全文获取类型
收费全文 | 610篇 |
免费 | 38篇 |
国内免费 | 2篇 |
专业分类
化学 | 405篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 118篇 |
物理学 | 115篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 23篇 |
2020年 | 22篇 |
2019年 | 22篇 |
2018年 | 13篇 |
2017年 | 4篇 |
2016年 | 27篇 |
2015年 | 20篇 |
2014年 | 27篇 |
2013年 | 39篇 |
2012年 | 43篇 |
2011年 | 40篇 |
2010年 | 21篇 |
2009年 | 27篇 |
2008年 | 31篇 |
2007年 | 41篇 |
2006年 | 38篇 |
2005年 | 36篇 |
2004年 | 26篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 8篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有650条查询结果,搜索用时 15 毫秒
641.
Eugenio E. Vogel Gonzalo Saravia 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(8):1-15
The use of data compressor techniques has allowed to recognize magnetic transitions and their associated critical temperatures [E.E. Vogel, G. Saravia, V. Cortez, Physica A 391, 1591 (2012)]. In the present paper we introduce some new concepts associated to data recognition and extend the use of these techniques to econophysics to explore the variations of stock market indicators showing that information theory can help to recognize different regimes. Modifications and further developments to previously introduced data compressor wlzip are introduced yielding two measurements. Additionally, we introduce an algorithm that allows to tune the number of significant digits over which the data compression is due to act complementing, this with an appropriate method to round off the truncation. The application is done to IPSA, the main indicator of the Chilean Stock Market during the year 2010 due to availability of quality data and also to consider a rare effect: the earthquake of the 27th of February on that year which is as of now the sixth strongest earthquake ever recorded by instruments (8.8 Richter scale) according to United States Geological Survey. Along the year 2010 different regimes are recognized. Calm days show larger compression than agitated days allowing for classification and recognition. Then the focus turns onto selected days showing that it is possible to recognize different regimes with the data of the last hour (60 entries) allowing to determine actions in a safer way. The “day of the week” effect is weakly present but “the hour of the day” effect is clearly present; its causes and implications are discussed. This effect also establishes the influence of Asian, European and American stock markets over the smaller Chilean Stock Market. Then dynamical studies are conducted intended to search a system that can help to realize in real time about sudden variations of the market; it is found that information theory can be really helpful in this respect. 相似文献
642.
Manuel J. Llansola‐Portoles Jesse J. Bergkamp John Tomlin Thomas A. Moore Gerdenis Kodis Ana L. Moore Gonzalo Cosa Rodrigo E. Palacios 《Photochemistry and photobiology》2013,89(6):1375-1382
The photosensitization effect of three perylene dye derivatives on titanium dioxide nanoparticles (TiO2 NPs) has been investigated. The dyes used, 1,7‐dibromoperylene‐3,4,9,10‐tetracarboxy dianhydride (1), 1,7‐dipyrrolidinylperylene‐3,4,9,10‐tetracarboxy dianhydride (2) and 1,7‐bis(4‐tert‐butylphenyloxy)perylene‐3,4,9,10‐tetracarboxy dianhydride (3) have in common bisanhydride groups that convert into TiO2 binding groups upon hydrolysis. The different substituents on the bay position of the dyes enable tuning of their redox properties to yield significantly different driving forces for photoinduced electron transfer (PeT). Recently developed TiO2 NPs having a small average size and a narrow distribution (4 ± 1 nm) are used in this work to prepare the dye‐TiO2 systems under study. Whereas successful sensitization was obtained with 1 and 2 as evidenced by steady‐state spectral shifts and transient absorption results, no evidence for the attachment of 3 to TiO2 was observed. The comparison of the rates of PeT (kPeT) for 1‐ and 2‐TiO2 systems studied in this work with those obtained for previously reported analogous systems, having TiO2 NPs covered by a surfactant layer (Hernandez et al. [2012] J. Phys. Chem. B., 117, 4568–4581), indicates that kPeT for the former systems is slower than that for the later. These results are interpreted in terms of the different energy values of the conduction band edge in each system. 相似文献
643.
