全文获取类型
收费全文 | 1258篇 |
免费 | 52篇 |
国内免费 | 5篇 |
专业分类
化学 | 1073篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 157篇 |
物理学 | 70篇 |
出版年
2023年 | 12篇 |
2022年 | 21篇 |
2021年 | 38篇 |
2020年 | 23篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 44篇 |
2015年 | 37篇 |
2014年 | 35篇 |
2013年 | 57篇 |
2012年 | 78篇 |
2011年 | 88篇 |
2010年 | 50篇 |
2009年 | 51篇 |
2008年 | 75篇 |
2007年 | 79篇 |
2006年 | 79篇 |
2005年 | 71篇 |
2004年 | 63篇 |
2003年 | 64篇 |
2002年 | 43篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1973年 | 3篇 |
排序方式: 共有1315条查询结果,搜索用时 31 毫秒
71.
Multivariate optimization of a headspace solid‐phase microextraction method followed by gas chromatography with mass spectrometry for the determination of terpenes in Nicotiana langsdorffii
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Francisco Ardini Marina Di Carro Maria Luisa Abelmoschi Marco Grotti Emanuele Magi 《Journal of separation science》2014,37(13):1570-1577
A simple and sensitive procedure based on headspace solid‐phase microextraction and gas chromatography with mass spectrometry was developed for the determination of five terpenes (α‐pinene, limonene, linalool, α‐terpineol, and geraniol) in the leaves of Nicotiana langsdorffii. The microextraction conditions (extraction temperature, equilibration time, and extraction time) were optimized by means of a Doehlert design. The experimental design showed that, for α‐pinene and limonene, a low temperature and a long extraction time were needed for optimal extraction, while linalool, α‐terpineol, and geraniol required a high temperature and a long extraction time. The chosen compromise conditions were temperature 60°C, equilibration time 15 min and extraction time 50 min. The main analytical figures of the optimized method were evaluated; LODs ranged from 0.07 ng/g (α‐pinene) to 8.0 ng/g (geraniol), while intraday and interday repeatability were in the range 10–17% and 9–13%, respectively. Finally, the procedure was applied to in vitro wild‐type and transgenic specimens of N. langsdorffii subjected to abiotic stresses (chemical and heat stress). With the exception of geraniol (75–374 ng/g), low concentration levels of terpenes were measured (ng/g level or lower); some interesting variations in terpene concentration induced by abiotic stress were observed. 相似文献
72.
Andrea Mosseri Dr. Maria Sancho-Albero Dr. Marilisa Leone Donatella Nava Dr. Francesco Secundo Prof. Daniela Maggioni Prof. Luisa De Cola Prof. Alessandra Romanelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(37):e202200693
Self-assembly of biomolecules such as peptides, nucleic acids or their analogues affords supramolecular objects, exhibiting structures and physical properties dependent on the amino-acid or nucleobase composition. Conjugation of the peptide diphenylalanine (FF) to peptide nucleic acids triggers formation of self-assembled structures, mainly stabilized by interactions between FF. In this work we report formation of homogeneous chiral fibers upon self-assembly of the hybrid composed of the tetraphenylalanine peptide (4F) conjugated to the PNA dimer adenine-thymine (at). In this case nucleobases seem to play a key role in determining the morphology and chirality of the fibers. When the PNA “at” is replaced by guanine-cytosine dimer “gc”, disordered structures are observed. Spectroscopic characterization of the self-assembled hybrids, along with AFM and SEM studies is reported. Finally, a structural model consistent with the experimental evidence has also been obtained, showing how the building blocks of 4Fat arrange to give helical fibers. 相似文献
73.
74.
Basma Najar Giulia Mecacci Valeria Nardi Claudio Cervelli Simona Nardoni Francesca Mancianti Valentina Virginia Ebani Simone Giannecchini Luisa Pistelli 《Molecules (Basel, Switzerland)》2021,26(9)
Spontaneous emissions of S. dentata Aiton and S. scabra Thunb., as well as the essential oil (EO) composition of the cited species, together with S. aurea L., were investigated. The chemical profile of the first two species is reported here for the first time. Moreover, in vitro tests were performed to evaluate the antifungal activity of these EOs on Trichophyton mentagrophytes, Microsporum canis, Aspergillus flavus, Aspergillus niger, and Fusarium solani. Secondly, the EO antibacterial activity against Escherichia coli, Staphylococcus aureus, and Staphylococcus pseudointermedius was examined, and their antiviral efficacy against the H1N1 influenza virus was assessed. Leaf volatile organic compounds (VOCs), as well as the EOs obtained from the arial part of Salvia scabra, were characterized by a high percentage of sesquiterpene hydrocarbons (97.8% and 76.6%, respectively), mostly represented by an equal amount of germacrene D (32.8% and 32.7%, respectively). Both leaf and flower spontaneous emissions of S. dentata, as well as the EO composition, showed a prevalence of monoterpenes divided into a more or less equal amount of hydrocarbon and oxygenated compounds. Interestingly, its EO had a non-negligible percentage of oxygenated sesquiterpenes (29.5%). S. aurea EO, on the contrary, was rich in sesquiterpenes, both hydrocarbons and oxygenated compounds (41.5% and 33.5%, respectively). S. dentata EO showed good efficacy (Minimal Inhibitory Concentration (MIC): 0.5%) against M. canis. The tested EOs were not active against E. coli and S. aureus, whereas a low inhibition of S. dentata EO was observed on S. pseudointermedius (MIC = 10%). Once again, S. dentata EO showed a very good H1N1 inhibition; contrariwise, S. aurea EO was completely inactive against this virus. The low quantity of S. scabra EO made it impossible to test its biological activity. S. dentata EO exhibited interesting new perspectives for medicinal and industrial uses. 相似文献
75.
