全文获取类型
收费全文 | 3756篇 |
免费 | 219篇 |
国内免费 | 12篇 |
专业分类
化学 | 2743篇 |
晶体学 | 10篇 |
力学 | 140篇 |
数学 | 483篇 |
物理学 | 611篇 |
出版年
2023年 | 34篇 |
2022年 | 33篇 |
2021年 | 69篇 |
2020年 | 87篇 |
2019年 | 86篇 |
2018年 | 73篇 |
2017年 | 58篇 |
2016年 | 126篇 |
2015年 | 110篇 |
2014年 | 145篇 |
2013年 | 181篇 |
2012年 | 306篇 |
2011年 | 343篇 |
2010年 | 154篇 |
2009年 | 147篇 |
2008年 | 287篇 |
2007年 | 247篇 |
2006年 | 243篇 |
2005年 | 237篇 |
2004年 | 198篇 |
2003年 | 117篇 |
2002年 | 123篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 25篇 |
1998年 | 10篇 |
1997年 | 28篇 |
1996年 | 28篇 |
1995年 | 16篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 9篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 17篇 |
排序方式: 共有3987条查询结果,搜索用时 281 毫秒
41.
Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All‐Organic Redox Flow Battery 下载免费PDF全文
Dr. Xiaoliang Wei Dr. Wu Xu Dr. Jinhua Huang Dr. Lu Zhang Dr. Eric Walter Dr. Chad Lawrence Dr. M. Vijayakumar Dr. Wesley A. Henderson Dr. Tianbiao Liu Dr. Lelia Cosimbescu Dr. Bin Li Dr. Vincent Sprenkle Dr. Wei Wang 《Angewandte Chemie (International ed. in English)》2015,54(30):8684-8687
Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all‐organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical‐based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries. 相似文献
42.
Experiments have been made to measure some of the near wake properties of axisymmetric bluff body flows with fixed points
of separation, including the detention or residence time of fluid borne scalar entities, base pressure coefficient, wake bubble
length parameter and shape parameter. Measurements were made in smooth and turbulent air flow for Reynolds number in the range
2×103<Re<4×104. The results for a given bluff body were found to be uniquely controlled by a free-stream turbulence parameter. The data
for all the shapes of bluff body in the class under consideration were found to collapse into unique inter-relationships by
the introduction of the face pressure coefficient as a quantitative measure of “bluffness”.
This paper was originally presented at the 14th International Congress of Theoretical and Applied Mechanics, Delft (August–September,
1976). 相似文献
43.
Pierre Lubin Stéphane Vincent Jean-Paul Caltagirone Stéphane Abadie 《Comptes Rendus Mecanique》2003,331(7):495-501
The scope of this paper is to show the results obtained for simulating three-dimensional breaking waves by solving the Navier–Stokes equations in air and water. The interface tracking is achieved by a Lax–Wendroff TVD scheme (Total Variation Diminishing), which is able to handle interface reconnections. We first present the equations and the numerical methods used in this work. We then proceed to the study of a three-dimensional plunging breaking wave, using initial conditions corresponding to unstable periodic sinusoidal waves of large amplitudes. We compare the results obtained for two simulations, a longshore depth perturbation has been introduced in the solution of the flow equations in order to see the transition from a two-dimensional velocity field to a fully three-dimensional one after plunging. Breaking processes including overturning, splash-up and breaking induced vortex-like motion beneath the surface are presented and discussed. To cite this article: P. Lubin et al., C. R. Mecanique 331 (2003). 相似文献
44.
The nature of the instability governing the self-sustained tones produced by a low Mach number plane jet impinging on a slotted plate, known as slot-tone, is identified experimentally. For a given Reynolds number, the natural shear-layer and the jet column mode frequencies of the free jet delimit the values of the measured slot-tone operating frequencies. The oscillations at lower frequencies are the result of the amplification of the jet column mode, and those at higher frequencies correspond to the shear layer instabilities. To cite this article: A. Billon et al., C. R. Mecanique 332 (2004). 相似文献
45.
