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501.
Lukas Hleba Miroslava Hlebova Anton Kovacik Jana Petrova Zuzana Maskova Juraj Cubon Peter Massanyi 《Molecules (Basel, Switzerland)》2022,27(22)
Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins. One of the producers of AFB1 is Aspergillus flavus. Therefore, its rapid identification plays a key role in various sectors of the food and feed industry. MALDI-TOF mass spectrometry is one of the fastest and most accurate methods today. Therefore, the aim of this research was to develop the rapid identification of producing and non-producing strains of A. flavus based on the entire mass spectrum. To accomplish the main goal a different confirmatory MALDI-TOF MS and TLC procedures such as direct AFB1 identification by scraping from TLC plates, A. flavus mycelium, nutrient media around A. flavus growth, and finally direct AFB1 identification from infected wheat and barley grains had to be conducted. In this experiment, MALDI-TOF mass spectrometry with various modifications was the main supporting technology. All confirmatory methods confirmed the presence of AFB1 in the samples of aflatoxin-producing strains of A. flavus and vice versa; AFB1 was not detected in the case of non-producing strains. Entire mass spectra (from 2 to 20 kDa) of aflatoxin-producing and non-producing A. flavus strains were collected, statistically analyzed and clustered. An in-depth analysis of the obtained entire mass spectra showed differences between AFB1-producing and non-producing strains of A. flavus. Statistical and cluster analysis divided AFB1-producing and non-producing strains of A. flavus into two monasteries. The results indicate that it is possible to distinguish between AFB1 producers and non-producers by comparing the entire mass spectra using MALDI-TOF MS. Finally, we demonstrated that if there are established local AFB1-producing and non-producing strains of A. flavus, the entire mass spectrum database identification of aflatoxigenic A. flavus strains can be even faster and cheaper, without the need to identify the toxin itself. 相似文献
502.
《Arabian Journal of Chemistry》2022,15(12):104281
Quality control of traditional Chinese medicine (TCM) should be linked with the authentication and efficacy of TCM. Selaginella tamariscina is a frequently used traditional Chinese herbal medicine. However, its quality control is still difficult due to its multiple adulterants. We established quality markers (Q-markers) of S. tamariscina by using metabolomics, molecular networking and network pharmacology to improve the authenticity study and quality control of S. tamariscina. In this study, ultra high performance liquid chromatography-mass spectrum (UHPLC-MS) coupled with multivariate statistical analyses was applied to distinguish between S. tamariscina samples and their confusing adulterants. Principal component analysis, hierarchical clustering analysis (PCA), hierarchical clustering analysis (HCA) and partial least squares discriminant analysis (PLS-DA) were employed to screen the distinguishing markers from S. tamariscina samples and their adulterants. The top-2 distinguishing markers were isolated from S. tamariscina and identified by molecular networking together with nuclear magnetic resonance spectroscopy (NMR). Network pharmacology predicted the bioactivity and cytotoxicity of the top-2 distinguishing markers. The top-2 distinguishing markers were adopted as Q-markers of S. tamariscina for content determination. Based on the results of ultra performance liquid chromatography-quardrupole-time of flight mass spectrometry (UHPLC-QTOF-MS) metabolomics, we revealed that selaginellins could only be detected in S. tamariscina samples and contributed greatly to discriminating S. tamariscina samples from their confused species. The top-2 distinguishing markers were isolated and purified from S. tamariscina extract. Then, they were further identified as selaginellin and selaginellin A by molecular networking and NMR. Network pharmacology predicted the antitumor activity of selaginellin and selaginellin A, while the cytotoxicity assay verified their bioactivity. In conclusion, selaginellin and selaginellin A were selected as Q-markers for the determination and quality evaluation of S. tamariscina based on ultra performance liquid chromatography-triple quadrupole tandem mass spectrometry (UHPLC-QQQ-MS). The ranges of the concentrations of selaginellin and selaginellin A were 41.57–44.89 μg/g and 15.09–16.75 μg/g, respectively. This study provides a novel strategy combining Ultra performance liquid chromatography mass spectrometry based (UHPLC-MS-based) metabolomics with molecular networking for rapid species identification of S. tamariscina and discovery of the Q-markers of TCM. 相似文献
503.
We examined the ability of two human cytosolic transaminases, aspartate aminotransferase (GOT1) and alanine aminotransferase (GPT), to transform their preferred substrates whilst discriminating against similar metabolites. This offers an opportunity to survey our current understanding of enzyme selectivity and specificity in a biological context. Substrate selectivity can be quantitated based on the ratio of the kcat/KM values for two alternative substrates (the ‘discrimination index’). After assessing the advantages, implications and limits of this index, we analyzed the reactions of GOT1 and GPT with alternative substrates that are metabolically available and show limited structural differences with respect to the preferred substrates. The transaminases’ observed selectivities were remarkably high. In particular, GOT1 reacted ~106-fold less efficiently when the side-chain carboxylate of the ’physiological’ substrates (aspartate and glutamate) was replaced by an amido group (asparagine and glutamine). This represents a current empirical limit of discrimination associated with this chemical difference. The structural basis of GOT1 selectivity was addressed through substrate docking simulations, which highlighted the importance of electrostatic interactions and proper substrate positioning in the active site. We briefly discuss the biological implications of these results and the possibility of using kcat/KM values to derive a global measure of enzyme specificity. 相似文献
504.
505.
