全文获取类型
收费全文 | 2352篇 |
免费 | 60篇 |
国内免费 | 197篇 |
专业分类
化学 | 2291篇 |
晶体学 | 24篇 |
力学 | 7篇 |
综合类 | 4篇 |
物理学 | 283篇 |
出版年
2024年 | 6篇 |
2023年 | 69篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 39篇 |
2019年 | 81篇 |
2018年 | 34篇 |
2017年 | 84篇 |
2016年 | 49篇 |
2015年 | 61篇 |
2014年 | 58篇 |
2013年 | 79篇 |
2012年 | 279篇 |
2011年 | 125篇 |
2010年 | 100篇 |
2009年 | 113篇 |
2008年 | 152篇 |
2007年 | 171篇 |
2006年 | 127篇 |
2005年 | 120篇 |
2004年 | 123篇 |
2003年 | 68篇 |
2002年 | 78篇 |
2001年 | 77篇 |
2000年 | 69篇 |
1999年 | 65篇 |
1998年 | 46篇 |
1997年 | 39篇 |
1996年 | 31篇 |
1995年 | 32篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2609条查询结果,搜索用时 343 毫秒
61.
二溴硝基偶氮氯膦催化动力学光度法测定痕量钴的研究 总被引:4,自引:0,他引:4
研究了在pH7.0磷酸盐介质中,钴催化H2O2氧化二溴硝基偶氮氯膦色反应,建立了催化光度法测定痕量钴的新方法,其检出限为5×10^-7g/L,在0.5-32μg/L范围内,钴与lg呈良好的关系。 相似文献
62.
一种基于形成杂多核配合物的荧光增敏效应的研究(Ⅱ)──钴(Ⅱ)-7-(8-羟基-3,6-二磺基萘偶氮)-8-羟基喹啉-5-磺酸-硼(Ⅲ)三元体系的荧光性质及其分析应用熊国华,刘虹,俞英,黄坚锋(九江师范专科学校化学系,九江,332000)(江西大学实... 相似文献
63.
64.
Korolczuk M Moroziewicz A Grabarczyk M 《Analytical and bioanalytical chemistry》2005,382(7):1678-1682
Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10–10 to 2 × 10–8 mol L–1. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10–9 mol L–1 was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10–11 mol L–1. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples. 相似文献
65.
Abhimanyu S. Paraskar 《Tetrahedron》2006,62(20):4907-4916
Sodium borohydride in combination with a catalytic amount of CoCl2 has been found to be an excellent catalytic system in reductive cyclizations of suitably substituted azido and cyano groups of α,β-unsaturated esters to afford γ and δ-lactams in high yields. The process has been demonstrated for the enantioselective synthesis of (R)-baclofen, (R)-rolipram, and (R)-4-fluorophenylpiperidinone, a key intermediate for (−)-paroxetine. 相似文献
66.
Joongjai Panpranot Sujaree Kaewgun and Piyasan Praserthdam 《Reaction Kinetics and Catalysis Letters》2005,85(2):299-304
Summary The pore structure of silica supports (SiO2 or MCM-41) has little influence on the metal-support interaction in silica supported cobalt catalysts. Cobalt dispersion, reduction behavior, and catalytic properties for the Fischer-Tropsch synthesis were primarily affected by the metal particle size. 相似文献
67.
钴(Ⅱ)与5-(5-硝基-2-吡啶偶氮)-2,4-二氨基甲苯络合物吸附波及其应用 总被引:4,自引:1,他引:4
钴 (Ⅱ )在NH3·H2O -NH2OH·HCl-5_(5_硝基_2_吡啶偶氮)_2,4_二氨基甲苯体系中有一灵敏的极谱波 ,其峰电位Vp 为 -1.20V(vsSCE) ,钴质量浓度在0.25~25μg/L范围内与峰电流Ip′有良好的线性关系 ,检出限为0.12μg/L;经多种电化学方法证明该波为络合物吸附波 ,其电极过程为不可逆过程 ,电子转移数为2 ,此外还试验了多种离子对峰电流Ip′的影响;所拟方法已用于维生素B12 和模拟样中痕量钴的测定 相似文献
68.
Stefan TsakovskiKarima Benkhedda Elisaveta IvanovaFreddy C Adams 《Analytica chimica acta》2002,453(1):143-154
8-Hydroxyquinoline (HQ), 2-methyl-8-hydroxyquinoline (CH3-HQ), 5,7-dichloro-2-methyl-8-hydroxyquinoline (Cl2-CH3-HQ), 5,7-dibromo-8-hydroxyquinoline (Br2-HQ), 5-sulfo-7-iodo-8-hydroxyquinoline (ferron) and 5-sulfo-8-hydroxyquinoline (SO3H-HQ) were compared as chelating reagents for on-line sorption preconcentration of cobalt in a knotted reactor (KR) precoated with the reagent. The results obtained with the different HQ derivatives reveal those properties of the chelating reagent responsible for the processes taking place in the KR. The influence of hydrophobicity, acidity, stability of the cobalt chelate and type of substituents in the HQ ring system on the separate steps of the flow injection (FI) preconcentration procedure are discussed. According to the performance characteristics of the different HQ derivatives, the most important parameters for on-line preconcentration in a KR are the hydrophobicity of the reagent and the stability of the chelate complex with the analyte. 相似文献
69.
Yasar Gok 《无机化学与普通化学杂志》1995,621(7):1243-1246
The new dinuclear, octahedral cobalt(III) complexes have been synthesized and then their ability to interact with 4,4′-trimethylene dipyridine investigated. The 1H and 13C-NMR, IR and elemental analysis data indicated that the cobalt(III) complexes are dinuclear. 相似文献
70.
Chandra S Kumar R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,62(4-5):1050-1057
Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism. 相似文献