全文获取类型
收费全文 | 1577篇 |
免费 | 69篇 |
国内免费 | 7篇 |
专业分类
化学 | 1245篇 |
晶体学 | 23篇 |
力学 | 15篇 |
数学 | 166篇 |
物理学 | 204篇 |
出版年
2023年 | 20篇 |
2022年 | 25篇 |
2021年 | 40篇 |
2020年 | 44篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 19篇 |
2016年 | 76篇 |
2015年 | 39篇 |
2014年 | 57篇 |
2013年 | 94篇 |
2012年 | 119篇 |
2011年 | 146篇 |
2010年 | 57篇 |
2009年 | 61篇 |
2008年 | 117篇 |
2007年 | 88篇 |
2006年 | 75篇 |
2005年 | 87篇 |
2004年 | 70篇 |
2003年 | 54篇 |
2002年 | 48篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1982年 | 10篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1968年 | 5篇 |
1960年 | 4篇 |
1932年 | 3篇 |
1927年 | 3篇 |
排序方式: 共有1653条查询结果,搜索用时 15 毫秒
131.
Mono‐ and Bis(pyrrolo)tetrathiafulvalene Derivatives Tethered to C60: Synthesis,Photophysical Studies,and Self‐Assembled Monolayers 下载免费PDF全文
Dr. Marta Vico Solano Dr. Eduardo Antonio Della Pia Dr. Martyn Jevric Christina Schubert Xintai Wang Dr. Cornelia van der Pol Prof. Dr. Anders Kadziola Prof. Dr. Kasper Nørgaard Prof. Dr. Dirk M. Guldi Prof. Dr. Mogens Brøndsted Nielsen Prof. Dr. Jan O. Jeppesen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9918-9929
A series of mono‐ (MPTTF) and bis(pyrrolo)tetrathiafulvalene (BPTTF) derivatives tethered to one or two C60 moieties was synthesized and characterized. The synthetic strategy for these dumbbell‐shaped compounds was based on a 1,3‐dipolar cycloaddition reaction between aldehyde‐functionalized MPTTF/BPTTF derivatives, two different tailor‐made amino acids, and C60. Electronic communication between the MPTTF/BPTTF units and the C60 moieties was studied by a variety of techniques including cyclic voltammetry and absorption spectroscopy. These solution‐based studies indicated no observable electronic communication between the MPTTF/BPTTF units and the C60 moieties. In addition, femtosecond and nanosecond transient absorption spectroscopy revealed, rather surprisingly, that no charge transfer from the MPTTF/BPTTF units to the C60 moieties takes place on excitation of the fullerene moiety. Finally, it was shown that the MPTTF–C60 and C60–BPTTF‐C60 dyad and triad molecules formed self‐assembled monolayers on a Au(111) surface by anchoring to C60. 相似文献
132.
Enzyme Design from the Bottom Up: An Active Nickel Electrocatalyst with a Structured Peptide Outer Coordination Sphere 下载免费PDF全文
Dr. Matthew L. Reback Dr. Garry W. Buchko Dr. Brandon L. Kier Bojana Ginovska‐Pangovska Dr. Yijia Xiong Dr. Sheri Lense Dr. Jianbo Hou Dr. John A. S. Roberts Dr. Christina M. Sorensen Dr. Simone Raugei Dr. Thomas C. Squier Dr. Wendy J. Shaw 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1510-1514
Catalytic, peptide‐containing metal complexes with a well‐defined peptide structure have the potential to enhance molecular catalysts through an enzyme‐like outer coordination sphere. Here, we report the synthesis and characterization of an active, peptide‐based metal complex built upon the well‐characterized hydrogen production catalyst [Ni(PPh2NPh)2]2+ (PPh2NPh=1,3,6‐triphenyl‐1‐aza‐3,6‐diphosphacycloheptane). The incorporated peptide maintains its β‐hairpin structure when appended to the metal core, and the electrocatalytic activity of the peptide‐based metal complex (≈100,000 s?1) is enhanced compared to the parent complex ([Ni(PPh2NAPPA)2]2+; ≈50,500 s‐1). The combination of an active molecular catalyst with a structured peptide provides a scaffold that permits the incorporation of features of an enzyme‐like outer‐coordination sphere necessary to create molecular electrocatalysts with enhanced functionality. 相似文献
133.
