全文获取类型
收费全文 | 648篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
化学 | 427篇 |
晶体学 | 5篇 |
力学 | 23篇 |
数学 | 94篇 |
物理学 | 115篇 |
出版年
2022年 | 6篇 |
2021年 | 11篇 |
2019年 | 4篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 44篇 |
2012年 | 28篇 |
2011年 | 33篇 |
2010年 | 23篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 25篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 28篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1935年 | 4篇 |
1933年 | 3篇 |
排序方式: 共有664条查询结果,搜索用时 0 毫秒
21.
Randall Claywell Laszlo Nadai Imre Felde Sina Ardabili Amirhosein Mosavi 《Entropy (Basel, Switzerland)》2020,22(11)
The accurate prediction of the solar diffuse fraction (DF), sometimes called the diffuse ratio, is an important topic for solar energy research. In the present study, the current state of Diffuse irradiance research is discussed and then three robust, machine learning (ML) models are examined using a large dataset (almost eight years) of hourly readings from Almeria, Spain. The ML models used herein, are a hybrid adaptive network-based fuzzy inference system (ANFIS), a single multi-layer perceptron (MLP) and a hybrid multi-layer perceptron grey wolf optimizer (MLP-GWO). These models were evaluated for their predictive precision, using various solar and DF irradiance data, from Spain. The results were then evaluated using frequently used evaluation criteria, the mean absolute error (MAE), mean error (ME) and the root mean square error (RMSE). The results showed that the MLP-GWO model, followed by the ANFIS model, provided a higher performance in both the training and the testing procedures. 相似文献
22.
Ragulan Ramanathan Laszlo Prokai 《Journal of the American Society for Mass Spectrometry》1995,6(9):866-871
Electrospray ionization (ESI) mass spectrometry has been used to study inclusion (host-guest) complexes of cyclodextrins (CDs) with amino acids. Host-guest complexes formed in solution are stable for characterization by ESI mass spectrometry: The relative abundances and the stoichiometry of the complexes formed in solution can, thus, be determined in the gas phase. The studies verified that β- and γ-cyclodextrin better accommodate protonated amino acids than α-cyclodextrin, and that chemically modified cyclodextrins such as heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) may show profound improvement in complexation. The preferential formation of DM-β-CD-aromatic amino acid over DM-β-CD-aliphatic amino acid complexes is confirmed by the experiments, and the relative gas-phase stabilities determined by repeller-collimator collision-induced dissociation show an identical trend to the complexation in solution. Although molecular mechanics studies also may predict the encapsulation preference of protonated amino acids by cyclodextrins, only small differences in the total complexation energies are obtained because of the inability of the calculations to consider hydrophobic interactions. An experimental approach based on ESI mass spectrometry is, therefore, more reliable in predicting host-guest interactions that involve cyclodextrins and amino acids than the theoretical calculations that employ molecular mechanics models. 相似文献
23.
Serena Indelicato David Bongiorno Sergio Indelicato Laszlo Drahos Vincenzo Turco Liveri Lilla Turiák Karoly Vékey Leopoldo Ceraulo 《Journal of mass spectrometry : JMS》2013,48(3):379-383
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine–enkephalin. Positively and negatively charged aggregates behave similarly, but the slope of the CCE versus DoF plot is steeper for positive ions, suggesting that these are more stable than their negative counterparts. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
24.
Renz M Blasco T Corma A Fornés V Jensen R Nemeth L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(20):4708-4717
Sn-Beta is used as a heterogeneous catalyst for the Baeyer-Villiger reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones, while unsaturated ketones are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. The catalyst is also selective for the oxidation of aromatic aldehydes with H2O2, producing the formate ester or the corresponding hydrolyzed product, that is the alcohol. Shape-selective oxidations are observed for isomeric reactants with different molecular shapes. The catalytic Sn sites have been characterized by 119Sn MAS-NMR spectroscopy, and tetrahedral incorporation into the zeolite framework has been demonstrated. In situ IR spectroscopy and 18O labeling experiments have shown that the oxidation mechanism involves an intermediate of the Criegee type. 相似文献
25.
