全文获取类型
收费全文 | 375篇 |
免费 | 29篇 |
专业分类
化学 | 369篇 |
晶体学 | 1篇 |
数学 | 10篇 |
物理学 | 24篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 56篇 |
2020年 | 20篇 |
2019年 | 22篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 22篇 |
2015年 | 23篇 |
2014年 | 21篇 |
2013年 | 28篇 |
2012年 | 27篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 28篇 |
2007年 | 23篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 1篇 |
2002年 | 2篇 |
1998年 | 3篇 |
1976年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 15 毫秒
41.
Agata Górska Karolina Szulc Ewa Ostrowska-Ligęza Joanna Bryś Magdalena Wirkowska-Wojdyła 《Journal of Thermal Analysis and Calorimetry》2017,128(1):177-183
Epoxy-based nanocomposites containing different concentrations (0–3%) of surface-modified graphene nanosheets (GNS) with 3-aminopropyltriethoxysilane were prepared and their thermal and mechanical properties including dynamic mechanical analysis, tensile strength, hardness, and abrasion tests were evaluated in order to have a database for thermo-mechanical properties of epoxy nanocomposites. The main aim of this study was to understand the optimum percentage of GNS which would perform the best reinforcing influence on mechanical and physical performance of an epoxy nanocomposite. The results explain how applying the analysis of variance (ANOVA) method as a useful tool in optimization of GNS concentration in preparation of high-performance epoxy-based nanocomposites. 相似文献
42.
Virender K. Sharma Karolina M. Siskova Radek Zboril Jorge L. Gardea-Torresdey 《Advances in colloid and interface science》2014
This review paper presents the overview of processes involved in transformation of organic-coated silver nanoparticles (AgNPs) in biological systems and in the aquatic environment. The coating on AgNPs greatly influences the fate, stability, and toxicity of AgNPs in aqueous solutions, biological systems, and the environment. Several organic-coated AgNP systems are discussed to understand their stability and toxicity in biological media and natural water. Examples are presented to demonstrate how a transformation of organic-coated AgNPs in an aqueous solution is affected by the type of coating, pH, kind of electrolyte (mono- or divalent), ionic strength, organic ligands (inorganic and organic), organic matter (fulvic and humic acids), redox conditions (oxic and anoxic), and light. Results of cytotoxicity, genotoxicity, and ecotoxicity of coated AgNPs to food chain members (plants, bacteria, and aquatic and terrestrial organisms) are reviewed. Key factors contributing to toxicity are the size, shape, surface coating, surface charge, and conditions of silver ion release. AgNPs may directly damage the cell membranes, disrupt ATP production and DNA replication, alternate gene expressions, release toxic Ag+ ion, and produce reactive oxygen species to oxidize biological components of the cell. A progress made on understanding the mechanism of organic-coated AgNP toxicity using different analytical techniques is presented. 相似文献
43.
Tian F Cziferszky M Jiao D Wahlström K Geng J Scherman OA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(4):1387-1390
We demonstrate a supramolecular peptide separation approach by the selective immobilization of peptides bearing an N-terminal tryptophan onto a CB[8]-modified gold substrate, followed by electrochemical release. The CB[8]-stabilized heteroternary complexes were characterized by (1)H NMR, ESI-MS, UV/vis, and fluorescence spectroscopy and cyclic voltammetry. Micropatterned CB[8]-modified gold substrates were found to trap only the recognizable N-tryptophan-containing peptides from a peptide mixture that could be visualized as green peptide arrays under fluorescence microscopy. Subsequently, the bound peptides were released from the modified substrates by the controlled single-electron reduction of viologen. The fully reversible trap-and-release process was repeated for 13 cycles, and the cumulative release profile of the dye-peptide conjugate was monitored by fluorescence spectroscopy, indicating that no degradation occurred. 相似文献
44.
Karolina Kazmierczak 《Journal of solid state chemistry》2011,184(5):1221-1226
The lanthanide sulphate octahydrates Ln2(SO4)3·8H2O (Ln=Ho, Tm) and the respective tetrahydrate Pr2(SO4)3·4H2O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln2(SO4)3·8H2O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, aHo=13.4421(4) Å, bHo=6.6745(2) Å, cHo=18.1642(5) Å, βHo=102.006(1) Å3 and aTm=13.4118(14) Å, bTm=6.6402(6) Å, cTm=18.1040(16) Å, βTm=101.980(8) Å3), Pr2(SO4)3·4H2O adopts space group P21/n (a=13.051(3) Å, b=7.2047(14) Å, c=13.316(3) Å, β=92.55(3) Å3). The vibrational and optical spectra of Ho2(SO4)3·8H2O and Pr2(SO4)3·4H2O are also reported. 相似文献
45.
