全文获取类型
收费全文 | 3437篇 |
免费 | 280篇 |
国内免费 | 346篇 |
专业分类
化学 | 616篇 |
晶体学 | 14篇 |
力学 | 1601篇 |
综合类 | 40篇 |
数学 | 527篇 |
物理学 | 1265篇 |
出版年
2024年 | 8篇 |
2023年 | 48篇 |
2022年 | 43篇 |
2021年 | 56篇 |
2020年 | 99篇 |
2019年 | 81篇 |
2018年 | 87篇 |
2017年 | 112篇 |
2016年 | 132篇 |
2015年 | 117篇 |
2014年 | 168篇 |
2013年 | 311篇 |
2012年 | 112篇 |
2011年 | 187篇 |
2010年 | 141篇 |
2009年 | 179篇 |
2008年 | 186篇 |
2007年 | 209篇 |
2006年 | 207篇 |
2005年 | 172篇 |
2004年 | 196篇 |
2003年 | 136篇 |
2002年 | 132篇 |
2001年 | 99篇 |
2000年 | 108篇 |
1999年 | 102篇 |
1998年 | 98篇 |
1997年 | 91篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 46篇 |
1993年 | 46篇 |
1992年 | 52篇 |
1991年 | 49篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4063条查询结果,搜索用时 15 毫秒
241.
Hongbo Lu Yutian Chu Shuaicheng Jing Guobing Zhang Juntao Hu Guoqiang Lv 《Liquid crystals》2017,44(3):437-443
In reverse-mode polymer-stabilised cholesteric texture (PSCT), the dynamic response is derived from local director reorientation governed by dielectric coupling effect/self-assembly and polymer network deformation. A double exponential rise/decay model is proposed to investigate the underlying physical mechanisms. Through simulation of the transient rise and decay processes, the polymer network deformation in PSCT can be quantitatively evaluated. Less deformation and faster restoration speed of the polymer network can suppress hysteresis. These results provide useful guidelines for future PSCT fabrication and performance optimisation. 相似文献
242.
GUAN Linbo 《力学与实践》1979,42(5):622
对地基土沉降计算的课程内容提出改革思路,从讨论土体固结度的角度展开,进而引出最终沉降量的计算,最终引出不同的试验方法和压缩性指标。新的教学思路将土力学固结沉降的基本理论与实践应用进行合理的区隔,既能保证基本理论的纯粹性、合理性,也不回避实践中土体复杂 性质对理论进一步发展和丰富所提出的挑战。 相似文献
243.
244.
Temporal sequences of planar laser-induced fluorescence (PLIF) images of several high-speed, transient flowfields created in a reflection-type shock tunnel facility were acquired. In each case, the test gas contained either nitric oxide or the hydroxyl radical, the fluorescent species. The processes of shock reflection from an endwall with a converging nozzle and of underexpanded free jet formation were examined. A comparison was also made between PLIF imaging and shadow photography. The investigation demonstrated some of the capabilities of PLIF imaging diagnostics in complex, transient, hypersonic flowfields, including those with combustion.Nomenclature
A
spontaneous emission rate
-
A
las
cross sectional area of laser sheet
-
B
laser absorption rate
-
C
opt
constant dependent on optical arrangement, collection efficiency, etc.
-
D
nozzle throat diameter
-
E
p
laser pulse energy
-
f
J
Boltzmann fraction of absorbing state
-
g
spectral convolution of laser and absorption lineshapes
-
k
Boltzmann constant
-
M
s
incident shock Mach number
-
N
noise, root-mean-square signal fluctuation
-
P
static pressure
-
P
1
initial pressure of test gas in shock tube
-
P
a
free jet ambient pressure
-
P
s
stagnation pressure
-
Q
electronic quenching rate of excited state
-
S
PLIF signal
-
t
time between shock reflection and image acquisition
-
T
static temperature
-
T
s
stagnation temperature
-
a
mole fraction of absorbing species 相似文献
245.
Constitutive branching analysis of cylindrical bodies under in-plane equibiaxial dead-load tractions
Finite homogeneous deformations of hyperelastic cylindrical bodies subjected to in-plane equibiaxial dead-load tractions are analyzed. Four basic equilibrium problems are formulated considering incompressible and compressible isotropic bodies under plane stress and plane deformation condition. Depending on the form of the stored energy function, these plane problems, in addition to the obvious symmetric solutions, may admit asymmetric solutions. In other words, the body may assume an equilibrium configuration characterized by two unequal in-plane principal stretches corresponding to equal external forces. In this paper, a mathematical condition, in terms of the principal invariants, governing the global development of the asymmetric deformation branches is obtained and examined in detail with regard to different choices of the stored energy function. Moreover, explicit expressions for evaluating critical loads and bifurcation points are derived. With reference to neo-Hookean, Mooney-Rivlin and Ogden-Ball materials, a broad numerical analysis is performed and the qualitatively more interesting asymmetric equilibrium branches are shown. Finally, using the energy criterion, a number of considerations are put forward about the stability of the computed solutions. 相似文献
246.
消减舰船变形的影响和为全舰提供高精度姿态基准 总被引:10,自引:2,他引:10
引用国内外一些文献列举的现代舰船船体变形的数据,论证了消减船体变形的影响和为全舰提供精确的姿态基准的重要意义。对舰载航向姿态基准的功能、性能与特点进行了综述。介绍了基于激光陀螺和光纤Bragg光栅传感器测量船体变形的新方法。最后,探讨了分布式姿态基准系统的技术方案。 相似文献
247.
本文在文献[1]的基础上,将加权残数法用于复合材料多层板壳分析,并推导出相应的关系式。文中给出了算例,并与解析解进行了比较,结果表明,本文方法精度较高,用于复合材料多层板壳分析是有效的。 相似文献
248.
The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening, rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results. 相似文献
249.
Exact analytical solutions for a class of unsteady unidirectional flows of an incompressible second-order fluid are constructed. The flows are generated impulsively from rest by motion of a plate or two plates or by sudden application of a pressure gradient. Expressions for velocity, flux and skin friction are obtained for both large and small times. It is found that large and small times solutions are dependent on the coefficient of viscoelasticity. The solutions corresponding to Newtonian fluids can be easily obtained from those for fluids of second order by letting the viscoelastic parameter to be zero. 相似文献
250.
粘塑性损伤模型模拟准超塑性单轴拉伸行为 总被引:1,自引:0,他引:1
发展了Chaboche粘塑性本构模型的大变形隐式算法,用损伤(DM)和无损伤(NDM)模型模拟准超塑性单轴拉伸。发现变形过程可分为三个阶段:均匀变形、颈缩发展、断裂破坏阶段。DM可准确模拟前两个阶段变形,NDM只能较好地模拟均匀变形阶段,表明DM可以较精确地描述稳定发展的动态过程。由于有限元方法只能描述连续介质,因此对于断裂破坏阶段,NDM模拟载荷大于试验结果,DM的载荷小于试验结果,这是由高应变速率敏感性造成。DM能够描述试验中出现地多处颈缩现象,局部应变速率分布随时间演化反映了颈缩发展程度。严重颈缩部位的距离代表着超塑性变形能力,距离越大,抗颈缩能力越好。 相似文献