全文获取类型
收费全文 | 1279篇 |
免费 | 43篇 |
国内免费 | 13篇 |
专业分类
化学 | 948篇 |
晶体学 | 5篇 |
力学 | 37篇 |
数学 | 133篇 |
物理学 | 212篇 |
出版年
2023年 | 12篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 24篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 9篇 |
2016年 | 43篇 |
2015年 | 28篇 |
2014年 | 24篇 |
2013年 | 43篇 |
2012年 | 65篇 |
2011年 | 92篇 |
2010年 | 50篇 |
2009年 | 38篇 |
2008年 | 76篇 |
2007年 | 73篇 |
2006年 | 76篇 |
2005年 | 73篇 |
2004年 | 54篇 |
2003年 | 54篇 |
2002年 | 37篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 20篇 |
1993年 | 13篇 |
1992年 | 19篇 |
1990年 | 12篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1876年 | 7篇 |
排序方式: 共有1335条查询结果,搜索用时 62 毫秒
81.
BoRa Lee Anthony C. Willis Jas S. Ward Warren T. Smith Ping Lan Martin G. Banwell 《化学:亚洲杂志》2020,15(19):3059-3081
Syntheses of a range of chemically well‐defined oligopyrrole/benzenoid hybrids are described using tandem Suzuki‐Miyaura cross‐coupling/bromo‐desilyation reaction sequences for linking borylated pyrroles, halogenated pyrroles and/or dibromobenzenes to one another. By such means, including iterative variants, a range of all α‐linked, all β‐linked oligopyrroles as well as certain combinations thereof have been assembled, some of them for the first time. The conductivities of iodine‐treated thin films formed from certain such systems have been determined. 相似文献
82.
Photoprotection of Mammalian Acid-Soluble Collagen by Cuttlefish Sepia Melanin In Vitro 总被引:1,自引:0,他引:1
Julian M. Menter Abrienne M. Patta Thomas D. Hollins Cyril L. Moore Isaac Willis 《Photochemistry and photobiology》1998,68(4):532-537
Several important clinical conditions can result in close association between the pigment melanin and dermal collagen. Because melanin and its precursors can be chemically reactive in ground and excited states, it is important to know whether the resulting melanin-collagen interaction results in photoprotection or photoaggression. Acidic and neutral air-saturated collagen suspensions (0.033%) were irradiated with0–2.6 times 104 J/m2 UVC or with0–83 times 104 J/m2 solar-simulating UV radiation (SSR). Photochemical destruction of a photolabile collagen fluorophore (δem 360 nm) and collagen chain degradation were monitored as functions of irradiation time in the presence and absence of added (0–100μg) sepia eumelanin. Melanin retarded collagen photodamage but did not qualitatively alter the fluorescence fading kinetics. Both H202 and 02 can be produced by UV irradiation of eumelanin. Added H202 and K02 destroyed collagen fluorescence and caused 50% chain degradation at ca10–20-fold molar excess. Previous studies have demonstrated that eumelanins efficiently scavenge 02 . We demonstrated that eumelanin also efficiently scavenges H202 as evidenced by its ability to (a) compete with scopoletin for peroxide uptake and (b) directly take up H202 through a dialysis bag. The latter observation suggests that peroxide scavenging could occur in vivo by melanin sequestered in melanophages. Thus, neither UV-generated 02 nor H202 are likely to be present in concentrations high enough to cause measurable collagen damage. Absorption and/or scattering of excitation radiation away from the target chromophore appears to be the primary photoprotection mechanism, although scavenging of active 02 intermediates may play an important, if subtle role. 相似文献
83.
Xianhong Feng Anthony East Willis Hammond Zohar Ophir Yi Zhang Michael Jaffe 《Journal of Thermal Analysis and Calorimetry》2012,109(3):1267-1275
Sugar-based new monomers, polymers, and low molar mass additives have emerged as an exciting topic on green chemistry research, due to the worldwide focus on sustainable material. Isosorbide and its isomers, as ??Generally Recognized as Safe?? GRAS materials, possess unique stereochemistry and molecular geometry suitable for making cost-effective chemicals and polymers. With growing awareness of bisphenol A (BPA) as a xenoestrogen, isosorbide and its isomers holding the remarkable chemical properties and attractive price can be attached to glycidyl ether to make crosslinkable epoxy resin monomers with similar properties to BPA diglycidyl ether. By adding the hydrophobic functional group into the backbone of isosorbide epoxy or adjusting the amount and type of crosslinker, the mechanical properties and the water uptake ratios (from <1 to >50?wt%) of the isosorbide-derived epoxies could be optimized for different applications. The high water uptake epoxy with controllable biodegradation rate could be used as a drug delivery system or extracellular matrix for biomedical applications while the low water uptake epoxy with strong mechanical properties could be used for can coatings, bone cements, and other industrial additives and adhesives. The chemical structures and properties of the synthesized epoxy monomers and polymers were characterized by DSC, TG, and 1H NMR. 相似文献
84.
