全文获取类型
收费全文 | 31983篇 |
免费 | 5404篇 |
国内免费 | 4035篇 |
专业分类
化学 | 23167篇 |
晶体学 | 350篇 |
力学 | 2046篇 |
综合类 | 283篇 |
数学 | 3887篇 |
物理学 | 11689篇 |
出版年
2024年 | 89篇 |
2023年 | 629篇 |
2022年 | 1071篇 |
2021年 | 1140篇 |
2020年 | 1237篇 |
2019年 | 1334篇 |
2018年 | 1060篇 |
2017年 | 1034篇 |
2016年 | 1486篇 |
2015年 | 1518篇 |
2014年 | 1871篇 |
2013年 | 2280篇 |
2012年 | 2880篇 |
2011年 | 2889篇 |
2010年 | 2019篇 |
2009年 | 1903篇 |
2008年 | 2078篇 |
2007年 | 1822篇 |
2006年 | 1759篇 |
2005年 | 1427篇 |
2004年 | 1123篇 |
2003年 | 965篇 |
2002年 | 1030篇 |
2001年 | 833篇 |
2000年 | 661篇 |
1999年 | 682篇 |
1998年 | 541篇 |
1997年 | 488篇 |
1996年 | 501篇 |
1995年 | 411篇 |
1994年 | 351篇 |
1993年 | 313篇 |
1992年 | 271篇 |
1991年 | 272篇 |
1990年 | 211篇 |
1989年 | 203篇 |
1988年 | 152篇 |
1987年 | 111篇 |
1986年 | 119篇 |
1985年 | 105篇 |
1984年 | 81篇 |
1983年 | 62篇 |
1982年 | 56篇 |
1981年 | 42篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1976年 | 27篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
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
73.
物理模型教学与创新能力的培养 总被引:1,自引:0,他引:1
现代教学以能力培养为重点.学生获得研究问题、探索问题的能力是十分重要的,物理模型的教学过程对培养学生研究问题、探索问题、发展创造思维、培养辩证唯物主义思想方法都极为有利,因此,必须重视物理模型教学. 相似文献
74.
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
75.
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
76.
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
77.
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
78.
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
79.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
80.