全文获取类型
收费全文 | 498篇 |
免费 | 44篇 |
国内免费 | 1篇 |
专业分类
化学 | 427篇 |
晶体学 | 12篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 55篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 27篇 |
2014年 | 21篇 |
2013年 | 38篇 |
2012年 | 28篇 |
2011年 | 49篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 21篇 |
2007年 | 40篇 |
2006年 | 34篇 |
2005年 | 28篇 |
2004年 | 15篇 |
2003年 | 11篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1978年 | 2篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有543条查询结果,搜索用时 703 毫秒
81.
Alberto Castellón Serrano José Antonio Cuenca Mira Cándido Martín González 《代数通讯》2013,41(10):4699-4706
This work, jointly with [9], completes the structure theory and classification of the Jordan H *- triple systems. The problem of describing the Jordan H *-triple systems is reduced in [5] to that of describing the topologically simple ones. Ruling out the finite-dimensional case, we have that any of these H *-triples has an underlying triple system structure of quadratic type (and these can be fully described), or it is the H *-triple system associated to the odd part of a topologically simple Z2-graded Jordan H *-algebra, whose classification is given in [13]. 相似文献
82.
Carolina Castao Mariana P. Serrano Carolina Lorente Claudio D. Borsarelli Andrs H. Thomas 《Photochemistry and photobiology》2019,95(1):220-226
Unconjugated oxidized pterins accumulate in the skin of patients suffering from vitiligo and, under UVA irradiation, photosensitize the oxidation of amino acids. In this work, we study the interaction of the singlet and triplet excited states of pterin (Ptr), the parent compound of oxidized pterins, with four oxidizable amino acids: tryptophan (Trp), tyrosine (Tyr), histidine (His) and methionine (Met). Steady‐state and time‐resolved fluorescence measurements and laser flash photolysis experiments were performed to investigate the quenching of the Ptr excited states by the amino acids in aqueous solution. The singlet excited states of Ptr are quenched by Met mainly via a dynamic process and by Trp via a combination of dynamic and static processes. His does not quench singlet excited states of Ptr, and quenching by Tyr could not be investigated due to the low solubility of this amino acid. The triplet excited states of Ptr are quenched by the four studied amino acids, and the corresponding bimolecular quenching rate constants are in the range of diffusion controlled limit. The assessment of the results in the context of the Ptr‐photosensitization of amino acids suggests that triplet excited state of Ptr is the species that initiates the photochemical processes. 相似文献
83.
Javier S. Acevedo Cortez Thelma Serrano Lucy T. González Oxana V. Kharissova 《Journal of Dispersion Science and Technology》2019,40(6):884-891
Natural sorbent materials have practical advantages for the oil spill cleanup, whose advantages are their low-cost, feasibility for real-life applications and environmental adaptability. In this work, absorption capacity was determined for lyophilized aloe, nopal and agar and their composites with silica, Fe3O4/polysterene and multi-wall carbon nanotubes (MWCNTs). Freeze-drying was performed in order to preserve the structure and increase the internal volume of sorbents. The structures of lyophilized sorbents and composites were analyzed by scanning electron microscopy (SEM). SEM images for lyophilized sorbents show a tridimensional arrangement formed by plant-derived materials, which allows the oil absorption. The composites keep their tridimensional structure after freeze-drying and composite formation and exhibit coupling between both materials. Absorption capacity of aloe, nopal and agar are 9?g/g, 3?g/g, and 26?g/g, respectively without any pretreatment. Composites with Fe3O4/polysterene own capacities of 5.8?g/g, 2.8?g/g, and 14?g/g, respectively. Finally, for MWCNT composites, capacities are 7.8?g/g, 2.9?g/g and 23?g/g. A significant difference of adsorption capacity between lyophilized sorbents and composites is attributed to lyophilized materials absorbing oil, water and other compounds. Meanwhile, for composites the absorption is a more selective process, since the hydrophobization does not allow the absorption of water. 相似文献
84.
Dihydrogen Catalysis of the Reversible Formation and Cleavage of CH and NH Bonds of Aminopyridinate Ligands Bound to (η5‐C5Me5)IrIII 下载免费PDF全文
Dr. Ana Zamorano Dr. Nuria Rendón Dr. Joaquín López‐Serrano Dr. José E. V. Valpuesta Dr. Eleuterio Álvarez Prof. Dr. Ernesto Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2576-2587
This study focuses on a series of cationic complexes of iridium that contain aminopyridinate (Ap) ligands bound to an (η5‐C5Me5)IrIII fragment. The new complexes have the chemical composition [Ir(Ap)(η5‐C5Me5)]+, exist in the form of two isomers ( 1+ and 2+ ) and were isolated as salts of the BArF? anion (BArF=B[3,5‐(CF3)2C6H3]4). Four Ap ligands that differ in the nature of their bulky aryl substituents at the amido nitrogen atom and pyridinic ring were employed. In the presence of H2, the electrophilicity of the IrIII centre of these complexes allows for a reversible prototropic rearrangement that changes the nature and coordination mode of the aminopyridinate ligand between the well‐known κ2‐N,N′‐bidentate binding in 1+ and the unprecedented κ‐N,η3‐pseudo‐allyl‐coordination mode in isomers 2+ through activation of a benzylic C?H bond and formal proton transfer to the amido nitrogen atom. Experimental and computational studies evidence that the overall rearrangement, which entails reversible formation and cleavage of H?H, C?H and N?H bonds, is catalysed by dihydrogen under homogeneous conditions. 相似文献
85.
