全文获取类型
收费全文 | 7554篇 |
免费 | 1010篇 |
国内免费 | 2055篇 |
专业分类
化学 | 9569篇 |
晶体学 | 33篇 |
力学 | 63篇 |
综合类 | 60篇 |
数学 | 14篇 |
物理学 | 880篇 |
出版年
2024年 | 23篇 |
2023年 | 132篇 |
2022年 | 266篇 |
2021年 | 338篇 |
2020年 | 416篇 |
2019年 | 318篇 |
2018年 | 302篇 |
2017年 | 285篇 |
2016年 | 387篇 |
2015年 | 393篇 |
2014年 | 487篇 |
2013年 | 794篇 |
2012年 | 522篇 |
2011年 | 487篇 |
2010年 | 430篇 |
2009年 | 428篇 |
2008年 | 512篇 |
2007年 | 529篇 |
2006年 | 452篇 |
2005年 | 394篇 |
2004年 | 392篇 |
2003年 | 429篇 |
2002年 | 357篇 |
2001年 | 226篇 |
2000年 | 215篇 |
1999年 | 173篇 |
1998年 | 138篇 |
1997年 | 147篇 |
1996年 | 136篇 |
1995年 | 116篇 |
1994年 | 89篇 |
1993年 | 68篇 |
1992年 | 69篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 24篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
141.
Alkanes (cyclohexane, hexane, heptane isomers) are effectively oxidized in CH3CN at 20–70°C by hydrogen peroxide when catalyzed by a Bu4NVO3-pyrazine-2-carboxylic acid system. Alkyl hydroperoxide is the main product; an alcohol and a ketone or an aldehyde are also formed. Under these conditions benzene is oxidized to give phenol, while alkyl benzenes yield oxygenation products both of the ring and the side chain. It has been assumed that the interaction of H2O2 with VO3
– gives rise to generation of HO radicals and other radical-like vanadium containing species that abstract a hydrogen atom from an alkane, RH. The radical R. formed reacts with O2 to produce ROO. which is then transformed to alkyl hydroperoxide.Presented at the VIII International Symposium on Homogeneous Catalysis (Amsterdam, 1992).Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 64–68, January, 1993. 相似文献
142.
Jesse L. Kuiper 《Journal of organometallic chemistry》2007,692(8):1653-1660
The reaction between the new hydroxy compound [PPh4][Ru(N)(OH)2Me2] and Pd(OSiMe3)2((−)-sparteine) produces (Me3Si)2O, H2O and a new heterobimetallic compound [PPh4][Ru(N)Me2(μ2-O)2Pd((−)-sparteine)] in good yield. The Ru/Pd bimetallic compound catalyzes the oxidation of aryl and allyl alcohols to the corresponding carbonyl compound in air and the rearrangement of allylic alcohols unsaturated aldehydes. It also oxidizes PPh3 to O-PPh3 under O2. 相似文献
143.
The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine
(E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO4 was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT]
o
, fractional-order in [substrate]
o
, and inverse fractional-order in [H+]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The
variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect
on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was
studied using D2O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for
CAT-catecholamine complexes have been evaluated. CH3C6H4SO2NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic
relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed
and the derived rate law are consistent with the observed kinetics. 相似文献
144.
Catalytic oxidation of alcohols with polymer-supported ruthenium complex under mild conditions 总被引:1,自引:0,他引:1
Qiao-xiang Kang Ju-jie Luo Yan-bin Bai Zhi-wang Yang Zi-qiang Lei 《Journal of organometallic chemistry》2005,690(26):6309-6313
Polymer-supported ruthenium-containing complex PS–Phen–Ru was synthesized (where PS = chloromethyl polystyrene resin, Phen = 1,10-phenanthroline) and was characterized by FT-IR, ICP, and XPS. The supported complex was used to catalyze the oxidation of primary aliphatic alcohols as well as aromatic alcohols in the presence of iodosylbenzene. The oxidations were carried out in acetonitrile solution, affording the corresponding aldehydes or ketones in high substrate conversion and high selectivities under mild reaction conditions. The catalyst can be easily prepared and can be recycled. 相似文献
145.
Qing Hua Zhang Shou Feng Wang Zi Qiang Lei 《中国化学快报》2007,18(1):4-6
Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex. 相似文献
146.
Yu. N. Ogibin A. I. Ilovaisky V. M. Merkulova G. I. Nikishin 《Russian Chemical Bulletin》1995,44(3):507-510
The effect of anions of the supporting electrolyte (F–, dialkylphosphate, TsO–, and BF
4
–
and other electrolysis conditions (anode material, temperature, substrate concentration) on the selectivity of the direct anodic oxidation ofp-methoxytoluene in methanol into 4-methoxybenzaldehyde dimethylacetal was studied. The highest selectivity was obtained in the presence of fluoride anion.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 524–527, March, 1995.This work was financially supported by the Ministry of Science, High School and Technical Policy of the Russian Federation within the scope of the State scientific-technical program Ecologically harmless processes of chemistry and chemical technology (project No. 1.140 Low-tonnage chemical products) and by the International Science Foundation (Grant Ch-2-1246-0923). 相似文献
147.
BEHAVIOR OF SUPPORTED NANO-COPPER CATALYST IN CO OXIDATION 总被引:1,自引:0,他引:1
IntroductionNanomaterialisanewkindofmaterialwithparticlesizebetWeenIurnand100urn.Becauseofthesmallparticlesizeandthelargespecificsufficearea,nanomaterialpossessesmanyparticularproperties,suchashighersufficeenergyandhighersurfaceactivity.t.[l]Thehigheracti… 相似文献
148.
Massimo Lucarini Fabio Sciubba Donatella Capitani Maria Enrica Di Cocco Laura D’Evoli Alessandra Durazzo 《Natural product research》2020,34(1):53-62
AbstractThe study focuses on the understanding, at molecular level, the mechanism of interaction between protein and flavonoids. Collagen and catechin interactions were investigated by NMR in solution and solid state. The effect of catechin on the stability of collagen to oxidation was also explored. Collagen was treated with two concentrations of catechin solutions. Oxidation was carried out by incubation of collagen solution with three oxidation systems: Fe(II)/H2O2, Cu(II)/H2O2, and NaOCl/H2O2. The effects of oxidation systems were evaluated by high resolution 1?D and 2?D proton spectroscopy and solid state NMR (13C CP MAS) experiments. Interactions between collagen and catechin preferentially occur between catechin B ring and the amino acids Pro and Hyp of collagen. Results showed that both iron and copper oxidation systems were able to interact with collagen by site specific attack. Moreover, catechin protects collagen proline from oxidation by metal/H2O2 systems, preventing copper and iron approach to collagene molecule;this behaviour was more evident for the copper/H2O2 system. 相似文献
149.
Xiucheng Zheng Xiaoli Zhang Shuping Wang Xiangyu Wang Shihua Wu 《天然气化学杂志》2007,16(2):179-185
In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials. 相似文献
150.
Qingde Zhang Yisheng Tan Caihong Yang Yizhuo Han Jun Shamoto Noritatsu Tsubaki 《天然气化学杂志》2007,16(3):322-325
The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40(40%)/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40(40%)/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthe- sized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40(40%)/SiO2. 相似文献