全文获取类型
收费全文 | 44229篇 |
免费 | 8722篇 |
国内免费 | 15010篇 |
专业分类
化学 | 31799篇 |
晶体学 | 1794篇 |
力学 | 3337篇 |
综合类 | 1639篇 |
数学 | 7291篇 |
物理学 | 22101篇 |
出版年
2024年 | 109篇 |
2023年 | 525篇 |
2022年 | 1709篇 |
2021年 | 1651篇 |
2020年 | 1657篇 |
2019年 | 1682篇 |
2018年 | 1552篇 |
2017年 | 2146篇 |
2016年 | 1693篇 |
2015年 | 2404篇 |
2014年 | 2791篇 |
2013年 | 3742篇 |
2012年 | 3658篇 |
2011年 | 3979篇 |
2010年 | 3908篇 |
2009年 | 3923篇 |
2008年 | 4327篇 |
2007年 | 3799篇 |
2006年 | 3762篇 |
2005年 | 3158篇 |
2004年 | 2540篇 |
2003年 | 1741篇 |
2002年 | 1846篇 |
2001年 | 1820篇 |
2000年 | 1978篇 |
1999年 | 1138篇 |
1998年 | 597篇 |
1997年 | 465篇 |
1996年 | 440篇 |
1995年 | 373篇 |
1994年 | 369篇 |
1993年 | 348篇 |
1992年 | 291篇 |
1991年 | 258篇 |
1990年 | 231篇 |
1989年 | 208篇 |
1988年 | 204篇 |
1987年 | 180篇 |
1986年 | 130篇 |
1985年 | 92篇 |
1984年 | 99篇 |
1983年 | 88篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 45篇 |
1979年 | 44篇 |
1978年 | 20篇 |
1971年 | 11篇 |
1965年 | 25篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
制作了掺杂rubrene和4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9,enyl)-4H-pyran(DCJTB)两种荧光染料的红光有机电致发光器件。N,N’-diphenyl-N,N’-bis(1-naphthyl)-(1,1’-biphenyl)-4,4’-diamine(NPB)和掺杂的Tri-(8-hydroxyquinoline)aluminum(Alq3)分别作为空穴和电子传输层。我们发现掺rubrene和DCJTB的器件性能与只掺DCJTB的器件性能相比有所提高。器件性能的改善是因为掺入的rubrene能够促进从Alq3到DCJTB的能量转移。根据荧光衰减曲线,计算出从Alq3到DCJTB、从Alq3到rubrene以及从rubrene到DCJTB的能量转移速率分别为1.04×109,3.89×109,2.79×109s-1。可以看出能量通过rubrene从Alq3到DCJTB的转移速率是能量直接从Alq3到DCJTB的2.7倍。 相似文献
102.
Taking advantage of our knowledge of the capacity of DIBAL-H to de-O-alkylate, we propose an alternative mechanism for a spiroketal rearrangement described by E. Suàrez. We also show that this proposal can account for the formation of the secondary product, whose original structure we propose to correct. 相似文献
103.
104.
X. H. Li Y. Z. Meng S. J. Wang A. Varada Rajulu S. C. Tjong 《Journal of Polymer Science.Polymer Physics》2004,42(4):666-675
The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004 相似文献
105.
A new method for the synthesis of exfoliated graphite and polyaniline (PANI)/graphite nanocomposites was developed. Exfoliated graphite nanosheets were prepared through the microwave irradiation and sonication of synthesized expandable graphite. The nanocomposites were fabricated via the in situ polymerization of the monomer at the presence of graphite nanosheets. The as-synthesized graphite nanosheets and PANI/graphite nanocomposite materials were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis (TGA). The conductivity of the PANI/graphite nanocomposites was dramatically increased over that of pure PANI. TGA indicated that the incorporation of graphite greatly improved the thermal stability of PANI. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1972–1978, 2004 相似文献
106.
Aging of concrete buildings and determining the pH value on the surface of concrete by using a handy semi-conductive pH meter. 总被引:1,自引:0,他引:1
A new method was devised for measuring the pH of a concrete surface by pHBOY-P2 with a piece of filter paper by extracting the pH value from concrete. This is a simple and inexpensive method that does not damage the concrete building, and is easy to apply on concrete samples for monitoring. By using the method mentioned above, a drastic decrease of the pH value of concrete bridges and buildings has investigated. The method is environmentally friendly to detect the pH value change of concrete as an environmental sample investigation. 相似文献
107.
108.
阐述了阶跃型塑料光纤和渐变型塑料光纤的发展过程及其国内外研究现状,介绍了塑料光纤在局域网、汽车工业、传感器等领域的应用.通过对石英光纤、金属电缆与塑料光纤的性能进行比较,得到了塑料光纤具有芯径大、柔韧性好、价格低廉、制作简单等特点.就塑料光纤在局域网、汽车工业、传感器等领域的应用进行了分析、总结,结果表明降低塑料光纤的传输损耗可以进一步扩大其应用领域.最后分析了我国塑料光纤的研究、生产现状与国际水平的差距,并提出了提高国产塑料光纤技术水平的建议. 相似文献
109.
110.