全文获取类型
收费全文 | 662篇 |
免费 | 62篇 |
国内免费 | 139篇 |
专业分类
化学 | 341篇 |
晶体学 | 20篇 |
力学 | 44篇 |
综合类 | 23篇 |
数学 | 103篇 |
物理学 | 332篇 |
出版年
2023年 | 4篇 |
2022年 | 18篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 22篇 |
2018年 | 20篇 |
2017年 | 33篇 |
2016年 | 18篇 |
2015年 | 29篇 |
2014年 | 33篇 |
2013年 | 30篇 |
2012年 | 37篇 |
2011年 | 41篇 |
2010年 | 51篇 |
2009年 | 43篇 |
2008年 | 53篇 |
2007年 | 47篇 |
2006年 | 54篇 |
2005年 | 45篇 |
2004年 | 33篇 |
2003年 | 26篇 |
2002年 | 27篇 |
2001年 | 30篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1988年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1972年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有863条查询结果,搜索用时 140 毫秒
51.
用脉冲微反装置评价了正丁烷和异丁烷在氢型和锌改性的纳米ZSM-5催化剂上的反应活性和芳构化选择性.结果表明,在550℃下,异丁烷在氢型和不同锌负载量的纳米ZSM-5催化剂上的转化率都远高于正丁烷,但其芳构化选择性低于正丁烷.脱甲基活化是异丁烷和正丁烷的重要活化方式,也是影响其芳构化选择性的主要因素.锌改性在提高异丁烷和正丁烷转化率的同时,也促进了正丁烷和异丁烷的脱甲基活化.在混合丁烷进料反应的情况下,正丁烷和异丁烷的转化率与其单独进料时十分接近,这说明正丁烷和异丁烷共存时不会发生明显的竞争吸附和反应.纳米ZSM-5因晶粒度小,孔道短和微孔扩散阻力低而有利于异丁烷转化. 相似文献
52.
53.
54.
研究了漂浮基空间机器人捕获非合作航天器过程对系统产生的冲击效应及其后联合体系统镇定运动的控制问题。为此,利用拉格朗日方法及牛顿-欧拉法分别获得了捕获前空间机器人及目标航天器的动力学模型;结合动量守恒定律、系统运动几何关系及力的传递规律,分析了捕获过程相互碰撞所产生的冲击效应,建立了捕获完成后两者联合体的系统动力学模型。在此基础上,针对同时存在不确定参数及外部扰动的联合体系统,设计了基于无源性理论的镇定运动神经网络H_∞鲁棒控制算法。本文提出的基于无源性理论设计的鲁棒控制算法具有良好的动态特性及较强的鲁棒性,可快速完成系统的镇定控制,实现轨迹的精确跟踪。系统数值模拟仿真验证了本文控制方案的正确性。 相似文献
55.
Transport of a Brownian particle moving in a periodic potential is investigated in the presence of an asymmetric unbiased external force. The asymmetry of the external force and the asymmetry of the potential are the two ways of inducing a net current. It is found that the competition of the spatial asymmetry of potential with the temporal asymmetry of the external force leads to the phenomena like current reversal. The competition between the two opposite driving factors is a necessary but not a sufficient condition for current reversals. 相似文献
56.
The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased in the diffusive-convective region. The growth rate of branch had the same change trends as the arm's. Based on the EPMA-EDS data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface during the growth process. 相似文献
57.
58.
Yu. M. Nikolaenko A. B. Mukhin V. A. Chaika V. V. Burkhovetskii 《Technical Physics》2010,55(8):1189-1192
The design of an additional thermal and electric shield intended to improve the quality (crystal lattice, thickness uniformity)
of deposited films is described. This shield makes it possible to use a more powerful heat source to heat a substrate and
to optimize epitaxial film growth. Simultaneously, the shield plays the role of an additional anode, which changes the plasma
dynamics in the working space and homogenizes the radial distribution of the neutral particle flux density from a target to
a substrate. 相似文献
59.
S. Issing F. Fuchs C. Ziereis E. Batke A. Pimenov Y. Vu. Ivanov A. A. Mukhin J. Geurts 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,73(3):353-360
A systematic and detailed study of Raman and infrared active lattice excitations in the orthorhombic multiferroic manganite
Eu1−xYxMnO3 (0 ≤ x ≤ 0.5) was carried out at room temperature. For the infrared active phonon modes the eigenfrequencies, damping constants
and oscillator strengths were analyzed by Fourier-Transform Infrared Spectroscopy in the far infrared frequency range. For
the Raman active phonons the same analysis for eigenfrequencies and damping constants was carried out using Raman spectroscopy
in the range from 200 cm−1 to 700 cm−1. Y doping leads to mode-dependent phonon frequency shifts up to 8%. These are interpreted in terms of the interplay between
the decrease of the reduced ion masses and the axis-dependent change of bond lengths. The latter leads to a bond softening
along the a-axis and a strengthening along the c-axis, for which the highest phonon frequency increase is observed. The application
of both Raman and Infrared Spectroscopy gives us sensitivity not only to symmetry properties via the selection rules but also
to the involvement of different ion types within the unit cell. It is clearly shown that the disorder induced effects are
of minor impact on the lattice properties and solely detected on the rare earth sites. The MnO6 octahedra remain unaffected and show the same behavior as in the stochiometric RMnO3 making Eu1−xYxMnO3 an excellent model system for a quasi-continuous fine-tuning of the lattice parameters relevant for the appearance of multiferroicity. 相似文献
60.
A. Ya. Bunicheva S. I. Mukhin N. V. Sosnin A. P. Favorskii A. B. Khrulenko 《Computational Mathematics and Modeling》2002,13(4):382-412
The present study discusses some basic issues of mathematical modeling in medicine and describes examples of specific results of analytical and numerical investigations in haemodynamics. It briefly describes a method for constructing exact solutions of the linearized equations of haemodynamics on a graph, an analysis of these solutions, and a particular application of the proposed theory for solving practical medical problems. A number of nonspecific aortoarteritis syndromes are simulated. Examples of mathematical modeling of blood flow in the systemic circulatory circuit under the action of a periodically contracting heart are presented. These examples reproduce some of the main physiological regularities of the circulatory system as a whole. One of the applications of mathematical modeling in haemodynamics includes the stealing of cerebral blood supply during a temporary occlusion of the subclavian artery. 相似文献