全文获取类型
收费全文 | 32078篇 |
免费 | 5285篇 |
国内免费 | 4782篇 |
专业分类
化学 | 24651篇 |
晶体学 | 452篇 |
力学 | 1805篇 |
综合类 | 335篇 |
数学 | 3512篇 |
物理学 | 11390篇 |
出版年
2024年 | 71篇 |
2023年 | 597篇 |
2022年 | 858篇 |
2021年 | 1082篇 |
2020年 | 1242篇 |
2019年 | 1293篇 |
2018年 | 1066篇 |
2017年 | 1146篇 |
2016年 | 1514篇 |
2015年 | 1591篇 |
2014年 | 1980篇 |
2013年 | 2460篇 |
2012年 | 3099篇 |
2011年 | 3172篇 |
2010年 | 2273篇 |
2009年 | 2046篇 |
2008年 | 2290篇 |
2007年 | 2061篇 |
2006年 | 1961篇 |
2005年 | 1517篇 |
2004年 | 1116篇 |
2003年 | 951篇 |
2002年 | 993篇 |
2001年 | 869篇 |
2000年 | 614篇 |
1999年 | 629篇 |
1998年 | 448篇 |
1997年 | 404篇 |
1996年 | 394篇 |
1995年 | 329篇 |
1994年 | 273篇 |
1993年 | 237篇 |
1992年 | 222篇 |
1991年 | 213篇 |
1990年 | 153篇 |
1989年 | 159篇 |
1988年 | 99篇 |
1987年 | 94篇 |
1986年 | 101篇 |
1985年 | 73篇 |
1984年 | 59篇 |
1983年 | 48篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1974年 | 21篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
61.
62.
Orlicz-Sobolev空间的中点局部一致凸性 总被引:2,自引:0,他引:2
本文研究了Orlicz-Sobolev空间的中点局部一致凸性,通过结合Orlicz空间和Sobolev空间的技巧得到分别赋Luxemburg范数和赋Orlicz范数的Orlicz-Sobolev空间具有中点局部一致凸性的充要条件. 相似文献
63.
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
64.
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
65.
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
66.
67.
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
68.
Based on the rate equations and the power propagation equations, the amplified model is obtained which considers the cross-phase modulation (XPM)-induced intensity fluctuation between pump power and signal power in erbium-doped fiber amplifier (EDFA). Simulation results show: a higher nonlinear coefficient and a stronger pump power cause a stronger XPM in EDFA. Before the optimal length of EDF, the intensity caused by XPM increases with the increasing length, but after the optimal length, the XPM presents saturation. A bigger nonlinear coefficient γ corresponds to a smaller optimal length and gain, and makes gain saturation more easy. XPM effect will decrease EDFA’s amplified efficiency. 相似文献
69.
Jing Lin 《Tetrahedron letters》2004,45(1):103-106
Bisbinaphthyl-based macrocycles are found to carry out enantioselective fluorescent recognition of α-amino acid derivatives. It is observed that one enantiomer of a N-protected phenyl glycine can increase the fluorescence intensity of the binaphthyl fluorophores by over 4-fold but the other enantiomer does not cause much fluorescence enhancement. This highly enantioselective fluorescent response makes the binaphthyl macrocycles practically useful for the enantioselective fluorescent recognition of the amino acid substrate. 相似文献
70.
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