全文获取类型
收费全文 | 3892篇 |
免费 | 518篇 |
国内免费 | 263篇 |
专业分类
化学 | 966篇 |
晶体学 | 15篇 |
力学 | 1197篇 |
综合类 | 62篇 |
数学 | 754篇 |
物理学 | 1679篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 54篇 |
2021年 | 61篇 |
2020年 | 72篇 |
2019年 | 74篇 |
2018年 | 74篇 |
2017年 | 88篇 |
2016年 | 91篇 |
2015年 | 84篇 |
2014年 | 143篇 |
2013年 | 273篇 |
2012年 | 160篇 |
2011年 | 200篇 |
2010年 | 182篇 |
2009年 | 243篇 |
2008年 | 256篇 |
2007年 | 280篇 |
2006年 | 241篇 |
2005年 | 218篇 |
2004年 | 208篇 |
2003年 | 217篇 |
2002年 | 179篇 |
2001年 | 154篇 |
2000年 | 136篇 |
1999年 | 116篇 |
1998年 | 134篇 |
1997年 | 113篇 |
1996年 | 106篇 |
1995年 | 69篇 |
1994年 | 81篇 |
1993年 | 57篇 |
1992年 | 56篇 |
1991年 | 37篇 |
1990年 | 34篇 |
1989年 | 22篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 25篇 |
1983年 | 2篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有4673条查询结果,搜索用时 15 毫秒
981.
改进分形模型的图像降噪算法 总被引:1,自引:0,他引:1
利用分形几何中的迭代函数系统理论,针对空间域建立图像分形模型存在相似匹配速度慢的缺点,提出了一种变换域的改进分形模型方法,该方法用频域的搜索匹配代替空间域的搜索匹配,不但域块和区块达到相似匹配的速度更快,而且可以自适应的调整参与计算相似匹配的参数个数.实验结果表明改进的分形模型应用于图像降噪不但可以有效的保护图像的细节和边缘信息,并避免原方法在降噪的同时带来块效应的缺点. 相似文献
982.
Measurement and correlation of volumetric heat transfer coefficients of cellular ceramics 总被引:12,自引:0,他引:12
The volumetric heat transfer coefficients (hv) between cellular ceramics and a stream of air were measured using the single-blow transient experimental technique in conjunction with an inverse analysis. Test specimen made of mullite, YZA, SiC, cordierite and cordierite with LS-2 coating was studied. The number of pores per centimeter (PPC) ranged from 4 to 26 and the specimen thickness ranged from 6 to 12 mm. Based on the experimental data, the volumetric heat transfer coefficients were generalized by developing Nusselt number vs. Reynolds number correlations of the form Nuv=C Rem for the materials studied. The effects of pore length-scale and specimen thickness on the volumetric heat transfer coefficients are presented and discussed. 相似文献
983.
984.
光折变介质的相位共轭波强度的近似表达式 总被引:1,自引:0,他引:1
以光折变介质中非线性耦合波微分方程的一种精确解为基础,对在推导这种精确解过程中起重要作用的一个守恒量进行讨论,通过初等变换,在不同的特殊条件下得到相位共轭波强度的几处近似表达式。与报道的其它近似方法相比,本近似方法不需要建立及求解简化的微分方程因而具有普适,简单的特点。 相似文献
985.
脉冲在时域二次折射率介质中的传播 总被引:3,自引:1,他引:2
从空域与时域的相似性出发,把克尔介质近似为时域二次折射率介质,从而得到了脉冲在该介质中的解析形式,并给出了相应的时域传输矩阵。 相似文献
986.
T.D. Blake J. De Coninck 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):395-402
Using large-scale molecular-dynamic (MD) simulations, we have shown previously that the classical Lucas–Washburn equation commonly employed to describe capillary imbibition and drainage should be modified to include dynamic contact-angle effects. In addition, we have demonstrated how these effects can be accounted for using the molecular-kinetic theory of dynamic wetting. In a further publication, we presented theoretical arguments and experimental evidence that the velocity of wetting depends on the intrinsic wettability of the solid surface in such a way that there exists an optimum contact angle at which the velocity of wetting is a maximum. Here, we combine these ideas to show how the maximum speeds of capillary imbibition and drainage are affected both by the pore wettability and the pressures used to drive capillary displacement. In particular, we introduce the concept of dynamic wetting transitions (DWTs) and discuss how these limit displacement efficiency and can be manipulated by controlling pore wettability. The results of this work may be beneficial in optimising the performance of capillary processes such as those involved in oil recovery. 相似文献
987.
Brahim Amaziane Alain Bourgeat Mariya Goncharenko Leonid Pankratov 《Comptes Rendus Mecanique》2004,332(1):79-84
The aim of this Note is to quantify the change of characteristics of the media of an Excavated Damaged Zone (EDZ) affected by several fractures. For this, we consider Darcy flow through matrix blocks and fractures with permeability of order ε2δθ and 1 respectively. ε is the size of a typical porous block, δ representing the relative size of the fracture and θ is a parameter characterising the permeability ratio. We derive the global behavior from the limit as ε and δ tend to zero. The resulting homogenized equation is of dual-porosity type for θ=2, but it is a simple-porosity model with effective coefficients for θ>2, and there is no flow at the macroscopic level when 0<θ<2. To cite this article: B. Amaziane et al., C. R. Mecanique 332 (2004). 相似文献
988.
研究分形插值函数的矩量积分问题.对于一类分形插值函数,给出了它在各阶区间上的(p,q)阶矩量积分的计算公式.此外,考虑含有扰动项的迭代函数系所产生的分形插值函数的矩量,讨论了扰动项对于矩量的影响,给出扰动前后矩量的误差估计式. 相似文献
989.
The non‐linear stability of plane parallel shear flows in an incompressible homogeneous fluid heated from below and saturating a porous medium is studied by the Lyapunov direct method.In the Oberbeck–Boussinesq–Brinkman (OBB) scheme, if the inertial terms are negligible, as it is widely assumed in literature, we find global non‐linear exponential stability (GNES) independent of the Reynolds number R. However, if these terms are retained, we find a restriction on R (depending on the inertial convective coefficient) both for a homogeneous fluid and a mixture heated and salted from below. In the case of a mixture, when the normalized porosity ε is equal to one, the laminar flows are GNES for small R and for heat Rayleigh numbers less than the critical Rayleigh numbers obtained for the motionless state. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
990.