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691.
Sieving gels are used in capillary gel electrophoresis to resolve DNA strands of different lengths. For complex samples, however, such as those encountered in metagenomic analysis of microbial communities or biofilms, length-based separation may mask the true genetic diversity of the community since different organisms may contribute same-length DNA with different sequences. There is a need, therefore, for DNA separations based on both the length and sequence. Previous work has demonstrated the ability of guanosine gels (G-gels) to separate four single-stranded DNA 76-mers that differ by only a few A/G base substitutions. The goal of the present work is to determine whether G-gels could be combined with commercial sieving gels in order to simultaneously separate DNA based on both length and sequence. The results are given for the four 76-mers and for a standard dsDNA ladder. Commercial sieving gels were used alone and in combination with G-gels. For the 76-mers, the combined medium was less efficient than the G-gel alone but was able to achieve partial resolution. The combined medium was at least as effective as the sieving gel alone at resolving the denatured DNA ladder and showed indications of sequence-based resolution as well, as supported by MALDI-MS. The results show that the combined sieving gel/G-gel medium retains the selectivity of the individual media, providing a promising approach to simultaneous length- and sequence-based DNA separation for metagenomic analysis of complex systems. 相似文献
692.
Through a biomimetic pathway, hyperolactone D, 4-hydroxyhyperolactone D, and hyperolactone C were synthesized from methyl acetoacetate via Weiler's dianion method, asymmetric allylic alkylation, biomimetic lactonization, oxidation, and cyclization. The stereochemistry of the quaternary carbon was controlled efficiently by Palladium-catalyzed asymmetric allylic alkylation. This strategy was also used for the synthesis of hyperolactone B. 相似文献
693.
Cassidy LM Dong Y Joshi PC Aldersley MF Ferris JP McGown LB 《Journal of the American Society for Mass Spectrometry》2011,22(6):1100-1104
Metal is the standard desorption platform for MALDI-MS but other surfaces have been shown to offer advantages for particular types of analytes or applications. One such substrate is fused silica, which has been employed for matrix-free detection of low mass analytes and for affinity MALDI-MS in which binding ligands are immobilized at the fused silica surface. The present work reports improved MALDI-MS detection of RNA oligonucleotides, including polyA, polyU, and polyA/U, at the high end of the mass range when unmodified fused silica is used instead of stainless steel as the MALDI target. The RNA oligonucleotides were abiotically synthesized from activated monomers on catalytic clay surfaces. Further investigation found enhanced signals as well for other anionic biopolymers, including DNA oligonucleotides and heparin. Enhancement also was observed for dextran, which is neutral, indicating that the effect is not restricted to anionic biopolymers. Among more general analytical applications, the results are particularly relevant to rapid screening of abiotic RNA polymerization toward elucidating pathways to life on Earth. 相似文献
694.
Evaluation of the influence of sulfur fumigation on the pharmacokinetics of four active ingredients in Si Wu Tang 下载免费PDF全文
Ke Pei Hao Cai Xiao Liu Sicong Tu Gang Cao Huan Li Yingying Zhao Xiaoqing Song Yajing Lou Fengxian Qiao Baochang Cai 《Journal of separation science》2015,38(1):25-33
Sulfur fumigation may induce the decrease or the chemical transformation of some active ingredients of traditional Chinese medicines in vitro. Whether sulfur fumigation can cause the pharmacokinetic changes of the active ingredients in vivo is related to the efficacy and the safety of Chinese medicines’ application clinically. A sensitive, specific, and accurate method for the simultaneous determination of paeoniflorin, ferulic acid, senkyunolide A, and senkyunolide I in rat plasma by ultra high performance liquid chromatography coupled with triple quadrupole mass spectrometry was developed to evaluate the influence of sulfur fumigation to Si Wu Tang for the first time. Each compound was extracted from plasma samples by liquid–liquid extraction with ethyl acetate, and the chromatographic separation was accomplished on an Agilent Extend C18 column with a linear gradient elution. The mass spectrometric detection and analysis were performed by using an AB Sciex triple quadrupole 5500 mass spectrometer in multiple reaction monitoring mode. The validated method was successfully applied to a pharmacokinetic study of four compounds in rats after oral administration of sun‐dried and sulfur‐fumigated Si Wu Tang. The results provided a meaningful basis for evaluating the affection of sulfur fumigation to the clinical application and the efficacy of Si Wu Tang. 相似文献
695.
