全文获取类型
收费全文 | 22970篇 |
免费 | 4055篇 |
国内免费 | 3104篇 |
专业分类
化学 | 16967篇 |
晶体学 | 246篇 |
力学 | 1344篇 |
综合类 | 196篇 |
数学 | 2949篇 |
物理学 | 8427篇 |
出版年
2024年 | 42篇 |
2023年 | 491篇 |
2022年 | 653篇 |
2021年 | 836篇 |
2020年 | 1051篇 |
2019年 | 1069篇 |
2018年 | 844篇 |
2017年 | 769篇 |
2016年 | 1102篇 |
2015年 | 1165篇 |
2014年 | 1405篇 |
2013年 | 1735篇 |
2012年 | 2094篇 |
2011年 | 2177篇 |
2010年 | 1506篇 |
2009年 | 1469篇 |
2008年 | 1492篇 |
2007年 | 1304篇 |
2006年 | 1259篇 |
2005年 | 1005篇 |
2004年 | 822篇 |
2003年 | 667篇 |
2002年 | 780篇 |
2001年 | 542篇 |
2000年 | 481篇 |
1999年 | 509篇 |
1998年 | 385篇 |
1997年 | 349篇 |
1996年 | 346篇 |
1995年 | 286篇 |
1994年 | 245篇 |
1993年 | 220篇 |
1992年 | 169篇 |
1991年 | 157篇 |
1990年 | 129篇 |
1989年 | 120篇 |
1988年 | 106篇 |
1987年 | 56篇 |
1986年 | 64篇 |
1985年 | 68篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
91.
92.
93.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
94.
95.
96.
Xinhuan Feng Lei Sun Yange Liu Lingyun Xiong Shuzhong Yuan Guiyun Kai Xiaoyi Dong 《Optical and Quantum Electronics》2004,36(10):919-926
A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated. 相似文献
97.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
98.
J. MALINEN O. NEVANLINNA V. TURUNEN Z. YUAN 《数学学报(英文版)》2007,23(4):745-748
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences. 相似文献
99.
全固态多波长飞秒脉冲激光系统 总被引:1,自引:1,他引:0
利用棱镜对引进频谱空间啁啾来补偿飞秒脉冲激光二次谐波产生中的相位失配,提高了倍频效率建立了一套全固态、多波长(1065nm, 532nm,823.1nm, 402nm)飞秒脉冲激光系统自制的Nd:YVO4激光器输出532nm绿光激光,最高平均功率可达5.6W当用2.5W绿光激光泵浦时,从自制的钛宝石激光器及经BBO倍频可分别输出中心波长为823.1nm和402nm,平均功率300mW和73mW,谱宽32.3nm和5.1nm,脉宽22fs和33.3fs、重复率108MHz的近红外和蓝光激光整个系统具有结构紧凑、倍频效率高、运行稳定的特点. 相似文献
100.