This paper considers the model discrimination problem among a finite number of models in safety–critical systems that are subjected to constraints that can be disjunctive and where state and input constraints can be coupled with each other. In particular, we consider both the optimal input design problem for active model discrimination that is solved offline as well as the online passive model discrimination problem via a model invalidation framework. To overcome the issues associated with non-convex and generalized semi-infinite constraints due to the disjunctive and coupled constraints, we propose some techniques for reformulating these constraints in a computationally tractable manner by leveraging the Karush–Kuhn–Tucker (KKT) conditions and introducing binary variables, thus recasting the active and passive model discrimination problems into tractable mixed-integer linear/quadratic programming (MILP/MIQP) problems. When compared with existing approaches, our method is able to obtain the optimal solution and is observed in simulations to also result in less computation time. Finally, we demonstrate the effectiveness of the proposed active model discrimination approach for estimating driver intention with disjunctive safety constraints and state–input coupled curvature constraints, as well as for fault identification. 相似文献
506.
507.
Chiral discrimination by nuclear magnetic resonance (NMR) spectroscopy might be achieved through the pseudo‐scalar derived from the dipole shielding polarizability tensor. Coupled Cluster Singles and Doubles‐Quadratic Response (CCSD‐QR) calculations inside the continuous translation of the origin of the current density formalism have been carried out to determine the effects of basis set, electron correlation, and gauge translation on the determination of this magnitude in oxaziridine derivatives. Inclusion of electronic correlation is needed for adequately describing the pseudo‐scalar for the heavier nuclei, making CCSD a rigorous and affordable method to compute these high order properties in medium‐sized molecules. The observable magnitudes for chiral discrimination (produced RF voltage and required electric field) are calculated. Half of the considered molecules show values of the observable magnitudes near the lower limit for experimental detection. Nuclei 19F, 31P, and 79Br produce the largest values of RF voltage (50–80 nV). Moreover, 31P and 79Br are the nuclei requiring smallest electric fields (3 MVm?1) to separate the NMR signals, being then suitable for both the techniques. © 2014 Wiley Periodicals, Inc. 相似文献
508.
A multi‐channel surface acoustic wave (SAW) detection system which is employed to detect various organic molecules in a static system was prepared using 315 MHz one‐port quartz resonators and a home‐made computer interface for signal acquisition and data process. The oscillating frequency of the quartz crystal decreases on adsorption of organic molecules on the coating materials. The principal component analysis (PCA) method with SAS software was applied to select the appropriate coating materials onto the SAW crystals for organic vapors, e.g. hexane, 1‐hexene, 1‐hexyne, 1‐propanol, propionaldehyde, propionic acid, and 1‐propylamine. A dataset for a multi‐channel sensor with 19 SAW crystals for 7 analyses was collected after comparing the correlation between the 19 coating materials and the first six principal component (PC) factor. Furthermore, linear discriminate analysis (LDA) with SPSS software and a profile discrimination map were also applied and discussed for the discrimination of these organic vapors. These organic molecules could be clearly distinguished by the six‐channel SAW static sensor. The effect of concentration for various organic vapors was investigated and discussed. 相似文献
509.
For the first time, the discrimination of different chiral forms of 1:1 complexes with hydrogen peroxide and methyl hydroperoxide have been investigated using density functional theory (DFT) and Møller–Plesset type 2 (MP2) methods at varied basis set levels from 6‐31+G(d,p) to 6‐31++G(2d,2p). Three pairs of chiral enantiomers were considered. The optimized geometric parameters, interaction energies, and chirodiastatic energies for various isomers at different levels are estimated. To take into account the water solvation effect, the polarized continuum model (PCM) method has been used to evaluate the ΔGsolv. The gas phase results show that the heterochiral six‐membered ring complex (structure I) and homochiral five‐membered ring complexes (structures IV and V) are preferred configurations for the three pairs of chiral enantiomers. The solvation effect on six‐membered ring complexes (structures I and II) shows nonsignificant changes in the configurations preferred, but on five‐membered ring complexes, the homo‐/heterochiral preference is found to be inverse in the polar solvent. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
510.
Bhaskar G Prabhakar S Ramanjaneyulu GS Vairamani M Srinivasu VN Srinivas K 《Journal of mass spectrometry : JMS》2007,42(9):1194-1206
A series of meso-dialkyl, alkyl aryl and cycloalkyl calix(4)pyrroles (1-15) are studied under positive and negative ion electrospray ionization (ESI) conditions. The positive ion spectra show abundant [M + H](+) and [M + Na](+) ions and the negative ion spectra show the [M + Cl](-) (the Cl(-) ions from the solvent) and [M - H](-) ions. The collision induced dissociation (CID) spectra of [M + H](+), [M + Na](+), [M + Cl](-) and [M - H](-) ions are studied to understand their dissociation pathway and compared to that reported for M(+) under electron ionization (EI) conditions. The beta-cleavage process that was diagnostic to M(+) is absent in all the CID spectra of the ions studied under ESI. Dissociation of all the studied ions resulted in the fragment ions formed by sequential elimination of pyrrole (A) and/or dialkyl/alkyl aryl/cycloalkyl (B) groups involving hydrogen migration to pyrrole ring at each cleavage of A--B bond, which clearly reveals the arrangement of A and B groups in the calix(4)pyrroles. The source of hydrogen that migrates to pyrrole ring during A--B bond cleavage is investigated by the experiments on deuterated compounds and [M + D](+) ions; and confirmed that the hydrogen attached to pyrrole nitrogen, hydrogen on alpha-carbon of alkyl group and the H(+)/Na(+) ion that added during ESI process to generate [M + H](+)/[M + Na](+) ions involve in the migration. The yields of [M + Na](+) ions are found to be different for the isomeric meso-cycloalkyl compounds (cycloheptyl, and 2-, 3- and 4-methyl cyclohexyl) and for normal and N-confused calix(4)pyrroles. The isomeric methyl and 3-hydroxy/4-hydroxy phenyl calix(4)pyrroles show specific fragmentation pattern during the dissociation of their [M - H](-) ions. 相似文献