全文获取类型
收费全文 | 539篇 |
免费 | 4篇 |
专业分类
化学 | 323篇 |
晶体学 | 4篇 |
力学 | 18篇 |
综合类 | 1篇 |
数学 | 77篇 |
物理学 | 120篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 21篇 |
2012年 | 16篇 |
2011年 | 21篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 25篇 |
2007年 | 26篇 |
2006年 | 24篇 |
2005年 | 29篇 |
2004年 | 18篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 16篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1967年 | 6篇 |
1964年 | 4篇 |
1962年 | 4篇 |
1955年 | 4篇 |
1936年 | 6篇 |
排序方式: 共有543条查询结果,搜索用时 31 毫秒
51.
High-efficiency parametric oscillation and spectral control in the red spectral region with periodically poled KTiOPO(4) 总被引:1,自引:0,他引:1
Pasiskevicius V Karlsson H Laurell F Butkus R Smilgevicius V Piskarskas A 《Optics letters》2001,26(10):710-712
Narrow-linewidth optical pulses at wavelengths near 630 nm with 2.2-mJ energy were generated with 61% efficiency in a periodically poled KTiOPO(4) parametric oscillator pumped by a frequency-doubled Q -switched Nd:YAG laser. The tuning range was extended to 30 nm by a noncollinear elliptical pumping geometry. We demonstrate that by angular dispersion a noncollinear optical parametric oscillator can be used to control the spectral and spatial characteristics of the output signal beam. 相似文献
52.
Fornberg Bengt; Flyer Natasha; Hovde Susan; Piret Cecile 《IMA Journal of Numerical Analysis》2008,28(1):121-142
53.
54.
Summary Some aspects on the situation of analytical chemistry as science are presented. Two examples can illustrate the influence of other sciences on the progress of analytical chemistry. 相似文献
55.
56.
57.
58.
59.
60.
Abdullah S. AlRamadan Moez Ben Houidi Julien Sotton Marc Bellenoue Bengt Johansson S. Mani Sarathy 《Proceedings of the Combustion Institute》2021,38(4):5539-5548
One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture. 相似文献