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121.
Dr. Venubabu Kotikam Julien A. Viel Prof. Dr. Eriks Rozners 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):685-690
The success of RNA interference (RNAi) as a research tool and potential therapeutic approach has reinvigorated interest in chemical modifications of RNA. Replacement of the negatively charged phosphates with neutral amides may be expected to improve bioavailability and cellular uptake of small interfering RNAs (siRNAs) critical for in vivo applications. In this study, we introduced up to seven consecutive amide linkages at the 3′-end of the guide strand of an siRNA duplex. Modified guide strands having four consecutive amide linkages retained high RNAi activity when paired with a passenger strand having one amide modification between its first and second nucleosides at the 5′-end. Further increase in the number of modifications decreased the RNAi activity; however, siRNAs with six and seven amide linkages still showed useful target silencing. While an siRNA duplex having nine amide linkages retained some silencing activity, the partial reduction of the negative charge did not enable passive uptake in HeLa cells. Our results suggest that further chemical modifications, in addition to amide linkages, are needed to enable cellular uptake of siRNAs in the absence of transfection agents. 相似文献
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123.
外商直接投资技术溢出机制研究——基于江苏省制造业面板数据的实证分析 总被引:1,自引:0,他引:1
本文利用2000-2007年江苏省制造业的面板数据,对外商直接投资水平溢出效应和垂直溢出效应进行了检验。结果表明,江苏省外商直接投资存在显著的水平溢出效应、后向溢出效应和前向溢出效应,但水平溢出效应较垂直溢出效应更为明显。并且水平溢出效应和前向溢出效应显示为边际递减,而后向溢出效应的影响是持久的。 相似文献
124.
N. Yousfi M. Sekkal‐Rahal A. Sayede M. Springborg 《Journal of computational chemistry》2010,31(6):1312-1320
The B3LYP density function was used with the 6‐31G(d) basis set to perform relaxed energetic contour maps of the charged form of κ‐carrabiose in the gas phase and for the neutral form first in the gas phase and then by simulating the presence of water as solvent using the Onsager model. Only one starting conformation has been considered to perform all the calculations. Rigid energetic maps have been then constructed either by addition of diffuse or polarization functions to the basis set obtaining in that way 6‐31+G(d)//6‐31G(d), 6‐31+G(d,p)//6‐31G(d), and 6‐311++G(d,p)//6‐31G(d) energetic maps that have been carefully examined. The obtained structures corresponding to the lower energy conformers have been then fully optimized using different basis sets with the B3LYP method, a reversion in term of energy has been observed for the two first minima in the case of the charged disaccharide in the gas phase, this was attributed to the large grid of 30° that could lead to the exclusion of an intermediate value corresponding to the real minimum of energy. We thus suggest that after establishing potential energy maps it is essential to proceed to full optimizations of the lower energy conformers. Calculations using the more accurate correlated method MP2 with the 6‐31G(d) basis set have also been performed for conformers of the two disaccharides in the gas phase. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
125.
Postsource decay (PSD) spectra of isomeric neutral lactooligosaccharide mixtures were measured from the chlorinated molecules [M + Cl]- by negative-ion mode ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI TOF MS) to estimate quantitatively the mixing ratios in their mixtures. The PSD ions specific to each isomeric structure were used to distinguish the linkage and branching isomers, and the molar ratios of the isomers were estimated from their ion abundances. The relative ion abundances changed linearly in the PSD spectra of the mixtures of the isomers as their molar ratio was varied in the analyte solutions. Therefore, the molar ratios of the isomers in the analyte mixtures could be estimated semiquantitatively. In addition, we studied their fragmentation mechanisms in N-acetyl hexosamines such as GlcNAc, which enabled us to quantitatively analyze the structures of the isomers of lactooligosaccharides. The conjugated systems elongate in the chemical species of the Z-type fragmentation on the 3-linked GlcNAc owing to the acetoamido groups at the C-2 positions, which made the chemical species of the Z-type ions stable. The glycosyl bonds of the front of GlcNAc cleaved easily as a C-type fragmentation because the negative charge at the anomeric position could be delocalized to the carbonyl oxygen atom at the acetoamido group of GlcNAc. These factors caused the stabilization of the chemical species of the C/Z fragment ions produced by the double cleavage around GlcNAc. 相似文献
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127.
