全文获取类型
收费全文 | 1191篇 |
免费 | 61篇 |
国内免费 | 6篇 |
专业分类
化学 | 973篇 |
晶体学 | 9篇 |
力学 | 14篇 |
数学 | 135篇 |
物理学 | 127篇 |
出版年
2023年 | 12篇 |
2022年 | 37篇 |
2021年 | 47篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 29篇 |
2017年 | 11篇 |
2016年 | 46篇 |
2015年 | 50篇 |
2014年 | 43篇 |
2013年 | 81篇 |
2012年 | 90篇 |
2011年 | 119篇 |
2010年 | 55篇 |
2009年 | 63篇 |
2008年 | 99篇 |
2007年 | 72篇 |
2006年 | 54篇 |
2005年 | 77篇 |
2004年 | 54篇 |
2003年 | 30篇 |
2002年 | 33篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有1258条查询结果,搜索用时 316 毫秒
991.
992.
Starch nanocrystals obtained from acid hydrolysis of waxy maize starch granules consist in crystalline nanoplatelets about 6–8 nm thick with a length of 20–40 nm and a width of 15–30 nm. New nanocomposite materials, i.e. natural rubber (NR) filled with waxy maize starch nanocrystals were processed by casting. Dynamic mechanical analysis has shown that starch nanocrystals were a good reinforcing agent for NR at temperatures higher than the glass transition temperature of NR. Tensile tests have shown that until a weight fraction of 20 wt%, this new filler presented the advantage to reinforce natural rubber without decreasing significantly the strain at break of the material. These properties may be due to both the morphological nature of starch nanocrystals, and the formation of a percolating starch nanocrystals network within the NR matrix, resulting from hydrogen bonding forces between starch aggregates. 相似文献
993.
Xiuqi Wu Ying Zhang Junsong Peng Sonia Boscolo Christophe Finot Heping Zeng 《Laser \u0026amp; Photonics Reviews》2024,18(4):2200470
Extreme wave events or rogue waves (RWs) are both statistically rare and of exceptionally large amplitude. They are observed in many complex systems ranging from oceanic and optical environments to financial models and Bose–Einstein condensates. As they appear from nowhere and disappear without a trace, their emergence is unpredictable and non-repetitive, which makes them particularly challenging to control. Here, the use of genetic algorithms (GAs), which are exclusively designed for searching and optimizing stationary or repetitive processes in nonlinear optical systems, is extended to the active control of extreme events in a fiber laser cavity. Feeding real-time spectral measurements into a GA controlling the electronics to optimize the cavity parameters, the wave events are able to be triggered in the cavity that have the typical statistics of RWs in the frequency domain. The intensity of the induced RWs can also be tailored. This accurate control enables the generation of optical RWs with a spectral peak intensity 32.8 times higher than the significant intensity threshold. A rationale is proposed and confirmed by numerical simulations of the laser model for the related frequency up- and downshifting of the optical spectrum that are experimentally observed. 相似文献
994.
We have explored the performance of a simulation model for Gaussian chains at different concentrations in a good solvent. The Gaussian statistics for the distances between contiguous beads in the model is directly implemented in the individual moves of a Monte Carlo algorithm. When the results of conformational properties for the Gaussian model are compared with those provided by a freely jointed model in the same conditions, significant differences arise at finite concentrations. The modeled Gaussian chain yields incorrect results for the quadratic average dimensions 〈R2〉 and 〈S2〉 at high concentrations, but correctly reproduces the results for the scaled end-to-end distance distribution function at any concentration, showing the effects of the screening of excluded volume when concentration increases. The reason for the wrong behavior of the simulated Gaussian model comes from a strong distortion of the “bond distance” distribution as a result of the concentration increase. We conclude that this model can only be safely applied to infinitely dilute solutions. 相似文献
995.
996.
997.
998.
Walther Caminati Laura B. Favero Paolo G. Favero Assimo Maris Sonia Melandri 《Angewandte Chemie (International ed. in English)》1998,37(6):792-795
Completely planar is the hydrogen-bonded complex of pyrazine and water (see sketch), which was obtained by supersonic expansion and investigated by rotational spectroscopy. The water molecule lies in the plane of the aromatic ring, and the lone pair of electrons on the nitrogen atom functions as the acceptor in the N⋅⋅⋅H–O hydrogen bond, not—as in the corresponding benzene complex—the π electrons. 相似文献
999.
Melinda Fogarasi Maria-Ioana Socaciu Claudiu-Dan Slgean Floricua Ranga Anca Corina Frca Sonia Ancua Socaci Carmen Socaciu Dorin
ibulc Szabolcs Fogarasi Cristina Anamaria Semeniuc 《Molecules (Basel, Switzerland)》2021,26(24)
Edible mushrooms are well-known for their nutritional benefits and low energy density. In addition, mushroom extracts contain various bioactive compounds that account for their antioxidant activity; the applied extraction conditions influence the extraction efficiency of such compounds. Therefore, this study investigates the effects of four extractants on the content of polyphenols and antioxidant properties of Boletus edulis and Cantharellus cibarius mushrooms, aiming to optimize the extraction process. Powders of B. edulis and C. cibarius mushrooms were subjected to extraction with acidic water (10% CH3COOH), ethanol/water/acetic acid (15:76.5:8.5, v/v/v), hexane, and diethyl ether to measure their total phenolic content (TPC), total flavonoid content (TFC), and Trolox equivalent antioxidant capacity (TEAC). Furthermore, the level of individual polyphenolic compounds in these extracts was quantified using an HPLC-DAD-ESI-MS method. Results showed that the type of solvent significantly influenced the TPC and TEAC of mushroom powder but insignificantly influenced the TFC. A very strong positive correlation was found between TPC and TEAC, but no correlation was found between TFC and TEAC or TPC and TFC. Acidic water extracted the highest amount of polyphenolic compounds from these mushroom powders. Therefore, the aqueous extract showed the highest TPC and strongest antioxidant activity. Thus, acidic water is recommended for polyphenol analysis in B. edulis and C. cibarius mushrooms. 相似文献
1000.