全文获取类型
收费全文 | 862篇 |
免费 | 40篇 |
国内免费 | 80篇 |
专业分类
化学 | 917篇 |
力学 | 4篇 |
综合类 | 3篇 |
数学 | 2篇 |
物理学 | 56篇 |
出版年
2023年 | 3篇 |
2022年 | 22篇 |
2021年 | 14篇 |
2020年 | 27篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 27篇 |
2015年 | 27篇 |
2014年 | 28篇 |
2013年 | 54篇 |
2012年 | 41篇 |
2011年 | 48篇 |
2010年 | 57篇 |
2009年 | 62篇 |
2008年 | 56篇 |
2007年 | 45篇 |
2006年 | 53篇 |
2005年 | 39篇 |
2004年 | 51篇 |
2003年 | 50篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 18篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有982条查询结果,搜索用时 15 毫秒
31.
Antifouling coatings are the most reliable way to prevent biofouling of immersed surfaces. As concerning the high toxicity of organotin paints, the tendency is the development of coatings, which do not present environmental risks. In this work, we prepare binders from modification of acrylic copolymers containing free carboxylic acid groups. Biocides chosen are tertiary ammonium salts; alkyl chain substituents with different length are considered. The chemical modifications of resins are carried out via a single step reaction. Modification extents are monitored through proton nuclear magnetic resonance and thermogravimetric analysis and the modified resins are characterised by Fourier transform infrared spectroscopy. The glass transition temperature of the acrylate systems is assessed by dynamical mechanical analysis (pin point method) and compared with data obtained by differential scanning calorimetry. The erosion and antifouling properties of the binders are followed during an exposure to marine environment by a visual observation. 相似文献
32.
I.?S.?TerekhovaEmail author a?A.?Yu.?Manakov V.?V.?Feklistov Yu.?A.?Dyadin V.?YU.?Komarov D.?Yu.?Naumov 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(3-4):207-211
X-ray powder diffraction studies were performed of the polyhydrates, formed at positive temperature in swelled grains of carboxylic cation-exchange resins in the form of tetraisoamylammonium (cross-linked tetraisoamylammonium polyacrylates, differing in the degree of cross-linking: 1, 2 and 3%). It was shown that the polyhydrates exist as the crystalline phase under specific conditions, determined earlier by DTA technique. Diffraction patterns of the samples, recorded at the temperature +3 ± 1 °C, indicate that the polyhydrates crystallize in hexagonal symmetry, the unit cell parameters are close to a=12.25 Å, c=12.72 Å and do not depend significantly upon the degree of cross-linking. The suppositions were made concerning the size of hydrate crystallites, formed in the swelled grains of the studied resins.This revised version was published online in July 2005 with a corrected issue number. 相似文献
33.
34.
M. L. Scheepers P. J. Adriaensens J. M. Gelan R. A. Carleer D. J. Vanderzande N. K. De Vries P. M. Brandts 《Journal of polymer science. Part A, Polymer chemistry》1995,33(6):915-920
1H and 13C NMR have been used for the quantitative determination of methylene-ether bridges in melamine-formaldehyde (MF) resins. The amount of methylene-ether bridges was determined by 13C NMR from the number of monomethylolated amino groups consumed in the condensation reactions and is in agreement with that calculated from the condensation water contents. This latter method, which involves a combination of 1H and 13C NMR, is based on the amount of condensation water released during the formation of both methylene and methylene-ether bridges. © 1995 John Wiley & Sons, Inc. 相似文献
35.
36.
Low concentrations of Pt and Pd in industrial (µgg–1 level) and environmental samples (ngg–1 level) together with the complexity of the matrix causing many interferences during the determination of noble metals often require elaboration and application of pre-concentration/matrix separation procedures before detection of the analyte. Different pre-concentration/matrix separation procedures applied prior to the determination of Pt and Pd by atomic spectrometric techniques are reviewed and critically compared taking into account potential interferences. The methods studied are divided into 5 groups including precipitation and coprecipitation, liquid–liquid extraction, solid phase extraction, electrochemical pre-concentration and biosorption. The main analytical problems occuring during sample preparation and storage are discussed. 相似文献
37.
F. Langmaier P. Mokrejs K. Kolomazník M. Mládek R. Karnas 《Journal of Thermal Analysis and Calorimetry》2007,88(3):857-862
Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of
mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The
reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or
aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C,
at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction
enthalpy, 519.19 J g−1 (= 101.24 kJ mol−1 of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction
heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving
the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min−1) and activation energy E
a (kJ mol−1)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics
is determined by diffusion. 相似文献
38.
This work describes the influence of silica fillers on the thermomechanical properties of diglycidyl ether of bisphenol A/triethylenetetramine (DGEBA/TETA) epoxy resins during ageing under electron beam irradiation. Whatever be the silica filler (pure micrometric ground and spherical silicas, nanometric silicas and coupling agent treated silicas), the glass transition temperature of the epoxy resins decreases with increasing irradiation dose, meaning that the main effect of the irradiation is chain scission. No influence of the silica fillers has been detected from the changes in the glass transition temperature with the increase in the irradiation dose. The disappearance of the cooperativity of the γ relaxation, the decrease of the α relaxation and the decrease of the elastic modulus at the rubbery plateau observed by dynamic mechanical analyses involve a decrease in the crosslink density of the epoxy resins. The occurrence of chemical reactions between the epoxy resin and the silica surface at high irradiation doses has been shown. Moreover, we show evidence that chemical reactions between the epoxy resin and the silica surface occur at high irradiation dose. 相似文献
39.
Xiu Xia WANG Zhi Gang JIANG Yi Feng ZHANG 《中国化学快报》2006,17(1):125-128
Epoxy resins are widely used in coatings, adhesives and polymer composites, but the applications of cured epoxy resins are often restricted by their poor toughness. HBP can be used as toughener to improve the toughness of epoxy resins due to its high-dens… 相似文献
40.
Biodegradable polyurethane elastomers with potential for applications in medical implants with tunable degradation rate and physical properties were synthesized from reaction of epoxy terminated polyurethanes (EUP) with 1,6-hexamethylene diamine (HMDA) as curing agent. Poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) as well as 1,6-hexamethylene diisocyanate (HDI) were used for preparation of isocyanate terminated polyurethanes which were subsequently blocked with glycidol to prepare EUPs. All materials were characterized by conventional methods, and their properties were studied fully. Results showed that elastomers based on PEG exhibit superior degradation rate and inferior mechanical properties in comparison to elastomers based on PCL. Optimum degradation rate and mechanical properties were obtained from elastomers made from mixture of PCL and PEG base EUPs. 相似文献