全文获取类型
收费全文 | 16259篇 |
免费 | 2777篇 |
国内免费 | 1664篇 |
专业分类
化学 | 11900篇 |
晶体学 | 237篇 |
力学 | 824篇 |
综合类 | 138篇 |
数学 | 1688篇 |
物理学 | 5913篇 |
出版年
2024年 | 41篇 |
2023年 | 385篇 |
2022年 | 543篇 |
2021年 | 614篇 |
2020年 | 769篇 |
2019年 | 710篇 |
2018年 | 575篇 |
2017年 | 532篇 |
2016年 | 831篇 |
2015年 | 764篇 |
2014年 | 883篇 |
2013年 | 1246篇 |
2012年 | 1509篇 |
2011年 | 1533篇 |
2010年 | 1005篇 |
2009年 | 964篇 |
2008年 | 1029篇 |
2007年 | 960篇 |
2006年 | 809篇 |
2005年 | 753篇 |
2004年 | 547篇 |
2003年 | 408篇 |
2002年 | 404篇 |
2001年 | 343篇 |
2000年 | 292篇 |
1999年 | 290篇 |
1998年 | 249篇 |
1997年 | 197篇 |
1996年 | 197篇 |
1995年 | 211篇 |
1994年 | 183篇 |
1993年 | 134篇 |
1992年 | 114篇 |
1991年 | 116篇 |
1990年 | 108篇 |
1989年 | 60篇 |
1988年 | 66篇 |
1987年 | 53篇 |
1986年 | 48篇 |
1985年 | 44篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 11篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
43.
44.
45.
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
46.
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
47.
The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004 相似文献
48.
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
49.
Su Nee Tan Daniel Fornasiero Rossen Sedev John Ralston 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):307-315
The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol−1). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability. 相似文献
50.
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