全文获取类型
收费全文 | 890篇 |
免费 | 53篇 |
国内免费 | 22篇 |
专业分类
化学 | 928篇 |
晶体学 | 1篇 |
力学 | 7篇 |
综合类 | 2篇 |
数学 | 4篇 |
物理学 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 30篇 |
2018年 | 18篇 |
2017年 | 24篇 |
2016年 | 38篇 |
2015年 | 33篇 |
2014年 | 37篇 |
2013年 | 61篇 |
2012年 | 46篇 |
2011年 | 40篇 |
2010年 | 54篇 |
2009年 | 52篇 |
2008年 | 74篇 |
2007年 | 57篇 |
2006年 | 51篇 |
2005年 | 70篇 |
2004年 | 59篇 |
2003年 | 53篇 |
2002年 | 42篇 |
2001年 | 20篇 |
2000年 | 7篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有965条查询结果,搜索用时 15 毫秒
91.
R. Renuka S. Rajasekaran Ganga Radhakrishnan 《Applied biochemistry and biotechnology》2001,96(1-3):83-92
Among the possible new materials for microelectronics, quinones have a number of significant advantages. Similarly, polymers
with quinone functionality possess biodegradability. Because natural polymers are promising candidates for functional materials
for the future, we have initiated studies on the polymers of natural products. In the present study, a natural quinone (a
plant substance) extracted from Embelier libes distributed in the Kerala state of India was electrochemically polymerized and its properties were investigated. The redox
activity, electrical conductivity, and biodegradability are discussed. 相似文献
92.
Jen‐Taut Yeh Chi‐Hui Tsou Wei Lu Ya‐Ming Li Han Wen Xiao Chi‐Yuan Huang Kan‐Nan Chen Chin‐San Wu Wan‐Lan Chai 《Journal of Polymer Science.Polymer Physics》2010,48(9):913-920
Fourier transform infrared and nuclear magnetic resonance results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the hydroxyl groups of FePol (FP) molecules during the melt‐blending of PLAxFPy specimens. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) experiments of PLA and PLA/FP specimens suggest that only small amounts of poor PLA and/or FP crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature, and onset re‐crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to a minimum value as the FP contents of PLAxFPy specimens reach 6 wt %. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt %, as no distinguished phase‐separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA were successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tearing properties of PLA/FP specimens are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 913–920, 2010 相似文献
93.
Wenling Zhang Jinlin He Zhuang Liu Peihong Ni Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1079-1091
A series of well‐defined amphiphilic triblock copolymers [polyethylene glycol monomethyl ether]‐block‐poly(ε‐caprolactone)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] (mPEG‐b‐PCL‐b‐PDMAEMA or abbreviated as mPEG‐b‐PCL‐b‐PDMA) were prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization. The chemical structures and compositions of these copolymers have been characterized by Fourier transform infrared spectroscopy, 1H NMR, and thermogravimetric analysis. The molecular weights of the triblock copolymers were obtained by calculating from 1H NMR spectra and gel permeation chromatography measurements. Subsequently, the self‐assembly behavior of these copolymers was investigated by fluorescence probe method and transmission electron microscopy, which indicated that these amphiphilic triblock copolymers possess distinct pH‐dependent critical aggregation concentrations and can self‐assemble into micelles or vesicles in PBS buffer solution, depending on the length of PDMA in the copolymer. Agarose gel retardation assays demonstrated that these cationic nanoparticles can effectively condense plasmid DNA. Cell toxicity tests indicated that these triblock copolymers displayed lower cytotoxicity than that of branched polyethylenimine with molecular weight of 25 kDa. In addition, in vitro release of Naproxen from these nanoparticles in pH buffer solutions was conducted, demonstrating that higher PCL content would result in the higher drug loading content and lower release rate. These biodegradable and biocompatible cationic copolymers have potential applications in drug and gene delivery. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1079–1091, 2010 相似文献
94.
Yuan You Yi Chen Chong Hua Chang‐Ming Dong 《Journal of polymer science. Part A, Polymer chemistry》2010,48(3):709-718
Dendron‐like poly(γ‐benzyl‐L ‐glutamate)/linear poly(ε‐caprolactone)/dendron‐like poly(γ‐benzyl‐L ‐glutamate) triblock copolymers having 2m + 1 PBLG branches (denoted as PBLG‐Dm‐PCL‐Dm‐PBLG, m = 0, 1, 2, and 3) were for the first time synthesized by utilizing ring‐opening polymerization (ROP) and click chemistry. The bifunctional azide‐terminated PCL (N3‐PCL‐N3) was click conjugated with propargyl focal point PAMAM‐typed dendrons Dm to generate Dm‐PCL‐Dm, which was then used as macroinitiator for the ROP of BLG‐NCA monomer to produce the targeted PBLG‐Dm‐PCL‐Dm‐PBLG triblock copolymers. Their molecular structures and physical properties were characterized in detail by FTIR, NMR, gel permeation chromatography, differential scanning calorimetry, and wide angle X‐ray diffraction (WAXD). The crystallinity of the central PCL segment within these copolymers is increasingly suppressed by the flanking PBLG wedges, whereas the PBLG segments gradually changed from a β‐sheet conformation to an α‐helix conformation with the increasing PBLG branches. These triblock copolymers formed thermoreversible organogels in toluene, and the dendritic topology of PBLG wedges controlled their critical gelation concentrations. The self‐assembled structure of organogels was further characterized by means of transmission electron microscopy, WAXD, and small‐angle X‐ray scattering. The fibers with flat ribbon morphology were clearly shown, and the gelation occurred through a self‐assembled nanoribbon mechanism. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 709–718, 2010 相似文献
95.
