prof. Yoshihito Shiota Prof. Michio Koinuma Prof. Sakae Takenaka Prof. Takaaki Sakai Prof. Elif Ertekin Prof. Tatsumi Ishihara 《Angewandte Chemie (International ed. in English)》2018,57(29):9073-9077
The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO2 nanosheets doped with Rh at Ti sites as one‐atom cocatalysts. A hydride species adsorbed on the one‐atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo‐excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride. 相似文献