全文获取类型
收费全文 | 498篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 243篇 |
晶体学 | 2篇 |
力学 | 32篇 |
数学 | 94篇 |
物理学 | 129篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 38篇 |
2011年 | 43篇 |
2010年 | 30篇 |
2009年 | 20篇 |
2008年 | 25篇 |
2007年 | 38篇 |
2006年 | 31篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 27篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 16篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 7篇 |
1985年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1940年 | 1篇 |
1939年 | 2篇 |
1932年 | 2篇 |
1931年 | 1篇 |
1928年 | 3篇 |
1924年 | 2篇 |
1923年 | 1篇 |
1916年 | 1篇 |
1866年 | 1篇 |
排序方式: 共有500条查询结果,搜索用时 171 毫秒
491.
Barboni T Paolini J Tomi P Luro F Muselli A Costa J 《Natural product communications》2011,6(10):1495-1498
The volatile compositions of juice and peel of clementine (Citrus reticulata x Citrus sinensis var. Commune), mandarin (Citrus reticulata Blanco var. Willow Leaf) and their hybrids were analyzed by headspace solid-phase extraction (HS-SPME) coupled with gas chromatography and either a flame ionization detector (FID) or a mass spectrometer (MS). The major compounds of the volatile fractions of clementine and mandarin were limonene and limonene/gamma-terpinene, respectively. The volatile compositions of juice and peel of the same fruit showed qualitative and quantitative differences. The data analysis established the existence of three main groups based on volatile compounds that correlated with sample genotypes (clementine and mandarin) and fruit samples (peel and juice). 相似文献
492.
G. Løvoll M. Jankov K. J. Måløy R. Toussaint J. Schmittbuhl G. Schäfer Y. Méheust 《Transport in Porous Media》2011,86(1):305-324
We report on results from primary drainage experiments on quasi-two-dimensional porous models. The models are transparent,
allowing the displacement process and structure to be monitored in space and time during primary drainage experiments carried
out at various speeds. By combining detailed information on the displacement structure with global measurements of pressure,
saturation and the capillary number Ca, we obtain a scaling relation relating pressure, saturation, system size and capillary
number. This scaling relation allows pressure–saturation curves for a wide range of capillary numbers to be collapsed on the
same master curve. We also show that in the case of primary drainage, the dynamic effect in the capillary pressure–saturation
relationship observed on partially water saturated soil samples might be explained by the combined effect of capillary pressure
along the invasion front of the gaseous phase, and pressure changes caused by viscous effects in the wetting fluid phase. 相似文献
493.
494.
A ruthenium phosphane aryl sulfonate was found to be an efficient catalyst for the polymerization of ethene. Surprisingly, the resulting polyethylene is crosslinked. 相似文献
495.
496.
Electron-deficient 1- and 2-azabuta-1,3-dienes are reagents intrinsically able to provide a wide range of cyclic and acyclic N-containing building blocks. Depending on their substitution, they behave as dienes for Diels-Alder reactions, as partners for [4+1], [3+2], [2+2]-cycloadditions, for aziridinations and as electrophiles for 1,2 and 1,4-additions. Nowadays, they are a very versatile family of compounds, despite their usual instability and complex reactivity. Four decades of research in this challenging area are reviewed in this critical review: their synthetic aspects and their reactivity towards a wide range of dienophiles, dipoles and nucleophiles are described as well. The introduction focuses on their electronic properties in order to get a clear picture of their reactivity (190 references). 相似文献
497.
Boudraa AO Cexus JC Abed-Meraim K 《The Journal of the Acoustical Society of America》2008,123(6):4283-4289
In this paper, two methods for signal detection and time-delay estimation based on the cross Psi(B)-energy operator are proposed. These methods are well suited for mono-component AM-FM signals. The Psi(B) energy operator measures how much one signal is present in another one. The peak of the Psi(B) operator corresponds to the maximum of interaction between the two signals. Compared to the cross-correlation function, the Psi(B) operator includes temporal information and relative changes of the signal which are reflected in its first and second derivatives. The discrete version of the continuous-time form of the Psi(B) operator, which is used in its implementation, is presented. The methods are illustrated on synthetic and real signals and the results compared to those of the matched filter and the cross correlation. The real signals correspond to impulse responses of buried objects obtained by active sonar in iso-speed single path environments. 相似文献
498.
Moreau S Bailliet H Valière JC 《The Journal of the Acoustical Society of America》2008,123(2):640-647
Measurements of the axial streaming velocity are performed by means of laser doppler velocimetry in an experimental apparatus consisting of a waveguide having loudspeakers at each end for high intensity sound levels. Streaming is characterized by an appropriate Reynolds number Re(NL), the case Re(NL)<1 corresponding to the so-called slow streaming and the case Re(NL)>/=1 being referred to as fast streaming. The variation of axial streaming velocity with respect to the transverse coordinate is compared to the available slow streaming theory. Streaming fluid flow is measured both in the core region and in the near wall region. Streaming velocity in the center of the guide agrees reasonably well with the slow streaming theory for small Re(NL) but deviates significantly from such predictions for Re(NL)>20 and its evolution for further increasing Re(NL) is discussed. Then streaming behavior in the near wall region is particularly studied. For Re(NL)<70, two vortices are present across the guide section as predicted by slow streaming theory. Then it appears that, when the Reynolds number is increased, two other vortices become visible in the near wall region. Different stages for the generation and evolution of these inner streaming vortices are presented. 相似文献
499.
Jean-Philippe Tourrenc Sophie Bouchoule Aghiad Khadour Jean-Christophe Harmand Audrey Miard Jean Decobert Nadine Lagay Xavier Lafosse Isabelle Sagnes Laetitia Leroy Jean-Louis Oudar 《Optical and Quantum Electronics》2008,40(2-4):155-165
We report on the thermal design and the characterization of InP-based 1.55 μm wavelength large diameter (~100 μm) optically pumped vertical external cavity surface emitting lasers (OP-VECSELs). The device is thermally optimized for high power ( > 70 mW) room-temperature (RT) continuous-wave (CW) single-mode operation. Efficient bottom heat dissipation in the 1/2-VCSEL chip is obtained thanks to the use of a hybrid metal– metamorphic GaAs/AlAs mirror integrated to the InP-based active region, and to subsequent soldering on a SiC substrate. A single-mode output power of 77mW is obtained under CW-RT laser operation, limited by the pump power. Moreover thermal simulations and characterizations of the 1/2-VCSEL chip show that even higher power could be obtained at higher pumping levels, using a CVD diamond substrate. 相似文献
500.
We report a time-resolved study of the dynamics associated with the slow compaction of a granular column submitted to thermal cycles. The column height displays a complex behavior: for a large amplitude of the temperature cycles, the granular column settles continuously, experiencing a small settling at each cycle. By contrast, for a small-enough amplitude, the column exhibits a discontinuous and intermittent activity: successive collapses are separated by quiescent periods whose duration is exponentially distributed. We then discuss potential mechanisms which would account for both the compaction and the transition at finite amplitude. 相似文献