全文获取类型
收费全文 | 12970篇 |
免费 | 1368篇 |
国内免费 | 323篇 |
专业分类
化学 | 1162篇 |
晶体学 | 12篇 |
力学 | 241篇 |
综合类 | 188篇 |
数学 | 2457篇 |
物理学 | 1623篇 |
无线电 | 8978篇 |
出版年
2024年 | 25篇 |
2023年 | 126篇 |
2022年 | 303篇 |
2021年 | 501篇 |
2020年 | 446篇 |
2019年 | 323篇 |
2018年 | 307篇 |
2017年 | 512篇 |
2016年 | 595篇 |
2015年 | 629篇 |
2014年 | 1057篇 |
2013年 | 1014篇 |
2012年 | 968篇 |
2011年 | 963篇 |
2010年 | 614篇 |
2009年 | 601篇 |
2008年 | 746篇 |
2007年 | 798篇 |
2006年 | 654篇 |
2005年 | 604篇 |
2004年 | 537篇 |
2003年 | 455篇 |
2002年 | 308篇 |
2001年 | 269篇 |
2000年 | 231篇 |
1999年 | 164篇 |
1998年 | 136篇 |
1997年 | 108篇 |
1996年 | 109篇 |
1995年 | 110篇 |
1994年 | 72篇 |
1993年 | 63篇 |
1992年 | 52篇 |
1991年 | 42篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
841.
Experimental results of fluid multiphase equilibria occurring in ternary mixtures of near-critical carbon dioxide, certain n-alkanols and tetradecane are presented. The following n-alkanols were used in this investigation: decanol, octanol, heptanol, hexanol and pentanol. In the ternary systems with decanol, octanol or heptanol a closed loop liquid-vapor two-phase region in the three-phase surface liquid-liquid-vapor was found. As far as the ternary system with decanol is concerned, this phenomenon is in agreement with an earlier and unexpected finding of Patton et al. (1993). In addition, it was also found in this study that the phase diagrams of the ternary mixtures with hexanol or pentanol as the n-alkanol show further complications. 相似文献
842.
843.
基于概率加权平均的Mel子带特征重建算法 总被引:1,自引:0,他引:1
本文提出基于概率加权平均的Mel子带特征数据重建算法.该算法选择K个最优重建结果的概率加权平均作为被加性噪声掩蔽的语音特征分量的估计.实验结果表明,基于概率加权平均的语音特征数据重建算法降低了重建误差,减少了帧间突变现象,增强了Mel子带特征的帧间连续性,从而显著提高了语音识别系统对加性噪声的鲁棒性能. 相似文献
844.
845.
Based on the relationship defining the dependence of the capacity ratio upon the composition of the mobile phase, a simple numerical procedure is proposed for evaluating the heterogeneity parameter and the ratio of molecular sizes of solute and solvent. This procedure is examined by using HPLC data for pesticides chromatographed in isooctane/dichloromethane eluent on Lichrosorb at 291 K. 相似文献
846.
** Email: vutsinas{at}upatras.gr Recently there has been increasing interest in On Line AnalyticalProcessing (OLAP) to satisfy the organizational needs of high-levelinformation delivery and advanced data analysis. The actualapplication of OLAP tools involves the use of various functions,such as the common drilling down and slicing and dicing. Usuallyeach particular OLAP function is comprehensive and intuitive.However, sophisticated use of OLAP tools requires complicatedcombinations of different OLAP functions that are not straight-forwardfor end users or designers. In this paper we attempt to enumerateand formally define OLAP functions by defining a new OLAP modelthat provides a broader view of OLAP. We demonstrate the expressiveadequacy of the new OLAP model with application examples. 相似文献
847.
ZHANG Zhenyue & ZHA Hongyuan Department of Mathematics Zhejiang University Yuquan Campus Hangzhou China Department of Computer Science Engineering The Pennsylvania State University University Park PA U.S.A. 《中国科学A辑(英文版)》2004,47(6):908-920
We present our recent work on both linear and nonlinear data reduction methods and algorithms: for the linear case we discuss results on structure analysis of SVD of column-partitioned matrices and sparse low-rank approximation; for the nonlinear case we investigate methods for nonlinear dimensionality reduction and manifold learning. The problems we address have attracted great deal of interest in data mining and machine learning. 相似文献
848.
A detailed study of abstract semilinear evolution equations of the form is undertaken, where generates an analytic semigroup and is a Banach space valued measure depending on the solution. Then it is shown that the general theorems apply to a variety of semilinear parabolic boundary value problems involving measures in the interior and on the boundary of the domain. These results extend far beyond the known results in this field. A particularly new feature is the fact that the measures may depend nonlinearly and possibly nonlocally on the solution.
849.
The topological analysis of grids of data is used for determination of surfaces or volumes around maxima. The volumes are then related to chemical information such as atoms or bonds, and can be used for integration of local properties such as electronic population. The problem of global connectivity is reversed into the question of local connectivity yielding a linear scaling partition algorithm. Two packages are developed for a very fast analysis and partition of 2D or 3D grids of data, applications being made to C2H2, C2H4, C6H6, H2CO, and H2CS molecules using the Atoms in Molecule (AIM) or Electron Localization Function (ELF). 相似文献
850.
Monica Finsrud Mats E. Høvin Tor S. Lande 《Analog Integrated Circuits and Signal Processing》2003,36(1-2):21-29
MASH delta-sigma () modulators consist of a cascade of several lower order single-loop modulators. In an ideal cascade, the quantization error from all but the last stage are digitally canceled. The drawback with a cascaded design is the requirement of precise matching of contributions from different quantizers to cancel lower order quantization noise from intermediate delta-sigma stages. This paper presents a new, adaptive improvement to the residue coupled MASH delta sigma modulator. The adaptive corrections significantly reduce the sensitivity to analog imperfections. The result is a simple MASH delta-sigma modulator with high precision. Simulations of a 1-1 MASH circuit structure with errors and corrections are included to confirm the theory. 相似文献