全文获取类型
收费全文 | 614篇 |
免费 | 65篇 |
国内免费 | 84篇 |
专业分类
化学 | 661篇 |
晶体学 | 4篇 |
力学 | 2篇 |
综合类 | 2篇 |
物理学 | 94篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 34篇 |
2020年 | 49篇 |
2019年 | 59篇 |
2018年 | 27篇 |
2017年 | 32篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 38篇 |
2013年 | 55篇 |
2012年 | 42篇 |
2011年 | 31篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 24篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有763条查询结果,搜索用时 15 毫秒
1.
《Mendeleev Communications》2022,32(6):777-779
The reactions of aryllithium reagents o-LiC6H4CH2NR2 with (MeO)2CO afford two new tris(aryl)carbinols bearing pendant-NR2 donor groups in the side chain [o-R NCH C H ] COH [R = Me, R + R = (CH) ]. These alcohols feature helical chirality due to differently inclined aromatic fragments and are presented in a crystalline cell as two M and P enantiomers. Carbinol (R = Me) readily reacts with (Me3SiCH2)3Sc(THF)2 to give a scandium bis(alkyl) complex [(o-C6H4CH2NMe2)3CO]Sc(CH2SiMe3)2 featuring rigid binding of the alkoxy anion through a κ1-O, κ2-N chelating coordination mode 相似文献
2.
Nongelatin dichromated holographic film(NGD) is a new holographic recordingmaterial.Holograms recorded on this material have better environmental stability, higherdiffraction efficiency and stronger real time effect, etc..An experimental study to ascertainthe influence of two electron donors, namely,N,N-dimethylformamide(DMF) and dimethyl-sulfoxide(DMSO),on the real time diffraction efficiency(RTDE) of NGD holograms is car-ried out.The pressence of electron donors not only improves the sensitivity,but also enhancesthe real time effect greatly.RTDE of above 60% at±1 orders of NGD plane transimissiongrating is achieved by introducing electron donors. 相似文献
3.
We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We
have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than
we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs
only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence
intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 554–556, July–August, 2006. 相似文献
4.
5.
Alternative Ligands. XXIII Rhodium(I) Complexes with Donor/Acceptor Ligands of the Type (Me2PCH2CH2)2SiX2 and (2-Me2PC6H4)SiXMe2 (X = F, Cl) Donor/acceptor ligands of the type (Me2PCH2CH2)2SiX2 and (2-Me2PC6H4)SiXMe2 (X = F, Cl) react with [Rh(CO)2Cl]2 (1) to give the mononuclear complexes RhCl(CO)(Me2PCH2CH2)2SiX2 [X = F( 4 ), Cl ( 5 )] and RhCl(CO)[2-Me2PC6H4)SixMe2]2 [X = F ( 8 ), Cl ( 9 )], respectively. In case of the ligands (Me2PCH2CH2)2SiCl2 ( 3 ) and (2-Me2PC6H6)SiClMe2 ( 7 ) the Rh(I) complexes formed in the first step partly undergo oxidative addition reactions of SiCl bonds yielding rhodium(III) compounds of low solubility. Only for 8 the coordination shifts Δδ = δ(complex)?δ(ligand) and coupling constants give some indication to possible Rh→Si interactions. However, the molecular structure of 8 determined by X-ray diffraction does not show RhSi or RhF bonding contacts. The new compounds were characterized by analytical (C, H) and spectroscopic investigations (MS, IR,-NMR). 相似文献
6.
Francis D. de Kőrösy 《Mikrochimica acta》1989,97(1-2):25-29
Donor or acceptor compounds in apolar organic solvents become charged at a high-field strength electrode and are driven to a surrounding low-field strength electrode of opposite sign. At 10 kV per cm the solutions conduct 3–7 times better when the highly charged electrode is positive in donor solutions. The opposite situation occurs in acceptor solutions. 相似文献
7.
