全文获取类型
收费全文 | 1116篇 |
免费 | 46篇 |
国内免费 | 5篇 |
专业分类
化学 | 917篇 |
力学 | 19篇 |
数学 | 86篇 |
物理学 | 145篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 58篇 |
2021年 | 80篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 41篇 |
2015年 | 40篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 77篇 |
2011年 | 91篇 |
2010年 | 60篇 |
2009年 | 52篇 |
2008年 | 77篇 |
2007年 | 82篇 |
2006年 | 48篇 |
2005年 | 61篇 |
2004年 | 50篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有1167条查询结果,搜索用时 0 毫秒
81.
Giovanna Bruni Ines Ghione Vittorio Berbenni Andrea Cardini Doretta Capsoni Alessandro Girella Chiara Milanese Amedeo Marini 《Molecules (Basel, Switzerland)》2021,26(11)
The present work is a concrete example of how physico-chemical studies, if performed in depth, are crucial to understand the behavior of pharmaceutical solids and constitute a solid basis for the control of the reproducibility of the industrial batches. In particular, a deep study of the thermal behavior of glipizide, a hypoglycemic drug, was carried out with the aim of clarifying whether the recognition of its polymorphic forms can really be done on the basis of the endothermic peak that the literature studies attribute to the melting of the compound. A number of analytical techniques were used: thermal techniques (DSC, TGA), X-ray powder diffraction (XRPD), FT-IR spectroscopy and scanning electron microscopy (SEM). Great attention was paid to the experimental design and to the interpretation of the combined results obtained by all these techniques. We proved that the attribution of the endothermic peak shown by glipizide to its melting was actually wrong. The DSC peak is no doubt triggered by a decomposition process that involves gas evolution (cyclohexanamine and carbon dioxide) and formation of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which remains as decomposition residue. Thermal treatments properly designed and the combined use of DSC with FT-IR and XRPD led to identifying a new polymorphic form of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which is obtained by crystallization from the melt. Hence, our results put into evidence that the check of the polymorphic form of glipizide cannot be based on the temperature values of the DSC peak, since such a peak is due to a decomposition process whose Tonset value is strongly affected by the particle size. Kinetic studies of the decomposition process show the high stability of solid glipizide at room temperature. 相似文献
82.
Dr. Chiara Platella Dr. Ettore Napolitano Dr. Claudia Riccardi Prof. Domenica Musumeci Prof. Daniela Montesarchio 《ChemistryOpen》2022,11(5):e202200090
DNA G-quadruplexes (G4s) are key structures for the development of targeted anticancer therapies. In this context, ligands selectively interacting with G4s can represent valuable anticancer drugs. Aiming at speeding up the identification of G4-targeting synthetic or natural compounds, we developed an affinity chromatography-based assay, named G-quadruplex on Oligo Affinity Support (G4-OAS), by synthesizing G4-forming sequences on commercially available polystyrene OAS. Then, due to unspecific binding of several hydrophobic ligands on nude OAS, we moved to Controlled Pore Glass (CPG). We thus conceived an ad hoc functionalized, universal support on which both the on-support elongation and deprotection of the G4-forming oligonucleotides can be performed, along with the successive affinity chromatography-based assay, renamed as G-quadruplex on Controlled Pore Glass (G4-CPG) assay. Here we describe these assays and their applications to the screening of several libraries of chemically different putative G4 ligands. Finally, ongoing studies and outlook of our G4-CPG assay are reported. 相似文献
83.
Gioria Esteban Signorini Chiara Taleb María C. Thomas Arne Mihályi Magdolna R. Gutierrez Laura 《Cellulose (London, England)》2021,28(14):9135-9147
Cellulose - Palladium was incorporated into carboxymethylated cellulose fibers as a support, thereby becoming an efficient and stable catalyst for low temperature gas phase reaction. Thus, NO was... 相似文献
84.
Multiresidue determination of UV filters in water samples by solid‐phase extraction and liquid chromatography with tandem mass spectrometry analysis 下载免费PDF全文
Anna Laura Capriotti Chiara Cavaliere Susy Piovesana Roberto Samperi Serena Stampachiacchiere Salvatore Ventura Aldo Laganà 《Journal of separation science》2014,37(20):2882-2891
UV filters, contained in sunscreens and other cosmetic products, as well as in some plastics and industrial products, are nowadays considered contaminants of emerging concern because their widespread and increasing use has lead to their presence in the environment. Furthermore, some UV filters are suspected to have endocrine disruption activity. In the present work, we developed an analytical method based on liquid chromatography with tandem mass spectrometry for the determination of UV filters in tap and lake waters. Sixteen UV filters were extracted from water samples by solid‐phase extraction employing graphitized carbon black as adsorbent material. Handling 200 mL of water sample, satisfactory recoveries were obtained for almost all the analytes. The limits of detection and quantification of the method were comparable to those reported in other works, and ranged between 0.7–3.5 and 1.9–11.8 ng/L, respectively; however in our case the number of investigated compounds was larger. The major encountered problem in method development was to identify the background contamination sources and reduce their contribution. UV filters were not detected in tap water samples, whereas the analyses conducted on samples collected from three different lakes showed that the swimming areas are most subject to UV filter contamination. 相似文献
85.
