全文获取类型
收费全文 | 29212篇 |
免费 | 3621篇 |
国内免费 | 1685篇 |
专业分类
化学 | 4893篇 |
晶体学 | 68篇 |
力学 | 4784篇 |
综合类 | 231篇 |
数学 | 14711篇 |
物理学 | 9831篇 |
出版年
2024年 | 62篇 |
2023年 | 429篇 |
2022年 | 383篇 |
2021年 | 541篇 |
2020年 | 840篇 |
2019年 | 746篇 |
2018年 | 759篇 |
2017年 | 809篇 |
2016年 | 819篇 |
2015年 | 752篇 |
2014年 | 1339篇 |
2013年 | 2555篇 |
2012年 | 1379篇 |
2011年 | 1887篇 |
2010年 | 1537篇 |
2009年 | 1940篇 |
2008年 | 1888篇 |
2007年 | 1876篇 |
2006年 | 1672篇 |
2005年 | 1475篇 |
2004年 | 1346篇 |
2003年 | 1232篇 |
2002年 | 1065篇 |
2001年 | 918篇 |
2000年 | 864篇 |
1999年 | 745篇 |
1998年 | 681篇 |
1997年 | 631篇 |
1996年 | 483篇 |
1995年 | 377篇 |
1994年 | 318篇 |
1993年 | 293篇 |
1992年 | 233篇 |
1991年 | 216篇 |
1990年 | 170篇 |
1989年 | 149篇 |
1988年 | 119篇 |
1987年 | 108篇 |
1986年 | 70篇 |
1985年 | 100篇 |
1984年 | 128篇 |
1983年 | 67篇 |
1982年 | 100篇 |
1981年 | 84篇 |
1980年 | 69篇 |
1979年 | 68篇 |
1978年 | 60篇 |
1977年 | 39篇 |
1976年 | 30篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
本文考虑一带有人工粘性的二维定常等熵无旋平面流方程组的初-边值问题. 在一定的假设下,我们证明其驻波解是渐近稳定的. 相似文献
102.
103.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
104.
周焕松 《数学物理学报(B辑英文版)》1998,(2)
1IntroductionIntillspaper,weare(follccrlledwitlltileexistellccofPositly(tsollltiollsoftilefollowillgnonhonlogelleousellipticProblclll:whereg(x)EL'(R'),g(:v)Z0alldg(x)t0,f(x,t)=h(x,t).hi=withb>0,h(x,t)EC(R=xR,R)alldtilefollowing(CI)-(C3)11old:(CI)sliphillM0.linljfl- x,h(T,t)(t--if-=011llif'orllllyforxeR2.hill}t:l-:,t)(axle(~ltJ')= lx,11lliforllllyl'Ora:6RZ.ltl~la(C3)ThereexistM>0,aE(0,1]sucllthatFOllowing[1,5],wesaythatf(x,t)=h(x,f… 相似文献
105.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
106.
讨论了浅海中波导的声波散射问题,我们将该问题归结为一个第一类边界积分方程,利用正同化方法求解,并证明了该方法的收敛性,数值例子表明了该方法的简单与有效性。 相似文献
107.
An analytic and numerical study of the behavior of the linear nonhomogeneous wave equation of the form ε2utt = Δu + tf with high wave speed (ε 1) is carried out. This study was initially motivated by meteorological observations which have indicated the presence of large spatial scale gravity waves in the neighborhood of a number of summer and winter storms, mainly from visible images of ripples in clouds in satellite photos. There is a question as to whether the presence of these waves is caused by the nearby storms. Since the linear wave equation is an approximation to the full system describing pressure waves in the atmosphere, yet is considerably more tractable, we have chosen to analyze the behavior of the linear nonhomogeneous wave equation with high wave speed. The analysis is shown to be valid in one, two, and three space dimensions. Partly because of the high wave speed, the solution is known to consist of behavior which changes on two different time scales, one rapid and one slow. Additionally, because of the presence of the nonhomogeneous forcing term tf, we show that there is a component of the solution which will vary only on a very large spatial scale. Since even the linearized wave equation can give rise to persistent large spatial scale waves under the right conditions, the implication is that certain storms could be responsible for the generation of large-scale waves. Numerical simulations in one and two dimensions confirm analytic results. 相似文献
108.
109.
Dielectric effect on the rf characteristics of a helical groove travelling wave tube 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT) is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain. 相似文献
110.
I. Ogawa Y. Miyake T. Idehara S. Sabchevski 《International Journal of Infrared and Millimeter Waves》2002,23(1):1-19
A novel focusing mirror based on the shifting of the beam phase according to the Gaussian beam optics enabled us to realize a focusing elements with different focal lengths in different directions and to convert the gyrotron output into a Gaussian-like beam. In this paper, we compare the quality of beams produced by the new system (which includes novel mirrors) and a conventional system consisting of a quasi-optical antenna, an ellipsoidal mirror and two parabolic cylinder mirrors. 相似文献