全文获取类型
收费全文 | 1284篇 |
免费 | 36篇 |
国内免费 | 254篇 |
专业分类
化学 | 1314篇 |
晶体学 | 10篇 |
力学 | 33篇 |
综合类 | 4篇 |
数学 | 16篇 |
物理学 | 197篇 |
出版年
2024年 | 2篇 |
2023年 | 44篇 |
2022年 | 41篇 |
2021年 | 36篇 |
2020年 | 48篇 |
2019年 | 32篇 |
2018年 | 19篇 |
2017年 | 51篇 |
2016年 | 42篇 |
2015年 | 31篇 |
2014年 | 44篇 |
2013年 | 107篇 |
2012年 | 53篇 |
2011年 | 78篇 |
2010年 | 59篇 |
2009年 | 74篇 |
2008年 | 87篇 |
2007年 | 93篇 |
2006年 | 95篇 |
2005年 | 62篇 |
2004年 | 66篇 |
2003年 | 45篇 |
2002年 | 38篇 |
2001年 | 34篇 |
2000年 | 38篇 |
1999年 | 40篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有1574条查询结果,搜索用时 11 毫秒
811.
Ghanshyam?S.?ChauhanEmail author Lalit?Guleria Rajeev?Sharma 《Cellulose (London, England)》2005,12(1):97-110
To develop low-cost and environmentally friendly polymeric materials for enrichment, separation and remediation of metal ions from water, novel reactive graft copolymers based on cellulose extracted from pine needles were synthesized by grafting of poly(glycidyl methacrylate) alone and with comonomers acrylic acid, acrylamide and acrylonitrile by benzoyl peroxide initiation. Structural aspects of graft copolymers have been characterized by elemental analysis, FTIR, and solvent uptake behaviour. An attempt has been made to study sorption of Fe2+, Cu2+ and Cr6+ ions on candidate graft copolymers by an equilibration method and to investigate the structural aspects of graft copolymers and establish a relationship between the structural aspects of graft copolymers and metal ion uptake efficiency and selectivity. 相似文献
812.
We have synthesized the composition x = 0.01 of the (Sr1-xLax)2(Ta1-xTix)2O7 solid solution, mixing the ferroelectric perovskite phases Sr2Ta2O7 and La2Ti2O7. Related oxide and oxynitride materials have been produced as thin films by magnetron radio frequency sputtering. Reactive sputter deposition was conducted at 750 °C under a 75 vol.% (Ar) + 25 vol.% (N2,O2) mixture. An oxygen-free plasma leads to the deposition of an oxynitride film (Sr0.99La0.01) (Ta0.99Ti0.01)O2N, characterized by a band gap Eg = 2.30 eV and a preferential (001) epitaxial growth on (001) SrTiO3 substrate. Its dielectric constant and loss tangent are respectively Epsilon' = 60 (at 1 kHz) and tanDelta = 62.5 × 10−3. In oxygen-rich conditions (vol.%N2 ≤ 15%), (110) epitaxial (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 oxides films are deposited, associated to a larger band gap value (Eg = 4.55 eV). The oxide films permittivity varies from 45 to 25 (at 1 kHz) in correlation with the decrease in crystalline orientation; measured losses are lower than 5.10−3. For 20 ≤ vol.% N2 ≤ 24.55, the films are poorly crystallized, leading to very low permittivities (minimum Epsilon' = 3). A correlation between the dielectric losses and the presence of an oxynitride phase in the samples is highlighted. 相似文献
813.
Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C2H2 precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C2H2 concentration during deposition. A higher C2H2 flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H3/E2. The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp3 bond content shows the highest elastic recovery during scratching. 相似文献
814.
Qiang Shi Lian-chao Zhu Chuan-lun Cai Jing-hua Yin State Key Laboratory of Polymer Physics Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China 《高分子科学》2005,(6):603-610
The kinetics of melt grafting acrylic acid(AA)onto linear low density polyethylene(LLDPE)by using reactive extrusion was investigated.The polymeric peroxides(POOP and POOH)generated by electron beam irradiation were used to initiate the graft reaction.The samples taken out from the barrel at five ports along screw axis were analyzed by FTIR.The spectra show that both the graft copolymerization and homopolymerization proceed in two stages:the graft degree(or mass of homopolymer)increases linearly with the reaction time in the initial stage,and then gradually in the second stage.The rate of graft copolymerization R_g is always faster than that of homopolymerization R_h in the present system and the activation energy is 131 kJ·mol~(-1) for graft copolymerization and 127 kJ·mol~(-1) for homopolymeirzation.These results were interpreted in terms of solubility and diffusion of monomer,as well as the reactivity and the concentration of reactive species. The relationships between reaction rate and monomer concentration and peroxide concentration were found to he:R_g ∝ [M]~(1.46)[POOP+POOH]~(0.53) and R_h ∝[M]~(1.08)[POOH]~(0.51),which indicate that the addition of monomer to polymeric radicals is a slow step for the graft copolymerization. 相似文献
815.
816.
