全文获取类型
收费全文 | 25645篇 |
免费 | 3882篇 |
国内免费 | 2622篇 |
专业分类
化学 | 18749篇 |
晶体学 | 307篇 |
力学 | 1557篇 |
综合类 | 184篇 |
数学 | 2844篇 |
物理学 | 8508篇 |
出版年
2024年 | 59篇 |
2023年 | 484篇 |
2022年 | 660篇 |
2021年 | 802篇 |
2020年 | 940篇 |
2019年 | 930篇 |
2018年 | 744篇 |
2017年 | 739篇 |
2016年 | 1136篇 |
2015年 | 1070篇 |
2014年 | 1327篇 |
2013年 | 1745篇 |
2012年 | 2305篇 |
2011年 | 2352篇 |
2010年 | 1525篇 |
2009年 | 1417篇 |
2008年 | 1655篇 |
2007年 | 1528篇 |
2006年 | 1448篇 |
2005年 | 1228篇 |
2004年 | 891篇 |
2003年 | 745篇 |
2002年 | 761篇 |
2001年 | 641篇 |
2000年 | 509篇 |
1999年 | 513篇 |
1998年 | 432篇 |
1997年 | 378篇 |
1996年 | 405篇 |
1995年 | 369篇 |
1994年 | 320篇 |
1993年 | 249篇 |
1992年 | 248篇 |
1991年 | 237篇 |
1990年 | 194篇 |
1989年 | 156篇 |
1988年 | 124篇 |
1987年 | 102篇 |
1986年 | 115篇 |
1985年 | 91篇 |
1984年 | 77篇 |
1983年 | 53篇 |
1982年 | 52篇 |
1981年 | 45篇 |
1980年 | 36篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 30篇 |
1974年 | 26篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
51.
52.
S. J. Cheng W. Sheng P. Hawrylak S. Raymond S. Studenikin A. Sachrajda Z. Wasilewski A. Babinski M. Potemski G. Ortner M. Bayer 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):211
We present results of calculations and experiments on electron–hole complexes in InGaAs/GaAs self-assembled quantum dots in high magnetic field (B). Due to hidden symmetries, the chemical potential of an N-exciton system at special B fields becomes insensitive to the exciton number as well as the magnetic field. This results in plateau regions of high intensity in measured magneto-PL spectrum. Theoretical calculations using exact diagonalization techniques successfully explain the measured magneto-photoluminescence spectrum with B fields up to 28 T. 相似文献
53.
54.
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
55.
56.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
57.
Wang Qing-Lun Zhao Bin Liao Dai-Zheng Yan Shi-Ping Cheng Peng Jiang Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer. 相似文献
58.
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
59.
Tian-Xi ZhouGuan-Hu Bao Qin-Gao MaGuo-Wei Qin Chu-Tao CheYang Lv Cheng WangQi-Tai Zheng 《Tetrahedron letters》2003,44(1):135-137
Langduin C, a novel dimeric diterpenoid, was isolated from the roots of Euphorbia fischeriana and its structure was established by spectral data and single-crystal X-ray diffraction analysis. 相似文献
60.
Yang Dai Faquan Li Xuewu Cheng Zhiling Jiang Shunsheng Gong 《Optics & Laser Technology》2007,39(7):1374-1379
In Shack–Hartmann wavefront sensor (SHWS), the behavior of the irradiance pattern produced by the micro-lens array is important for an accurate centroid estimation. In this paper, the behavior of a micro-lens array in SHWS is analyzed using Fourier optics, and reveals that in addition to the main, expected spots, secondary spots with smaller intensities also appeared as a result of diffraction by the small dimensions of the micro-lens and interference from the different micro-lenses. This result is confirmed by comparing with a irradiance pattern taken from an actual SHWS. The additional error in centroid estimation caused by these secondary spots is discussed and relationship to the parameters of the micro-lens of SHWS is analyzed. 相似文献