全文获取类型
收费全文 | 499篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 199篇 |
晶体学 | 2篇 |
力学 | 49篇 |
数学 | 111篇 |
物理学 | 147篇 |
出版年
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2016年 | 14篇 |
2015年 | 5篇 |
2014年 | 13篇 |
2013年 | 19篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 15篇 |
2008年 | 24篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1967年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有508条查询结果,搜索用时 0 毫秒
61.
62.
William M. Litchman Ulrich Hollstein E. Paul Papadopoulos 《Magnetic resonance in chemistry : MRC》1978,11(3):137-142
Carbon-13 NMR data for 15 substituted 1,2,4-triazol-3-ones are presented and discussed with regard to enolization in the neutral molecules. The coupling constant and chemical shift data show that the proton at N-2 is not exchanging rapidly in the DMSO-d6 solvent. Using D2O? OD? as a solvent, it is found that the C-3 and C-5 resonances are shifted downfield by nearly the same amount, suggesting that the proton at N-4 is being removed. Enolization in the neutral molecules does not occur to any significant extent. 相似文献
63.
64.
65.
66.
67.
X. Chen L. Canova A. Malvache A. Jullien R. Lopez-Martens C. Durfee D. Papadopoulos F. Druon 《Applied physics. B, Lasers and optics》2010,99(1-2):149-157
We report the routine generation of sub-5-fs laser pulses with 1-mJ energy and stable carrier–envelope phase at 1-kHz repetition rate, obtained by compressing the multi-mJ output from a phase-locked Ti:sapphire amplifier in a rare-gas-filled hollow fiber. The dual-stage amplifier features a hybrid transmission grating/chirped mirror compressor providing 2.2-mJ, 26-fs pulses at 1 kHz with standard phase deviation of 190 mrad rms. We demonstrate hour-long phase stability without feedback control of grating position or rigorous control of the laser environment, simply by using small pulse stretching factors in the amplifier, which minimize the beam pathway in the compressor. The amplifier also integrates a versatile AOPDF (acousto-optic programmable dispersive filter) for closed-loop spectral phase optimization. The various factors influencing the overall phase stability of the system are discussed in detail. Using the optimized output, 1-mJ, 4.5-fs pulses are generated by seeding the neon gas filled hollow fiber with a circularly polarized input beam. A standard phase deviation of 230 mrad after the HCF is obtained by direct f-to-2f detection and slow-loop feedback to the oscillator locking electronics without any additional spectral broadening. 相似文献
68.
69.
The development of new models that would enhance predictability for time series with dynamic time-varying, nonlinear features is a major challenge for speculators. Boundedly rational investors called “chartists” use advanced heuristics and rules-of-thumb to make profit by trading, or even hedge against potential market risks. This paper introduces a hybrid neurofuzzy system for decision-making and trading under uncertainty. The efficiency of a technical trading strategy based on the neurofuzzy model is investigated, in order to predict the direction of the market for 10 of the most prominent stock indices of U.S.A, Europe and Southeast Asia. It is demonstrated via an extensive empirical analysis that the neurofuzzy model allows technical analysts to earn significantly higher returns by providing valid information for a potential turning point on the next trading day. The total profit of the proposed neurofuzzy model, including transaction costs, is consistently superior to a recurrent neural network and a Buy & Hold strategy for all indices, particularly for the highly speculative, emerging Southeast Asian markets. Optimal prediction is based on the dynamic update and adaptive calibration of the heuristic fuzzy learning rules, which reflect the psychological and behavioral patterns of the traders. 相似文献
70.
In this paper two 10th graders having an accumulated experience on problem-solving ancillary to the concept of area confronted the task to find Pick's formula for a lattice polygon's area. The formula was omitted from the theorem in order for the students to read the theorem as a problem to be solved. Their working is examined and emphasis is given to highlighting the students’ range of systematic approaches to experimentation in the context of problem solving and aspects of control that are reflected in these approaches. 相似文献