全文获取类型
收费全文 | 333篇 |
免费 | 5篇 |
国内免费 | 30篇 |
专业分类
化学 | 343篇 |
力学 | 1篇 |
物理学 | 24篇 |
出版年
2023年 | 4篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 48篇 |
2012年 | 22篇 |
2011年 | 11篇 |
2010年 | 11篇 |
2009年 | 27篇 |
2008年 | 30篇 |
2007年 | 37篇 |
2006年 | 12篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有368条查询结果,搜索用时 31 毫秒
51.
A new method for the non-specific determination of iron-porphyrin-like complexes in natural waters has been developed. It is based on the chemiluminescent oxidation of the luminol in the presence of dioxygen (O2) at pH 13. The method has been implemented in a FIA manifold that allowed the direct injection of seawater. The limit of detection is 0.11 nM of equivalent hemin (Fe-protoporphyrin IX). Fe2+, Fe3+, H2O2, siderophore (deferoxamin mesylate), humic acid and phytic acid did not interfere when they were present at the concentrations expected in seawater. Metal free porphyrin and Mg, Cu, Co porphyrin complexes did not induce a significant chemiluminescent signal. Poisoned unfiltered samples could be stored for several weeks before analyses. The new method was successfully applied to the determination of the Fe-porphyrin complexes contained in cultured phytoplankton and in natural samples. 相似文献
52.
在二(2-乙基己基)磷酸(D2EHPA)络合萃取邻氨基苯酚(OAP)实验中,研究了稀释剂种类、溶液的初始pH值等因素对OAP稀溶液分配比(D)的影响。溶液的初始pH值对萃取结果影响较大,当初始pH值在pKa1和pKa2之间时,分配比出现峰值;二(2-乙基己基)磷酸主要是通过离子缔合和质子交换来实现萃取的,而稀释剂则主要是物理萃取,在同一浓度下,二(2-乙基己基)磷酸的萃取能力随稀释剂的极性增大而提高,极性环境优于惰性稀释剂环境。红外光谱分析证明萃取过程存在离子交换和离子缔合反应。 相似文献
53.
二(2-乙基己基)磷酸络合萃取对氨基苯酚 总被引:6,自引:3,他引:3
二 (2 -乙基己基 )磷酸 (D2 EHPA)络合萃取对氨基苯酚 (PAP)。研究了稀释剂种类、溶液的初始 p H值等因素对稀溶液分配比 (D)的影响。溶液的初始 p H值 (p H2— 1 1 )对萃取结果影响较大 ,当初始 p H值在p Ka1 和 p Ka2 之间时 ,分配比出现峰值。稀释剂则主要是通过物理萃取实现。在同一浓度下 ,二 (2 -乙基己基 )磷酸的萃取能力随稀释剂的极性增大而提高 ,极性环境明显优于惰性稀释剂环境。红外光谱分析表明 ,络合萃取过程存在离子交换和离子缔合两种反应机制。 相似文献
54.
A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg2+. When Mg2+ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by 1H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg2+ by the amide functions to form a 1:1 complex. 相似文献
55.
56.
Jamil Rima Soula Kyriacos Maurice Abou Rida 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(1):10-15
The solubilization of pyrene in aqueous solution of β-cyclodextrin (β-CD) or its derivatives such as β-CD-hexanoyl, β-CD-benzoyl and β-CD-dodecylsulfonate was investigated by spectrophotometry. Linear and non-linear regression methods were used to estimate the association constants (K1). A 1:1 stoichiometric ratio and different effects of the hexanoyl, benzoyl and dodecylsulfonate groups on the association constant were observed for the binary inclusion complex between pyrene and β-CD. The formation constant was shown to decrease when β-CD was modified by a dodecylsulfonate chain. The value of K1 was 190 ± 10 L mol−1 for the [pyrene/β-CD] complex and 145 L mol−1 for the [pyrene/β-CD-dodecylsulfonate] complex. Partitioning of the pyrene molecules between the dodecylsulfonate chains and cyclodextrin cavities can explain the decrease in the association constant value. In the cases of β-CD-hexanoyl and β-CD-benzoyl derivatives, no association constants were detected. Results suggest that the high hydrophobicity of the hexanoyl and benzoyl groups prevents the inclusion of pyrene molecules inside the cyclodextrin cavity. 相似文献
57.
