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91.
Troy D. Wood Charles W. Ross Alan G. Marshall 《Journal of the American Society for Mass Spectrometry》1994,5(10):900-907
We have systematically established the excitation frequency, amplitude, duration, and buffer gas pressure for optimal axialization efficiency and mass selectivity of quadrupolar excitation-collisional cooling for isolation of parent ions for collision-induced dissociation in Fourier transform ion cyclotron resonance mass spectrometry. For example, at high quadrupolar excitation amplitude, ion axialization efficiency and selectivity are optimal when the applied quadrupolar excitation frequency is lower than the unperturbed ion cyclotron frequency by up to several hundred hertz. Moreover, at high buffer gas pressure (10?6 Torr), quadrupolar excitation duration can be quite short because of efficient collisional cooling of the cyclotron motion produced by magnetron-to-cyclotron conversion. Efficiency, detected signal magnitude, and mass resolving power for collision-induced dissociation (CID) product ions are significantly enhanced by prior parent ion axialization. With this method, we use argon CID to show that C 94 + (m/z 1128) formed by Nd:YAG laser desorption-ionization behaves as a closed-cage structure. 相似文献
92.
Aikaterini Vriza Angelos B. Canaj Rebecca Vismara Laurence J. Kershaw Cook Troy D. Manning Michael W. Gaultois Peter A. Wood Vitaliy Kurlin Neil Berry Matthew S. Dyer Matthew J. Rosseinsky 《Chemical science》2021,12(5):1702
The implementation of machine learning models has brought major changes in the decision-making process for materials design. One matter of concern for the data-driven approaches is the lack of negative data from unsuccessful synthetic attempts, which might generate inherently imbalanced datasets. We propose the application of the one-class classification methodology as an effective tool for tackling these limitations on the materials design problems. This is a concept of learning based only on a well-defined class without counter examples. An extensive study on the different one-class classification algorithms is performed until the most appropriate workflow is identified for guiding the discovery of emerging materials belonging to a relatively small class, that being the weakly bound polyaromatic hydrocarbon co-crystals. The two-step approach presented in this study first trains the model using all the known molecular combinations that form this class of co-crystals extracted from the Cambridge Structural Database (1722 molecular combinations), followed by scoring possible yet unknown pairs from the ZINC15 database (21 736 possible molecular combinations). Focusing on the highest-ranking pairs predicted to have higher probability of forming co-crystals, materials discovery can be accelerated by reducing the vast molecular space and directing the synthetic efforts of chemists. Further on, using interpretability techniques a more detailed understanding of the molecular properties causing co-crystallization is sought after. The applicability of the current methodology is demonstrated with the discovery of two novel co-crystals, namely pyrene-6H-benzo[c]chromen-6-one (1) and pyrene-9,10-dicyanoanthracene (2).Machine learning using one class classification on a database of existing co-crystals enables the identification of co-formers which are likely to form stable co-crystals, resulting in the synthesis of two co-crystals of polyaromatic hydrocarbons. 相似文献
93.
The typical shallowness of the potential surfaces of weakly bound clusters implies sizable ground-state vibrational excursions in the weak modes, a feature often complicated by considerable anharmonicity. The difficulties of vibrational analysis are exacerbated as the number of weak modes increases with the number of molecules in a cluster. Quantum Monte Carlo (QMC) approaches offer a general suitability to the problem of vibrational dynamics of weakly bound clusters in that they can fully account for anharmonicity and large amplitude motions. We report on the effectiveness and convergence behavior of diffusion quantum Monte Carlo for both energies and the key spectroscopic values of vibrationally averaged rotational constants. QMC involves recurring evaluations of the interaction potential, and we show how property-based, two-and three-body potentials (e.g., those involving intrinsic molecular tensor properties) may be carefully linked to the QMC propagation steps. © 1997 by John Wiley & Sons, Inc. 相似文献
94.