86.
Guiera senegalensis J. F. Gmel. (Combretaceae) is one of the most important West African medicinal plants, often used to treat a variety of microbial infections. The most frequently used plant part is the leaf, its medicinal use being corroborated by several in vitro antimicrobial activity studies. However, quality criteria for pharmaceutical use, including botanical identification, are not yet determined. Aiming the establishment of such criteria, the present work deepens today's knowledge on G. senegalensis leaf morphology and anatomy, the anatomical characters of both leaf transversal section and powdered leaves being hereby presented for the first time. The most useful characters for identification purposes are leaf isobilateral organization, with similar upper and lower surfaces and a palisade parenchyma on both surfaces; trichome insertion points on both epidermis, surrounded by polar arrangements of cells; tomentose indumentum on the upper epidermis consisting of compartmented and uniseriated trichomes with long, curved, or straight terminal cells; brown scales, isolated or inserted into the epidermis, formed by radially arranged cells surrounding a central cell, with a more or less circular form and a conspicuous base; calcium oxalate cluster crystals, isolated or inserted into the palisade parenchyma and absent in lateral veins. 相似文献
87.
Alberto Concellón Iván Marín Joaquín Barberá Mercedes Marcos José L. Serrano 《Helvetica chimica acta》2023,106(5):e202300010
We have developed a new strategy for the preparation of a light-responsive ionic liquid crystal (LC) that shows photo-switchable proton conduction. The ionic LC consists of a bowl-shaped calix[4]arene core ionically functionalized with azobenzene moieties. The non-covalent architectures were obtained by the formation of ionic salts between the carboxylic acid group of an azo-derivative and the terminal amine groups of a calixarene core. The presence of ionic salts results in a hierarchical self-assembly process that extends to the formation of a nanostructured lamellar LC arrangement (smectic A phase). In this LC phase, the ionic LC calixarene is able to display proton conductive properties, since the ionic nanosegregated areas (formed by the ionic pairs) generate the continuous channels that favor proton transport. The optical and photo-responsive properties were studied by UV-Vis spectroscopy, demonstrating that the azobenzene moieties of the ionic LC undergo reversible (E)-to-(Z) isomerization by irradiation with UV light. Interestingly, this (E)-to-(Z) photoisomerization results in a decrease of the proton conductivity values since the bent-shaped (Z)-isomer disrupts the lamellar LC phase. This isomerization process is totally reversible and leads to an ionic LC material with unique photo-switchable proton conductive properties. 相似文献
88.
Sayra L. Orozco Erick R. Bandala Camilo A. Arancibia-Bulnes Benito Serrano Raúl Surez-Parra Isaias Hernndez-Prez 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):144-149
The effect of chloride, sulfate and nitrate anions on the color removal of water containing the azo-dye reactive blue 69 (RB69) in acidic solution, by using photo-assisted Fenton process with Fe(II)/H2O2 and Fe(III)/H2O2 systems was investigated. Experiments were conducted in a batch reactor irradiated during 5 h with a domestic 15 W lamp with emission in the visible spectra. Experimental results showed color disappearance in the first 5 min of reaction in the photo-assisted process for all of the different salts, greatly enhancing the reaction rate with respect to the corresponding systems under dark conditions. The exception of the general trend was the Fe2(SO4)3/H2O2/UV system, where the decolorization process is slower probably because the oxidative species generated by rupture of Fe(III)–peroxo complexes are less reactive. Total organic matter depletion and mineralization of the effluent were also tested during the experimental runs by means of total organic carbon (TOC) showing that, for most of the photo-assisted experiments high mineralization was reached after 3 h of reaction. 相似文献
89.
Nitrosylation of Nitric‐Oxide‐Sensing Regulatory Proteins Containing [4Fe‐4S] Clusters Gives Rise to Multiple Iron–Nitrosyl Complexes 下载免费PDF全文
Pauline N. Serrano Dr. Hongxin Wang Dr. Jason C. Crack Christopher Prior Prof. Matthew I. Hutchings Prof. Andrew J. Thomson Dr. Saeed Kamali Dr. Yoshitaka Yoda Dr. Jiyong Zhao Dr. Michael Y. Hu Dr. Ercan E. Alp Dr. Vasily S. Oganesyan Prof. Nick E. Le Brun Prof. Stephen P. Cramer 《Angewandte Chemie (International ed. in English)》2016,55(47):14575-14579
The reaction of protein‐bound iron–sulfur (Fe‐S) clusters with nitric oxide (NO) plays key roles in NO‐mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe‐S clusters has been hampered by a lack of information about the nature of the iron‐nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe‐4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe2(NO)4(Cys)2]) and Roussin's Black Salt (RBS, [Fe4(NO)7S3]. In the latter case, the absence of 32S/34S shifts in the Fe?S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates. 相似文献
90.