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以铵交换和高温水热处理法制备了不同硅铝比的超稳Y型分子筛(USY),利用X射线衍射、扫描电镜、氮气吸附脱附和吡啶红外等技术对USY进行了表征。以USY为催化剂,考察了USY的骨架硅铝比对气相甘油脱水制丙烯醛的影响。X射线衍射和扫描电镜结果表明,铵交换和高温水热处理只是提高USY的硅铝比,相对结晶度略有降低,而对Y型分子筛的结构和形貌没有影响。氮气吸附-脱附和吡啶红外结果表明,随USY骨架SiO2/Al2O3比提高,总酸量和B酸酸量逐渐降低,L酸酸量有所增多,介孔孔体积和平均孔径有所增大。气相甘油脱水反应结果表明,催化剂织构性质对甘油转化率和丙烯醛选择性的影响大于酸性的影响,因而SiO2/Al2O3比为29的USY催化剂的反应性能最好,甘油转化率和丙烯醛收率分别达到了84.5%和51.8%。 相似文献
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Stephanie K. Stckl Roberto de Col Milos R. Filipovic Karl Messlinger 《International journal of molecular sciences》2022,23(4)
The role of TRPA1 receptor channels in meningeal nociception underlying the generation of headaches is still unclear. Activating as well as inhibitory effects of TRPA1 agonists have been reported in animal models of headache. The aim of the present study was to clarify the effect of the TRPA1 agonist nitroxyl (HNO) delivered by Angeli’s salt in two rodent models of meningeal nociception. Single fibre recordings were performed using half-skull preparations of mice (C57BL/6) in vitro. Angeli’s salt solution (AS, 300 µM) caused short-lasting vigorous increases in neuronal activity of primary meningeal afferents, followed by deactivation and desensitisation. These effects were similar in TRPA1 knockout and even more pronounced in TRPA1/TRPV1 double-knockout mice in comparison to wild-type mice. The activity of spinal trigeminal neurons with afferent input from the dura mater was recorded in vivo in anesthetised rats. AS (300 µM) or the TRPA1 agonist acrolein (100 and 300 µM) was applied to the exposed dura mater. AS caused no significant changes in spontaneous activity, while the mechanically evoked activity was reduced after acrolein application. These results do not confirm the assumption that activation of trigeminal TRPA1 receptor channels triggers the generation of headaches or contributes to its aggravation. Instead, there is evidence that TRPA1 activation may have an inhibitory function in the nociceptive trigeminal system. 相似文献
47.
Magdalena Kwolek-Mirek Sabina Bednarska Aleksandra Dubicka-Lisowska Roman Maslanka Renata Zadrag-Tecza Pawel Kaszycki 《International journal of molecular sciences》2023,24(1)
Alcohol and aldehyde dehydrogenases are especially relevant enzymes involved in metabolic and detoxification reactions that occur in living cells. The comparison between the gene expression, protein content, and enzymatic activities of cytosolic alcohol and aldehyde dehydrogenases of the wild-type strain and the Δsod1 mutant lacking superoxide dismutase 1, which is hypersensitive to alcohols and aldehydes, shows that the activity of these enzymes is significantly higher in the Δsod1 mutant, but this is not a mere consequence of differences in the enzymatic protein content nor in the expression levels of genes. The analysis of the NAD(H) and NADP(H) content showed that the higher activity of alcohol and aldehyde dehydrogenases in the Δsod1 mutant could be a result of the increased availability of pyridine nucleotide cofactors. The higher level of NAD+ in the Δsod1 mutant is not related to the higher level of tryptophan; in turn, a higher generation of NADPH is associated with the upregulation of the pentose phosphate pathway. It is concluded that the increased sensitivity of the Δsod1 mutant to alcohols and aldehydes is not only a result of the disorder of redox homeostasis caused by the induction of oxidative stress but also a consequence of the unbalance between pyridine nucleotide cofactors. 相似文献
48.
Kinetic studies were made on the polymerization of acrolein initated by potassium peroxodiphosphate (PP) in aqueous solution, in the presence and absence of Ag+ ions. The rate of polymerization was found to depend on [M]3/2 (M = monomer) and was independent of both [PP] and [Ag+]. The overall activation energy was calculated to be 4.8 kcal mol−1. A mechanism involving termination by PO2-4 radicals is proposed and discussed. 相似文献
49.
The mode of action of the oxidation‐active centres in Mo–V mixed oxides on the selective oxidation of an unsaturated aldehyde
was investigated by non‐steady‐state methods. Various oxidation‐active centres, differing in activity and selectivity, were
identified by non‐steady‐state methods. In addition, the influence of the crystallinity of the Mo–V mixed oxides on the activity
and selectivity properties were investigated. It was shown that, in contrast to crystalline samples, only X‐ray‐amorphous
Mo–V mixed oxides contained selective oxidation centres. The measurements were used to derive a model based on the interaction
of active centres with various redox properties.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
50.
Robert K. Grasselli James D. Burrington Douglas J. Buttrey Peter DeSanto Jr. Claus G. Lugmair Anthony F. Volpe Jr. Thomas Weingand 《Topics in Catalysis》2003,23(1-4):5-22
Catalytic centers in selective (allylic) oxidation and ammoxidation catalysts are multimetallic and multifunctional. In the historically important bismuth molybdates, used for propylene (amm)oxidation, they are composed of (Bi3+)(Mo6+)2 complexes in which the Bi3+ site is associated with the -H abstraction and the (Mo6+)2 site with the propylene chemisorption and O or NH insertion. An updated reaction mechanism is presented. In the Mo–V–Nb–Te–O
x
systems, three crystalline phases (orthorhombic Mo7.5V1.5NbTeO29, pseudohexagonal Mo6Te2VO20, and monoclinic TeMo5O16) were identified, with the orthorhombic phase being the most important one for propane (amm)oxidation. Its active centers contain all necessary key catalytic elements (2V5+/Mo6+, 1V4+/Mo5+, 2Mo6+/Mo5+, 2Te4+) for this reaction wherein a V5+ surface site (V5+ = O 4+V–O) is associated with paraffin activation, a Te4+ site with -H abstraction once the olefin has formed, and a (Mo6+)2 site with the NH insertion. Four Nb5+ centers, each surrounded by five molybdenum octahedra, stabilize and structurally isolate the catalytically active centers from each other (site isolation), thereby leading to high selectivity of the desired acrylonitrile product. A detailed reaction mechanism of propane ammoxidation to acrylonitrile is proposed. Combinatorial methodology identified the nominal composition Mo0.6V0.187Te0.14Nb0.085O
x
for maximum acrylonitrile yield from propane, 61.8% (86% conversion, 72% selectivity at 420 °C). We propose that this system, composed of 60% Mo7.5V1.5NbTeO29, 40% Mo6Te2VO20, and trace TeMo5O16, functions with a combination of compositional pinning of the optimum orthorhombic Mo7.5V1.5±x
Nb1±y
Te1±z
O29±
phase and symbiotic mop-up of olefin intermediates through phase cooperation. Under mild reaction conditions, a single optimum orthorhombic composition might suffice as the catalyst; under demanding conditions this symbiosis is additionally required. Improvements in catalyst performance could be attained by further optimization of the elemental distributions at the active catalytic center of Mo7.5V1.5NbTeO29, by promoter/modifier substitutions, and incorporation of compatible cocatalytic phases (preferably epitaxially matched). High-throughput methods will greatly accelerate the rational catalyst design processes. 相似文献