全文获取类型
收费全文 | 34372篇 |
免费 | 5843篇 |
国内免费 | 4639篇 |
专业分类
化学 | 25757篇 |
晶体学 | 648篇 |
力学 | 1883篇 |
综合类 | 362篇 |
数学 | 3930篇 |
物理学 | 12274篇 |
出版年
2024年 | 62篇 |
2023年 | 589篇 |
2022年 | 917篇 |
2021年 | 1109篇 |
2020年 | 1348篇 |
2019年 | 1370篇 |
2018年 | 1116篇 |
2017年 | 1080篇 |
2016年 | 1564篇 |
2015年 | 1666篇 |
2014年 | 1821篇 |
2013年 | 2555篇 |
2012年 | 3139篇 |
2011年 | 3127篇 |
2010年 | 2330篇 |
2009年 | 2300篇 |
2008年 | 2625篇 |
2007年 | 2217篇 |
2006年 | 2153篇 |
2005年 | 1959篇 |
2004年 | 1528篇 |
2003年 | 1209篇 |
2002年 | 1253篇 |
2001年 | 983篇 |
2000年 | 828篇 |
1999年 | 711篇 |
1998年 | 458篇 |
1997年 | 348篇 |
1996年 | 373篇 |
1995年 | 324篇 |
1994年 | 303篇 |
1993年 | 251篇 |
1992年 | 178篇 |
1991年 | 182篇 |
1990年 | 151篇 |
1989年 | 111篇 |
1988年 | 106篇 |
1987年 | 68篇 |
1986年 | 68篇 |
1985年 | 76篇 |
1984年 | 55篇 |
1983年 | 33篇 |
1982年 | 28篇 |
1981年 | 36篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
81.
ZhongJunMA XianLI YangLU ChengWANG QiTaiZHENG 《中国化学快报》2003,14(6):594-596
A novel cycloartane,named sphaerophysone A,9,19-cycloart-7β,24β,25-triol-1-en-3-one,was isolated from the ethanol extract of Sphaerophysa salsula DC.The structure was elucidated on the basis of spectral evidences and confirmed by X-ray analysis,the stereochemistry of the compound was also defined by X-ray analysis. 相似文献
82.
83.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
84.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
85.
86.
87.
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
88.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
89.
报道了硅基有机微腔的电致发光(EL).该微腔由上半透明金属膜、中心有源多层膜和多孔硅分布Bragg反射镜(PS DBR)组成.半透明金属膜由Ag(20nm)构成,充当发光器件的负电极和微腔的上反射镜.有源多层膜由Al (1 nm) / LiF(05 nm) /Alq3/Alq3:DCJTB/NPB/CuPc/ITO/SiO2组成,其中的Al/LiF为电子注入层,ITO为正电极,SiO2为使正、负电极电隔离的介质层.该PS DBR是采用设备简单、成本低廉且非常省时的电化学腐蚀法用单晶Si来制备的;该PS
关键词:
电化学腐蚀
电致发光
窄峰发射
硅基有机微腔 相似文献
90.
In this Letter we consider the Abelian Chern–Simons vortices on a bounded simply connected domain. We establish the existence of solutions for the self-duality equations. We prove the uniqueness of solutions when all the vortex points are equal and the domain is star-shaped. We also show the radial symmetry of solutions on balls centered at the vortex point. 相似文献