全文获取类型
收费全文 | 3864篇 |
免费 | 655篇 |
国内免费 | 421篇 |
专业分类
化学 | 2362篇 |
晶体学 | 37篇 |
力学 | 163篇 |
综合类 | 17篇 |
数学 | 296篇 |
物理学 | 1016篇 |
无线电 | 1049篇 |
出版年
2024年 | 22篇 |
2023年 | 117篇 |
2022年 | 156篇 |
2021年 | 202篇 |
2020年 | 204篇 |
2019年 | 197篇 |
2018年 | 167篇 |
2017年 | 150篇 |
2016年 | 229篇 |
2015年 | 245篇 |
2014年 | 237篇 |
2013年 | 322篇 |
2012年 | 322篇 |
2011年 | 330篇 |
2010年 | 233篇 |
2009年 | 203篇 |
2008年 | 278篇 |
2007年 | 203篇 |
2006年 | 182篇 |
2005年 | 133篇 |
2004年 | 114篇 |
2003年 | 95篇 |
2002年 | 103篇 |
2001年 | 65篇 |
2000年 | 48篇 |
1999年 | 64篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 37篇 |
1995年 | 31篇 |
1994年 | 38篇 |
1993年 | 23篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4940条查询结果,搜索用时 15 毫秒
81.
Biranje Santosh Shivaji Sun Jianzhong Shi Yifei Yu Sujie Jiao Haixin Zhang Meng Wang Qianqian Wang Jin Liu Jun 《Cellulose (London, England)》2021,28(14):8899-8937
Cellulose - Excessive hemorrhage is a leading cause of death to trauma patients, especially in combat and civilian accidents. The main priority in the medical treatment of trauma patients is to... 相似文献
82.
Prof. Jiao Jiao Wenzheng Nie Tao Yu Fan Yang Prof. Dr. Qian Zhang Feierdaiweisi Aihemaiti Tingjun Yang Xuanyu Liu Jiachen Wang Prof. Dr. Pengfei Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(15):4817-4838
Continuous-flow multi-step synthesis takes the advantages of microchannel flow chemistry and may transform the conventional multi-step organic synthesis by using integrated synthetic systems. To realize the goal, however, innovative chemical methods and techniques are urgently required to meet the significant remaining challenges. In the past few years, by using green reactions, telescoped chemical design, and/or novel in-line separation techniques, major and rapid advancement has been made in this direction. This minireview summarizes the most recent reports (2017–2020) on continuous-flow synthesis of functional molecules. Notably, several complex active pharmaceutical ingredients (APIs) have been prepared by the continuous-flow approach. Key technologies to the successes and remaining challenges are discussed. These results exemplified the feasibility of using modern continuous-flow chemistry for complex synthetic targets, and bode well for the future development of integrated, automated artificial synthetic systems. 相似文献
83.
一种自适应多尺度积阈值的图像去噪算法 总被引:2,自引:0,他引:2
该文提出了平稳小波变换(Stationary Wavelet Transform, SWT )域自适应多尺度积阈值的图像去噪算法(SWT domain Multiscale Products, SWTMP)。与传统的阈值去噪算法不同,该阈值不是直接作用于小波系数,而是作用于小波系数的空间多尺度积。分析了SWT域含噪图像多尺度积的特点,提出了SWT域自适应多尺度积阈值的计算方法。多尺度积强化了图像的重要结构信息,弱化了噪声,在有效去噪的同时更多地保留了图像的边缘和细节。实验结果表明,所提算法对自然图像去噪后的视觉效果和性能指标均好于二进小波域多尺度积阈值(Adaptive Multiscale Products Thresholding, AMPT)去噪方法。 相似文献
84.
85.
Metabolic profiling of new synthetic cannabinoids AMB and 5F‐AMB by human hepatocyte and liver microsome incubations and high‐resolution mass spectrometry 下载免费PDF全文
86.
H. M. Noor ul Huda Khan Asghar Yi Tan Shuang Shi Dachuan Jiang Shiqiang Qin Jiao Liao Shutao Wen Wei Dong Yao Liu 《Applied Physics A: Materials Science & Processing》2014,115(3):753-757
Small amounts of multicrystalline silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the oxygen evaporation behavior during the electron beam melting (EBM) process. The oxygen content level before and after EBM was determined by secondary ion mass spectroscopy. The oxygen content was reduced from 6.177 to 1.629 ppmw when silicon was melted completely at 15 kW with removal efficiency up to 73.6 %. After that, it decreased continually to <0.0517 ppmw when the refining time exceeded 600 s with a removal efficiency of more than 99.08 %. During the melting process, the evaporation rate of silicon is 1.10 × 10?5 kg/s. The loss of silicon could be reduced up to 1.7 % during oxygen removal process to a desirable figure, indicating EBM is an effective method to remove oxygen from silicon and decrease the loss of silicon. 相似文献
87.
88.
89.
We investigate possible ways in which a quantum wavepacket spreads. We show that in a general class of double kicked rotor system, a wavepacket may undergo superballistic spreading; i.e., its variance increases as the cubic of time. The conditions for the observed superballistic spreading and two related characteristic time scales are studied. Our results suggest that the symmetry of the studied model and whether it is a Kolmogorov-Arnold-Moser system are crucial to its wavepacket spreading behavior. Our study also sheds new light on the exponential wavepacket spreading phenomenon previously observed in the double kicked rotor system. 相似文献
90.