全文获取类型
收费全文 | 200篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 122篇 |
力学 | 7篇 |
数学 | 54篇 |
物理学 | 32篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 16篇 |
2012年 | 14篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有215条查询结果,搜索用时 78 毫秒
41.
Shu-Chia Shiu 《Applied Surface Science》2009,255(20):8566-8570
Si nanowires (NWs) are promising materials for future electronic, photovoltaic, and sensor applications. So far the Si NWs are mainly formed on particular substrates or at high temperatures, greatly limiting their application flexibility. Here we report a low temperature process for forming and massively transferring vertically aligned Si NWs on alien substrates with a large density of about (3-5) × 107 NWs/mm2. The X-ray diffraction spectrum reveals that the transferred NWs exhibit almost the same crystal property as the bulk Si. Our investigation further shows that the transferred NWs have exceptional optical characteristics. The transferred Si NWs of 12.14 μm exhibit the transmittance as low as 0.3% in the near infrared region and 0.07% in the visible region. The extracted absorption coefficient of Si NWs in the near infrared region is about 3 × 103 cm−1, over 30 times larger than that of the bulk Si. Because of the low temperature process, it enables a large variety of alien substrates such as glass and plastics to be used. In addition, the exceptional properties of the transferred NWs offer potential applications for photovoltaic, photo-detectors, sensors, and flexible electronics. 相似文献
42.
The dependence of the rate of the reaction CO+OH-->H+CO2 on the CO-vibrational excitation is treated here theoretically. Both the Rice-Ramsperger-Kassel-Marcus (RRKM) rate constant kRRKM and a nonstatistical modification knon [W.-C. Chen and R. A. Marcus, J. Chem. Phys. 123, 094307 (2005).] are used in the analysis. The experimentally measured rate constant shows an apparent (large error bars) decrease with increasing CO-vibrational temperature Tv over the range of Tv's studied, 298-1800 K. Both kRRKM(Tv) and knon(Tv) show the same trend over the Tv-range studied, but the knon(Tv) vs Tv plot shows a larger effect. The various trends can be understood in simple terms. The calculated rate constant kv decreases with increasing CO vibrational quantum number v, on going from v=0 to v=1, by factors of 1.5 and 3 in the RRKM and nonstatistical calculations, respectively. It then increases when v is increased further. These results can be regarded as a prediction when v state-selected rate constants become available. 相似文献
43.
Xiao-Hua Ding Xiang Li Dan Liu Wei-Chen Cui Xuan Ju Shaozhong Wang Zhu-Jun Yao 《Tetrahedron》2012,68(31):6240-6248
A target-oriented highly enantioselective multifunctional organocatalytic approach has been developed to construct the bicycle-[3.3.1]nona-2,6-dien-9-one core of (?)-huperzine A for the first time, with up to 95% ee in the gram-scale procedure. The newly established methodology is also eligible to synthesize a variety of bicyclo[3.3.1]nona-2,6-dien-9-ones in high enantiopurities, and thus is useful for the future development of novel huperzine A analogs with medicinal interests. 相似文献
44.
Wai Chee SHIU 《数学学报(英文版)》2006,22(6):1621-1628
The notion of super-edge-graceful graphs was introduced by Mitchem and Simoson in 1994.However, few examples except trees are known. In this paper, we exhibit two classes of infinitely many cubic graphs which are super-edge-graceful. A conjecture is proposed. 相似文献
45.
Given a prime p and distinct non-zero integers a1, a2,..., ak (mod p), we investigate the number N = N(a1, a2,..., ak; p) of residues n (mod p) for which (na1)p < (na2)p < ... < (nak)p, where (b)p is the least non-negative residue of b (mod p). We give complete solutions to the problem when k = 2,3,4, and establish some general results corresponding to k≥5.
The first author is a Presidential Faculty Fellow. He is also supported, in part, by the National Science Foundation.
2000 Mathematics Subject Classification Primary—11A07; Secondary—11F20 相似文献
46.
Let (n) be the error term associated with the asymptotic formulafor the counting function on the set of numbers that are sumsof three squares. By considering (n) as a correlated digitalsum and applying the method of H. Delange on ordinary digitalsums we give very precise information on the average value of(n) in terms of a periodic continuous nowhere differentiablefunction having an absolutely convergent Fourier series withcoefficients expressed in terms of the Hurwitz zeta function. 相似文献
47.
48.
Ender Ercan Yan-Cheng Lin Chun-Kai Chen Yi-Kai Fang Wei-Chen Yang Yun-Fang Yang Wen-Chang Chen 《Journal of polymer science. Part A, Polymer chemistry》2022,60(3):525-537
Photonic field-effect transistor (FET) memory devices offer unique advantages owing to their solution processability, low cost production, and their lightweight and structural flexibility. Despite the plethora of research demonstrated the photon based programming process, limited reports are available for photoinduced recovery mechanism in such devices. To investigate the influence of polymer electret design on photonic memory performance, poly(9,9-dioctylfluorene) (PFO)–block–poly (vinylphenyl oxadiazole) (POXD) conjugated block copolymers were employed to a photonic FET memory with n-type semiconducting channel. The studied device exhibited bistable ON/OFF current states after electrical programming and photoinduced recovery (erasing) processes. The device operating mechanism was elaborated by comparing the device performance with respective electrets of PFO-b-POXD and PFO-b-polystyrene (PS) and PFO homopolymer. We found that PFO-b-POXD can efficiently generate photoexciton under UV illumination to neutralize the trapped hole, and assuage the hole trapping propensity of PFO segment, simultaneously. By optimizing the POXD content in the block copolymer, a decent memory ratio (ION/IOFF) of ~105 was achieved after 104 s, indicating its superior long-term stability and data discernibility. This research shows the judicious strategy to design polymer electret for photonic memory, and it opens up the possibility of developing photonic memory, human perception and futuristic communication systems using simple, convenient and reliable optoelectronic technique. 相似文献
49.
50.
A graph G is dot-critical if contracting any edge decreases the domination number. Nader Jafari Rad (2009) [3] posed the problem: Is it true that a connected k-dot-critical graph G with G′=0? is 2-connected? In this note, we give a family of 1-connected 2k-dot-critical graph with G′=0? and show that this problem has a negative answer. 相似文献