全文获取类型
收费全文 | 7288篇 |
免费 | 154篇 |
国内免费 | 152篇 |
专业分类
化学 | 3382篇 |
晶体学 | 128篇 |
力学 | 302篇 |
综合类 | 35篇 |
数学 | 1237篇 |
物理学 | 2510篇 |
出版年
2023年 | 30篇 |
2022年 | 70篇 |
2021年 | 127篇 |
2020年 | 123篇 |
2019年 | 121篇 |
2018年 | 134篇 |
2017年 | 158篇 |
2016年 | 207篇 |
2015年 | 133篇 |
2014年 | 264篇 |
2013年 | 302篇 |
2012年 | 148篇 |
2011年 | 215篇 |
2010年 | 192篇 |
2009年 | 248篇 |
2008年 | 255篇 |
2007年 | 287篇 |
2006年 | 215篇 |
2005年 | 332篇 |
2004年 | 557篇 |
2003年 | 423篇 |
2002年 | 367篇 |
2001年 | 321篇 |
2000年 | 247篇 |
1999年 | 199篇 |
1998年 | 158篇 |
1997年 | 136篇 |
1996年 | 185篇 |
1995年 | 149篇 |
1994年 | 193篇 |
1993年 | 141篇 |
1992年 | 132篇 |
1991年 | 78篇 |
1990年 | 60篇 |
1989年 | 57篇 |
1988年 | 50篇 |
1987年 | 71篇 |
1986年 | 50篇 |
1985年 | 40篇 |
1984年 | 42篇 |
1982年 | 39篇 |
1981年 | 41篇 |
1980年 | 43篇 |
1979年 | 58篇 |
1978年 | 48篇 |
1977年 | 50篇 |
1976年 | 37篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 18篇 |
排序方式: 共有7594条查询结果,搜索用时 687 毫秒
1.
为了获得纯度更高的碳纳米管膜, 保证材料发热稳定性, 需要对通过化学气相沉积法得到的碳纳米管膜进行二次纯化. 通过使用高温纯化炉, 在真空状态下, 从1700℃到3200℃分7挡温度对碳纳米管进行纯化, 并对其含碳量和方块电阻进行比较. 结果表明, 高温纯化后的碳纳米管膜含碳量从95.0%提高到99.9%, 解决了含碳量低的问题. 同时, 在高温纯化中发现碳纳米管膜方块电阻从纯化前3Ω降低到0.5Ω, 方块电阻的降低对碳纳米管膜具有十分重要的意义, 同样对碳纳米管膜后续产品的开发也有重要作用. 相似文献
2.
3.
Non-adiabatic tapered fibers are basic photonic components used in a wide range of applications. Here we investigate a way to increase their utility through the controllable bending of one of their tapered sections. The experiments carried out explain, for the first time, the mechanics of this approach showing how these tapers can be used to build more sensitive sensors. Their use as highly efficient mode converters is also discussed. 相似文献
4.
Surimi from silver carp with different salt contents (0–5%) was obtained treated by high intensity ultrasound (HIU, 100 kHz 91 W·cm−2). The gelation properties of samples were evaluated by puncture properties, microstructures, water-holding capacity, dynamic rheological properties and intermolecular interactions. As the salt content increased from 0 to 5%, gel properties of surimi without HIU significantly improved. For samples with low-salt (0–2% NaCl) content, HIU induced obvious enhancement in breaking force and deformation. HIU promoted the protein aggregation linked by SS bonds, hydrophobic interactions and non-disulfide covalent bonds in surimi gels with low-salt content. Moreover, microstructures of HIU surimi gels with low-salt content were more compact than those of the corresponding control samples. HIU also improved the gelation properties of surimi with 3% NaCl to an extent. However, for high-salt (4–5% NaCl) samples, HIU decreased the breaking force and deformation of surimi gels due to the degradation of proteins suggested by increased TCA-soluble peptides. In conclusion, HIU effectively improved the gelation properties of surimi with low-salt content (0–2% NaCl), but was harmful for high-salt (4–5% NaCl) surimi. This might provide the theoretical basis for the production of low-salt surimi gels. 相似文献
5.
The present study was designed to evaluate the contents of different antioxidants compounds and their antioxidant activities in Jalopeno peppers (Capsicum annuum) cultivars (El Dorido, Grande, Tula, Sayula and El Rey) extracts. Free radical scavenging activity of Grande was recorded as high as 87% followed by El Dorido (83%). Results of reducing power (Fe3+ to Fe2+) showed that Grande (0.85%) and El Dorido (0.81%) fruit extract absorbance value were close to synthetic antioxidant BHT (0. 97%) obtained at100 μg/mL. The results showed that total phenolic content of El Dorido and Grande were significantly higher compared to other Jalapeno pepper. Results indicated strong and positive correlation between antioxidant activity and carotenoids content (r = 0.75), vitamin C (r = 0.78) and total capsaicinoids (r = 0.84), respectively. The results of the antioxidant activity assays showed that the El Dorido and Grande had strongest antioxidant activity compared to other peppers cultivars in this study. 相似文献
6.
温度/应变/扭曲三参量同时测量低成本传感系统 总被引:9,自引:3,他引:6
提出了一种利用布喇格光纤光栅反射光作信号源、高频CO2激光脉冲写入的长周期光纤光栅和超周期光纤光栅作传感器实现温度、应变和扭曲同时测量的全光栅型低成本强度解调传感方案.文中利用长周期光纤光栅边缘滤波效应实现了温度、应变和扭曲传感信号的实时解调.实验结果表明,其温度和应变的测量灵敏度分别为-0.211 dB/℃和-0.012 dB/10με;而扭曲率的测量灵敏度为0.4394 dB/(rad·m-1),是该法写入普通LPFG的4倍以上. 相似文献
7.
8.
9.
10.
Ludmila C. Fidale Sarah Köhler Martin H.G. Prechtl Thomas Heinze Omar A. El Seoud 《Cellulose (London, England)》2006,13(5):581-592
The concentrations of water, W, and electrolytes present in solutions of LiCl in N,N-dimethylacetamide, LiCl/DMAc, and of tetrabutylammonium fluoride. x-hydrate in DMSO, TBAF.xW/DMSO can be accurately and expediently determined by three independent methods, UV–vis, FTIR and EMF measurement. The first relies on the use of solvatochromic probes whose spectra are sensitive to solution composition. It is applicable to W/LiCl/DMAc solutions but not to TBAF.xW/DMSO, because the charge-transfer complex bands of the probes are suppressed by strong interactions with the latter electrolyte. Integration of νOH band of water may be employed in order to determine [W], hence [electrolyte] by weight difference. EMF measurement uses ion-selective electrodes in order to determine [electrolyte], hence [W] by weight difference. Results of the latter method were in excellent agreement with those of FTIR. The reason for the failure of Karl Fischer titration is addressed, and the relevance of the results obtained to functionalization of cellulose under homogenous solution conditions is briefly commented on. 相似文献