全文获取类型
收费全文 | 2011篇 |
免费 | 56篇 |
国内免费 | 1篇 |
专业分类
化学 | 1341篇 |
晶体学 | 40篇 |
力学 | 22篇 |
数学 | 126篇 |
物理学 | 539篇 |
出版年
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 17篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2016年 | 34篇 |
2015年 | 54篇 |
2014年 | 43篇 |
2013年 | 87篇 |
2012年 | 83篇 |
2011年 | 91篇 |
2010年 | 60篇 |
2009年 | 44篇 |
2008年 | 84篇 |
2007年 | 82篇 |
2006年 | 55篇 |
2005年 | 71篇 |
2004年 | 58篇 |
2003年 | 53篇 |
2002年 | 43篇 |
2001年 | 41篇 |
2000年 | 55篇 |
1999年 | 30篇 |
1998年 | 43篇 |
1997年 | 29篇 |
1996年 | 39篇 |
1995年 | 30篇 |
1994年 | 37篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 38篇 |
1983年 | 22篇 |
1982年 | 29篇 |
1981年 | 20篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 23篇 |
1977年 | 36篇 |
1976年 | 17篇 |
1975年 | 11篇 |
1974年 | 28篇 |
1973年 | 12篇 |
1968年 | 13篇 |
排序方式: 共有2068条查询结果,搜索用时 46 毫秒
71.
The influence of the surfactant charge on micellization was studied on sodium n-dodecane-phosphonates, varying the charge of the surfactant ion from 0 to 2. The effects on the cmc, hydrolysis, micelle
composition, and micelle ionization degree were studied. The increase of one e unit in the charge of the surfactant species reduces the cmc by about one order of magnitude.
Received: 18 November 1996 Accepted: 5 March 1997 相似文献
72.
Preparation and Spectroscopic Investigations of Highly Branched Functional Siloxanes The preparation of the siloxanes [(Me3SiO)3SiO]n(Me3SiO)3?nSiX and (Me3SiO)3Si[OSi(OSiMe3)2]2X (n = 1?3, X = H, Cl, OC2H5, OH) is described. The hydride-siloxanes and the siloxanoles have been investigated by i.r. and 29Si-n.m.r. spectroscopy. The frequencies of the Si? H stretching vibration, the 29Si? 1H coupling constants and the 29Si-chemical shifts of the Si(H) signal for the hydride-siloxanes as well as the frequencies of the (Si)O? H stretching vibration, the relative (Si)O? H acidity, and the 29Si-chemical shifts of the Si(OH) signal for the siloxanoles show a dependence on the number of the (Me3SiO)3SiO groups. The spectroscopic data are discussed with respect to the silicate environment of the Si(H) and Si(OH) atom, respectively. In the siloxanoles intramolecular hydrogen bondings were observed. 相似文献
73.
Cao C Dahal S Shang M Beatty AM Hibbs W Schulz CE Scheidt WR 《Inorganic chemistry》2003,42(17):5202-5210
The effect of a sixth ligand in a series of low-spin thiocarbonyl-ligated iron(II)octaethylporphyrinates has been investigated. Six-coordinate complexes have been synthesized and characterized by M?ssbauer and infrared spectroscopy and single-crystal X-ray structure determinations. The results are compared with the five-coordinate parent complex. The crystal structures of [Fe(OEP)(CS)(1-MeIm)] and [Fe(OEP)(CS)(Py)] are reported and discussed. The 1-methylimidazole and pyridine derivatives exhibit Fe-C(CS) bond distances of 1.703(4) and 1.706(2) A that are significantly longer than the 1.662(3) A reported for five-coordinate [Fe(OEP)(CS)] (Scheidt, W. R.; Geiger, D. K. Inorg. Chem. 1982, 21, 1208). The trans Fe-N(ligand) distances of 2.112(3) and 2.1550(15) A observed for the 1-methylimidazole and pyridine complex are approximately 0.13 A longer than those observed for analogous bis-ligated complexes and are consistent with a significant structural trans effect for the CS ligand. M?ssbauer investigations carried out for five- and six-coordinate thiocarbonyl derivatives with several different sixth axial ligands reveal interesting features. All derivatives exhibit very small isomer shift values, consistent with a very strong interaction between iron and CS. The five-coordinate derivative has delta(Fe) = 0.08 mm/s, and the six-coordinate complexes exhibit delta(Fe) = 0.14 to 0.19 mm/s at 4.2 K. The five-coordinate complex shows a large quadrupole splitting (DeltaE(q) = 1.93 mm/s at 4.2 K) which is reduced on coordination of the sixth ligand (DeltaE(q) = 0.42-0.80 mm/s at 4.2 K). Addition of a sixth ligand also leads to a small decrease in the value of nu(CS). Correlations in structural, IR, and M?ssbauer results suggest that the sixth ligand effect is primarily induced by changes in sigma-bonding. The structure of [Fe(OEP)(CS)(CH(3)OH)] is briefly reported. Crystal data: [Fe(OEP)(CS)(1-MeIm)] crystallizes in the monoclinic system, space group P2(1)/n, Z = 4, a = 9.5906(5) A, b = 16.704(4) A, c = 23.1417(6) A, beta = 100.453(7) degrees. [Fe(OEP)(CS)(Py)] crystallizes in the triclinic system, space group P1, Z = 5, a = 13.9073(6) A, b = 16.2624(7) A, c = 22.0709(9) A, alpha = 70.586(1) degrees, beta = 77.242(1) degrees, gamma = 77.959(1) degrees. [Fe(OEP)(CS)(CH(3)OH)] crystallizes in the triclinic system, space group P1, Z = 1, a = 9.0599(5) A, b = 9.4389(5) A, c = 11.0676(6) A, alpha = 90.261(1) degrees, beta = 100.362(1) degrees, gamma = 114.664(1) degrees. 相似文献
74.