96.
Tzong‐Ming Wu Sung‐Fu Hsu Yeng‐Fong Shih Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2008,46(12):1207-1213
The thermal degradation behaviors of biodegradable poly(3‐hydroxybutyrate) (PHB) and PHB/poly(ethylene glycol) phosphonates (PEOPAs)‐modified layered double hydroxide (PMLDH) nanocomposites have been investigated using thermogravimetric analysis. Effects of PMLDH contents on the isothermal degradation kinetics of PHB were explored. These experimental results show that the degradation kinetics of PHB/PMLDH nanocomposites is the chain‐scission process of cyclic β‐elimination reaction with the following autocatalytic reactions, which is very similar to that of pure PHB matrix. Further calculated data based on the autocatalytic model can fit very well with the experimental data. The Ea value of PHB/PMLDH nanocomposites is increased as the content of PMLDH increases. This can be attributed to the incorporation of more PMLDH loading to PHB induced a decrease in the degradation rate and an increase in the residual weight for PHB/PMLDH nanocomposites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1207–1213, 2008 相似文献
97.
Kyung‐Moo Shin Tungalag Dong Kouji Yazawa Seung‐Soon Im Yoshio Inoue 《Journal of Polymer Science.Polymer Physics》2008,46(9):879-891
The inclusion complexes (ICs) of unmodified natural and methylated α‐cyclodextrins (CDs) with biodegradable polymers, polyethylene glycol and poly(ε‐caprolactone), were prepared by two methods, that is, the one using water and the other using chloroform as the solvent for the respective CDs. The ICs obtained were characterized by IR, WAXD, DSC, and 13C CP/MAS NMR. It was found that the possibility and the phenomena of IC formation could be varied with the degree of methyl substitution of CD as well as the type of solvents used. Methylated α‐CDs showed the prominent characteristics of IC formation with polymers in the case where chloroform was used than in the case where water was used as the solvent for CDs, while vice versa in the case of native α‐CD. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 879–891, 2008 相似文献
98.
Hans R. Kricheldorf Heiko Hachmann‐Thiessen 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3268-3277
ε‐Caprolactone and glycolide were copolymerized in bulk either with tin(II) 2‐ethylhexanoate (SnOct2) or with bismuth(III) n‐hexanoate (BiHex3) as initiators and with tetra(ethylene glycol) as a coinitiator. The temperature was varied from 100 to 160 °C. The sequences were characterized with 1H and 13C NMR spectroscopy. Surprisingly, it was found that higher temperatures favored the formation of alternating sequences. Furthermore, the content of alternating dyads was significantly higher when BiHex3 was used instead of SnOct2. An increase in reaction time caused partial randomization of the sequences regardless of the initiator. Size exclusion chromatography measurements in chloroform yielded number‐average molecular weights in agreement with the feed ratios. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3268–3277, 2005 相似文献
99.
Shimon Ben‐Shabat Elias Abuganima Aliza Raziel Abraham J. Domb 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3781-3787
Biodegradable polymers based on a blend of polycaprolactone (PCL) and aliphatic polyanhydrides with various monomer lengths were prepared to obtain desired polymer blends for use as drug carriers. The physicochemical, mechanical, and drug‐release properties of these blends were investigated by various techniques to evaluate the uniformity degree of the polymer blends to establish their potential applications in drug delivery. The results demonstrated that the heat of fusion (ΔH) of the polyanhydride or the blend is increased in relation to the length of the aliphatic chain. However, the blends had different properties than pure polyanhydride, and the crystallization degree of the blends, as expressed by the ΔH, decreased in relation to the ΔH of the pure polyanhydride. Drug‐release studies from blends of PCL and aliphatic polyanhydrides demonstrated first‐order kinetics of the release rate. Polymer degradation was independent at the polyanhydride monomer length. On the basis of theoretical calculation of the interaction factor, a blend of PCL and poly(dodecanedeoic anhydride) was chosen for further elucidation of its thermal, mechanical, and degradation properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3781–3787, 2003 相似文献
100.
Acid‐Labile Thermoresponsive Copolymers That Combine Fast pH‐Triggered Hydrolysis and High Stability under Neutral Conditions 下载免费PDF全文
Dr. Qilu Zhang Zhanyao Hou Benoit Louage Dr. Dingying Zhou Nane Vanparijs Prof. Dr. Bruno G. De Geest Prof. Dr. Richard Hoogenboom 《Angewandte Chemie (International ed. in English)》2015,54(37):10879-10883
Biodegradable polymeric materials are intensively used in biomedical applications. Of particular interest for drug‐delivery applications are polymers that are stable at pH 7.4, that is, in the blood stream, but rapidly hydrolyze under acidic conditions, such as those encountered in the endo/lysosome or the tumor microenvironment. However, an increase in the acidic‐degradation rate of acid‐labile groups goes hand in hand with higher instability of the polymer at pH 7.4 or during storage, thus posing an intrinsic limitation on fast degradation under acidic conditions. Herein, we report that a combination of acid‐labile dimethyldioxolane side chains and hydroxyethyl side chains leads to acid‐degradable thermoresponsive polymers that are quickly hydrolyzed under slightly acidic conditions but stable at pH 7.4 or during storage. We ascribe these properties to high hydration of the hydroxy‐containing collapsed polymer globules in conjunction with autocatalytic acceleration of the hydrolysis reactions by the hydroxy groups. 相似文献