全文获取类型
收费全文 | 3147篇 |
免费 | 307篇 |
国内免费 | 222篇 |
专业分类
化学 | 1572篇 |
晶体学 | 59篇 |
力学 | 81篇 |
综合类 | 26篇 |
数学 | 333篇 |
物理学 | 908篇 |
无线电 | 697篇 |
出版年
2024年 | 17篇 |
2023年 | 71篇 |
2022年 | 90篇 |
2021年 | 102篇 |
2020年 | 89篇 |
2019年 | 87篇 |
2018年 | 88篇 |
2017年 | 95篇 |
2016年 | 123篇 |
2015年 | 108篇 |
2014年 | 130篇 |
2013年 | 164篇 |
2012年 | 202篇 |
2011年 | 197篇 |
2010年 | 155篇 |
2009年 | 168篇 |
2008年 | 169篇 |
2007年 | 158篇 |
2006年 | 116篇 |
2005年 | 112篇 |
2004年 | 83篇 |
2003年 | 88篇 |
2002年 | 86篇 |
2001年 | 55篇 |
2000年 | 40篇 |
1999年 | 42篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 35篇 |
1995年 | 42篇 |
1994年 | 29篇 |
1993年 | 35篇 |
1992年 | 43篇 |
1991年 | 30篇 |
1990年 | 36篇 |
1989年 | 40篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 26篇 |
1985年 | 31篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 17篇 |
1980年 | 15篇 |
1979年 | 19篇 |
1976年 | 17篇 |
1975年 | 13篇 |
1974年 | 18篇 |
1973年 | 26篇 |
1972年 | 14篇 |
排序方式: 共有3676条查询结果,搜索用时 15 毫秒
101.
102.
Physically cross‐linked networks of POSS‐capped poly(acrylate amide)s: Synthesis,morphologies, and shape memory behavior 下载免费PDF全文
In this work, we synthesized a novel organic–inorganic semitelechelic polymer from polyhedral oligomeric silsesquioxane (POSS) and poly(acrylate amide) (PAA) via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The organic–inorganic semitelechelic polymers have been characterized by means of nuclear magnetic resonance spectroscopy, thermal gravimetric analysis, and dynamic mechanical thermal analysis. It was found that capping POSS groups to the single ends of PAA chains caused a series of significant changes in the morphologies and thermomechanical properties of the polymer. The organic–inorganic semitelechelics were microphase‐separated; the POSS microdomains were formed via the POSS–POSS interactions. In a selective solvent (e.g., methanol), the organic–inorganic semitelechelics can be self‐assembled into the micelle‐like nanoobjects. Compared to plain PAA, the POSS‐capped PAAs significantly displayed improved surface hydrophobicity as evidenced by the measurements of static contact angles and surface atomic force microscopy. More importantly, the organic–inorganic semitelechelics displayed typical shape memory properties, which was in marked contrast to plain PAA. The shape memory behavior is attributable to the formation of the physically cross‐linked networks from the combination of the POSS–POSS interactions with the intermolecular hydrogen‐bonding interactions in the organic–inorganic semitelechelics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 587–600 相似文献
103.
104.
105.
为获得10 km/s左右的超高速发射能力,以内爆发射器为研究对象,利用AUTODYN 2D软件对口径为8 mm的内爆发射器进行有限元仿真分析,获得了典型状态下的弹丸发射速度。研制了口径为8 mm的内爆发射器,并在压缩管中填充5 MPa氦气进行实验,分别获得了0.55 g铝合金弹丸7.95 km/s和0.37 g镁合金弹丸10.28 km/s的发射速度,与有限元仿真计算结果的速度偏差分别为15.3%和3.7%。结果表明,设计的内爆发射器具备10 km/s发射能力,满足空间碎片撞击和防护研究的超高速发射需求。 相似文献
106.
107.
108.
A new AB type of monomer 4′-fluoro-3,5-dimethyl-3′-trifluoromethyl-biphenyl-4-ol has been synthesized that leads to a new poly(arylene ether) by self polycondensation reaction. The monomer and the polymer have been well characterized by elemental analyses, FT-IR and NMR spectroscopy. Both FT-IR and NMR spectra of the polymers did not show any terminal phenoxy group indicating high conversion. The polymer showed glass transition at 278°C and very good thermal stability in synthetic air. GPC results indicate high molar mass development; Mw = 53200 and MWD = 2.29. 相似文献
109.
Kinshuk Dasgupta D. Sen T. Mazumdar R. K. Lenka R. Tewari S. Mazumder J. B. Joshi S. Banerjee 《Journal of nanoparticle research》2012,14(3):728
For the first time, bamboo-shaped multiwalled carbon nanotubes, having diameter of the order of 50 nm, have been grown on
carbon black in a fluidized bed in bulk amount. The activation energy for the synthesis of the product was found out to be
around 33 kJ/mol in the temperature range of 700−900 °C. The carbon nanotubes were separated from the carbon black by preferential
oxidation of the later, the temperature of which was determined by thermogravimetry. The transmission electron microscopy
revealed different features of the nanotubes such as “Y” junction, bend, and catalyst filling inside the nanotubes. Small
angle neutron scattering was performed on the nanotubes synthesized at different temperatures. The data were fitted into a
suitable model in order to find out the average diameter, which decreases with increase in synthesis temperature. The Monte
Carlo simulation predicts the same behavior. Based on the above observations, a possible growth mechanism has been predicted.
The oscillation in carbon saturation value inside the catalyst in the fluidized bed has been indicated as the responsible
factor for the bamboo-shaped structure. 相似文献
110.
Tikhonov I. V. Pliss E. M. Borodin L. I. Sen’ V. D. 《Russian Chemical Bulletin》2016,65(12):2985-2987
Russian Chemical Bulletin - The kinetics of oxidation of methyl linoleate in micelles inhibited by stable nitroxyl radicals in the presence of superoxide dismutase was studied. In the presence of... 相似文献