We study the underwater light field seasonality in a turbid lake, Laguna Chascomús (Buenos Aires, Argentina). We report (1) relationships between optical properties (OPs) and optically active substances (OASs); (2) relationships between inherent (IOPs) and apparent (AOPs) optical properties; and (3) the seasonal variability in OASs and OPs. Light absorption was dominated by the particulate fraction. The contributions of phytoplankton pigments and unpigmented components were similar. The best predictors of total particulate absorption, unpigmented particulate absorption, turbidity and vertical attenuation coefficient were total suspended solids or their ash content. Many OASs and OPs varied seasonally. The concentrations of OASs were higher during spring and summer, resulting in lower transparency and higher turbidity. However, mass-specific absorption coefficients displayed lower values during spring and summer. Thus, the higher light attenuation observed during spring and summer resulted from higher concentrations of relatively less absorptive OASs. Collectively, these results suggest that: (1) light extinction is enhanced during spring and summer; (2) the enhanced light extinction is due to changes in the particulate fraction; (3) the enhanced light extinction is mostly due to an increase in the amount of particulate material; and (4) the increase of particulate matter also enhanced light extinction through increased scattering. 相似文献
644.
Gonzalo Abellán Hermenegildo García Carlos J. Gómez-García Antonio Ribera 《Journal of photochemistry and photobiology. A, Chemistry》2011,217(1):157-163
The photochemistry of three azobenzenes representing contrasting photochemical behaviors is described in the present work. Thus, Methyl Orange (MO, 4-[[(4-dimethylamino)phenyl]-azo]benzenesulfonic acid sodium salt, hereinafter (1) and 4-hydroxyazobenzene-4′-sulfonic acid (2) undergo in water fast photochemical proton shift, with decays in the microsecond timescale. In contrast to the previous cases, azobenzene-4,4′-dicarboxylic acid (3) undergoes photoisomerization in water. This photochemical behavior allows the preparation of aqueous gels with Aerosil as gelating agent (5% weight) exhibiting high cyclability and photoreversible isomerization of the trans to cis (300 nm irradiation) and cis to trans (visible white light irradiation). Gels containing azobenzene 3 as photoresponsive molecule and well-dispersed magnetite (Fe3O4) nanoparticles exhibit simultaneously high photoresponse and magnetic properties. Photoisomerization of compound 3 in these gels leads to small but reliable changes (25 G coercive field) in the magnetic hysteresis loop of magnetite nanoparticles. This novel concept of optical modulation of magnetism in iron oxide nanoparticles paves the way for the study of new systems, with a stronger coupling between trans–cis photoisomerization and magnetic properties. 相似文献
645.
Recently a chaotic cryptosystem based on discrete-time synchronization has been proposed. Some weaknesses of that new encryption system are addressed and exploited in order to successfully cryptanalyze the system. 相似文献
646.
Victor I. Afonso Gonzalo J. Olmo Emanuele Orazi Diego Rubiera-Garcia 《The European Physical Journal C - Particles and Fields》2018,78(10):866
We show that families of nonlinear gravity theories formulated in a metric-affine approach and coupled to a nonlinear theory of electrodynamics can be mapped into general relativity (GR) coupled to another nonlinear theory of electrodynamics. This allows to generate solutions of the former from those of the latter using purely algebraic transformations. This correspondence is explicitly illustrated with the Eddington-inspired Born–Infeld theory of gravity, for which we consider a family of nonlinear electrodynamics and show that, under the map, preserve their algebraic structure. For the particular case of Maxwell electrodynamics coupled to Born–Infeld gravity we find, via this correspondence, a Born–Infeld-type nonlinear electrodynamics on the GR side. Solving the spherically symmetric electrovacuum case for the latter, we show how the map provides directly the right solutions for the former. This procedure opens a new door to explore astrophysical and cosmological scenarios in nonlinear gravity theories by exploiting the full power of the analytical and numerical methods developed within the framework of GR. 相似文献
647.
