全文获取类型
收费全文 | 127篇 |
免费 | 10篇 |
专业分类
化学 | 110篇 |
力学 | 1篇 |
数学 | 11篇 |
物理学 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 4篇 |
2008年 | 3篇 |
2007年 | 7篇 |
2006年 | 1篇 |
2005年 | 5篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2000年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有137条查询结果,搜索用时 187 毫秒
21.
M. Nasim V. S. Petrosyan G. S. Zaitseva
J. Lorberth
《Journal of organometallic chemistry》1992,430(3):269-272Treatment of silatranyl- and 3,7,10-trimethylsilatranyl-ethylenes with diazomethane/Pd(OAc)2 gives the corresponding silatranylcyclopropanes in high yields. 相似文献
22.
Reaction of cis-[Ptph2(SMe2)2] with Me2PCH2PMe2 (dmpm) gave cis-[PtPh2(dmpm-P)2] (1) or cis,cis-[Pt2Ph4(μ-dmpm)2] (2) and reaction of 1 with [Pt2Me4(μ-SMe2)2] gave cis,cis-[Ph2Pt(μ-dmpm)2PtMe2] (3). Reaction of 1 with trans-[PtClR(SMe2)2] gave cis,trans-[Ph2Pt(μ-dmpm)2PtClR], R = Me (5) or Ph (6), and in polar solvents, these isomerized to give [Ph2Pt(μ-dmpm)2PtR]+Cl−. When R = Me, further isomerization via the phenyl group transfer gave [PhMePt(μ-dmpm)2PtPh]+Cl−. Oxidative addition of methyl iodide occurred reversibly at the cis-[PtMe2P2 unit of 3 to give cis,fac-[Ph2Pt(μ-dmpm)2PtIMe3] but complex 2 failed to react with MeI. A comparison with similar known complexes of Ph2PCH2PPh2 (dppm) is made and differences are attributed primarily to the lower steric hindrance of dmpm. 相似文献
23.
In the present work, gel polymer electrolytes (GPEs) were prepared using poly(methyl methacrylate) (PMMA), lithium perchlorate (LiClO4) and dimethylacetamide as a plasticizer. Solution-casting technique was used to fabricate GPEs containing different weight percentage of PMMA. The degree of crystallinity of GPE samples was studied by X-ray diffraction (XRD) analysis. Fourier transform infrared (FT-IR) spectroscopy was applied to study the level of interactions between lithium salt and PMMA in the prepared GPEs. Electrochemical properties were studied by electrochemical impedance spectroscopy, linear sweep voltammetry and DC polarization techniques. Lithium ion conductivity of GPEs was determined by calculating the bulk resistance of polymer electrolytes from Nyquist plot. Increasing PMMA content of GPEs resulted in an improvement in the electrochemical potential window from 4.2 to 4.5 V. The highest lithium transference number (0.42) and also the best electrochemical properties were obtained for GPE containing 0.75 M LiClO4 and 10 wt% PMMA. Scanning electron microscopy images of the optimized GPE showed a porous and heterogeneous surface structure which is desirable for application in Li-ion batteries. 相似文献
24.
Ramin Maleki Nasim Mohammad Nezhad Naser Samadi Khalil Farhadi 《Mikrochimica acta》2009,165(1-2):97-101
Dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography-diode array detection (HPLC-DAD) has been applied to the extraction and determination of EDTA in sediments and water samples. The effect of extraction, nature and volume of disperser solvent, pH value of sample solution, extraction time and extraction temperature were investigated. Under the optimal conditions the analytical range of EDTA was from 3.0 to 50.0 μg L?1 with a correlation coefficient of 0.9982 and a detection limit of 1.7 μg L?1. The relative standard deviation (RSD) was less than 5.4% (n?=?5), and the recovery values were in the range of 89–95%. The simplicity, high enrichment, high recovery and good repeatability are the main advantages of the method presented. The DLLME-HPLC-DAD method was successfully applied to the analysis of EDTA in aqueous samples. 相似文献
25.
