全文获取类型
收费全文 | 16519篇 |
免费 | 1476篇 |
国内免费 | 5087篇 |
专业分类
化学 | 16995篇 |
晶体学 | 484篇 |
力学 | 543篇 |
综合类 | 207篇 |
数学 | 1699篇 |
物理学 | 3154篇 |
出版年
2024年 | 31篇 |
2023年 | 149篇 |
2022年 | 307篇 |
2021年 | 378篇 |
2020年 | 444篇 |
2019年 | 369篇 |
2018年 | 376篇 |
2017年 | 463篇 |
2016年 | 539篇 |
2015年 | 479篇 |
2014年 | 704篇 |
2013年 | 1242篇 |
2012年 | 1581篇 |
2011年 | 936篇 |
2010年 | 783篇 |
2009年 | 1001篇 |
2008年 | 1128篇 |
2007年 | 1228篇 |
2006年 | 1149篇 |
2005年 | 1105篇 |
2004年 | 1022篇 |
2003年 | 858篇 |
2002年 | 789篇 |
2001年 | 641篇 |
2000年 | 608篇 |
1999年 | 644篇 |
1998年 | 549篇 |
1997年 | 520篇 |
1996年 | 450篇 |
1995年 | 440篇 |
1994年 | 380篇 |
1993年 | 287篇 |
1992年 | 354篇 |
1991年 | 271篇 |
1990年 | 222篇 |
1989年 | 164篇 |
1988年 | 131篇 |
1987年 | 77篇 |
1986年 | 71篇 |
1985年 | 56篇 |
1984年 | 36篇 |
1983年 | 20篇 |
1982年 | 28篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
1INTRODUCTIONRecently,therehasbeenconsiderableinterestinthelanthanide(III)hexacyanoferrates,theanalogoushexacyanocobaltateandhexacyanochromiumatecom-plexesbecauseoftheirpotentialapplicationsascata-lyticandsemi-conductivematerials.InitialstudiesofmetalhexacyanocobaltateswerecarriedoutbyJa-mesandWilland[1]whoreportedtheamountofhy-drationassociatedwithmicroscopiccrystalsofsever-allanthanidecomplexes.FurtherBonnetandParis[2]studiedtheLNCo(CN)6?nH2Oseries(n=4)byusinginfraredandX-raymethod… 相似文献
952.
The Schiff base‐containing pendant monoaza crown ether HL1, HL2, HL3 and HL4 have been synthesized by condensation of salicylaldehyde with N‐(4‐aminoaryl) monoaza crown ethers, which were prepared conveniently from 4‐nitro‐N, N‐di(hydroxyethyl) aniline or 4‐nitrobenzyl chloride via cyclization or condensation and reduction. The structures of HL1—HL4 were verified by 1H NMR, IR spectra, MS and elemental analysis. Moreover, the oxygenation constants (KO2) and thermodynamic parameters (δH0 and δS0) of their cobalt(II) complexes were determined in the range of ?5 °C to 25 °C, and the effect of crown ring bonded to a Schiff base on the dioxygen affinities of cobalt(II) complexes was also observed as compared to the uncrowned analogue (CoL). 相似文献
953.
《Journal of Molecular Structure》2002,616(1-3):259-264
The molecular structure of the title complex [ZnBr2(C7H6N2)2] was investigated by X-ray diffraction and IR spectroscopy methods. Molecules of zinc(II) complex crystallize in the triclinic crystal system with cell constants a=7.526(2) Å, b=7.8971(8) Å, c=13.431(1) Å, Z=2 and V=791.3(2) Å3. In the molecular structure, the Zn atom is coordinated tetrahedrally by two Br− anions and two benzimidazole ligands. Intramolecular steric repulsions between Br− anions and benzimidazole groups have been caused to cis configuration around the central metal atom. 相似文献
954.
CHANG Kai-Guo LU Xiang-Ping DU Fu-Ying ZHAO Min-ShouChangchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun Jilin China 《中国化学》1994,(6)
The apparent standard potential of Dy/Dy(III) system in the LiCl-KCl eutectic has been determined by the logarithmic analysis of the semi-integrals of voltammograms, logarithmic analysis of chronopotentiograms and the open circuit potentiometry. The dysprosium equilibrium potentiab for various concentration of dysprosium chloride in the LiCl-KCl eutectic melt between 400-500℃ were first determined experimentally, and the apparent standard potential of this system and its temperature dependance have been calculated. 相似文献
955.
