全文获取类型
收费全文 | 22703篇 |
免费 | 2389篇 |
国内免费 | 1079篇 |
专业分类
化学 | 5897篇 |
晶体学 | 36篇 |
力学 | 1485篇 |
综合类 | 215篇 |
数学 | 12210篇 |
物理学 | 6328篇 |
出版年
2024年 | 19篇 |
2023年 | 197篇 |
2022年 | 217篇 |
2021年 | 458篇 |
2020年 | 536篇 |
2019年 | 571篇 |
2018年 | 447篇 |
2017年 | 556篇 |
2016年 | 819篇 |
2015年 | 631篇 |
2014年 | 1055篇 |
2013年 | 1765篇 |
2012年 | 1092篇 |
2011年 | 1111篇 |
2010年 | 1010篇 |
2009年 | 1329篇 |
2008年 | 1538篇 |
2007年 | 1543篇 |
2006年 | 1345篇 |
2005年 | 1067篇 |
2004年 | 921篇 |
2003年 | 910篇 |
2002年 | 931篇 |
2001年 | 745篇 |
2000年 | 698篇 |
1999年 | 626篇 |
1998年 | 556篇 |
1997年 | 432篇 |
1996年 | 366篇 |
1995年 | 328篇 |
1994年 | 289篇 |
1993年 | 247篇 |
1992年 | 240篇 |
1991年 | 172篇 |
1990年 | 144篇 |
1989年 | 139篇 |
1988年 | 142篇 |
1987年 | 113篇 |
1986年 | 106篇 |
1985年 | 147篇 |
1984年 | 124篇 |
1983年 | 37篇 |
1982年 | 82篇 |
1981年 | 63篇 |
1980年 | 65篇 |
1979年 | 58篇 |
1978年 | 42篇 |
1977年 | 47篇 |
1976年 | 35篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
Marina Frank Dr. Mark D. Johnstone Prof. Dr. Guido H. Clever 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14104-14125
This Review covers design strategies, synthetic challenges, host–guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal–organic frameworks, but the main focus is on discrete coordination architectures, that is, metal‐mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana‐shaped bis‐pyridyl ligands together with square‐planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double‐cages obeying the formula [M4L8]. The peculiar topology of these double‐cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template‐controlled selectivity. In stimuli‐responsive systems, anionic triggers can toggle the binding of neutral guests or even induce complete structural conversions. The increasing structural and functional complexity in this class of self‐assembled hosts promises the construction of intelligent receptors, novel catalytic systems, and functional materials. 相似文献
43.
Modulation of the Physicochemical Properties of Donor–Spiro–Acceptor Derivatives through Donor Unit Planarisation: Phenylacridine versus Indoloacridine—New Hosts for Green and Blue Phosphorescent Organic Light‐Emitting Diodes (PhOLEDs) 下载免费PDF全文
Dr. Sébastien Thiery Dr. Denis Tondelier Bernard Geffroy Dr. Olivier Jeannin Dr. Joëlle Rault‐Berthelot Dr. Cyril Poriel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10136-10149
This work reports a detailed structure–property relationship study of a series of efficient host materials based on the donor–spiro–acceptor (D‐spiro‐A) design for green and sky‐blue phosphorescent organic light‐emitting diodes (PhOLEDs). The electronic and physical effects of the indoloacridine (IA) fragment connected through a spiro bridge to different acceptor units, namely, fluorene, dioxothioxanthene or diazafluorene moiety, have been investigated in depth. The resulting host materials have been easily synthesised through short, efficient, low‐cost, and highly adaptable synthetic routes by using common intermediates. The dyes possess a very high triplet energy (ET) and tuneable HOMO/LUMO levels, depending on the strength of the donor/acceptor combination. The peculiar electrochemical and optical properties of the IA moiety have been investigated though a fine comparison with their phenylacridine counterparts to study the influence of planarisation. Finally, these molecules have been incorporated as hosts in green and sky‐blue PhOLEDs. For the derivative SIA‐TXO2 as a host, external quantum efficiencies as high as 23 and 14 % have been obtained for green and sky‐blue PhOLEDs, respectively. 相似文献
44.