The complexation behavior of Aldrich humic acid (AHA) and a modified humic acid (AHA-PB) with blocked phenolic hydroxyl groups for trivalent lanthanides (Ln) is compared, and their influence on the mobility of Ln(III) in an aquifer is analyzed. As speciation technique, capillary electrophoresis (CE) was hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). For metal loading experiments 25 mg L−1 of AHA and different concentrations (cLn(Eu+Gd) = 100–6000 μg L−1) of Eu(III) and Gd(III) in 10 mM NaClO4 at pH 5 were applied. By CE-ICP-MS, three Ln-fractions, assumed to be uncomplexed, weakly and strongly AHA-complexed metal can be detected. For the used Ln/AHA-ratios conservative complex stability constants log βLnAHA decrease from 6.33 (100 μg L−1 Ln3+) to 4.31 (6000 μg L−1 Ln3+) with growing Ln-content. In order to verify the postulated weaker and stronger humic acid binding sites for trivalent Eu and Gd, a modified AHA with blocked functional groups was used. For these experiments 500 μg L−1 Eu and 25 mg L−1 AHA and AHA-PB in 10 mM NaClO4 at pH-values ranging from 3 to 10 have been applied. With AHA-PB, where 84% of the phenolic OH-groups and 40% of the COOH-groups were blocked, Eu complexation was significantly lower, especially at the strong binding sites. The log β-values decrease from 6.11 (pH 10) to 5.61 at pH 3 (AHA) and for AHA-PB from 6.01 (pH 7) to 3.94 at pH 3. As a potential consequence, particularly humic acids with a high amount of strong binding sites (e.g. phenolic OH- and COOH-groups) can be responsible for a higher metal mobility in the aquifer due to the formation of dissolved negatively charged metal-humate species. 相似文献
134.
Dr. Christina I. Schroeder Dr. Lachlan D. Rash Xavier Vila‐Farrés Dr. K. Johan Rosengren Dr. Mehdi Mobli Prof. Glenn F. King Prof. Paul F. Alewood Prof. David J. Craik Dr. Thomas Durek 《Angewandte Chemie (International ed. in English)》2014,53(4):1017-1020
Mambalgins are a novel class of snake venom components that exert potent analgesic effects mediated through the inhibition of acid‐sensing ion channels (ASICs). The 57‐residue polypeptide mambalgin‐2 (Ma‐2) was synthesized by using a combination of solid‐phase peptide synthesis and native chemical ligation. The structure of the synthetic toxin, determined using homonuclear NMR, revealed an unusual three‐finger toxin fold reminiscent of functionally unrelated snake toxins. Electrophysiological analysis of Ma‐2 on wild‐type and mutant ASIC1a receptors allowed us to identify α‐helix 5, which borders on the functionally critical acidic pocket of the channel, as a major part of the Ma‐2 binding site. This region is also crucial for the interaction of ASIC1a with the spider toxin PcTx1, thus suggesting that the binding sites for these toxins substantially overlap. This work lays the foundation for structure–activity relationship (SAR) studies and further development of this promising analgesic peptide. 相似文献
135.
Unprecedented Strong Lewis Bases—Synthesis and Methyl Cation Affinities of Dimethylamino‐Substituted Terpyridines 下载免费PDF全文
Dr. Paul Hommes Christina Fischer Dr. Christoph Lindner Prof. Dr. Hendrik Zipse Prof. Dr. Hans‐Ulrich Reissig 《Angewandte Chemie (International ed. in English)》2014,53(29):7647-7651
A versatile method for the synthesis of functionalized 2,2′:6′,2′′‐terpyridines by assembly of the terminal pyridine rings is presented. The cyclization precursors—bis‐β‐ketoenamides—are prepared from 4‐substituted 2,6‐pyridinedicarboxylic acids and acetylacetone or its corresponding enamino ketone. Treatment with trimethylsilyl trifluoromethanesulfonate induces a twofold intramolecular condensation providing an efficient access to 4,4′′‐di‐ and 4,4′,4′′‐trifunctionalized 6,6′′‐dimethyl‐2,2′:6′,2′′‐terpyridines. Using this method, hitherto unknown 4,4′′‐bis(dimethylamino)‐ and 4,4′,4′′‐tris(dimethylamino)terpyridines have been prepared that show remarkably high calculated Lewis basicities. 相似文献
136.
Christina Schjoeth-Eskesen Paul Robert Hansen Andreas Kjaer Nic Gillings 《ChemistryOpen》2015,4(1):65-71
Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridine-2-carboxylates with [18F]fluoride. The aziridine was activated for nucleophilic attack by substitution of various groups on the aziridine nitrogen atom. Fluorine-18 radiolabelling was followed by ester hydrolysis and removal of the activation group. Totally regioselective ring opening and subsequent deprotection was achieved with tert-butyloxycarbonyl- and carboxybenzyl-activated aziridines to give α-[18F]fluoro-β-alanine in good radiochemical yield. 相似文献
137.
