全文获取类型
收费全文 | 86433篇 |
免费 | 17160篇 |
国内免费 | 24601篇 |
专业分类
化学 | 62692篇 |
晶体学 | 2999篇 |
力学 | 6514篇 |
综合类 | 2468篇 |
数学 | 12853篇 |
物理学 | 40668篇 |
出版年
2024年 | 263篇 |
2023年 | 1194篇 |
2022年 | 3164篇 |
2021年 | 3211篇 |
2020年 | 3274篇 |
2019年 | 3233篇 |
2018年 | 2966篇 |
2017年 | 3815篇 |
2016年 | 3481篇 |
2015年 | 4528篇 |
2014年 | 5568篇 |
2013年 | 7065篇 |
2012年 | 7565篇 |
2011年 | 7947篇 |
2010年 | 7110篇 |
2009年 | 7413篇 |
2008年 | 8119篇 |
2007年 | 7125篇 |
2006年 | 6912篇 |
2005年 | 5720篇 |
2004年 | 4348篇 |
2003年 | 3311篇 |
2002年 | 3233篇 |
2001年 | 3155篇 |
2000年 | 3117篇 |
1999年 | 1989篇 |
1998年 | 1146篇 |
1997年 | 943篇 |
1996年 | 878篇 |
1995年 | 765篇 |
1994年 | 789篇 |
1993年 | 697篇 |
1992年 | 652篇 |
1991年 | 445篇 |
1990年 | 428篇 |
1989年 | 395篇 |
1988年 | 369篇 |
1987年 | 295篇 |
1986年 | 284篇 |
1985年 | 194篇 |
1984年 | 175篇 |
1983年 | 161篇 |
1982年 | 117篇 |
1981年 | 100篇 |
1980年 | 86篇 |
1979年 | 106篇 |
1978年 | 30篇 |
1977年 | 30篇 |
1974年 | 18篇 |
1965年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
ZHONG Hui WAN Mingxi JIANG Yifeng WANG Supin 《声学学报:英文版》2006,25(2):104-115
The present study was to investigate the differential imaging method for detecting HIFU (High Intensity Focused Ultrasound)-induced lesions and the estimation of variation of attenuation for lesion evaluation with log spectral difference algorithm. Experiment results of bovine muscle and liver in vitro were acquired. Several algorithms for lesion detection - Absolute Difference (AD), Sum Absolute Differences (SAD) and Sum Squared Differences (SSD) - were analyzed with several window sizes and threshold values. Then three attenuation parameters were compared to evaluate the degree of tissue damage. It was found that variation of the mean attenuation △α was an effective parameter to evaluate lesions. 相似文献
12.
13.
本文主要研究的是相函数为齐次椭圆多项式的自由高阶Schrodinger方程.通过相函数等值面的几何性质,得到了解算子的Strichartz加权估计和极大算子加权估计. 相似文献
14.
15.
16.
1 INTRODUCTION Carbon nanotubes have many potential applica- tions due to their unique structures and properties[1~4]. Physicists have been studying their electrical, me- chanical and other properties since their discove- ries[5, 6]. Recently, chemists are interested in carbon nanotubes because their properties can be altered by chemical functionalization[7~14], and these functiona- lized nanotubes can undergo further chemical trea- tment. So the potential application range of such na- … 相似文献
17.
This paper undertakes a systematic treatment of the low regularity local wellposedness and ill-posedness theory in Hs andHs for semilinear wave equations with polynomial nonlinearity in u and (e)u. This ill-posed result concerns the focusing type equations with nonlinearity on u and (e)tu. 相似文献
18.
Inspired by the recent work [HHM03], we prove two stability results for compact Riemannian manifolds with nonzero parallel spinors. Our first result says that Ricci flat metrics which also admit nonzero parallel spinors are stable (in the direction of changes in conformal structures) as the critical points of the total scalar curvature functional. Our second result, which is a local version of the first one, shows that any metric of positive scalar curvature cannot lie too close to a metric with nonzero parallel spinor. We also prove a rigidity result for special holonomy metrics. In the case of SU(m) holonomy, the rigidity result implies that scalar flat deformations of Calabi-Yau metric must be Calabi-Yau. Finally we explore the connection with a positive mass theorem of [D03], which presents another approach to proving these stability and rigidity results. Dedicated to Jeff Cheeger for his sixtieth birthday 相似文献
19.
20.