全文获取类型
| 收费全文 | 1776篇 |
| 免费 | 21篇 |
| 国内免费 | 6篇 |
专业分类
| 化学 | 1155篇 |
| 晶体学 | 15篇 |
| 力学 | 79篇 |
| 数学 | 319篇 |
| 物理学 | 235篇 |
出版年
| 2023年 | 15篇 |
| 2022年 | 16篇 |
| 2021年 | 29篇 |
| 2020年 | 37篇 |
| 2019年 | 33篇 |
| 2018年 | 20篇 |
| 2017年 | 19篇 |
| 2016年 | 50篇 |
| 2015年 | 33篇 |
| 2014年 | 37篇 |
| 2013年 | 77篇 |
| 2012年 | 71篇 |
| 2011年 | 108篇 |
| 2010年 | 63篇 |
| 2009年 | 49篇 |
| 2008年 | 82篇 |
| 2007年 | 97篇 |
| 2006年 | 83篇 |
| 2005年 | 85篇 |
| 2004年 | 78篇 |
| 2003年 | 69篇 |
| 2002年 | 58篇 |
| 2001年 | 24篇 |
| 2000年 | 27篇 |
| 1999年 | 19篇 |
| 1998年 | 12篇 |
| 1997年 | 18篇 |
| 1996年 | 23篇 |
| 1995年 | 17篇 |
| 1994年 | 21篇 |
| 1993年 | 21篇 |
| 1992年 | 24篇 |
| 1991年 | 19篇 |
| 1990年 | 19篇 |
| 1989年 | 25篇 |
| 1988年 | 20篇 |
| 1987年 | 16篇 |
| 1986年 | 11篇 |
| 1985年 | 27篇 |
| 1984年 | 31篇 |
| 1983年 | 20篇 |
| 1982年 | 20篇 |
| 1981年 | 17篇 |
| 1980年 | 20篇 |
| 1979年 | 18篇 |
| 1978年 | 14篇 |
| 1977年 | 13篇 |
| 1976年 | 14篇 |
| 1975年 | 9篇 |
| 1974年 | 15篇 |
排序方式： 共有1803条查询结果，搜索用时 0 毫秒
991.
992.
Guoyi Ke Eugenio Aulisa Giorgio Bornia Victoria Howle 《Numerical Linear Algebra with Applications》2017,24(5)
In this paper, we compare two block triangular preconditioners for different linearizations of the Rayleigh–Bénard convection problem discretized with finite element methods. The two preconditioners differ in the nested or nonnested use of a certain approximation of the Schur complement associated to the Navier–Stokes block. First, bounds on the generalized eigenvalues are obtained for the preconditioned systems linearized with both Picard and Newton methods. Then, the performance of the proposed preconditioners is studied in terms of computational time. This investigation reveals some inconsistencies in the literature that are hereby discussed. We observe that the nonnested preconditioner works best both for the Picard and for the Newton cases. Therefore, we further investigate its performance by extending its application to a mixed Picard–Newton scheme. Numerical results of two‐ and three‐dimensional cases show that the convergence is robust with respect to the mesh size. We also give a characterization of the performance of the various preconditioned linearization schemes in terms of the Rayleigh number. 相似文献
993.
Ru-Jin Li Andrew Tarzia Victor Posligua Kim E. Jelfs Nicolas Sanchez Adam Marcus Ananya Baksi Guido H. Clever Farzaneh Fadaei-Tirani Kay Severin 《Chemical science》2022,13(40):11912
Cuboctahedral coordination cages of the general formula [Pd12L24]24+ (L = low-symmetry ligand) were analyzed theoretically and experimentally. With 350 696 potential isomers, the structural space of these assemblies is vast. Orientational self-sorting refers to the preferential formation of particular isomers within the pool of potential structures. Geometric and computational analyses predict the preferred formation of cages with a cis arrangement at the metal centers. This prediction was corroborated experimentally by synthesizing a [Pd12L24]24+ cage with a bridging 3-(4-(pyridin-4-yl)phenyl)pyridine ligand. A crystallographic analysis of this assembly showed exclusive cis coordination of the 3- and the 4-pyridyl donor groups at the Pd2+ ions.Cuboctahedral [Pd12L24]24+ cages based on low-symmetry ligands can potentially form a vast number of isomers, but the self-assembly process was found to be highly selective. 相似文献
994.
