全文获取类型
收费全文 | 2317篇 |
免费 | 95篇 |
国内免费 | 387篇 |
专业分类
化学 | 2615篇 |
晶体学 | 18篇 |
力学 | 12篇 |
综合类 | 11篇 |
数学 | 4篇 |
物理学 | 139篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 38篇 |
2021年 | 34篇 |
2020年 | 62篇 |
2019年 | 62篇 |
2018年 | 53篇 |
2017年 | 79篇 |
2016年 | 68篇 |
2015年 | 52篇 |
2014年 | 88篇 |
2013年 | 272篇 |
2012年 | 114篇 |
2011年 | 91篇 |
2010年 | 94篇 |
2009年 | 118篇 |
2008年 | 149篇 |
2007年 | 149篇 |
2006年 | 143篇 |
2005年 | 144篇 |
2004年 | 128篇 |
2003年 | 118篇 |
2002年 | 148篇 |
2001年 | 87篇 |
2000年 | 63篇 |
1999年 | 51篇 |
1998年 | 51篇 |
1997年 | 44篇 |
1996年 | 65篇 |
1995年 | 37篇 |
1994年 | 42篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1979年 | 1篇 |
排序方式: 共有2799条查询结果,搜索用时 15 毫秒
961.
Virgil Percec Anatoliy V. Popov 《Journal of polymer science. Part A, Polymer chemistry》2005,43(6):1255-1260
The chloroiodomethyl chain ends of poly(vinyl chloride) (PVC) obtained by the single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride initiated with iodoform were quantitatively functionalized by the reaction with 2‐allyloxyethanol (CH2?CHCH2OCH2CH2OH). This reaction was performed in dimethyl sulfoxide at 70 °C and was catalyzed by sodium dithionite/sodium bicarbonate. The resulting product is the first example of telechelic PVC [α,ω‐di(hydroxy)PVC]. A possible mechanism for this reaction was suggested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1255–1260, 2005 相似文献
962.
Lipase specificity for the hydrolysis of poly (vinyl acetate) 总被引:2,自引:0,他引:2
Sujay Chattopadhyay G. Sivalingam Giridhar Madras 《Polymer Degradation and Stability》2003,80(3):477-483
The effect of lipases on the side chain hydrolysis of poly (vinyl acetate) (PVAc) was investigated in toluene by various lipases, Hog-pancreas (HP), Candida Rugosa (CR), Lipolase-100T (LL), and Novozyme 435 (NV) at 60 °C. Gas chromatographs and GC–MS spectra showed the presence of different ester side chains. The different size side chain esters in PVAc get hydrolyzed at different specific rates by the various lipases. Longer side chains are hydrolyzed in the order HP>NV>LL>CR whereas the short chains are hydrolyzed in the reverse order. A continuous distribution kinetics model was proposed that accounts for lipase deactivation and determines the rate coefficients of hydrolysis of various chain lengths. Lipase deactivation and hydrolysis rate coefficients were determined for each case. The proposed model predicts the experimental data satisfactorily. 相似文献
963.
Masayoshi Satoh Kumi Shirai Hiroshi Saitoh Takeshi Yamauchi Norio Tsubokawa 《Journal of polymer science. Part A, Polymer chemistry》2005,43(3):600-606
The photograft polymerization of various vinyl monomers onto nanosized silica surfaces was investigated. It was initiated by eosin moieties introduced onto the silica surface. The preparation of the silica with eosin moieties was achieved by the reaction of eosin with benzyl chloride groups on the silica surface.These were introduced by the reaction of surface silanol groups with 4‐(chloromethyl)phenyltrimethoxysilane in the presence of t‐butyl ammonium bromide as a phase‐transfer catalyst. The photopolymerization of various vinyl monomers, such as styrene, acrylamide, acrylic acid, and acrylonitrile was successfully initiated by eosin moieties on the silica surface in the presence of ascorbic acid as a reducing agent and by oxygen. The corresponding polymers were grafted from the silica surface. The grafting efficiency (percentage of grafted polymer to total polymer formed) in the photoinitiation system was much larger than that in the radical polymerization initiated by surface radicals; these radicals were formed by the thermal decomposition of azo groups introduced onto the silica surface. It was found that the polymer‐grafted silica gave stable dispersions in good solvents of grafted polymer and the wettability of the surfaces can be easily controlled by grafting of polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 600–606, 2005 相似文献
964.
A. Ajji L. Choplin R. E. Prud'Homme 《Journal of Polymer Science.Polymer Physics》1991,29(13):1573-1578
Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature Ts was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from Ts, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to Ts deviations were observed for G' at low frequencies (the so-called terminal zone). Above Ts G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near Ts can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″2) as a function of temperature were shown to be sensitive to this anomalous behavior. 相似文献
965.
966.
Oxidation of -(trifluoroacetyl)vinyl sulfides afforded a series of the corresponding sulfones. The reactions of sulfones with various alkyl- and arylthiols were studied. These reactions provide the basis for a new procedure for the synthesis of -(trifluoroacetyl)vinyl sulfides. 相似文献
967.
Isabelle Roth Abdel Aziz Jbarah Rudolf Holze Manfred Friedrich Stefan Spange 《Macromolecular rapid communications》2006,27(3):193-199
Summary: Nucleophilic aromatic substitution of 2,6‐O‐dimethyl‐β‐cyclodextrin (β‐DMCD)‐complexed 4‐fluoro‐3‐nitroaniline derivatives with poly(vinyl amine) (PVAm) in water results in 2‐nitro‐1,4‐benzenediamine‐functionalized water‐soluble PVAms in one step. The 2‐nitro‐1,4‐benzenediamine moiety linked to the polymer is solvatochromic and undergoes protonation and deprotonation as function of pH as shown by UV‐Vis spectroscopy. The occurrence of an isosbestic point in the UV‐Vis spectrum is suitable to directly determine the pKa value using the Henderson‐Hasselbalch equation. The influence of the methyl group substitution of the polymer and the 2‐nitro‐1,4‐benzenediamine moiety on the pKa is discussed.
968.
Marianne Gilbert Siavash Haghighat Soo Keow Chua Soo Yeng Ng 《Macromolecular Symposia》2006,233(1):198-202
A novel method for producing a plasticised PVC with increased porosity has been developed, by the use of an organic-inorganic hybrid. Silica was produced in situ from tetraethoxysilane via a hydrolytic sol-gel processing route. Tetrahydrofuran was used as co-solvent, and γ-glycidyloxypropyl-trimethoxysilane as coupling agent. The films produced were transparent, with moderate mechanical properties. A film containing 20% silica showed a 45% increase in water vapour permeability. 相似文献
969.
970.
聚氯乙烯/炭黑导电复合体系的压阻行为 总被引:1,自引:0,他引:1
研究了聚氯乙烯/炭黑(PVC/CB)导电复合体系在单轴压力作用下的压阻行为,发现CB含量对电阻-机械响应具有显著的影响.当CB含量低于渗流阈值时,PVC/CB复合材料呈现PPC效应;而高于渗流阈值时,呈现NPC效应.在渗流阈值附近,单轴压缩可诱导NPC效应的出现,或者抑制PPC效应. 相似文献