P. Svoboda J. Hetflej W. Schulz H. Pracejus 《Reaction Kinetics and Catalysis Letters》1986,32(1):39-44
Supported Ziegler catalysts prepared by the reaction of a Ni(II) 1-butylsalicylaldiminate or Ni(II) 2-ethylhexanoate with Al2O3/SiO2 treated with AlEt3 or NaAlH2 (OCH2CH2OCH3)2 are efficient catalysts for hydrogenation of simple alkenes. The factors influencing their activity are reported.
, qp - Ni(II) - Ni(II) 2- Al2O3/SiO2, AlEt3 NaAlH2 (OCH2CH2OCH3)2, . , .相似文献
75.
Spectroscopic Investigations on Substituent Effects in Silylmethylsilanes The silanes Me3?n(Me3SiCH2)nSiH (n = 1–3), (RMe2SiCH2)3SiH (R = n-Bu, n-Pr, Et, PhCH2, Ph) and Me3ElCH2SiMe2H (El = Ge, Sn) were prepared. The frequencies of the Si? H stretching vibration, the 29Si? 1H coupling constants and the 29Si n.m.r. chemical shifts were measured. The ?(SiH) and J(29Si? 1H) values in the silanes Me3?n(Me3SiCH2)nSiH depend on the number of trimethylsilymethyl groups. There is hardly an influence of the substituents R on these values in the silanes (RMe2SiCH2)3SiH. The frequencies of the Si? H stretching vibrations in the silanes Me3ElCH2SiMe2H (El = Si, Ge, Sn) show the order Si?Ge > Sn. The 29Si n.m.r. chemical shifts of the Si(H) signals are approximately equal in the silanes Me3?n(Me3SiCH2)nSiH and (RMe2SiCH2)3SiH. 相似文献
76.
Karlsson NG Schulz BL Packer NH 《Journal of the American Society for Mass Spectrometry》2004,15(5):659-672
Neutral O-linked oligosaccharides released from the salivary mucin MUC5B were separated and detected by negative ion LC-MS and LC-MS(2). The resolution of the chromatography and the information obtained from collision induced dissociation of detected [M - H](-) ions were usually sufficient to identify the sequence of individual oligosaccharides, illustrated by the fact that 50 different oligosaccharides ranging from disaccharides to nonasaccharides could be assigned from the sample. Fragmentation was shown to yield mostly reducing end sequence fragments (Z(i) and Y(i)), enabling primary sequence assignment. Specific fragmentation pathways or patterns were also detected giving specific linkage information. The reducing end core (Gal/GlcNAcbeta1-3GalNAcol or Gal/GlcNAcbeta1-3(GlcNAcbeta1-6)GalNAcol) could be deduced from the pronounced glycosidic C-3 cleavage and A(i) type cleavages of the reducing end GalNAcol, together with the non reducing end fragment from the loss of a single substituted GalNAcol. Substitution patterns on GlcNAc residues were also found, indicative for C-4 substitution ((0,2)A(i) - H(2)O cleavage) and disubstitution of C-3 and C-4 (Z(i)/Z(i) cleavages). This kind of fragmentation can be used for assigning the mode of chain elongation (Galbeta1-3/4GlcNAcbeta1-) and identification of Lewis type antigens like Lewis a/x and Lewis b/y on O-linked oligosaccharides. In essence, negative ion LC-MS(2) was able to generate extensive data for understanding the overall glycosylation pattern of a sample, especially when only a limited amount of material is available. 相似文献
77.
