全文获取类型
收费全文 | 896篇 |
免费 | 62篇 |
国内免费 | 35篇 |
专业分类
化学 | 68篇 |
力学 | 356篇 |
综合类 | 14篇 |
数学 | 141篇 |
物理学 | 414篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 20篇 |
2021年 | 23篇 |
2020年 | 29篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 41篇 |
2016年 | 43篇 |
2015年 | 38篇 |
2014年 | 33篇 |
2013年 | 45篇 |
2012年 | 36篇 |
2011年 | 66篇 |
2010年 | 45篇 |
2009年 | 50篇 |
2008年 | 47篇 |
2007年 | 32篇 |
2006年 | 45篇 |
2005年 | 33篇 |
2004年 | 42篇 |
2003年 | 47篇 |
2002年 | 22篇 |
2001年 | 31篇 |
2000年 | 30篇 |
1999年 | 19篇 |
1998年 | 23篇 |
1997年 | 21篇 |
1996年 | 12篇 |
1995年 | 21篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有993条查询结果,搜索用时 421 毫秒
71.
将社会网络嵌入理论从单一网络拓展至双重网络,分析上市公司同时嵌入风险投资网络和承销商网络对公司IPO上市后市场表现的影响。利用2004~2017年有风险投资支持的IPO公司数据,实证检验结果表明:(1)单独嵌入风险投资网络中心位置、单独嵌入承销商网络中心位置,均会提高公司IPO后市场表现;(2)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后短期市场表现的正向影响会相互替代;(3)同时嵌入风险投资网络中心位置和承销商网络中心位置,对公司IPO后长期市场表现的正向影响会互相补充。 相似文献
72.
73.
给出了弹性系统瞬时势能泛函的一般表达式,得到了其关于任意挠曲输液管道的具体表达式,根据瞬时最小势能原理建立了该结构的有限元动力方程,并首次推导出其离心力载荷公式,讨论了管道结构静平衡位置的发散流速的确定,最后,用简单的实验结果对理论分析作了验证。 相似文献
74.
M.Emin Erdo?an 《International Journal of Non》2003,38(5):781-797
Some properties of the time-dependent Navier-Stokes equations are discussed for flows impulsively started from rest by sudden application of a constant pressure gradient or by the impulsive motion of a boundary. Five illustrative examples are given. They are: unsteady flow in a circular cylinder moving parallel to its length, starting flow in a circular pipe, unsteady flow in a rotating cylinder, starting flow in a rectangular channel moving parallel to its length and unsteady flow in a channel of rectangular cross-section. It is found that the expressions of the quantities such as velocity, flux and skin friction are in series forms which may be rapidly convergent for large values of the time but slowly convergent for small values of the time or vice versa. It is shown that if their expressions can be found for one of large values of the time or small values of the time, these expressions can be used for the other. 相似文献
75.
This article presents an experimental study of the vibro-acoustic response of a pipe excited by a fully-developed turbulent
air flow. First, the wall pressure field acting on the internal pipe wall is investigated. The power spectral density of the
wall pressure fluctuations is analyzed after cancellation of contaminating background noise. The convection velocity and correlation
lengths are calculated from measured cross-spectra, and the cross-spectra are expressed in Corcos model form. Second, the
vibro-acoustic response of the pipe is analyzed by referring to the structural modes of the pipe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
DRIVING FORCE AND DEFORMATION ANALYSIS FOR DYNAMIC CRACK PROPAGATION IN GAS PIPELINES UNDER DIFFERENT BOUNDARY CONDITIONS 总被引:1,自引:0,他引:1
Zhuang Zhuo 《Acta Mechanica Solida Sinica》1997,10(1):86-94
In the light of a growing need for fracture control of rapid crack propagation(RCP)ingas pipelines,a program PFRAC(Pipeline FRacture Analysis Code)has been developed to analysethc various events.In this paper,by using PFRAC for the simulation of axial crack propagation in gaspipelines,a number of dynamic analysis issues rclating to boundary effects for uncracked and crackedpipes are investigated.This indicates that the boundary conditions along the length of the pipe play animportant role for fracture analysis in the pipe.In contrast.the boundary condutions at thc ends of along pipeline have little effect on the dynamic fracture events. 相似文献
77.