Qing‐Feng Zhang Hon‐Yeung Cheung Xinchen Shangguan Guodong Zheng 《Journal of separation science》2012,35(23):3347-3353
The complexation of five polyphenols, namely trans‐resveratrol, astilbin, taxifolin, ferulic acid, and syringic acid (guest molecules) with α‐, β‐, and γ‐cyclodextrin (host molecules), was investigated by capillary electrokinetic chromatography. The binding constants were calculated based on the effective electrophoretic mobility change of guests with the addition of cyclodextrins into the background electrolyte. Because of cavity size, cyclodextrins showed structure‐selective complexation property to different guest. The stability of the trans‐resveratrol complexes was in the order of β‐ > α‐ > γ‐cyclodextrin. The cavity size of α‐cyclodextrin was too small for astilbin and taxifolin molecules, and thus they could not form complexes. The molecular size of syringic acid was too big for all cyclodextrins cavity, and no cyclodextrin could form complexes with it. Temperature studies showed that the binding constants decreased with the rise of temperature. Enthalpy and entropy values were calculated and the negative values of these parameters indicated that the complexation process was enthalpy‐controlled. Van der Waals force and release of high‐enthalpy water molecules from the cyclodextrins cavity played important roles in the process. 相似文献
58.
59.
《Journal of Coordination Chemistry》2012,65(23):3719-3737
Spectroscopy has been used to determine the number of coordinated water molecules bound to Eu(III) and Cm(III) in a series of binary complexes of polyaminocarboxylate and their ternary complexes with dicarboxylates as well as with similar ligands with additional O-, N-, and S-donors. Complexes of Eu(III) and Cm(III) with polyaminocarboxylate alone contain ca. 2.5–3.0 waters of hydration. Increasing the steric requirement of a polyaminocarboxylate by increasing the number of groups in the ligand backbone does not appreciably change the hydration of these cations. The stability constants of the binary and ternary complexes of Cm(III), Am(III), and Eu(III) with these ligands were measured by solvent extraction in a solution of 0.1 M (NaClO4). The size, basicity, specific M3+-second ligand interactions, and steric requirement of the ligands are the factors which affect the ternary complexation. Knowledge of the chemical species formed by actinide cations with organic ligands (carboxylates and aminocarboxylates), which are present in all nuclear waste, is important to understand the behavior of waste forms and the migration behavior of actinides in the environment. 相似文献
60.
Peng Song Shi-guo Sun Pan-wang Zhou Jian-yong Liu Yong-qian Xu Xiao-jun Peng 《化学物理学报(中文版)》2010,23(5):558-564
Spectral and photophysical investigations of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine (APT) have been performed in various solvents with different polarity and hydrogen-bonding ability.The emission spectra of APT are found to exhibit dual fluorescence in polar solvents, which attributes to the local excited and intramolecular charge transfer states, respectively. The two-state model is proven out for APT in polar solvent by the time-correlated single photon counting emission decay measurement. Interestingly, the linear relationships of different emission maxima and solvent polarity parameter are found for APT in protic and aprotic solvents, because of the hydrogen bond formation between APT and alcohols at the amino nitrogen N25. Furthermore, the effects of the complexation of the metal ion with tpy group of APT and the hydrogen bond formation between APT with methanol at the terpyridinenitrogen N4—N8—N14 are also presented. The appearance of new long-wave absorption and fluorescence bands indicates that a new ground state of the complexes is formed. 相似文献