Evangelos I. Tolis Dikaia E. Saraga George Z. Ammari Evangelos I. Gkanas Theofilos Gougoulas Christina C. Papaioannou Anastasios K. Sarioglou Eleftherios Kougioumtzidis Athina Skemperi John G. Bartzis 《Central European Journal of Chemistry》2014,12(6):643-651
Eordaia basin located in northwest of Greece, comprises an area which is characterized by intense energy related activities, including coal burning at four power plants and the associated mining operations. Air samples of inhalable (PM10) and respirable particles (PM2.5) were collected in cold and warm periods in 2010 at an urban background site of Kozani, the major city and capital of the region which is located close to the power plants. Particulate matter concentration, particle-bound polycyclic aromatic hydrocarbons and anionic species concentrations were determined using gravimetric, GC-MS in SIM mode and Ion Chromatography analysis, respectively. For the cold period, the mean PM10 and PM2.5 mass concentration was found to be 19.62 and 14.68 µg m?3, respectively. Correspondingly, for the warm period, the mean PM10 and PM2.5 values were 35.29 and 25.75 µg m?3, respectively. In general, the results indicated that the major sources of air pollution in Kozani are traffic, combustion from agricultural activities and lignite power plants emissions, contributing by different percentages to each particle fraction. 相似文献
138.
Different Complexation Behavior of P‐Functionalized Ferrocene Derivatives Towards SnCl2, SnCl4 and SnPh2Cl2: Auto‐ionization and Redox‐Type Reactions 下载免费PDF全文
Dipl.‐Chem. Matthias Gawron Dr. Christina Dietz Michael Lutter Dr. Andrew Duthie Prof. Dr. Viatcheslav Jouikov Prof. Dr. Klaus Jurkschat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(46):16609-16622
The novel phosphonyl‐substituted ferrocene derivatives [Fe(η5‐Cp)(η5‐C5H3{P(O)(O‐iPr)2}2‐1,2)] ( Fc1,2 ) and [Fe{η5‐C5H4P(O)(O‐iPr)2}2] ( Fc1,1′ ) react with SnCl2, SnCl4, and SnPh2Cl2, giving the corresponding complexes [(Fc1,2)2SnCl][SnCl3] ( 1 ), [{(Fc1,1′)SnCl2}n] ( 2 ), [(Fc1,1′)SnCl4] ( 3 ), [{(Fc1,1′)SnPh2Cl2}n] ( 4 ), and [(Fc1,2)SnCl4] ( 5 ), respectively. The compounds are characterized by elemental analyses, 1H, 13C, 31P, 119Sn NMR and IR spectroscopy, 31P and 119Sn CP‐MAS NMR spectroscopy, cyclovoltammetry, electrospray ionization mass spectrometry, and single‐crystal as well as powder X‐ray diffraction analyses. The experimental work is accompanied by DFT calculations, which help to shed light on the origin for the different reaction behavior of Fc1,1′ and Fc1,2 towards tin(II) chloride. 相似文献
139.
140.
Structure Elucidation and Activity of Kolossin A,the D‐/L‐Pentadecapeptide Product of a Giant Nonribosomal Peptide Synthetase 下载免费PDF全文
Prof. Dr. Helge B. Bode Dr. Alexander O. Brachmann Dr. Kirtikumar B. Jadhav Dr. Lydia Seyfarth Dipl.‐Chem. Christina Dauth Dr. Sebastian W. Fuchs Dr. Marcel Kaiser Dr. Nick R. Waterfield Dipl.‐Phys. Holger Sack Prof. Dr. Stefan H. Heinemann Prof. Dr. Hans‐Dieter Arndt 《Angewandte Chemie (International ed. in English)》2015,54(35):10352-10355
The largest continuous bacterial nonribosomal peptide synthetase discovered so far is described. It consists of 15 consecutive modules arising from an uninterrupted, fully functional gene in the entomopathogenic bacterium Photorhabdus luminescens. The identification of its cryptic biosynthesis product was achieved by using a combination of genome analysis, promoter exchange, isotopic labeling experiments, and total synthesis of a focused collection of peptide candidates. Although it belongs to the growing class of D ‐/ L ‐peptide natural products, the encoded metabolite kolossin A was found to be largely devoid of antibiotic activity and is likely involved in interspecies communication. A stereoisomer of this peculiar natural product displayed high activity against Trypanosoma brucei rhodesiense, a recalcitrant parasite that causes the deadly disease African sleeping sickness. 相似文献