Federica Arena Dr. Giorgio Giuffredi Dr. Andrea Perego Dr. Stefano Donini Hilmar Guzmán Simelys Hernández Eduardo Stancanelli Cesare Cosentino Dr. Emilio Parisini Dr. Fabio Di Fonzo 《ChemElectroChem》2021,8(15):2846-2857
The electrochemical reduction of CO2 to value-added products like formate represents a promising technology for the valorization of carbon dioxide. We propose a proof-of-concept bioelectrochemical system (BES) for the reduction of CO2 to formate. For the first time, our device employs a nanostructured titanium nitride (TiN) support for the immobilization of a formate dehydrogenase (FDH) enzyme. The hierarchical TiN nanostructured support exhibits high surface area and wide pore size distribution, achieving high catalytic loading, and is characterized by higher conductivity than other oxide-based supports employed for FDHs immobilization. We select the oxygen-tolerant FDH from Thiobacillus sp. KNK65MA (TsFDH) as enzymatic catalyst, which selectively reduces CO2 to formate. We identify an optimal TiN morphology for the enzyme immobilisation through enzymatic assay, reaching a catalyst loading of 59 μg cm−2 of specifically-adsorbed TsFDH and achieving a complete saturation of the anchoring sites available on the surface. We evaluate the electrochemical CO2 reduction performance of the TiN/TsFDH system, achieving a remarkable HCOO− Faradaic efficiency up to 76 %, a maximum formate yield of 44.1 μmol mg−1FDH h−1 and high stability. Our results show the technological feasibility of BES devices employing novel, nanostructured TiN-based supports, representing an important step in the optimization of these devices. 相似文献
995.
Giorgio Viavattene Mariarita Murabito Salvatore L. Guglielmino Ilaria Ermolli Giuseppe Consolini Fabrizio Giorgi Shahin Jafarzadeh 《Entropy (Basel, Switzerland)》2021,23(4)
The solar photosphere and the outer layer of the Sun’s interior are characterized by convective motions, which display a chaotic and turbulent character. In this work, we evaluated the pseudo-Lyapunov exponents of the overshooting convective motions observed on the Sun’s surface by using a method employed in the literature to estimate those exponents, as well as another technique deduced from their definition. We analyzed observations taken with state-of-the-art instruments at ground- and space-based telescopes, and we particularly benefited from the spectro-polarimetric data acquired with the Interferometric Bidimensional Spectrometer, the Crisp Imaging SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following previous studies in the literature, we computed maps of four quantities which were representative of the physical properties of solar plasma in each observation, and estimated the pseudo-Lyapunov exponents from the residuals between the values of the quantities computed at any point in the map and the mean of values over the whole map. In contrast to previous results reported in the literature, we found that the computed exponents hold negative values, which are typical of a dissipative regime, for all the quantities derived from our observations. The values of the estimated exponents increase with the spatial resolution of the data and are almost unaffected by small concentrations of magnetic field. Finally, we showed that similar results were also achieved by estimating the exponents from residuals between the values at each point in maps derived from observations taken at different times. The latter estimation technique better accounts for the definition of these exponents than the method employed in previous studies. 相似文献
996.
Dr. Francesco Manoli Dr. Filippo Doria Prof. Giorgio Colombo Dr. Barbara Zambelli Mauro Freccero Dr. Ilse Manet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11707-11720
Human telomeric DNA with hundreds of repeats of the 5’-TTAGGG-3’ motif plays a crucial role in several biological processes. It folds into G-quadruplex (G4) structures and features a pocket at the interface of two contiguous G4 blocks. Up to now no structural NMR and crystallographic data are available for ligands interacting with contiguous G4s. Naphthalene diimide monomers and dyads were investigated as ligands of a dimeric G4 of human telomeric DNA comparing the results with those of the model monomeric G4. Time-resolved fluorescence, circular dichroism, isothermal titration calorimetry and molecular modeling were used to elucidate binding features. Ligand fluorescence lifetime and induced circular dichroism unveiled occupancy of the binding site at the interface. Thermodynamic parameters confirmed the hypothesis as they remarkably change for the dyad complexes of the monomeric and dimeric telomeric G4. The bi-functional ligand structure of the dyads is a fundamental requisite for binding at the G4 interface as only the dyads engage in complexes with 1 : 1 stoichiometry, lodging in the pocket at the interface and establishing multiple interactions with the DNA skeleton. In the absence of NMR and crystallographic data, our study affords important proofs of binding at the interface pocket and clues on the role played by the ligand structure. 相似文献
997.