Dr. Mandeep Singh Ephrath Solel Prof. Ehud Keinan Dr. Ofer Reany 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):536-540
Semithiobambusurils, which represent a new family of macrocyclic host molecules, have been prepared by a convenient, scalable synthesis. These new cavitands are double functional: they strongly bind a broad variety of anions in their interiors and metal ions at their sulfur‐edged portals. The solid‐state structure of semithiobambus[4]uril with HgCl2 demonstrates the ability of these compounds to form linear chains of coordination polymers with thiophillic metal ions. The crystal structure of semithiobambus[6]uril with tetraphenylphosphonium bromide exhibits the unique anion‐binding properties of the host cavity and the characteristics of the binding site. 相似文献
45.
Back Cover: Ultrasound‐Driven Secondary Self‐Assembly of Amphiphilic β‐Cyclodextrin Dimers (Chem. Eur. J. 13/2015) 下载免费PDF全文
46.
Marli Ferreira Dr. Edivandro Girotto Ahmed Bentaleb Dr. Elizabeth A. Hillard Prof. Dr. Hugo Gallardo Dr. Fabien Durola Dr. Harald Bock 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4391-4397
Although the double Friedel–Crafts acylation of arenes with ethyl chloroglyoxylate is hindered by the strongly deactivating effect of the first‐entering glyoxylic substituent, the double reaction is successful with the reactive arene perylene under long reaction times and with concomitant ester hydrolysis. The reaction is regiospecific, giving the 3,9‐regioisomer exclusively. This perylenylenediglyoxylic acid is condensed first with o‐bromophenylacetic acid and then with α‐branched alkylamines to yield the title compounds. Whilst the corresponding tetraalkyl esters only show monotropic mesophases, these diimides show enantiotropic columnar mesophases that can be maintained at room temperature if racemically branched alkyl chains of moderate size are used. A palladium‐induced C?C bond migration during the build‐up of the arene system leads to an isomeric side product of reduced symmetry that can be isolated by aggregation‐controlled chromatographic separation. The HOMO and LUMO energies of the title compounds are considerably higher than those of established perylenetetracarboxdiimides. 相似文献
47.
Supramolecular Recognition Influences Magnetism in [X@HVIV8VV14O54]6− Self‐Assemblies with Symmetry‐Breaking Guest Anions 下载免费PDF全文
Dr. Kirill Yu. Monakhov Oliver Linnenberg Dr. Piotr Kozłowski Dr. Jan van Leusen Dr. Claire Besson Tim Secker Dr. Arkady Ellern Dr. Xavier López Prof. Dr. Josep M. Poblet Prof. Dr. Paul Kögerler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2387-2397
Mixed‐valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all‐inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self‐assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra‐weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {VIV/V22O54}‐type polyoxoanions of D2d symmetry enclosing diamagnetic VO2F2? (C2v), SCN? (C∞v), or ClO4? (Td) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V22O54} shells. We also include the synthesis and characterization of the novel [VVO2F2@HVIV8VV14O54]6? system that comprises the rarely encountered discrete difluorovanadate anion as a quasi‐isolated guest species. 相似文献
48.
Host–Guest Chemistry between Perylene Diimide (PDI) Derivatives and 18‐Crown‐6: Enhancement in Luminescence Quantum Yield and Electrical Conductivity 下载免费PDF全文
P. Lasitha Prof. Dr. Edamana Prasad 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10558-10564
Perylene diimide (PDI) derivatives exhibit a high propensity for aggregation, which causes the aggregation‐induced quenching of emission from the system. Host–guest chemistry is one of the best‐known methods for preventing aggregation through the encapsulation of guest molecules. Herein we report the use of 18‐crown‐6 (18‐C‐6) as a host system to disaggregate suitably substituted PDI derivatives in methanol. 18‐C‐6 formed complexes with amino‐substituted PDIs in methanol, which led to disaggregation and enhanced emission from the systems. Furthermore, the embedding of the PDI ? 18‐C‐6 complexes in poly(vinyl alcohol) (PVA) films generated remarkably high emission quantum yields (60–70 %) from the PDI derivatives. More importantly, the host–guest systems were tested for their ability to conduct electricity in PVA films. The electrical conductivities of the self‐assembled systems in PVA were measured by electrochemical impedance spectroscopy (EIS) and the highest conductivity observed was 2.42×10?5 S cm?1. 相似文献
49.
