全文获取类型
收费全文 | 234篇 |
免费 | 6篇 |
专业分类
化学 | 141篇 |
力学 | 7篇 |
数学 | 42篇 |
物理学 | 50篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 15篇 |
2012年 | 12篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 14篇 |
2006年 | 23篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 31 毫秒
51.
Xenon porometry is a method in which porous material is immersed in a medium and the properties of the material are studied by means of 129Xe nuclear magnetic resonance (NMR) of xenon gas dissolved in the medium. For instance, the chemical shift of a particular signal (referred to as signal D) arising from xenon inside small pockets formed in the pores during the freezing of the confined medium is highly sensitive to the pore size. In the present study, we show that when naphthalene is used as the medium the pore size distribution of the material can be determined by measuring a single one-dimensional spectrum near room temperature and converting the chemical shift scale of signal D to the pore radius scale by using an experimentally determined correlation. A model has been developed that explains the curious behavior of the chemical shift of signal D as a function of pore radius. The other signals of the spectra measured at different temperatures have also been identified, and the influence of xenon pressure on the spectra has been studied. For comparison, 129Xe NMR spectra of pure xenon gas adsorbed to porous materials have been measured and analyzed. 相似文献
52.
Tuomela Jukka; Arponen Teijo; Normi Villesamuli 《IMA Journal of Numerical Analysis》2006,26(4):811-846
** Email: jukka.tuomela{at}joensuu.fi*** Corresponding author. Email: arponen{at}maths.warwick.ac.uk**** Email: villesamuli.normi{at}joensuu.fi We analyse some RungeKutta type methods for computing1D integral manifolds, i.e. solutions to ordin-ary differentialequations and differential-algebraic equations. We show thatwe can compute the solutions which respect all the constraintsof the problem reliably and reasonably quickly. Moreover, weshow that the so-called impasse points are regular points inour approach and hence require no special attention. 相似文献
53.
Refractive index change of liquids was detected using a temperature compensated prism cavity together with a diffractive optical element fabricated by electron beam lithography. Small changes of refractive index could be detected from image data of the sensor. 相似文献
54.
Paloniemi H Aäritalo T Laiho T Liuke H Kocharova N Haapakka K Terzi F Seeber R Lukkari J 《The journal of physical chemistry. B》2005,109(18):8634-8642
HiPco single-wall carbon nanotubes (SWNTs) have been noncovalently modified with ionic pyrene and naphthalene derivatives to prepare water-soluble SWNT polyelectrolytes (SWNT-PEs), which are analogous to polyanions and polycations. The modified nanotubes have been characterized with UV-vis-NIR, fluorescence, Raman and X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The nanotube-adsorbate interactions consist of pi-pi stacking interactions between the aromatic core of the adsorbate and the nanotube surface and specific contributions because of the substituents. The interaction between nanotubes and adsorbates also involves charge transfer from adsorbates to SWNTs, and with naphthalene sulfonates the role of a free amino group was important. The ionic surface charge density of the modified SWNTs is constant and probably controlled by electrostatic repulsion between like charges. The linear ionic charge density of the modified SWNTs is similar to that of common highly charged polyelectrolytes. 相似文献
55.
Usama Abo Ramadan Antti T Markkola Juha Halavaara Jukka Tanttu Anna-Maija Häkkinen Hannu J Aronen 《Magnetic resonance imaging》1998,16(10):1191-1199
The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1ρ) and off-resonance spin lock relaxation parameters (T1ρoff, Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T1ρoff for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (Beff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T1ρ of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1ρoff decreased significantly with increasing θ (p < 0.001). T1ρ and T1ρoff with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging. 相似文献
56.
Niskanen Ilpo Räty Jukka Soetedjo Hariyadi Hibino Kenichi Oohashi Hiroshi Heikkilä Rauno Matsuda Kiyofumi Otani Yukitoshi 《Optical Review》2020,27(2):178-182
Optical Review - This study measured the polarised light reflected from the surface of thermally modified Scots pine (Pinus sylvestris L.) wood using a Stokes imaging polarimeter. The data were... 相似文献
57.
We give a generalization of the Stone–Weierstrass property for subalgebras of C (X), with X a completely regular Hausdorff space. In particular, we study in this paper some subalgebras of C0(X), with X a locally compact Hausdorff space, provided with weighted norm topology. By using the Stone–Weierstrass property, we then describe the ideal structure of these algebras. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
58.
Jukka Tuomela 《BIT Numerical Mathematics》1996,36(1):158-165
We show that it is possible to construct arbitrary order stable schemes for the homogeneous and heterogeneous wave equation in any dimension. The construction is elementary and uses formal power series techniques. We shall also calculate exact stability limits in various cases, and apparently this limit depends only on the dimension of the space. 相似文献
59.
We introduce a Cooper pair "sluice" for the implementation of a frequency-locked current source. The device consists of two mesoscopic SQUIDs and of a single superconducting island with a gate. We demonstrate theoretically that it is possible to obtain a current as high as 0.1 nA at better than ppm accuracy via periodically modulating both the gate charge and the effective Josephson coupling. We find that the device is tolerant against background charge noise and operates well even in a dissipative environment. The effect of the imperfect suppression of the Josephson coupling and the finite operating frequency are also investigated. 相似文献
60.
Jukka Jokisaari 《Magnetic resonance in chemistry : MRC》1978,11(3):157-159
The 13C? 13C spin–spin coupling constants in natural abundance oxetane, thietane, cyclobutanone, bromo-and chlorocyclobutane have been measured. Furthermore, the 13C isotope-induced changes in the chemical shifts of the different 13C nuclei in the molecules mentioned above are reported. These shifts are normally to higher magnetic field; in cyclobutanone, however, the resonance of the carbonyl carbon has shifted to lower field because of the substitution of 13C?3 for 12C?3. 相似文献