全文获取类型
收费全文 | 1217篇 |
免费 | 49篇 |
国内免费 | 4篇 |
专业分类
化学 | 921篇 |
晶体学 | 2篇 |
力学 | 22篇 |
数学 | 203篇 |
物理学 | 122篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 9篇 |
2021年 | 76篇 |
2020年 | 36篇 |
2019年 | 32篇 |
2018年 | 26篇 |
2017年 | 13篇 |
2016年 | 41篇 |
2015年 | 39篇 |
2014年 | 43篇 |
2013年 | 69篇 |
2012年 | 81篇 |
2011年 | 94篇 |
2010年 | 50篇 |
2009年 | 35篇 |
2008年 | 83篇 |
2007年 | 96篇 |
2006年 | 68篇 |
2005年 | 74篇 |
2004年 | 64篇 |
2003年 | 55篇 |
2002年 | 42篇 |
2001年 | 27篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1270条查询结果,搜索用时 15 毫秒
71.
Dr. Andrea Previtali Dr. Wei He Dr. Alessandra Forni Dr. Daniele Malpicci Dr. Elena Lucenti Dr. Daniele Marinotto Prof. Lucia Carlucci Prof. Pierluigi Mercandelli Dr. Marco Aldo Ortenzi Prof. Giancarlo Terraneo Dr. Chiara Botta Prof. Ryan Tsz Kin Kwok Dr. Jacky Wing Yip Lam Prof. Ben Zhong Tang Prof. Elena Cariati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(67):16690-16700
Organic materials with multiple emissions tunable by external stimuli represent a great challenge. TTPyr, crystallizing in different polymorphs, shows a very rich photophyisics comprising excitation-dependent fluorescence and phosphorescence at ambient conditions, and mechanochromic and thermochromic behavior. Transformation among the different species has been followed by thermal and X-ray diffraction analyses and the emissive features interpreted through structural results and DFT/TDDFT calculations. Particularly intriguing is the polymorph TTPyr(HT), serendipitously obtained at high temperature but stable also at room temperature, whose non-centrosymmetric structure guarantees an SHG efficiency 10 times higher than that of standard urea. Its crystal packing, where only the TT units are strongly rigidified by π-π stacking interactions while the Pyr moieties possess partial conformational freedom, is responsible for the observed dual fluorescence. The potentialities of TTPyr for bioimaging have been successfully established. 相似文献
72.
Tuning the phase transition of ZnO thin films through lithography: an integrated bottom‐up and top‐down processing 下载免费PDF全文
Luca Malfatti Alessandra Pinna Stefano Enzo Paolo Falcaro Benedetta Marmiroli Plinio Innocenzi 《Journal of synchrotron radiation》2015,22(1):165-171
An innovative approach towards the physico‐chemical tailoring of zinc oxide thin films is reported. The films have been deposited by liquid phase using the sol–gel method and then exposed to hard X‐rays, provided by a synchrotron storage ring, for lithography. The use of surfactant and chelating agents in the sol allows easy‐to‐pattern films made by an organic–inorganic matrix to be deposited. The exposure to hard X‐rays strongly affects the nucleation and growth of crystalline ZnO, triggering the formation of two intermediate phases before obtaining a wurtzite‐like structure. At the same time, X‐ray lithography allows for a fast patterning of the coatings enabling microfabrication for sensing and arrays technology. 相似文献
73.
Inside Cover: Rational Design of Carboxyl Groups Perpendicularly Attached to a Graphene Sheet: A Platform for Enhanced Biosensing Applications (Chem. Eur. J. 1/2014) 下载免费PDF全文
74.
Dr. Pushpak Mizar Alessandra Burrelli Erika Günther Martin Söftje Prof. Dr. Umar Farooq Prof. Dr. Thomas Wirth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13113-13116
A new chiral thiohydantoin catalyst is used for the stereoselective iodoamination of alkenes. N‐iodosuccinimide as the source of the electrophilic iodine is activated by catalytic amounts of different additives which also influence the regioselectivity of some cyclizations. 相似文献
75.
Eleonora Bolli Alessandra Fava Saulius Kaciulis Alessio Mezzi Roberto Montanari Alessandra Varone 《Surface and interface analysis : SIA》2020,52(12):1089-1092
Cr martensitic steels are promising materials for structural applications in future nuclear fusion reactors. Because the embrittlement after tempering treatments can be a serious problem, the fracture mode of a steel with 10.5 wt% of Cr treated at 700°C for 18 h has been investigated through Charpy tests in the temperature range from −100°C to +150°C. X-ray photoelectron spectroscopy (XPS) analyses carried out on the fracture surfaces evidenced the segregation of Cr in both ductile and brittle (quasicleavage) fields. The unexpected result indicates that Cr segregation weakens the atomic bonds; thus, the fracture path in both the cases corresponds to the zones with higher Cr content. 相似文献
76.
Yuri A. de Oliveira Só Mônica de Abreu Silva Fernando M. Carvalho Alessandra S. Kiametis Ricardo Gargano 《International journal of quantum chemistry》2020,120(11):e26194
Oxidative stress is an imbalance between the production of free radicals and the antioxidant defenses of the organism. Heart diseases, anemia, inflammation, and neurodegenerative disorders have been associated with this biological condition. Trolox is a notable antioxidant drug similar to vitamin E, and it is used to decrease the oxidative stress or repair the damage caused by it. In this work, the virtual screening technique is applied to identify compounds with antioxidant activities similar to Trolox. The antioxidant activity of these compounds was assessments by the mechanisms of hydrogen atom transfer and single electron transfer. Properties such as bond dissociation enthalpy, adiabatic ionization potential, Gibbs free reaction energy, spin density, highest occupied molecular orbital (HOMO), and GAP (HOMO-LUMO) energies, obtained from the DFT approach, point out to the predominance of the HAT mechanism for the antioxidant action of these compounds. The obtained results contribute to a better understanding of the chemical and physical properties responsible for antioxidant activity and the design of new antioxidant agents. 相似文献
77.