696.
697.
Nanoporous silver (NPS) is fabricated by selectively dissolving Al from AgAl alloys in corrosive electrolytes at room temperature. Electron spectroscopy characterizations demonstrate that the NaOH electrolyte is beneficial to the formation of a three‐dimensional bicontinuous porous nanostructure with uniform and tunable pore and ligament dimensions of a few tens of nanometers, while processing in HCl electrolyte easily lead to coarsened porous nanostructures. The high‐surface‐area Ag nanostructures are demonstrated as novel effective template materials to the construction of nanotubular mesoporous Pt/Ag and Pd/Ag alloy structures, which are realized via room temperature galvanic replacement reactions with H2PtCl6 and K2PdCl4 solutions by adding a high concentration of Cl? ions as a coordinating agent. Electrochemical measurements indicate that the resulting hollow and porous bimetallic nanostructures show enhanced electrocatalytic activities and CO‐tolerance with better durability toward methanol and formic acid oxidation due to alloying with Ag. 相似文献
698.
699.
A Ni/TiO2(TBT) catalyst was prepared through in situ precipitation, using tetrabutyl titanate(TBT) as the TiO2 precursor, and was studied in CO methanation. A Ni catalyst supported on commercial TiO2 was also prepared through post precipitation and studied to compare the influence of Ni precipitation conditions on the catalyst's performance. To gain insight on their structure and physicochemical properties, the catalysts were characterized with N2-adsorption, X-ray diffraction, transimission electron microscopy, H2 temperature programmed reduction and temperature programmed desorption. The results showed that the in situ precipitation method was beneficial to the dispersion of Ni and the formation of more active sites on the Ni/TiO2 catalyst. In addition, the density of the metal-support boundary and its interaction with the active component were also increased. These characteristics of Ni/TiO2(TBT) led to a lower light-off temperature and a suppression of Ni sintering during CO methanation. As a consequence, the Ni/TiO2(TBT) exhibited better catalytic behavior, with a CO conversion of 99.4% and CH4 selecti-vity of 90.4% under the following conditions:p=1 MPa, t=320℃, n(H2)/n(CO)=3, gas hour space velocity (GHSV)=2×104 mL·g-1·h-1. The life test results of the two catalysts showed that Ni/TiO2(TBT) was more stable and the catalytic activity remained at its initial level after being used for 30 h. 相似文献
700.
Combination of Optimization and Metalated‐Ligand Exchange: An Effective Approach to Functionalize UiO‐66(Zr) MOFs for CO2 Separation 下载免费PDF全文
Zhigang Hu Samuel Faucher Yingying Zhuo Yao Sun Songnan Wang Prof. Dr. Dan Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17246-17255
The strategy to functionalize water‐stable metal–organic frameworks (MOFs) in order to improve their CO2 uptake capacities for efficient CO2 separation remains limited and challenging. We herein present an effective approach to functionalize a prominent water‐stable MOF, UiO‐66(Zr), by a combination of optimization and metalated‐ligand exchange. In particular, by systematic optimization, we have successfully obtained UiO‐66(Zr) of the highest BET surface area reported so far (1730 m2 g?1). Moreover, it shows a hybrid Type I/IV N2 isotherm at 77 K and a mesopore size of 3.9 nm for the first time. The UiO‐66 MOF underwent a metalated‐ligand‐exchange (MLE) process to yield a series of new UiO‐66‐type MOFs, among which UiO‐66‐(COONa)2‐EX and UiO‐66‐(COOLi)4‐EX MOFs have both enhanced CO2 working capacity and IAST CO2/N2 selectivity. Our approach has thus suggested an alternative design to achieve water‐stable MOFs with high crystallinity and gas uptake for efficient CO2 separation. 相似文献