全文获取类型
收费全文 | 7377篇 |
免费 | 972篇 |
国内免费 | 550篇 |
专业分类
化学 | 2636篇 |
晶体学 | 24篇 |
力学 | 2439篇 |
综合类 | 168篇 |
数学 | 1721篇 |
物理学 | 1911篇 |
出版年
2024年 | 25篇 |
2023年 | 79篇 |
2022年 | 227篇 |
2021年 | 215篇 |
2020年 | 293篇 |
2019年 | 214篇 |
2018年 | 228篇 |
2017年 | 278篇 |
2016年 | 321篇 |
2015年 | 274篇 |
2014年 | 289篇 |
2013年 | 591篇 |
2012年 | 382篇 |
2011年 | 368篇 |
2010年 | 311篇 |
2009年 | 305篇 |
2008年 | 332篇 |
2007年 | 351篇 |
2006年 | 401篇 |
2005年 | 350篇 |
2004年 | 334篇 |
2003年 | 331篇 |
2002年 | 245篇 |
2001年 | 242篇 |
2000年 | 252篇 |
1999年 | 229篇 |
1998年 | 184篇 |
1997年 | 166篇 |
1996年 | 167篇 |
1995年 | 143篇 |
1994年 | 121篇 |
1993年 | 107篇 |
1992年 | 95篇 |
1991年 | 67篇 |
1990年 | 66篇 |
1989年 | 39篇 |
1988年 | 56篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 10篇 |
1982年 | 28篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1957年 | 13篇 |
排序方式: 共有8899条查询结果,搜索用时 15 毫秒
991.
992.
The influence of the pH of precipitation and the ionic medium nature on the composition, surface charge, and kinetic sorption characteristics of aluminum oxyhydroxides formed by alkaline hydrolysis of an aqueous solution of aluminum nitrate was studied. The methods of drop titration with alkali, argentometric titration, point of zero charge, and indicator reactions of heterogeneous hydrolysis were used. The composition of the freshly precipitated hydrogels of aluminum(iii) oxyhydroxide, rate constants of heterogeneous hydrolysis of the IrCl6
2– ions as indicator reactions, and the pH of the point of zero charge were determined. The rate of indicator reactions (as for other oxyhydroxide hydrogels) depends strongly on the pH of precipitation. However, it is lower than the rates characteristics of iron(iii) and chromium(iii) oxyhydroxides obtained under similar conditions. The pH of the point of zero charge for the alumogels in a chloride medium is 8.3 and that in a sulfate medium is 9.5. 相似文献
993.
苯乙烯-马来酸酐共聚物单分子膜的静、动态性质 总被引:3,自引:0,他引:3
对不同分子量的苯乙烯-马来酸酐共聚物(PSM)单分子膜的π-A等温线、微 分曲线进行了研究,讨论了PSM单分子膜成膜过程及分子量对膜相变的影响,并用 动态膜障振动法测定了PSM单分子膜的动态弹性,结果表明,分子链的相互作用( 如卷曲和缠结)在膜的形成中起着重要的作用,并影响膜的静、动态性质,单分子 膜的动态弹性曲线有双峰,且前者比后者小,随分子量增大,膜的凝聚性、刚性和 稳定性都增强,动态弹性都增大;且分子链的相互作用对PSM单分子性质影响增大 ,压缩过程中单分子膜的相变更明显。 相似文献
994.
采用半经典动力学方法模拟了5-甲基胞嘧啶(5m-Cyt)和胞嘧啶(Cyt)在267 nm紫外光辐射下的光物理失活过程. 模拟发现, 5m-Cyt 和Cyt 的激发态通过C5-C6键的扭曲以及甲基(或H5)和H6原子平面外振动失活.失活时, 甲基(或H5)和H6原子几乎与环面垂直并指向不同方向, 形成“双自由基态”. 由于甲基的体积比H原子的大, 振动频率较小, 使得C5原子的变形受到抑制, 导致5m-Cyt 的激发态寿命比胞嘧啶更长. 完全活性空间自洽场(CASSCF)计算显示, 5m-Cyt的圆锥交叉(CI)点能量比Cyt 高0.3 eV, 这也证明5m-Cyt演化至CI 需要克服更大的能垒, 因此激发态寿命长于胞嘧啶. 相似文献
995.
The relaxation behavior of four amorphous poly(aryl ether ketone)s was investigated using dielectric relaxation spectroscopy and dynamic mechanical analysis. The temperature dependence of the relaxation times of the glass transition process and the cooperative nature of this process were unaffected by changes in polymer structure. The temperature location of the loss peaks for all polymers progressed smoothly between the low frequency of the mechanical measurements and the higher frequencies of the dielectric probe. Differences were observed in mechanical activation energy and dielectric relaxation strength for one polymer which contained a significant concentration of meta linkages, compared with the para-linked polymers, while relaxation broadness was generally greater in the dynamic mechanical mode. Changes in chemical structure had little effect on the shape, intensity, and location of the β-relaxation peak, the main observation being that the Arrhenius activation energy measured by dynamic mechanical analysis was significantly higher than that calculated from the dielectric data. The dielectric β-relaxation was sensitive to absorbed moisture. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 851–859, 1998 相似文献
996.