Alternative Ligands. XXII. Rhodium(I) complexes with Donor/Acceptor Ligands of the Typs Me2PCH2CH2SiXnMe3?n(X = F, Cl, OMe) Donor/acceptor ligand of the type Me2PCH2SiXnMe3?n react with [Rh(CO)2Cl]2 ( 1 ) to give the mononuclear complexes RhCl(CO)(PMe2CH2CH2SiXnMe3?n)2 ( 2-6 , Table 1) with planar geometry of the donor atoms, one exception being Me2PCH2CH2CH2SiCl3, yielding the crystalline RhIII-complex RhCl2(CO)(PMe2CH2CH2SiCl2)(PMe2CH2CH2SiCl3) ( 7 ) by oxidative addition of one of the SiCl bonds to the Rh1 precursor. Structures with Rh → Si interaction between the basic central atoms and the acceptor group SiXnMe3?n could be detected in the isolated products neither spectroscopically nor by X-ray diffraction of the two representatives RhCl(CO)(PMe2CH2CH2SiF3)2 ( 2 ) and RhCl(CO)[PMe2CH2CH2siF3]2 ( 2 ) and RhCl(CO) [PMe2CH2CH2Si(OMe3]2 ( 6 ). The presence of such acid/base adducts in the reaction mixture is indicated for the more acidic acceptor groups SiXnMe3?n byvco values near 1990cm?1, (see Table 3). The complex RhCl(CO)PMe3)(PMe2CH2CH2SiF3 ( 8 ) is obtained by the reaction of RhCl(CO)(PMe3)2 ( 9 ) with Me2PCH2SiF3 and has been identified spectroscopically in a mixture with 2 and 9 . 相似文献
8.
A novel conjugation-elongated bis(ethylenedithio)tetraselenafulvalene (BETS) type donor, 2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene (BEDT-HBDST) and its magnetic and non-magnetic anion salts, (BEDT-HBDST)2MX4 (MX4−=FeCl4−, GaCl4−, FeBr4− and GaBr4−), were prepared. These four salts are isostructural and belong to the space group of P2/c. They showed semiconducting behavior with small activation energies (59-64 meV). The band structures of these salts are quasi one-dimensional and there is a midgap between the upper band and the lower band, since the degree of dimerization is significant in the stacking direction. The MX4− ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl4− and FeBr4− salts follow the Curie-Weiss law with Curie constants of 4.6 and 4.8 emu K mol−1 (sum of the spins of S=5/2 and S=1/2) and negative Weiss temperatures of θ=−1.2 and −4.9 K, respectively, revealing a weak antiferromagnetic interaction of 3d spins of the FeCl4− and FeBr4− anions. The Fe?Fe (6.66-7.60 Å), Cl?Cl (4.81-4.82 Å) and Br?Br (4.74-4.77 Å) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe3+ ions appears to be not readily accessible. 相似文献
9.
从甲基弯菌M ethylosinus trichosporium IMV3011的膜中分离出颗粒性甲烷单加氧酶(Particulate MMO,Pmmo)t和NADH脱氢酶,只有当两者同时存在,并添加去垢剂解离膜组分时,NDAH才能为pMMO提供还原当量,对苯二酚能够在整细胞和膜水平代替NADH作为PMMO的电子供体,对于纯化的PMMO,对苯二分配仍是有效的电子供体,而NADH却是无效的电子供体。在NADH脱氢酶存在下,NADH可将对苯醌还原为对苯二酚,纯化过程中,采用对苯二酚作为PMMO活性分析时的电子供体,不必共纯化NADH脱氢酶,且有利于对PMMO活性中心进行深入研究。 相似文献
10.
Several novel substituted bis(2‐pyridylimino)isoindolato (BPI) cobalt(II) and iron(II) complexes [M(BPI)(OAc)(H2O)] (M = Co: 1 ‐ 6, Fe: 7) have been synthesized by reaction of bis(2‐pyridylimino)isoindole derivatives with the corresponding metal(II) acetates. Reaction of 1‐6 with 1.5 ‐ 2 molar equivalents of t‐BuOOH gave the corresponding alkylperoxocobalt(III) complexes [Co(BPI)(OAc)(OOtBu)] (10 ‐ 15). Using an aqueous solution of t‐BuOOH (70 %), cyclohexene was selectively catalytically oxidized to the dialkylperoxide cyclohex‐2‐ene‐1‐t‐butylperoxide. 相似文献