全文获取类型
收费全文 | 2685篇 |
免费 | 99篇 |
国内免费 | 13篇 |
专业分类
化学 | 2097篇 |
晶体学 | 29篇 |
力学 | 29篇 |
数学 | 371篇 |
物理学 | 271篇 |
出版年
2023年 | 10篇 |
2022年 | 31篇 |
2021年 | 50篇 |
2020年 | 39篇 |
2019年 | 42篇 |
2018年 | 33篇 |
2017年 | 29篇 |
2016年 | 82篇 |
2015年 | 82篇 |
2014年 | 79篇 |
2013年 | 159篇 |
2012年 | 216篇 |
2011年 | 245篇 |
2010年 | 145篇 |
2009年 | 117篇 |
2008年 | 186篇 |
2007年 | 195篇 |
2006年 | 178篇 |
2005年 | 151篇 |
2004年 | 118篇 |
2003年 | 100篇 |
2002年 | 98篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 32篇 |
1998年 | 15篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 6篇 |
1894年 | 5篇 |
排序方式: 共有2797条查询结果,搜索用时 31 毫秒
151.
Jarosaw Korus Rafa Ziobro Teresa Witczak Kamila Kapusniak Lesaw Juszczak 《Molecules (Basel, Switzerland)》2021,26(8)
The study focused on the influence of starch modified by octenyl succinic anhydride (OSA) on the rheological and thermal properties of gluten-free dough containing corn and potato starch with the addition of pectin and guar gum as structure-forming substances. The starch blend used in the original dough recipe was partially (5% to 15%) replaced with OSA starch. The rheological properties of dough samples were determined, and the properties of the resulting bread were analyzed. It was found that the dough samples behaved as weak gels, and the values of storage and loss moduli (G′ and G″, respectively) significantly depended on angular frequency. Various shares of OSA starch in recipes modified dough in different ways, causing changes in its rheological characteristics. The introduction of OSA starch preparations resulted in changes in the bread volume and physical characteristics of the crumb. All the applied preparations caused an increase in bread porosity and the number of pores larger than 5 mm, and there was a parallel decrease in pore density. The presence of OSA starch preparations modified bread texture depending on the amount and type of the applied preparation. The introduction of OSA starches in gluten-free bread formulation caused a significant drop in the enthalpy of retrograded amylopectin decomposition, indicating a beneficial influence of such type of additive on staling retardation in gluten-free bread. 相似文献
152.
Brito Ciro José Miarka Bianca García-Pastor Teresa Pérez Diego Ignácio Valenzuela Marins Joao Carlos Bouzas Sillero-Quintana Manuel 《Journal of Thermal Analysis and Calorimetry》2021,145(5):2467-2475
Journal of Thermal Analysis and Calorimetry - This study investigated the thermal skin (Tsk) response of lower limbs in older adults with or without osteoarthritis before and after a concurrent... 相似文献
153.
Jouini Houda Mejri Imène Rhimi Baker Mhamdi Mourad Blasco Teresa Delahay Gérard 《Research on Chemical Intermediates》2021,47(7):2901-2915
Research on Chemical Intermediates - Fe–Cu–ZSM-5 and Ce–Fe–Cu–ZSM-5 solids prepared using solid-state ion exchange method (SSIE) were tested in the NH3–SCR of NO... 相似文献
154.
Iván da Silva Germán R. Castro Zakariae Amghouz Aránzazu Espina Sergei A. Khainakov Santiago García-Granda José R. García 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1179-1186
(C4N2H12)CrO(H1.5PO4)2·H2O has been synthesized hydrothermally using piperazine as organic template. Its crystal structure was solved ab initio using synchrotron powder X-ray diffraction data [monoclinic, a = 16.9649(4) Å, b = 9.8609(2) Å, c = 7.14375(14) Å, and β = 94.896(3)°, space group P21/a, Z = 4]. 1D structure is composed by isolated infinite anionic chains [CrO(H1.5PO4)2]n (vertex-sharing {CrO6} octahedra joined by phosphate moieties). Their 2D plate-like morphology is propitiated by a very strong inter-chain interaction (P–O···H···O–P symmetric hydrogen bonds). KAS isoconversional method was applied to determine the activation energy for both thermal and thermo-oxidative decomposition of (C4N2H12)CrO(H1.5PO4)2·H2O. 相似文献
155.
