全文获取类型
收费全文 | 140篇 |
免费 | 2篇 |
国内免费 | 7篇 |
专业分类
化学 | 73篇 |
力学 | 3篇 |
数学 | 42篇 |
物理学 | 31篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2016年 | 5篇 |
2013年 | 10篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 5篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1951年 | 2篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1932年 | 2篇 |
1931年 | 2篇 |
1930年 | 1篇 |
1929年 | 1篇 |
1927年 | 1篇 |
1921年 | 3篇 |
1918年 | 2篇 |
1916年 | 1篇 |
排序方式: 共有149条查询结果,搜索用时 31 毫秒
1.
Ragnar Sigurdsson 《Arkiv f?r Matematik》1991,29(1):285-305
2.
The gas phase reaction between CO2 and lanthanide atoms. A test of a model for the isokinetic effect
Summary Co3O4, NiCo2O4 and LaCo2O4catalysts were synthesizedby the citric acid-ligated method. These catalysts containing Co-oxide active components can largely
lower the temperature of soot combustion under tight contact conditions. Under the conditions of loose contact NiCo2O4 cannot promote soot combustion, but LaCo2O4 can effectively promote soot combustion because the nanometric perovskite-type catalyst LaCoO3produced in the LaCo2O4sample.</o:p> 相似文献
3.
The two new compounds [Fe(tren)]FeSbS4 ( 1 ) (tren = tris(2‐aminoethyl)amine) and [Fe(dien)2]Fe2Sb4S10 ( 2 ) (dien = diethylendiamine) were prepared under solvothermal conditions and represent the first thioantimonates(III) with iron cations integrated into the anionic network. In both compounds Fe3+ is part of a [2FeIII‐2S] cluster which is often found in ferredoxines. In addition, Fe2+ ions are present which are surrounded by the organic ligands. In ( 1 ) the Fe2+ ion is also part of the thioantimonate(III) network whereas in ( 2 ) the Fe2+ ion is isolated. In both compounds the primary SbS3 units are interconnected into one‐dimensional chains. The mixed‐valent character of [Fe(tren)]FeSbS4 was unambiguously determined with Mössbauer spectroscopy. Both compounds exhibit paramagnetic behaviour and for ( 1 ) a deviation from linearity is observed due to a strong zero‐field splitting. Both compounds decompose in one single step. 相似文献
4.
Erik Allard Rikard Åslund Tröger Björn Arvidsson Per Johan Ragnar Sjöberg 《Rapid communications in mass spectrometry : RCM》2010,24(4):429-435
Precision, reproducibility and lower limit of quantitation (LLOQ) are important characteristics of a quantitative method. We have investigated these properties for Ximelagatran (Xi), which has a high tendency to form doubly charged ions in electrospray ionization (ESI), by studying the percentage of doubly charged species formed when varying the formic acid (FA) concentration, analyte concentration, amount of organic modifier and flow rate. It was found that the percentage of [Xi + 2H]2+ can be controlled to be more than 90% or less than 10% by varying the amount of FA present, and that the change between these values is dramatic. Furthermore, the percentage of [Xi + 2H]2+ formed decreases with increased analyte concentration and increased flow rate. No apparent relationship with the amount of organic modifier was found. The results have the implication that, by carefully controlling the selected parameters, the LLOQ, precision and reproducibility can be improved. We have compared the fragmentation of the singly and doubly charged species and concluded that the [Xi + 2H]2+ ion is more inclined to undergo fragmentation than [Xi + H]+. As a consequence, unusual instrumental settings had to be used for the experiments. The fragmentation patterns are to a great extent similar, but the doubly charged species is more inclined to generate low‐mass product ions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
5.
6.
Ragnar Bengtsson 《Hyperfine Interactions》1992,75(1-4):3-22
A survey is made of new regions of nuclei, which may become accessible to nuclear orientation experiments as the on-line technique
matures. Basic nuclear properties that can be investigated by means of nuclear orientation are briefly reviewed. Examples
of systematic use of nuclear moments for revealing nuclear properties are given as is an example of of the combined use of
low-spin nuclear orientation data and high-spin heavy-ion reaction data. 相似文献
7.
We study the simultaneous one-dimensional flow of water and oil in a heterogeneous medium modelled by the Buckley-Leverett equation. It is shown both by analytical solutions and by numerical experiments that this hyperbolic model is unstable in the following sense: Perturbations in physical parameters in a tiny region of the reservoir may lead to a totally different picture of the flow. This means that simulation results obtained by solving the hyperbolic Buckley-Leverett equation may be unreliable.Symbols and Notation
f
fractional flow function varying withs andx
-
value off outsideI
-
value off insideI
-
local approximation off around¯x
-
f
–,f
+
values of
-
f
j
n
value off atS
j
n
andx
j
-
g
acceleration due to gravity [ms–2]
-
I
interval containing a low permeable rock
-
k
dimensionless absolute permeability
-
k
*
absolute permeability [m2]
-
k
c
*
characteristic absolute permeability [m2]
-
k
ro
relative oil permeability
-
k
rw
relative water permeability
-
L
*
characteristic length [m]
-
L
1
the space of absolutely integrable functions
-
L
the space of bounded functions
-
P
c
dimensionless capillary pressure function
-
P
c
*
capillary pressure function [Pa]
-
P
c
*
characteristic pressure [Pa]
-
S
similarity solution
-
S
j
n
numerical approximation tos(xj, tn)
-
S
1, S2,S
3
constant values ofs
-
s
water saturation
-
value ofs at
-
s
L
left state ofs (wrt.
