全文获取类型
收费全文 | 3862篇 |
免费 | 732篇 |
国内免费 | 768篇 |
专业分类
化学 | 3545篇 |
晶体学 | 52篇 |
力学 | 41篇 |
综合类 | 52篇 |
数学 | 316篇 |
物理学 | 1356篇 |
出版年
2024年 | 10篇 |
2023年 | 37篇 |
2022年 | 78篇 |
2021年 | 92篇 |
2020年 | 136篇 |
2019年 | 117篇 |
2018年 | 111篇 |
2017年 | 99篇 |
2016年 | 162篇 |
2015年 | 160篇 |
2014年 | 206篇 |
2013年 | 328篇 |
2012年 | 271篇 |
2011年 | 256篇 |
2010年 | 234篇 |
2009年 | 268篇 |
2008年 | 280篇 |
2007年 | 271篇 |
2006年 | 280篇 |
2005年 | 237篇 |
2004年 | 250篇 |
2003年 | 201篇 |
2002年 | 131篇 |
2001年 | 123篇 |
2000年 | 142篇 |
1999年 | 120篇 |
1998年 | 104篇 |
1997年 | 84篇 |
1996年 | 83篇 |
1995年 | 84篇 |
1994年 | 75篇 |
1993年 | 51篇 |
1992年 | 57篇 |
1991年 | 59篇 |
1990年 | 30篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有5362条查询结果,搜索用时 62 毫秒
71.
Zareen Ahkter Andrew J. Edwards Scott L. Ingham Jack Lewis Ana M. Martin Castro Paul R. Raithby Gregory P. Shields 《Journal of Cluster Science》2000,11(1):217-226
The reaction of the di-gold cation [Au2(dppx)]2+ with the heptanuclear cluster dianion [Os7(CO)20]2– affords the mixed metal cluster [Os7(CO)20{Au2(dppx)}] (x=m (1), e (2), b (3)). On standing, in solution, this complex undergoes decarbonylation to give the cluster [Os7(CO)19{Au2(dppx)}] (x=m (4), e (5), b (6)). The complexes have been characterised spectroscopically, and an X-ray structure determination of the dppm derivative shows that it contains a metal core based on an Os7 edge-bridged bicapped tetrahedron with the two
3-Au atoms capping adjacent triangular Os3 faces of the central tetrahedron. In an analogous reaction, the carbido anion [Os7(H)C(CO)19]– affords the neutral cluster [Os7C(CO)19{Au2(dppm)}] (7) when treated with [Au2(dppm)]2+ in the presence of base. 相似文献
72.
73.
The localized molecular orbitals and their energy levels for the clusters [Fe3S4(SH)3]2–, [(HS)3Fe3S4·Ni(PH3)]2–, [Mo3S4(OH2)9]4+, and [Mo3S4·Ni]4+ have been calculated by mean of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation in order to reveal the resemblance between [Fe3S4]+ and [Mo3S4]4+ in the geometrical configurations and the addition reactivities with heterometal atoms. It is shown that in these two cluster species with core {M
3(3-S)(-S)3} of similar structure (M = Mo, Fe) there exist three synergically connected three-centered two-electron (M-S-M) -bonds around the puckered six-membered {M3S3} rings on account of delocalization of a lone electron pair on each bridging S atom; these (M-S-M) -bonds are thus capable of forming cubane-like heterometal clusters with intruder metal atoms through the ( M) bonding. It is therefore seen that unlike the [Mo3S4]4+ with appreciable bonding between the Mo atoms, the extra d-electrons on the metal atoms in the [Fe3S4]+ cluster are localized on the Fe atoms, exhibiting an electronic structure significantly different from that of the [Mo3S4]4+ cluster. 相似文献
74.
75.
76.
