全文获取类型
收费全文 | 2248篇 |
免费 | 263篇 |
国内免费 | 110篇 |
专业分类
化学 | 188篇 |
晶体学 | 11篇 |
力学 | 1232篇 |
综合类 | 5篇 |
数学 | 153篇 |
物理学 | 1032篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 26篇 |
2021年 | 41篇 |
2020年 | 32篇 |
2019年 | 51篇 |
2018年 | 57篇 |
2017年 | 74篇 |
2016年 | 84篇 |
2015年 | 65篇 |
2014年 | 92篇 |
2013年 | 244篇 |
2012年 | 89篇 |
2011年 | 148篇 |
2010年 | 86篇 |
2009年 | 107篇 |
2008年 | 89篇 |
2007年 | 123篇 |
2006年 | 126篇 |
2005年 | 139篇 |
2004年 | 104篇 |
2003年 | 71篇 |
2002年 | 87篇 |
2001年 | 68篇 |
2000年 | 78篇 |
1999年 | 58篇 |
1998年 | 56篇 |
1997年 | 68篇 |
1996年 | 64篇 |
1995年 | 33篇 |
1994年 | 37篇 |
1993年 | 44篇 |
1992年 | 22篇 |
1991年 | 36篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1957年 | 5篇 |
排序方式: 共有2621条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
955.
956.
957.
The conformational preferences of the ester group have the potential to facilitate the large amplitude folding of long alkyl chains in the gas phase. They are monitored by Raman spectroscopy in supersonic jet expansions for the model system methyl butanoate, after establishing a quantitative relationship with quantum–chemical predictions for methyl methanoate. This requires a careful analysis of experimental details, and a simulation of the rovibrational contours for near-symmetric top molecules. The technique is shown to be complementary to microwave spectroscopy in quantifying coexisting conformations. It confirms that a chain segment can be collapsed into a single all-trans conformation by collisional cooling, whereas alkyl chain isomerism beyond this five-membered chain largely survives the jet expansion. This sets the stage for the investigation of linear alkyl alkanoates in terms of dispersion-induced stretched-chain to hairpin transitions by Raman spectroscopy. 相似文献
958.
Preparation of novel Ni-Ir/r-Al2O3 catalyst via high-frequency cold plasma direct reduction process 下载免费PDF全文
The novel Ni-Ir/γ-Al2O3 catalyst was prepared by high-frequency cold plasma direct reduction method (NIA-P) under ambient conditions
without thermal treatment, and the conventional sample was prepared by impregnation, thermal calcination, and then by H2 reduction method
(NIA-CR). The effects of reduction methods on catalysts for ammonia decomposition were studied, and the catalysts were characterized by
XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over
which ammonia conversion was 68.9%, at T = 450 ℃, P = 1 atm, and GHSV = 30, 000 h−1. It was 31.7% higher than that of the conventional
NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active
components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted
in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst. 相似文献
959.
Simone Diverio 《Mathematische Annalen》2009,344(2):293-315
Let be a smooth complex projective hypersurface. In this paper we show that, if the degree of X is large enough, then there exist global sections of the bundle of invariant jet differentials of order n on X, vanishing on an ample divisor. We also prove a logarithmic version, effective in low dimension, for the log-pair , where D is a smooth irreducible divisor of high degree. Moreover, these result are sharp, i.e. one cannot have such jet differentials
of order less than n. 相似文献
960.
LIF diagnostics of hydroxyl radical in a methanol containing atmospheric-pressure plasma jet 下载免费PDF全文
In this paper, a pulsed-dc CH_3OH/Ar plasma jet generated at atmospheric pressure is studied by laser-induced fluorescence(LIF) and optical emission spectroscopy(OES). A gas–liquid bubbler system is proposed to introduce the methanol vapor into the argon gas, and the CH3OH/Ar volume ratio is kept constant at about 0.1%. Discharge occurs in a 6-mm needle-to-ring gap in an atmospheric-pressure CH_3OH/Ar mixture. The space-resolved distributions of OH LIF inside and outside the nozzle exhibit distinctly different behaviors. And, different production mechanisms of OH radicals in the needle-to-ring discharge gap and afterglow of plasma jet are discussed. Besides, the optical emission lines of carbonaceous species, such as CH, CN, and C_2 radicals, are identified in the CH_3OH/Ar plasma jet. Finally, the influences of operating parameters(applied voltage magnitude, pulse frequency, pulsewidth) on the OH radical density are also presented and analyzed. 相似文献