全文获取类型
收费全文 | 105045篇 |
免费 | 19480篇 |
国内免费 | 11899篇 |
专业分类
化学 | 72858篇 |
晶体学 | 1176篇 |
力学 | 6796篇 |
综合类 | 809篇 |
数学 | 12463篇 |
物理学 | 42322篇 |
出版年
2024年 | 255篇 |
2023年 | 2222篇 |
2022年 | 3211篇 |
2021年 | 3692篇 |
2020年 | 4485篇 |
2019年 | 4081篇 |
2018年 | 3646篇 |
2017年 | 3322篇 |
2016年 | 5165篇 |
2015年 | 4935篇 |
2014年 | 6091篇 |
2013年 | 7807篇 |
2012年 | 9569篇 |
2011年 | 9998篇 |
2010年 | 6747篇 |
2009年 | 6615篇 |
2008年 | 7091篇 |
2007年 | 6220篇 |
2006年 | 5839篇 |
2005年 | 4710篇 |
2004年 | 3712篇 |
2003年 | 2873篇 |
2002年 | 2743篇 |
2001年 | 2351篇 |
2000年 | 2035篇 |
1999年 | 2199篇 |
1998年 | 1891篇 |
1997年 | 1861篇 |
1996年 | 1811篇 |
1995年 | 1532篇 |
1994年 | 1337篇 |
1993年 | 1127篇 |
1992年 | 956篇 |
1991年 | 896篇 |
1990年 | 731篇 |
1989年 | 562篇 |
1988年 | 436篇 |
1987年 | 364篇 |
1986年 | 360篇 |
1985年 | 290篇 |
1984年 | 178篇 |
1983年 | 139篇 |
1982年 | 123篇 |
1981年 | 72篇 |
1980年 | 58篇 |
1979年 | 16篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1959年 | 5篇 |
1957年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
241.
242.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
243.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
244.
245.
Shujiang Tu Fang Fang Tuanjie Li Songlei Zhu Xiaojing Zhang 《Journal of heterocyclic chemistry》2005,42(4):707-710
A series of pyrimidoquinoline derivatives were synthesized through one‐pot condensation of 2,6‐diaminopyrimidin‐4‐one, aldehyde and cyclic a 1,3‐dicarbonyl compound in glycol under microwave irradiation without catalyst. The protocol in the absence of catalyst has the advantage of good yield (87‐95%), short reaction time (4‐7 min) and an environmentally friendly technique. 相似文献
246.
247.
Zhang Xinliang Huang Dexiu Sun Junqiang Liu Deming 《Optical and Quantum Electronics》2004,36(7):627-634
A simple scheme for single to multi-channel wavelength conversion based on cross-gain modulation of amplified spontaneous emission (ASE) spectrum in semiconductor optical amplifier (SOA) is described. Single to 16-channel wavelength conversion at 10 Gb/s is first demonstrated without any additional probe lights, the modulation information carried by input signal could be converted into arbitrary many channels if only the demultiplexer with enough channels is exploited. Output performance and pattern effects are investigated experimentally. 相似文献
248.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
249.
250.
In this paper, we use weighted modules ω(?)(f,t)w to study the pointwise approximation on Szasz-type operators, and obtain the direct and converse theorem, as well as characterizations of the pointwise approximation of Jacobi-weighted Szasz-type operators. 相似文献