全文获取类型
收费全文 | 10996篇 |
免费 | 1009篇 |
国内免费 | 936篇 |
专业分类
化学 | 2742篇 |
晶体学 | 28篇 |
力学 | 836篇 |
综合类 | 226篇 |
数学 | 6400篇 |
物理学 | 2709篇 |
出版年
2024年 | 22篇 |
2023年 | 146篇 |
2022年 | 173篇 |
2021年 | 227篇 |
2020年 | 286篇 |
2019年 | 292篇 |
2018年 | 262篇 |
2017年 | 334篇 |
2016年 | 428篇 |
2015年 | 275篇 |
2014年 | 517篇 |
2013年 | 970篇 |
2012年 | 477篇 |
2011年 | 657篇 |
2010年 | 608篇 |
2009年 | 674篇 |
2008年 | 693篇 |
2007年 | 718篇 |
2006年 | 618篇 |
2005年 | 579篇 |
2004年 | 498篇 |
2003年 | 486篇 |
2002年 | 442篇 |
2001年 | 360篇 |
2000年 | 321篇 |
1999年 | 278篇 |
1998年 | 259篇 |
1997年 | 212篇 |
1996年 | 184篇 |
1995年 | 150篇 |
1994年 | 116篇 |
1993年 | 107篇 |
1992年 | 91篇 |
1991年 | 89篇 |
1990年 | 48篇 |
1989年 | 51篇 |
1988年 | 40篇 |
1987年 | 26篇 |
1986年 | 32篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
We study the problems of stability and stabilization for Takagi-Sugeno (T-S) fuzzy time-delay systems. First, by constructing a less-redundant Lyapunov-Krasovskii function and introducing a useful inequality, an innovative stability criterion is obtained, which gives a significant improvement on the performance. Compared with the exiting references, our result can use fewer unknown variables and get better results. Furthermore, based on the derived stability criteria, a new stabilization condition is developed, in which the controller gain and the maximum allowable delay bound can be obtained simultaneously. The conditions are all derived in the form of linear matrix inequality, which are easy to verify. Finally, numerical examples are given to show the effectiveness of the proposed methods. 相似文献
212.
213.
Sanghyun AhnJaewon Choi Gyuchang LimKil Young Cha Sooyong KimKyungsik Kim 《Physica A》2011,390(11):1991-2001
We investigate the structure of the cross-correlation in the Korean stock market. We analyze daily cross-correlations between price fluctuations of 586 different Korean stock entities for the 6-year time period from 2003 to 2008. The main purpose is to investigate the structure of group correlation and its stability by undressing the market-wide effect using the Markowitz multi-factor model and the network-based approach. We find the explicit list of significant firms in the few largest eigenvectors from the undressed correlation matrix. We also observe that each contributor is involved in the same business sectors. The structure of group correlation can not remain constant during each 1-year time period with different starting points, whereas only two largest eigenvectors are stable for 6 years 8-9 eigenvectors remain stable for half-year. The structure of group correlation in the Korean financial market is disturbed during a sufficiently short time period even though the group correlation exists as an ensemble for the 6-year time period in the evolution of the system. We verify the structure of group correlation by applying a network-based approach. In addition, we examine relations between market capitalization and businesses. The Korean stock market shows a different behavior compared to mature markets, implying that the KOSPI is a target for short-positioned investors. 相似文献
214.