Aziz Bouymajane Yassine Oulad El Majdoub Francesco Cacciola Marina Russo Fabio Salafia Alessandra Trozzi Fouzia Rhazi Filali Paola Dugo Luigi Mondello 《Molecules (Basel, Switzerland)》2020,25(22)
Olive oil is an important product in the Mediterranean diet, due to its health benefits and sensorial characteristics. Picholine marocaine is the most cultivated variety in Morocco. The present research aims to evaluate the phenolic compounds, vitamin E and fatty acids of commercial Picholine marocaine virgin olive oils (VOOs) from five different North Moroccan provinces (Chefchaouen, Taounate, Errachidia, Beni Mellal and Taza), using HPLC-photodiode array (PDA)/electrospray ionization (ESI)-MS, normal phase (NP)-HPLC/ fluorescence detector (FLD) and GC-flame ionization detector (FID)/MS, respectively. The obtained results showed an average content of 130.0 mg kg−1 of secoiridoids (oleuropein aglycone, 10-hydroxy-oleuropein aglycone and ligstroside aglycone, oleocanthal and oleacein), 108.1 mg kg−1 of phenolic alcohols (tyrosol and hydroxytyrosol), 34.7 mg kg−1 of phenolic acids (caffeic acid, ferulic acid and elenolic acid), and 8.24 mg kg−1 of flavonoids (luteolin, luteolin glucoside, apigenin). With regard to vitamin E, α-tocopherol was the most abundant vitamin E (57.9 mg kg−1), followed by α-tocotrienol (2.5 mg kg−1), γ-tocopherol (4.5 mg kg−1) and β-tocopherol (1.9 mg kg−1), while δ-tocopherol was not detected. Moreover, 14 fatty acids were found and, among them, oleic acid (76.1%), linoleic acid (8.1%) palmitic acid (8.7%) and stearic acid (2.5%) were the major fatty acids detected. Finally, heat map and principal component analysis allowed us to classify the studied provinces in terms of VOO chemical composition: Chefchaouen (tyrosol and hydroxytyrosol), Taounate (oleuropein aglycone), Errachidia (ferulic acid, w-3 and w-6), Beni Mellal (oleocanthal) and Taza (luteolin and oleic acid). 相似文献
78.
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
79.
Xinyi. Cai Dr. Alessandra Lucini Paioni Agnes Adler Ru Yao Wenxiao Zhang David Beriashvili Adil Safeer Andrei Gurinov Prof. Antal Rockenbauer Prof. Dr. Yuguang Song Prof. Dr. Marc Baldus Prof. Dr. Yangping Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12758-12762
Dynamic nuclear polarization (DNP) is a powerful method to enhance the sensitivity of solid-state magnetic nuclear resonance (ssNMR) spectroscopy. However, its biomolecular applications at high magnetic fields (preferably>14 T) have so far been limited by the intrinsically low efficiency of polarizing agents and sample preparation aspects. Herein, we report a new class of trityl-nitroxide biradicals, dubbed SNAPols that combine high DNP efficiency with greatly enhanced hydrophilicity. SNAPol-1, the best compound in the series, shows DNP enhancement factors at 18.8 T of more than 100 in small molecules and globular proteins and also exhibits strong DNP enhancements in membrane proteins and cellular preparations. By integrating optimal sensitivity and high resolution, we expect widespread applications of this new polarizing agent in high-field DNP/ssNMR spectroscopy, especially for complex biomolecules. 相似文献
80.
Irene Bravo-Osuna Christine Vauthier Alessandra Farabollini Gioconda Millotti Gilles Ponchel 《Journal of nanoparticle research》2008,10(8):1293-1301
Surface modified nanoparticles composed of poly(isobutylcyanoacrylate) (PIBCA) cores surrounded by a chitosan and thiolated
chitosan gel layer were prepared and characterized in previous works. The presence of such biopolymers on the nanoparticle
surface conferred those nanosystems interesting characteristics that might partially overcome the gastrointestinal enzymatic
barrier, improving the oral administration of pharmacologically active peptides. In the present work, the antiprotease behaviour
of this family of core–shell nanoparticles was in vitro tested against two model metallopeptidases present in the gastrointestinal
tract (GIT): Carboxypeptidase A -CP A- (luminal protease) and Leucine Aminopeptidase M -LAP M- (membrane protease). As previous
step, the zinc-binding capacity of these nanoparticles was evaluated. Interestingly, an improvement of both the zinc-binding
capacity and the antiprotease effect of chitosan was observed when the biopolymers (chitosan and thiolated chitosan) were
used as coating component of the core–shell nanoparticles, in comparison with their behaviour in solution, thanks to the different
biopolymer chains rearrangement. The presence of amino, hydroxyl and thiol groups on the nanoparticle surface promoted zinc
binding and hence the inhibition of the metallopeptidases analysed. On the contrary, the occurrence of a cross-linked structure
in the gel layer surrounding the PIBCA cores of thiolated formulations, due to the formation of interchain and intrachain
disulphide bonds, partially limited the inhibition of the proteases. The low accessibility of cations to the active groups
of the cross-linked polymeric shell was postulated as a possible explanation of this behaviour. Results obtained in this work
make this family of surface-modified nanocarriers promising candidates for the successfull administration of pharmacologically
active peptides and proteins by the oral route. 相似文献