Marianna Pioli Nicol Orsoni Mirco Scaccaglia Rossella Alinovi Silvana Pinelli Giorgio Pelosi Franco Bisceglie 《Molecules (Basel, Switzerland)》2021,26(4)
The synthesis, photoactivation and biological activity of a new piano-stool Ru(II) complex is herein reported. The peculiarity of this complex is that its monodentate ligand which undergoes the photodissociation is an asymmetric bis-thiocarbohydrazone ligand that possesses a pyridine moiety binding to Ru(II) and the other moiety contains a quinoline that endows the ligand with the capacity of chelating other metal ions. In this way, upon dissociation, the ligand can be released in the form of a metal complex. In this article, the double ability of this new Ru(II) complex to photorelease the ligand and to chelate copper and nickel is explored and confirmed. The biological activity of this compound is studied in cell line A549 revealing that, after irradiation, proliferation inhibition is reached at very low half maximal inhibitory concentration (IC50) values. Further, biological assays reveal that the dinuclear complex containing Ni is internalized in cells. 相似文献
998.
Clia M. Silveira Lidia Zuccarello Catarina Barbosa Giorgio Caserta Ingo Zebger Peter Hildebrandt Smilja Todorovic 《Molecules (Basel, Switzerland)》2021,26(16)
Vibrational spectroscopy and in particular, resonance Raman (RR) spectroscopy, can provide molecular details on metalloproteins containing multiple cofactors, which are often challenging for other spectroscopies. Due to distinct spectroscopic fingerprints, RR spectroscopy has a unique capacity to monitor simultaneously and independently different metal cofactors that can have particular roles in metalloproteins. These include e.g., (i) different types of hemes, for instance hemes c, a and a3 in caa3-type oxygen reductases, (ii) distinct spin populations, such as electron transfer (ET) low-spin (LS) and catalytic high-spin (HS) hemes in nitrite reductases, (iii) different types of Fe-S clusters, such as 3Fe-4S and 4Fe-4S centers in di-cluster ferredoxins, and (iv) bi-metallic center and ET Fe-S clusters in hydrogenases. IR spectroscopy can provide unmatched molecular details on specific enzymes like hydrogenases that possess catalytic centers coordinated by CO and CN− ligands, which exhibit spectrally well separated IR bands. This article reviews the work on metalloproteins for which vibrational spectroscopy has ensured advances in understanding structural and mechanistic properties, including multiple heme-containing proteins, such as nitrite reductases that house a notable total of 28 hemes in a functional unit, respiratory chain complexes, and hydrogenases that carry out the most fundamental functions in cells. 相似文献
999.
Stefania Villa Giorgio Cignarella Michela M. Curzu Grard A. Pinna Elena Pini Lucio Toma 《Journal of heterocyclic chemistry》1999,36(5):1253-1257
The isomeric compounds 5,6-dihydrothieno[2,3-h]cinnolin-3(2H)-one ( 7a ) and 5,6-dihydrothieno-[3,2-h]cinnolin-3(2H)-one ( 7b ) rapidly tautomerise to the corresponding 1,4-dihydrothienocinnolinones 8a,b when kept in refluxing hydrazine hydrate. With longer reaction times the initially formed 8a,b dehydrogenate to the thienocinnolinones 9a,b which eventually are aminated to 4-aminothienocinnolinones 10a,b . This behaviour recalls that reported for the related 5,6-dihydrobenzocinnolin-3(2H)-one ( 1 ) which under the same conditions undergoes dehydrogenation to benzo[h]cinnolin-3(2H)-one ( 2 ) followed by 4-amination to 3 , but differs for the stability of the intermediates, for the mechanism of the final amination, and for the higher reaction rate. All these differences can be rationalised in terms of the heats of formation of the intermediates and products of the two series of transformations. 相似文献
1000.