全文获取类型
收费全文 | 1107篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 786篇 |
晶体学 | 14篇 |
力学 | 19篇 |
数学 | 58篇 |
物理学 | 235篇 |
出版年
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 17篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 22篇 |
2014年 | 38篇 |
2013年 | 69篇 |
2012年 | 35篇 |
2011年 | 57篇 |
2010年 | 29篇 |
2009年 | 47篇 |
2008年 | 49篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 39篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 37篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 21篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1991年 | 11篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 23篇 |
1972年 | 11篇 |
1971年 | 7篇 |
1970年 | 14篇 |
1969年 | 8篇 |
1968年 | 7篇 |
1967年 | 7篇 |
排序方式: 共有1112条查询结果,搜索用时 640 毫秒
61.
62.
Jordanka Petrova Snejana Momchilova Nikolay G. Vassilev 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):45-52
Abstract The interaction of Li-diethylbenzylphosphonate 1-Li with aldehydes 2 is studied at different reaction conditions, the corresponding β-hydroxyethanephosphonate 3 being isolated. It is found that in these cases the aldol stage of the HWE reaction is not stereoselective or threo isomers predominate. The elimination stage leads only to trans-alkene due to the electron and steric influence of the substituents at the phosphorus atom. 相似文献
63.
Emil Tashev Tania Tosheva Stoycho Shenkov Anne-Sophie Chauvin Victoria Lachkova Rosica Petrova 《Supramolecular chemistry》2013,25(7):447-457
The synthesis and characterization of several new phosphorus-containing partially lower rim substituted derivatives of 5,11,17,23-tetra(t-butyl) calix(4)arene (I) and 5,11,17,23-tetra(t-octyl)calix(4)arene (II), namely 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(diphenylphosphinoyl-oxy) calix(4)arene (IV); 5,11,17,23-tetra(t-butyl)-25-hydroxy-26,27,28-tris(tetramethyldiamido-phosphinoyl-oxy) calix(4)arene (Vb); 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VI); 5,11,17,23-tetra (t-octyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VII) are reported. The structure of the synthesized calix(4)arene derivatives are identified and confirmed by elemental analysis, IR, 1H, 13C, 31P{1H} NMR spectroscopy and mass spectrometry as and X-ray crystallographic analysis of 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene VI. According to the NMR spectra, all calix(4)arenes are in cone conformation. 相似文献
64.
L. N. Sobenina Z. V. Stepanova O. V. Petrova J. Sh. Ma G. Yang A. A. Tatarinova A. I. Mikhaleva B. A. Trofimov 《Russian Chemical Bulletin》2013,62(1):88-92
Cross-coupling of 2-(biphenyl-4-yl)pyrroles derived from 1-(biphenyl-4-yl)ethanone oximes and acetylene with 3-bromo-1-phenylprop-2-yn-1-one on aluminum oxide gave 3-[5-(biphe-nyl-4-yl)pyrrol-2-yl]-1-phenylprop-2-yn-1-ones in 35–46% yields. 相似文献
65.
A. N. Yarkevich Z. V. Safronova L. N. Petrova A. V. Gabrelyan V. L. Zamoyski V. V. Grigor’ev S. O. Bachurin N. S. Zefirov 《Russian Journal of General Chemistry》2013,83(1):41-45
Bis(dialkylamides) of phosphoryl-substituted α,ω-dicarboxylic acids were synthesized and their biological activity was studied. 相似文献
66.
L. L. Zamigailo O. N. Petrova M. G. Shirobokova V. V. Lipson 《Russian Journal of Organic Chemistry》2013,49(2):288-293
Reactions of 4-oxo benz[1,3-e]oxazinium perchlorates with 1-R1-3-R2-5-aminopyrazoles lead to the formation of derivatives of pyrazolo[3,4-d]pyrimidine and pyrazolo[1,5-a]1,3,5]triazine series, and with 3-amino-1,2,4-triazole, to [1,2,4]triazolo[1,5-a][1,3,5]triazines. 相似文献
67.
New method for obtaining highly dispersed manganese oxide under the action of a dc electric field was suggested. It was found that the electric field parameters affect the phase composition, shape, morphology and size of manganese oxide particles and the content of water. It is demonstrated that the manganese oxide synthesized can be used as a vulcanizing agent in manufacture of sealants based on thiocol and surpasses in application efficiency the analog produced by the conventional method. 相似文献
68.
Z. A. Mikhailovskaya E. S. Buyanova S. A. Petrova V. M. Zhukovskii 《Russian Journal of Electrochemistry》2013,49(7):658-664
The possibility of synthesizing oxygen-ionic conductors from substituted bismuth molybdates containing [Bi12O14] n 8n+ columns, MoO4 tetrahedra, and isolated Bi ions in their structure was studied. The specifics of their structure and electric conductivity were investigated. The general formula of the solid solutions can be recorded as Bi13Mo5 ? x Me x O34 ? δ, where Me is the fouror five-valent d metal (Ti, Zr, V, Nb). The electric conductivity of doped bismuth molybdates considerably increased compared with that of the matrix compound. The electric conductivity reached 5.5 × 10?3 S cm?1 at 700°C and 1.8 × 10?4 S cm?1 at 350°C for the zirconium-doped compound with x = 0.4. The porosity of the ceramics was less than 5%; the thermal expansion coefficient was of the order of 14 × 10?6 K?1. Based on the set of their characteristics, these compounds are recommended as materials for membranes of electrochemical devices. 相似文献
69.
Nina I. Giricheva Georgiy V. Girichev Marwan Dakkouri Sergey N. Ivanov Vjacheslav M. Petrov Valentina N. Petrova 《Structural chemistry》2013,24(3):819-826
α-Naphthalenesulfonyl chloride, α-NaphSC, was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (HF/6-311 + G**, HF/aug-cc-pVDZ, B3LYP/cc-pVDZ, B3LYP/cc-pVTZ, B3LYP/aug-cc-pVDZ, B3LYP/aug-cc-pVTZ, MP2/cc-pVDZ, and MP2/cc-pVTZ). The calculations predict the existence of two conformers with C 1 (I) and C s (II) symmetries. The most stable conformer I has an enantiomer. The experimental data of α-NaphSC obtained at 370(5) K could be best fitted by a C 1 symmetry model indicating that only this form exists in the gas-phase. In this model the Cα–S–Cl plane deviates from the perpendicular orientation relative to the plane of the naphthalene skeleton. Under the applied experimental conditions, the mole fraction of a second less stable conformer II of α-NaphSC predicted by calculations is no more than 1 %. The following geometrical parameters of conformer I were obtained from the experiment (Å and °; uncertainties are in parentheses): r h1(C–H) = 1.082(6), r h1(C–C)cp = 1.407(3), r h1(C–S) = 1.764(5), r h1(S–O)av = 1.425(3), r h1(S–Cl) = 2.051(5), ∠C–Cα–C = 122.5(1), ∠Cα–S–Cl = 101.5(10); C9–C1–S–Cl = 71.4(21). The calculated barriers to internal rotation of the sulfonyl chloride group exceed considerably the thermal energy values corresponding to the temperatures of the GED experiments. Natural bond orbitals analysis of the electron density distribution was carried out to explain the peculiarities of the molecular structure of the studied compound and the deviation from the structures of β-NaphSHal molecules and their benzene analogs. 相似文献
70.