The π‐Back‐Bonding Modulation and Its Impact in the Electronic Properties of CuII Antineoplastic Compounds: An Experimental and Theoretical Study
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Juan Carlos García‐Ramos Dr. Rodrigo Galindo‐Murillo Araceli Tovar‐Tovar Ana Luisa Alonso‐Saenz Virginia Gómez‐Vidales Dr. Marcos Flores‐Álamo Dr. Luis Ortiz‐Frade Dr. Fernando Cortes‐Guzmán Dr. Rafael Moreno‐Esparza Prof. Antonio Campero Prof. Lena Ruiz‐Azuara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13730-13741
76.
Álvaro Dávila García Sylvain Bernès Fernando Sartillo-Piscil Rosa Luisa Meza-León 《Journal of heterocyclic chemistry》2020,57(12):4373-4379
The enantiopure synthesis of a truncated tetradenolide is presented. Starting from the versatile Chiron 7,3-lactone-xylofuranose derivative (7,3-LXF), the enantiomerically pure synthesis of the title compound is obtained in six steps with a 40% overall yield. 相似文献
77.
Luisa Pieroni Federica Iavarone Alessandra Olianas Viviana Greco Claudia Desiderio Claudia Martelli Barbara Manconi Maria Teresa Sanna Irene Messana Massimo Castagnola Tiziana Cabras 《Journal of separation science》2020,43(1):313-336
More than 300 different protein post‐translational modifications are currently known, but only a few have been extensively investigated because modified proteoforms are commonly present in sub‐stoichiometry amount. For this reason, improvement of specific enrichment techniques is particularly useful for the proteomic characterization of post‐translationally modified proteins. Enrichment proteomic strategies could help the researcher in the challenging issue to decipher the complex molecular cross‐talk existing between the different factors influencing the cellular pathways. In this review the state of art of the platforms applied for the enrichment of specific and most common post‐translational modifications, such as glycosylation and glycation, phosphorylation, sulfation, redox modifications (i.e. sulfydration and nitrosylation), methylation, acetylation, and ubiquitinylation, are described. Enrichments strategies applied to characterize less studied post‐translational modifications are also briefly discussed. 相似文献
78.
79.
Mechanical properties of anion exchange membranes by combination of tensile stress–strain tests and dynamic mechanical analysis
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Riccardo Narducci J.‐F. Chailan A. Fahs Luca Pasquini Maria Luisa Di Vona Philippe Knauth 《Journal of Polymer Science.Polymer Physics》2016,54(12):1180-1187
The thermomechanical properties of anion exchange polymers based on polysulfone (PSU) quaternized with trimethylamine (TMA) or 1,4‐diazabicyclo[2.2.2]octane (DABCO) and containing hydroxide or chloride anions by tensile stress–strain tests and dynamic mechanical analysis (DMA) have been determined. The reported mechanical properties included the Young's modulus, tensile strength, and elongation at break from tensile tests and the storage and loss modulus and glass transition temperature from DMA. The anion exchange membranes behaved as stiff polymers with Young's modulus in the order of 1 GPa, relatively with high strength (about 30 MPa) and low elongation at break (around 10%) was observed. Tensile tests were also made with membranes exchanged with hydrogen‐carbonate and carbonate anions to control the absence of important carbonation of the OH form. The glass transition temperatures were of the order of 150 °C (PSU‐TMA) or 200 °C (PSU‐DABCO) for the hydroxide form, confirmed by differential scanning calorimetry; they increase further by about 50 K, when hydroxide ions are replaced by chloride. This result and the increase of the storage modulus could be interpreted by the higher hydration of hydroxide ions and the plasticizing effect of water, which reduced the Van der Waals interactions between the macromolecular chains. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1180–1187 相似文献
80.
Dendronized Anionic Gold Nanoparticles: Synthesis,Characterization, and Antiviral Activity
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cornelia E. Peña‐González Pilar García‐Broncano Prof. M. Francesca Ottaviani Dr. Michela Cangiotti Dr. Alberto Fattori Margarita Hierro‐Oliva Prof. M. Luisa González‐Martín Dr. Jorge Pérez‐Serrano Dr. Rafael Gómez Prof. M. Ángeles Muñoz‐Fernández Dr. Javier Sánchez‐Nieves Dr. F. Javier de la Mata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):2987-2999
Anionic carbosilane dendrons decorated with sulfonate functions and one thiol moiety at the focal point have been used to synthesize water‐soluble gold nanoparticles (AuNPs) through the direct reaction of dendrons, gold precursor, and reducing agent in water, and also through a place‐exchange reaction. These nanoparticles have been characterized by NMR spectroscopy, TEM, thermogravimetric analysis, X‐ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, elemental analysis, and zeta‐potential measurements. The interacting ability of the anionic sulfonate functions was investigated by EPR spectroscopy with copper(II) as a probe. Different structures and conformations of the AuNPs modulate the availability of sulfonate and thiol groups for complexation by copper(II). Toxicity assays of AuNPs showed that those produced through direct reaction were less toxic than those obtained by ligand exchange. Inhibition of HIV‐1 infection was higher in the case of dendronized AuNPs than in dendrons. 相似文献