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排序方式: 共有1234条查询结果,搜索用时 15 毫秒
981.
Mathias Destarac Wojciech Bzducha Daniel Taton Isabelle Gauthier‐Gillaizeau Samir Z. Zard 《Macromolecular rapid communications》2002,23(17):1049-1054
The capability of three chain‐transfer agents, O‐alkyl‐S‐(1‐ethoxycarbonyl)ethyl xanthates (CH3CHCO2C2H5)S(CS)OZ′, to control the free‐radical polymerization of styrene and ethyl acrylate by the MADIX process was examined. The reactivity of the xanthates varied according to the following trend: Z′ CH2CH3 < CH2CF3 < CH[P(O)(OEt)2]CF3. This change in reactivity allowed a lowering of the polydispersity index from 2.0 for Z′ CH2CH3 to 1.15 for Z′ CH[P(O)(OEt)2]CF3 in the case of the polymerization of styrene.
982.
Hikaru Sekiguchi Bernard Coutin Soufiane Bechaouch And Isabelle Gachard 《Macromolecular Symposia》1994,84(1):55-64
Polyisopeptides are non-peptidic polymers formed by α,ω-polycondensation of tri- or multi-functional α-amino acids. They are expected to possess physical and mechanical properties of synthetic polyamides (or polyesters) and to be biodegradable. In the present paper, the methods of polyisopeptide synthesis are reviewed. Many of them are specific to a given α-amino acid (and sometimes its derivatives, too). We discuss here about two methods giving satisfactory results. One is the polymerization of L-aspartic β-lactam α-esters, in which the structure of a resulting polymer varies according to the solvent used. A new interpretation on the basis of the nature of catalyst anion species (free ion, ion pair) is presented. The other subject is the active ester polycondensation method applied to the amino- and carboxyl- protected L-cystine polyisopeptide and its selective deprotection successively until total deprotection to free amino- and free carboxylic groups. The final polymer is the first poly-L-cystine ever reported in the literature. 相似文献
983.
Fabienne Faÿ Isabelle Linossier Gaëlle Legendre Karine Vallée-Réhel 《Macromolecular Symposia》2008,272(1):45-51
Summary: Environmental legislation compels marine paints companies to develop non toxic antifouling coatings respecting ecosystems. In this work, biodegradable polymers are used to conceive delivery systems with a lifetime of many months. For this purpose, chlorhexidine was encapsulated in poly(L-lactide) microspheres and incorporated in antifouling formulations. The characterization (encapsulation yield, surface morphology, particle size) and antibacterial activity (bacteriostatic and bactericidal effects) of microspheres were carried out by using scanning electronic (SEM) and confocal laser scanning microscopies (CLSM). The results indicate a good ability of loaded microspheres to be formulated even though an excellent activity against selected marine bacteria is conserved. This is a promising approach to develop biodegradable antifouling paints based on non toxic molecules and bioactive surfaces. 相似文献
984.
In an attempt to synthesize LiEu3S3[SiS4] utilizing elemental europium and sulfur as well as SiS2 and an excess of LiCl as flux and lithium source, dark red, platelet‐shaped single crystals of Li3Eu6[SiS4]4 were obtained. This new compound crystallizes in the cubic space group I4 3d (a = 1369.22(5) pm) with four formula units per unit cell. Both the Li+ and the Si4+ cations are surrounded by four sulfide anions. The [SiS4]4– tetrahedra show merely a slight trigonal distortion, while the [LiS4]7– units are best described as flattened bisphenoids. The europium cations exhibit an eightfold, rather irregular coordination environment by eight S2– anions and have to be regarded mixed‐valent with a +2:+3 charge‐ratio of 5:1 in order to gain electroneutrality. The lack of an inversion center is caused by the [SiS4]4– tetrahedra being stacked exclusively top up along [111] in this acentric crystal structure. 相似文献
985.
Anne‐Sophie Marques Thibaut Duhail Jrome Marrot Isabelle Chataigner Vincent Coeffard Guillaume Vincent Xavier Moreau 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):10074-10078
We report an unprecedented domino polycyclization from readily available 2,4‐dienals and cyclic α,β‐unsaturated imines that is initiated by an iso‐Nazarov reaction. This Brønsted acid promoted reaction enables the concomitant formation of four bonds, three cycles, and four contiguous stereogenic centers to yield elaborated structures in a single operation. A range of fused hexacyclic molecules is obtained in a highly diastereoselective manner. 相似文献
986.
