全文获取类型
收费全文 | 8061篇 |
免费 | 916篇 |
国内免费 | 486篇 |
专业分类
化学 | 1006篇 |
晶体学 | 14篇 |
力学 | 1058篇 |
综合类 | 154篇 |
数学 | 4221篇 |
物理学 | 3010篇 |
出版年
2024年 | 9篇 |
2023年 | 97篇 |
2022年 | 146篇 |
2021年 | 170篇 |
2020年 | 219篇 |
2019年 | 188篇 |
2018年 | 195篇 |
2017年 | 324篇 |
2016年 | 326篇 |
2015年 | 222篇 |
2014年 | 481篇 |
2013年 | 583篇 |
2012年 | 508篇 |
2011年 | 456篇 |
2010年 | 356篇 |
2009年 | 458篇 |
2008年 | 484篇 |
2007年 | 512篇 |
2006年 | 473篇 |
2005年 | 398篇 |
2004年 | 322篇 |
2003年 | 358篇 |
2002年 | 307篇 |
2001年 | 291篇 |
2000年 | 245篇 |
1999年 | 218篇 |
1998年 | 188篇 |
1997年 | 167篇 |
1996年 | 136篇 |
1995年 | 117篇 |
1994年 | 81篇 |
1993年 | 68篇 |
1992年 | 54篇 |
1991年 | 40篇 |
1990年 | 33篇 |
1989年 | 25篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 18篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1969年 | 2篇 |
排序方式: 共有9463条查询结果,搜索用时 31 毫秒
141.
Further expansion of optical communication systems depends strongly on the development of cheap component technologies for
functions such as switching, demultiplexing and amplification. Silica-on-silicon is increasingly recognised as the best approach
to low cost integrated optics for such applications, but so far the functionality is limited. The purpose of NODES, a basic
research collaboration sponsored by the European Union under the programme ESPRIT, has been to examine the application of
sol-gel to a highly functional silica-on-silicon technology. In particular, the project has investigated film processing and
characterisation, rare-earth doping for amplification, and semiconductor nanocrystallite doping for nonlinear functions. This
paper presents the background and context to this work, summarises the technical results obtained, and discusses requirements
and challenges for successful application of sol-gel in photonics. 相似文献
142.
Robert M. Ianniello 《Mikrochimica acta》1989,98(1-3):1-6
A direct voltammetric method for the rapid determination of butylated hydroxytoluene has been developed. The procedure utilizes a hydrolyzed cellulose acetate film in intimate contact with a glassy carbon electrode and square wave voltammetry. The coated electrode prevents passivation due to adsorption of polymeric oxidation products by way of a size exclusion principle. BHT solutions containing lipid-like surfactants can be analyzed without the need for frequent resurfacing of the electrode. 相似文献
143.
许多物理现象可以在数学上描述为受曲率驱动的自由界面运动,例如薄膜和泡沫的演变、晶体生长,等等.这些薄膜和界面的运动常依赖于其表面曲率,从而可以用相应的曲率流来描述,其相关自由界面问题的数值计算和误差分析一直是计算数学领域中的难点.参数化有限元法是曲率流的一类有效计算方法,已经能够成功模拟一些曲面在几类基本的曲率流下的演化过程.本文重点讨论曲率流的参数化有限元逼近,它的产生、发展和当前的一些挑战. 相似文献
144.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
145.
本文研究了无界域上的带有随机初值的复值Ginzburg-Landau方程.首先, 基于解过程的全局适定性, 建立了带有随机初值的Ginzburg-Landau方程的平均随机动力系统.然后, 证明了弱拉回平均随机吸引子的存在唯一性以及随机吸引子的周期性,并将其进一步推广到加权空间L2(?, L2σ(R)). 相似文献
146.
矩阵平方根在数学的许多应用中起着重要的作用.本文研究M-矩阵平方根的计算问题,提出一种计算正则M-矩阵平方根的迭代方法.首先将这个问题转化为M-矩阵代数Riccati方程,进而提出一种有效的方法来求解这个特殊的MARE.理论分析表明,该方法在一定条件下是收敛的.数值实验表明该方法是可行的,且优于二项式迭代法. 相似文献
147.
148.
Xiaojing Xiang 《Annals of the Institute of Statistical Mathematics》1995,47(1):105-117
A necessary condition for the asymptotic normality of the sample quantile estimator isf(Q(p))=F(Q(p))>0, whereQ(p) is thep-th quantile of the distribution functionF(x). In this paper, we estimate a quantile by a kernel quantile estimator when this condition is violated. We have shown that the kernel quantile estimator is asymptotically normal in some nonstandard cases. The optimal convergence rate of the mean squared error for the kernel estimator is obtained with respect to the asymptotically optimal bandwidth. A law of the iterated logarithm is also established.This research was partially supported by the new faculty award from the University of Oregon. 相似文献
149.
Summary The calculation of the effects of temperature and isotopic composition on the energy weighted moments of the dipole oscillator strength distribution of H2 in the random phase approximation to the polarization propagator are reported. It is seen that the effect of isotopic composition is small, while that of temperature is of an order accessible to experiment. We find that all the mean excitation energiesI
, for =–1, 0, 1, decrease with temperature as does the dipole oscillator strength momentS() for >0, while the opposite is true for <0. These effects are interpreted in terms of the bond length dependence of the excitation energies. 相似文献
150.
汪嘉冈 《应用数学学报(英文版)》1994,10(1):59-68
ALAWOFTHEITERATEDLOGARITHMFORPROCESSESWITHINDEPENDENTINCREMENTSWANGJIAGANG(汪嘉冈)(EastChinaUniversityofScience&Technology,Shang... 相似文献