Natural estrogens in dairy products: Determination of free and conjugated forms by ultra high performance liquid chromatography with tandem mass spectrometry 下载免费PDF全文
Chiara Cavaliere Anna Laura Capriotti Patrizia Foglia Susy Piovesana Roberto Samperi Salvatore Ventura Aldo Lagan 《Journal of separation science》2015,38(20):3599-3606
Natural estrogens are synthesized by mammals in different amounts depending on the developmental stage and pregnancy/lactation period, and they may pass into milk, where they are mostly present as glucuronated and sulfated forms. In modern dairy practices, about 75% of milk is produced from pregnant cows; therefore, the amount of hormones that may pass into milk could be of concern. While estrogen determination in milk has been investigated in depth, the individual determination of estrogens and their conjugated forms in dairy products has not been fully addressed. The aim of this work was to develop and assess a sensitive method, using the peculiar retention properties of graphitized carbon black, to extract natural free estrogens and their major conjugated metabolites, without any enzymatic cleavage, from yogurt, cheese, and butter. The free and conjugated estrogens were eluted in two distinct fractions from the solid‐phase extraction cartridge and analyzed separately by ultra high performance liquid chromatography coupled to tandem mass spectrometry. Recoveries were higher than 80% for all the three sample typologies. The highest matrix effects were observed for butter, which was richest in lipid content, but was below 30%. A survey on some commercial dairy products suggests that production processes decreased estrogen content. 相似文献
86.
87.
Alma Mejri Giacomo Mandriota Hamza Elfil Maria Lucia Curri Chiara Ingrosso Abdelmoneim Mars 《Molecules (Basel, Switzerland)》2022,27(23)
Monitoring hazardous chemical compounds such as hydrazine (N2H4), 4-nitrophenol (4-NP) and Hg2+ in natural water resources is a crucial issue due to their toxic effects on human health and catastrophic impact on the environment. Electrochemical nanostructured platforms integrating hybrid nanocomposites based on graphene derivatives and inorganic nanoparticles (NPs) are of great interest for such a purpose. In this work, disposable screen-printed carbon electrodes (SPCEs) have been modified with a hybrid nanocomposite formed by reduced graphene oxide (RGO), functionalized by 1-pyrene carboxylic acid (PCA), and decorated by colloidal Au NPs. These hybrid platforms have been tested for the electrocatalytic detection of N2H4 and 4-NP by differential pulse voltammetry and have been modified with an electropolymerized film of Hg2+ ions imprinted polycurcumin for the electroanalytical detection of Hg2+ by DPV. LODs, lower and in line with the lowest ones reported for state-of-the-art electrochemical sensors, integrating similar Au-graphene < nanocomposites, have been estimated. Additionally, good repeatability, reproducibility, and storage stability have been assessed, as well as a high selectivity in the presence of a 100-fold higher concentration of interfering species. The applicability of the proposed platforms for the detection of the compounds in real complex matrices, such as tap and river water samples, has been effectively demonstrated. 相似文献
88.
Carmen Bocchino Mariagrazia Napoli Chiara Costabile Pasquale Longo 《Journal of polymer science. Part A, Polymer chemistry》2011,49(4):862-870
The synthesis and characterization of a zirconium complex, having two alkoxide functionalized N‐heterocyclic carbene ligands, and its behavior as catalyst in the polymerization of ethylene and propylene, have been reported. NMR analysis showed that more than one species was obtained during synthesis. These data were confirmed by ethylene polymerization that gave rise to a linear polyethylene having a high Molecular weight and a polydispersity index (MDI) > 2 and often bimodal. The same catalytic system was able to produce highly isotactic polypropylene together with an atactic fraction. DFT studies on the complex stereoisomer stability gave indications on the species possibly involved in the polymerizations. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
89.
90.
Maria Luisa Dalla Chiara Roberto Giuntini Antonio Ledda Roberto Leporini Giuseppe Sergioli 《Foundations of Physics》2010,40(9-10):1494-1518
The characteristic holistic features of the quantum theoretic formalism and the intriguing notion of entanglement can be applied to a field that is far from microphysics: logical semantics. Quantum computational logics are new forms of quantum logic that have been suggested by the theory of quantum logical gates in quantum computation. In the standard semantics of these logics, sentences denote quantum information quantities: systems of qubits (quregisters) or, more generally, mixtures of quregisters (qumixes), while logical connectives are interpreted as special quantum logical gates (which have a characteristic reversible and dynamic behavior). In this framework, states of knowledge may be entangled, in such a way that our information about the whole determines our information about the parts; and the procedure cannot be, generally, inverted. In spite of its appealing properties, the standard version of the quantum computational semantics is strongly “Hilbert-space dependent”. This certainly represents a shortcoming for all applications, where real and complex numbers do not generally play any significant role (as happens, for instance, in the case of natural and of artistic languages). We propose an abstract version of quantum computational semantics, where abstract qumixes, quregisters and registers are identified with some special objects (not necessarily living in a Hilbert space), while gates are reversible functions that transform qumixes into qumixes. In this framework, one can give an abstract definition of the notions of superposition and of entangled pieces of information, quite independently of any numerical values. We investigate three different forms of abstract holistic quantum computational logic. 相似文献