Julia Pieper Christian Hemken Rene Büttgen Isabelle Graf Nils Hansen K. Alexander Heufer Katharina Kohse-Höinghaus 《Proceedings of the Combustion Institute》2019,37(2):1683-1690
Small methyl ketones are known to have high octane numbers, impressive knock resistance, and show low emissions of soot, NOx, and unburnt hydrocarbons. However, previous studies have focused on the analysis of smaller ketones and 3-pentanone, while the asymmetric 2-pentanone (methyl propyl ketone) has not gained much attention before. Considering ketones as possible fuels or additives, it is of particular importance to fully understand the combustion kinetics and the effect of the functional carbonyl group. Due to the higher energy density in a C5-ketone compared to the potential biofuel 2-butanone, the flame structure and the mole fraction profiles of species formed in 2-pentanone combustion are of high interest, especially to evaluate harmful species formations. In this study, a laminar premixed low-pressure (p?=?40 mbar) fuel-rich (??=?1.6) flat flame of 2-pentanone has been analyzed by vacuum-ultraviolet photoionization molecular-beam mass-spectrometry (VUV-PI-MBMS) enabling isomer separation. Quantitative mole fraction profiles of 47 species were obtained and compared to a model consisting of an existing base mechanism and a newly developed high-temperature sub-mechanism for 2-pentanone. High-temperature reactions for 2-pentanone were adapted in analogy to 2-butanone and n-pentane, and the thermochemistry for 2-pentanone and the respective fuel radicals was derived by ab initio calculations. Good agreement was found between experiment and simulation for the first decomposition products, supporting the initial branching reactions of the 2-pentanone sub-mechanism. Also, species indicating low-temperature chemistry in the preheating zone of the flame have been observed. The present measurements of a 2-pentanone flame provide useful validation targets for further kinetic model development. 相似文献
987.
The main purpose of this study was to investigate the relationship between some coffee roasting variables (weight loss, density and moisture) with near infrared (NIR) spectra of original green (i.e. raw) and differently roasted coffee samples, in order to test the availability of non-destructive NIR technique to predict coffee roasting degree. Separate calibration and validation models, based on partial least square (PLS) regression, correlating NIR spectral data of 168 representatives and suitable green and roasted coffee samples with each roasting variable, were developed. Using PLS regression, a prediction of the three modelled roasting responses was performed. High accuracy results were obtained, whose root mean square errors of the residuals in prediction (RMSEP) ranged from 0.02 to 1.23%. Obtained data allowed to construct robust and reliable models for the prediction of roasting variables of unknown roasted coffee samples, considering that measured vs. predicted values showed high correlation coefficients (r from 0.92 to 0.98). Results provided by calibration models proposed were comparable in terms of accuracy to the conventional analyses, revealing a promising feasibility of NIR methodology for on-line or routine applications to predict and/or control coffee roasting degree via NIR spectra. 相似文献
988.
Yael Juarez-Martinez Dr. Pablo Labra-Vázquez Dr. Alejandro Enríquez-Cabrera Andrés F. Leon-Rojas Diego Martínez-Bourget Dr. Pascal G. Lacroix Marine Tassé Sonia Mallet-Ladeira Dr. Norberto Farfán Dr. Rosa Santillan Dr. Gabriel Ramos-Ortiz Dr. Jean-Pierre Malval Prof. Isabelle Malfant 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202201692
One monometallic and three bimetallic ruthenium nitrosyl (RuNO) complexes are presented and fully characterized in reference to a parent monometallic complex of formula [FTRu(bpy)(NO)]3+, where FT is a fluorenyl-substituted terpyridine ligand, and bpy the 2,2’-bipyridine. These new complexes are built with the new ligands FFT, TFT, TFFT, and TF-CC-TF (where an alkyne C≡C group is inserted between two fluorenes). The crystal structures of the bis-RuNO2 and bis-RuNO complexes built from the TFT ligand are presented. The evolution of the spectroscopic features (intensities and energies) along the series, at one-photon absorption (OPA) correlates well with the TD-DFT computations. A spectacular effect is observed at two-photon absorption (TPA) with a large enhancement of the molecular cross-section (σTPA), in the bimetallic species. In the best case, σTPA is equal to 1523±98 GM at 700 nm, in the therapeutic window of transparency of biological tissues. All compounds are capable of releasing NO⋅ under irradiation, which leads to promising applications in TPA-based drug delivery. 相似文献
989.
Divergente Koordinationschemie: Parallele Synthese von [2×2]‐Eisen(II)‐Gitterkomplextautokonformeren
990.
Dr. Alain Manceau Dr. Paco Bustamante Dr. Ahmed Haouz Prof. Dr. Jean Paul Bourdineaud Maria Gonzalez-Rey Dr. Cyprien Lemouchi Prof. Dr. Isabelle Gautier-Luneau Valérie Geertsen Elodie Barruet Dr. Mauro Rovezzi Dr. Pieter Glatzel Dr. Serge Pin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):997-1009
Of all divalent metals, mercury (HgII) has the highest affinity for metallothioneins. HgII is considered to be enclosed in the α and β domains as tetrahedral α-type Hg4Cys11-12 and β-type Hg3Cys9 clusters similar to CdII and ZnII. However, neither the four-fold coordination of Hg nor the existence of Hg–Hg atomic pairs have ever been demonstrated, and the HgII partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (β-HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions. 相似文献