)
-
s
R
right state ofs (wrt.
)
-
s
s for a fixed value of in Section 3
-
T
value oft
-
t
dimensionless time coordinate
-
t
*
time coordinate [s]
-
t
c
*
characteristic time [s]
-
t
n
temporal grid point,t
n=n t
-
v
*
total filtration (Darcy) velocity [ms–1]
-
W, , v
dimensionless numbers defined by Equations (4), (5) and (6)
-
x
dimensionless spatial coordinate [m]
-
x
*
spatial coordinate [m]
-
x
j
spatial grid piont,x
j=j x
-
discontinuity curve in (x, t) space
-
right limiting value of¯x
-
left limiting value of¯x
-
angle between flow direction and horizontal direction
- t
temporal grid spacing
- x
spatial grid spacing
-
length ofI
-
parameter measuring the capillary effects
-
argument ofS
-
o
dimensionless dynamic oil viscosity
- w
dimensionless dynamic water viscosity
-
c
*
characteristic viscosity [kg m–1s–1]
-
o
*
dynamic oil viscosity [kg m–1s–1]
-
w
*
dynamic water viscosity [k gm–1s–1]
-
o
dimensionless density of oil
-
w
dimensionless density of water
-
c
*
characteristic density [kgm–3]
-
o
*
density of oil [kgm–3]
-
w
*
density of water [kgm–3]
-
porosity
-
dimensionless diffusion function varying withs andx
-
*
dimensionless function varying with s andx
* [kg–1m3s]
-
j
n
value of atS
j
n
andx
j
This research has been supported by VISTA, a research cooperation between the Norwegian Academy of Science and Letters and Den norske stats oljeselskap a.s. (Statoil). 相似文献
8.
This paper establishes the convergence of a multi point flux approximation control volume method on rough quadrilateral grids. By rough grids we refer to a family of refined quadrilateral grids where the cells are not required to approach parallelograms in the asymptotic limit. In contrast to previous convergence results for these methods we consider here a version where the flux approximation is derived directly in the physical space, and not on a reference cell. As a consequence, less regular grids are allowed. However, the extra cost is that the symmetry of the method is lost. 相似文献
9.
Börje Folkesson Ragnar Larsson 《Journal of Electron Spectroscopy and Related Phenomena》1982,26(2):157-166
A series of simple thiocyanato complex ions have been investigated as their tetraphenylphosphonium and potassium salts. The binding energies of N, C and S were determined as well as those of the metals. From the first-mentioned data effective charge-values were estimated for the atoms of the ligands. For this purpose linear relations Eb = kq + Eb0 were used that had been previously established within a scheme having C1s (phenyl) as the internal standard.From the data thus obtained the effective charge on the metal atoms was estimated. For elements where we have sufficient data the same type of linear relation seems to he followed. Tentatively valid examples are Eb(Ni) = 6.74qNi + 848.3 eV and Eb(Pd) = 4.45qPd + 333.9 eV.In this interpretation the atoms of the metals are considered to be positively charged and surrounded by the negative charge of the electrons occupying the s band.It is further suggested for complexes with pronounced π backbonding (Pt(SCN)42?, Pd(SCN)42? and Hg(SCN)42?) that the C 1s binding energy measured for the carbon atom of the SCN? ligand is composed of the ionisation energy from the 1s level and an additional term corresponding to the intraligand π → π* transition. 相似文献
10.
Summary Pyrite is digested in a (3 + 1) nitric-hydrochloric acid mixture. Nitrate is removed by warming the solution after addition of sulphuric acid. Strong hydrochloric acid is added to hydride prior generation to eliminate interference from iron. The result is compared with that obtained by neutron activation analysis. Standard deviation was in the range of 1–2 ppm.
Selenbestimmung in Pyrit über das Hydrid mit Hilfe der AAS
Zusammenfassung Die Pyritprobe wird mit Salpetersäure/ Salzsäure aufgeschlossen und anschließend werden die Nitrationen durch Erhitzen mit Schwefelsäure entfernt. Zur Hydriderzeugung wird starke Salzsäure zugesetzt, um Störungen durch Eisen zu verhindern. Die Ergebnisse wurden mit denen der Neutronenaktivierung verglichen, wobei sich gute Übereinstimmung ergab. Die Standardabweichung liegt im Bereich von 1–2 ppm.相似文献