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771.
Dichotomy in the Lithiation Pathway of Ellipsoidal and Platelet LiFePO4 Particles Revealed through Nanoscale Operando State‐of‐Charge Imaging 下载免费PDF全文
Yiyang Li Johanna Nelson Weker William E. Gent David N. Mueller Jongwoo Lim Daniel A. Cogswell Tolek Tyliszczak William C. Chueh 《Advanced functional materials》2015,25(24):3677-3687
LiFePO4 is a promising phase‐separating battery electrode and a model system for studying lithiation. The role of particle synthesis and the corresponding particle morphology on the nanoscale insertion and migration of Li is not well understood, and elucidating the intercalation pathway is crucial toward improving battery performance. A synchrotron operando liquid X‐ray imaging platform is developed to track the migration of Li in LiFePO4 electrodes with single‐particle sensitivity. Lithiation is tracked in two particle types—ellipsoidal and platelet—while the particles cycle in an organic liquid electrolyte, and the results show a clear dichotomy in the intercalation pathway. The ellipsoidal particles intercalate sequentially, concentrating the current in a small number of actively intercalating particles. At the same cycling rate, platelet particles intercalate simultaneously, leading to a significantly more uniform current distribution. Assuming that the particles intercalate through a single‐phase pathway, it is proposed that the two particle types exhibit different surface properties, a result of different synthesis procedures, which affect the surface reactivity of LiFePO4. Alternatively, if the particles intercalate through nucleation and growth, the larger size of platelet particles may account for the dichotomy. Beyond providing particle engineering insights, the operando microscopy platform enables new opportunities for nanoscale chemical imaging of liquid‐based electrochemical systems. 相似文献
772.
Deshpande PP Ellsworth BA Buono FG Pullockaran A Singh J Kissick TP Huang MH Lobinger H Denzel T Mueller RH 《The Journal of organic chemistry》2007,72(25):9746-9749
An efficient and practical process to generate beta-C-arylglucoside derivatives was achieved. The process described involves Lewis acid mediated ionic reduction of a peracetylated 1-C-aryl methyl glucoside derived from the addition of an aryl-Li to selectively protected delta-D-gluconolactone. The reduction of the 2-acetoxy-1-C-oxacarbenium ion intermediates proceeds with a high degree of selectivity to give beta-C-arylglucosides without 2-acetoxy group participation. Furthermore, during the reduction process we also identified an unprecedented critical role of water. By changing from the usual benzyl ether protecting groups because of cost and chemical compatibility concerns, the new process is made additionally efficient and highly selective. 相似文献
773.
In high-throughput proteomics, the bottom-up approach has become a widely used method for the identification of proteins that is based on tryptic peptide MS/MS analysis. Separation methodologies that use IEF of tryptic peptides have recently been introduced and provide an extra dimension of peptide separation. In addition to its great fractionation capability, tryptic peptide prefractionation by IEF can also increase the protein identification success. The pI information of the peptide gained can be successfully used in a post-database search filtering step. We introduce a filtering algorithm that is based on the comparison of the experimental and theoretical pI's to validate peptide identifications by MS/MS data search engines. 相似文献
774.
We study the time scales for adiabaticity of trapped cold bosons subject to a time-varying lattice potential using a dynamic Gutzwiller mean-field theory. We explain apparently contradictory experimental observations by demonstrating a clear separation of time scales for local dynamics (~ ms) and global mass redistribution (~1 s). We provide a simple explanation for the short and fast time scales, finding that while density or energy transport is dominated by low energy phonons, particle-hole excitations set the adiabaticity time for fast ramps. We show how mass transport shuts off within Mott-insulator domains, leading to a chemical potential gradient that fails to equilibrate on experimental time scales. 相似文献
775.
N-Acylated N-chlorohydantoins are shown to be competent chlorenium sources in the (DHQD)(2)PHAL-mediated asymmetric chlorolactonization. The derivatives demonstrate the exact role of the N1 and N3 chlorine atoms in the parent dichlorohydantoins with the N1 chlorine serving as an inductive activator and the N3 chlorine being delivered to the substrate. The putative associated catalyst/chlorine source complex was experimentally demonstrated through a series of matched/mismatched experiments employing chiral N-chlorinated hydantoins. 相似文献
776.
Leonhard Jaitz Bernhard Mueller Gunda Koellensperger Daniela Huber Eva Oburger Markus Puschenreiter Stephan Hann 《Analytical and bioanalytical chemistry》2011,400(8):2587-2596
A sensitive method for quantification of citric, fumaric, malic, malonic, oxalic, trans aconitic, and succinic acid in soil-
and root-related samples is presented. The method is based on a novel, fast, and simple esterification procedure and subsequent
analysis via liquid chromatography–mass spectrometry. Derivatization comprises in situ generation of HCl, which catalyzes
the Fischer esterification with benzyl alcohol. As a key advance, the esterification with the aromate allows reversed-phase
separation and improves electrospray ionization efficiency. The method provided procedural detection limits of 1 nM for citric,
47 nM for fumaric, 10 nM for malic, 10 nM for malonic, 16 nM for oxalic, 15 nM for succinic, and 2 nM for aconitic acid utilizing
500 μL of liquid sample. The working range was 3 nM to 10 μM for citric acid, 158 nM to 10 μM for fumaric acid, 34 nM to 10 μM
for malic acid, 33 nM to 10 μM for malonic acid, 53 nM to 10 μM for oxalic acid, 48 nM to 10 μM for succinic acid, and 6 nM
to 10 μM for aconitic acid. Quantification of the analytes in soil-related samples was performed via external calibration
of the entire procedure utilizing 13C-labeled oxalic and citric acid as internal standards. The robustness of the method was tested with soil extracts and samples
from hydroponic experiments. The latter concerned the regulation of phosphorus solubilization via plant root exudation of
citric, malic, and oxalic acid. 相似文献
777.
