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排序方式: 共有163条查询结果,搜索用时 31 毫秒
41.
42.
详细研究了Ti─Si沸石在H_2O_2存在下对氯丙烯的环氧化、苯乙烯的氧化和环己烯的氧化等反应的催化作用.发现上述三种结构的烯烃其主要定向产物并不一致:氯丙烯氧化产物主要为环氧氯丙烷,苯乙烯氧化主要产物为苯乙醛、环己烯氧化主要产物为环己二酮.说明烯烃氧化的主要定向产物的结构依赖于有机底物的结构,并不全都给出环氧产物.在三个反应中,Ti─Si沸石均表现出显著的催化活性,这可能与沸石骨架中钛的存在有关.发现在氯丙烯环氧化反应中,只有TS-1及TS-2表现出环氧化活性.推测沸石骨架位中存在的钛在氧化反应中起重要作用. 相似文献
43.
An HPLC-ECD method is described for the indirect determination of the hydroxyl (OH) radical. Fenton's reaction is used to produce OH, which simultaneously attacks phenols (phenol or pyrocatechol) to form the adducts, pyrocatechol or pyrogallic acid. Thus, [OH] quantification is based on the separation and detection of pyrogallic acid and/or pyrocatechol by an isocratic HPLC-ECD method. The quantification of OH is also performed alternatively by a chronoamperometric detection in an electrochemical cell, where simultaneously formed FeIII (Fenton's reaction) combines [FeII(CN)6]4− to produce the Prussian blue (PB) molecules (Fe4III[FeII(CN)6]3). Newly formed PB molecules are then immediately converted to colorless Everitts salt (K4Fe4II[FeII(CN)6]3) with the reduction of the high-spin FeIII to FeII at the surface of a glassy carbon electrode at +0.150 V (versus Ag/AgCl). The calculated concentration of OH during incubation (0.626 ppm) can be detected with negative errors by the HPLC-ECD (0.595 and 0.615 ppm with the errors −5.2 and −1.8%, respectively) and by the chronoamperometric method (0.552 and 0.607 ppm with the errors −11.8 and −3.0%, respectively). For the comparison of the two sets of data, HPLC-ECD method is much more promising. 相似文献
44.
Baylis–Hillman adducts were oxidized by iodoxybenzoic acid (IBX) to 2-methylene-1,3-dicarbonyl compounds, which can act as oxodiene to react with electron-rich alkenes to generate a variety of oxo Diels–Alder adducts in good yields. 相似文献
45.
Renato P. Orenha Sergio E. Galembeck 《International journal of quantum chemistry》2019,119(20):e25999
The pH influence has important role in the bioavailability of coordination compounds. fac-[Ru(NO)Cl2(κ3N4,N8,N11[1-carboxypropyl]cyclam)]+, 1 , and the species found at different pHs, 2 - 4 , were investigated. One series of computational methodologies has been used to investigate these compounds. One special highlight is to interacting quantum atoms method, where the total interaction energy, , between two atoms has been used as base to estimate the chemical bonds strength. The deprotonation of -CO2H, 1 ➔ 2 (pKa = 3.3), creates a hydrogen bond in the complex 2 , N( 3 )-H⋯ ·OCO−, with a more favorable than the presents in 1 , N( 3 )-H⋯ ·OCOH. There are no changes in in Ru-NO bond. The second deprotonation occurs in the N(2) atom of the cyclam group, 2 ➔ 3 (pKa = 8.0). It promotes an increase in the covalent character of Ru-N( 2 ). In contrast, there is no changes in Ru-N( 5 )O bond. For higher pHs, there is a 3 ➔ 4 equilibrium (pKa = 11.5) and the conversion of Ru-N( 5 )O for Ru-N( 5 )O2. The Ru-N( 5 ) of 4 shows a larger ionic character than 3 . Thus, Ru-NO in 1 - 4 has worthy stability about a large pH range, showing potential application as NO scavengers. 相似文献
46.
Here, we propose a new strategy that employs a functional separator composed of radical scavenging agents for removal of radical species in the cell. In detail, a radical scavenger, trimesitylborane (TRMSB), is embedded on the surface of nano-sized tungsten oxide (WO3) by a simple one-step process and the resulting nanoparticles are coated onto conventional separators by a dip-coating process. Our screening test performed by chemical reaction of TRMSB with a radical indicator (2,2-diphenyl-1-picrylhydrazyl, DPPH) confirms that TRMSB effectively scavenges radical species via a chemical reaction, implying that the use of a WO3-TRMSB–functionalized separator would be effective for decreasing radical concentrations during electrochemical processes. In our electrochemical tests, the cell cycled with a WO3-TRMSB–functionalized separator exhibit showed both improved cycling retention compared to a cell cycled with a bare separator and improved physical and mechanical properties. 相似文献
47.
