全文获取类型
收费全文 | 1298篇 |
免费 | 45篇 |
国内免费 | 168篇 |
专业分类
化学 | 1237篇 |
晶体学 | 12篇 |
力学 | 6篇 |
综合类 | 3篇 |
物理学 | 23篇 |
综合类 | 230篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 16篇 |
2020年 | 24篇 |
2019年 | 33篇 |
2018年 | 24篇 |
2017年 | 33篇 |
2016年 | 23篇 |
2015年 | 28篇 |
2014年 | 56篇 |
2013年 | 97篇 |
2012年 | 61篇 |
2011年 | 68篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 68篇 |
2007年 | 62篇 |
2006年 | 79篇 |
2005年 | 75篇 |
2004年 | 96篇 |
2003年 | 64篇 |
2002年 | 61篇 |
2001年 | 65篇 |
2000年 | 57篇 |
1999年 | 47篇 |
1998年 | 37篇 |
1997年 | 37篇 |
1996年 | 34篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1511条查询结果,搜索用时 15 毫秒
31.
Novel meander with Co3+ und Au3+: Na4[AuCoO5] = Na8 1∞ [(O2/2 (CoO)O2AuO2/2)2] By “reaction with the wall” we obtained for the first time transparent brown single crystals of Na4[AuCoO5] while heating intimate mixtures of Co3O4, Na2O2, and K2O2 (Co: Na: K = 1.00:4.91:2.20; 650°C/44d) in a sealed gold-tube: monoclinic, P21/m, with a = 555.69(4) pm, b = 1042.11 (8) pm, c = 555.69(4) pm, β = 117.387(5)°, Z = 2. Characteristic features of Na4[AuCoO5] are meandric chains [(O2/2 (CoO)O2AuO2/2)2]. The structure has been determined by four-circle diffractometer data (Siemens AED 2; Mo? Kα , graphite, 881 I0(hkl), R = 0.0366, Rw = 0.0316), parameters as given in the text. The Madelung Part of Lattice Energy, MAPLE, Effective Coordination Numbers, these via Mean Fictive Ionic Radii, and Charge-distribution, CHARDI, are calculated and discussed. 相似文献
32.
33.
研究了腰果酚在无光引发剂条件下的紫外光固化反应,并用IR、UV、元素分析、GPC等分析手段分析了腰果酚的紫外光固化机理及其固化膜性能。结果表明:在紫外光辐照下,腰果酚通过侧链发生氧化聚合反应,和酚羟基的邻对位失去质子形成的自由基引起的苯环缩合反应,最终形成体型高聚物。腰果酚的紫外光固化膜的常规物理机械性能、抗溶剂性、耐化学介质腐蚀性、热稳定性和抗紫外线性能均优于腰果酚醛缩聚物(PC)涂膜。 相似文献
34.
Eri Yoshida Kazuaki Nakamura Toshikazu Takata Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》1993,31(6):1505-1512
Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as 1H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF6) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc. 相似文献
35.
Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2139-2155
The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006 相似文献
36.
A series of monodispersed polydimenthylsiloxanes (PDMS) with molecular weights from 3K to 156K were synthesized. The intrinsic viscosity and absolute molecular weight of each monodispersed PDMS was measured and the Mark-Houwink equation for the PDMS series in toluene at 25°C was derived: [eta;]=2.88 × 10?4 M0.613. It was proven that the accurate molecular weight determination of polysiloxanes is not possible using polystyrene (PS) standards. It can be achieved either by using a gel permeation chromatographic method with PDMS standards or by a calculation from the Mark-Houwink equation using experimental values of intrinsic viscosity. 相似文献
37.
偶联表面活性剂与传统表面活性剂混合溶液的双水相 总被引:2,自引:2,他引:2
研究了偶联表面活性剂(Geminis,l2—3—l2,2Br)和传统表面活性剂(SDS)混合体系双水相的性质。结果表明:该系统在很低的总浓度下(0.03mol/L)能够形成双水相。双水相约区域非常狭窄,且分相溶液中正负离子表面活性剂的比值随着表面活性剂总浓度的变化而线性改变。双水相的表观现象也因表面活性剂总浓度的不同而异。采用冷冻蚀刻技术、负染色技术及透射电子显微镜观察得到的结果表明,双水相中两相的微观结构明显不同,胶团和囊泡可以共存。偏光显微照片显示该系统有独特的液晶结构。 相似文献
38.
对2,3-二氰基-2,3-二苯基丁二酸二乙酯碳-碳键均裂引发苯乙烯的悬浮聚合反应进行了研究.结果表明,羟乙基纤维素是比较好的悬浮剂,有利于聚合体的形成,虽然悬浮聚合反应因分散体系各种因素的影响比较复杂,但反应条件对聚合体分子量的影响与本体聚合机理基本一致 相似文献
39.
BaY2F8晶体生长基元与结晶机理的探讨 总被引:1,自引:0,他引:1
本文通过对BaY2F8晶体结构的分析,从晶体的生长基元为负离子配位多面体理论出发,对自然冷却条件下BaY2F8晶体自发结晶习性进行了研究,提出了以Ba2+为中心的近八配位十二面体和以Y3+为中心的近八配位十二面体是晶体生长的基元.并根据自发结晶的BaY2F8的XRD,说明了BaY2F8晶体的{200}、{130}、{021}、{330}、{-111}、{111}、{221}、{002}等面族比较发育的原因.本文证实了仲维卓的负离子配位多面体理论对BaY2F8晶体生长的适用性,并对探索新的BaY2F8单晶生长方法有参考作用. 相似文献
40.
Lei Ren Feng Xu Wei Jian Xu 《Journal of polymer science. Part A, Polymer chemistry》2016,54(15):2291-2301
The anionic polymerization of (E)‐1,3‐pentadiene (EP) and (Z)‐1,3‐pentadiene (ZP) together with mixture of the E/Z isomers are investigated, respectively. The kinetic analysis shows that the activation energy for EP (86.17 kJ/mol) is much higher than that for ZP (59.03 kJ/mol). GPC shows that it is the EP rather than the ZP isomer that undergoes anionic living polymerization affording quantitative products of the polymers with well‐controlled molecular weights and narrow molecular weight distributions (1.05 ≤? ≤ 1.09). In addition, THF as polar additive has proved its validity to reduce the molecular weight distribution of poly(ZP) from 1.38 to as low as 1.19. The microstructure and sequence distributions of polypentadiene are characterized by 1H NMR and quantitative 13C NMR. Finally, the distinctive reaction activity of two isomers can be elucidated by two different mechanisms which involve the presence of four forms of zwitterions for EP and the typical [1,5]‐sigmatropic hydrogen‐shift phenomenon for ZP. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2291–2301 相似文献