A new approach to improve the performance of composite propellants was developed in which reactive nanocomposites (RNCs) are used as replacements for aluminum powders in composite solid rocket propellants. The new materials are mechanically activated nanothermites comprising of nano‐powders of aluminum as the fuel as well as oxides of copper, iron, molybdenum, or nickel as the oxidizer. The obtained RNCs were characterized using X‐ray diffraction, scanning electron microscopy, and laser diffraction particle size analyzer. The obtained RNCs were used for preparation of modified composite solid rocket propellants (CSRPs). Burning rate, thermal decomposition behavior, heat of combustion, sensitivity, and mechanical properties of CSRPs were determined. The results showed increases in the combustion energy and the burning rate of the modified propellants were achieved, and that RNCs can be considered to be promising multi‐function additives for composite solid rocket propellants. In addition, the mechanical properties and sensitivities of the modified propellants are within the desired range. 相似文献
817.
3, 4-乙烯二氧噻吩单体用作锂离子电池安全性改善添加剂的研究 总被引:1,自引:0,他引:1
安全性是制约锂离子电池向电动汽车领域应用拓展的主要障碍. 本工作提出了一种能够有效改善锂离子电池安全性的电解液添加剂-3,4-乙烯二氧噻吩单体(EDOT),研究了其在有机电解液中的电氧化聚合行为,以及对LiCoO2电极高温热行为和电池安全性、电化学性能的影响. 循环伏安(CV)和透射电镜(TEM)表征结果表明,单体添加剂能够在电池充电过程发生电氧化聚合,在正极表面形成一层聚(3,4-乙烯二氧噻吩)(PEDOT)导电聚合物膜;差示扫描量热(DSC)分析结果显示,PEDOT隔离了电解液与正极表面的直接接触,减少了过热条件下电解液在正极表面的分解放热. 安全性测试结果表明,在电解液中仅添加0.1%的EDOT单体,即可将电池在150 oC高温热冲击下发生热失控的时间推迟13.8分钟. 电化学性能测试结果表明,聚合产物良好的电子导电性能有效改善正极的电子传导能力,在一定程度上提高电池的倍率性能和循环稳定性,而容量、低温性能等基本不受影响,展示出良好的应用前景. 相似文献
818.
离子型表面活性单体存在下的MMA/BA乳液聚合(Ⅰ)——表面活性单体的合成及其(共)聚合活性 总被引:6,自引:0,他引:6
合成了两种离子型表面活性单体(Surfmer)磺化-十二醇-烯丙基甘油-丁二酸酯钠盐(ZC-L)和磺化-十二醇-甲基丙烯酰甘油-丁二酸酯钠盐(ZD-L).着重研究了ZC-L的结构、表面张力行为、均聚及共聚能力.实验结果表明,不同Surfmer用量以及不同固含量下,MMA/BA/Surfmer,MMA/Surfmer及BA/Surfmer共聚乳液的表面张力较高,说明Surfmer已通过共聚结合在乳胶粒上,乳液中残留甚少.对MMA/BA体系,ZC-L的共聚性能比ZD-L好. 相似文献
819.
聚丙烯共混物一步法反应共混增容的研究 总被引:3,自引:0,他引:3
研究了影响聚丙烯/(丙烯腈 苯乙烯)共聚物(PP/AS)合金反应挤出生成的各项因素,发现在过氧化二异丙苯(DCP)存在的条件下进行反应共混可以发生接枝反应,生成PP与AS的相互接枝物.接枝物的生成显著地细化了分散相粒子,改善了合金相形态.为抑制反应共混过程中聚丙烯的降解,同时促进接枝反应,在PP/AS/DCP反应共混中加入了含适量双键组分的添加剂亚油酸三甘酯(GTL).结果发现,较少量GTL的加入就显著抑制了聚丙烯的降解,且进一步改善了合金的相形态.在合适的GTL与DCP用量下,反应共混不但显著改善了PP/AS合金的相形态,而且提高了合金的力学性能,初步确立了聚丙烯共混物一步反应共混挤出增溶的方法. 相似文献
820.
Masatoshi Miyamoto Shin-Ya Kanetaka 《Journal of polymer science. Part A, Polymer chemistry》1999,37(19):3671-3679
A novel ionic polymerization of methyl methacrylate (MMA) with a series of enamines (1) in the presence of methylaluminum bis(2,6-di-tert-butylphenoxide) (2) was examined. Both nucleophile (1) and electrophile (2) are indispensable for the present polymerization, in which (1) acts as initiator and (2) as activator. MMA polymerization proceeded smoothly in toluene at or below room temperature (r.t.) in the presence of 1 and 2 (1 ∼ 4 mol %, respectively), went to completion within 1 h, and afforded syndiotactic-rich PMMA with molecular weight distribution (Mw/Mn) in the 1.1 ∼ 1.4 range. The number-average molecular weight (Mn) of the polymer was significantly higher than that calculated from the feed ratio of 1 to the monomer, indicating low initiating efficiency. Kinetic studies coupled with isolation of an intermediate species proved that the real monomeric species involved in both initiation and propagation was a complex of MMA with 2. The effects of the concentrations of 1, 2, and MMA as well as the temperature of polymerization were also examined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3671–3679, 1999 相似文献