Ryan E Campbell-Anson Diane Kentor Yi J Wang Kathryn M Bushnell Yufeng Li Luis M Vence Laszlo G Radvanyi 《Journal of immune based therapies and vaccines》2008,6(1):1
Background
Human monocyte-derived DC (mDC) loaded with peptides, protein, tumor cell lysates, or tumor cell RNA, are being tested as vaccines against multiple human malignancies and viral infection with great promise. One of the factors that has limited more widespread use of these vaccines is the need to generate mDC in large scale. Current methods for the large-scale cultivation of mDC in static culture vessels are labor- and time- intensive, and also require many culture vessels. Here, we describe a new method for the large-scale generation of human mDC from human PBMC from leukopheresis or buffy coat products using roller bottles, never attempted before for mDC generation. We have tested this technology using 850 cm2 roller bottles compared to conventional T-175 flat-bottom static culture flasks. 相似文献26.
Hegedus L Kirschner N Wittmann M Simon P Noszticzius Z Amemiya T Ohmori T Yamaguchi T 《Chaos (Woodbury, N.Y.)》1999,9(2):283-297
The polarization curve of an acid-base interface in a hydrogel medium has a diode characteristic. Two of each such electrolyte diodes can be combined to give an electrolyte transistor. When a salt is added to the alkaline or to the acidic part of a reverse biased electrolyte diode, the current response is highly nonlinear. If the salt is added to the acidic side, even bistability can be observed. This bistability can generate complex oscillations in a base-acid-base electrolyte transistor. These nonlinear effects are studied experimentally and theoretically. While the nonlinear salt effect can be explained with the Nernst-Planck equations, to understand the bistable behavior further investigations are necessary. (c) 1999 American Institute of Physics. 相似文献
27.
Amine(N? B)-aminoborane internal complexes and 1,3,2-diazaborolidines were recently identified as intermediates of the borane reduction of imidazolidino[1,2-d]dithiazepines. Theoretical Mo calculations were used to obtain the structural, conformational, and electronic properties and heats of formation of the boron compounds in the framework of the semiempirical AM 1 approximation. Internal constraints in the bicyclic system were analyzed through comparisons with the calculated molecular geometries, electron distribution of monocyclic, and open-chain models. The geometry of the five-membered diazaborolidine systems becomes distorted upon building up the complex bicyclic structure, compared to the nearly planar monocycles. The weak coordinative nitrogen–boron bond (calculated bond order around 0.5) in the internal complexes exerts less conformational strains in the adjoining nine-membered ring containing the disulfide than does the covalent N? B bond in the corresponding 1,2,3-diazaborolidine. Thus, the internal constraints of the bicyclic system is taken up by the five-membered ring to a lesser degree in the 1,3,2diazaborolidine than in the internal complex. © 1992 John Wiley & Sons, Inc. 相似文献
28.
M. Petrascu A. Isbasescu I. Lazar I. Mihai H. Petrascu A. T. Rudchik V. A. Chernievski O. A. Ponkratenko V. A. Ziman 《Zeitschrift für Physik A Hadrons and Nuclei》1993,345(4):395-399
The energy spectra and angular distributions of products in the reaction27Al(14N,X) have been measured at 116 MeV bombarding energy. It is shown that the energy spectra of the products lighter than the projectile, are well described by a three-body breakup calculation. The experimental total breakup cross-section estimated in the present work, together with Glas-Mosel calculation of the fusion cross-section, are in a reasonable agreement with the optical model total reaction cross-section. 相似文献
29.
Stéphane Chalais Alfred Delville Christian Detellier André Gerstmans Pierre Laszlo 《Journal of solution chemistry》1983,12(1):33-40
Intrinsic formation constants for complexes of Na+ ions with a series of polyamines have been determined from23Na NMR measurements in binary mixtures of tetrahydrofuran (THF) and amines. The results show in a totally unambiguous manner a regular decrease in the magnitude of the chelate effect with the number of atoms intervening between the nitrogen ligators. The key assumption, tetracoordination of the cation, is critically examined, and experimental evidence is adduced in its support. 相似文献
30.
A. J. Lazar 《Israel Journal of Mathematics》1969,7(4):357-364
LetX be a polyhedral Banach space whose dual is anL
1(μ) space for some measureμ. Then for each Banach spacesY ⊆Z and each compact operatorT: Y →X there exists a norm preserving compact extension
Z →X. 相似文献