全文获取类型
收费全文 | 60663篇 |
免费 | 10285篇 |
国内免费 | 6491篇 |
专业分类
化学 | 42452篇 |
晶体学 | 713篇 |
力学 | 3752篇 |
综合类 | 382篇 |
数学 | 7055篇 |
物理学 | 23085篇 |
出版年
2024年 | 211篇 |
2023年 | 1260篇 |
2022年 | 2333篇 |
2021年 | 2392篇 |
2020年 | 2547篇 |
2019年 | 2412篇 |
2018年 | 2073篇 |
2017年 | 2034篇 |
2016年 | 2981篇 |
2015年 | 3004篇 |
2014年 | 3503篇 |
2013年 | 4511篇 |
2012年 | 5514篇 |
2011年 | 5511篇 |
2010年 | 3817篇 |
2009年 | 3588篇 |
2008年 | 3882篇 |
2007年 | 3375篇 |
2006年 | 3128篇 |
2005年 | 2613篇 |
2004年 | 2018篇 |
2003年 | 1617篇 |
2002年 | 1489篇 |
2001年 | 1201篇 |
2000年 | 1075篇 |
1999年 | 1224篇 |
1998年 | 1019篇 |
1997年 | 966篇 |
1996年 | 951篇 |
1995年 | 854篇 |
1994年 | 713篇 |
1993年 | 620篇 |
1992年 | 515篇 |
1991年 | 457篇 |
1990年 | 405篇 |
1989年 | 296篇 |
1988年 | 217篇 |
1987年 | 195篇 |
1986年 | 192篇 |
1985年 | 160篇 |
1984年 | 105篇 |
1983年 | 107篇 |
1982年 | 70篇 |
1981年 | 42篇 |
1980年 | 36篇 |
1979年 | 20篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1972年 | 19篇 |
1957年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
应用TGT法生长了直径为75mm的U:CaF2晶体,宏观上透明完整.应用公式K0=Cs/Cl计算了U在CaF2晶体中的分凝系数等于0.53.应用溶质分布一般公式Cs=K0C0(1-g)K0-1,计算U的浓度分布与测量值,数值符合说明晶体生长过程接近平衡状态.分析不同条件下生长的U: CaF2晶体的晶胞参数和吸收光谱,结果表明生长气氛决定U的价态及电荷补偿机理:无PbF2存在的条件下,U为+4价,晶体呈绿色;PbF2的加入起到氟化去氧作用,U倾向于以离子半径最接近于Ca2+的U3+存在,晶体呈红色.从晶体生长开始到结束的部位,U3+:CaF2晶体吸收光谱的峰位不变,峰强呈现与U浓度相同的增加趋势.U3+:CaF2晶体外层厚约5mm处呈黄色,含有U3+和U2+的混合价态离子,其原理是石墨坩埚的还原作用通过单质铅,使部分的U3+进一步还原成了U2+.
关键词:
铀
氟化钙晶体
分凝系数
晶胞参数 相似文献
102.
Yang Mujie Zhao Jian Li Aibing Shen Zhiquan Zhang Mingjian Lin Senhao 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3829-3835
This paper reports that 60Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 103 Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with 60Co γ-ray (dose: 2 × 105 Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of 60Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films. 相似文献
103.
The Iyengar Type Inequalities with Exact Estimations and the Chebyshev Central Algorithms of Integrals 总被引:3,自引:0,他引:3
Xing Hua WANG Shi Jun YANG 《数学学报(英文版)》2005,21(6):1361-1376
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated. 相似文献
104.
105.
106.
Deposition of Hydrogen-Free Silicon Nitride Thin Films by Microwave ECR plasma Enhanced Magnetron Sputtering at Room Temperature 下载免费PDF全文
Hydrogen-free silicon nitride (SiNx) films were deposited at room temperature by microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalance magnetron sputtering system. Both Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy are used to study the bonding type and the change of bonding structures of the silicon nitride films. The results indicate that the chemical structure and composition of SiNx films deposited by this technique depend strongly on the N2 flow rates, the stoichiometric SiNx film, which has the highest hardness of 22.9 GPa, could be obtained at lower N2 flow rate of 4 sccm. 相似文献
107.
108.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
109.
证明了当超越亚纯函数的级小于1时,其Norel例外值最多只有一个.由于存在任何级的整函数,因此一个例外值总可达到,故所得结果不能再改进。 相似文献
110.
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