Kneissl B Mueller SC Tautermann CS Hildebrandt A 《Journal of chemical information and modeling》2011,51(11):3017-3025
The reasons for distortions from optimal α-helical geometry are widely unknown, but their influences on structural changes of proteins are significant. Hence, their prediction is a crucial problem in structural bioinformatics. For the particular case of kink prediction, we generated a data set of 132 membrane proteins containing 1014 manually labeled helices and examined the environment of kinks. Our sequence analysis confirms the great relevance of proline and reveals disproportionately high occurrences of glycine and serine at kink positions. The structural analysis shows significantly different solvent accessible surface area mean values for kinked and nonkinked helices. More important, we used this data set to validate string kernels for support vector machines as a new kink prediction method. Applying the new predictor, about 80% of all helices could be correctly predicted as kinked or nonkinked even when focusing on small helical fragments. The results exceed recently reported accuracies of alternative approaches and are a consequence of both the method and the data set. 相似文献
778.
Shibata S Zhang Z Korotkov KV Delarosa J Napuli A Kelley AM Mueller N Ross J Zucker FH Buckner FS Merritt EA Verlinde CL Van Voorhis WC Hol WG Fan E 《Analytical and bioanalytical chemistry》2011,401(5):1585-1591
Ultrafiltration provides a generic method to discover ligands for protein drug targets with millimolar to micromolar K(d), the typical range of fragment-based drug discovery. This method was tailored to a 96-well format, and cocktails of fragment-sized molecules, with molecular masses between 150 and 300 Da, were screened against medical structural genomics target proteins. The validity of the method was confirmed through competitive binding assays in the presence of ligands known to bind the target proteins. 相似文献
779.
Beran GJ Chronister EL Daemen LL Moehlig AR Mueller LJ Oomens J Rice A Santiago-Dieppa DR Tham FS Theel K Yaghmaei S Morton TH 《Physical chemistry chemical physics : PCCP》2011,13(45):20380-20392
Vibrational spectra of the conjugate acid of Me(2)NCH(2)CH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethylputrescine) have been examined in the gaseous and crystalline phases using Infrared Multiple Photon Dissociation (IRMPD) spectroscopy, Inelastic Neutron Scattering (INS), and high pressure Raman spectroscopy. A band observed near 530 cm(-1) is assigned to the asymmetric stretch of the bridging proton between the two nitrogens, based on deuterium substitution and pressure dependence. The NN distance measured by X-ray crystallography gives a good match to DFT calculations, and the experimental band position agrees with the value predicted from theory using a 2-dimensional potential energy surface. The reduced dimensionality potential energy surface, which treats the ion as though it possesses a linear NHN geometry, shows low barriers to proton transit from one nitrogen to the other, with zero point levels close to the barrier tops. In contrast, two other related systems containing strong hydrogen bonds do not exhibit the same spectroscopic signature of a low barrier hydrogen bond (LBHB). On the one hand, the IRMPD spectra of the conjugate acid ions of the amino acid N,N,N',N'-tetramethylornithine (in which the two nitrogens have different basicities) show fewer bands and no comparable isotopic shifts in the low frequency domain. On the other hand, the IRMPD spectrum of the shorter homologue Me(2)NCH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethyl-1,3-propanediamine), for which the NHN bond angle deviates substantially from linearity, displays more than one band in the 1100-1400 cm(-1) domain, which vanish as a consequence of deuteration. 相似文献
780.
Lucangelo Dimesso Christina Spanheimer Mathis M. Mueller Hans-Joachim Kleebe Wolfram Jaegermann 《Ionics》2015,21(8):2101-2107
LiCo1???x Ca x PO4–graphitic carbon foam composites are prepared using a sol–gel method. The structural analysis reveals LiCoPO4 as major crystalline phase and Co2P2O7 (for x?=?0.0) and Co2P, Li3PO4, and (Ca,Co)3(PO4)2 (for x?≥?0.05) as secondary phases. The morphology consists of microcrystalline “islands” with acicular crystallites (5–50 μm size). Transmission electron microscopy (TEM) of the powders showed that the Ca is incorporated into the crystal structure evoking exaggerated grain growth. The voltammetric profiles show a decrease of the voltammetric surface between anodic and cathodic sweeps and a shift of the reduction potentials toward higher values (~4.6 V, x?=?0.1). The electrochemical measurements, at a discharge rate of C/10 (room temperature), show an increase of the discharge-specific capacity from 100 mAhg?1 for x?=?0.0 to 104 mAhg?1 for x?=?0.1. The ac impedance spectroscopy data revealed an improvement of the Li-ion conductivity at high content of Ca ions (x?=?0.1). 相似文献