Craig P. Dufresne Troy D. Wood Christopher L. Hendrickson 《Journal of the American Society for Mass Spectrometry》1998,9(11):1222-1225
Glucokinase (GK, EC 2.7.1.2), a member of the enzyme family of hexokinases, has been shown to be linked to maturity-onset diabetes of the young type II (MODY-2). Although nucleotide and amino acid sequence information are available for the human varieties, they are not known for the variety from Bacillus stearothermophilus, which is often used in protein binding studies. Here, a combination of electrospray Fourier transform mass spectrometry (FTMS) and infrared multiphoton dissociation (IRMPD) is used to obtain accurate molecular weight and preliminary amino acid sequence information for the protein. Electrospray FTMS provides evidence of a solution phase dimer. In addition, dithiothreitol reduction shows no shift in high-resolution isotopic distributions, indicating a probable absence of disulfide bonds in the protein. The partial sequence information obtained from IRMPD could be the basis for creating a DNA probe for the protein. 相似文献
95.
G. J. B. van den Berg L. A. Peletier W. C. Troy 《Archive for Rational Mechanics and Analysis》2001,158(2):91-153
In this paper we study the existence of single- and multi-bump periodic solutions of a class of fourth order ordinary differential
equations arising in problems of pattern formation. Measuring the tendency to form patterns by a parameter q∈ℝ, we view the problem as a nonlinear eigenvalue problem. With the use of analytical as well as numerical methods, branches
of periodic solutions are investigated, both locally and globally.
Accepted November 1, 2000?Published online May 7, 2001 相似文献
96.
Ernö Lindner Vasile V. Cosofret Stefan Ufer Timothy A. Johnson R. Bruce Ash H. Troy Nagle Michael R. Neuman Richard P. Buck 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):584-588
Summary Ion-sensitive, planar micro-electrode arrays were fabricated by photolithographic microelectronics technology on a flexible polyimide substrate. The steps of the microelectronics processing are summarized. The electrodes were tested in blood serum, whole blood and in the hamstring muscle of anesthetized rabbits. The performance characteristics of planar pH-sensors are compared with commercial glass electrodes. The close correlation of the data are encouraging for further acute and later chronic applications.Dedicated to Professor Dr. Wilhelm Fresenius 相似文献
97.
98.
J.N. Gau Yukap Hahn J.A. Retter 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,23(2):147-156
Dielectronic recombination rate coefficients for Mo32+ recombining to Mo32+ are given for electron temperatures of 1.4, 2.8, and 5.6 keV. Nonrelativistic results in the resonance approximation were obtained and tables of selected Auger (Aa) and radiative (Ar) rates, fluorescence yields, and dielectronic recombination rates are given. Excitation of 2p electrons to higher shells is found to be dominant over other transitions including direct capture at the temperatures considered. The effect of the cascade transitions is estimated to be of the order of 30%. Different angular momentum averaging procedures change the results very significantly. 相似文献
99.
100.
Jennifer M. Butler Troy E. Knight Sohrob Sotoudehnia Paul D. Kadle Jr. Susan L. Green Gary M. Gray 《Journal of chemical crystallography》2004,34(2):111-118
The X-ray crystal structures of four closely related Mo(CO)5(R2PXR) (R2 = OCH2CMe2CH2O, XR = S-2-Pr, NHC6H4-4-Me; R2 = Ph2, XR = NHC6H4-2-Me, OC6H4-4-SMe) complexes have been determined. The R2PXR ligands are oriented so that the P—X bond and one of the Mo—C bonds are nearly eclipsed. This results in the distortion of the octahedral coordination geometry via tilting of the Mo(CO)5 group away from the XR group. As observed in related complexes, the Mo—C bond of the carbonyl trans to the phosphorus-donor group is shorter than are the Mo—C bonds of the carbonyls trans to carbonyls. In contrast, no significant differences were observed between the Mo—C bonds of carbonyls trans to phosphites and the Mo—C bonds of carbonyls trans to phosphinites. The conformations of the 1,3,2-dioxaphosphorinanes were distorted chairs with the P end of the chair significantly flattened relative to the seat of the chair. This conformation is similar to that which has been observed for 1,3,2-dioxaphosphorinanes in other transition metal complexes. 相似文献