Hidenori Okuzaki Takayoshi Kuwabara Toshio Kunugi 《Journal of Polymer Science.Polymer Physics》1998,36(12):2237-2246
Polypyrrole films containing perchlorate were electrochemically synthesized and the bending and recovery motion of the films obtained has been investigated. It was found that the thickness of the film and ambient relative humidity (RH) were crucial to the motion of film: An increase of the film thickness decreased the displacement of the bending but increased the bending stress. On the other hand, an increase of the ambient RH decreased both functions. The motion of film was caused by the difference of expansion on both sides of the film owing to anisotropic sorption of water vapor, which could be expressed by the diffusion-limited bending model. The diffusion coefficients calculated from the bending and recovery motion at 25°C, RH 50% were 12.2 × 10−8 cm2 s−1 and 3.5 × 10−8 cm2 s−1, respectively. The maximum expansion of the film surface calculated from the bending curve was about 0.36%. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2237–2246, 1998 相似文献
997.
The metal-organic frameworks (three-dimensional porous coordination polymers) [Zn4O(Me4BPDC)3] × 9 DMF, 2 · 9 DMF and [Cu2(Me4BPDC)2] × 9 DMF, 3 · 9 DMF are representatives of the classical Zn-IRMOF series and Cu paddle-wheel complexes with H2Me4BPDC = 2,2′,6,6′-tetramethyl-4,4′-biphenyldicarboxylic acid, 1. The dicarboxylate linker of 1 is a representative of the non-planar biphenyl ligand family, known as an efficient scaffold for chiral molecules. There is a 90° twist angle between the phenyl rings in 1, dictated by the methyl groups, which leads to assembly of doubly interpenetrated pcu-a (in 2) and nbo-a (in 3) nets under low temperature solvothermal conditions in dimethylformamide (DMF). Activation by degassing (to yield 2), exchange with methanol or tetrahydrofuran and subsequent evacuation at elevated temperatures (to yield 3I) gave materials with BET surface areas of 1735 m2/g (2) and 1041 m2/g (3I). Adsorbed quantities of H2 were 1.26 wt% (2) and 1.02 wt% (3I) (77 K, 1 bar), CO2 30.8 cm3/g (2) and 50 cm3/g (3I) (273 K, 1 bar) and CH4 12.9 cm3/g (2) and 11.4 cm3/g (3I) (273 K, 1 bar). The H2 and CO2 sorption values for 2 are similar to those of MOF-5 (IRMOF-1) with its almost doubled BET surface area. An increase is found concerning the adsorbed amounts of N2, H2, and CO2 for 3I compared to related doubly interpenetrated nbo-a-type MOF-601, MOF-602, MOF-603 ([Cu2L2] with L = 2,2′-R2-4,4′-biphenyldicarboxylate, R = CN, Me, I, respectively). 相似文献
998.
The sol‐gel reaction of tetraethoxysilane in natural rubber (NR) latex was conducted to produce in situ silica‐filled NR latex, followed by adding sulfur cross‐linking reagents to the latex in a liquid state. The latex was cast and subjected to sulfur curing to result in a unique morphology in the NR composite of a flexible film form. The contents of in situ silica filling were controlled up to 35 parts per one hundred rubber by weight. The silica was locally dispersed around rubber particles to give a filler network. This characteristic morphology brought about the composite of good dynamic mechanical properties. Synchrotron X‐ray absorption near‐edge structure spectroscopy suggested that the sulfidic linkages of the sulfur cross‐linked composites were polysulfidic, Sx (x ≥ 2), and a fraction of shorter polysulfidic linkages became larger with the increase of in situ silica. The present observations will be of use for developing a novel in situ silica‐filled NR composite prepared in NR latex via liquid‐phase soft processing. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
999.
Elena Akhmatskaya José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2012,50(7):1383-1393
Modification of the polymer–polymer interfacial tension is a way to tailor‐make particle morphology of waterborne polymer–polymer hybrids. This allows achieving a broader spectrum of application properties and maximizing the synergy of the positive properties of both polymers, avoiding their drawbacks. In situ formation of graft copolymer during polymerization is an efficient way to modify the polymer–polymer interfacial tension. Currently, no dynamic model is available for polymer–polymer hybrids in which a graft copolymer is generated during polymerization. In this article, a novel model based on stochastic dynamics is developed for predicting the dynamics of the development of particle morphology for composite waterborne systems in which a graft copolymer is produced in situ during the process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
1000.
Various antimonate compounds are well known as important inorganic ion exchangers, since they resist radiation and chemical degradation and also exhibit selectivities towards different cations. Ceric, silicon, titanium and ferric antimonates were prepared as inorganic ion exchangers. Characterization of these materials has been described using different techniques, including thermal analysis, surface area measurements, X-ray diffraction and IR-spectroscopy. In batch distribution experiments the influence of HNO3 molarity and Mo concentration for Mo sorption on different matrices is described in terms of their retention capacities and distribution coefficients.The selectivities of these exchangers towards molybdenum are in the order: CeSb > SiSb > FeSb > TiSb. 相似文献