全文获取类型
收费全文 | 7984篇 |
免费 | 828篇 |
国内免费 | 569篇 |
专业分类
化学 | 1174篇 |
晶体学 | 24篇 |
力学 | 1338篇 |
综合类 | 141篇 |
数学 | 5031篇 |
物理学 | 1673篇 |
出版年
2024年 | 10篇 |
2023年 | 85篇 |
2022年 | 127篇 |
2021年 | 152篇 |
2020年 | 203篇 |
2019年 | 234篇 |
2018年 | 241篇 |
2017年 | 265篇 |
2016年 | 297篇 |
2015年 | 271篇 |
2014年 | 405篇 |
2013年 | 747篇 |
2012年 | 371篇 |
2011年 | 497篇 |
2010年 | 415篇 |
2009年 | 484篇 |
2008年 | 531篇 |
2007年 | 544篇 |
2006年 | 432篇 |
2005年 | 371篇 |
2004年 | 348篇 |
2003年 | 315篇 |
2002年 | 272篇 |
2001年 | 215篇 |
2000年 | 216篇 |
1999年 | 205篇 |
1998年 | 167篇 |
1997年 | 137篇 |
1996年 | 142篇 |
1995年 | 93篇 |
1994年 | 107篇 |
1993年 | 64篇 |
1992年 | 63篇 |
1991年 | 57篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 33篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 25篇 |
1984年 | 36篇 |
1983年 | 9篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有9381条查询结果,搜索用时 15 毫秒
1.
Patrick Imrie Jianyong Jin 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):149-174
4D printing is an exciting branch of additive manufacturing. It relies on established 3D printing techniques to fabricate objects in much the same way. However, structures which fall into the 4D printed category have the ability to change with time, hence the “extra dimension.” The common perception of 4D printed objects is that of macroscopic single-material structures limited to point-to-point shape change only, in response to either heat or water. However, in the area of polymer 4D printing, recent advancements challenge this understanding. A host of new polymeric materials have been designed which display a variety of wonderful effects brought about by unconventional stimuli, and advanced additive manufacturing techniques have been developed to accommodate them. As a result, the horizons of polymer 4D printing have been broadened beyond what was initially thought possible. In this review, we showcase the many studies which evolve the very definition of polymer 4D printing, and reveal emerging areas of research integral to its advancement. 相似文献
2.
The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献
3.
Florence Drui Emmanuel Franck Philippe Helluy Laurent Navoret 《Comptes Rendus Mecanique》2019,347(3):259-269
The over-relaxation approach is an alternative to the Jin–Xin relaxation method in order to apply the equilibrium source term in a more precise way. This is also a key ingredient of the lattice Boltzmann method for achieving second-order accuracy. In this work, we provide an analysis of the over-relaxation kinetic scheme. We compute its equivalent equation, which is particularly useful for devising stable boundary conditions for the hidden kinetic variables. 相似文献
4.
Vsevolod Khikhlovskyi Albert J. J. M. van Breemen Jasper J. Michels René A. J. Janssen Gerwin H. Gelinck Martijn Kemerink 《Journal of Polymer Science.Polymer Physics》2015,53(17):1231-1237
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237 相似文献
5.
6.
本文给出了C^n中子空间之间最大和最小主角在矩阵逼近,投影算子的扰动分析,群逆以及Oraxin逆的扰动估计,条件数理论,Bott-Duffin系统扰动分析中一些应用。 相似文献
7.
本文给出了混合型多项式Hammerstein积分方程正解的迭代求法,并将所得结果应用到二阶非线性常微分方程的边值问题 相似文献
8.
利用射影几何方法在小缺陷码中,NMDS码是链条件码;给出k维NμMDS(0μk-2)码满足链条件的一个充要条件与一些易判断的充分条件. 相似文献
9.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献
10.
就一般非完整约束系统,从约束方程满足的变分恒等式出发,利用增广位形流形上的向量场定义三类非自由变分,即非完整变分:vakonomic变分、Hlder变分、Suslov变分,并讨论它们之间的关系以及它们成为自由变分的充要条件.利用非完整变分以及相应的积分变分原理建立两类动力学方程:vakonomic方程和Routh方程或Chaplygin方程.通过vakonomic方程分别与Routh方程和Chaplygin方程比较,得到它们具有共同解的两类充分必要条件.这些条件并不是约束的可积性条件.
关键词:
非完整约束
非完整变分
Chetaev条件
vakonomic动力学 相似文献