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91.
Eugenia V. Kul''ko Aleksandra S. Ivanova Anna A. Budneva Evgenii A. Paukshtis 《Reaction Kinetics and Catalysis Letters》2006,88(2):381-390
Summary Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides,
representing γ-Al2O3, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was
found to exceed their concentration in γ-Al2O3 prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides
was lower than that in γ-Al2O3 prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits
of 2.80-4.14 mmol/m2 and is essentially above that in g-Al2O3 (2.25 mmol/m2). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with nCO = 2220 and 2238 cm-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al2O3, however, in contrast to g-Al2O3,they contain strong basic sites with nCDCl3 = 2200 cm-1. 相似文献
92.
将血浆中PaCO2作为自变量、△[HCO3-]/△PaCO2作为因变量,对慢性呼吸性酸碱平衡紊乱时,肾的代偿调节作用进行了量化处理.根据两者间的量化关系,看到:慢性呼吸性酸中毒时,随着血浆中PaCO2值越来越大,△[HCO3-]/△PaCO2的变化率越来越小;慢性呼吸性碱中毒时,随着血浆中PaCO2值越来越小,△[HCO3-]/△PaCO2的变化率也越来越小.这些结果完全符合生物学规律.提示这一量化处理对研究慢性呼吸性酸碱平衡紊乱时,肾代偿调节机制、代偿强度等有一定的意义. 相似文献
93.
The catalytic performance of Pt-based catalysts for the total oxidation of hydrocarbons was investigated.The activity of supported Pt catalysts(Pt/Al2O3,Pt/ZrO2,Pt/TiO2,and Pt/H-ZSM-5)depends on the metal oxide support.Pt/Al2O3 showed the highest catalytic activity when the catalysts were aged at 750°C for 50 h in air.The activity of Pt/Al2O3 was dependent on the valence state of the Pt surface.Pt/Al2O3 with the Pt surface in the metallic state was more active than with the surface in the cationic state.The surface density of acid and basic sites on the Al2O3 support controlled the valence state of the Pt surface and stability of the Pt particles in the highly dispersed state,respectively. 相似文献
94.
A Soft Grip: Magnesium Complexes with a Phosphine‐Modified Phosphonium Diylidic Lewis Base
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Dr. Jens Langer Irina Kosygin Dr. Ralph Puchta Jürgen Pahl Prof. Dr. Sjoerd Harder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17425-17435
Simple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph2PCHPPh2(fluorenylidene)]? (dppmflu?) were developed to evaluate the influence of the hard acid (cation) and soft base (anion) mismatch on the stability and reactivity of the formed derivatives. Deprotonation of the precursor Ph2PCH2PPh2(flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ‐nBu)}2], [Mg(dppmflu){N(SiMe3)2}], and [{Mg(dppmflu)(μ‐Me)}2], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ‐nBu)}2] with PhSiH3 in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ‐H)(thf)}2] without a stabilizing nitrogen donor ligand. Prolonged heating enforced ligand redistribution and [{Mg(dppmflu)(μ‐H)(thf)}2] was converted to [Mg(dppmflu)2] and MgH2. The homoleptic derivative [Mg(dppmflu)2], in which the magnesium center is in a very soft ligand environment, can open a THF molecule by frustrated Lewis pair reactivity to give [{Mg(dppmflu)(μ‐OC4H8dppmflu)}2]. 相似文献
95.
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98.
Vasil‘ev V. P. Kochergina L. A. Gorboletova G. G. 《Journal of Thermal Analysis and Calorimetry》1998,54(1):311-315
The protolytic equilibria in aqueous solutions of different amino acids and dipeptides were studied by a direct calorimetric
method at 288–328 K. The measurements were made with an isothermal-shell calorimeter with automatic temperature recording.
The thermodynamic characteristics of the processes of acid-base equilibria were found from the combined results of thermochemical
measurements and equilibrium constant data. Gurney concepts were used to analyse the thermodynamic characteristics of reactions.
Comparisons of the temperature-dependent and temperature-independent contributions to the Gibbs energy and enthalpy change
afford the criteria of the variability in sign of the ΔH of the process, i.e. they allow prediction of the magnitude of the
temperature θ at which ΔH = 0.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
99.
Juan C. Raposo Jon Sanz Olatz Zuloaga María A. Olazabal Juan M. Madariaga 《Journal of solution chemistry》2003,32(3):253-264
A potentiometric study of the hydrolysis of arsenious acid was carried out to define the thermodynamic model of the inorganic arsenic species in aqueous solutions. The protonation equilibrium of arsenious acid was determined at 25°C. The variation of the stoichiometric formation constant with the ionic strength was also studied up to ionic strength 3.0 mol-dm–3 in aqueous NaClO4, NaCl, and KCl. The thermodynamic formation constant of arsenious acid (log K
o = 9.22 ± 0.01) and the various interaction parameters were computed using the Modified Bromley Methodology (MBM), for both the molar and molal concentration scales at constant temperature (25°C). The results showed the importance, not only of ionic strength, but also of the composition of the ionic medium on the distribution of the acid-base As(III) species as a function of pH in natural waters. 相似文献
100.
采用共沉淀法, 固定Mg2+/(Al3++Ti4+)摩尔比为3.00, 改变Ti4+/(Al3++Ti4+)摩尔比(RTi, 0~0.40), 合成了5个Mg-Al-Ti-CO3层状双氢氧化物(LDHs)样品, 并进行了表征. 采用电势滴定、 盐滴定和电势质量滴定法, 测定了其结构电荷密度(σst)、 零净电荷点(pHPZNC)和零净质子电荷点(pHPZNPC)等, 并基于普适1-pK和2-pK模型得出其表面羟基酸碱反应特征平衡常数(pK, pK 和pK ), 考察了RTi对LDHs晶体结构和界面电化学性质的影响. 研究结果表明, 随着RTi增大,晶胞常数和层间距均增大, 可归因于Ti4+离子间强静电排斥作用. pHPZNC和pHPZNPC以及pK, pK 和pK 均随RTi的增大而有增大的趋势, 表明表面羟基去质子化趋势降低. 各LDHs样品的pHPZNPC值低于其pHPZNC值, 且随电解质(NaNO3)浓度的增大而升高, 可归因于结构正电荷效应. 相似文献