Frański R Klonowska-Wieszczyck K Borowiak-Resterna A Olszanowski A 《European journal of mass spectrometry (Chichester, England)》2006,12(5):311-316
The interactions of copper(II) with N-alkyl-pyridine-2-carboxamides (M) were studied by electrospray ionization mass spectrometry. The influence of solvent and counter ion (Cl-, ClO4-) on the type of ions (complexes) observed was discussed. By cone voltage increase, the fragmentation "in source" of the ions discussed was achieved. In methanol solution containing N-alkyl-pyridine-2-carboxamide (M) and CuCl2 the singly- and doubly charged-ions [M+CuCl]+ and [M2+Cu]+2 were detected. In acetonitrile solution containing N-alkyl-pyridine-2-carboxamide and CuCl2, the copper(I)-containing ions [M+CH3CN+Cu]+ were formed. The use of Cu(ClO4)2 instead of CuCl2 resulted in more abundant doubly-charged ions in both methanol and acetonitrlile solutions and, for the former solution, the ions containing methoxyl anion, namely [M+CuOCH3]+, were observed. When water was used as a solvent, the abundant ions corresponding to the protonated ligands were formed, while the ions corresponding to copper complexes were characterised by low abundances. 相似文献
46.
Karolina Sieradzka Danuta Kaczmarek Jerzy Morgiel Jaroslaw Domaradzki Eugeniusz Prociow Bogdan Adamiak 《Central European Journal of Physics》2013,11(2):251-257
Transparent oxide semiconducting thin films based on mixed Ti-V oxides were prepared using a modified reactive magnetron sputtering method. Based on structural investigations performed with the help of x-ray diffraction and transmission electron microscopy analysis, two distinct regions in the prepared thin film have been observed: a nanocrystalline TiO2-V2O3-V2O5 mixed composition, and a thin layer consisting of amorphous phase and nanocystalline TiO2 phase deposited directly at the substrate. Optical measurements show excellent transmission in the visible spectral range of 73%, on average. Resistivity of the thin film was found at the order of 105 Ω cm at room temperature. The preparation of mixed Ti-V oxides provides a combination of high transparency and semiconducting properties. 相似文献
47.
Anantaram Balakrishnan Mihai Banciu Karolina Glowacka Prakash Mirchandani 《European Journal of Operational Research》2013
A central design challenge facing network planners is how to select a cost-effective network configuration that can provide uninterrupted service despite edge failures. In this paper, we study the Survivable Network Design (SND) problem, a core model underlying the design of such resilient networks that incorporates complex cost and connectivity trade-offs. Given an undirected graph with specified edge costs and (integer) connectivity requirements between pairs of nodes, the SND problem seeks the minimum cost set of edges that interconnects each node pair with at least as many edge-disjoint paths as the connectivity requirement of the nodes. We develop a hierarchical approach for solving the problem that integrates ideas from decomposition, tabu search, randomization, and optimization. The approach decomposes the SND problem into two subproblems, Backbone design and Access design, and uses an iterative multi-stage method for solving the SND problem in a hierarchical fashion. Since both subproblems are NP-hard, we develop effective optimization-based tabu search strategies that balance intensification and diversification to identify near-optimal solutions. To initiate this method, we develop two heuristic procedures that can yield good starting points. We test the combined approach on large-scale SND instances, and empirically assess the quality of the solutions vis-à-vis optimal values or lower bounds. On average, our hierarchical solution approach generates solutions within 2.7% of optimality even for very large problems (that cannot be solved using exact methods), and our results demonstrate that the performance of the method is robust for a variety of problems with different size and connectivity characteristics. 相似文献
48.
Karolina Mroczyńska 《代数通讯》2013,41(3):916-934
The paper investigates the following problem. Let bimodules N, M yield a stable equivalence of Morita type between self-injective K-algebras A and E. Further, let bimodules S, T yield a stable equivalence of Morita type between self-injective K-algebras B and F. Then we want to know whether the functor M ? A ? ? B S: mod(A ? K B op ) → mod(E ? K F op ) induces a stable equivalence between A ? K B op and E ? K F op . There is given a reduction of this problem to some smaller subcategories for self-injective algebras. Moreover, new invariants of stable equivalences of Morita type are constructed in a general case of arbitrary finite-dimensional algebras over a field. 相似文献
49.
Influence of ZnO,SiO2 and TiO2 on the aging process of PLA fibers produced by electrospinning method
Kosowska Karolina Szatkowski Piotr 《Journal of Thermal Analysis and Calorimetry》2020,140(4):1769-1778
Journal of Thermal Analysis and Calorimetry - The aim of this work was to study the effect of ceramics particles addition (SiO2, ZnO, TiO2) on the ultraviolet (UV) aging of poly(lactic acid)... 相似文献
50.
Dr. Fredrik Schaufelberger Karolina Seigel Prof. Dr. Olof Ramström 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15581-15588
The reversibility of imine bonds has been exploited to great effect in the field of dynamic covalent chemistry, with applications such as preparation of functional systems, dynamic materials, molecular machines, and covalent organic frameworks. However, acid catalysis is commonly needed for efficient equilibration of imine mixtures. Herein, it is demonstrated that hydrogen bond donors such as thioureas and squaramides can catalyze the equilibration of dynamic imine systems under unprecedentedly mild conditions. Catalysis occurs in a range of solvents and in the presence of many sensitive additives, showing moderate to good rate accelerations for both imine metathesis and transimination with amines, hydrazines, and hydroxylamines. Furthermore, the catalyst proved simple to immobilize, introducing both reusability and extended control of the equilibration process. 相似文献