全文获取类型
收费全文 | 158篇 |
免费 | 2篇 |
专业分类
化学 | 123篇 |
晶体学 | 2篇 |
数学 | 2篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2017年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 4篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有160条查询结果,搜索用时 201 毫秒
1.
JiŘí Kvapil Josef Kvapil Bohumil Perner Michal Košelja Helena Jelínková 《Czechoslovak Journal of Physics》1990,40(11):1283-1287
The methods of growing YAG:Nd crystals with a flat interface and YAP:Nd crystals with a sharp conical interface are described. The form of the interface was controlled by the He and H2O content in the reducing atmosphere composed mainly of Ar and H2 as well as by axial temperature gradient above the melt level. The crystals of 120–180 mm in length were machined to the high-quality slabs. 相似文献
2.
J. Kvapil B. Perner Jos Kvapil B. Mánek K. Hamal M. Košelja V. Kubeček 《Czechoslovak Journal of Physics》1988,38(11):1281-1287
YAP:Nd, Cr grown under Ar-H2 or Ar-He-H2 atmosphere possesses good energy transfer from Cr3+ to Nd3+ but suffers from the colour centre formation. The centre formation was completely prevented using further admixture of Ce3+ and 10–4–10–3 wt. % Fe. Small luminescence quenching of Cr3+ or Nd3+ due to iron ions is negligible in the presence of Ce3+. The crystals may be also heavily doped with Nd3+ because the increased pumping efficiency compensates the shortening of the luminescence lifetime. YAP: Nd, Ce, Cr, Fe is advisible active laser material particularly for all the types of pulsed lasers. 相似文献
3.
Alginate Properties and Heavy Metal Biosorption by Marine Algae 总被引:10,自引:0,他引:10
The physical properties of the alginate component in four different brown seaweeds (Sargassumfluitans, Ascophyllum nodosum, Fucus vesiculo-sus, andLaminaria japonica) were characterized using potentiometric titration,13C-nuclear magnetic resonance (NMR), chemical analysis, and viscosity measurements. The heavy metal binding capacities of the
corresponding seaweeds were directly proportional to their respective total carboxyl group content, and related to the electronegativity
of the elements investigated (Ca, Zn, Cd, Cu, and Pb). The uronic acid composition or sequence of the alginate component did
not affect the metal uptake properties of the biosorbents studied here. However, the alginate leaching owing to its solubilization
by Na ions was observed to decrease with increasing intrinsic viscosity of the extracted alginate, related to its molecular
weight, and with increasing apparent acidic dissociation constant, related to the alginate density inside the biomass. 相似文献
4.
Bohumír Grüner Jaroslav Ba?kovský Bohumil Štíbr 《Journal of organometallic chemistry》2005,690(11):2850-2852
The compounds with a single and double -CH2C6H4CH2- spacer, [CpFeC3B8H10-NH-CH2C6H4CH2-NH-C3B8H10FeCp] and [CpFeC3B8H10-N-(CH2C6H4CH2)2-N-C3B8H10FeCp], represent the first example of designed shaping by extremely stable cyclopentadienyl-ferratricarbollide (CpFeTCB) cages into rigid molecular constructions approaching linear arrangement. 相似文献
5.
Composition and hydrolysis products of a biotechnical available complex of macrolides were analyzed by HPLC and ESI-CID-MSn. Major components are leucomycin-type antibiotics (leucomycins A1 (5), A7 (3), A9 (2), 9-desoxy-9-oxo-turimycin H3 (4) and niddamycin B (6). Hydrolysis of the complex mixture yielded 9-, 13-isoforocidins (7, 8, 9, 11) and 9-oxo-forocidin (10). A preparative separation procedure was elaborated furnishing compounds 3 - 11 for semisynthetic experiments.Prof. Dr. Udo Gräfe deceased on 14.2.2003. For obituarity see: Schlegel B (2003) J Peptide Sci 9: 661–661. 相似文献
6.