The central mechanism in ferroptosis linking lipid hydroperoxide accumulation with cell death remains poorly understood. Although lipid hydroperoxides are known to break down to reactive lipid-derived electrophiles (LDEs), the ability of cells to detoxify increasing LDE levels during ferroptosis has not been studied. Here, we developed an assay (ElectrophileQ) correlating the cellular retention vs. excretion of a fluorogenic lipophilic electrophile (AcroB) that enables live-cell assessment of the glutathione-mediated LDE conjugation and adduct export steps of the LDE detoxification pathway. This method revealed that during ferroptosis, LDE detoxification failure occurs through decreased conjugation or export impairment, amplifying cellular electrophile accumulation. Notably, ferroptosis susceptibility was increased following exacerbation of LDE-adduct export impairment through export channel inhibition. Our results expand understanding of the ferroptosis molecular cell death mechanism to position the LDE detoxification pathway as a ferroptosis-relevant therapeutic target. We envision the ElectrophileQ assay becoming an invaluable tool for studying ferroptosis and cellular health.A link between altered lipid-derived electrophile (LDE) metabolism during ferroptosis and associated cell death was uncovered using a new imaging method developed to monitor cellular LDE detoxification that employs a fluorogenic LDE analogue. 相似文献
648.
Dr. Gonzalo García-Espejo Dr. Konstantis F. Konidaris Dr. Pietro Anzini Prof. Stefano Brenna Dr. Antonietta Guagliardi Prof. Norberto Masciocchi 《欧洲无机化学杂志》2023,26(23):e202300282
The discovery of new 3D perovskites and their 2D and 1D analogues continues to attract the interest of the scientific community and therefore the understanding of their structural, optical, and physicochemical properties is of fundamental importance. Here, we report the one-pot synthesis and the full characterization of 1D and 2D lead halide polycrystalline solids containing the rather rigid 1,4-xylylenediammonium (pXDA) organic cation as spacer. We isolated 2D Dion-Jacobson (DJ) perovskites, namely (pXDA)PbX4 (X=Cl, Br) and the mixed halide (pXDA)Pb(Br1–xIx)4 species (all based on 2D monolayers of corner-sharing lead halide octahedra), and, for iodine, the (pXDA)Pb2I6 . 2H2O phase, which contains 1D ribbons. The latter species can be reversibly dehydrated by gentle heating, forming the isomorphous (pXDA)Pb2I6. crystal phase. These species, some of which have recently been studied in the frame of broad light emitters and for photovoltaic applications, have been characterized by variable-temperature X-ray diffraction methods, shedding light onto their anisotropic thermal responses, of utmost importance for day-night cycling in functional devices. Spin-coated thin films were also prepared and studied by means of synchrotron radiation grazing incidence X-ray diffraction, SEM imaging and fluorescence spectroscopy experiments. 相似文献
649.
Protoglobin-Catalyzed Formation of cis-Trifluoromethyl-Substituted Cyclopropanes by Carbene Transfer
Lucas Schaus Dr. Anuvab Das Dr. Anders M. Knight Dr. Gonzalo Jimenez-Osés Prof. Dr. K. N. Houk Dr. Marc Garcia-Borràs Prof. Dr. Frances H. Arnold Prof. Dr. Xiongyi Huang 《Angewandte Chemie (International ed. in English)》2023,62(4):e202208936
Trifluoromethyl-substituted cyclopropanes (CF3-CPAs) constitute an important class of compounds for drug discovery. While several methods have been developed for synthesis of trans-CF3-CPAs, stereoselective production of corresponding cis-diastereomers remains a formidable challenge. We report a biocatalyst for diastereo- and enantio-selective synthesis of cis-CF3-CPAs with activity on a variety of alkenes. We found that an engineered protoglobin from Aeropyrnum pernix (ApePgb) can catalyze this unusual reaction at preparative scale with low-to-excellent yield (6–55 %) and enantioselectivity (17–99 % ee), depending on the substrate. Computational studies revealed that the steric environment in the active site of the protoglobin forced iron-carbenoid and substrates to adopt a pro-cis near-attack conformation. This work demonstrates the capability of enzyme catalysts to tackle challenging chemistry problems and provides a powerful means to expand the structural diversity of CF3-CPAs for drug discovery. 相似文献
650.