全文获取类型
收费全文 | 1803篇 |
免费 | 408篇 |
国内免费 | 302篇 |
专业分类
化学 | 1029篇 |
晶体学 | 5篇 |
力学 | 179篇 |
综合类 | 10篇 |
数学 | 622篇 |
物理学 | 668篇 |
出版年
2024年 | 16篇 |
2023年 | 54篇 |
2022年 | 105篇 |
2021年 | 104篇 |
2020年 | 148篇 |
2019年 | 120篇 |
2018年 | 101篇 |
2017年 | 90篇 |
2016年 | 113篇 |
2015年 | 107篇 |
2014年 | 139篇 |
2013年 | 150篇 |
2012年 | 127篇 |
2011年 | 112篇 |
2010年 | 72篇 |
2009年 | 90篇 |
2008年 | 95篇 |
2007年 | 75篇 |
2006年 | 99篇 |
2005年 | 56篇 |
2004年 | 69篇 |
2003年 | 42篇 |
2002年 | 58篇 |
2001年 | 60篇 |
2000年 | 34篇 |
1999年 | 35篇 |
1998年 | 43篇 |
1997年 | 35篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有2513条查询结果,搜索用时 15 毫秒
991.
Ferrocenylaldimines (Fc-CH=N-R) were prepared by condensation of Schiff base of formylferrocene with polyacenylamines RNH2; R = naphthyl, anthracenyl and pyrenyl groups. This step was followed by oxidation with FeCl3 to give [Fc-CH=NR]-FeCl3 adducts. The electronic state of iron in these adducts was investigated by means of 57Fe Mössbauer spectra except for [Fc-CH=N-Pyr]-FeCl3 showed that only a doublet was observed at ambient temperature. As the temperature was decreased below 200 K, additional magnetic hyperfine splitting was observed characteristic of ferric oxide. 相似文献
992.
Aleksandar R. Zeradjanin Praveen Narangoda Ioannis Spanos Justus Masa Robert Schlögl 《Current Opinion in Electrochemistry》2021
- Download : Download high-res image (117KB)
- Download : Download full-size image
993.
Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C60 (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d N atomic states in the icosahedral field generated by fullerene C60 (I h ) on a metal atom (ion) remain non-split for different charged states of the metal and C60. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures. 相似文献
994.
- Download : Download high-res image (186KB)
- Download : Download full-size image
995.
The effect of zero-field splitting on the magnetic susceptibility of inuclear complexes formed by high-spin iron(III) ions
was studied. An analytic expression describing the magnetic susceptibility of such systems is presented. It was shown that
in dimers with weak magnetic exchange the experimental data only fit adequately if the effect of zero-field splitting (ZFS)
is taken into account. The effect of ZFS on the accuracy of the values obtained for the exchange parameters with various D/J
ratios is discussed.
__________
Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 4, pp. 219–224, July–August, 2005. 相似文献
996.
A. Yu. Sizov A. N. Kovregin R. N. Serdyuk M. V. Vorob’ev V. A. Porosyatnikov A. A. Tsvetkov D. O. Korneev A. F. Ermolov 《Russian Chemical Bulletin》2006,55(7):1200-1208
A route to α-hydropolyfluoroalkanethiols and polyfluorothioacyl halides via thermal splitting of benzyl polyfluoroalkyl sulfides under the action of phosphorus pentoxide was proposed. The thiols obtained
were used as starting materials for the synthesis of α-hydropolyfluoroalkanesulfenyl chlorides. The properties of the resulting
F,S-containing compounds were studied.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1156–1163, July, 2006. 相似文献
997.
Pt/TiO2光催化分解四硼酸钾水溶液制氢 总被引:1,自引:1,他引:1
研究了以四硼酸钾溶液作反应体系,在1%Pt/TiO2光催化剂的作用下光催化分解水制氢的反应,发现该体系能使放氢速率明显提高.放氢速率还随B4O7^2-浓度的增大而增大.在此基础上,还对B4O7^2-的作用机理进行了探讨,BRO7^2-在该反应体系中主要是通过物理作用有效的阻止了逆反应的发生,从而使放氢速率得以提高. 相似文献
998.
Nanocrystalline mesoporous TiO2 was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO2 had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m2/g. The photocatalytic activity of synthesized TiO2 was evaluated with photocatalytic H2 production from water-splitting reaction. The photocatalytic activity of synthesized TiO2 treated with appropriate calcination temperature was considerably higher than that of commercial TiO2 (Ishihara ST-01). The utilization of mesoporous TiO2 photocatalyst with high crystallinity of anatase phase promoted great H2 production. Furthermore, the reaction temperature significantly influences the water-splitting reaction. 相似文献
999.
《Surface and interface analysis : SIA》2004,36(12):1564-1574
Ferrous (Fe2+) and ferric (Fe3+) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high‐resolution iron 2p3/2 spectra from high‐spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake‐up satellites were included. This information was useful for fitting of the complex Fe 2p3/2 spectra for Fe3O4 where both Fe2+ and Fe3+ species are present. It was found that as the ionic bond character of the iron —ligand bond increased, the binding energy associated with either the ferrous or ferric 2p3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high‐spin iron 2p3/2 peak and its corresponding shake‐up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
1000.
N-Silylation and Si? O Bond Splitting at the Reaction of Lithiated Siloxy-silylamino-silanes with Chlorotrimethylsilane Lithiated Siloxy-silylamino-silanes were allowed to react in tetrahydrofurane (THF) and in n-octane (favoured) and n-hexane, resp., with chlorotrimethylsilane. The monoamide (Me3SiO)Me2Si(NLiSiMe3) gives in THF and in n-octane the N-substitution product (Me3SiO)Me2Si · [N(SiMe3)2] 1 , the diamide (Me3SiO)MeSi(NLiSiMe3)2 only in THF the N-substitution products (Me3SiO)MeSi[N(SiMe3)2]2 2 (main product) and (Me3SiO)MeSi[N(SiMe3)2](NHSiMe3) 3 . In n-octane the diamide reacts mainly under Si? O bond splitting. The cyclodisilazane [(Me3SiNH)MeSi? NSiMe3]2 6 is obtained as the main product. Byproducts are 2, 3 and the tris(trimethylsilylamino) substituted disilazane (Me3SiO)(Me3SiNH)MeSi? N · (SiMe3)? SiMe(NHSiMe3)2 7 . The triamide (Me3SiO)Si · (NLiSiMe3)3 reacts under Si? O and Si? N bond splitting in n-octane as well as in THF. The cyclodisilazanes [(Me3SiNH)2 · Si? NSiMe3]2 10 and ( 11 : R = Me3SiNH, 12 : R = (Me3Si)2N) are formed. in THF furthermore the N-substitution products (Me3SiO)Si[N(SiMe3)2] · (NHSiMe3)2 4 and (Me3SiO)Si[N(SiMe3)2]2(NHSiMe3) 5 . The Si? O bond splitting occurs in boiling n-octane also in absence of the chlorotrimethylsilane. An amide solution of (Me3SiO)MeSi(NHSiMe3)2 with n-butyllithium in the molar ratio 1 : 1 leads in n-octane and n-hexane to 6 and 7 , in THF to 3 . The amide solutions of (Me3SiO)Si · (NHSiMe3)3 with n-butyllithium the molar ratio 1 : 1 and 1 : 2 give in THF 4 and 5 , respectively. 相似文献