全文获取类型
收费全文 | 1440篇 |
免费 | 101篇 |
国内免费 | 252篇 |
专业分类
化学 | 1388篇 |
晶体学 | 11篇 |
力学 | 167篇 |
综合类 | 13篇 |
数学 | 13篇 |
物理学 | 201篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 38篇 |
2021年 | 65篇 |
2020年 | 60篇 |
2019年 | 62篇 |
2018年 | 62篇 |
2017年 | 55篇 |
2016年 | 90篇 |
2015年 | 58篇 |
2014年 | 78篇 |
2013年 | 160篇 |
2012年 | 70篇 |
2011年 | 79篇 |
2010年 | 56篇 |
2009年 | 64篇 |
2008年 | 78篇 |
2007年 | 70篇 |
2006年 | 58篇 |
2005年 | 69篇 |
2004年 | 71篇 |
2003年 | 58篇 |
2002年 | 50篇 |
2001年 | 49篇 |
2000年 | 43篇 |
1999年 | 29篇 |
1998年 | 25篇 |
1997年 | 24篇 |
1996年 | 44篇 |
1995年 | 32篇 |
1994年 | 21篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 14篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有1793条查询结果,搜索用时 15 毫秒
101.
To improve the oil absorbency of caster oil‐based polyurethane foam, nano‐organic‐montmorillonite (OMMT) was used for the additives. The aim of this study is to evaluate the oil diffusion mechanism and dispersion uniformity of OMMT modified caster oil‐based polyurethane (MPU) using experiments and molecular dynamic simulation. Molecule movement and molecule trajectory of oil was investigated by molecular dynamic simulation and numerical simulation. According to the quantitative analyzing results, the diffusion model was put forward. The average diffusion coefficient of crude oil in 0, 1, 2 wt%, 4, and 6 wt% MPU is 2.4 × 10?4 cm2/s, 2.6 × 10?4 cm2/s, 3.0 × 10?4 cm2/s, 3.2 × 10?4 cm2/s, and 3.3 × 10?4 cm2/s, respectively. It indicated that crude oil appeared gradient in the MPU. The optimal diffusion direction of crude oil is (0, 0, 1) crystal face, and the small particles of crude oil are easy to be adsorbed. The two‐dimensional diffusion trajectory of crude oil is nonlinear. The diffusion model includes the diffusion of crude oil at the interface of oil and polyurethane, surface diffusion and pore diffusion, and pore adsorption. Furthermore, the diffusion model showed that the van der Waals force was the main reason for crude oil diffusion or adsorption. OMMT could improve the ability of oil/water separation of polyurethane. 相似文献
102.
Water splitting has attracted more and more attention as a promising strategy for the production of clean hydrogen fuel. In this work, a new synthesis strategy was proposed, and Co0.85Se was synthesized on nickel foam as the main matrix. The doping of appropriate Cr amount into the target of Co0.85Se and the Cr‐Co0.85Se resulted in an excellent electrochemical performance. The doping of Cr introduces Cr3+ ions which substitute Co2+ and Co3+ ions in Co0.85Se, so that the lattice parameters of the main matrix were changed. It is worth noting that the Cr0.15‐Co0.85Se/NF material exhibits an excellent performance in the oxygen evolution reaction (OER) test. When the current density reaches 50 mA cm?2 for OER, the overpotential is only 240 mV. For the hydrogen evolution reaction (HER) tests, the overpotential is only 117 mV to drive 10 mA cm?2 of current density. Moreover, when the Cr0.15‐Co0.85Se/NF material is used as a two‐electrode device for whole water splitting, the required cell voltage is only 1.43 V to reach a current density of 10 mA cm?2, which is among the lowest values of the published catalysts up to now. In addition, the Cr0.15‐Co0.85Se/NF catalyst also exhibits excellent stability during a long period of water splitting. The experimental result demonstrates that the change of the lattice structure has an obvious influence on the electrocatalytic activity of the material. When an external electric field is applied, it facilitates the rapid electron transfer rate and enhances the electrocatalytic performance and stability of the material. 相似文献
103.
The epoxy resin/polyurethane semi-IPN was prepared and the glass transition behavior of the semi-IPN was discussed with DSC and DMA methods. The results show that the two glass transition temperatures (Tg) referring to epoxy resin and polyurethane respectively get closer. Between the two Tg there exists another Tg related to the interface between the two polymers. SEM indicates that this semi-IPN has a two-phase continuous structure which changes with different weight compositions. This is also proved by testing the Young's modulus. It is found that the IPN system has a cellular structure. Comparatively, the compatibility between the two polymers is the best when the weight ratio of EP/PU is 70/30. © 1996 John Wiley & Sons, Inc. 相似文献
104.
B. Nabeth I. Corniglion J. P. Pascault 《Journal of Polymer Science.Polymer Physics》1996,34(3):401-417
Linear polyurethane, linear segmented polyurethane, polyurethane networks, and polyurethane acrylate networks of various composition were synthesized. The variation of Tg with the type of macrodiol, its length, and the chemical composition of the polymer were studied in relation with the percentage of soft segments, the molar mass between crosslinks, and the concentration of urethane bonds. In this work, the networks were considered as composed of chain segments of various composition between point-like crosslinks. The chemical heterogeneities of the networks were not taken into account. For polyurethanes, it was shown that Tg values are essentially controlled by the amount of urethane bonds. For polyurethane acrylates, the Tg values are dependent on the amount of urethane bonds but also on the presence of crosslinks whose number is varying with the excess of diisocyanate of the first step three times faster for PUA compared with PU. No clear relation was observed between Tg and the molar mass between point-like crosslinks. Another approach considering the network heterogeneities is indispensable and will be used in a following work. © 1996 John Wiley & Sons, Inc. 相似文献
105.
106.
Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented. 相似文献
107.
108.
109.
Chenxi Zhai Yang Yu Yumei Zhu Jing Zhang Ying Zhong Jingjie Yeo Mingchao Wang 《Molecules (Basel, Switzerland)》2022,27(3)
Foaming effect strongly impacts the physical and mechanical properties of foam glass materials, but an understanding of its mechanism especially at the molecular level is still limited. In this study, the foaming effects of dextrin, a mixture of dextrin and carbon, and different carbon allotropes are investigated with respect to surface morphology as well as physical and mechanical properties, in which 1 wt.% carbon black is identified as an optimal choice for a well-balanced material property. More importantly, the different foaming effects are elucidated by all-atomistic molecular dynamics simulations with molecular-level insights into the structure–property relationships. The results show that smaller pores and more uniform pore structure benefit the mechanical properties of the foam glass samples. The foam glass samples show excellent chemical and thermal stability with 1 wt.% carbon as the foaming agent. Furthermore, the foaming effects of CaSO4 and Na2HPO4 are investigated, which both create more uniform pore structures. This work may inspire more systematic approaches to control foaming effect for customized engineering needs by establishing molecular-level structure–property–process relationships, thereby, leading to efficient production of foam glass materials with desired foaming effects. 相似文献
110.