全文获取类型
收费全文 | 269篇 |
免费 | 15篇 |
国内免费 | 16篇 |
专业分类
化学 | 144篇 |
力学 | 11篇 |
数学 | 27篇 |
物理学 | 118篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 2篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有300条查询结果,搜索用时 0 毫秒
41.
X-ray photoelectron spectroscopy has shown how both chemisorbed oxygen present at a Cu(III) surface and nitric oxide introduced into the gas phase can induce hydroxylation of the surface from an adlayer of molecularly adsorbed water at 80 K. The interaction of water vapour with a clean Cu(III) surface is also reported. 相似文献
42.
C.K. Au 《Physics letters. [Part B]》1976,61(3):300-302
We include the effect of the Δ-isobar resonance in the equation of state for neutron star matter in the presence of a pion condensate. We find matter undergoing a first order phase transition after a seconf order phase transition at a much lower density. 相似文献
43.
It is shown that power exchange is possible in photorefractive materials even though the grating produced by the two incident waves is in phase with their interference pattern. The reason is that the interaction of the principal waves will produced higher order waves and their presence will form further gratings which assist power transfer between the principle beams. Under favourable conditions significant amounts of power may be transferred. 相似文献
44.
We reply to the charges by K.H. Yang in his paper “Gauge invariance and experimental processes”. 相似文献
45.
46.
47.
The dehydrogenation of the known 3-methyl-5,8-dihydropyrazolo[1,2-a]pyridazin-1-one (2) to the ten π electron heteroaromatic 3-methylpyrazolo[1,2-a]pyridazin-1-one ( 3 ) is reported. Conversions of the pyrazolone 2 to the pyrazoloselenone 6 via the chloropyrazolium chloride 7 , and of pyrazolones 2 and 3 and pyrazoloselenone 6 into the corresponding O or Se ethyl pyrazolium fluoroborates 5, 4 , and 8 by triethyloxonium fluoroborate are also described. 相似文献
48.
Delong CM Au WW Lemonds DW Harley HE Roitblat HL 《The Journal of the Acoustical Society of America》2006,119(3):1867-1879
The focus of this study was to investigate how dolphins use acoustic features in returning echolocation signals to discriminate among objects. An echolocating dolphin performed a match-to-sample task with objects that varied in size, shape, material, and texture. After the task was completed, the features of the object echoes were measured (e.g., target strength, peak frequency). The dolphin's error patterns were examined in conjunction with the between-object variation in acoustic features to identify the acoustic features that the dolphin used to discriminate among the objects. The present study explored two hypotheses regarding the way dolphins use acoustic information in echoes: (1) use of a single feature, or (2) use of a linear combination of multiple features. The results suggested that dolphins do not use a single feature across all object sets or a linear combination of six echo features. Five features appeared to be important to the dolphin on four or more sets: the echo spectrum shape, the pattern of changes in target strength and number of highlights as a function of object orientation, and peak and center frequency. These data suggest that dolphins use multiple features and integrate information across echoes from a range of object orientations. 相似文献
49.
Benoit-Bird KJ Au WW Kastelein R 《The Journal of the Acoustical Society of America》2006,120(2):1118-1123
The hypothesis that sounds produced by odontocetes can debilitate fish was examined. The effects of simulated odontocete pulsed signals on three species of fish commonly preyed on by odontocetes were examined, exposing three individuals of each species as well as groups of four fish to a high-frequency click of a bottlenose dolphin [peak frequency (PF) 120 kHz, 213-dB peak-to-peak exposure level (EL)], a midfrequency click modeled after a killer whale's signal (PF 55 kHz, 208-dB EL), and a low-frequency click (PF 18 kHz, 193-dB EL). Fish were held in a 50-cm diameter net enclosure immediately in front of a transducer where their swimming behavior, orientation, and balance were observed with two video cameras. Clicks were presented at constant rates and in graded sweeps simulating a foraging dolphin's "terminal buzz." No measurable change in behavior was observed in any of the fish for any signal type or pulse modulation rate, despite the fact that clicks were at or near the maximum source levels recorded for odontocetes. Based on the results, the hypothesis that acoustic signals of odontocetes alone can disorient or "stun" prey cannot be supported. 相似文献
50.
The momentum transfer to absorbing particles is derived from the Lorentz force density without prior assumption of the momentum of light in media. We develop a view of momentum conservation rooted in the stress tensor formalism that is based on the separation of momentum contributions to bound and free currents and charges consistent with the Lorentz force density. This is in contrast with the usual separation of material and field contributions. The theory is applied to predict a decrease in optical momentum transfer to Mie particles due to absorption, which contrasts the common intuition based on the scattering and absorption by Rayleigh particles. 相似文献