Correlations predicting frictional pressure drop and liquid holdup during horizontal gas-liquid pipe flow with a small liquid holdup 总被引:1,自引:0,他引:1
Experimental data and correlations available in the literature for the liquid holdup εL and the pressure gradient ΔPTP/L for gas-liquid pipe flow, generally, do not cover the domain 0 < εL < 0.06. Reliable pressure-drop correlations for this holdup range are important for calculating flow rates of natural gas, containing traces of condensate. In the present paper attention is focused on reliable measurements of εL and ΔPTPIL values and on the development of a phenomenological model for the liquid-holdup range 0 < εL < 0.06. This model is called the “apparent rough surface” model and is referred to as the ARS model. The experimental results presented in this paper refer to air-water and air-water + ethyleneglycol systems with varying transport properties in horizontal straight smooth glass tubes under steady-state conditions. The holdup and pressure gradient values predicted with the ARS model agree satisfactorily with both our experimental results and data obtained from the literature referring to small liquid-holdup values 0 < εL < 0.06. Further, it has been shown that in the domain 38 < < 72 mPa m the interfacial tension of the gas-liquid system has no significant effect on the liquid holdup. The pressure gradient, however, increases slightly with decreasing surface tension values. 相似文献
78.
Heat transfer coefficients were measured and new correlations were developed for two-phase, two-component (air and water) heat transfer in a horizontal pipe for different flow patterns. Flow patterns were observed in a transparent circular pipe using an air–water mixture. Visual identification of the flow patterns was supplemented with photographic data, and the results were plotted on the flow regime map proposed by Taitel and Dukler and agreed quite well with each other. A two-phase heat transfer experimental setup was built for this study and a total of 150 two-phase heat transfer data with different flow patterns were obtained under a uniform wall heat flux boundary condition. For these data, the superficial Reynolds number ranged from 640 to 35,500 for the liquid and from 540 to 21,200 for the gas. Our previously developed robust two-phase heat transfer correlation for a vertical pipe with modified constants predicted the horizontal pipe air–water heat transfer experimental data with very good accuracy. Overall the proposed correlations predicted the data with a mean deviation of 1.0% and an rms deviation of 12%. 相似文献
79.
An experimental investigation of heat transfer to pulsating pipe air flow with different amplitudes 总被引:1,自引:0,他引:1
Heat transfer characteristics to both laminar and turbulent pulsating pipe flows under different conditions of Reynolds number,
pulsation frequency, pulsator location and tube diameter were experimentally investigated. The tube wall of uniform heat flux
condition was considered for both cases. Reynolds number varied from 750 to 12,320 while the frequency of pulsation ranged
from 1 to 10 Hz. With locating the pulsator upstream of the inlet of the test section tube, results showed an increase in
heat transfer rate due to pulsation by as much as 30% with flow Reynolds number of 1,643 and pulsation frequency of 1 Hz,
depending on the upstream location of the pulsator valve. Closer the valve to the tested section inlet, the better improvement
in the heat transfer coefficient is achieved. Upon comparing the heat transfer results of the upstream and the downstream
pulsation, at Reynolds number of 1,366 and 1,643, low values of the relative mean Nusselt number were obtained with the upstream
pulsation. Comparing the heat transfer results of the two studied test sections tubes for Reynolds number range from 8,000
to 12,000 and pulsation frequency range from 1.0 to 10 Hz showed that more improvement in heat transfer rate was observed
with a larger tube diameter. For Reynolds number ranging from 8,000 to 12,000 and pulsation frequency of 10 Hz, an improvement
in the relative mean Nusselt number of about 50% was obtained at Reynolds number of 8,000 for the large test section diameter
of 50 mm. While, for the small test section diameter of 15 mm, at same conditions of Reynolds number and frequency, a reduction
in the relative mean Nusselt number of up to 10% was obtained. 相似文献
80.
Based on an analytical study, a numerical analysis is made of the dynamic stability of a cantilevered steel pipe conveying a fluid. The pipe is modeled by a beam restrained at the left end and supported by a special device (a rotational elastic restraint plus a Q-apparatus) at the right end. The numerical analysis reveals that the critical velocity of the fluid depends on the governing parameters of the problem such as the ratio of the fluid mass to the pipe mass per unit length and the rotational elastic constant at the right end 相似文献