R.?R.?NazmutdinovEmail author T.?T.?Zinkicheva 《Russian Journal of Electrochemistry》2005,41(2):206-212
The fluoride ion adsorption from a gas phase on various faces of a single crystal of silver is studied by a density functional method within a cluster model for metal. The adsorption bond energy is found to increase in the series Ag(100) < Ag(111) < Ag(311) < Ag(110). A substantial structural and energetic heterogeneity of various adsorption sites is revealed. The results are utilized to simulate the electrochemical interface between individual faces of a single crystal of silver and aqueous solutions containing the fluoride ion. It is assumed that the adsorption potential may be represented as the sum of two contributions, one of which describes the metal–ion interaction and the other, the ion solvation energy. The plotted adsorption terms take into account partial degradation of the fluoride ion when adsorbed from an aqueous solution. Estimates of discreteness of the electrical double layer are presented. A conclusion on the maximum manifestation of specific adsorption of the fluoride ion for the Ag(100) face is made.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 232–238.Original Russian Text Copyright © 2005 by Nazmutdinov, Zinkicheva.This revised version was published online in April 2005 with corrections to the article note and article title and cover date. 相似文献
77.
三核钨钼簇合物对苯乙烯氧化反应的催化 总被引:2,自引:0,他引:2
关于烯烃的催化氧化,报道较多。Takao等研究了苯乙烯在Ir和Rh络合物存在下的氧化反应;Collman曾报道环己烯在Vaska络合物[IrX(CO)(PPh_3)_2]催化下氧化成环己酮和环已烯氧化物。本文采用Cotton合成的簇合物[W_3O_2(CH_3CO_2)_6(H_2O)_3]Br_2· 相似文献
78.
Pt(PPh_3)_2Cl_2在碱性介质中,与一氧化碳直接进行还原及羰基化反应,得到五种膦取代的羰基铂配合物:Pt_5(μ_2-CO)_5(CO)(PPh_3)_4 1,Pt_3(μ_2-CO)_3(PPh_3)_3 2,Pt_3(μ_2-CO)_3(PPh_3)_4 3,Pt_4(μ_2-CO)_5(PPh_3)_4 4,以及Pt(Cl)(PPh_3)_2(COOCH_3) 5。经X-射线单晶衍射分析,确定了新的三核铂羰基簇2以及配合物5的分子结构。还讨论了1和5的生成机理。 相似文献
79.
Antonio Doménech María Teresa Doménech‐Carbó Howell G. M. Edwards 《Electroanalysis》2007,19(18):1890-1900
Multivariate chemometric methods are applied for identifying earth pigments from square‐wave voltammetric measurements performed at pigment‐modified paraffin‐impregnated graphite electrodes allowing for a separation between hematite‐based earths, French ochres, Spanish ochres, siennas, umbers and green earths. This methodology is applied to the identification of the pigments in samples from the ceiling frescoes of Antonio Palomino (dated 1707) in the vaulted nave of the Sant Joan del Mercat church in Valencia (Spain). These frescoes suffered considerable damage by fire during the Spanish Civil War in 1936, resulting in severe chemical and chromatic alterations. Electrochemical data, supported by scanning electron microscopy/energy dispersive X‐ray microanalysis and Raman spectroscopy, indicate that thermal stress induced the transformation of goethite‐based yellow ochres into hematite and magnetite. 相似文献
80.
用量子化学从头算方法(HF/6-31G)和密度泛函理论(DFT)的B3LYP方法,以6-31G标准基组加一个极化函数,对(ClAlNH)n(n=1-10)簇合物的几何构型,电子结构和红外光谱进行了优化,并讨论了聚合反应(ClAlNH)m→(ClAlNH)n的热力学效应,结果表明,(ClAlNH)n系列簇合物的基态稳定结构为Cs(n=1),D2h(n=2),D3h(n=3),Td(n=4),Cs(n=5),D3d(n=6),Cs(n=7),S4(n=8),D3h(n=9),C2h(n=10,n=2,4,6,8,10等偶数对应的(ClAlNH)n簇化合物的结构比n等于奇数量更稳定。 相似文献