Xiaofu Wu Bowei Xu Hui Tong Lixiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2012,50(8):1521-1529
Water‐soluble, meta‐ and para‐linked poly(arylene ethynylene)s containing L ‐aspartic acid‐functionalized fluorene units (P1 and P2) and their model compounds (M1 and M2) have been synthesized, and their photophysical properties and fluorescent sensing properties were investigated in aqueous solution. P1 and M1 with the meta‐linkage show blue‐shifted absorption and emission spectra, and decreased photoluminescence quantum yields compared with those of P2 and M2 with para‐linkage. Their absorption and fluorescence spectra are pH dependent perhaps due to the aggregation of the polymer chains at low pH values. In buffer solutions, both polymers and their model compounds exhibit the excellent selectivity and sensitivity to Hg2+ over other common metal ions. Furthermore, the quenching constant and detection limit of P1 are determined to be 1.04 × 107 M?1 and 10 nM, and show the higher sensitivity compared to P2. Further comparison of their model compounds reveal that the sensitivity and quenching efficiency of M1 is also higher than that of M2, indicating that the meta‐linkage pattern plays a key role in improving their Hg2+ ion sensing properties. In addition, both meta‐ and para‐linked polymers exhibit the higher quenching efficiency than their model compounds due to the amplified fluorescence response of conjugated polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
128.
Lan‐Ying Zhang Yang‐Fei Zhang 《Journal of polymer science. Part A, Polymer chemistry》2013,51(12):2545-2554
The work focuses on the design, synthesis, and characterization of a series of mesogen‐jacketed liquid crystalline polymers (MJLCPs) based on the octyl substituted biphenyl mesogenic core through different linkage groups. The molecular characterizations of the polymers obtained by conventional free radical polymerization were performed with 1H NMR, gel permeation chromatography, and thermogravimetric analysis. Their thermotropic liquid crystalline (LC) behaviors were investigated in detail by a combination of various techniques, such as polarized light microscopy, differential scanning calorimetry, and 1D and 2D wide‐angle X‐ray diffraction. Our results showed that all the polymers were thermally stable, and their LC phases were greatly dependent on the linking groups between the biphenyl mesogenic core and terminal alkyl group substituent. Polymers with ether/ester or ether linkage group exhibited an unusual phase behavior with temperature increasing, tetragonal columnar nematic LC phase, or columnar nematic phase developed at high temperatures for the polymers transformed into amorphous phase during cooling process, showing a re‐entrant phase behaviors. However, polymers with ester linkage group were not LC with temperature varied. It is illustrated that subtle changes in the molecular structure brought about tremendous variation of the LC phase properties for MJLCPs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2545–2554 相似文献
129.
《Journal of computational chemistry》2017,38(20):1780-1788
The (nitro)(N‐methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO2)(S2CNHMe)(PMe3)] complex catalyses efficiently the O‐atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO2)(S2CNHMe)(PMe3)] ↔ Ni(NO2)(S2CNHMe)(PMe3) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five‐member metallacycle intermediate, via a [3 + 2] cyclo‐addition reaction of HC≡CH to the Ni‐N = O moiety of the Ni(NO2)(S2CNHMe)(PMe3)] complex, followed by a β H‐atom migration toward the Cα carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( ‐NO2)(S2CNHMe)(PMe3)] [Ni( ‐ONO)(S2CNHMe)(PMe3)] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc. 相似文献
130.
Silica nanoparticles were linked by using 3‐mercaptopropyltrimethoxysilane (MPS) as a coupling agent and Cd2+ as bridging ions. The TEM micrographs showed approximately linear linkage between the silica nanoparticles rather than dense packing. The UV‐visible absorption spectra confirmed the formation of S‐Cd‐S bonds between the silica nanoparticles. The alternative films of MPS‐modified SiO2 nanoparticles and Cd2+ ions were also prepared using the layer‐by‐layer self‐assembly technique and characterized by AFM. 相似文献