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
221.
Payam Mehdipour Kaldiani 《理论物理通讯》2021,73(7):75303
The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model. The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments. The collective temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of collective temperature on mass yields results is investigated. The fragment temperature has been calculated with the generalized superfluid model. The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data. To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model. The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model. The calculated results are in good agreement with the experimental data with Tcoll= 2 Me V at intermediate excitation energy and with T_(coll)= 1MeV for spontaneous fission.Despite the Langevin model, in the scission point model, a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield. 相似文献
222.
This investigation examines the transient deformation and heat generation of a solid polyurethane subjected to dynamic compression. A special method is presented to prepare the solid polyurethane from raw materials which are commonly used to make polyurethane foams. Testing methods including infrared spectrum, differential scanning calorimetry, quasi-static and dynamic compression were applied to study the basic physical properties of the solid polyurethane. High-speed optical and infrared imaging systems are used to obtain visual and thermo-graphic images during impact tests. Under quasi-static compression, the solid polyurethane presents a good performance in toughness. This is confirmed by its Poisson's ratio. Under impact compression, the adiabatic heat generation are identified statistically. Temperature distribution confirms the fact of transient heat generation in specimens. Adiabatic self-heating mechanism provides a consideration to understand the negative strain-rate effect and post-yield softening effect found in the solid polyurethane. Mechanical properties including quasi-static and dynamic responses are related with the composition of molecular and structure of polymer. 相似文献
223.
224.
The effects of strain rate and deformation temperature on the deformation behaviors of polyether-ether-ketone (PEEK) were studied by uniaxial tensile tests with the temperature range of 23–150 °C and strain rate of 0.01–1 s−1. The effects of deformation temperature and strain rate on the hot tensile deformation behavior and fracture characteristics were investigated by scanning electron microscope (SEM) and discussed in detail. SEM experimental results suggest that fracture morphology is not strain rate sensitive but temperature sensitive. Based on the tensile results, the Johnson-Cook and modified Johnson-Cook constitutive models were established for PEEK. Furthermore, a comparative study has been made on the accuracy and effectiveness of the developed models to predict the flow stress. The results show that the original Johnson-Cook model reflects the deformation behavior more accurately throughout the entire test temperature and strain rate range under uniaxial tensile conditions. 相似文献
225.
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
226.
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
227.
228.
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
229.
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
230.
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