Lv C Hu J Zhou H Li Z Khan RN Wei Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8681-8691
The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile. 相似文献
26.
Nasim Ahmed Syed Alwee Aljunid R. Badlishah Ahmad Hilal A. Fadhil Mohd Abdur Rashid 《Optical Review》2012,19(1):1-6
The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system
has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is
the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal
cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with
the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with
those obtained using the complementary detection technique for the same number of active users. The comparison results revealed
that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to
the complementary technique. 相似文献
27.
28.
Nasim Najjarzadeh Leonidas Matsakas Ulrika Rova Paul Christakopoulos 《Molecules (Basel, Switzerland)》2020,25(24)
Xylan is one of the most abundant carbohydrates on Earth. Complete degradation of xylan is achieved by the collaborative action of endo-β-1,4-xylanases and β-d-xylosidases and a number of accessories enzymes. In filamentous fungi, the xylanolytic system is controlled through induction and repression. However, the exact mechanism remains unclear. Substrates containing xylan promote the induction of xylanases, which release xylooligosaccharides. These, in turn, induce expression of xylanase-encoding genes. Here, we aimed to determine which xylan degradation products acted as inducers, and whether the size of the released oligomer correlated with its induction strength. To this end, we compared xylanase production by different inducers, such as sophorose, lactose, cellooligosaccharides, and xylooligosaccharides in Fusarium oxysporum f. sp. lycopersici. Results indicate that xylooligosaccharides are more effective than other substrates at inducing endoxylanase and β-xylosidases. Moreover, we report a correlation between the degree of xylooligosaccharide polymerization and induction efficiency of each enzyme. Specifically, xylotetraose is the best inducer of endoxylanase, xylohexaose of extracellular β-xylosidase, and xylobiose of cell-bound β-xylosidase. 相似文献
29.
Abdolghafar Abolhosseini Shahrnoy Ali Reza Mahjoub Sudabeh Shokrollahi Nasim Ezzati Kristiane Elsner Christoph T. Koch 《应用有机金属化学》2020,34(7):e5645
In this study, a step-by-step method for the synthesis of platinum nanoparticles and copper(I) complex supported on mesoporous silica hollow spheres (Pt-MSHSs-Cu) is introduced. Scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption, energy-dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, and elemental and thermogravimetric analyses were applied for characterization of the surface, structure, size, phase composition, and morphology of the synthesized materials. The characterized material, Pt-MSHSs-Cu, was used as an efficient and heterogeneous catalyst in the Sonogashira coupling reaction under different reaction conditions. In comparison with MSHSs, Cu(I)-functionalized MSHSs (MSHSs-Cu), and Pt-MSHSs samples, the Pt-MSHSs-Cu catalyst exhibited significantly increased catalytic performance with 91.50% yield. Therefore, the results obtained suggested a synergistic effect derived from platinum nanoparticles, MSHSs substrate, and copper(I) complex, which enhanced the rate of the Sonogashira coupling reaction. 相似文献
30.
Farzin Marandi Dr. Nasim Asghari Massomeh Gorbanloo Ali A. Soudi Peter Mayer 《无机化学与普通化学杂志》2007,633(4):536-538
[Pb(trz)(tfpb)(H2O)] ( 1 ) (trz and tfpb are the abbreviations of 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine and 4,4,4‐trifluoro‐1‐phenyl‐1,3‐butandionate, respectively) have been synthesized and characterized by elemental analysis and IR, 1H NMR, spectroscopy. The single‐crystal structure of 1 shows the coordination number of the Pb2+ ions is eight with three N‐donor atoms from a “trz” ligand and four O‐donors from the dionate ligand and one molecule of water. The supramolecular features in this complex are guided by lone pair activity and control of strong hydrogen bonds, weak directional intermolecular interactions and aromatic π‐π stacking interactions. 相似文献