Surface effects on the diagnostic of carbon/nitrogen low‐pressure plasmas studied by differentially pumped mass spectrometry 下载免费PDF全文
Daniel Alegre Jose A. Ferreira Francisco L. Tabarés 《Journal of mass spectrometry : JMS》2014,49(5):342-352
In this work, the characterization of the species produced in reactive plasmas by differentially pumped mass spectrometry is addressed. A H2/CH4/N2 mixture (90 : 5 : 5) was fed into a direct current glow discharge and analysed by conventional and cryo‐trap assisted mass spectrometry. The gaseous mixture was chosen because of its particular relevance in the inhibition of tritium‐rich carbon film deposition in fusion plasmas (scavenger technique) and in the deposition of amorphous hydrogenated carbon films by plasma‐assisted chemical vapour deposition. Important changes in the composition of the detected species upon surface modification of the reactor walls (stainless steel or covered by an amorphous hydrogenated carbon layer) or in the way they are sampled (length and spatial configuration of the stainless steel duct) were detected. They are analysed in terms of radical formation and recombination on the reactor walls or into the sampling duct, thus providing some insight into the underlying chemistry. In general, when the reactor walls are covered by an amorphous hydrogenated carbon layer, more hydrocarbons are produced, but the radical production is lower and seem to be less reactive than in stainless steel. Also, two sources of oxygen contamination in the plasma have been identified, from the native oxide layer in stainless steel and from unintended water contamination in the chamber, which modify considerably the detected species. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
48.
An improved synthesis of N,N′‐disuccinimidyl carbonate (DSC) is described where α‐pinene is utilized as an efficient scavenger of HCl liberated during the reaction of N‐hydroxysuccinimide with triphosgene in THF. The α‐pinene hydrochloride formed is soluble in THF and gives very pure DSC in good yields. 相似文献
49.
采用浸渍-提拉法将 TiO2 薄膜负载在具有一定电极构型的氧化铟锡 (ITO) 基底上, 制备了全固态 TiO2 平面型器件 (ITO/TiO2/ITO). 采用扫描电镜对器件的表面形貌和膜厚进行了表征. 以紫外光下器件光电协同催化降解罗丹明 B(RhB) 为模型反应, 考察了器件的构型和空穴捕获剂 (乙醇) 对其光电催化性能的影响. 结果表明, 初始浓度为 10 mg/L 的 RhB 在 1.5 V 偏压和 NaCl (1.5 mol/L) 为电解质的条件下, 光照 60 min 脱色率达到 83%; 阳极面积较大的器件光电催化性能较好, 刻蚀宽度为 2 mm 时光电催化活性最高; 空穴与 TiO2表面吸附的 H2O 氧化生成的羟基自由基对液相光电催化降解 RhB 起着重要作用. 相似文献
50.
WESTON THATCHER BORDEN 《Molecular physics》2013,111(3):337-347
This paper describes a collaboration between Professor Ernest Davidson and the author, which began in 1976 and lasted until Ernest left the University of Washington in 1984. During those 9 years we co-authored a total of 34 papers that described the results of ab initio calculations on a variety of different types of organic molecules, These included anti-aromatic annulenes, carbanions, carbenes, conjugated radicals and radical cations, and non-Keklé hydrocarbon diradicals. Our collaboration led to insights about symmetry breaking, both real and artefactual, which formed the basis for a frequently-cited review article on this subject that we co-authored. However, our most often-referenced paper was concerned with predicting the sizes and signs of the singlet-triplet splittings in diradicals, based on whether or not the non-bonding Hückel molecular orbitals of a diradical can be chosen so that they are confined to disjoint sets of atoms. In 1984, we co-authored a paper on the Cope rearrangement. Since then, we have both continued to publish papers on this interesting reaction, but independently, rather than together. The results of the calculations that we each performed on the Cope rearrangement and how this reaction is affected by radical-stabilizing substituents are described. Our independent discoveries, that calculations beyond the CASSCF level are necessary in order to describe correctly the transition structure for the Cope rearrangement, led to our most recent joint publication, a 1996 review on the general importance of including dynamic correlation in ab initio calculations. 相似文献