全文获取类型
收费全文 | 1222篇 |
免费 | 180篇 |
国内免费 | 120篇 |
专业分类
化学 | 443篇 |
晶体学 | 13篇 |
力学 | 118篇 |
综合类 | 8篇 |
数学 | 381篇 |
物理学 | 559篇 |
出版年
2024年 | 4篇 |
2023年 | 62篇 |
2022年 | 65篇 |
2021年 | 86篇 |
2020年 | 91篇 |
2019年 | 54篇 |
2018年 | 51篇 |
2017年 | 69篇 |
2016年 | 75篇 |
2015年 | 65篇 |
2014年 | 76篇 |
2013年 | 83篇 |
2012年 | 93篇 |
2011年 | 76篇 |
2010年 | 87篇 |
2009年 | 86篇 |
2008年 | 50篇 |
2007年 | 63篇 |
2006年 | 45篇 |
2005年 | 47篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 35篇 |
2000年 | 13篇 |
1999年 | 36篇 |
1998年 | 27篇 |
1997年 | 11篇 |
1996年 | 3篇 |
1988年 | 2篇 |
1959年 | 1篇 |
排序方式: 共有1522条查询结果,搜索用时 384 毫秒
91.
In this paper, an active set limited BFGS algorithm is proposed for bound constrained optimization. The global convergence will be established under some suitable conditions. Numerical results show that the given method is effective. 相似文献
92.
光漏斗聚光定向传光中央接收太阳能集热系统 总被引:1,自引:0,他引:1
提出了一种新型中央接收式太阳能高温集热系统,介绍了系统的运行原理,分析了系统的热效率影响因素。这个新型的太阳能高温集热系统具有如下特点:可将多个光漏斗和偏光器组成一个太阳能聚光器阵列,每个聚光器都能将低能流密度的太阳光束会聚成高能流密度的平行光束,并由偏光器传送到中央接收器,于是中央接收器可获得很高的太阳光照射能流,转化为热能后将产生很高的温度,从而实现太阳光高温聚能。本系统的中央接收器无需建在高塔上,节省了建设费用,而且所有光漏斗跟踪太阳的方式相同,控制策略简单,定向偏光器的出光方向设定后可以固定不变,因而使整个系统结构简单,技术上易于实现。 相似文献
93.
94.
《Solid State Ionics》2006,177(19-25):1691-1695
Li3InBr6 undergoes a phase transition to a superionic phase at 314 K associated with a steep increase of the conductivity (σ = 4 × 10− 3 Scm− 1 at 330 K). This superionic phase is isomorphous with Li3InCl6 in which a positional disorder at the In3+ site is introduced. A pseudo cubic-close-packing of the bromide ions is formed in this phase. On the other hand, a new superionic phase of LiInBr4 was found above ca 315 K and its structure was confirmed to be a defect spinel. The dynamic properties of the cations in these two superionic phases were investigated by 7Li and 115In NMR spectroscopy. 相似文献
95.
96.
A Complex Mode Method for Wind-Induced Responses of 6-Parameter Practical Viscoelastic Damping Energy Dissipation Structures Based on the Davenport Wind Speed Spectrum北大核心CSCD 下载免费PDF全文
针对六参数实用黏弹性阻尼耗能结构,基于Davenport风速谱系列响应问题进行了系统的研究.首先,利用六参数黏弹性阻尼器的微分型本构关系,建立了耗能结构基于Davenport风速谱激励下的运动方程;然后,运用复模态法将耗能结构的运动方程由二阶微分方程转化为一阶方程,获得了耗能结构系统对风振激励响应的频域解和功率谱密度函数表达式;最后,利用数学恒等式,基于随机振动理论获得了耗能结构系统在Davenport风速谱激励下的响应和阻尼器受力的解析解.该文方法不仅考虑了结构系统在风振激励作用下全振型展开的结果,表达式较现有结果更为简便,效率及精度更高,且适用于非经典阻尼结构. 相似文献
97.
This article is concerned with solving the high order Stein tensor equation arising in control theory. The conjugate gradient squared (CGS) method and the biconjugate gradient stabilized (BiCGSTAB) method are attractive methods for solving linear systems. Compared with the large-scale matrix equation, the equivalent tensor equation needs less storage space and computational costs. Therefore, we present the tensor formats of CGS and BiCGSTAB methods for solving high order Stein tensor equations. Moreover, a nearest Kronecker product preconditioner is given and the preconditioned tensor format methods are studied. Finally, the feasibility and effectiveness of the new methods are verified by some numerical examples. 相似文献
98.
入射声波激励下非均匀流体介质内部散射声场的重建方法对超声层析成像具有重要意义。以往采用矩量法求解,但该方法全域离散形成的复数满秩矩阵规模随着分辨率与计算精度的提高而急剧增大,对算力具有很高的要求,一定程度上限制了其在实际中的应用。为克服上述缺陷,本文以逐层离散、逐层计算为核心思想,以声散射基本公式与近场声全息理论为基础,推导出逐层计算非均匀流体介质内部散射声场的理论公式并给出对应的几何离散模型。为验证该方法的可行性,以矩量法为参照,对同样的介质模型进行介质内部声场重构仿真。结果表明,逐层算法不仅可以有效地重建非均匀流体介质内部散射声场,且大幅度减小了求解规模。 相似文献
99.
《Fluid Dynamics Research》2007,39(7):526-551
A review is made of a two-point closure approximation called Lagrangian renormalized approximation (LRA), which is derived by a simple truncation of systematic Lagrangian renormalized expansions and is free from any ad hoc adjusting parameters or quantities. Emphasis is given to three key ideas: (i) representative, (ii) mapping and (iii) renormalized expansion underlying the LRA. The nature of the method of the expansion is explained by simple models, and general properties of the expansion as well as the truncated approximation are discussed in a general framework. A brief survey of the consequences of the LRA applied to three- and two-dimensional turbulences and passive scalar fields convected by turbulence is also presented. 相似文献
100.
Lu Zhixing Wang Xuyue Yu Shouwen Feng Xiqiao 《Acta Mechanica Solida Sinica》2007,20(2):103-109
The effects of dislocation configuration,crack blunting and free surfaces on the triggering load of dislocation sources in the vicinity of a crack or a wedge tip subjected to a tensile load in the far field are investigated.An appropriate triggering criterion for dislocation sources is proposed by considering the configurational forces acting on each dislocation.The triggering behaviors of dislocation sources near the tips of a crack and a wedge are compared.It is also found that the blunting of crack tip and the presence of free surfaces near the crack or the wedge have considerable influences on the triggering load of dislocation sources.This study might be of significance to gaining a deeper understanding of the brittle-to-ductile transition of materials. 相似文献