全文获取类型
收费全文 | 730篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 398篇 |
晶体学 | 9篇 |
力学 | 10篇 |
数学 | 61篇 |
物理学 | 262篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 58篇 |
2012年 | 17篇 |
2011年 | 38篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 35篇 |
2007年 | 27篇 |
2006年 | 46篇 |
2005年 | 26篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 8篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1974年 | 13篇 |
1973年 | 13篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1969年 | 7篇 |
排序方式: 共有740条查询结果,搜索用时 15 毫秒
101.
102.
Following collection of diesel particulate samples on high efficiency glass fibre papers, and Soxhlet extraction with cyclohexane, a two-stage clean-up involving DMF/H2O partition and silica gel thin-layer chromatography is required in order to simplify the extract. Individual compound identification can then be achieved by high resolution gas chromatography using WCOT quartz capillary columns with flame ionisation or computer-assisted electron impact mass spectrometry detection systems. The technique provides a relatively quick and simple enrichment step, whilst the high separating power of the capillary column is able to resolve the many chromatographically similar isomers and substituted PAH members that are present. Investigations indicate that presence of a vast range of PAH species, comprising both substituted and unsubstituted two- to seven-membered ring systems, many of which are known carcinogens and mutagens. 相似文献
103.
We report measurements of the electron and positron work functions of submonolayer contaminated single crystal surfaces of Cr(100) in ultra high vacuum. The positron work function ø+ is obtained by measuring the spectrum of slow positrons reemitted by the Cr(100) surface when it is bombarded with keV energy positrons. The electron work function ø- is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain ø+ = ?1.76(10) eV and ø- = 4.46(6) eV for our Cr(100) surface using the value ø- = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The ø+ value is in agreement with the ?2.2 eV calculated by Nieminen and Hodges. The positronium work function for Cr implied by these results is ?4.10(10) eV; the positronium negative ion (Ps-) work function for this surface is calculated to be + 0.37(7) eV. A search for Ps- showed that at a 90% confidence level less than one in 103 thermalized positrons reaching the Cr surface are emitted as Ps-. The slow positron emission spectrum was observed not to change over the 70–300 K range in contrast to recent theoretical predictions. 相似文献
104.
M. J. Radler B. G. Landes S. J. Nolan C. F. Broomall T. C. Chritz P. R. Rudolf M. E. Mills R. A. Bubeck 《Journal of Polymer Science.Polymer Physics》1994,32(16):2567-2573
The results of a series of novel synchrontron-based in situ x-ray scattering experiments of monofilament fiber drawing from lyotropic solutions of poly(cis-benzoxazole) (PBO) and poly(trans-benzothiazole) (PBZT) are reported. The purpose of the study is to determine orientation and microstructure development in the draw zone as a function of shear rate in the capillary die, and spin draw ratio (SDR). The transition of the extrudate from opaque to the transparent is complete at about a SDR = 3 and f of 0.9. The filament orientation parameter (f) was found to depend strongly on spin draw ratio, but not shear rate. The orientation was found to increase down the extrudate toward completion of the draw down as one proceeds further from the die face up to an extrudate length of 3.8 cm. Coherence lengths on the order of 19 nm (axial), and 4.5 nm (lateral) have been observed. These “microdomain” sizes are consistent with the “crystallite” sizes typically observed in coagulated fiber. The occurrence of these microdomains in the draw zone as a precursor to the microfibrillar structure is believed to be the origin of low filament compressive strength. © 1994 John Wiley & Sons, Inc. 相似文献
105.
The extent and duration of trapping of argon resonance radiation (106.7 and 104.8 nm) in the ICP was calculated using a model incorporating line shape contributions from both Doppler and pressure broadening. The trap was found to be at the pressure-broadened limit, giving an escape factor of 7.9 × 10?4 when excitation of the 4s states in the plasma annulus is assumed. Theoretical apparent radiative lifetimes τapp for argon 3P1 and 1P1 resonance states are calculated to be 8 and 1.9μs respectively. The quartet of 4s states, rapidly mixed by electron collisions, are presumed to share an overall apparent radiative lifetime τapp = 1.6μs for the purpose of plasma modeling. Effects of this radiation trapping on the argon 4s atom density and on electron-ion recombination are discussed. 相似文献
106.
107.
108.
The different types of surface intersection which may occur in linear configurations of triatomic molecules are reviewed, particularly with regard to the way in which the degeneracy is split as the molecule bends. The Renner-Teller effect in states of symmetry Π, Δ, Φ, etc., and intersections between Σ and Π, Σ and Δ, and Π and Δ states are discussed. A general method of modelling such intersecting potential surfaces is proposed, as a development of the model previously used by Murrell and Carter and co-workers for single-valued surfaces. Some of the lower energy surfaces of H2O, NH2, O3, C3, and HNO are discussed as examples. 相似文献
109.
110.
Matrices of bisimple regular semigroups 总被引:1,自引:0,他引:1
Janet E. Mills 《Semigroup Forum》1983,26(1):117-123
A semigroup S is a matrix of subsemigroups Siμ, i ε I, μ ε M if the Siμ form a partition of S and SiμSjν≤Siν for all i, j in I, μ, ν in M. If all the Siμ are bisimple regular semigroups, then S is a bisimple regular semigroup. Properties of S are considered when the Siμ are bisimple and regular; for example, if S is orthodox then each element of S has an inverse in every component Siμ. 相似文献