Facile synthesis of thermosensitive functional polyaspartamide derivatives by click chemistry 下载免费PDF全文
Guangyan Zhang Yunti Zhang Yanfeng Chu Yingying Ma Renxi Zhuo Xulin Jiang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(10):1296-1303
Biodegradable and thermosensitive polyaspartamide derivatives containing pendant azide groups P(Asp‐Az)X‐HPAs were synthesized from poly(l ‐succinimide) via the ring‐opening reaction with 2‐azidoethylamine (Az) and 5‐hydroxypentylamine (HPA). Then hydrophobic phenethyl (PEA) and imidazole (IMZ) moieties were introduced successfully with very high reaction efficiency above 90% to the side chains of P(Asp‐Az)X‐HPA by click reaction to obtain thermoresponsive polyaspartamide derivatives containing pendant aromatic rings P(Asp‐Az)X‐HPA‐PEAs and the thermo/pH‐responsive polyaspartamide derivatives containing pendant imidazole rings P(Asp‐Az)X‐HPA‐IMZs, respectively. The thermoresponsive behaviors of P(Asp‐Az)X‐HPA‐PEAs and P(Asp‐Az)X‐HPA‐IMZs were confirmed by dynamic light scattering (DLS) and transmittance measurements, and the cloud point can be tuned by designed amounts of azide groups and can be further adjusted by the grafting molar percentage of hydrophobic phenethyl or imidazole moieties to the side chains of P(Asp‐Az)X‐HPA via click chemistry. The pH‐responsive behavior of P(Asp‐Az)X‐HPA‐IMZs can also be tuned. These results indicate that the obtained polyaspartamide‐based functional polymers can be further functionalized with hydrophilic long PEG chain and/or targeted moieties via click chemistry for drug delivery. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1296–1303 相似文献
50.
Bio‐Inspired Transition Metal–Organic Hydride Conjugates for Catalysis of Transfer Hydrogenation: Experiment and Theory 下载免费PDF全文
Alex McSkimming Dr. Bun Chan Dr. Mohan M. Bhadbhade Dr. Graham E. Ball Prof. Stephen B. Colbran 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2821-2834
Taking inspiration from yeast alcohol dehydrogenase (yADH), a benzimidazolium (BI+) organic hydride‐acceptor domain has been coupled with a 1,10‐phenanthroline (phen) metal‐binding domain to afford a novel multifunctional ligand ( L BI+) with hydride‐carrier capacity ( L BI++H?? L BIH). Complexes of the type [Cp*M( L BI)Cl][PF6]2 (M=Rh, Ir) have been made and fully characterised by cyclic voltammetry, UV/Vis spectroelectrochemistry, and, for the IrIII congener, X‐ray crystallography. [Cp*Rh( L BI)Cl][PF6]2 catalyses the transfer hydrogenation of imines by formate ion in very goods yield under conditions where the corresponding [Cp*Ir( L BI)Cl][PF6] and [Cp*M(phen)Cl][PF6] (M=Rh, Ir) complexes are almost inert as catalysts. Possible alternatives for the catalysis pathway are canvassed, and the free energies of intermediates and transition states determined by DFT calculations. The DFT study supports a mechanism involving formate‐driven Rh?H formation (90 kJ mol?1 free‐energy barrier), transfer of hydride between the Rh and BI+ centres to generate a tethered benzimidazoline (BIH) hydride donor, binding of imine substrate at Rh, back‐transfer of hydride from the BIH organic hydride donor to the Rh‐activated imine substrate (89 kJ mol?1 barrier), and exergonic protonation of the metal‐bound amide by formic acid with release of amine product to close the catalytic cycle. Parallels with the mechanism of biological hydride transfer in yADH are discussed. 相似文献