全文获取类型
收费全文 | 25712篇 |
免费 | 4117篇 |
国内免费 | 2434篇 |
专业分类
化学 | 17996篇 |
晶体学 | 311篇 |
力学 | 1540篇 |
综合类 | 109篇 |
数学 | 2940篇 |
物理学 | 9367篇 |
出版年
2024年 | 70篇 |
2023年 | 525篇 |
2022年 | 954篇 |
2021年 | 938篇 |
2020年 | 1013篇 |
2019年 | 994篇 |
2018年 | 830篇 |
2017年 | 732篇 |
2016年 | 1208篇 |
2015年 | 1155篇 |
2014年 | 1350篇 |
2013年 | 1791篇 |
2012年 | 2408篇 |
2011年 | 2415篇 |
2010年 | 1582篇 |
2009年 | 1503篇 |
2008年 | 1651篇 |
2007年 | 1507篇 |
2006年 | 1358篇 |
2005年 | 1153篇 |
2004年 | 843篇 |
2003年 | 643篇 |
2002年 | 609篇 |
2001年 | 447篇 |
2000年 | 440篇 |
1999年 | 521篇 |
1998年 | 426篇 |
1997年 | 440篇 |
1996年 | 460篇 |
1995年 | 368篇 |
1994年 | 310篇 |
1993年 | 245篇 |
1992年 | 245篇 |
1991年 | 203篇 |
1990年 | 174篇 |
1989年 | 149篇 |
1988年 | 98篇 |
1987年 | 111篇 |
1986年 | 94篇 |
1985年 | 82篇 |
1984年 | 47篇 |
1983年 | 47篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
771.
In this work, a series of novel shape memory liquid crystalline (LC) epoxides with lateral substituent were prepared and characterized. Dynamic mechanical analysis (DMA) and shape memory testing were used to investigate on the thermo-mechanical properties and shape memory effects of prepared samples. The results showed that the modulus in the rubbery region (ER ) decreased as the length of lateral alkyl group increases. And more than 95% of the deformation can be fixed as the sample was cooled down below the glass transition temperature (Tg), which was determined by differential scanning calorimetry (DSC) measurement, and can be recovered completely as heating. Effects of the curing agent and substituent on the shape memory behavior were also studied. We found that LC epoxides cured by aromatic diamine have a higher recovery speed. The recovering speeds of the shape memory decreased as the length of lateral alkyl group inscreased. The local ordered structures and the lateral substituent played an important role in shape memory effects. 相似文献
772.
773.
774.
In this paper, the Taguchi method combined with fuzzy approach was applied to find the extended optimization for a multi-objective design of a miniature 2.5× zoom fold optics with liquid elements. Relative illuminance (RI) and modulation transfer function (MTF) were considered to be optimized. The experiments were simulated and the results were evaluated by the optical software tool CODE V. It was concluded that the method used in this research was successful in optimizing the values. In our proposed method, the appropriate weight of MTF and RI for the inputs of fuzzy controllers increased the MTF by 9.92%, but the RI only reduced by 0.19% in systematic wide-angle end, respectively. 相似文献
775.
776.
777.
Lingjie Sun Dr. Weigang Zhu Wei Wang Dr. Fangxu Yang Congcong Zhang Prof. Shufeng Wang Dr. Xiaotao Zhang Prof. Rongjin Li Prof. Huanli Dong Prof. Wenping Hu 《Angewandte Chemie (International ed. in English)》2017,56(27):7831-7835
Cocrystals of 4-styrylpyridine and 1,2,4,5-tetracyanobenzene were successfully prepared by supramolecular self-assembly. Donor–acceptor interactions between the molecular components are the main driving force for self-assembly and contribute to intermolecular charge transfer. The cocrystals possess two-photon absorption properties that are not observed in the individual components; suggesting that two-photon absorption originates from intermolecular charge-transfer interactions in the donor–acceptor system. The origin of two-photon absorption in multichromophore systems remains under-researched; thus, the system offers a rare demonstration of two-photon absorption by cocrystallization. Cocrystal engineering may facilitate further design and development of novel materials for nonlinear optical and optoelectronic applications. 相似文献
778.
We observed a novel voltage peak in the proximity-induced superconducting gold (Au) nanowire while cooling the sample through the superconducting transition temperature. The voltage peak turned dip during warming. The voltage peak or dip was found to originate respectively from the emergence or vanishing of the proximity-induced superconductivity in the Au nanowire. The amplitude of the voltage signal depends on the temperature scanning rate, and it cannot be detected when the temperature is changed slower than 0.03 K/min. This transient feature suggests the non-equilibrium property of the effect. Ginzburg-Landau model clarified the voltage peak by considering the emergence of Cooper pairs of relatively lower free energy in superconducting W contact and the non-equilibrium diffusion of Cooper pairs and quasiparticles. 相似文献
779.
Journal of Radioanalytical and Nuclear Chemistry - As a result of nuclear power plant accidents such as Chernobyl and Fukushima, and even their maintenance, the soil is contaminated due to the... 相似文献
780.
A novel Pt/C‐catalyzed transfer hydrogenation reaction of p‐benzoquinone to produce p‐hydroquinone using cyclohexanone as an unexpectedly effective hydrogen source 下载免费PDF全文
A new method for the production of p‐hydroquinone via a Pt/C‐catalyzed reduction of p‐benzoquinone is developed. Different from the conventional transfer hydrogenation reactions that usually use secondary alcohols such as isopropanol as the hydrogen source, in this work, it is unexpectedly found that cyclohexanone is a more effective hydrogen source than secondary alcohols, even cyclohexanol. This reaction affords acceptable yields of p‐hydroquinone with very high turnover number (1109) of the Pt/C catalyst. A mechanism of this interesting reaction is proposed on the basis of the results of a series of control experiments, GC–MS analysis as well as dynamic studies. 相似文献