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771.
Murphy BT Cao S Brodie PJ Miller JS Ratovoson F Birkinshaw C Rakotobe E Rasamison VE Tendyke K Suh EM Kingston DG 《Natural product research》2008,22(13):1169-1175
Bioassay-guided fractionation of an ethanol extract of Artabotrys madagascariensis led to the isolation of the new compound artabotrene (1), two butenolides (2 and 3), and the tetracyclic triterpene polycarpol (4). Structure elucidation was determined on the basis of one and two-dimensional NMR, and absolute configuration of compounds 2-4 was verified by analysis of CD and optical rotation spectra. Two of the isolates, melodorinol (2) and acetylmelodorinol (3), were found to display antiproliferative activity against five different tumour cell lines with IC50 values ranging from 2.4 to 12 microM. 相似文献
772.
A Highly Active and Magnetically Recoverable Tris(triazolyl)–CuI Catalyst for Alkyne–Azide Cycloaddition Reactions 下载免费PDF全文
Dr. Dong Wang Laetitia Etienne María Echeverria Prof. Sergio Moya Prof. Dr. Didier Astruc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4047-4054
Nanoparticle‐supported tris(triazolyl)–CuBr, with a diameter of approximately 25 nm measured by TEM spectroscopy, has been easily prepared, and its catalytic activity was evaluated in the copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction. In initial experiments, 0.5 mol % loading successfully promoted the CuAAC reaction between benzyl azide and phenylacetylene, in water at room temperature (25 °C). During this process, the iron oxide nanoparticle‐supported tris(triazolyl)–CuBr displayed good monodispersity, excellent recoverability, and outstanding reusability. Indeed, it was simply collected and separated from the reaction medium by using an external magnet, then used for another five catalytic cycles without significant loss of catalytic activity. Inductively coupled plasma (ICP) analysis for the first cycle revealed that the amount of copper leached from the catalyst into the reaction medium is negligible (1.5 ppm). The substrate scope has been examined, and it was found that the procedure can be successfully extended to various organic azides and alkynes and can also be applied to the one‐pot synthesis of triazoles, through a cascade reaction involving benzyl bromides, alkynes, and sodium azide. In addition, the catalyst was shown to be an efficient CuAAC catalyst for the synthesis of allyl‐ and TEG‐ended (TEG=triethylene glycol) 27‐branch dendrimers. 相似文献
773.
Laurent Nyssen Marianne Fillet Etienne Cavalier Anne‐Catherine Servais 《Electrophoresis》2019,40(11):1550-1557
Parathyroid hormone (PTH) is a common clinical marker whose quantification relies on immunoassays, giving variable results as batch, brand, or target epitope changes. Sheathless CE‐ESI‐MS, combining CE resolution power and low‐flow ESI sensitivity, was applied to the analysis of PTH in its native conformation in the presence of related forms. Fused silica and neutral‐coated capillaries were investigated, as well as preconcentration methods such as transient isotachophoresis, field‐amplified sample injection (FASI), and electrokinetic supercharging (EKS). The method for the separation of PTH and its variants was first developed using fused‐silica capillary with UV detection. An acidic BGE was used to separate 1–84 PTH (full length), 7–84 PTH, and 1–34 PTH. Acetonitrile was added to the BGE to reduce peptide adsorption onto the capillary wall and transient isotachophoresis was used as analyte preconcentration method. The method was then transferred to a sheathless CE‐ESI‐MS instrument. When using a fused silica capillary, CE‐MS was limited to μg/mL levels. The use of a neutral coating combined with FASI or EKS allowed a significant increase in sensitivity. Under these conditions, 1–84 PTH, 7–84 PTH, and 1–34 PTH were detected at concentrations in the low ng/mL (FASI) or pg/mL (EKS) range. 相似文献
774.
M. Ángeles Fuentes Dr. Bianca K. Muñoz Kane Jacob Dr. Laure Vendier Dr. Ana Caballero Prof. Michel Etienne Prof. Pedro J. Pérez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1327-1334
The complexes Fn‐TpAg(L) (Fn‐Tp=a perfluorinated hydrotris(indazolyl) borate ligand; L=acetone or tetrahydrofuran) efficiently catalyze the functionalization of non‐activated alkanes such as hexane, 2,3‐dimethylbutane, or 2‐methylpentane by insertion of CHCO2Et units (from N2CHCO2Et, ethyl diazoacetate, EDA) into their C? H bonds. The reactions are quantitative (EDA‐based), with no byproducts derived from diazo coupling being formed. In the case of hexane, the functionalization of the methyl C? H bonds has been achieved with the highest regioselectivity known to date with this diazo compound. This catalytic system also operates under biphasic conditions by using fluorous solvents such as Fomblin or perfluorophenanthrene. Several cycles of catalyst recovery and reuse have been performed, with identical chemo‐ and regioselectivities. 相似文献
775.
Dyed natural rubber (NR) and styrene-butadiene rubber (SBR) designed for outdoor applications were exposed to accelerated
artificial aging in xenon light. The aging results in the deterioration of the properties of the exposed surface material.
The ability of dyed polymers to withstand prolonged sunlight exposure without fading or undergoing any physical deterioration
is largely determined not only by the photochemical characteristics of the absorbing dyestuff itself but also by the polymer
structure and fillers. Results indicate that dyed filled NR and SBR samples behave differently during photooxidation. The
photodegradation products were observed by Fourier transform infrared spectroscopy (FTIR) to characterize the changes occurring
in the polymer matrix during UV aging. The fading of the dyed polymers was found to be promoted in the NR sample. Moreover,
the effects of photooxidation on the dyed SBR and NR materials were assessed by the formation of cracks and the thickness
of the degraded area. The degradation thickness is more important for the NR sample than for the SBR one according to environmental
scanning electron microscopy (ESEM) observations. For the NR sample, cracks appear initially at the surface and then grow
through the thickness of the specimen, while for the SBR sample cracks are small and discontinuous.
Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1081–1085.
This article was submitted by the authors in English. 相似文献
776.
Asmis KR Santambrogio G Zhou J Garand E Headrick J Goebbert D Johnson MA Neumark DM 《The Journal of chemical physics》2007,126(19):191105
Infrared multiple photon dissociation spectra for size-selected water cluster anions (H2O)(n)(-), n=15-50, are presented covering the frequency range of 560-1820 cm(-1). The cluster ions are trapped and cooled by collisions with ambient He gas at 20 K, with the goal of defining the cluster temperature better than in previous investigations of these species. Signal is seen in two frequency regions centered around 700 and 1500-1650 cm(-1), corresponding to water librational and bending motions, respectively. The bending feature associated with a double-acceptor water molecule binding to the excess electron is clearly seen up to n=35, but above n=25; this feature begins to blueshift and broadens, suggesting a more delocalized electron binding motif for the larger clusters in which the excess electron interacts with multiple water molecules. 相似文献
777.
778.
779.
We consider the definition of possibility measures on complete lattices rather than on complete Boolean algebras of sets. We give a necessary and sufficient condition for the extendability of any mapping to such a possibility measure. We also associate two types of integrals with these possibility measures, and discuss some of their more important properties, amongst which a monotone convergence theorem. 相似文献
780.