The strictly regioselective hydrocarboxylation of vinyl acetate to ethylidene diacetate by acetic acid formed in situ from vinyl acetate was realized for the first time with Rh(PPh3)3Cl as catalyst. The transformation of vinyl acetate into benzene, acetophenone, and acetylene was also realized.Institute of Organic Chemistry, Urals Branch, Russian Academy of Sciences, 420083 Ufa. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1406–1408, June, 1992. 相似文献
956.
On the Reaction of Macrocycles with Lanthanoids. I. The Crystal Structure of [Li(thf)][(C22H22N4)2Ce] · THF In THF CeBr3 forms with [(TMTAA)Li2] the paramagnetic doubledecker complex [Li(thf)][(TMTAA)2Ce]. The complex crystallizes with 1 Mol THF per formula unit. The structure was characterized by X-ray single crystal structure analysis (space group C2 (No. 5), z = 6, a = 1741.8(2) pm, b = 1622.1(2) pm, c = 2540.4(3) pm, β = 104.72(1)°). The sandwich-like arrangement of the heterocyclic ligands leads to a quadratic-prismatic coordination of the Ce3+ ion. One macrocyclic ligand is additionally coordinated by a [Li(thf)]+ fragment. The coordination of the Li ion is square pyramidal. 相似文献
957.
V. A. D’yakonov R. K. Timerkhanov A. G. Ibragimov U. M. Dzhemilev 《Russian Chemical Bulletin》2007,56(11):2232-2235
Catalytic cycloalumination of cyclonona-1,2-diene upon treatment with Et3Al and EtAlCl2 in the presence of Cp2ZrCl2, leading to 10-ethyl-10-aluminabicyclo[7.3.01,9]dodec-8-ene (1) and 11-ethyl-11-aluminatricyclo[10.7.01,12.02,10]nonadeca-9,12-diene, respectively, was accomplished in high yields. A possibility for the selective transformation of compound
1 to 1-allyl-9-(pent-4-enyl)cyclonon-1-ene and 10-hydroxybicyclo[7.3.01,9]dodec-8-ene in one preparative step was demonstrated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2156–2159, November, 2007. 相似文献
958.
Three hexakis(imidazole)metallo complexes of Co, Cd and Ni were synthesized and spectroscopically characterized. The crystal and molecular structures have been determined by X-ray crystallography analysis. The metal ions have an octahedral geometry with the MN6 chromophore. The electrochemical experimental results indicate that both [Co(Im)6]C12·2HCl·2H2O (1) and [Ni(Im)6]C12·4H2O (3) [Im=imidazole] could interact with DNA mainly by intercalation. 相似文献
959.
The catalyst of rare earth(III) perfluorooctanesulfonates (RE(OSO2C8F17)3, RE = Sc, Y, La-Lu) were prepared from either rare earth chlorides(III) or oxides and perfluorooctanesulfonic acid. The perflates thus obtained act as novel catalysts for Friedel-Crafts alkylation in fluorous biphasic system. Perfluorohexane (C6F14), perfluoromethylcyclohexane (C7F14), perfluorotoluene (C7F8), perfluorooctane (C8F18), perfluorooctyl bromide (C8F17Br) and perfluorodecalin (C10F18, cis- and trans-mixture) can be used as fluorous solvents for this reaction. By simple separation of the fluorous phase containing only catalyst, alkylation can be repeated many times. 相似文献
960.
近十几年来,对小分子过渡金属配合物与大分子DNA键合与识别机理的研究一直是国际上生物无机化学领域十分活跃的研究课题[1 ̄3],已发展了一系列具有特定功能的配合物,如DNA结构探针和DNA荧光探针等。与其他类型的金属配合物相比,八面体过渡金属多吡啶配合物具有丰富的光化学和光物理信息,当这些配合物与DNA相互作用时,由于结构匹配或微环境的差异,配合物的光谱特征会出现不同程度的改变,从而达到对DNA的检测。传统的DNA荧光探针有[Ru(bpy)2dppz]2 和[Ru(phen)2dppz]2 (bpy=2,2′-联吡啶,phen=1,10-菲咯啉,dppz=二吡啶[3,2-a∶2′,3′… 相似文献