Bis(cyclopentadienyl)methane-bridged Dinuclear Complexes, V[1]. – Heteronuclear Co/Rh-, Co/Ir-, Rh/Ir-, and Ti/Ir Complexes with the Bis(cyclopentadienyl)methane Dianion as Bridging Ligand* The lithium and sodium salts of the [C5H5CH2C5H4]- anion, 1 and 2 , react with [Co(CO)4I], [Rh(CO)2Cl]2, and [Ir(CO)3Cl]n to give predominantly the mononuclear complexes [(C5H5-CH2C5H4)M(CO)2] ( 3, 5, 7 ) together with small amounts of the dinuclear compounds [CH2(C5H4)2][M(CO)2]2 ( 4, 6, 8 ). The 1H- and 13C-NMR spectra of 3, 5 , and 7 prove that the CH2C5H5 substituent is linked to the π-bonded ring in two isomeric forms. Metalation of 5 and 7 with nBuLi affords the lithiated derivatives 9 and 10 from which on reaction with [Co(CO)4I], [Rh(CO)2Cl]2, and [C5H5TiCl3] the heteronuclear complexes [CH2(C5H4)2][M(CO)2][M′(CO)2] ( 11–13 ) and [CH2(C5H4)2]-[Ir(CO)2][C5H5TiCl2] ( 17 ) are obtained. Photolysis of 11 and 12 leads almost quantitatively to the formation of the CO-bridged compounds [CH2(C5H4)2][M(CO)(μ-CO)M′(CO)] ( 14, 15 ). According to an X-ray crystal structure analysis the Co/Rh complex 14 is isostructural to [CH2(C5H4)2][Rh2(CO)2(μ-CO)] ( 16 ). 相似文献
78.
G. O. Schulz R. Milkovich 《Journal of polymer science. Part A, Polymer chemistry》1984,22(7):1633-1652
Copolymerization studies of methacrylate-terminated polystyrene macromonomers (M1) with several comonomers (M2) verified the modified kinetic scheme and permitted prediction of graft polymer compositions and structures. Instantaneous and cumulative copolymer compositions, average graft distributions, and grafts per molecule are predicted from FORTRAN IV or BASIC programs. The r2 relative reactivity ratios determined from styrene copolymerization (0.61) or from low conversion acrylic monomer in aqueous suspension (~0.4) had good agreement with literature values (about 0.6 and 0.4, respectively). Decreased macromonomer reactivity determined at high acrylic monomer conversions was attributed to phase separation phenomena. The Macromers also exhibited lower reactivity than predicted when copolymerized with acrylic monomers in DMSO/benzene solutions (r2 ~ 0.8). 相似文献
79.
Heinz Berner Gerhard Schulz Gernot Fischer Hellmuth Reinshagen 《Monatshefte für Chemie / Chemical Monthly》1978,109(3):557-566
In order to obtain a better partition of a prodigiosin derivative in biological media, two hydroxy groups were introduced into theansa-part of the molecule. The synthesis of the title compound is described in detail. 相似文献
80.
Axel Schulz Thomas M. Klap tke
T. Stanley Cameron
P. K. Bakshi 《Journal of organometallic chemistry》1994,480(1-2):191-194The oxidation of Cp2NbCl2 with pure WF6 in SO2 solution yielded the cationic metallocene species [Cp2NbCl2]+[WF6]− essentially in quantitative yield. The same reaction carried out in the presence of either equimolar amounts or a two-fold excess of HCN led to the preparation of the new niobocenium salt [Cp2NbCl2]4+[WF6]2− which was studied by single crystal X-ray diffraction. This compound represents the first example of a structurally characterized metallocene-WF6− complex, and crystallizes in the tetragonal system: space group, P41212(No. 92), a = 11.083(8) Å, c = 48.285 (9) Å; Z = 8; R = 0.0759, RW = 0.0841. ab]Die Oxidation von Cp2NbCl2 mit reinem WF6 führt in SO2-Lösung zur Synthese von [Cp2NbCl2 ]+[WF6]− in nahezu quantitativer Ausbeute. Die analoge Reaktion führt unter Anwesenheit der äquimolaren Menge oder eines zweifachen Überschusses an HCN zur Ausbildung des Niobocenium-Komplexsalzes [Cp2NbCl2]4+ [WF6]2−[WCl6]2−, von dem eine Röntgenstrukturanalyse angefertigt wurde. Diese Verbindung repräsentiert den ersten structurell charakterisierten Vertreter eines Metallocen-WF6−-Komplexes und kristallisiert im tetragonalen System: Raumgruppe P41212 (Nr. 92), a = 11.083(8) Å, c = 48.285(9) Å; Z = 8; R = 0.0759, RW = 0.0841. kw]Niobium; X-ray diffraction; Oxidation; Metallocenes 相似文献