Direct Synthesis of Highly Substituted Pyrroles and Dihydropyrroles Using Linear Selective Hydroacylation Reactions 下载免费PDF全文
Manjeet K. Majhail Dr. Paul M. Ylioja Prof. Michael C. Willis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7879-7884
Rhodium(I) catalysts incorporating small bite‐angle diphosphine ligands, such as (Cy2P)2NMe or bis(diphenylphosphino)methane (dppm), are effective at catalysing the union of aldehydes and propargylic amines to deliver the linear hydroacylation adducts in good yields and with high selectivities. In situ treatment of the hydroacylation adducts with p‐TSA triggers a dehydrative cyclisation to provide the corresponding pyrroles. The use of allylic amines, in place of the propargylic substrates, delivers functionalised dihydropyrroles. The hydroacylation reactions can also be combined in a cascade process with a RhI‐catalysed Suzuki‐type coupling employing aryl boronic acids, providing a three‐component assembly of highly substituted pyrroles. 相似文献
85.
A Flexible Photoactive Titanium Metal–Organic Framework Based on a [TiIV3(μ3‐O)(O)2(COO)6] Cluster 下载免费PDF全文
Bart Bueken Dr. Frederik Vermoortele Dr. Danny E. P. Vanpoucke Dr. Helge Reinsch Dr. Chih‐Chin Tsou Dr. Pieterjan Valvekens Dr. Trees De Baerdemaeker Prof. Dr. Rob Ameloot Prof. Dr. Christine E. A. Kirschhock Prof. Dr. Veronique Van Speybroeck Prof. Dr. James M. Mayer Prof. Dr. Dirk De Vos 《Angewandte Chemie (International ed. in English)》2015,54(47):13912-13917
The synthesis of titanium–carboxylate metal–organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium‐based MOFs by the use of titanocene dichloride to synthesize COK‐69, the first breathing Ti MOF, which is built up from trans‐1,4‐cyclohexanedicarboxylate linkers and an unprecedented [TiIV3(μ3‐O)(O)2(COO)6] cluster. The photoactive properties of COK‐69 were investigated in depth by proton‐coupled electron‐transfer experiments, which revealed that up to one TiIV center per cluster can be photoreduced to TiIII while preserving the structural integrity of the framework. The electronic structure of COK‐69 was determined by molecular modeling, and a band gap of 3.77 eV was found. 相似文献
86.
87.
The scalable, divergent synthesis of all four monomers required for the preparation of sulfonamide-based RNA mimetics is described. Such mimetics may combine excellent mimicry of the parent RNA with enhanced (bio)chemical robustness and convenient oligomerization. As a proof of principle, a dimer resulting from the monomers is described. 相似文献
88.
Dimitrios A. Lamprou James R. Smith Thomas G. Nevell Eugen Barbu Corinne Stone Colin R. Willis Richard J. Ewen John Tsibouklis 《Surface science》2010,604(5-6):541-547
Self-assembled structures of alkanethiols that have been deposited on gold from ethanolic solutions are susceptible to both chemical and physical changes: ethanol provides a medium for the formation of S-alkyl hydrogen thiocarbonates and related compounds via reaction with dissolved, atmospheric, CO2. Deposition from ethanolic solutions results in multilayered structures incorporating these compounds, which at room temperature are susceptible to time-dependent structural rearrangement and molecular migration. 相似文献
89.
Rob G. Visser 《Accreditation and quality assurance》2016,21(3):237-238
The tentative arguments mentioned by Paul De Bievre are discussed and alternatives are given that may lead to different insights. 相似文献
90.
Linington RG Robertson M Gauthier A Finlay BB van Soest R Andersen RJ 《Organic letters》2002,4(23):4089-4092
Extracts of the marine sponge Caminus sphaeroconia showed potent activity in a screen for bacterial type III secretion inhibitors. Bioassay guided fractionation of the extract led to the isolation of the novel antimicrobial glycolipid caminoside A (1). The structure of caminoside A was elucidated by analysis of spectroscopic data and chemical degradation.[structure: see text] 相似文献