Multifunctional Supramolecular Dendrimers with an s‐Triazine Ring as the Central Core: Liquid Crystalline,Fluorescence and Photoconductive Properties
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)
Madalina Bucoş Dr. Teresa Sierra Dr. Attilio Golemme Dr. Roberto Termine Dr. Joaquín Barberá Dr. Raquel Giménez Prof. Dr. José Luis Serrano Dr. Pilar Romero Dr. Mercedes Marcos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):10027-10037
Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s‐triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties. The formation of the complexes was confirmed by IR and NMR spectroscopy data. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy and X‐ray diffractometry. All complexes displayed mesogenic properties, which were smectic in the case of symmetric dendrons and their complexes and nematic in the case of asymmetric dendrons and their dendrimers. A supramolecular model for the lamellar mesophase, based mainly on X‐ray diffraction studies, is proposed. The electrochemical behaviour of dendritic complexes was investigated by cyclic voltammetry. The UV/Vis absorption and emission properties of the compounds and the photoconductive properties of the dendrons and dendrimers were also investigated 相似文献
156.
Molecular Recognition of Nucleotides in Water by Scorpiand‐Type Receptors Based on Nucleobase Discrimination
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)
Mario Inclán Dr. M. Teresa Albelda Dr. Esther Carbonell Dr. Salvador Blasco Antonio Bauzá Prof. Antonio Frontera Prof. Enrique García‐España 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(13):3730-3741
The detection of nucleotides is of crucial importance because they are the basic building blocks of nucleic acids. Scorpiand‐based polyamine receptors functionalized with pyridine or anthracene units are able to form stable complexes with nucleotides in water, based on coulombic, π–π stacking, and hydrogen‐bonding interactions. This behavior has been rationalized by means of an exploration with NMR spectroscopy and DFT calculations. Binding constants were determined by potentiometry. Fluorescence spectroscopy studies have revealed the potential of these receptors as sensors to effectively and selectively distinguish guanosine‐5′‐triphosphate (GTP) from adenosine‐5′‐triphosphate (ATP). 相似文献
157.
Intermolecular and Regioselective Access to Polysubstituted Benzo‐ and Dihydrobenzo[c]azepine Derivatives: Modulating the Reactivity of Group 6 Non‐Heteroatom‐Stabilized Alkynyl Carbene Complexes
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)
Jairo González Dr. Aránzazu Gómez Ignacio Funes‐Ardoiz Dr. Javier Santamaría Diego Sampedro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7061-7068
We highlight the versatility of non‐heteroatom‐stabilized tungsten–carbene complexes 3 synthesized in situ, which have been used in a modular approach to access 2‐benzazepinium isolable intermediates 5 . By employing very mild conditions, benzazepinium derivatives 5 have been obtained in high yield from simple compounds, such as acetylides 2 , Fischer‐type alkoxycarbenes 1 , and phenylimines 4 . The process, involving a formal [4+3] heterocycloaddition, occurs in a totally regioselective manner, which differs from the approach previously observed in similar procedures for other carbene analogues. This work, which involves three components, reveals a control of the reactivity of non‐heteroatom‐stabilized carbene complexes 3 ([4+3] vs. [2+2]‐heterocycloaddition reactions) depending on the acetylide substitution pattern. The influence of the substitution pattern in the behavior of the complexes has been computationally analyzed and rationalized. Finally, elaboration of the 2‐benzazepinium intermediates allows access to 3H‐benzo[c]azepines 6 and 3H‐1,2‐dihydrobenzo[c]azepines 7 – 9 with high control of the substitution of the nine positions of the heterocycle. 相似文献
158.
