全文获取类型
收费全文 | 310篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 262篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 26篇 |
物理学 | 36篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 16篇 |
2013年 | 65篇 |
2012年 | 23篇 |
2011年 | 23篇 |
2010年 | 20篇 |
2009年 | 17篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 0 毫秒
71.
The crystal structure of NaSbF4 has been redetermined by X-ray diffraction. The coordination about antimony is AX6E with a 2.2.2.1 geometry. The units are linked by fluorine bridges and form a double layer perpendicular to the a axis. Infrared and Raman spectra were recorded and are discussed in terms of the distorted octahedral arrangement of fluorines about each antimony. 相似文献
72.
Saeed Balalaie Mohammad Ali Bigdeli Enayatollah Sheikhhosseini Azizollah Habibi Hamed Piri Moghadam Mehrnoush Naderi 《Helvetica chimica acta》2012,95(3):528-535
The novel coumarin‐3‐carboxamides (=2‐oxo‐2H‐1‐benzopyran‐3‐carboxamides) 5a – 5g containing lipophilic spacers were synthesized through the Ugi‐four‐component reaction (Scheme 1). The reactions of aromatic aldehydes 1 , 4,4′‐oxybis[benzenamine] or 4,4′‐methylenebis[benzenamine] as diamine 2 , coumarin‐3‐carboxylic acid (=2‐oxo‐2H‐benzopyran‐3‐carboxylic acid; 3 ), and alkyl isocyanides 4 lead to the desired substituted coumarin‐3‐carboxamides 5a – 5g at room temperature with high bond‐forming efficiency. These novel coumarin derivatives exhibit brilliant fluorescence at 544 nm in CHCl3. 相似文献
73.
A rapid and simple quantitative method for the simultaneous determination of the four aflatoxins (AFs) B1, B2, G1 and G2 was developed using reverse homogeneous liquid–liquid extraction (RHLEE) and HPLC post-column derivatization-fluorescence (HPLC-FL) detection. The method based on the rapid extraction of AFs from a methanolic sample into chloroform after addition of water containing KBr, with a method we called reverse homogeneous liquid–liquid extraction. Recoveries were in the range of 88–125% and the limits of detection were between 0.001–0.042 ng g?1 for different AFs. Wheat and pistachio were chosen for the analysis of real samples and the method was also successfully applied to a FAPAS® TEST MATERIAL (T04151). 相似文献
74.
Fainerman-Melnikova M Nezhadali A Rounaghi G McMurtrie JC Kim J Gloe K Langer M Lee SS Lindoy LF Nishimura T Park KM Seo J 《Dalton transactions (Cambridge, England : 2003)》2004,(1):122-128
The interaction of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O2N3-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log K values for the respective 1 : 1 complexes in 95% methanol (I= 0.1; Et4NClO4, 25 degrees C) of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 : 1 silver(I) complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 : 1 copper(II) complex. The log K results are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor (positive or negative) influence on the affinity towards silver(I) while the corresponding binding strengths towards the remaining six metal ions are significantly reduced-behaviour we term 'selective detuning'. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log K results, transport selectivity for copper(II) was exhibited by both systems, with similar transport efficiencies being evident when compared on a 'per macrocyclic cavity' basis. 相似文献
75.
An efficient and facile one-pot synthesis is described for the preparation of novel tricyclic fused pyranothiazolopyrimidines containing both biologically active thiazolopyrimidine and pyranopyrimidine templates via three-component reaction involving an isocyanide with a dialkylacetylenedicarboxylate (DAAD) and 2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine-5,7(6H)-dione, in high yields. 相似文献
76.
Alkylidene Meldrum's acids and 2,6‐dimethylphenyl isocyanide react smoothly in the presence of arylhydroxylamines at room temperature to produce 2,5‐dioxo‐pyrrolidines in fairly high yield. 相似文献
77.