Sridhar S. KannurpattiMichael A. Motes Bart RypmaBharat B. Biswal 《Magnetic resonance imaging》2011,29(1):140-146
Block and event-related stimulus designs are typically used in fMRI studies depending on the importance of detection power or estimation efficiency. The extent of vascular contribution to variability in block and event-related fMRI-BOLD response is not known. With scaling, the extent of vascular variability in the fMRI-BOLD response during block and event-related design tasks was investigated. Blood oxygen level-dependent (BOLD) contrast data from healthy volunteers performing a block design motor task and an event-related memory task requiring performance of a motor response were analyzed from the regions of interest (ROIs) surrounding the primary and supplementary motor cortices. Average BOLD signal change was significantly larger during the block design compared to the event-related design. In each subject, BOLD signal change across voxels in the ROIs had higher variation during the block design task compared to the event-related design task. Scaling using the resting state fluctuation of amplitude (RSFA) and breath-hold (BH), which minimizes BOLD variation due to vascular origins, reduced the within-subject BOLD variability in every subject during both tasks but significantly reduced BOLD variability across subjects only during the block design task. The strong non-neural source of intra- and intersubject variability of BOLD response during the block design compared to event-related task indicates that study designs optimizing for statistical power through enhancement of the BOLD contrast (for, e.g., block design) can be affected by enhancement of non-neural sources of BOLD variability. 相似文献
215.
In this paper, the synthesis and implementation of three-qubit SWAP gate is discussed. The three-qubit SWAP gate can be decomposed into product of 2 two-qubit SWAP gates, and it can be realized by 6 CNOT gates. Research illustrated that although the result is very simple, the current methods of matrix decomposition for multi-qubit gate can not get that. Then the implementation of three-qubit SWAP gate in the three spin system with Ising interaction is investigated and the sequence of control pulse and drift process to implement the gate is given. It needs 23 control pulses and 12 drift processes. Since the interaction can not be switched on and off at will, the realization of three-qubit SWAP gate in specific quantum system also can not simply come down to 2 two-qubit SWAP gates. 相似文献
216.
榕树型互连网络及光学实现 总被引:1,自引:0,他引:1
讨论了一种用扭曲向列相液晶器件和偏振分光棱镜实现光学榕树上互连网络的结构,这种结构具有直线式传输、无错位、无缩放,并能够实现模块化和集成化的优点。 相似文献
217.
218.
Shudong Wu Zhi HuangYuan Liu Qiufeng HuangWang Guo Yongge Cao 《Superlattices and Microstructures》2009
We solve analytically the Schrödinger equation taking into account the shape changes of GaInAs/GaAs quantum wells due to indium segregation during the MBE growth by using transfer matrix method. The indium compositional profiles of the quantum wells are provided using the phenomenological model. The fundamental transition energy, binding energy and oscillator strength of excitons as a function of indium segregation coefficient R and well width are studied. For narrow wells (less than 40 ML), the exciton binding energy and oscillator strength decrease, but for wide wells (larger than 40 ML), increase with increasing the segregation coefficient R. It is shown that indium segregation degrades the optical properties and results in a blue-shift of exciton transition energy in GaInAs/GaAs quantum wells. 相似文献
219.
Andriy Romanyuk Viktor Melnik Yaroslav Olikh Johannes Biskupek Ute Kaiser Martin Feneberg Klaus Thonke Peter Oelhafen 《Journal of luminescence》2010,130(1):87-91
Silicon clusters embedded in a silicon dioxide matrix were prepared by ultrasound-assisted implantation resulting in a modified concentration of suboxide states as revealed by high-resolution photoelectron spectroscopy. It is suggested that ultrasound treatment results in formation of different interface structure between silicon cluster and silicon dioxide matrix which is characterized by a distinctly reduced concentration of the suboxide states. It is observed that photoluminescence properties are strongly correlated with the concentration of the suboxide states thereby providing an evidence that besides a quantum confinement effect a closer look at the chemical composition of the nc-Si/SiO2 system is important. 相似文献
220.
Cornelis van der Mee Pietro Contu Paolo Pintus 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(1):214-225
In this article we present a method to determine the band spectrum, band gaps, and discrete energy levels, of a one-dimensional photonic crystal with localized impurities. For one-dimensional crystals with piecewise constant refractive indices we develop an algorithm to recover the refractive index distribution from the period map. Finally, we derive the relationship between the period map and the scattering matrix containing the information on the localized modes. 相似文献