Dr. Albert Ferrer‐Ugalde Dr. Arántzazu González‐Campo Prof. Dr. Clara Viñas Dr. Jesús Rodríguez‐Romero Dr. Rosa Santillan Dr. Norberto Farfán Prof. Dr. Reijo Sillanpää Dr. Antonio Sousa‐Pedrares Dr. Rosario Núñez Prof. Dr. Francesc Teixidor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9940-9951
Two sets of o‐carborane derivatives incorporating fluorene and anthracene fragments as fluorophore groups have been successfully synthesized and characterized, and their photophysical properties studied. The first set, comprising fluorene‐containing carboranes 6 – 9 , was prepared by catalyzed hydrosilylation reactions of ethynylfluorene with appropriate carboranylsilanes. The compound 1‐[(9,9‐dioctyl‐fluorene‐2‐yl)ethynyl]carborane ( 11 ) was synthesized by the reaction of 9,9‐dioctyl‐2‐ethynylfluorene and decaborane (B10H14). Furthermore, reactions of the lithium salt of 11 with 1 equivalent of 4‐(chloromethyl)styrene or 9‐(chloromethyl)anthracene yielded compounds 12 and 13 . Members of the second set of derivatives, comprising anthracene‐containing carboranes, were synthesized by reactions of monolithium or dilithium salts of 1‐Me‐1,2‐C2B10H11, 1‐Ph‐1,2‐C2B10H11, and 1,2‐C2B10H12 with 1 or 2 equivalents of 9‐(chloromethyl)anthracene, respectively, to produce compounds 14 – 16 . In addition, 2 equivalents of the monolithium salts of 1‐Me‐1,2‐C2B10H11 (Me‐o‐carborane) and 1‐Ph‐1,2‐C2B10H11 (Ph‐o‐carborane) were reacted with 9,10‐bis(chloromethyl)anthracene to produce compounds 17 and 18 , respectively. Fluorene derivatives 6 – 9 exhibit moderate fluorescence quantum yields (32–44 %), whereas 11 – 13 , in which the fluorophore is bonded to the Ccluster (Cc), show very low emission intensity (6 %) or complete fluorescence quenching. The anthracenyl derivatives containing the Me‐o‐carborane moiety exhibit notably high fluorescence emissions, with ?F=82 and 94 %, whereas their Ph‐o‐carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the Cc?Cc bond length and the fluorescence intensity in CH2Cl2 solution, comparable to that observed for previously reported styrene‐containing carboranes. Thus, our hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent Cc. 相似文献
159.
Supermolecular Columnar Liquid‐Crystalline Phosphorus Dendrimers Decorated with Sulfonamide Derivatives
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)
Cesar Augusto Hincapié Rosa María Sebastián Joaquín Barberá José Luis Serrano Teresa Sierra Jean‐Pierre Majoral Anne‐Marie Caminade 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):17047-17058
A series of supermolecular liquid crystals has been synthesized by combining phosphorus dendrimers of the zero, first, and fourth generations with sulfonamide derivatives, thus generating dendromesogens bearing 6, 12, and 96 mesogenic units on their surfaces. The relevant reactions could be monitored by 1H, 19F, and 31P{1H} NMR spectroscopies. The thermal and mesomorphic properties of the products have been studied by optical microscopy, differential scanning calorimetry, and X‐ray diffraction. All of the new macromolecules prepared in this work have been found to show mesomorphic properties over a wide temperature range; moreover, for all of the compounds, the columnar mesophases observed were maintained or vitrified at room temperature. On increasing the generation of these dendromesogens, mesophases appear at lower temperatures and remain stable over a wider temperature interval. In all cases, on the basis of X‐ray analysis, a cylindrical symmetry of the molecules can be proposed to promote the supramolecular columnar arrangement observed in the mesophases. In this type of model, the height of the dendrimer clearly increases with increasing dendrimer generation, whereas its cross‐ sectional area increases only slightly, probably due to compression of the highly hyperbranched structures as a consequence of their progressive steric constraints. The mesomorphic arrangement is governed by the peripheral sulfonamide units. 相似文献
160.
Dr. Martín Regueiro‐Figueroa Dr. David Esteban‐Gómez Dr. Andrés de Blas Dr. Teresa Rodríguez‐Blas Dr. Carlos Platas‐Iglesias 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3974-3981
The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA4? (H4TETA=2,2′,2′′,2′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetraacetic acid), BCAED4? (H4BCAED=2,2′,2′′,2′′′‐{[(1,4‐diazepane‐1,4‐diyl)bis(ethane‐2,1‐diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C62? (H2BP18C6=6,6′‐[(1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐7,16‐diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calculations. Geometry optimizations performed at the TPSSh/6‐31G(d,p) level, and using a 46+4fn ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the experimental values observed in the X‐ray structures. The contractions of the Ln3+ coordination spheres follow quadratic trends, as observed previously for different isostructural series of complexes. We show here that the parameters obtained from the quantitative analysis of these data can be used to rationalize the observed stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calculating the free energy for the reaction [La( L )]n+/?(sol)+Ln3+(sol)→[Ln( L )]n+/?(sol)+La3+(sol). A parameterization of the Ln3+ radii was performed by minimizing the differences between experimental and calculated standard hydration free energies. The calculated stability trends are in good agreement with the experimental stability constants, which increase markedly across the series for BCAED4? complexes, increase smoothly for the TETA4? analogues, and decrease in the case of BP18C62? complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the absolute values of hydration energies along the 4f period. 相似文献