Nona Habibi Mahmoud Ebrahimi 《International journal of environmental analytical chemistry》2013,93(14):1459-1470
ABSTRACTA novel ion-selective electrochemical sensor based on kryptofix-22DD (1,10-didecyl-1,10-diaza-18-crown-6) as an ionophore was constructed for determination of lanthanum(III) cation in solutions. The D-Optimal Mixture Design(D-OMD) was used as an experimental design strategy for optimal formulation of the membrane ingredients, and the actual values of the ingredients were compared with their predicted values. The amounts of the ionophore, plasticizer, PVC, and also the graphite powder which influence the performance of the fabricated electrode were analyzed using D-OMD. A non-linear relationship was observed between the slope of the electrochemical response of the electrode and these variables and the interaction between the variables as well. The experimental results showed that the amount of the ionophore has the most positive effect on the electrochemical response of the electrode. The constructed electrode exhibits a Nernstian slope (20.60 ± 0.21 mv.decade?1) in a wide linear concentration range from 1.0 × 10?7 to 1.0 × 10?1 M with respect to La3+ cation at pH range of 4.0 to 6.0, and its detection limit was found to be:0.8 × 10?7M. The selectivity of the proposed electrode towards some of the metal cations present in lanthanum(III) cation solutions was tested, and the experimental results showed a good selectivity towards this metal cation. 相似文献
78.
Seyed Sajad Sajadikhah Nourallah Hazeri Malek Taher Maghsoodlou Sayyed Mostafa Habibi‐Khorassani 《中国化学会会志》2013,60(8):1003-1006
A mild and efficient method for the one‐pot synthesis of substituted dihydropyrrol‐2‐one derivatives is described via four‐component domino reaction of amines, dialkyl acetylenedicarboxyaltes and formaldehyde in the presence of 1‐methyl‐2‐oxopyrrolidinium hydrogen sulfate ([Hpyro][HSO4]) as ionic liquid catalyst. This facile approach proceeded smoothly in good to high yields and pure products are separated from the reaction mixture by simple filtration. 相似文献
79.
A. Ebrahimi S. M. Habibi Khorasani R. S. Neyband 《International journal of quantum chemistry》2010,110(10):1871-1879
The relationships among geometrical parameters, estimated binding energies, and nuclear magnetic resonance data in –C?O···H? O? intramolecular H‐bond of some substituted 2‐hydroxybenzaldehyde have theoretically been studied by B3LYP and MP2 methods with 6‐311++G** and AUG‐cc‐PVTZ basis sets. All substituents increase estimated hydrogen bond energies EHBs (with the exception of NO2 and C2H5), which are in good correlation with geometrical parameters, topological properties of electron density calculated at O···H bond critical points and ring critical points by using atoms in molecules method, the results of natural bond orbital analysis, and calculated nuclear magnetic resonance data. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
80.
Mohammad Hossein Habibi Morteza Montazerozohori Ross W. Harrington 《Journal of fluorine chemistry》2006,127(6):769-773
The Schiff base compound, N,N′-bis(trifluoromethylbenzylidene)ethylenediamine (C18H14F6N2) (1), CF3C6H4CHNCH2CH2NCHC6H4CF3 has been synthesized by adding a solution of ethylenediammine (en), 0.1 mmol in chloroform to 4-(trifluoromethyl)-benzaldehyde, CF3C6H4CHO (0.2 mmol) and the product was crystallized in ethanol with the mp, 109.2 °C and 75% yield. The crystal structure was investigated by a single-crystal X-ray diffraction study at 150 K. The compound crystallizes in monoclinic space group, P21/c with a = 9.295(3), b = 5.976(5), c = 15.204(9) Å and α = 90°, β = 96.56(5)° and γ = 90°. The crystal structure is stabilized by intermolecular CH · · · F hydrogen bonds. The asymmetric unit contains only one-half of the molecule related to the center of symmetry coinciding with C(1)-C(1′) and as a whole, the title molecule is in the staggered conformation. The phenyl rings and the CN imine bonds are co-planar. The infrared spectrum showed a sharp peak at 1640 cm−1 which is typical of the conjugated CN stretching and strong peaks at 800-1400 cm−1 regions are due to the C-C and C-H stretching modes. Electronic absorption spectra exhibits strong absorption in the UV region (240 nm wavelength) which have been ascribed to , and electronic transitions. The 1H NMR spectra showed three distinct peaks at 2.5, 7.8 and 8.5 ppm which are assigned based on the splitting of resonance signals and are clearly confirmed by the X-ray molecular structure. The aromatic protons appear at about 7.8 ppm and the imine protons at 8.5 ppm. The sharp singlet at about 3.95 ppm is assigned to the CH2-CH2 protons. Mass spectra of the titled compound showed the molecular ion peak at m/e 372 (M+), and fragments at m/e 353 (M-F), 342 (M-2F), 200 (M-CF3C6H4CHN), 186 (M-CF3C6H4CHNCH2). 相似文献