Henri Bertin Michel Quintard Ph. Vincent Corpel Stephen Whitaker 《Transport in Porous Media》1990,5(6):543-590
Two-phase flow in stratified porous media is a problem of central importance in the study of oil recovery processes. In general, these flows are parallel to the stratifications, and it is this type of flow that we have investigated experimentally and theoretically in this study. The experiments were performed with a two-layer model of a stratified porous medium. The individual strata were composed of Aerolith-10, an artificial: sintered porous medium, and Berea sandstone, a natural porous medium reputed to be relatively homogeneous. Waterflooding experiments were performed in which the saturation field was measured by gamma-ray absorption. Data were obtained at 150 points distributed evenly over a flow domain of 0.1 × 0.6 m. The slabs of Aerolith-10 and Berea sandstone were of equal thickness, i.e. 5 centimeters thick. An intensive experimental study was carried out in order to accurately characterize the individual strata; however, this effort was hampered by both local heterogeneities and large-scale heterogeneities.The theoretical analysis of the waterflooding experiments was based on the method of large-scale averaging and the large-scale closure problem. The latter provides a precise method of discussing the crossflow phenomena, and it illustrates exactly how the crossflow influences the theoretical prediction of the large-scale permeability tensor. The theoretical analysis was restricted to the quasi-static theory of Quintard and Whitaker (1988), however, the dynamic effects described in Part I (Quintard and Whitaker 1990a) are discussed in terms of their influence on the crossflow.Roman Letters
A
interfacial area between the -region and the -region contained within V, m2
-
a
vector that maps
onto
, m
-
b
vector that maps
onto
, m
-
b
vector that maps
onto
, m
-
B
second order tensor that maps
onto
, m2
-
C
second order tensor that maps
onto
, m2
-
E
energy of the gamma emitter, keV
-
f
fractional flow of the -phase
- g
gravitational vector, m/s2
-
h
characteristic length of the large-scale averaging volume, m
-
H
height of the stratified porous medium
, m
-
i
unit base vector in the x-direction
-
K
local volume-averaged single-phase permeability, m2
-
K - {K}, large-scale spatial deviation permeability
-
{
K}
large-scale volume-averaged single-phase permeability, m2
-
K
*
large-scale single-phase permeability, m2
-
K
**
equivalent large-scale single-phase permeability, m2
-
K
local volume-averaged -phase permeability in the -region, m2
-
K
local volume-averaged -phase permeability in the -region, m2
-
K
- {K
}
, large-scale spatial deviation for the -phase permeability, m2
-
K
*
large-scale permeability for the -phase, m2
-
l
thickness of the porous medium, m
-
l
characteristic length for the -region, m
-
l
characteristic length for the -region, m
-
L
length of the experimental porous medium, m
-
characteristic length for large-scale averaged quantities, m
-
n
outward unit normal vector for the -region
-
n
outward unit normal vector for the -region
-
n
unit normal vector pointing from the -region toward the -region (n
= - n
)
-
N
number of photons
-
p
pressure in the -phase, N/m2
-
p
0
reference pressure in the -phase, N/m2
-
local volume-averaged intrinsic phase average pressure in the -phase, N/m2
-
large-scale volume-averaged pressure of the -phase, N/m2
-
large-scale intrinsic phase average pressure in the capillary region of the -phase, N/m2
-
-
, large-scale spatial deviation for the -phase pressure, N/m2
- pc
, capillary pressure, N/m2
-
p
c
capillary pressure in the -region, N/m2
-
p
capillary pressure in the -region, N/m2
- {p
c
}
c
large-scale capillary pressure, N/m2
-
q
-phase velocity at the entrance of the porous medium, m/s
-
q
-phase velocity at the entrance of the porous medium, m/s
- Swi
irreducible water saturation
-
S
/, local volume-averaged saturation for the -phase
-
S
i
initial saturation for the -phase
-
S
r
residual saturation for the -phase
-
S
*
{
}*/}*, large-scale average saturation for the -phase
-
S
saturation for the -phase in the -region
-
S
saturation for the -phase in the -region
-
t
time, s
-
v
-phase velocity vector, m/s
- v
local volume-averaged phase average velocity for the -phase, m/s
- {v
}
large-scale averaged velocity for the -phase, m/s
- v
local volume-averaged phase average velocity for the -phase in the -region, m/s
- v
local volume-averaged phase average velocity for the -phase in the -region, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity in the -region, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity in the -region, m/s
-
V
large-scale averaging volume, m3
-
y
position vector relative to the centroid of the large-scale averaging volume, m
- {y}c
large-scale average of y over the capillary region, m
Greek Letters
local porosity
-
local porosity in the -region
-
local porosity in the -region
-
local volume fraction for the -phase
-
local volume fraction for the -phase in the -region
-
local volume fraction for the -phase in the -region
- {}*
{
}*+{
}*, large-scale spatial average volume fraction
- {
}*
large-scale spatial average volume fraction for the -phase
-
mass density of the -phase, kg/m3
-
mass density of the -phase, kg/m3
-
viscosity of the -phase, N s/m2
-
viscosity of the -phase, Ns/m2
-
V
/V
, volume fraction of the -region (
+
=1)
-
V
/V
, volume fraction of the -region (
+
=1)
-
attenuation coefficient to gamma-rays, m-1
-
-
相似文献
46.
Dr. Song Song Vincent Fung Kin Yuen Dr. Lu Di Dr. Qiming Sun Prof. Dr. Kang Zhou Prof. Dr. Ning Yan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20018-20022
Production of renewable, high-value N-containing chemicals from lignocellulose will expand product diversity and increase the economic competitiveness of the biorefinery. Herein, we report a single-step conversion of furfural to pyrrole in 75 % yield as a key N-containing building block, achieved via tandem decarbonylation–amination reactions over tailor-designed Pd@S-1 and H-beta zeolite catalytic system. Pyrrole was further transformed into dl -proline in two steps following carboxylation with CO2 and hydrogenation over Rh/C catalyst. After treating with Escherichia coli, valuable d -proline was obtained in theoretically maximum yield (50 %) bearing 99 % ee. The report here establishes a route bridging commercial commodity feedstock from biomass with high-value organonitrogen chemicals through pyrrole as a hub molecule. 相似文献
47.
Letters in Mathematical Physics - By considering the closure property of a Lagrangian multiform as a conservation law, we use Noether’s theorem to show that every variational symmetry of a... 相似文献
48.
Dr. Dhanaji V. Jawale Dr. Edmond Gravel Dr. Nimesh Shah Dr. Vincent Dauvois Prof. Dr. Haiyan Li Prof. Dr. Irishi N. N. Namboothiri Dr. Eric Doris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7039-7042
Rhodium nanoparticles were anchored on carbon nanotubes and the resulting nanohybrid was studied as co‐catalyst, along with tert‐butylcatechol, for the dehydrogenation of various N‐heterocycles. The co‐catalytic system operates in high yields, under the mildest conditions reported so far, and can be applied to a wide variety of secondary amine‐containing scaffolds. 相似文献
49.
50.