Treatment of a solution of excess PCl(3) and PS (PS = "proton sponge" = 1,8-dimethylamino naphthalene) with arachno-4-CB(8)H(14) (1) in CH(2)Cl(2), followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven-vertex diphosphacarbaborane nido-7,8,9-P(2)CB(8)H(10) (2) (yield 34%) as the main product. Other products isolated from this reaction were the phosphacarboranes nido-7,8,9,10-P(3)CB(7)H(8) (3) (yield 5%) and closo-2,1-PCB(8)H(9) (4) (yield 15%). Compound 2 can be deprotonated by PS in CH(2)Cl(2) or NaH in diethyl ether to give the [nido-7,8,9-P(2)CB(8)H(9)](-) (2(-)()) anion, which gives back the original compound, 2, upon re-protonation. Thermal rearrangement of anion 2(-) (Na(+) salt) at 350 degrees C for 2 h produced the isomeric [nido-7,8,10-P(2)CB(8)H(9)](-) (5(-)()) anion, which was isolated as a PPh(4)(+) salt (yield 86%). Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B] COSY, (1)H{(11)B(selective)}, (1)H{(31)P(selective)}, and gradient-enhanced ([(1)H-(13)C] HSQC) magnetic resonance measurements led to complete assignments of all resonances which are in excellent agreement with the structures proposed. Coupling constants, (1)J((31)P,(13)C), (2)J((31)P,C,(1)H), and (1)J((31)P,(31)P), were calculated using the DFT method B3LYP/6-311+G(d,p). The molecular geometries of all compounds were optimized ab initio at a correlated level of theory (RMP2(fc)) using the 6-31G basis set, and their correctness was assessed by comparison of the experimental (11)B and (13)C chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G method. The computations also include the structures and chemical shieldings of the still unknown isomers [nido-7,10,8-P(2)CB(8)H(9)](-) (6(-)) and [nido-7,9,8-P(2)CB(8)H(9)](-) (7(-)). 相似文献
7.
The reaction between arachno-4-CB(8)H(14) and PCl(3) in the presence of PS (PS = proton sponge = 1,8-dimethylamino naphthalene) (dichloromethane, rt, 24 h) produced the neutral phosphacarborane closo-2,1-PCB(8)H(9) (35% yield), while a similar reaction of nido-1-CB(8)H(12) gave the isomeric compound closo-6,1-PCB(8)H(9) (27% yield). The structures of both compounds were derived on the basis of the combined ab initio/GIAO/NMR ((1)H, (11)B, (13)C) approach. The optimized structures at a correlated level of theory (MP2) with 6-31G* basis set were used as a basis for calculations of the (11)B and (13)C chemical shifts at GIAO-SCF/II and GIAO-MP2/II, the latter showing excellent agreement with experimental data. 相似文献
8.
Dmitry S. Perekalin Pavel V. Petrovskii Bohumil Štíbr Alexander R. Kudinov 《Journal of organometallic chemistry》2005,690(11):2775-2779
The reaction of the tricarbollide salt Tl[7-tBuNH-7,8,9-C3B8H10] (Tl1) with [(cod)Rh(THF)x]+ gives the rhodium complex [1-(cod)-12-tBuNH-1,2,4,12-RhC3B8H10] in almost quantitative yield. Analogous reactions of Tl1 with [(ring)M(THF)x]2+ ((ring)M = Cp*Rh and (1,3,5-C6H3Me3)Ru) afford the corresponding metallatricarbollides [1-(ring)-12-tBuNH-1,2,4,12-MC3B8H10] in ca. 50% yield. Refluxing Tl1 with [Mn(CO)3(MeCN)3]+ in THF give the tricarbollide analogue of cymantrene, [1,1,1-(CO)3-12-tBuNH-1,2,4,12-MnC3B8H10], the structure of which was determined by single-crystal X-ray diffraction analysis. In all cases, the formation of the metallatricarbollide complexes is accompanied by polyhedral rearrangement leading to the maximum separation of the cage carbon atoms. 相似文献
9.
Grüner B Stíbr B Kivekäs R Sillanpää R Stopka P Teixidor F Viñas C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(24):6115-6121
Treatment of the [2-Cp-9-tBuNH-closo-2,1,7,9-FeC(3)B(8)H(10)] (1) ferratricarbollide (Cp = eta(5)-C(5)H(5) (-)) with Na(+) C(10)H(8) (-) in 1,2-dimethoxyethane (DME) at room temperature produced an air-sensitive transient anion with a tentatively identified nido-[tBuNH-CpFeC(3)B(8)H(10)](2-) constitution. In-situ reaction of this low-stability ion with [CpFe(CO)(2)I] or [CpFe(CO)(2)](2) generated three violet diferratricarbaboranes identified as paramagnetic subcloso complexes [4,5-Cp(2-)-4,5,1,6,7-Fe(2)C(3)B(8)H(11)] (2; yield 2 %), [4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(11)] (3; yield 2 %), and [7-tBuNH-4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(10)] (4; yield 14 %). These first representatives of the 13-vertex dimetallatricarbaborane family were characterized by EPR and IR spectroscopy, and mass spectrometry, and their structures were determined by X-ray diffraction analysis. 相似文献
10.
Stíbr B Holub J Bakardjiev M Pavlík I Tok OL Císarová I Wrackmeyer B Herberhold M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2239-2244
The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed. 相似文献